Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/mm/vmscan.c

  1 /*
  2  *  linux/mm/vmscan.c
  3  *
  4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
  5  *
  6  *  Swap reorganised 29.12.95, Stephen Tweedie.
  7  *  kswapd added: 7.1.96  sct
  8  *  Removed kswapd_ctl limits, and swap out as many pages as needed
  9  *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
 10  *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
 11  *  Multiqueue VM started 5.8.00, Rik van Riel.
 12  */
 13 
 14 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 15 
 16 #include <linux/mm.h>
 17 #include <linux/module.h>
 18 #include <linux/gfp.h>
 19 #include <linux/kernel_stat.h>
 20 #include <linux/swap.h>
 21 #include <linux/pagemap.h>
 22 #include <linux/init.h>
 23 #include <linux/highmem.h>
 24 #include <linux/vmpressure.h>
 25 #include <linux/vmstat.h>
 26 #include <linux/file.h>
 27 #include <linux/writeback.h>
 28 #include <linux/blkdev.h>
 29 #include <linux/buffer_head.h>  /* for try_to_release_page(),
 30                                         buffer_heads_over_limit */
 31 #include <linux/mm_inline.h>
 32 #include <linux/backing-dev.h>
 33 #include <linux/rmap.h>
 34 #include <linux/topology.h>
 35 #include <linux/cpu.h>
 36 #include <linux/cpuset.h>
 37 #include <linux/compaction.h>
 38 #include <linux/notifier.h>
 39 #include <linux/rwsem.h>
 40 #include <linux/delay.h>
 41 #include <linux/kthread.h>
 42 #include <linux/freezer.h>
 43 #include <linux/memcontrol.h>
 44 #include <linux/delayacct.h>
 45 #include <linux/sysctl.h>
 46 #include <linux/oom.h>
 47 #include <linux/prefetch.h>
 48 #include <linux/printk.h>
 49 #include <linux/dax.h>
 50 
 51 #include <asm/tlbflush.h>
 52 #include <asm/div64.h>
 53 
 54 #include <linux/swapops.h>
 55 #include <linux/balloon_compaction.h>
 56 
 57 #include "internal.h"
 58 
 59 #define CREATE_TRACE_POINTS
 60 #include <trace/events/vmscan.h>
 61 
 62 struct scan_control {
 63         /* How many pages shrink_list() should reclaim */
 64         unsigned long nr_to_reclaim;
 65 
 66         /* This context's GFP mask */
 67         gfp_t gfp_mask;
 68 
 69         /* Allocation order */
 70         int order;
 71 
 72         /*
 73          * Nodemask of nodes allowed by the caller. If NULL, all nodes
 74          * are scanned.
 75          */
 76         nodemask_t      *nodemask;
 77 
 78         /*
 79          * The memory cgroup that hit its limit and as a result is the
 80          * primary target of this reclaim invocation.
 81          */
 82         struct mem_cgroup *target_mem_cgroup;
 83 
 84         /* Scan (total_size >> priority) pages at once */
 85         int priority;
 86 
 87         /* The highest zone to isolate pages for reclaim from */
 88         enum zone_type reclaim_idx;
 89 
 90         unsigned int may_writepage:1;
 91 
 92         /* Can mapped pages be reclaimed? */
 93         unsigned int may_unmap:1;
 94 
 95         /* Can pages be swapped as part of reclaim? */
 96         unsigned int may_swap:1;
 97 
 98         /* Can cgroups be reclaimed below their normal consumption range? */
 99         unsigned int may_thrash:1;
100 
101         unsigned int hibernation_mode:1;
102 
103         /* One of the zones is ready for compaction */
104         unsigned int compaction_ready:1;
105 
106         /* Incremented by the number of inactive pages that were scanned */
107         unsigned long nr_scanned;
108 
109         /* Number of pages freed so far during a call to shrink_zones() */
110         unsigned long nr_reclaimed;
111 };
112 
113 #ifdef ARCH_HAS_PREFETCH
114 #define prefetch_prev_lru_page(_page, _base, _field)                    \
115         do {                                                            \
116                 if ((_page)->lru.prev != _base) {                       \
117                         struct page *prev;                              \
118                                                                         \
119                         prev = lru_to_page(&(_page->lru));              \
120                         prefetch(&prev->_field);                        \
121                 }                                                       \
122         } while (0)
123 #else
124 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
125 #endif
126 
127 #ifdef ARCH_HAS_PREFETCHW
128 #define prefetchw_prev_lru_page(_page, _base, _field)                   \
129         do {                                                            \
130                 if ((_page)->lru.prev != _base) {                       \
131                         struct page *prev;                              \
132                                                                         \
133                         prev = lru_to_page(&(_page->lru));              \
134                         prefetchw(&prev->_field);                       \
135                 }                                                       \
136         } while (0)
137 #else
138 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
139 #endif
140 
141 /*
142  * From 0 .. 100.  Higher means more swappy.
143  */
144 int vm_swappiness = 60;
145 /*
146  * The total number of pages which are beyond the high watermark within all
147  * zones.
148  */
149 unsigned long vm_total_pages;
150 
151 static LIST_HEAD(shrinker_list);
152 static DECLARE_RWSEM(shrinker_rwsem);
153 
154 #ifdef CONFIG_MEMCG
155 static bool global_reclaim(struct scan_control *sc)
156 {
157         return !sc->target_mem_cgroup;
158 }
159 
160 /**
161  * sane_reclaim - is the usual dirty throttling mechanism operational?
162  * @sc: scan_control in question
163  *
164  * The normal page dirty throttling mechanism in balance_dirty_pages() is
165  * completely broken with the legacy memcg and direct stalling in
166  * shrink_page_list() is used for throttling instead, which lacks all the
167  * niceties such as fairness, adaptive pausing, bandwidth proportional
168  * allocation and configurability.
169  *
170  * This function tests whether the vmscan currently in progress can assume
171  * that the normal dirty throttling mechanism is operational.
172  */
173 static bool sane_reclaim(struct scan_control *sc)
174 {
175         struct mem_cgroup *memcg = sc->target_mem_cgroup;
176 
177         if (!memcg)
178                 return true;
179 #ifdef CONFIG_CGROUP_WRITEBACK
180         if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
181                 return true;
182 #endif
183         return false;
184 }
185 #else
186 static bool global_reclaim(struct scan_control *sc)
187 {
188         return true;
189 }
190 
191 static bool sane_reclaim(struct scan_control *sc)
192 {
193         return true;
194 }
195 #endif
196 
197 /*
198  * This misses isolated pages which are not accounted for to save counters.
199  * As the data only determines if reclaim or compaction continues, it is
200  * not expected that isolated pages will be a dominating factor.
201  */
202 unsigned long zone_reclaimable_pages(struct zone *zone)
203 {
204         unsigned long nr;
205 
206         nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
207                 zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
208         if (get_nr_swap_pages() > 0)
209                 nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
210                         zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
211 
212         return nr;
213 }
214 
215 unsigned long pgdat_reclaimable_pages(struct pglist_data *pgdat)
216 {
217         unsigned long nr;
218 
219         nr = node_page_state_snapshot(pgdat, NR_ACTIVE_FILE) +
220              node_page_state_snapshot(pgdat, NR_INACTIVE_FILE) +
221              node_page_state_snapshot(pgdat, NR_ISOLATED_FILE);
222 
223         if (get_nr_swap_pages() > 0)
224                 nr += node_page_state_snapshot(pgdat, NR_ACTIVE_ANON) +
225                       node_page_state_snapshot(pgdat, NR_INACTIVE_ANON) +
226                       node_page_state_snapshot(pgdat, NR_ISOLATED_ANON);
227 
228         return nr;
229 }
230 
231 bool pgdat_reclaimable(struct pglist_data *pgdat)
232 {
233         return node_page_state_snapshot(pgdat, NR_PAGES_SCANNED) <
234                 pgdat_reclaimable_pages(pgdat) * 6;
235 }
236 
237 unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru)
238 {
239         if (!mem_cgroup_disabled())
240                 return mem_cgroup_get_lru_size(lruvec, lru);
241 
242         return node_page_state(lruvec_pgdat(lruvec), NR_LRU_BASE + lru);
243 }
244 
245 unsigned long lruvec_zone_lru_size(struct lruvec *lruvec, enum lru_list lru,
246                                    int zone_idx)
247 {
248         if (!mem_cgroup_disabled())
249                 return mem_cgroup_get_zone_lru_size(lruvec, lru, zone_idx);
250 
251         return zone_page_state(&lruvec_pgdat(lruvec)->node_zones[zone_idx],
252                                NR_ZONE_LRU_BASE + lru);
253 }
254 
255 /*
256  * Add a shrinker callback to be called from the vm.
257  */
258 int register_shrinker(struct shrinker *shrinker)
259 {
260         size_t size = sizeof(*shrinker->nr_deferred);
261 
262         if (shrinker->flags & SHRINKER_NUMA_AWARE)
263                 size *= nr_node_ids;
264 
265         shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
266         if (!shrinker->nr_deferred)
267                 return -ENOMEM;
268 
269         down_write(&shrinker_rwsem);
270         list_add_tail(&shrinker->list, &shrinker_list);
271         up_write(&shrinker_rwsem);
272         return 0;
273 }
274 EXPORT_SYMBOL(register_shrinker);
275 
276 /*
277  * Remove one
278  */
279 void unregister_shrinker(struct shrinker *shrinker)
280 {
281         down_write(&shrinker_rwsem);
282         list_del(&shrinker->list);
283         up_write(&shrinker_rwsem);
284         kfree(shrinker->nr_deferred);
285 }
286 EXPORT_SYMBOL(unregister_shrinker);
287 
288 #define SHRINK_BATCH 128
289 
290 static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
291                                     struct shrinker *shrinker,
292                                     unsigned long nr_scanned,
293                                     unsigned long nr_eligible)
294 {
295         unsigned long freed = 0;
296         unsigned long long delta;
297         long total_scan;
298         long freeable;
299         long nr;
300         long new_nr;
301         int nid = shrinkctl->nid;
302         long batch_size = shrinker->batch ? shrinker->batch
303                                           : SHRINK_BATCH;
304         long scanned = 0, next_deferred;
305 
306         freeable = shrinker->count_objects(shrinker, shrinkctl);
307         if (freeable == 0)
308                 return 0;
309 
310         /*
311          * copy the current shrinker scan count into a local variable
312          * and zero it so that other concurrent shrinker invocations
313          * don't also do this scanning work.
314          */
315         nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
316 
317         total_scan = nr;
318         delta = (4 * nr_scanned) / shrinker->seeks;
319         delta *= freeable;
320         do_div(delta, nr_eligible + 1);
321         total_scan += delta;
322         if (total_scan < 0) {
323                 pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n",
324                        shrinker->scan_objects, total_scan);
325                 total_scan = freeable;
326                 next_deferred = nr;
327         } else
328                 next_deferred = total_scan;
329 
330         /*
331          * We need to avoid excessive windup on filesystem shrinkers
332          * due to large numbers of GFP_NOFS allocations causing the
333          * shrinkers to return -1 all the time. This results in a large
334          * nr being built up so when a shrink that can do some work
335          * comes along it empties the entire cache due to nr >>>
336          * freeable. This is bad for sustaining a working set in
337          * memory.
338          *
339          * Hence only allow the shrinker to scan the entire cache when
340          * a large delta change is calculated directly.
341          */
342         if (delta < freeable / 4)
343                 total_scan = min(total_scan, freeable / 2);
344 
345         /*
346          * Avoid risking looping forever due to too large nr value:
347          * never try to free more than twice the estimate number of
348          * freeable entries.
349          */
350         if (total_scan > freeable * 2)
351                 total_scan = freeable * 2;
352 
353         trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
354                                    nr_scanned, nr_eligible,
355                                    freeable, delta, total_scan);
356 
357         /*
358          * Normally, we should not scan less than batch_size objects in one
359          * pass to avoid too frequent shrinker calls, but if the slab has less
360          * than batch_size objects in total and we are really tight on memory,
361          * we will try to reclaim all available objects, otherwise we can end
362          * up failing allocations although there are plenty of reclaimable
363          * objects spread over several slabs with usage less than the
364          * batch_size.
365          *
366          * We detect the "tight on memory" situations by looking at the total
367          * number of objects we want to scan (total_scan). If it is greater
368          * than the total number of objects on slab (freeable), we must be
369          * scanning at high prio and therefore should try to reclaim as much as
370          * possible.
371          */
372         while (total_scan >= batch_size ||
373                total_scan >= freeable) {
374                 unsigned long ret;
375                 unsigned long nr_to_scan = min(batch_size, total_scan);
376 
377                 shrinkctl->nr_to_scan = nr_to_scan;
378                 ret = shrinker->scan_objects(shrinker, shrinkctl);
379                 if (ret == SHRINK_STOP)
380                         break;
381                 freed += ret;
382 
383                 count_vm_events(SLABS_SCANNED, nr_to_scan);
384                 total_scan -= nr_to_scan;
385                 scanned += nr_to_scan;
386 
387                 cond_resched();
388         }
389 
390         if (next_deferred >= scanned)
391                 next_deferred -= scanned;
392         else
393                 next_deferred = 0;
394         /*
395          * move the unused scan count back into the shrinker in a
396          * manner that handles concurrent updates. If we exhausted the
397          * scan, there is no need to do an update.
398          */
399         if (next_deferred > 0)
400                 new_nr = atomic_long_add_return(next_deferred,
401                                                 &shrinker->nr_deferred[nid]);
402         else
403                 new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
404 
405         trace_mm_shrink_slab_end(shrinker, nid, freed, nr, new_nr, total_scan);
406         return freed;
407 }
408 
409 /**
410  * shrink_slab - shrink slab caches
411  * @gfp_mask: allocation context
412  * @nid: node whose slab caches to target
413  * @memcg: memory cgroup whose slab caches to target
414  * @nr_scanned: pressure numerator
415  * @nr_eligible: pressure denominator
416  *
417  * Call the shrink functions to age shrinkable caches.
418  *
419  * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
420  * unaware shrinkers will receive a node id of 0 instead.
421  *
422  * @memcg specifies the memory cgroup to target. If it is not NULL,
423  * only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan
424  * objects from the memory cgroup specified. Otherwise, only unaware
425  * shrinkers are called.
426  *
427  * @nr_scanned and @nr_eligible form a ratio that indicate how much of
428  * the available objects should be scanned.  Page reclaim for example
429  * passes the number of pages scanned and the number of pages on the
430  * LRU lists that it considered on @nid, plus a bias in @nr_scanned
431  * when it encountered mapped pages.  The ratio is further biased by
432  * the ->seeks setting of the shrink function, which indicates the
433  * cost to recreate an object relative to that of an LRU page.
434  *
435  * Returns the number of reclaimed slab objects.
436  */
437 static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
438                                  struct mem_cgroup *memcg,
439                                  unsigned long nr_scanned,
440                                  unsigned long nr_eligible)
441 {
442         struct shrinker *shrinker;
443         unsigned long freed = 0;
444 
445         if (memcg && (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)))
446                 return 0;
447 
448         if (nr_scanned == 0)
449                 nr_scanned = SWAP_CLUSTER_MAX;
450 
451         if (!down_read_trylock(&shrinker_rwsem)) {
452                 /*
453                  * If we would return 0, our callers would understand that we
454                  * have nothing else to shrink and give up trying. By returning
455                  * 1 we keep it going and assume we'll be able to shrink next
456                  * time.
457                  */
458                 freed = 1;
459                 goto out;
460         }
461 
462         list_for_each_entry(shrinker, &shrinker_list, list) {
463                 struct shrink_control sc = {
464                         .gfp_mask = gfp_mask,
465                         .nid = nid,
466                         .memcg = memcg,
467                 };
468 
469                 /*
470                  * If kernel memory accounting is disabled, we ignore
471                  * SHRINKER_MEMCG_AWARE flag and call all shrinkers
472                  * passing NULL for memcg.
473                  */
474                 if (memcg_kmem_enabled() &&
475                     !!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
476                         continue;
477 
478                 if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
479                         sc.nid = 0;
480 
481                 freed += do_shrink_slab(&sc, shrinker, nr_scanned, nr_eligible);
482         }
483 
484         up_read(&shrinker_rwsem);
485 out:
486         cond_resched();
487         return freed;
488 }
489 
490 void drop_slab_node(int nid)
491 {
492         unsigned long freed;
493 
494         do {
495                 struct mem_cgroup *memcg = NULL;
496 
497                 freed = 0;
498                 do {
499                         freed += shrink_slab(GFP_KERNEL, nid, memcg,
500                                              1000, 1000);
501                 } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
502         } while (freed > 10);
503 }
504 
505 void drop_slab(void)
506 {
507         int nid;
508 
509         for_each_online_node(nid)
510                 drop_slab_node(nid);
511 }
512 
513 static inline int is_page_cache_freeable(struct page *page)
514 {
515         /*
516          * A freeable page cache page is referenced only by the caller
517          * that isolated the page, the page cache radix tree and
518          * optional buffer heads at page->private.
519          */
520         return page_count(page) - page_has_private(page) == 2;
521 }
522 
523 static int may_write_to_inode(struct inode *inode, struct scan_control *sc)
524 {
525         if (current->flags & PF_SWAPWRITE)
526                 return 1;
527         if (!inode_write_congested(inode))
528                 return 1;
529         if (inode_to_bdi(inode) == current->backing_dev_info)
530                 return 1;
531         return 0;
532 }
533 
534 /*
535  * We detected a synchronous write error writing a page out.  Probably
536  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
537  * fsync(), msync() or close().
538  *
539  * The tricky part is that after writepage we cannot touch the mapping: nothing
540  * prevents it from being freed up.  But we have a ref on the page and once
541  * that page is locked, the mapping is pinned.
542  *
543  * We're allowed to run sleeping lock_page() here because we know the caller has
544  * __GFP_FS.
545  */
546 static void handle_write_error(struct address_space *mapping,
547                                 struct page *page, int error)
548 {
549         lock_page(page);
550         if (page_mapping(page) == mapping)
551                 mapping_set_error(mapping, error);
552         unlock_page(page);
553 }
554 
555 /* possible outcome of pageout() */
556 typedef enum {
557         /* failed to write page out, page is locked */
558         PAGE_KEEP,
559         /* move page to the active list, page is locked */
560         PAGE_ACTIVATE,
561         /* page has been sent to the disk successfully, page is unlocked */
562         PAGE_SUCCESS,
563         /* page is clean and locked */
564         PAGE_CLEAN,
565 } pageout_t;
566 
567 /*
568  * pageout is called by shrink_page_list() for each dirty page.
569  * Calls ->writepage().
570  */
571 static pageout_t pageout(struct page *page, struct address_space *mapping,
572                          struct scan_control *sc)
573 {
574         /*
575          * If the page is dirty, only perform writeback if that write
576          * will be non-blocking.  To prevent this allocation from being
577          * stalled by pagecache activity.  But note that there may be
578          * stalls if we need to run get_block().  We could test
579          * PagePrivate for that.
580          *
581          * If this process is currently in __generic_file_write_iter() against
582          * this page's queue, we can perform writeback even if that
583          * will block.
584          *
585          * If the page is swapcache, write it back even if that would
586          * block, for some throttling. This happens by accident, because
587          * swap_backing_dev_info is bust: it doesn't reflect the
588          * congestion state of the swapdevs.  Easy to fix, if needed.
589          */
590         if (!is_page_cache_freeable(page))
591                 return PAGE_KEEP;
592         if (!mapping) {
593                 /*
594                  * Some data journaling orphaned pages can have
595                  * page->mapping == NULL while being dirty with clean buffers.
596                  */
597                 if (page_has_private(page)) {
598                         if (try_to_free_buffers(page)) {
599                                 ClearPageDirty(page);
600                                 pr_info("%s: orphaned page\n", __func__);
601                                 return PAGE_CLEAN;
602                         }
603                 }
604                 return PAGE_KEEP;
605         }
606         if (mapping->a_ops->writepage == NULL)
607                 return PAGE_ACTIVATE;
608         if (!may_write_to_inode(mapping->host, sc))
609                 return PAGE_KEEP;
610 
611         if (clear_page_dirty_for_io(page)) {
612                 int res;
613                 struct writeback_control wbc = {
614                         .sync_mode = WB_SYNC_NONE,
615                         .nr_to_write = SWAP_CLUSTER_MAX,
616                         .range_start = 0,
617                         .range_end = LLONG_MAX,
618                         .for_reclaim = 1,
619                 };
620 
621                 SetPageReclaim(page);
622                 res = mapping->a_ops->writepage(page, &wbc);
623                 if (res < 0)
624                         handle_write_error(mapping, page, res);
625                 if (res == AOP_WRITEPAGE_ACTIVATE) {
626                         ClearPageReclaim(page);
627                         return PAGE_ACTIVATE;
628                 }
629 
630                 if (!PageWriteback(page)) {
631                         /* synchronous write or broken a_ops? */
632                         ClearPageReclaim(page);
633                 }
634                 trace_mm_vmscan_writepage(page);
635                 inc_node_page_state(page, NR_VMSCAN_WRITE);
636                 return PAGE_SUCCESS;
637         }
638 
639         return PAGE_CLEAN;
640 }
641 
642 /*
643  * Same as remove_mapping, but if the page is removed from the mapping, it
644  * gets returned with a refcount of 0.
645  */
646 static int __remove_mapping(struct address_space *mapping, struct page *page,
647                             bool reclaimed)
648 {
649         unsigned long flags;
650 
651         BUG_ON(!PageLocked(page));
652         BUG_ON(mapping != page_mapping(page));
653 
654         spin_lock_irqsave(&mapping->tree_lock, flags);
655         /*
656          * The non racy check for a busy page.
657          *
658          * Must be careful with the order of the tests. When someone has
659          * a ref to the page, it may be possible that they dirty it then
660          * drop the reference. So if PageDirty is tested before page_count
661          * here, then the following race may occur:
662          *
663          * get_user_pages(&page);
664          * [user mapping goes away]
665          * write_to(page);
666          *                              !PageDirty(page)    [good]
667          * SetPageDirty(page);
668          * put_page(page);
669          *                              !page_count(page)   [good, discard it]
670          *
671          * [oops, our write_to data is lost]
672          *
673          * Reversing the order of the tests ensures such a situation cannot
674          * escape unnoticed. The smp_rmb is needed to ensure the page->flags
675          * load is not satisfied before that of page->_refcount.
676          *
677          * Note that if SetPageDirty is always performed via set_page_dirty,
678          * and thus under tree_lock, then this ordering is not required.
679          */
680         if (!page_ref_freeze(page, 2))
681                 goto cannot_free;
682         /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
683         if (unlikely(PageDirty(page))) {
684                 page_ref_unfreeze(page, 2);
685                 goto cannot_free;
686         }
687 
688         if (PageSwapCache(page)) {
689                 swp_entry_t swap = { .val = page_private(page) };
690                 mem_cgroup_swapout(page, swap);
691                 __delete_from_swap_cache(page);
692                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
693                 swapcache_free(swap);
694         } else {
695                 void (*freepage)(struct page *);
696                 void *shadow = NULL;
697 
698                 freepage = mapping->a_ops->freepage;
699                 /*
700                  * Remember a shadow entry for reclaimed file cache in
701                  * order to detect refaults, thus thrashing, later on.
702                  *
703                  * But don't store shadows in an address space that is
704                  * already exiting.  This is not just an optizimation,
705                  * inode reclaim needs to empty out the radix tree or
706                  * the nodes are lost.  Don't plant shadows behind its
707                  * back.
708                  *
709                  * We also don't store shadows for DAX mappings because the
710                  * only page cache pages found in these are zero pages
711                  * covering holes, and because we don't want to mix DAX
712                  * exceptional entries and shadow exceptional entries in the
713                  * same page_tree.
714                  */
715                 if (reclaimed && page_is_file_cache(page) &&
716                     !mapping_exiting(mapping) && !dax_mapping(mapping))
717                         shadow = workingset_eviction(mapping, page);
718                 __delete_from_page_cache(page, shadow);
719                 spin_unlock_irqrestore(&mapping->tree_lock, flags);
720 
721                 if (freepage != NULL)
722                         freepage(page);
723         }
724 
725         return 1;
726 
727 cannot_free:
728         spin_unlock_irqrestore(&mapping->tree_lock, flags);
729         return 0;
730 }
731 
732 /*
733  * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
734  * someone else has a ref on the page, abort and return 0.  If it was
735  * successfully detached, return 1.  Assumes the caller has a single ref on
736  * this page.
737  */
738 int remove_mapping(struct address_space *mapping, struct page *page)
739 {
740         if (__remove_mapping(mapping, page, false)) {
741                 /*
742                  * Unfreezing the refcount with 1 rather than 2 effectively
743                  * drops the pagecache ref for us without requiring another
744                  * atomic operation.
745                  */
746                 page_ref_unfreeze(page, 1);
747                 return 1;
748         }
749         return 0;
750 }
751 
752 /**
753  * putback_lru_page - put previously isolated page onto appropriate LRU list
754  * @page: page to be put back to appropriate lru list
755  *
756  * Add previously isolated @page to appropriate LRU list.
757  * Page may still be unevictable for other reasons.
758  *
759  * lru_lock must not be held, interrupts must be enabled.
760  */
761 void putback_lru_page(struct page *page)
762 {
763         bool is_unevictable;
764         int was_unevictable = PageUnevictable(page);
765 
766         VM_BUG_ON_PAGE(PageLRU(page), page);
767 
768 redo:
769         ClearPageUnevictable(page);
770 
771         if (page_evictable(page)) {
772                 /*
773                  * For evictable pages, we can use the cache.
774                  * In event of a race, worst case is we end up with an
775                  * unevictable page on [in]active list.
776                  * We know how to handle that.
777                  */
778                 is_unevictable = false;
779                 lru_cache_add(page);
780         } else {
781                 /*
782                  * Put unevictable pages directly on zone's unevictable
783                  * list.
784                  */
785                 is_unevictable = true;
786                 add_page_to_unevictable_list(page);
787                 /*
788                  * When racing with an mlock or AS_UNEVICTABLE clearing
789                  * (page is unlocked) make sure that if the other thread
790                  * does not observe our setting of PG_lru and fails
791                  * isolation/check_move_unevictable_pages,
792                  * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
793                  * the page back to the evictable list.
794                  *
795                  * The other side is TestClearPageMlocked() or shmem_lock().
796                  */
797                 smp_mb();
798         }
799 
800         /*
801          * page's status can change while we move it among lru. If an evictable
802          * page is on unevictable list, it never be freed. To avoid that,
803          * check after we added it to the list, again.
804          */
805         if (is_unevictable && page_evictable(page)) {
806                 if (!isolate_lru_page(page)) {
807                         put_page(page);
808                         goto redo;
809                 }
810                 /* This means someone else dropped this page from LRU
811                  * So, it will be freed or putback to LRU again. There is
812                  * nothing to do here.
813                  */
814         }
815 
816         if (was_unevictable && !is_unevictable)
817                 count_vm_event(UNEVICTABLE_PGRESCUED);
818         else if (!was_unevictable && is_unevictable)
819                 count_vm_event(UNEVICTABLE_PGCULLED);
820 
821         put_page(page);         /* drop ref from isolate */
822 }
823 
824 enum page_references {
825         PAGEREF_RECLAIM,
826         PAGEREF_RECLAIM_CLEAN,
827         PAGEREF_KEEP,
828         PAGEREF_ACTIVATE,
829 };
830 
831 static enum page_references page_check_references(struct page *page,
832                                                   struct scan_control *sc)
833 {
834         int referenced_ptes, referenced_page;
835         unsigned long vm_flags;
836 
837         referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
838                                           &vm_flags);
839         referenced_page = TestClearPageReferenced(page);
840 
841         /*
842          * Mlock lost the isolation race with us.  Let try_to_unmap()
843          * move the page to the unevictable list.
844          */
845         if (vm_flags & VM_LOCKED)
846                 return PAGEREF_RECLAIM;
847 
848         if (referenced_ptes) {
849                 if (PageSwapBacked(page))
850                         return PAGEREF_ACTIVATE;
851                 /*
852                  * All mapped pages start out with page table
853                  * references from the instantiating fault, so we need
854                  * to look twice if a mapped file page is used more
855                  * than once.
856                  *
857                  * Mark it and spare it for another trip around the
858                  * inactive list.  Another page table reference will
859                  * lead to its activation.
860                  *
861                  * Note: the mark is set for activated pages as well
862                  * so that recently deactivated but used pages are
863                  * quickly recovered.
864                  */
865                 SetPageReferenced(page);
866 
867                 if (referenced_page || referenced_ptes > 1)
868                         return PAGEREF_ACTIVATE;
869 
870                 /*
871                  * Activate file-backed executable pages after first usage.
872                  */
873                 if (vm_flags & VM_EXEC)
874                         return PAGEREF_ACTIVATE;
875 
876                 return PAGEREF_KEEP;
877         }
878 
879         /* Reclaim if clean, defer dirty pages to writeback */
880         if (referenced_page && !PageSwapBacked(page))
881                 return PAGEREF_RECLAIM_CLEAN;
882 
883         return PAGEREF_RECLAIM;
884 }
885 
886 /* Check if a page is dirty or under writeback */
887 static void page_check_dirty_writeback(struct page *page,
888                                        bool *dirty, bool *writeback)
889 {
890         struct address_space *mapping;
891 
892         /*
893          * Anonymous pages are not handled by flushers and must be written
894          * from reclaim context. Do not stall reclaim based on them
895          */
896         if (!page_is_file_cache(page)) {
897                 *dirty = false;
898                 *writeback = false;
899                 return;
900         }
901 
902         /* By default assume that the page flags are accurate */
903         *dirty = PageDirty(page);
904         *writeback = PageWriteback(page);
905 
906         /* Verify dirty/writeback state if the filesystem supports it */
907         if (!page_has_private(page))
908                 return;
909 
910         mapping = page_mapping(page);
911         if (mapping && mapping->a_ops->is_dirty_writeback)
912                 mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
913 }
914 
915 /*
916  * shrink_page_list() returns the number of reclaimed pages
917  */
918 static unsigned long shrink_page_list(struct list_head *page_list,
919                                       struct pglist_data *pgdat,
920                                       struct scan_control *sc,
921                                       enum ttu_flags ttu_flags,
922                                       unsigned long *ret_nr_dirty,
923                                       unsigned long *ret_nr_unqueued_dirty,
924                                       unsigned long *ret_nr_congested,
925                                       unsigned long *ret_nr_writeback,
926                                       unsigned long *ret_nr_immediate,
927                                       bool force_reclaim)
928 {
929         LIST_HEAD(ret_pages);
930         LIST_HEAD(free_pages);
931         int pgactivate = 0;
932         unsigned long nr_unqueued_dirty = 0;
933         unsigned long nr_dirty = 0;
934         unsigned long nr_congested = 0;
935         unsigned long nr_reclaimed = 0;
936         unsigned long nr_writeback = 0;
937         unsigned long nr_immediate = 0;
938 
939         cond_resched();
940 
941         while (!list_empty(page_list)) {
942                 struct address_space *mapping;
943                 struct page *page;
944                 int may_enter_fs;
945                 enum page_references references = PAGEREF_RECLAIM_CLEAN;
946                 bool dirty, writeback;
947                 bool lazyfree = false;
948                 int ret = SWAP_SUCCESS;
949 
950                 cond_resched();
951 
952                 page = lru_to_page(page_list);
953                 list_del(&page->lru);
954 
955                 if (!trylock_page(page))
956                         goto keep;
957 
958                 VM_BUG_ON_PAGE(PageActive(page), page);
959 
960                 sc->nr_scanned++;
961 
962                 if (unlikely(!page_evictable(page)))
963                         goto cull_mlocked;
964 
965                 if (!sc->may_unmap && page_mapped(page))
966                         goto keep_locked;
967 
968                 /* Double the slab pressure for mapped and swapcache pages */
969                 if (page_mapped(page) || PageSwapCache(page))
970                         sc->nr_scanned++;
971 
972                 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
973                         (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
974 
975                 /*
976                  * The number of dirty pages determines if a zone is marked
977                  * reclaim_congested which affects wait_iff_congested. kswapd
978                  * will stall and start writing pages if the tail of the LRU
979                  * is all dirty unqueued pages.
980                  */
981                 page_check_dirty_writeback(page, &dirty, &writeback);
982                 if (dirty || writeback)
983                         nr_dirty++;
984 
985                 if (dirty && !writeback)
986                         nr_unqueued_dirty++;
987 
988                 /*
989                  * Treat this page as congested if the underlying BDI is or if
990                  * pages are cycling through the LRU so quickly that the
991                  * pages marked for immediate reclaim are making it to the
992                  * end of the LRU a second time.
993                  */
994                 mapping = page_mapping(page);
995                 if (((dirty || writeback) && mapping &&
996                      inode_write_congested(mapping->host)) ||
997                     (writeback && PageReclaim(page)))
998                         nr_congested++;
999 
1000                 /*
1001                  * If a page at the tail of the LRU is under writeback, there
1002                  * are three cases to consider.
1003                  *
1004                  * 1) If reclaim is encountering an excessive number of pages
1005                  *    under writeback and this page is both under writeback and
1006                  *    PageReclaim then it indicates that pages are being queued
1007                  *    for IO but are being recycled through the LRU before the
1008                  *    IO can complete. Waiting on the page itself risks an
1009                  *    indefinite stall if it is impossible to writeback the
1010                  *    page due to IO error or disconnected storage so instead
1011                  *    note that the LRU is being scanned too quickly and the
1012                  *    caller can stall after page list has been processed.
1013                  *
1014                  * 2) Global or new memcg reclaim encounters a page that is
1015                  *    not marked for immediate reclaim, or the caller does not
1016                  *    have __GFP_FS (or __GFP_IO if it's simply going to swap,
1017                  *    not to fs). In this case mark the page for immediate
1018                  *    reclaim and continue scanning.
1019                  *
1020                  *    Require may_enter_fs because we would wait on fs, which
1021                  *    may not have submitted IO yet. And the loop driver might
1022                  *    enter reclaim, and deadlock if it waits on a page for
1023                  *    which it is needed to do the write (loop masks off
1024                  *    __GFP_IO|__GFP_FS for this reason); but more thought
1025                  *    would probably show more reasons.
1026                  *
1027                  * 3) Legacy memcg encounters a page that is already marked
1028                  *    PageReclaim. memcg does not have any dirty pages
1029                  *    throttling so we could easily OOM just because too many
1030                  *    pages are in writeback and there is nothing else to
1031                  *    reclaim. Wait for the writeback to complete.
1032                  */
1033                 if (PageWriteback(page)) {
1034                         /* Case 1 above */
1035                         if (current_is_kswapd() &&
1036                             PageReclaim(page) &&
1037                             test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
1038                                 nr_immediate++;
1039                                 goto keep_locked;
1040 
1041                         /* Case 2 above */
1042                         } else if (sane_reclaim(sc) ||
1043                             !PageReclaim(page) || !may_enter_fs) {
1044                                 /*
1045                                  * This is slightly racy - end_page_writeback()
1046                                  * might have just cleared PageReclaim, then
1047                                  * setting PageReclaim here end up interpreted
1048                                  * as PageReadahead - but that does not matter
1049                                  * enough to care.  What we do want is for this
1050                                  * page to have PageReclaim set next time memcg
1051                                  * reclaim reaches the tests above, so it will
1052                                  * then wait_on_page_writeback() to avoid OOM;
1053                                  * and it's also appropriate in global reclaim.
1054                                  */
1055                                 SetPageReclaim(page);
1056                                 nr_writeback++;
1057                                 goto keep_locked;
1058 
1059                         /* Case 3 above */
1060                         } else {
1061                                 unlock_page(page);
1062                                 wait_on_page_writeback(page);
1063                                 /* then go back and try same page again */
1064                                 list_add_tail(&page->lru, page_list);
1065                                 continue;
1066                         }
1067                 }
1068 
1069                 if (!force_reclaim)
1070                         references = page_check_references(page, sc);
1071 
1072                 switch (references) {
1073                 case PAGEREF_ACTIVATE:
1074                         goto activate_locked;
1075                 case PAGEREF_KEEP:
1076                         goto keep_locked;
1077                 case PAGEREF_RECLAIM:
1078                 case PAGEREF_RECLAIM_CLEAN:
1079                         ; /* try to reclaim the page below */
1080                 }
1081 
1082                 /*
1083                  * Anonymous process memory has backing store?
1084                  * Try to allocate it some swap space here.
1085                  */
1086                 if (PageAnon(page) && !PageSwapCache(page)) {
1087                         if (!(sc->gfp_mask & __GFP_IO))
1088                                 goto keep_locked;
1089                         if (!add_to_swap(page, page_list))
1090                                 goto activate_locked;
1091                         lazyfree = true;
1092                         may_enter_fs = 1;
1093 
1094                         /* Adding to swap updated mapping */
1095                         mapping = page_mapping(page);
1096                 } else if (unlikely(PageTransHuge(page))) {
1097                         /* Split file THP */
1098                         if (split_huge_page_to_list(page, page_list))
1099                                 goto keep_locked;
1100                 }
1101 
1102                 VM_BUG_ON_PAGE(PageTransHuge(page), page);
1103 
1104                 /*
1105                  * The page is mapped into the page tables of one or more
1106                  * processes. Try to unmap it here.
1107                  */
1108                 if (page_mapped(page) && mapping) {
1109                         switch (ret = try_to_unmap(page, lazyfree ?
1110                                 (ttu_flags | TTU_BATCH_FLUSH | TTU_LZFREE) :
1111                                 (ttu_flags | TTU_BATCH_FLUSH))) {
1112                         case SWAP_FAIL:
1113                                 goto activate_locked;
1114                         case SWAP_AGAIN:
1115                                 goto keep_locked;
1116                         case SWAP_MLOCK:
1117                                 goto cull_mlocked;
1118                         case SWAP_LZFREE:
1119                                 goto lazyfree;
1120                         case SWAP_SUCCESS:
1121                                 ; /* try to free the page below */
1122                         }
1123                 }
1124 
1125                 if (PageDirty(page)) {
1126                         /*
1127                          * Only kswapd can writeback filesystem pages to
1128                          * avoid risk of stack overflow but only writeback
1129                          * if many dirty pages have been encountered.
1130                          */
1131                         if (page_is_file_cache(page) &&
1132                                         (!current_is_kswapd() ||
1133                                          !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
1134                                 /*
1135                                  * Immediately reclaim when written back.
1136                                  * Similar in principal to deactivate_page()
1137                                  * except we already have the page isolated
1138                                  * and know it's dirty
1139                                  */
1140                                 inc_node_page_state(page, NR_VMSCAN_IMMEDIATE);
1141                                 SetPageReclaim(page);
1142 
1143                                 goto keep_locked;
1144                         }
1145 
1146                         if (references == PAGEREF_RECLAIM_CLEAN)
1147                                 goto keep_locked;
1148                         if (!may_enter_fs)
1149                                 goto keep_locked;
1150                         if (!sc->may_writepage)
1151                                 goto keep_locked;
1152 
1153                         /*
1154                          * Page is dirty. Flush the TLB if a writable entry
1155                          * potentially exists to avoid CPU writes after IO
1156                          * starts and then write it out here.
1157                          */
1158                         try_to_unmap_flush_dirty();
1159                         switch (pageout(page, mapping, sc)) {
1160                         case PAGE_KEEP:
1161                                 goto keep_locked;
1162                         case PAGE_ACTIVATE:
1163                                 goto activate_locked;
1164                         case PAGE_SUCCESS:
1165                                 if (PageWriteback(page))
1166                                         goto keep;
1167                                 if (PageDirty(page))
1168                                         goto keep;
1169 
1170                                 /*
1171                                  * A synchronous write - probably a ramdisk.  Go
1172                                  * ahead and try to reclaim the page.
1173                                  */
1174                                 if (!trylock_page(page))
1175                                         goto keep;
1176                                 if (PageDirty(page) || PageWriteback(page))
1177                                         goto keep_locked;
1178                                 mapping = page_mapping(page);
1179                         case PAGE_CLEAN:
1180                                 ; /* try to free the page below */
1181                         }
1182                 }
1183 
1184                 /*
1185                  * If the page has buffers, try to free the buffer mappings
1186                  * associated with this page. If we succeed we try to free
1187                  * the page as well.
1188                  *
1189                  * We do this even if the page is PageDirty().
1190                  * try_to_release_page() does not perform I/O, but it is
1191                  * possible for a page to have PageDirty set, but it is actually
1192                  * clean (all its buffers are clean).  This happens if the
1193                  * buffers were written out directly, with submit_bh(). ext3
1194                  * will do this, as well as the blockdev mapping.
1195                  * try_to_release_page() will discover that cleanness and will
1196                  * drop the buffers and mark the page clean - it can be freed.
1197                  *
1198                  * Rarely, pages can have buffers and no ->mapping.  These are
1199                  * the pages which were not successfully invalidated in
1200                  * truncate_complete_page().  We try to drop those buffers here
1201                  * and if that worked, and the page is no longer mapped into
1202                  * process address space (page_count == 1) it can be freed.
1203                  * Otherwise, leave the page on the LRU so it is swappable.
1204                  */
1205                 if (page_has_private(page)) {
1206                         if (!try_to_release_page(page, sc->gfp_mask))
1207                                 goto activate_locked;
1208                         if (!mapping && page_count(page) == 1) {
1209                                 unlock_page(page);
1210                                 if (put_page_testzero(page))
1211                                         goto free_it;
1212                                 else {
1213                                         /*
1214                                          * rare race with speculative reference.
1215                                          * the speculative reference will free
1216                                          * this page shortly, so we may
1217                                          * increment nr_reclaimed here (and
1218                                          * leave it off the LRU).
1219                                          */
1220                                         nr_reclaimed++;
1221                                         continue;
1222                                 }
1223                         }
1224                 }
1225 
1226 lazyfree:
1227                 if (!mapping || !__remove_mapping(mapping, page, true))
1228                         goto keep_locked;
1229 
1230                 /*
1231                  * At this point, we have no other references and there is
1232                  * no way to pick any more up (removed from LRU, removed
1233                  * from pagecache). Can use non-atomic bitops now (and
1234                  * we obviously don't have to worry about waking up a process
1235                  * waiting on the page lock, because there are no references.
1236                  */
1237                 __ClearPageLocked(page);
1238 free_it:
1239                 if (ret == SWAP_LZFREE)
1240                         count_vm_event(PGLAZYFREED);
1241 
1242                 nr_reclaimed++;
1243 
1244                 /*
1245                  * Is there need to periodically free_page_list? It would
1246                  * appear not as the counts should be low
1247                  */
1248                 list_add(&page->lru, &free_pages);
1249                 continue;
1250 
1251 cull_mlocked:
1252                 if (PageSwapCache(page))
1253                         try_to_free_swap(page);
1254                 unlock_page(page);
1255                 list_add(&page->lru, &ret_pages);
1256                 continue;
1257 
1258 activate_locked:
1259                 /* Not a candidate for swapping, so reclaim swap space. */
1260                 if (PageSwapCache(page) && mem_cgroup_swap_full(page))
1261                         try_to_free_swap(page);
1262                 VM_BUG_ON_PAGE(PageActive(page), page);
1263                 SetPageActive(page);
1264                 pgactivate++;
1265 keep_locked:
1266                 unlock_page(page);
1267 keep:
1268                 list_add(&page->lru, &ret_pages);
1269                 VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
1270         }
1271 
1272         mem_cgroup_uncharge_list(&free_pages);
1273         try_to_unmap_flush();
1274         free_hot_cold_page_list(&free_pages, true);
1275 
1276         list_splice(&ret_pages, page_list);
1277         count_vm_events(PGACTIVATE, pgactivate);
1278 
1279         *ret_nr_dirty += nr_dirty;
1280         *ret_nr_congested += nr_congested;
1281         *ret_nr_unqueued_dirty += nr_unqueued_dirty;
1282         *ret_nr_writeback += nr_writeback;
1283         *ret_nr_immediate += nr_immediate;
1284         return nr_reclaimed;
1285 }
1286 
1287 unsigned long reclaim_clean_pages_from_list(struct zone *zone,
1288                                             struct list_head *page_list)
1289 {
1290         struct scan_control sc = {
1291                 .gfp_mask = GFP_KERNEL,
1292                 .priority = DEF_PRIORITY,
1293                 .may_unmap = 1,
1294         };
1295         unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
1296         struct page *page, *next;
1297         LIST_HEAD(clean_pages);
1298 
1299         list_for_each_entry_safe(page, next, page_list, lru) {
1300                 if (page_is_file_cache(page) && !PageDirty(page) &&
1301                     !__PageMovable(page)) {
1302                         ClearPageActive(page);
1303                         list_move(&page->lru, &clean_pages);
1304                 }
1305         }
1306 
1307         ret = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc,
1308                         TTU_UNMAP|TTU_IGNORE_ACCESS,
1309                         &dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
1310         list_splice(&clean_pages, page_list);
1311         mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -ret);
1312         return ret;
1313 }
1314 
1315 /*
1316  * Attempt to remove the specified page from its LRU.  Only take this page
1317  * if it is of the appropriate PageActive status.  Pages which are being
1318  * freed elsewhere are also ignored.
1319  *
1320  * page:        page to consider
1321  * mode:        one of the LRU isolation modes defined above
1322  *
1323  * returns 0 on success, -ve errno on failure.
1324  */
1325 int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1326 {
1327         int ret = -EINVAL;
1328 
1329         /* Only take pages on the LRU. */
1330         if (!PageLRU(page))
1331                 return ret;
1332 
1333         /* Compaction should not handle unevictable pages but CMA can do so */
1334         if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1335                 return ret;
1336 
1337         ret = -EBUSY;
1338 
1339         /*
1340          * To minimise LRU disruption, the caller can indicate that it only
1341          * wants to isolate pages it will be able to operate on without
1342          * blocking - clean pages for the most part.
1343          *
1344          * ISOLATE_CLEAN means that only clean pages should be isolated. This
1345          * is used by reclaim when it is cannot write to backing storage
1346          *
1347          * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1348          * that it is possible to migrate without blocking
1349          */
1350         if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
1351                 /* All the caller can do on PageWriteback is block */
1352                 if (PageWriteback(page))
1353                         return ret;
1354 
1355                 if (PageDirty(page)) {
1356                         struct address_space *mapping;
1357 
1358                         /* ISOLATE_CLEAN means only clean pages */
1359                         if (mode & ISOLATE_CLEAN)
1360                                 return ret;
1361 
1362                         /*
1363                          * Only pages without mappings or that have a
1364                          * ->migratepage callback are possible to migrate
1365                          * without blocking
1366                          */
1367                         mapping = page_mapping(page);
1368                         if (mapping && !mapping->a_ops->migratepage)
1369                                 return ret;
1370                 }
1371         }
1372 
1373         if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1374                 return ret;
1375 
1376         if (likely(get_page_unless_zero(page))) {
1377                 /*
1378                  * Be careful not to clear PageLRU until after we're
1379                  * sure the page is not being freed elsewhere -- the
1380                  * page release code relies on it.
1381                  */
1382                 ClearPageLRU(page);
1383                 ret = 0;
1384         }
1385 
1386         return ret;
1387 }
1388 
1389 
1390 /*
1391  * Update LRU sizes after isolating pages. The LRU size updates must
1392  * be complete before mem_cgroup_update_lru_size due to a santity check.
1393  */
1394 static __always_inline void update_lru_sizes(struct lruvec *lruvec,
1395                         enum lru_list lru, unsigned long *nr_zone_taken)
1396 {
1397         int zid;
1398 
1399         for (zid = 0; zid < MAX_NR_ZONES; zid++) {
1400                 if (!nr_zone_taken[zid])
1401                         continue;
1402 
1403                 __update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
1404 #ifdef CONFIG_MEMCG
1405                 mem_cgroup_update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
1406 #endif
1407         }
1408 
1409 }
1410 
1411 /*
1412  * zone_lru_lock is heavily contended.  Some of the functions that
1413  * shrink the lists perform better by taking out a batch of pages
1414  * and working on them outside the LRU lock.
1415  *
1416  * For pagecache intensive workloads, this function is the hottest
1417  * spot in the kernel (apart from copy_*_user functions).
1418  *
1419  * Appropriate locks must be held before calling this function.
1420  *
1421  * @nr_to_scan: The number of pages to look through on the list.
1422  * @lruvec:     The LRU vector to pull pages from.
1423  * @dst:        The temp list to put pages on to.
1424  * @nr_scanned: The number of pages that were scanned.
1425  * @sc:         The scan_control struct for this reclaim session
1426  * @mode:       One of the LRU isolation modes
1427  * @lru:        LRU list id for isolating
1428  *
1429  * returns how many pages were moved onto *@dst.
1430  */
1431 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1432                 struct lruvec *lruvec, struct list_head *dst,
1433                 unsigned long *nr_scanned, struct scan_control *sc,
1434                 isolate_mode_t mode, enum lru_list lru)
1435 {
1436         struct list_head *src = &lruvec->lists[lru];
1437         unsigned long nr_taken = 0;
1438         unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
1439         unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
1440         unsigned long scan, nr_pages;
1441         LIST_HEAD(pages_skipped);
1442 
1443         for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
1444                                         !list_empty(src);) {
1445                 struct page *page;
1446 
1447                 page = lru_to_page(src);
1448                 prefetchw_prev_lru_page(page, src, flags);
1449 
1450                 VM_BUG_ON_PAGE(!PageLRU(page), page);
1451 
1452                 if (page_zonenum(page) > sc->reclaim_idx) {
1453                         list_move(&page->lru, &pages_skipped);
1454                         nr_skipped[page_zonenum(page)]++;
1455                         continue;
1456                 }
1457 
1458                 /*
1459                  * Account for scanned and skipped separetly to avoid the pgdat
1460                  * being prematurely marked unreclaimable by pgdat_reclaimable.
1461                  */
1462                 scan++;
1463 
1464                 switch (__isolate_lru_page(page, mode)) {
1465                 case 0:
1466                         nr_pages = hpage_nr_pages(page);
1467                         nr_taken += nr_pages;
1468                         nr_zone_taken[page_zonenum(page)] += nr_pages;
1469                         list_move(&page->lru, dst);
1470                         break;
1471 
1472                 case -EBUSY:
1473                         /* else it is being freed elsewhere */
1474                         list_move(&page->lru, src);
1475                         continue;
1476 
1477                 default:
1478                         BUG();
1479                 }
1480         }
1481 
1482         /*
1483          * Splice any skipped pages to the start of the LRU list. Note that
1484          * this disrupts the LRU order when reclaiming for lower zones but
1485          * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
1486          * scanning would soon rescan the same pages to skip and put the
1487          * system at risk of premature OOM.
1488          */
1489         if (!list_empty(&pages_skipped)) {
1490                 int zid;
1491                 unsigned long total_skipped = 0;
1492 
1493                 for (zid = 0; zid < MAX_NR_ZONES; zid++) {
1494                         if (!nr_skipped[zid])
1495                                 continue;
1496 
1497                         __count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
1498                         total_skipped += nr_skipped[zid];
1499                 }
1500 
1501                 /*
1502                  * Account skipped pages as a partial scan as the pgdat may be
1503                  * close to unreclaimable. If the LRU list is empty, account
1504                  * skipped pages as a full scan.
1505                  */
1506                 scan += list_empty(src) ? total_skipped : total_skipped >> 2;
1507 
1508                 list_splice(&pages_skipped, src);
1509         }
1510         *nr_scanned = scan;
1511         trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, scan,
1512                                     nr_taken, mode, is_file_lru(lru));
1513         update_lru_sizes(lruvec, lru, nr_zone_taken);
1514         return nr_taken;
1515 }
1516 
1517 /**
1518  * isolate_lru_page - tries to isolate a page from its LRU list
1519  * @page: page to isolate from its LRU list
1520  *
1521  * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1522  * vmstat statistic corresponding to whatever LRU list the page was on.
1523  *
1524  * Returns 0 if the page was removed from an LRU list.
1525  * Returns -EBUSY if the page was not on an LRU list.
1526  *
1527  * The returned page will have PageLRU() cleared.  If it was found on
1528  * the active list, it will have PageActive set.  If it was found on
1529  * the unevictable list, it will have the PageUnevictable bit set. That flag
1530  * may need to be cleared by the caller before letting the page go.
1531  *
1532  * The vmstat statistic corresponding to the list on which the page was
1533  * found will be decremented.
1534  *
1535  * Restrictions:
1536  * (1) Must be called with an elevated refcount on the page. This is a
1537  *     fundamentnal difference from isolate_lru_pages (which is called
1538  *     without a stable reference).
1539  * (2) the lru_lock must not be held.
1540  * (3) interrupts must be enabled.
1541  */
1542 int isolate_lru_page(struct page *page)
1543 {
1544         int ret = -EBUSY;
1545 
1546         VM_BUG_ON_PAGE(!page_count(page), page);
1547         WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");
1548 
1549         if (PageLRU(page)) {
1550                 struct zone *zone = page_zone(page);
1551                 struct lruvec *lruvec;
1552 
1553                 spin_lock_irq(zone_lru_lock(zone));
1554                 lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
1555                 if (PageLRU(page)) {
1556                         int lru = page_lru(page);
1557                         get_page(page);
1558                         ClearPageLRU(page);
1559                         del_page_from_lru_list(page, lruvec, lru);
1560                         ret = 0;
1561                 }
1562                 spin_unlock_irq(zone_lru_lock(zone));
1563         }
1564         return ret;
1565 }
1566 
1567 /*
1568  * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
1569  * then get resheduled. When there are massive number of tasks doing page
1570  * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
1571  * the LRU list will go small and be scanned faster than necessary, leading to
1572  * unnecessary swapping, thrashing and OOM.
1573  */
1574 static int too_many_isolated(struct pglist_data *pgdat, int file,
1575                 struct scan_control *sc)
1576 {
1577         unsigned long inactive, isolated;
1578 
1579         if (current_is_kswapd())
1580                 return 0;
1581 
1582         if (!sane_reclaim(sc))
1583                 return 0;
1584 
1585         if (file) {
1586                 inactive = node_page_state(pgdat, NR_INACTIVE_FILE);
1587                 isolated = node_page_state(pgdat, NR_ISOLATED_FILE);
1588         } else {
1589                 inactive = node_page_state(pgdat, NR_INACTIVE_ANON);
1590                 isolated = node_page_state(pgdat, NR_ISOLATED_ANON);
1591         }
1592 
1593         /*
1594          * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
1595          * won't get blocked by normal direct-reclaimers, forming a circular
1596          * deadlock.
1597          */
1598         if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS))
1599                 inactive >>= 3;
1600 
1601         return isolated > inactive;
1602 }
1603 
1604 static noinline_for_stack void
1605 putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1606 {
1607         struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1608         struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1609         LIST_HEAD(pages_to_free);
1610 
1611         /*
1612          * Put back any unfreeable pages.
1613          */
1614         while (!list_empty(page_list)) {
1615                 struct page *page = lru_to_page(page_list);
1616                 int lru;
1617 
1618                 VM_BUG_ON_PAGE(PageLRU(page), page);
1619                 list_del(&page->lru);
1620                 if (unlikely(!page_evictable(page))) {
1621                         spin_unlock_irq(&pgdat->lru_lock);
1622                         putback_lru_page(page);
1623                         spin_lock_irq(&pgdat->lru_lock);
1624                         continue;
1625                 }
1626 
1627                 lruvec = mem_cgroup_page_lruvec(page, pgdat);
1628 
1629                 SetPageLRU(page);
1630                 lru = page_lru(page);
1631                 add_page_to_lru_list(page, lruvec, lru);
1632 
1633                 if (is_active_lru(lru)) {
1634                         int file = is_file_lru(lru);
1635                         int numpages = hpage_nr_pages(page);
1636                         reclaim_stat->recent_rotated[file] += numpages;
1637                 }
1638                 if (put_page_testzero(page)) {
1639                         __ClearPageLRU(page);
1640                         __ClearPageActive(page);
1641                         del_page_from_lru_list(page, lruvec, lru);
1642 
1643                         if (unlikely(PageCompound(page))) {
1644                                 spin_unlock_irq(&pgdat->lru_lock);
1645                                 mem_cgroup_uncharge(page);
1646                                 (*get_compound_page_dtor(page))(page);
1647                                 spin_lock_irq(&pgdat->lru_lock);
1648                         } else
1649                                 list_add(&page->lru, &pages_to_free);
1650                 }
1651         }
1652 
1653         /*
1654          * To save our caller's stack, now use input list for pages to free.
1655          */
1656         list_splice(&pages_to_free, page_list);
1657 }
1658 
1659 /*
1660  * If a kernel thread (such as nfsd for loop-back mounts) services
1661  * a backing device by writing to the page cache it sets PF_LESS_THROTTLE.
1662  * In that case we should only throttle if the backing device it is
1663  * writing to is congested.  In other cases it is safe to throttle.
1664  */
1665 static int current_may_throttle(void)
1666 {
1667         return !(current->flags & PF_LESS_THROTTLE) ||
1668                 current->backing_dev_info == NULL ||
1669                 bdi_write_congested(current->backing_dev_info);
1670 }
1671 
1672 static bool inactive_reclaimable_pages(struct lruvec *lruvec,
1673                                 struct scan_control *sc, enum lru_list lru)
1674 {
1675         int zid;
1676         struct zone *zone;
1677         int file = is_file_lru(lru);
1678         struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1679 
1680         if (!global_reclaim(sc))
1681                 return true;
1682 
1683         for (zid = sc->reclaim_idx; zid >= 0; zid--) {
1684                 zone = &pgdat->node_zones[zid];
1685                 if (!managed_zone(zone))
1686                         continue;
1687 
1688                 if (zone_page_state_snapshot(zone, NR_ZONE_LRU_BASE +
1689                                 LRU_FILE * file) >= SWAP_CLUSTER_MAX)
1690                         return true;
1691         }
1692 
1693         return false;
1694 }
1695 
1696 /*
1697  * shrink_inactive_list() is a helper for shrink_node().  It returns the number
1698  * of reclaimed pages
1699  */
1700 static noinline_for_stack unsigned long
1701 shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1702                      struct scan_control *sc, enum lru_list lru)
1703 {
1704         LIST_HEAD(page_list);
1705         unsigned long nr_scanned;
1706         unsigned long nr_reclaimed = 0;
1707         unsigned long nr_taken;
1708         unsigned long nr_dirty = 0;
1709         unsigned long nr_congested = 0;
1710         unsigned long nr_unqueued_dirty = 0;
1711         unsigned long nr_writeback = 0;
1712         unsigned long nr_immediate = 0;
1713         isolate_mode_t isolate_mode = 0;
1714         int file = is_file_lru(lru);
1715         struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1716         struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1717 
1718         if (!inactive_reclaimable_pages(lruvec, sc, lru))
1719                 return 0;
1720 
1721         while (unlikely(too_many_isolated(pgdat, file, sc))) {
1722                 congestion_wait(BLK_RW_ASYNC, HZ/10);
1723 
1724                 /* We are about to die and free our memory. Return now. */
1725                 if (fatal_signal_pending(current))
1726                         return SWAP_CLUSTER_MAX;
1727         }
1728 
1729         lru_add_drain();
1730 
1731         if (!sc->may_unmap)
1732                 isolate_mode |= ISOLATE_UNMAPPED;
1733         if (!sc->may_writepage)
1734                 isolate_mode |= ISOLATE_CLEAN;
1735 
1736         spin_lock_irq(&pgdat->lru_lock);
1737 
1738         nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1739                                      &nr_scanned, sc, isolate_mode, lru);
1740 
1741         __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
1742         reclaim_stat->recent_scanned[file] += nr_taken;
1743 
1744         if (global_reclaim(sc)) {
1745                 __mod_node_page_state(pgdat, NR_PAGES_SCANNED, nr_scanned);
1746                 if (current_is_kswapd())
1747                         __count_vm_events(PGSCAN_KSWAPD, nr_scanned);
1748                 else
1749                         __count_vm_events(PGSCAN_DIRECT, nr_scanned);
1750         }
1751         spin_unlock_irq(&pgdat->lru_lock);
1752 
1753         if (nr_taken == 0)
1754                 return 0;
1755 
1756         nr_reclaimed = shrink_page_list(&page_list, pgdat, sc, TTU_UNMAP,
1757                                 &nr_dirty, &nr_unqueued_dirty, &nr_congested,
1758                                 &nr_writeback, &nr_immediate,
1759                                 false);
1760 
1761         spin_lock_irq(&pgdat->lru_lock);
1762 
1763         if (global_reclaim(sc)) {
1764                 if (current_is_kswapd())
1765                         __count_vm_events(PGSTEAL_KSWAPD, nr_reclaimed);
1766                 else
1767                         __count_vm_events(PGSTEAL_DIRECT, nr_reclaimed);
1768         }
1769 
1770         putback_inactive_pages(lruvec, &page_list);
1771 
1772         __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
1773 
1774         spin_unlock_irq(&pgdat->lru_lock);
1775 
1776         mem_cgroup_uncharge_list(&page_list);
1777         free_hot_cold_page_list(&page_list, true);
1778 
1779         /*
1780          * If reclaim is isolating dirty pages under writeback, it implies
1781          * that the long-lived page allocation rate is exceeding the page
1782          * laundering rate. Either the global limits are not being effective
1783          * at throttling processes due to the page distribution throughout
1784          * zones or there is heavy usage of a slow backing device. The
1785          * only option is to throttle from reclaim context which is not ideal
1786          * as there is no guarantee the dirtying process is throttled in the
1787          * same way balance_dirty_pages() manages.
1788          *
1789          * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
1790          * of pages under pages flagged for immediate reclaim and stall if any
1791          * are encountered in the nr_immediate check below.
1792          */
1793         if (nr_writeback && nr_writeback == nr_taken)
1794                 set_bit(PGDAT_WRITEBACK, &pgdat->flags);
1795 
1796         /*
1797          * Legacy memcg will stall in page writeback so avoid forcibly
1798          * stalling here.
1799          */
1800         if (sane_reclaim(sc)) {
1801                 /*
1802                  * Tag a zone as congested if all the dirty pages scanned were
1803                  * backed by a congested BDI and wait_iff_congested will stall.
1804                  */
1805                 if (nr_dirty && nr_dirty == nr_congested)
1806                         set_bit(PGDAT_CONGESTED, &pgdat->flags);
1807 
1808                 /*
1809                  * If dirty pages are scanned that are not queued for IO, it
1810                  * implies that flushers are not keeping up. In this case, flag
1811                  * the pgdat PGDAT_DIRTY and kswapd will start writing pages from
1812                  * reclaim context.
1813                  */
1814                 if (nr_unqueued_dirty == nr_taken)
1815                         set_bit(PGDAT_DIRTY, &pgdat->flags);
1816 
1817                 /*
1818                  * If kswapd scans pages marked marked for immediate
1819                  * reclaim and under writeback (nr_immediate), it implies
1820                  * that pages are cycling through the LRU faster than
1821                  * they are written so also forcibly stall.
1822                  */
1823                 if (nr_immediate && current_may_throttle())
1824                         congestion_wait(BLK_RW_ASYNC, HZ/10);
1825         }
1826 
1827         /*
1828          * Stall direct reclaim for IO completions if underlying BDIs or zone
1829          * is congested. Allow kswapd to continue until it starts encountering
1830          * unqueued dirty pages or cycling through the LRU too quickly.
1831          */
1832         if (!sc->hibernation_mode && !current_is_kswapd() &&
1833             current_may_throttle())
1834                 wait_iff_congested(pgdat, BLK_RW_ASYNC, HZ/10);
1835 
1836         trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
1837                         nr_scanned, nr_reclaimed,
1838                         sc->priority, file);
1839         return nr_reclaimed;
1840 }
1841 
1842 /*
1843  * This moves pages from the active list to the inactive list.
1844  *
1845  * We move them the other way if the page is referenced by one or more
1846  * processes, from rmap.
1847  *
1848  * If the pages are mostly unmapped, the processing is fast and it is
1849  * appropriate to hold zone_lru_lock across the whole operation.  But if
1850  * the pages are mapped, the processing is slow (page_referenced()) so we
1851  * should drop zone_lru_lock around each page.  It's impossible to balance
1852  * this, so instead we remove the pages from the LRU while processing them.
1853  * It is safe to rely on PG_active against the non-LRU pages in here because
1854  * nobody will play with that bit on a non-LRU page.
1855  *
1856  * The downside is that we have to touch page->_refcount against each page.
1857  * But we had to alter page->flags anyway.
1858  */
1859 
1860 static void move_active_pages_to_lru(struct lruvec *lruvec,
1861                                      struct list_head *list,
1862                                      struct list_head *pages_to_free,
1863                                      enum lru_list lru)
1864 {
1865         struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1866         unsigned long pgmoved = 0;
1867         struct page *page;
1868         int nr_pages;
1869 
1870         while (!list_empty(list)) {
1871                 page = lru_to_page(list);
1872                 lruvec = mem_cgroup_page_lruvec(page, pgdat);
1873 
1874                 VM_BUG_ON_PAGE(PageLRU(page), page);
1875                 SetPageLRU(page);
1876 
1877                 nr_pages = hpage_nr_pages(page);
1878                 update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
1879                 list_move(&page->lru, &lruvec->lists[lru]);
1880                 pgmoved += nr_pages;
1881 
1882                 if (put_page_testzero(page)) {
1883                         __ClearPageLRU(page);
1884                         __ClearPageActive(page);
1885                         del_page_from_lru_list(page, lruvec, lru);
1886 
1887                         if (unlikely(PageCompound(page))) {
1888                                 spin_unlock_irq(&pgdat->lru_lock);
1889                                 mem_cgroup_uncharge(page);
1890                                 (*get_compound_page_dtor(page))(page);
1891                                 spin_lock_irq(&pgdat->lru_lock);
1892                         } else
1893                                 list_add(&page->lru, pages_to_free);
1894                 }
1895         }
1896 
1897         if (!is_active_lru(lru))
1898                 __count_vm_events(PGDEACTIVATE, pgmoved);
1899 }
1900 
1901 static void shrink_active_list(unsigned long nr_to_scan,
1902                                struct lruvec *lruvec,
1903                                struct scan_control *sc,
1904                                enum lru_list lru)
1905 {
1906         unsigned long nr_taken;
1907         unsigned long nr_scanned;
1908         unsigned long vm_flags;
1909         LIST_HEAD(l_hold);      /* The pages which were snipped off */
1910         LIST_HEAD(l_active);
1911         LIST_HEAD(l_inactive);
1912         struct page *page;
1913         struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1914         unsigned long nr_rotated = 0;
1915         isolate_mode_t isolate_mode = 0;
1916         int file = is_file_lru(lru);
1917         struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1918 
1919         lru_add_drain();
1920 
1921         if (!sc->may_unmap)
1922                 isolate_mode |= ISOLATE_UNMAPPED;
1923         if (!sc->may_writepage)
1924                 isolate_mode |= ISOLATE_CLEAN;
1925 
1926         spin_lock_irq(&pgdat->lru_lock);
1927 
1928         nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1929                                      &nr_scanned, sc, isolate_mode, lru);
1930 
1931         __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
1932         reclaim_stat->recent_scanned[file] += nr_taken;
1933 
1934         if (global_reclaim(sc))
1935                 __mod_node_page_state(pgdat, NR_PAGES_SCANNED, nr_scanned);
1936         __count_vm_events(PGREFILL, nr_scanned);
1937 
1938         spin_unlock_irq(&pgdat->lru_lock);
1939 
1940         while (!list_empty(&l_hold)) {
1941                 cond_resched();
1942                 page = lru_to_page(&l_hold);
1943                 list_del(&page->lru);
1944 
1945                 if (unlikely(!page_evictable(page))) {
1946                         putback_lru_page(page);
1947                         continue;
1948                 }
1949 
1950                 if (unlikely(buffer_heads_over_limit)) {
1951                         if (page_has_private(page) && trylock_page(page)) {
1952                                 if (page_has_private(page))
1953                                         try_to_release_page(page, 0);
1954                                 unlock_page(page);
1955                         }
1956                 }
1957 
1958                 if (page_referenced(page, 0, sc->target_mem_cgroup,
1959                                     &vm_flags)) {
1960                         nr_rotated += hpage_nr_pages(page);
1961                         /*
1962                          * Identify referenced, file-backed active pages and
1963                          * give them one more trip around the active list. So
1964                          * that executable code get better chances to stay in
1965                          * memory under moderate memory pressure.  Anon pages
1966                          * are not likely to be evicted by use-once streaming
1967                          * IO, plus JVM can create lots of anon VM_EXEC pages,
1968                          * so we ignore them here.
1969                          */
1970                         if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1971                                 list_add(&page->lru, &l_active);
1972                                 continue;
1973                         }
1974                 }
1975 
1976                 ClearPageActive(page);  /* we are de-activating */
1977                 list_add(&page->lru, &l_inactive);
1978         }
1979 
1980         /*
1981          * Move pages back to the lru list.
1982          */
1983         spin_lock_irq(&pgdat->lru_lock);
1984         /*
1985          * Count referenced pages from currently used mappings as rotated,
1986          * even though only some of them are actually re-activated.  This
1987          * helps balance scan pressure between file and anonymous pages in
1988          * get_scan_count.
1989          */
1990         reclaim_stat->recent_rotated[file] += nr_rotated;
1991 
1992         move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1993         move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1994         __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
1995         spin_unlock_irq(&pgdat->lru_lock);
1996 
1997         mem_cgroup_uncharge_list(&l_hold);
1998         free_hot_cold_page_list(&l_hold, true);
1999 }
2000 
2001 /*
2002  * The inactive anon list should be small enough that the VM never has
2003  * to do too much work.
2004  *
2005  * The inactive file list should be small enough to leave most memory
2006  * to the established workingset on the scan-resistant active list,
2007  * but large enough to avoid thrashing the aggregate readahead window.
2008  *
2009  * Both inactive lists should also be large enough that each inactive
2010  * page has a chance to be referenced again before it is reclaimed.
2011  *
2012  * The inactive_ratio is the target ratio of ACTIVE to INACTIVE pages
2013  * on this LRU, maintained by the pageout code. A zone->inactive_ratio
2014  * of 3 means 3:1 or 25% of the pages are kept on the inactive list.
2015  *
2016  * total     target    max
2017  * memory    ratio     inactive
2018  * -------------------------------------
2019  *   10MB       1         5MB
2020  *  100MB       1        50MB
2021  *    1GB       3       250MB
2022  *   10GB      10       0.9GB
2023  *  100GB      31         3GB
2024  *    1TB     101        10GB
2025  *   10TB     320        32GB
2026  */
2027 static bool inactive_list_is_low(struct lruvec *lruvec, bool file,
2028                                                 struct scan_control *sc)
2029 {
2030         unsigned long inactive_ratio;
2031         unsigned long inactive;
2032         unsigned long active;
2033         unsigned long gb;
2034         struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2035         int zid;
2036 
2037         /*
2038          * If we don't have swap space, anonymous page deactivation
2039          * is pointless.
2040          */
2041         if (!file && !total_swap_pages)
2042                 return false;
2043 
2044         inactive = lruvec_lru_size(lruvec, file * LRU_FILE);
2045         active = lruvec_lru_size(lruvec, file * LRU_FILE + LRU_ACTIVE);
2046 
2047         /*
2048          * For zone-constrained allocations, it is necessary to check if
2049          * deactivations are required for lowmem to be reclaimed. This
2050          * calculates the inactive/active pages available in eligible zones.
2051          */
2052         for (zid = sc->reclaim_idx + 1; zid < MAX_NR_ZONES; zid++) {
2053                 struct zone *zone = &pgdat->node_zones[zid];
2054                 unsigned long inactive_zone, active_zone;
2055 
2056                 if (!managed_zone(zone))
2057                         continue;
2058 
2059                 inactive_zone = lruvec_zone_lru_size(lruvec, file * LRU_FILE, zid);
2060                 active_zone = lruvec_zone_lru_size(lruvec, (file * LRU_FILE) + LRU_ACTIVE, zid);
2061 
2062                 inactive -= min(inactive, inactive_zone);
2063                 active -= min(active, active_zone);
2064         }
2065 
2066         gb = (inactive + active) >> (30 - PAGE_SHIFT);
2067         if (gb)
2068                 inactive_ratio = int_sqrt(10 * gb);
2069         else
2070                 inactive_ratio = 1;
2071 
2072         return inactive * inactive_ratio < active;
2073 }
2074 
2075 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
2076                                  struct lruvec *lruvec, struct scan_control *sc)
2077 {
2078         if (is_active_lru(lru)) {
2079                 if (inactive_list_is_low(lruvec, is_file_lru(lru), sc))
2080                         shrink_active_list(nr_to_scan, lruvec, sc, lru);
2081                 return 0;
2082         }
2083 
2084         return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
2085 }
2086 
2087 enum scan_balance {
2088         SCAN_EQUAL,
2089         SCAN_FRACT,
2090         SCAN_ANON,
2091         SCAN_FILE,
2092 };
2093 
2094 /*
2095  * Determine how aggressively the anon and file LRU lists should be
2096  * scanned.  The relative value of each set of LRU lists is determined
2097  * by looking at the fraction of the pages scanned we did rotate back
2098  * onto the active list instead of evict.
2099  *
2100  * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
2101  * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
2102  */
2103 static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
2104                            struct scan_control *sc, unsigned long *nr,
2105                            unsigned long *lru_pages)
2106 {
2107         int swappiness = mem_cgroup_swappiness(memcg);
2108         struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
2109         u64 fraction[2];
2110         u64 denominator = 0;    /* gcc */
2111         struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2112         unsigned long anon_prio, file_prio;
2113         enum scan_balance scan_balance;
2114         unsigned long anon, file;
2115         bool force_scan = false;
2116         unsigned long ap, fp;
2117         enum lru_list lru;
2118         bool some_scanned;
2119         int pass;
2120 
2121         /*
2122          * If the zone or memcg is small, nr[l] can be 0.  This
2123          * results in no scanning on this priority and a potential
2124          * priority drop.  Global direct reclaim can go to the next
2125          * zone and tends to have no problems. Global kswapd is for
2126          * zone balancing and it needs to scan a minimum amount. When
2127          * reclaiming for a memcg, a priority drop can cause high
2128          * latencies, so it's better to scan a minimum amount there as
2129          * well.
2130          */
2131         if (current_is_kswapd()) {
2132                 if (!pgdat_reclaimable(pgdat))
2133                         force_scan = true;
2134                 if (!mem_cgroup_online(memcg))
2135                         force_scan = true;
2136         }
2137         if (!global_reclaim(sc))
2138                 force_scan = true;
2139 
2140         /* If we have no swap space, do not bother scanning anon pages. */
2141         if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
2142                 scan_balance = SCAN_FILE;
2143                 goto out;
2144         }
2145 
2146         /*
2147          * Global reclaim will swap to prevent OOM even with no
2148          * swappiness, but memcg users want to use this knob to
2149          * disable swapping for individual groups completely when
2150          * using the memory controller's swap limit feature would be
2151          * too expensive.
2152          */
2153         if (!global_reclaim(sc) && !swappiness) {
2154                 scan_balance = SCAN_FILE;
2155                 goto out;
2156         }
2157 
2158         /*
2159          * Do not apply any pressure balancing cleverness when the
2160          * system is close to OOM, scan both anon and file equally
2161          * (unless the swappiness setting disagrees with swapping).
2162          */
2163         if (!sc->priority && swappiness) {
2164                 scan_balance = SCAN_EQUAL;
2165                 goto out;
2166         }
2167 
2168         /*
2169          * Prevent the reclaimer from falling into the cache trap: as
2170          * cache pages start out inactive, every cache fault will tip
2171          * the scan balance towards the file LRU.  And as the file LRU
2172          * shrinks, so does the window for rotation from references.
2173          * This means we have a runaway feedback loop where a tiny
2174          * thrashing file LRU becomes infinitely more attractive than
2175          * anon pages.  Try to detect this based on file LRU size.
2176          */
2177         if (global_reclaim(sc)) {
2178                 unsigned long pgdatfile;
2179                 unsigned long pgdatfree;
2180                 int z;
2181                 unsigned long total_high_wmark = 0;
2182 
2183                 pgdatfree = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
2184                 pgdatfile = node_page_state(pgdat, NR_ACTIVE_FILE) +
2185                            node_page_state(pgdat, NR_INACTIVE_FILE);
2186 
2187                 for (z = 0; z < MAX_NR_ZONES; z++) {
2188                         struct zone *zone = &pgdat->node_zones[z];
2189                         if (!managed_zone(zone))
2190                                 continue;
2191 
2192                         total_high_wmark += high_wmark_pages(zone);
2193                 }
2194 
2195                 if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) {
2196                         scan_balance = SCAN_ANON;
2197                         goto out;
2198                 }
2199         }
2200 
2201         /*
2202          * If there is enough inactive page cache, i.e. if the size of the
2203          * inactive list is greater than that of the active list *and* the
2204          * inactive list actually has some pages to scan on this priority, we
2205          * do not reclaim anything from the anonymous working set right now.
2206          * Without the second condition we could end up never scanning an
2207          * lruvec even if it has plenty of old anonymous pages unless the
2208          * system is under heavy pressure.
2209          */
2210         if (!inactive_list_is_low(lruvec, true, sc) &&
2211             lruvec_lru_size(lruvec, LRU_INACTIVE_FILE) >> sc->priority) {
2212                 scan_balance = SCAN_FILE;
2213                 goto out;
2214         }
2215 
2216         scan_balance = SCAN_FRACT;
2217 
2218         /*
2219          * With swappiness at 100, anonymous and file have the same priority.
2220          * This scanning priority is essentially the inverse of IO cost.
2221          */
2222         anon_prio = swappiness;
2223         file_prio = 200 - anon_prio;
2224 
2225         /*
2226          * OK, so we have swap space and a fair amount of page cache
2227          * pages.  We use the recently rotated / recently scanned
2228          * ratios to determine how valuable each cache is.
2229          *
2230          * Because workloads change over time (and to avoid overflow)
2231          * we keep these statistics as a floating average, which ends
2232          * up weighing recent references more than old ones.
2233          *
2234          * anon in [0], file in [1]
2235          */
2236 
2237         anon  = lruvec_lru_size(lruvec, LRU_ACTIVE_ANON) +
2238                 lruvec_lru_size(lruvec, LRU_INACTIVE_ANON);
2239         file  = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE) +
2240                 lruvec_lru_size(lruvec, LRU_INACTIVE_FILE);
2241 
2242         spin_lock_irq(&pgdat->lru_lock);
2243         if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
2244                 reclaim_stat->recent_scanned[0] /= 2;
2245                 reclaim_stat->recent_rotated[0] /= 2;
2246         }
2247 
2248         if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
2249                 reclaim_stat->recent_scanned[1] /= 2;
2250                 reclaim_stat->recent_rotated[1] /= 2;
2251         }
2252 
2253         /*
2254          * The amount of pressure on anon vs file pages is inversely
2255          * proportional to the fraction of recently scanned pages on
2256          * each list that were recently referenced and in active use.
2257          */
2258         ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
2259         ap /= reclaim_stat->recent_rotated[0] + 1;
2260 
2261         fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
2262         fp /= reclaim_stat->recent_rotated[1] + 1;
2263         spin_unlock_irq(&pgdat->lru_lock);
2264 
2265         fraction[0] = ap;
2266         fraction[1] = fp;
2267         denominator = ap + fp + 1;
2268 out:
2269         some_scanned = false;
2270         /* Only use force_scan on second pass. */
2271         for (pass = 0; !some_scanned && pass < 2; pass++) {
2272                 *lru_pages = 0;
2273                 for_each_evictable_lru(lru) {
2274                         int file = is_file_lru(lru);
2275                         unsigned long size;
2276                         unsigned long scan;
2277 
2278                         size = lruvec_lru_size(lruvec, lru);
2279                         scan = size >> sc->priority;
2280 
2281                         if (!scan && pass && force_scan)
2282                                 scan = min(size, SWAP_CLUSTER_MAX);
2283 
2284                         switch (scan_balance) {
2285                         case SCAN_EQUAL:
2286                                 /* Scan lists relative to size */
2287                                 break;
2288                         case SCAN_FRACT:
2289                                 /*
2290                                  * Scan types proportional to swappiness and
2291                                  * their relative recent reclaim efficiency.
2292                                  */
2293                                 scan = div64_u64(scan * fraction[file],
2294                                                         denominator);
2295                                 break;
2296                         case SCAN_FILE:
2297                         case SCAN_ANON:
2298                                 /* Scan one type exclusively */
2299                                 if ((scan_balance == SCAN_FILE) != file) {
2300                                         size = 0;
2301                                         scan = 0;
2302                                 }
2303                                 break;
2304                         default:
2305                                 /* Look ma, no brain */
2306                                 BUG();
2307                         }
2308 
2309                         *lru_pages += size;
2310                         nr[lru] = scan;
2311 
2312                         /*
2313                          * Skip the second pass and don't force_scan,
2314                          * if we found something to scan.
2315                          */
2316                         some_scanned |= !!scan;
2317                 }
2318         }
2319 }
2320 
2321 /*
2322  * This is a basic per-node page freer.  Used by both kswapd and direct reclaim.
2323  */
2324 static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memcg,
2325                               struct scan_control *sc, unsigned long *lru_pages)
2326 {
2327         struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
2328         unsigned long nr[NR_LRU_LISTS];
2329         unsigned long targets[NR_LRU_LISTS];
2330         unsigned long nr_to_scan;
2331         enum lru_list lru;
2332         unsigned long nr_reclaimed = 0;
2333         unsigned long nr_to_reclaim = sc->nr_to_reclaim;
2334         struct blk_plug plug;
2335         bool scan_adjusted;
2336 
2337         get_scan_count(lruvec, memcg, sc, nr, lru_pages);
2338 
2339         /* Record the original scan target for proportional adjustments later */
2340         memcpy(targets, nr, sizeof(nr));
2341 
2342         /*
2343          * Global reclaiming within direct reclaim at DEF_PRIORITY is a normal
2344          * event that can occur when there is little memory pressure e.g.
2345          * multiple streaming readers/writers. Hence, we do not abort scanning
2346          * when the requested number of pages are reclaimed when scanning at
2347          * DEF_PRIORITY on the assumption that the fact we are direct
2348          * reclaiming implies that kswapd is not keeping up and it is best to
2349          * do a batch of work at once. For memcg reclaim one check is made to
2350          * abort proportional reclaim if either the file or anon lru has already
2351          * dropped to zero at the first pass.
2352          */
2353         scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() &&
2354                          sc->priority == DEF_PRIORITY);
2355 
2356         blk_start_plug(&plug);
2357         while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
2358                                         nr[LRU_INACTIVE_FILE]) {
2359                 unsigned long nr_anon, nr_file, percentage;
2360                 unsigned long nr_scanned;
2361 
2362                 for_each_evictable_lru(lru) {
2363                         if (nr[lru]) {
2364                                 nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
2365                                 nr[lru] -= nr_to_scan;
2366 
2367                                 nr_reclaimed += shrink_list(lru, nr_to_scan,
2368                                                             lruvec, sc);
2369                         }
2370                 }
2371 
2372                 cond_resched();
2373 
2374                 if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
2375                         continue;
2376 
2377                 /*
2378                  * For kswapd and memcg, reclaim at least the number of pages
2379                  * requested. Ensure that the anon and file LRUs are scanned
2380                  * proportionally what was requested by get_scan_count(). We
2381                  * stop reclaiming one LRU and reduce the amount scanning
2382                  * proportional to the original scan target.
2383                  */
2384                 nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
2385                 nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
2386 
2387                 /*
2388                  * It's just vindictive to attack the larger once the smaller
2389                  * has gone to zero.  And given the way we stop scanning the
2390                  * smaller below, this makes sure that we only make one nudge
2391                  * towards proportionality once we've got nr_to_reclaim.
2392                  */
2393                 if (!nr_file || !nr_anon)
2394                         break;
2395 
2396                 if (nr_file > nr_anon) {
2397                         unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
2398                                                 targets[LRU_ACTIVE_ANON] + 1;
2399                         lru = LRU_BASE;
2400                         percentage = nr_anon * 100 / scan_target;
2401                 } else {
2402                         unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
2403                                                 targets[LRU_ACTIVE_FILE] + 1;
2404                         lru = LRU_FILE;
2405                         percentage = nr_file * 100 / scan_target;
2406                 }
2407 
2408                 /* Stop scanning the smaller of the LRU */
2409                 nr[lru] = 0;
2410                 nr[lru + LRU_ACTIVE] = 0;
2411 
2412                 /*
2413                  * Recalculate the other LRU scan count based on its original
2414                  * scan target and the percentage scanning already complete
2415                  */
2416                 lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
2417                 nr_scanned = targets[lru] - nr[lru];
2418                 nr[lru] = targets[lru] * (100 - percentage) / 100;
2419                 nr[lru] -= min(nr[lru], nr_scanned);
2420 
2421                 lru += LRU_ACTIVE;
2422                 nr_scanned = targets[lru] - nr[lru];
2423                 nr[lru] = targets[lru] * (100 - percentage) / 100;
2424                 nr[lru] -= min(nr[lru], nr_scanned);
2425 
2426                 scan_adjusted = true;
2427         }
2428         blk_finish_plug(&plug);
2429         sc->nr_reclaimed += nr_reclaimed;
2430 
2431         /*
2432          * Even if we did not try to evict anon pages at all, we want to
2433          * rebalance the anon lru active/inactive ratio.
2434          */
2435         if (inactive_list_is_low(lruvec, false, sc))
2436                 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2437                                    sc, LRU_ACTIVE_ANON);
2438 }
2439 
2440 /* Use reclaim/compaction for costly allocs or under memory pressure */
2441 static bool in_reclaim_compaction(struct scan_control *sc)
2442 {
2443         if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2444                         (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
2445                          sc->priority < DEF_PRIORITY - 2))
2446                 return true;
2447 
2448         return false;
2449 }
2450 
2451 /*
2452  * Reclaim/compaction is used for high-order allocation requests. It reclaims
2453  * order-0 pages before compacting the zone. should_continue_reclaim() returns
2454  * true if more pages should be reclaimed such that when the page allocator
2455  * calls try_to_compact_zone() that it will have enough free pages to succeed.
2456  * It will give up earlier than that if there is difficulty reclaiming pages.
2457  */
2458 static inline bool should_continue_reclaim(struct pglist_data *pgdat,
2459                                         unsigned long nr_reclaimed,
2460                                         unsigned long nr_scanned,
2461                                         struct scan_control *sc)
2462 {
2463         unsigned long pages_for_compaction;
2464         unsigned long inactive_lru_pages;
2465         int z;
2466 
2467         /* If not in reclaim/compaction mode, stop */
2468         if (!in_reclaim_compaction(sc))
2469                 return false;
2470 
2471         /* Consider stopping depending on scan and reclaim activity */
2472         if (sc->gfp_mask & __GFP_REPEAT) {
2473                 /*
2474                  * For __GFP_REPEAT allocations, stop reclaiming if the
2475                  * full LRU list has been scanned and we are still failing
2476                  * to reclaim pages. This full LRU scan is potentially
2477                  * expensive but a __GFP_REPEAT caller really wants to succeed
2478                  */
2479                 if (!nr_reclaimed && !nr_scanned)
2480                         return false;
2481         } else {
2482                 /*
2483                  * For non-__GFP_REPEAT allocations which can presumably
2484                  * fail without consequence, stop if we failed to reclaim
2485                  * any pages from the last SWAP_CLUSTER_MAX number of
2486                  * pages that were scanned. This will return to the
2487                  * caller faster at the risk reclaim/compaction and
2488                  * the resulting allocation attempt fails
2489                  */
2490                 if (!nr_reclaimed)
2491                         return false;
2492         }
2493 
2494         /*
2495          * If we have not reclaimed enough pages for compaction and the
2496          * inactive lists are large enough, continue reclaiming
2497          */
2498         pages_for_compaction = compact_gap(sc->order);
2499         inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
2500         if (get_nr_swap_pages() > 0)
2501                 inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
2502         if (sc->nr_reclaimed < pages_for_compaction &&
2503                         inactive_lru_pages > pages_for_compaction)
2504                 return true;
2505 
2506         /* If compaction would go ahead or the allocation would succeed, stop */
2507         for (z = 0; z <= sc->reclaim_idx; z++) {
2508                 struct zone *zone = &pgdat->node_zones[z];
2509                 if (!managed_zone(zone))
2510                         continue;
2511 
2512                 switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) {
2513                 case COMPACT_SUCCESS:
2514                 case COMPACT_CONTINUE:
2515                         return false;
2516                 default:
2517                         /* check next zone */
2518                         ;
2519                 }
2520         }
2521         return true;
2522 }
2523 
2524 static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
2525 {
2526         struct reclaim_state *reclaim_state = current->reclaim_state;
2527         unsigned long nr_reclaimed, nr_scanned;
2528         bool reclaimable = false;
2529 
2530         do {
2531                 struct mem_cgroup *root = sc->target_mem_cgroup;
2532                 struct mem_cgroup_reclaim_cookie reclaim = {
2533                         .pgdat = pgdat,
2534                         .priority = sc->priority,
2535                 };
2536                 unsigned long node_lru_pages = 0;
2537                 struct mem_cgroup *memcg;
2538 
2539                 nr_reclaimed = sc->nr_reclaimed;
2540                 nr_scanned = sc->nr_scanned;
2541 
2542                 memcg = mem_cgroup_iter(root, NULL, &reclaim);
2543                 do {
2544                         unsigned long lru_pages;
2545                         unsigned long reclaimed;
2546                         unsigned long scanned;
2547 
2548                         if (mem_cgroup_low(root, memcg)) {
2549                                 if (!sc->may_thrash)
2550                                         continue;
2551                                 mem_cgroup_events(memcg, MEMCG_LOW, 1);
2552                         }
2553 
2554                         reclaimed = sc->nr_reclaimed;
2555                         scanned = sc->nr_scanned;
2556 
2557                         shrink_node_memcg(pgdat, memcg, sc, &lru_pages);
2558                         node_lru_pages += lru_pages;
2559 
2560                         if (memcg)
2561                                 shrink_slab(sc->gfp_mask, pgdat->node_id,
2562                                             memcg, sc->nr_scanned - scanned,
2563                                             lru_pages);
2564 
2565                         /* Record the group's reclaim efficiency */
2566                         vmpressure(sc->gfp_mask, memcg, false,
2567                                    sc->nr_scanned - scanned,
2568                                    sc->nr_reclaimed - reclaimed);
2569 
2570                         /*
2571                          * Direct reclaim and kswapd have to scan all memory
2572                          * cgroups to fulfill the overall scan target for the
2573                          * node.
2574                          *
2575                          * Limit reclaim, on the other hand, only cares about
2576                          * nr_to_reclaim pages to be reclaimed and it will
2577                          * retry with decreasing priority if one round over the
2578                          * whole hierarchy is not sufficient.
2579                          */
2580                         if (!global_reclaim(sc) &&
2581                                         sc->nr_reclaimed >= sc->nr_to_reclaim) {
2582                                 mem_cgroup_iter_break(root, memcg);
2583                                 break;
2584                         }
2585                 } while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));
2586 
2587                 /*
2588                  * Shrink the slab caches in the same proportion that
2589                  * the eligible LRU pages were scanned.
2590                  */
2591                 if (global_reclaim(sc))
2592                         shrink_slab(sc->gfp_mask, pgdat->node_id, NULL,
2593                                     sc->nr_scanned - nr_scanned,
2594                                     node_lru_pages);
2595 
2596                 if (reclaim_state) {
2597                         sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2598                         reclaim_state->reclaimed_slab = 0;
2599                 }
2600 
2601                 /* Record the subtree's reclaim efficiency */
2602                 vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
2603                            sc->nr_scanned - nr_scanned,
2604                            sc->nr_reclaimed - nr_reclaimed);
2605 
2606                 if (sc->nr_reclaimed - nr_reclaimed)
2607                         reclaimable = true;
2608 
2609         } while (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
2610                                          sc->nr_scanned - nr_scanned, sc));
2611 
2612         return reclaimable;
2613 }
2614 
2615 /*
2616  * Returns true if compaction should go ahead for a costly-order request, or
2617  * the allocation would already succeed without compaction. Return false if we
2618  * should reclaim first.
2619  */
2620 static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
2621 {
2622         unsigned long watermark;
2623         enum compact_result suitable;
2624 
2625         suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
2626         if (suitable == COMPACT_SUCCESS)
2627                 /* Allocation should succeed already. Don't reclaim. */
2628                 return true;
2629         if (suitable == COMPACT_SKIPPED)
2630                 /* Compaction cannot yet proceed. Do reclaim. */
2631                 return false;
2632 
2633         /*
2634          * Compaction is already possible, but it takes time to run and there
2635          * are potentially other callers using the pages just freed. So proceed
2636          * with reclaim to make a buffer of free pages available to give
2637          * compaction a reasonable chance of completing and allocating the page.
2638          * Note that we won't actually reclaim the whole buffer in one attempt
2639          * as the target watermark in should_continue_reclaim() is lower. But if
2640          * we are already above the high+gap watermark, don't reclaim at all.
2641          */
2642         watermark = high_wmark_pages(zone) + compact_gap(sc->order);
2643 
2644         return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
2645 }
2646 
2647 /*
2648  * This is the direct reclaim path, for page-allocating processes.  We only
2649  * try to reclaim pages from zones which will satisfy the caller's allocation
2650  * request.
2651  *
2652  * If a zone is deemed to be full of pinned pages then just give it a light
2653  * scan then give up on it.
2654  */
2655 static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
2656 {
2657         struct zoneref *z;
2658         struct zone *zone;
2659         unsigned long nr_soft_reclaimed;
2660         unsigned long nr_soft_scanned;
2661         gfp_t orig_mask;
2662         pg_data_t *last_pgdat = NULL;
2663 
2664         /*
2665          * If the number of buffer_heads in the machine exceeds the maximum
2666          * allowed level, force direct reclaim to scan the highmem zone as
2667          * highmem pages could be pinning lowmem pages storing buffer_heads
2668          */
2669         orig_mask = sc->gfp_mask;
2670         if (buffer_heads_over_limit) {
2671                 sc->gfp_mask |= __GFP_HIGHMEM;
2672                 sc->reclaim_idx = gfp_zone(sc->gfp_mask);
2673         }
2674 
2675         for_each_zone_zonelist_nodemask(zone, z, zonelist,
2676                                         sc->reclaim_idx, sc->nodemask) {
2677                 /*
2678                  * Take care memory controller reclaiming has small influence
2679                  * to global LRU.
2680                  */
2681                 if (global_reclaim(sc)) {
2682                         if (!cpuset_zone_allowed(zone,
2683                                                  GFP_KERNEL | __GFP_HARDWALL))
2684                                 continue;
2685 
2686                         if (sc->priority != DEF_PRIORITY &&
2687                             !pgdat_reclaimable(zone->zone_pgdat))
2688                                 continue;       /* Let kswapd poll it */
2689 
2690                         /*
2691                          * If we already have plenty of memory free for
2692                          * compaction in this zone, don't free any more.
2693                          * Even though compaction is invoked for any
2694                          * non-zero order, only frequent costly order
2695                          * reclamation is disruptive enough to become a
2696                          * noticeable problem, like transparent huge
2697                          * page allocations.
2698                          */
2699                         if (IS_ENABLED(CONFIG_COMPACTION) &&
2700                             sc->order > PAGE_ALLOC_COSTLY_ORDER &&
2701                             compaction_ready(zone, sc)) {
2702                                 sc->compaction_ready = true;
2703                                 continue;
2704                         }
2705 
2706                         /*
2707                          * Shrink each node in the zonelist once. If the
2708                          * zonelist is ordered by zone (not the default) then a
2709                          * node may be shrunk multiple times but in that case
2710                          * the user prefers lower zones being preserved.
2711                          */
2712                         if (zone->zone_pgdat == last_pgdat)
2713                                 continue;
2714 
2715                         /*
2716                          * This steals pages from memory cgroups over softlimit
2717                          * and returns the number of reclaimed pages and
2718                          * scanned pages. This works for global memory pressure
2719                          * and balancing, not for a memcg's limit.
2720                          */
2721                         nr_soft_scanned = 0;
2722                         nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone->zone_pgdat,
2723                                                 sc->order, sc->gfp_mask,
2724                                                 &nr_soft_scanned);
2725                         sc->nr_reclaimed += nr_soft_reclaimed;
2726                         sc->nr_scanned += nr_soft_scanned;
2727                         /* need some check for avoid more shrink_zone() */
2728                 }
2729 
2730                 /* See comment about same check for global reclaim above */
2731                 if (zone->zone_pgdat == last_pgdat)
2732                         continue;
2733                 last_pgdat = zone->zone_pgdat;
2734                 shrink_node(zone->zone_pgdat, sc);
2735         }
2736 
2737         /*
2738          * Restore to original mask to avoid the impact on the caller if we
2739          * promoted it to __GFP_HIGHMEM.
2740          */
2741         sc->gfp_mask = orig_mask;
2742 }
2743 
2744 /*
2745  * This is the main entry point to direct page reclaim.
2746  *
2747  * If a full scan of the inactive list fails to free enough memory then we
2748  * are "out of memory" and something needs to be killed.
2749  *
2750  * If the caller is !__GFP_FS then the probability of a failure is reasonably
2751  * high - the zone may be full of dirty or under-writeback pages, which this
2752  * caller can't do much about.  We kick the writeback threads and take explicit
2753  * naps in the hope that some of these pages can be written.  But if the
2754  * allocating task holds filesystem locks which prevent writeout this might not
2755  * work, and the allocation attempt will fail.
2756  *
2757  * returns:     0, if no pages reclaimed
2758  *              else, the number of pages reclaimed
2759  */
2760 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2761                                           struct scan_control *sc)
2762 {
2763         int initial_priority = sc->priority;
2764         unsigned long total_scanned = 0;
2765         unsigned long writeback_threshold;
2766 retry:
2767         delayacct_freepages_start();
2768 
2769         if (global_reclaim(sc))
2770                 __count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
2771 
2772         do {
2773                 vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
2774                                 sc->priority);
2775                 sc->nr_scanned = 0;
2776                 shrink_zones(zonelist, sc);
2777 
2778                 total_scanned += sc->nr_scanned;
2779                 if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2780                         break;
2781 
2782                 if (sc->compaction_ready)
2783                         break;
2784 
2785                 /*
2786                  * If we're getting trouble reclaiming, start doing
2787                  * writepage even in laptop mode.
2788                  */
2789                 if (sc->priority < DEF_PRIORITY - 2)
2790                         sc->may_writepage = 1;
2791 
2792                 /*
2793                  * Try to write back as many pages as we just scanned.  This
2794                  * tends to cause slow streaming writers to write data to the
2795                  * disk smoothly, at the dirtying rate, which is nice.   But
2796                  * that's undesirable in laptop mode, where we *want* lumpy
2797                  * writeout.  So in laptop mode, write out the whole world.
2798                  */
2799                 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2800                 if (total_scanned > writeback_threshold) {
2801                         wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2802                                                 WB_REASON_TRY_TO_FREE_PAGES);
2803                         sc->may_writepage = 1;
2804                 }
2805         } while (--sc->priority >= 0);
2806 
2807         delayacct_freepages_end();
2808 
2809         if (sc->nr_reclaimed)
2810                 return sc->nr_reclaimed;
2811 
2812         /* Aborted reclaim to try compaction? don't OOM, then */
2813         if (sc->compaction_ready)
2814                 return 1;
2815 
2816         /* Untapped cgroup reserves?  Don't OOM, retry. */
2817         if (!sc->may_thrash) {
2818                 sc->priority = initial_priority;
2819                 sc->may_thrash = 1;
2820                 goto retry;
2821         }
2822 
2823         return 0;
2824 }
2825 
2826 static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2827 {
2828         struct zone *zone;
2829         unsigned long pfmemalloc_reserve = 0;
2830         unsigned long free_pages = 0;
2831         int i;
2832         bool wmark_ok;
2833 
2834         for (i = 0; i <= ZONE_NORMAL; i++) {
2835                 zone = &pgdat->node_zones[i];
2836                 if (!managed_zone(zone) ||
2837                     pgdat_reclaimable_pages(pgdat) == 0)
2838                         continue;
2839 
2840                 pfmemalloc_reserve += min_wmark_pages(zone);
2841                 free_pages += zone_page_state(zone, NR_FREE_PAGES);
2842         }
2843 
2844         /* If there are no reserves (unexpected config) then do not throttle */
2845         if (!pfmemalloc_reserve)
2846                 return true;
2847 
2848         wmark_ok = free_pages > pfmemalloc_reserve / 2;
2849 
2850         /* kswapd must be awake if processes are being throttled */
2851         if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2852                 pgdat->kswapd_classzone_idx = min(pgdat->kswapd_classzone_idx,
2853                                                 (enum zone_type)ZONE_NORMAL);
2854                 wake_up_interruptible(&pgdat->kswapd_wait);
2855         }
2856 
2857         return wmark_ok;
2858 }
2859 
2860 /*
2861  * Throttle direct reclaimers if backing storage is backed by the network
2862  * and the PFMEMALLOC reserve for the preferred node is getting dangerously
2863  * depleted. kswapd will continue to make progress and wake the processes
2864  * when the low watermark is reached.
2865  *
2866  * Returns true if a fatal signal was delivered during throttling. If this
2867  * happens, the page allocator should not consider triggering the OOM killer.
2868  */
2869 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2870                                         nodemask_t *nodemask)
2871 {
2872         struct zoneref *z;
2873         struct zone *zone;
2874         pg_data_t *pgdat = NULL;
2875 
2876         /*
2877          * Kernel threads should not be throttled as they may be indirectly
2878          * responsible for cleaning pages necessary for reclaim to make forward
2879          * progress. kjournald for example may enter direct reclaim while
2880          * committing a transaction where throttling it could forcing other
2881          * processes to block on log_wait_commit().
2882          */
2883         if (current->flags & PF_KTHREAD)
2884                 goto out;
2885 
2886         /*
2887          * If a fatal signal is pending, this process should not throttle.
2888          * It should return quickly so it can exit and free its memory
2889          */
2890         if (fatal_signal_pending(current))
2891                 goto out;
2892 
2893         /*
2894          * Check if the pfmemalloc reserves are ok by finding the first node
2895          * with a usable ZONE_NORMAL or lower zone. The expectation is that
2896          * GFP_KERNEL will be required for allocating network buffers when
2897          * swapping over the network so ZONE_HIGHMEM is unusable.
2898          *
2899          * Throttling is based on the first usable node and throttled processes
2900          * wait on a queue until kswapd makes progress and wakes them. There
2901          * is an affinity then between processes waking up and where reclaim
2902          * progress has been made assuming the process wakes on the same node.
2903          * More importantly, processes running on remote nodes will not compete
2904          * for remote pfmemalloc reserves and processes on different nodes
2905          * should make reasonable progress.
2906          */
2907         for_each_zone_zonelist_nodemask(zone, z, zonelist,
2908                                         gfp_zone(gfp_mask), nodemask) {
2909                 if (zone_idx(zone) > ZONE_NORMAL)
2910                         continue;
2911 
2912                 /* Throttle based on the first usable node */
2913                 pgdat = zone->zone_pgdat;
2914                 if (pfmemalloc_watermark_ok(pgdat))
2915                         goto out;
2916                 break;
2917         }
2918 
2919         /* If no zone was usable by the allocation flags then do not throttle */
2920         if (!pgdat)
2921                 goto out;
2922 
2923         /* Account for the throttling */
2924         count_vm_event(PGSCAN_DIRECT_THROTTLE);
2925 
2926         /*
2927          * If the caller cannot enter the filesystem, it's possible that it
2928          * is due to the caller holding an FS lock or performing a journal
2929          * transaction in the case of a filesystem like ext[3|4]. In this case,
2930          * it is not safe to block on pfmemalloc_wait as kswapd could be
2931          * blocked waiting on the same lock. Instead, throttle for up to a
2932          * second before continuing.
2933          */
2934         if (!(gfp_mask & __GFP_FS)) {
2935                 wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2936                         pfmemalloc_watermark_ok(pgdat), HZ);
2937 
2938                 goto check_pending;
2939         }
2940 
2941         /* Throttle until kswapd wakes the process */
2942         wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2943                 pfmemalloc_watermark_ok(pgdat));
2944 
2945 check_pending:
2946         if (fatal_signal_pending(current))
2947                 return true;
2948 
2949 out:
2950         return false;
2951 }
2952 
2953 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2954                                 gfp_t gfp_mask, nodemask_t *nodemask)
2955 {
2956         unsigned long nr_reclaimed;
2957         struct scan_control sc = {
2958                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2959                 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
2960                 .reclaim_idx = gfp_zone(gfp_mask),
2961                 .order = order,
2962                 .nodemask = nodemask,
2963                 .priority = DEF_PRIORITY,
2964                 .may_writepage = !laptop_mode,
2965                 .may_unmap = 1,
2966                 .may_swap = 1,
2967         };
2968 
2969         /*
2970          * Do not enter reclaim if fatal signal was delivered while throttled.
2971          * 1 is returned so that the page allocator does not OOM kill at this
2972          * point.
2973          */
2974         if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2975                 return 1;
2976 
2977         trace_mm_vmscan_direct_reclaim_begin(order,
2978                                 sc.may_writepage,
2979                                 gfp_mask,
2980                                 sc.reclaim_idx);
2981 
2982         nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2983 
2984         trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2985 
2986         return nr_reclaimed;
2987 }
2988 
2989 #ifdef CONFIG_MEMCG
2990 
2991 unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
2992                                                 gfp_t gfp_mask, bool noswap,
2993                                                 pg_data_t *pgdat,
2994                                                 unsigned long *nr_scanned)
2995 {
2996         struct scan_control sc = {
2997                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2998                 .target_mem_cgroup = memcg,
2999                 .may_writepage = !laptop_mode,
3000                 .may_unmap = 1,
3001                 .reclaim_idx = MAX_NR_ZONES - 1,
3002                 .may_swap = !noswap,
3003         };
3004         unsigned long lru_pages;
3005 
3006         sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
3007                         (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
3008 
3009         trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
3010                                                       sc.may_writepage,
3011                                                       sc.gfp_mask,
3012                                                       sc.reclaim_idx);
3013 
3014         /*
3015          * NOTE: Although we can get the priority field, using it
3016          * here is not a good idea, since it limits the pages we can scan.
3017          * if we don't reclaim here, the shrink_node from balance_pgdat
3018          * will pick up pages from other mem cgroup's as well. We hack
3019          * the priority and make it zero.
3020          */
3021         shrink_node_memcg(pgdat, memcg, &sc, &lru_pages);
3022 
3023         trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
3024 
3025         *nr_scanned = sc.nr_scanned;
3026         return sc.nr_reclaimed;
3027 }
3028 
3029 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
3030                                            unsigned long nr_pages,
3031                                            gfp_t gfp_mask,
3032                                            bool may_swap)
3033 {
3034         struct zonelist *zonelist;
3035         unsigned long nr_reclaimed;
3036         int nid;
3037         struct scan_control sc = {
3038                 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3039                 .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
3040                                 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
3041                 .reclaim_idx = MAX_NR_ZONES - 1,
3042                 .target_mem_cgroup = memcg,
3043                 .priority = DEF_PRIORITY,
3044                 .may_writepage = !laptop_mode,
3045                 .may_unmap = 1,
3046                 .may_swap = may_swap,
3047         };
3048 
3049         /*
3050          * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
3051          * take care of from where we get pages. So the node where we start the
3052          * scan does not need to be the current node.
3053          */
3054         nid = mem_cgroup_select_victim_node(memcg);
3055 
3056         zonelist = &NODE_DATA(nid)->node_zonelists[ZONELIST_FALLBACK];
3057 
3058         trace_mm_vmscan_memcg_reclaim_begin(0,
3059                                             sc.may_writepage,
3060                                             sc.gfp_mask,
3061                                             sc.reclaim_idx);
3062 
3063         current->flags |= PF_MEMALLOC;
3064         nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3065         current->flags &= ~PF_MEMALLOC;
3066 
3067         trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
3068 
3069         return nr_reclaimed;
3070 }
3071 #endif
3072 
3073 static void age_active_anon(struct pglist_data *pgdat,
3074                                 struct scan_control *sc)
3075 {
3076         struct mem_cgroup *memcg;
3077 
3078         if (!total_swap_pages)
3079                 return;
3080 
3081         memcg = mem_cgroup_iter(NULL, NULL, NULL);
3082         do {
3083                 struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
3084 
3085                 if (inactive_list_is_low(lruvec, false, sc))
3086                         shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
3087                                            sc, LRU_ACTIVE_ANON);
3088 
3089                 memcg = mem_cgroup_iter(NULL, memcg, NULL);
3090         } while (memcg);
3091 }
3092 
3093 static bool zone_balanced(struct zone *zone, int order, int classzone_idx)
3094 {
3095         unsigned long mark = high_wmark_pages(zone);
3096 
3097         if (!zone_watermark_ok_safe(zone, order, mark, classzone_idx))
3098                 return false;
3099 
3100         /*
3101          * If any eligible zone is balanced then the node is not considered
3102          * to be congested or dirty
3103          */
3104         clear_bit(PGDAT_CONGESTED, &zone->zone_pgdat->flags);
3105         clear_bit(PGDAT_DIRTY, &zone->zone_pgdat->flags);
3106 
3107         return true;
3108 }
3109 
3110 /*
3111  * Prepare kswapd for sleeping. This verifies that there are no processes
3112  * waiting in throttle_direct_reclaim() and that watermarks have been met.
3113  *
3114  * Returns true if kswapd is ready to sleep
3115  */
3116 static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, int classzone_idx)
3117 {
3118         int i;
3119 
3120         /*
3121          * The throttled processes are normally woken up in balance_pgdat() as
3122          * soon as pfmemalloc_watermark_ok() is true. But there is a potential
3123          * race between when kswapd checks the watermarks and a process gets
3124          * throttled. There is also a potential race if processes get
3125          * throttled, kswapd wakes, a large process exits thereby balancing the
3126          * zones, which causes kswapd to exit balance_pgdat() before reaching
3127          * the wake up checks. If kswapd is going to sleep, no process should
3128          * be sleeping on pfmemalloc_wait, so wake them now if necessary. If
3129          * the wake up is premature, processes will wake kswapd and get
3130          * throttled again. The difference from wake ups in balance_pgdat() is
3131          * that here we are under prepare_to_wait().
3132          */
3133         if (waitqueue_active(&pgdat->pfmemalloc_wait))
3134                 wake_up_all(&pgdat->pfmemalloc_wait);
3135 
3136         for (i = 0; i <= classzone_idx; i++) {
3137                 struct zone *zone = pgdat->node_zones + i;
3138 
3139                 if (!managed_zone(zone))
3140                         continue;
3141 
3142                 if (!zone_balanced(zone, order, classzone_idx))
3143                         return false;
3144         }
3145 
3146         return true;
3147 }
3148 
3149 /*
3150  * kswapd shrinks a node of pages that are at or below the highest usable
3151  * zone that is currently unbalanced.
3152  *
3153  * Returns true if kswapd scanned at least the requested number of pages to
3154  * reclaim or if the lack of progress was due to pages under writeback.
3155  * This is used to determine if the scanning priority needs to be raised.
3156  */
3157 static bool kswapd_shrink_node(pg_data_t *pgdat,
3158                                struct scan_control *sc)
3159 {
3160         struct zone *zone;
3161         int z;
3162 
3163         /* Reclaim a number of pages proportional to the number of zones */
3164         sc->nr_to_reclaim = 0;
3165         for (z = 0; z <= sc->reclaim_idx; z++) {
3166                 zone = pgdat->node_zones + z;
3167                 if (!managed_zone(zone))
3168                         continue;
3169 
3170                 sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX);
3171         }
3172 
3173         /*
3174          * Historically care was taken to put equal pressure on all zones but
3175          * now pressure is applied based on node LRU order.
3176          */
3177         shrink_node(pgdat, sc);
3178 
3179         /*
3180          * Fragmentation may mean that the system cannot be rebalanced for
3181          * high-order allocations. If twice the allocation size has been
3182          * reclaimed then recheck watermarks only at order-0 to prevent
3183          * excessive reclaim. Assume that a process requested a high-order
3184          * can direct reclaim/compact.
3185          */
3186         if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order))
3187                 sc->order = 0;
3188 
3189         return sc->nr_scanned >= sc->nr_to_reclaim;
3190 }
3191 
3192 /*
3193  * For kswapd, balance_pgdat() will reclaim pages across a node from zones
3194  * that are eligible for use by the caller until at least one zone is
3195  * balanced.
3196  *
3197  * Returns the order kswapd finished reclaiming at.
3198  *
3199  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
3200  * zones which have free_pages > high_wmark_pages(zone), but once a zone is
3201  * found to have free_pages <= high_wmark_pages(zone), any page is that zone
3202  * or lower is eligible for reclaim until at least one usable zone is
3203  * balanced.
3204  */
3205 static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
3206 {
3207         int i;
3208         unsigned long nr_soft_reclaimed;
3209         unsigned long nr_soft_scanned;
3210         struct zone *zone;
3211         struct scan_control sc = {
3212                 .gfp_mask = GFP_KERNEL,
3213                 .order = order,
3214                 .priority = DEF_PRIORITY,
3215                 .may_writepage = !laptop_mode,
3216                 .may_unmap = 1,
3217                 .may_swap = 1,
3218         };
3219         count_vm_event(PAGEOUTRUN);
3220 
3221         do {
3222                 bool raise_priority = true;
3223 
3224                 sc.nr_reclaimed = 0;
3225                 sc.reclaim_idx = classzone_idx;
3226 
3227                 /*
3228                  * If the number of buffer_heads exceeds the maximum allowed
3229                  * then consider reclaiming from all zones. This has a dual
3230                  * purpose -- on 64-bit systems it is expected that
3231                  * buffer_heads are stripped during active rotation. On 32-bit
3232                  * systems, highmem pages can pin lowmem memory and shrinking
3233                  * buffers can relieve lowmem pressure. Reclaim may still not
3234                  * go ahead if all eligible zones for the original allocation
3235                  * request are balanced to avoid excessive reclaim from kswapd.
3236                  */
3237                 if (buffer_heads_over_limit) {
3238                         for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
3239                                 zone = pgdat->node_zones + i;
3240                                 if (!managed_zone(zone))
3241                                         continue;
3242 
3243                                 sc.reclaim_idx = i;
3244                                 break;
3245                         }
3246                 }
3247 
3248                 /*
3249                  * Only reclaim if there are no eligible zones. Check from
3250                  * high to low zone as allocations prefer higher zones.
3251                  * Scanning from low to high zone would allow congestion to be
3252                  * cleared during a very small window when a small low
3253                  * zone was balanced even under extreme pressure when the
3254                  * overall node may be congested. Note that sc.reclaim_idx
3255                  * is not used as buffer_heads_over_limit may have adjusted
3256                  * it.
3257                  */
3258                 for (i = classzone_idx; i >= 0; i--) {
3259                         zone = pgdat->node_zones + i;
3260                         if (!managed_zone(zone))
3261                                 continue;
3262 
3263                         if (zone_balanced(zone, sc.order, classzone_idx))
3264                                 goto out;
3265                 }
3266 
3267                 /*
3268                  * Do some background aging of the anon list, to give
3269                  * pages a chance to be referenced before reclaiming. All
3270                  * pages are rotated regardless of classzone as this is
3271                  * about consistent aging.
3272                  */
3273                 age_active_anon(pgdat, &sc);
3274 
3275                 /*
3276                  * If we're getting trouble reclaiming, start doing writepage
3277                  * even in laptop mode.
3278                  */
3279                 if (sc.priority < DEF_PRIORITY - 2 || !pgdat_reclaimable(pgdat))
3280                         sc.may_writepage = 1;
3281 
3282                 /* Call soft limit reclaim before calling shrink_node. */
3283                 sc.nr_scanned = 0;
3284                 nr_soft_scanned = 0;
3285                 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(pgdat, sc.order,
3286                                                 sc.gfp_mask, &nr_soft_scanned);
3287                 sc.nr_reclaimed += nr_soft_reclaimed;
3288 
3289                 /*
3290                  * There should be no need to raise the scanning priority if
3291                  * enough pages are already being scanned that that high
3292                  * watermark would be met at 100% efficiency.
3293                  */
3294                 if (kswapd_shrink_node(pgdat, &sc))
3295                         raise_priority = false;
3296 
3297                 /*
3298                  * If the low watermark is met there is no need for processes
3299                  * to be throttled on pfmemalloc_wait as they should not be
3300                  * able to safely make forward progress. Wake them
3301                  */
3302                 if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
3303                                 pfmemalloc_watermark_ok(pgdat))
3304                         wake_up_all(&pgdat->pfmemalloc_wait);
3305 
3306                 /* Check if kswapd should be suspending */
3307                 if (try_to_freeze() || kthread_should_stop())
3308                         break;
3309 
3310                 /*
3311                  * Raise priority if scanning rate is too low or there was no
3312                  * progress in reclaiming pages
3313                  */
3314                 if (raise_priority || !sc.nr_reclaimed)
3315                         sc.priority--;
3316         } while (sc.priority >= 1);
3317 
3318 out:
3319         /*
3320          * Return the order kswapd stopped reclaiming at as
3321          * prepare_kswapd_sleep() takes it into account. If another caller
3322          * entered the allocator slow path while kswapd was awake, order will
3323          * remain at the higher level.
3324          */
3325         return sc.order;
3326 }
3327 
3328 static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
3329                                 unsigned int classzone_idx)
3330 {
3331         long remaining = 0;
3332         DEFINE_WAIT(wait);
3333 
3334         if (freezing(current) || kthread_should_stop())
3335                 return;
3336 
3337         prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3338 
3339         /* Try to sleep for a short interval */
3340         if (prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3341                 /*
3342                  * Compaction records what page blocks it recently failed to
3343                  * isolate pages from and skips them in the future scanning.
3344                  * When kswapd is going to sleep, it is reasonable to assume
3345                  * that pages and compaction may succeed so reset the cache.
3346                  */
3347                 reset_isolation_suitable(pgdat);
3348 
3349                 /*
3350                  * We have freed the memory, now we should compact it to make
3351                  * allocation of the requested order possible.
3352                  */
3353                 wakeup_kcompactd(pgdat, alloc_order, classzone_idx);
3354 
3355                 remaining = schedule_timeout(HZ/10);
3356 
3357                 /*
3358                  * If woken prematurely then reset kswapd_classzone_idx and
3359                  * order. The values will either be from a wakeup request or
3360                  * the previous request that slept prematurely.
3361                  */
3362                 if (remaining) {
3363                         pgdat->kswapd_classzone_idx = max(pgdat->kswapd_classzone_idx, classzone_idx);
3364                         pgdat->kswapd_order = max(pgdat->kswapd_order, reclaim_order);
3365                 }
3366 
3367                 finish_wait(&pgdat->kswapd_wait, &wait);
3368                 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3369         }
3370 
3371         /*
3372          * After a short sleep, check if it was a premature sleep. If not, then
3373          * go fully to sleep until explicitly woken up.
3374          */
3375         if (!remaining &&
3376             prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3377                 trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
3378 
3379                 /*
3380                  * vmstat counters are not perfectly accurate and the estimated
3381                  * value for counters such as NR_FREE_PAGES can deviate from the
3382                  * true value by nr_online_cpus * threshold. To avoid the zone
3383                  * watermarks being breached while under pressure, we reduce the
3384                  * per-cpu vmstat threshold while kswapd is awake and restore
3385                  * them before going back to sleep.
3386                  */
3387                 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
3388 
3389                 if (!kthread_should_stop())
3390                         schedule();
3391 
3392                 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
3393         } else {
3394                 if (remaining)
3395                         count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
3396                 else
3397                         count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
3398         }
3399         finish_wait(&pgdat->kswapd_wait, &wait);
3400 }
3401 
3402 /*
3403  * The background pageout daemon, started as a kernel thread
3404  * from the init process.
3405  *
3406  * This basically trickles out pages so that we have _some_
3407  * free memory available even if there is no other activity
3408  * that frees anything up. This is needed for things like routing
3409  * etc, where we otherwise might have all activity going on in
3410  * asynchronous contexts that cannot page things out.
3411  *
3412  * If there are applications that are active memory-allocators
3413  * (most normal use), this basically shouldn't matter.
3414  */
3415 static int kswapd(void *p)
3416 {
3417         unsigned int alloc_order, reclaim_order, classzone_idx;
3418         pg_data_t *pgdat = (pg_data_t*)p;
3419         struct task_struct *tsk = current;
3420 
3421         struct reclaim_state reclaim_state = {
3422                 .reclaimed_slab = 0,
3423         };
3424         const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
3425 
3426         lockdep_set_current_reclaim_state(GFP_KERNEL);
3427 
3428         if (!cpumask_empty(cpumask))
3429                 set_cpus_allowed_ptr(tsk, cpumask);
3430         current->reclaim_state = &reclaim_state;
3431 
3432         /*
3433          * Tell the memory management that we're a "memory allocator",
3434          * and that if we need more memory we should get access to it
3435          * regardless (see "__alloc_pages()"). "kswapd" should
3436          * never get caught in the normal page freeing logic.
3437          *
3438          * (Kswapd normally doesn't need memory anyway, but sometimes
3439          * you need a small amount of memory in order to be able to
3440          * page out something else, and this flag essentially protects
3441          * us from recursively trying to free more memory as we're
3442          * trying to free the first piece of memory in the first place).
3443          */
3444         tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
3445         set_freezable();
3446 
3447         pgdat->kswapd_order = alloc_order = reclaim_order = 0;
3448         pgdat->kswapd_classzone_idx = classzone_idx = 0;
3449         for ( ; ; ) {
3450                 bool ret;
3451 
3452 kswapd_try_sleep:
3453                 kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
3454                                         classzone_idx);
3455 
3456                 /* Read the new order and classzone_idx */
3457                 alloc_order = reclaim_order = pgdat->kswapd_order;
3458                 classzone_idx = pgdat->kswapd_classzone_idx;
3459                 pgdat->kswapd_order = 0;
3460                 pgdat->kswapd_classzone_idx = 0;
3461 
3462                 ret = try_to_freeze();
3463                 if (kthread_should_stop())
3464                         break;
3465 
3466                 /*
3467                  * We can speed up thawing tasks if we don't call balance_pgdat
3468                  * after returning from the refrigerator
3469                  */
3470                 if (ret)
3471                         continue;
3472 
3473                 /*
3474                  * Reclaim begins at the requested order but if a high-order
3475                  * reclaim fails then kswapd falls back to reclaiming for
3476                  * order-0. If that happens, kswapd will consider sleeping
3477                  * for the order it finished reclaiming at (reclaim_order)
3478                  * but kcompactd is woken to compact for the original
3479                  * request (alloc_order).
3480                  */
3481                 trace_mm_vmscan_kswapd_wake(pgdat->node_id, classzone_idx,
3482                                                 alloc_order);
3483                 reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx);
3484                 if (reclaim_order < alloc_order)
3485                         goto kswapd_try_sleep;
3486 
3487                 alloc_order = reclaim_order = pgdat->kswapd_order;
3488                 classzone_idx = pgdat->kswapd_classzone_idx;
3489         }
3490 
3491         tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
3492         current->reclaim_state = NULL;
3493         lockdep_clear_current_reclaim_state();
3494 
3495         return 0;
3496 }
3497 
3498 /*
3499  * A zone is low on free memory, so wake its kswapd task to service it.
3500  */
3501 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
3502 {
3503         pg_data_t *pgdat;
3504         int z;
3505 
3506         if (!managed_zone(zone))
3507                 return;
3508 
3509         if (!cpuset_zone_allowed(zone, GFP_KERNEL | __GFP_HARDWALL))
3510                 return;
3511         pgdat = zone->zone_pgdat;
3512         pgdat->kswapd_classzone_idx = max(pgdat->kswapd_classzone_idx, classzone_idx);
3513         pgdat->kswapd_order = max(pgdat->kswapd_order, order);
3514         if (!waitqueue_active(&pgdat->kswapd_wait))
3515                 return;
3516 
3517         /* Only wake kswapd if all zones are unbalanced */
3518         for (z = 0; z <= classzone_idx; z++) {
3519                 zone = pgdat->node_zones + z;
3520                 if (!managed_zone(zone))
3521                         continue;
3522 
3523                 if (zone_balanced(zone, order, classzone_idx))
3524                         return;
3525         }
3526 
3527         trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3528         wake_up_interruptible(&pgdat->kswapd_wait);
3529 }
3530 
3531 #ifdef CONFIG_HIBERNATION
3532 /*
3533  * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3534  * freed pages.
3535  *
3536  * Rather than trying to age LRUs the aim is to preserve the overall
3537  * LRU order by reclaiming preferentially
3538  * inactive > active > active referenced > active mapped
3539  */
3540 unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3541 {
3542         struct reclaim_state reclaim_state;
3543         struct scan_control sc = {
3544                 .nr_to_reclaim = nr_to_reclaim,
3545                 .gfp_mask = GFP_HIGHUSER_MOVABLE,
3546                 .reclaim_idx = MAX_NR_ZONES - 1,
3547                 .priority = DEF_PRIORITY,
3548                 .may_writepage = 1,
3549                 .may_unmap = 1,
3550                 .may_swap = 1,
3551                 .hibernation_mode = 1,
3552         };
3553         struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3554         struct task_struct *p = current;
3555         unsigned long nr_reclaimed;
3556 
3557         p->flags |= PF_MEMALLOC;
3558         lockdep_set_current_reclaim_state(sc.gfp_mask);
3559         reclaim_state.reclaimed_slab = 0;
3560         p->reclaim_state = &reclaim_state;
3561 
3562         nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3563 
3564         p->reclaim_state = NULL;
3565         lockdep_clear_current_reclaim_state();
3566         p->flags &= ~PF_MEMALLOC;
3567 
3568         return nr_reclaimed;
3569 }
3570 #endif /* CONFIG_HIBERNATION */
3571 
3572 /* It's optimal to keep kswapds on the same CPUs as their memory, but
3573    not required for correctness.  So if the last cpu in a node goes
3574    away, we get changed to run anywhere: as the first one comes back,
3575    restore their cpu bindings. */
3576 static int kswapd_cpu_online(unsigned int cpu)
3577 {
3578         int nid;
3579 
3580         for_each_node_state(nid, N_MEMORY) {
3581                 pg_data_t *pgdat = NODE_DATA(nid);
3582                 const struct cpumask *mask;
3583 
3584                 mask = cpumask_of_node(pgdat->node_id);
3585 
3586                 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3587                         /* One of our CPUs online: restore mask */
3588                         set_cpus_allowed_ptr(pgdat->kswapd, mask);
3589         }
3590         return 0;
3591 }
3592 
3593 /*
3594  * This kswapd start function will be called by init and node-hot-add.
3595  * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3596  */
3597 int kswapd_run(int nid)
3598 {
3599         pg_data_t *pgdat = NODE_DATA(nid);
3600         int ret = 0;
3601 
3602         if (pgdat->kswapd)
3603                 return 0;
3604 
3605         pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3606         if (IS_ERR(pgdat->kswapd)) {
3607                 /* failure at boot is fatal */
3608                 BUG_ON(system_state == SYSTEM_BOOTING);
3609                 pr_err("Failed to start kswapd on node %d\n", nid);
3610                 ret = PTR_ERR(pgdat->kswapd);
3611                 pgdat->kswapd = NULL;
3612         }
3613         return ret;
3614 }
3615 
3616 /*
3617  * Called by memory hotplug when all memory in a node is offlined.  Caller must
3618  * hold mem_hotplug_begin/end().
3619  */
3620 void kswapd_stop(int nid)
3621 {
3622         struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3623 
3624         if (kswapd) {
3625                 kthread_stop(kswapd);
3626                 NODE_DATA(nid)->kswapd = NULL;
3627         }
3628 }
3629 
3630 static int __init kswapd_init(void)
3631 {
3632         int nid, ret;
3633 
3634         swap_setup();
3635         for_each_node_state(nid, N_MEMORY)
3636                 kswapd_run(nid);
3637         ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
3638                                         "mm/vmscan:online", kswapd_cpu_online,
3639                                         NULL);
3640         WARN_ON(ret < 0);
3641         return 0;
3642 }
3643 
3644 module_init(kswapd_init)
3645 
3646 #ifdef CONFIG_NUMA
3647 /*
3648  * Node reclaim mode
3649  *
3650  * If non-zero call node_reclaim when the number of free pages falls below
3651  * the watermarks.
3652  */
3653 int node_reclaim_mode __read_mostly;
3654 
3655 #define RECLAIM_OFF 0
3656 #define RECLAIM_ZONE (1<<0)     /* Run shrink_inactive_list on the zone */
3657 #define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
3658 #define RECLAIM_UNMAP (1<<2)    /* Unmap pages during reclaim */
3659 
3660 /*
3661  * Priority for NODE_RECLAIM. This determines the fraction of pages
3662  * of a node considered for each zone_reclaim. 4 scans 1/16th of
3663  * a zone.
3664  */
3665 #define NODE_RECLAIM_PRIORITY 4
3666 
3667 /*
3668  * Percentage of pages in a zone that must be unmapped for node_reclaim to
3669  * occur.
3670  */
3671 int sysctl_min_unmapped_ratio = 1;
3672 
3673 /*
3674  * If the number of slab pages in a zone grows beyond this percentage then
3675  * slab reclaim needs to occur.
3676  */
3677 int sysctl_min_slab_ratio = 5;
3678 
3679 static inline unsigned long node_unmapped_file_pages(struct pglist_data *pgdat)
3680 {
3681         unsigned long file_mapped = node_page_state(pgdat, NR_FILE_MAPPED);
3682         unsigned long file_lru = node_page_state(pgdat, NR_INACTIVE_FILE) +
3683                 node_page_state(pgdat, NR_ACTIVE_FILE);
3684 
3685         /*
3686          * It's possible for there to be more file mapped pages than
3687          * accounted for by the pages on the file LRU lists because
3688          * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3689          */
3690         return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3691 }
3692 
3693 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
3694 static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat)
3695 {
3696         unsigned long nr_pagecache_reclaimable;
3697         unsigned long delta = 0;
3698 
3699         /*
3700          * If RECLAIM_UNMAP is set, then all file pages are considered
3701          * potentially reclaimable. Otherwise, we have to worry about
3702          * pages like swapcache and node_unmapped_file_pages() provides
3703          * a better estimate
3704          */
3705         if (node_reclaim_mode & RECLAIM_UNMAP)
3706                 nr_pagecache_reclaimable = node_page_state(pgdat, NR_FILE_PAGES);
3707         else
3708                 nr_pagecache_reclaimable = node_unmapped_file_pages(pgdat);
3709 
3710         /* If we can't clean pages, remove dirty pages from consideration */
3711         if (!(node_reclaim_mode & RECLAIM_WRITE))
3712                 delta += node_page_state(pgdat, NR_FILE_DIRTY);
3713 
3714         /* Watch for any possible underflows due to delta */
3715         if (unlikely(delta > nr_pagecache_reclaimable))
3716                 delta = nr_pagecache_reclaimable;
3717 
3718         return nr_pagecache_reclaimable - delta;
3719 }
3720 
3721 /*
3722  * Try to free up some pages from this node through reclaim.
3723  */
3724 static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
3725 {
3726         /* Minimum pages needed in order to stay on node */
3727         const unsigned long nr_pages = 1 << order;
3728         struct task_struct *p = current;
3729         struct reclaim_state reclaim_state;
3730         int classzone_idx = gfp_zone(gfp_mask);
3731         struct scan_control sc = {
3732                 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3733                 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
3734                 .order = order,
3735                 .priority = NODE_RECLAIM_PRIORITY,
3736                 .may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
3737                 .may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
3738                 .may_swap = 1,
3739                 .reclaim_idx = classzone_idx,
3740         };
3741 
3742         cond_resched();
3743         /*
3744          * We need to be able to allocate from the reserves for RECLAIM_UNMAP
3745          * and we also need to be able to write out pages for RECLAIM_WRITE
3746          * and RECLAIM_UNMAP.
3747          */
3748         p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3749         lockdep_set_current_reclaim_state(gfp_mask);
3750         reclaim_state.reclaimed_slab = 0;
3751         p->reclaim_state = &reclaim_state;
3752 
3753         if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) {
3754                 /*
3755                  * Free memory by calling shrink zone with increasing
3756                  * priorities until we have enough memory freed.
3757                  */
3758                 do {
3759                         shrink_node(pgdat, &sc);
3760                 } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3761         }
3762 
3763         p->reclaim_state = NULL;
3764         current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3765         lockdep_clear_current_reclaim_state();
3766         return sc.nr_reclaimed >= nr_pages;
3767 }
3768 
3769 int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
3770 {
3771         int ret;
3772 
3773         /*
3774          * Node reclaim reclaims unmapped file backed pages and
3775          * slab pages if we are over the defined limits.
3776          *
3777          * A small portion of unmapped file backed pages is needed for
3778          * file I/O otherwise pages read by file I/O will be immediately
3779          * thrown out if the node is overallocated. So we do not reclaim
3780          * if less than a specified percentage of the node is used by
3781          * unmapped file backed pages.
3782          */
3783         if (node_pagecache_reclaimable(pgdat) <= pgdat->min_unmapped_pages &&
3784             sum_zone_node_page_state(pgdat->node_id, NR_SLAB_RECLAIMABLE) <= pgdat->min_slab_pages)
3785                 return NODE_RECLAIM_FULL;
3786 
3787         if (!pgdat_reclaimable(pgdat))
3788                 return NODE_RECLAIM_FULL;
3789 
3790         /*
3791          * Do not scan if the allocation should not be delayed.
3792          */
3793         if (!gfpflags_allow_blocking(gfp_mask) || (current->flags & PF_MEMALLOC))
3794                 return NODE_RECLAIM_NOSCAN;
3795 
3796         /*
3797          * Only run node reclaim on the local node or on nodes that do not
3798          * have associated processors. This will favor the local processor
3799          * over remote processors and spread off node memory allocations
3800          * as wide as possible.
3801          */
3802         if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
3803                 return NODE_RECLAIM_NOSCAN;
3804 
3805         if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
3806                 return NODE_RECLAIM_NOSCAN;
3807 
3808         ret = __node_reclaim(pgdat, gfp_mask, order);
3809         clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
3810 
3811         if (!ret)
3812                 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3813 
3814         return ret;
3815 }
3816 #endif
3817 
3818 /*
3819  * page_evictable - test whether a page is evictable
3820  * @page: the page to test
3821  *
3822  * Test whether page is evictable--i.e., should be placed on active/inactive
3823  * lists vs unevictable list.
3824  *
3825  * Reasons page might not be evictable:
3826  * (1) page's mapping marked unevictable
3827  * (2) page is part of an mlocked VMA
3828  *
3829  */
3830 int page_evictable(struct page *page)
3831 {
3832         return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
3833 }
3834 
3835 #ifdef CONFIG_SHMEM
3836 /**
3837  * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3838  * @pages:      array of pages to check
3839  * @nr_pages:   number of pages to check
3840  *
3841  * Checks pages for evictability and moves them to the appropriate lru list.
3842  *
3843  * This function is only used for SysV IPC SHM_UNLOCK.
3844  */
3845 void check_move_unevictable_pages(struct page **pages, int nr_pages)
3846 {
3847         struct lruvec *lruvec;
3848         struct pglist_data *pgdat = NULL;
3849         int pgscanned = 0;
3850         int pgrescued = 0;
3851         int i;
3852 
3853         for (i = 0; i < nr_pages; i++) {
3854                 struct page *page = pages[i];
3855                 struct pglist_data *pagepgdat = page_pgdat(page);
3856 
3857                 pgscanned++;
3858                 if (pagepgdat != pgdat) {
3859                         if (pgdat)
3860                                 spin_unlock_irq(&pgdat->lru_lock);
3861                         pgdat = pagepgdat;
3862                         spin_lock_irq(&pgdat->lru_lock);
3863                 }
3864                 lruvec = mem_cgroup_page_lruvec(page, pgdat);
3865 
3866                 if (!PageLRU(page) || !PageUnevictable(page))
3867                         continue;
3868 
3869                 if (page_evictable(page)) {
3870                         enum lru_list lru = page_lru_base_type(page);
3871 
3872                         VM_BUG_ON_PAGE(PageActive(page), page);
3873                         ClearPageUnevictable(page);
3874                         del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3875                         add_page_to_lru_list(page, lruvec, lru);
3876                         pgrescued++;
3877                 }
3878         }
3879 
3880         if (pgdat) {
3881                 __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3882                 __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3883                 spin_unlock_irq(&pgdat->lru_lock);
3884         }
3885 }
3886 #endif /* CONFIG_SHMEM */
3887 

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