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/compaction.c

  1 /*
  2  * linux/mm/compaction.c
  3  *
  4  * Memory compaction for the reduction of external fragmentation. Note that
  5  * this heavily depends upon page migration to do all the real heavy
  6  * lifting
  7  *
  8  * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
  9  */
 10 #include <linux/cpu.h>
 11 #include <linux/swap.h>
 12 #include <linux/migrate.h>
 13 #include <linux/compaction.h>
 14 #include <linux/mm_inline.h>
 15 #include <linux/backing-dev.h>
 16 #include <linux/sysctl.h>
 17 #include <linux/sysfs.h>
 18 #include <linux/page-isolation.h>
 19 #include <linux/kasan.h>
 20 #include <linux/kthread.h>
 21 #include <linux/freezer.h>
 22 #include <linux/page_owner.h>
 23 #include "internal.h"
 24 
 25 #ifdef CONFIG_COMPACTION
 26 static inline void count_compact_event(enum vm_event_item item)
 27 {
 28         count_vm_event(item);
 29 }
 30 
 31 static inline void count_compact_events(enum vm_event_item item, long delta)
 32 {
 33         count_vm_events(item, delta);
 34 }
 35 #else
 36 #define count_compact_event(item) do { } while (0)
 37 #define count_compact_events(item, delta) do { } while (0)
 38 #endif
 39 
 40 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
 41 
 42 #define CREATE_TRACE_POINTS
 43 #include <trace/events/compaction.h>
 44 
 45 #define block_start_pfn(pfn, order)     round_down(pfn, 1UL << (order))
 46 #define block_end_pfn(pfn, order)       ALIGN((pfn) + 1, 1UL << (order))
 47 #define pageblock_start_pfn(pfn)        block_start_pfn(pfn, pageblock_order)
 48 #define pageblock_end_pfn(pfn)          block_end_pfn(pfn, pageblock_order)
 49 
 50 static unsigned long release_freepages(struct list_head *freelist)
 51 {
 52         struct page *page, *next;
 53         unsigned long high_pfn = 0;
 54 
 55         list_for_each_entry_safe(page, next, freelist, lru) {
 56                 unsigned long pfn = page_to_pfn(page);
 57                 list_del(&page->lru);
 58                 __free_page(page);
 59                 if (pfn > high_pfn)
 60                         high_pfn = pfn;
 61         }
 62 
 63         return high_pfn;
 64 }
 65 
 66 static void map_pages(struct list_head *list)
 67 {
 68         unsigned int i, order, nr_pages;
 69         struct page *page, *next;
 70         LIST_HEAD(tmp_list);
 71 
 72         list_for_each_entry_safe(page, next, list, lru) {
 73                 list_del(&page->lru);
 74 
 75                 order = page_private(page);
 76                 nr_pages = 1 << order;
 77 
 78                 post_alloc_hook(page, order, __GFP_MOVABLE);
 79                 if (order)
 80                         split_page(page, order);
 81 
 82                 for (i = 0; i < nr_pages; i++) {
 83                         list_add(&page->lru, &tmp_list);
 84                         page++;
 85                 }
 86         }
 87 
 88         list_splice(&tmp_list, list);
 89 }
 90 
 91 static inline bool migrate_async_suitable(int migratetype)
 92 {
 93         return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
 94 }
 95 
 96 #ifdef CONFIG_COMPACTION
 97 
 98 int PageMovable(struct page *page)
 99 {
100         struct address_space *mapping;
101 
102         VM_BUG_ON_PAGE(!PageLocked(page), page);
103         if (!__PageMovable(page))
104                 return 0;
105 
106         mapping = page_mapping(page);
107         if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
108                 return 1;
109 
110         return 0;
111 }
112 EXPORT_SYMBOL(PageMovable);
113 
114 void __SetPageMovable(struct page *page, struct address_space *mapping)
115 {
116         VM_BUG_ON_PAGE(!PageLocked(page), page);
117         VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
118         page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
119 }
120 EXPORT_SYMBOL(__SetPageMovable);
121 
122 void __ClearPageMovable(struct page *page)
123 {
124         VM_BUG_ON_PAGE(!PageLocked(page), page);
125         VM_BUG_ON_PAGE(!PageMovable(page), page);
126         /*
127          * Clear registered address_space val with keeping PAGE_MAPPING_MOVABLE
128          * flag so that VM can catch up released page by driver after isolation.
129          * With it, VM migration doesn't try to put it back.
130          */
131         page->mapping = (void *)((unsigned long)page->mapping &
132                                 PAGE_MAPPING_MOVABLE);
133 }
134 EXPORT_SYMBOL(__ClearPageMovable);
135 
136 /* Do not skip compaction more than 64 times */
137 #define COMPACT_MAX_DEFER_SHIFT 6
138 
139 /*
140  * Compaction is deferred when compaction fails to result in a page
141  * allocation success. 1 << compact_defer_limit compactions are skipped up
142  * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
143  */
144 void defer_compaction(struct zone *zone, int order)
145 {
146         zone->compact_considered = 0;
147         zone->compact_defer_shift++;
148 
149         if (order < zone->compact_order_failed)
150                 zone->compact_order_failed = order;
151 
152         if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
153                 zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
154 
155         trace_mm_compaction_defer_compaction(zone, order);
156 }
157 
158 /* Returns true if compaction should be skipped this time */
159 bool compaction_deferred(struct zone *zone, int order)
160 {
161         unsigned long defer_limit = 1UL << zone->compact_defer_shift;
162 
163         if (order < zone->compact_order_failed)
164                 return false;
165 
166         /* Avoid possible overflow */
167         if (++zone->compact_considered > defer_limit)
168                 zone->compact_considered = defer_limit;
169 
170         if (zone->compact_considered >= defer_limit)
171                 return false;
172 
173         trace_mm_compaction_deferred(zone, order);
174 
175         return true;
176 }
177 
178 /*
179  * Update defer tracking counters after successful compaction of given order,
180  * which means an allocation either succeeded (alloc_success == true) or is
181  * expected to succeed.
182  */
183 void compaction_defer_reset(struct zone *zone, int order,
184                 bool alloc_success)
185 {
186         if (alloc_success) {
187                 zone->compact_considered = 0;
188                 zone->compact_defer_shift = 0;
189         }
190         if (order >= zone->compact_order_failed)
191                 zone->compact_order_failed = order + 1;
192 
193         trace_mm_compaction_defer_reset(zone, order);
194 }
195 
196 /* Returns true if restarting compaction after many failures */
197 bool compaction_restarting(struct zone *zone, int order)
198 {
199         if (order < zone->compact_order_failed)
200                 return false;
201 
202         return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
203                 zone->compact_considered >= 1UL << zone->compact_defer_shift;
204 }
205 
206 /* Returns true if the pageblock should be scanned for pages to isolate. */
207 static inline bool isolation_suitable(struct compact_control *cc,
208                                         struct page *page)
209 {
210         if (cc->ignore_skip_hint)
211                 return true;
212 
213         return !get_pageblock_skip(page);
214 }
215 
216 static void reset_cached_positions(struct zone *zone)
217 {
218         zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
219         zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
220         zone->compact_cached_free_pfn =
221                                 pageblock_start_pfn(zone_end_pfn(zone) - 1);
222 }
223 
224 /*
225  * This function is called to clear all cached information on pageblocks that
226  * should be skipped for page isolation when the migrate and free page scanner
227  * meet.
228  */
229 static void __reset_isolation_suitable(struct zone *zone)
230 {
231         unsigned long start_pfn = zone->zone_start_pfn;
232         unsigned long end_pfn = zone_end_pfn(zone);
233         unsigned long pfn;
234 
235         zone->compact_blockskip_flush = false;
236 
237         /* Walk the zone and mark every pageblock as suitable for isolation */
238         for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
239                 struct page *page;
240 
241                 cond_resched();
242 
243                 if (!pfn_valid(pfn))
244                         continue;
245 
246                 page = pfn_to_page(pfn);
247                 if (zone != page_zone(page))
248                         continue;
249 
250                 clear_pageblock_skip(page);
251         }
252 
253         reset_cached_positions(zone);
254 }
255 
256 void reset_isolation_suitable(pg_data_t *pgdat)
257 {
258         int zoneid;
259 
260         for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
261                 struct zone *zone = &pgdat->node_zones[zoneid];
262                 if (!populated_zone(zone))
263                         continue;
264 
265                 /* Only flush if a full compaction finished recently */
266                 if (zone->compact_blockskip_flush)
267                         __reset_isolation_suitable(zone);
268         }
269 }
270 
271 /*
272  * If no pages were isolated then mark this pageblock to be skipped in the
273  * future. The information is later cleared by __reset_isolation_suitable().
274  */
275 static void update_pageblock_skip(struct compact_control *cc,
276                         struct page *page, unsigned long nr_isolated,
277                         bool migrate_scanner)
278 {
279         struct zone *zone = cc->zone;
280         unsigned long pfn;
281 
282         if (cc->ignore_skip_hint)
283                 return;
284 
285         if (!page)
286                 return;
287 
288         if (nr_isolated)
289                 return;
290 
291         set_pageblock_skip(page);
292 
293         pfn = page_to_pfn(page);
294 
295         /* Update where async and sync compaction should restart */
296         if (migrate_scanner) {
297                 if (pfn > zone->compact_cached_migrate_pfn[0])
298                         zone->compact_cached_migrate_pfn[0] = pfn;
299                 if (cc->mode != MIGRATE_ASYNC &&
300                     pfn > zone->compact_cached_migrate_pfn[1])
301                         zone->compact_cached_migrate_pfn[1] = pfn;
302         } else {
303                 if (pfn < zone->compact_cached_free_pfn)
304                         zone->compact_cached_free_pfn = pfn;
305         }
306 }
307 #else
308 static inline bool isolation_suitable(struct compact_control *cc,
309                                         struct page *page)
310 {
311         return true;
312 }
313 
314 static void update_pageblock_skip(struct compact_control *cc,
315                         struct page *page, unsigned long nr_isolated,
316                         bool migrate_scanner)
317 {
318 }
319 #endif /* CONFIG_COMPACTION */
320 
321 /*
322  * Compaction requires the taking of some coarse locks that are potentially
323  * very heavily contended. For async compaction, back out if the lock cannot
324  * be taken immediately. For sync compaction, spin on the lock if needed.
325  *
326  * Returns true if the lock is held
327  * Returns false if the lock is not held and compaction should abort
328  */
329 static bool compact_trylock_irqsave(spinlock_t *lock, unsigned long *flags,
330                                                 struct compact_control *cc)
331 {
332         if (cc->mode == MIGRATE_ASYNC) {
333                 if (!spin_trylock_irqsave(lock, *flags)) {
334                         cc->contended = true;
335                         return false;
336                 }
337         } else {
338                 spin_lock_irqsave(lock, *flags);
339         }
340 
341         return true;
342 }
343 
344 /*
345  * Compaction requires the taking of some coarse locks that are potentially
346  * very heavily contended. The lock should be periodically unlocked to avoid
347  * having disabled IRQs for a long time, even when there is nobody waiting on
348  * the lock. It might also be that allowing the IRQs will result in
349  * need_resched() becoming true. If scheduling is needed, async compaction
350  * aborts. Sync compaction schedules.
351  * Either compaction type will also abort if a fatal signal is pending.
352  * In either case if the lock was locked, it is dropped and not regained.
353  *
354  * Returns true if compaction should abort due to fatal signal pending, or
355  *              async compaction due to need_resched()
356  * Returns false when compaction can continue (sync compaction might have
357  *              scheduled)
358  */
359 static bool compact_unlock_should_abort(spinlock_t *lock,
360                 unsigned long flags, bool *locked, struct compact_control *cc)
361 {
362         if (*locked) {
363                 spin_unlock_irqrestore(lock, flags);
364                 *locked = false;
365         }
366 
367         if (fatal_signal_pending(current)) {
368                 cc->contended = true;
369                 return true;
370         }
371 
372         if (need_resched()) {
373                 if (cc->mode == MIGRATE_ASYNC) {
374                         cc->contended = true;
375                         return true;
376                 }
377                 cond_resched();
378         }
379 
380         return false;
381 }
382 
383 /*
384  * Aside from avoiding lock contention, compaction also periodically checks
385  * need_resched() and either schedules in sync compaction or aborts async
386  * compaction. This is similar to what compact_unlock_should_abort() does, but
387  * is used where no lock is concerned.
388  *
389  * Returns false when no scheduling was needed, or sync compaction scheduled.
390  * Returns true when async compaction should abort.
391  */
392 static inline bool compact_should_abort(struct compact_control *cc)
393 {
394         /* async compaction aborts if contended */
395         if (need_resched()) {
396                 if (cc->mode == MIGRATE_ASYNC) {
397                         cc->contended = true;
398                         return true;
399                 }
400 
401                 cond_resched();
402         }
403 
404         return false;
405 }
406 
407 /*
408  * Isolate free pages onto a private freelist. If @strict is true, will abort
409  * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
410  * (even though it may still end up isolating some pages).
411  */
412 static unsigned long isolate_freepages_block(struct compact_control *cc,
413                                 unsigned long *start_pfn,
414                                 unsigned long end_pfn,
415                                 struct list_head *freelist,
416                                 bool strict)
417 {
418         int nr_scanned = 0, total_isolated = 0;
419         struct page *cursor, *valid_page = NULL;
420         unsigned long flags = 0;
421         bool locked = false;
422         unsigned long blockpfn = *start_pfn;
423         unsigned int order;
424 
425         cursor = pfn_to_page(blockpfn);
426 
427         /* Isolate free pages. */
428         for (; blockpfn < end_pfn; blockpfn++, cursor++) {
429                 int isolated;
430                 struct page *page = cursor;
431 
432                 /*
433                  * Periodically drop the lock (if held) regardless of its
434                  * contention, to give chance to IRQs. Abort if fatal signal
435                  * pending or async compaction detects need_resched()
436                  */
437                 if (!(blockpfn % SWAP_CLUSTER_MAX)
438                     && compact_unlock_should_abort(&cc->zone->lock, flags,
439                                                                 &locked, cc))
440                         break;
441 
442                 nr_scanned++;
443                 if (!pfn_valid_within(blockpfn))
444                         goto isolate_fail;
445 
446                 if (!valid_page)
447                         valid_page = page;
448 
449                 /*
450                  * For compound pages such as THP and hugetlbfs, we can save
451                  * potentially a lot of iterations if we skip them at once.
452                  * The check is racy, but we can consider only valid values
453                  * and the only danger is skipping too much.
454                  */
455                 if (PageCompound(page)) {
456                         unsigned int comp_order = compound_order(page);
457 
458                         if (likely(comp_order < MAX_ORDER)) {
459                                 blockpfn += (1UL << comp_order) - 1;
460                                 cursor += (1UL << comp_order) - 1;
461                         }
462 
463                         goto isolate_fail;
464                 }
465 
466                 if (!PageBuddy(page))
467                         goto isolate_fail;
468 
469                 /*
470                  * If we already hold the lock, we can skip some rechecking.
471                  * Note that if we hold the lock now, checked_pageblock was
472                  * already set in some previous iteration (or strict is true),
473                  * so it is correct to skip the suitable migration target
474                  * recheck as well.
475                  */
476                 if (!locked) {
477                         /*
478                          * The zone lock must be held to isolate freepages.
479                          * Unfortunately this is a very coarse lock and can be
480                          * heavily contended if there are parallel allocations
481                          * or parallel compactions. For async compaction do not
482                          * spin on the lock and we acquire the lock as late as
483                          * possible.
484                          */
485                         locked = compact_trylock_irqsave(&cc->zone->lock,
486                                                                 &flags, cc);
487                         if (!locked)
488                                 break;
489 
490                         /* Recheck this is a buddy page under lock */
491                         if (!PageBuddy(page))
492                                 goto isolate_fail;
493                 }
494 
495                 /* Found a free page, will break it into order-0 pages */
496                 order = page_order(page);
497                 isolated = __isolate_free_page(page, order);
498                 if (!isolated)
499                         break;
500                 set_page_private(page, order);
501 
502                 total_isolated += isolated;
503                 cc->nr_freepages += isolated;
504                 list_add_tail(&page->lru, freelist);
505 
506                 if (!strict && cc->nr_migratepages <= cc->nr_freepages) {
507                         blockpfn += isolated;
508                         break;
509                 }
510                 /* Advance to the end of split page */
511                 blockpfn += isolated - 1;
512                 cursor += isolated - 1;
513                 continue;
514 
515 isolate_fail:
516                 if (strict)
517                         break;
518                 else
519                         continue;
520 
521         }
522 
523         if (locked)
524                 spin_unlock_irqrestore(&cc->zone->lock, flags);
525 
526         /*
527          * There is a tiny chance that we have read bogus compound_order(),
528          * so be careful to not go outside of the pageblock.
529          */
530         if (unlikely(blockpfn > end_pfn))
531                 blockpfn = end_pfn;
532 
533         trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
534                                         nr_scanned, total_isolated);
535 
536         /* Record how far we have got within the block */
537         *start_pfn = blockpfn;
538 
539         /*
540          * If strict isolation is requested by CMA then check that all the
541          * pages requested were isolated. If there were any failures, 0 is
542          * returned and CMA will fail.
543          */
544         if (strict && blockpfn < end_pfn)
545                 total_isolated = 0;
546 
547         /* Update the pageblock-skip if the whole pageblock was scanned */
548         if (blockpfn == end_pfn)
549                 update_pageblock_skip(cc, valid_page, total_isolated, false);
550 
551         count_compact_events(COMPACTFREE_SCANNED, nr_scanned);
552         if (total_isolated)
553                 count_compact_events(COMPACTISOLATED, total_isolated);
554         return total_isolated;
555 }
556 
557 /**
558  * isolate_freepages_range() - isolate free pages.
559  * @start_pfn: The first PFN to start isolating.
560  * @end_pfn:   The one-past-last PFN.
561  *
562  * Non-free pages, invalid PFNs, or zone boundaries within the
563  * [start_pfn, end_pfn) range are considered errors, cause function to
564  * undo its actions and return zero.
565  *
566  * Otherwise, function returns one-past-the-last PFN of isolated page
567  * (which may be greater then end_pfn if end fell in a middle of
568  * a free page).
569  */
570 unsigned long
571 isolate_freepages_range(struct compact_control *cc,
572                         unsigned long start_pfn, unsigned long end_pfn)
573 {
574         unsigned long isolated, pfn, block_start_pfn, block_end_pfn;
575         LIST_HEAD(freelist);
576 
577         pfn = start_pfn;
578         block_start_pfn = pageblock_start_pfn(pfn);
579         if (block_start_pfn < cc->zone->zone_start_pfn)
580                 block_start_pfn = cc->zone->zone_start_pfn;
581         block_end_pfn = pageblock_end_pfn(pfn);
582 
583         for (; pfn < end_pfn; pfn += isolated,
584                                 block_start_pfn = block_end_pfn,
585                                 block_end_pfn += pageblock_nr_pages) {
586                 /* Protect pfn from changing by isolate_freepages_block */
587                 unsigned long isolate_start_pfn = pfn;
588 
589                 block_end_pfn = min(block_end_pfn, end_pfn);
590 
591                 /*
592                  * pfn could pass the block_end_pfn if isolated freepage
593                  * is more than pageblock order. In this case, we adjust
594                  * scanning range to right one.
595                  */
596                 if (pfn >= block_end_pfn) {
597                         block_start_pfn = pageblock_start_pfn(pfn);
598                         block_end_pfn = pageblock_end_pfn(pfn);
599                         block_end_pfn = min(block_end_pfn, end_pfn);
600                 }
601 
602                 if (!pageblock_pfn_to_page(block_start_pfn,
603                                         block_end_pfn, cc->zone))
604                         break;
605 
606                 isolated = isolate_freepages_block(cc, &isolate_start_pfn,
607                                                 block_end_pfn, &freelist, true);
608 
609                 /*
610                  * In strict mode, isolate_freepages_block() returns 0 if
611                  * there are any holes in the block (ie. invalid PFNs or
612                  * non-free pages).
613                  */
614                 if (!isolated)
615                         break;
616 
617                 /*
618                  * If we managed to isolate pages, it is always (1 << n) *
619                  * pageblock_nr_pages for some non-negative n.  (Max order
620                  * page may span two pageblocks).
621                  */
622         }
623 
624         /* __isolate_free_page() does not map the pages */
625         map_pages(&freelist);
626 
627         if (pfn < end_pfn) {
628                 /* Loop terminated early, cleanup. */
629                 release_freepages(&freelist);
630                 return 0;
631         }
632 
633         /* We don't use freelists for anything. */
634         return pfn;
635 }
636 
637 /* Similar to reclaim, but different enough that they don't share logic */
638 static bool too_many_isolated(struct zone *zone)
639 {
640         unsigned long active, inactive, isolated;
641 
642         inactive = node_page_state(zone->zone_pgdat, NR_INACTIVE_FILE) +
643                         node_page_state(zone->zone_pgdat, NR_INACTIVE_ANON);
644         active = node_page_state(zone->zone_pgdat, NR_ACTIVE_FILE) +
645                         node_page_state(zone->zone_pgdat, NR_ACTIVE_ANON);
646         isolated = node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE) +
647                         node_page_state(zone->zone_pgdat, NR_ISOLATED_ANON);
648 
649         return isolated > (inactive + active) / 2;
650 }
651 
652 /**
653  * isolate_migratepages_block() - isolate all migrate-able pages within
654  *                                a single pageblock
655  * @cc:         Compaction control structure.
656  * @low_pfn:    The first PFN to isolate
657  * @end_pfn:    The one-past-the-last PFN to isolate, within same pageblock
658  * @isolate_mode: Isolation mode to be used.
659  *
660  * Isolate all pages that can be migrated from the range specified by
661  * [low_pfn, end_pfn). The range is expected to be within same pageblock.
662  * Returns zero if there is a fatal signal pending, otherwise PFN of the
663  * first page that was not scanned (which may be both less, equal to or more
664  * than end_pfn).
665  *
666  * The pages are isolated on cc->migratepages list (not required to be empty),
667  * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
668  * is neither read nor updated.
669  */
670 static unsigned long
671 isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
672                         unsigned long end_pfn, isolate_mode_t isolate_mode)
673 {
674         struct zone *zone = cc->zone;
675         unsigned long nr_scanned = 0, nr_isolated = 0;
676         struct lruvec *lruvec;
677         unsigned long flags = 0;
678         bool locked = false;
679         struct page *page = NULL, *valid_page = NULL;
680         unsigned long start_pfn = low_pfn;
681         bool skip_on_failure = false;
682         unsigned long next_skip_pfn = 0;
683 
684         /*
685          * Ensure that there are not too many pages isolated from the LRU
686          * list by either parallel reclaimers or compaction. If there are,
687          * delay for some time until fewer pages are isolated
688          */
689         while (unlikely(too_many_isolated(zone))) {
690                 /* async migration should just abort */
691                 if (cc->mode == MIGRATE_ASYNC)
692                         return 0;
693 
694                 congestion_wait(BLK_RW_ASYNC, HZ/10);
695 
696                 if (fatal_signal_pending(current))
697                         return 0;
698         }
699 
700         if (compact_should_abort(cc))
701                 return 0;
702 
703         if (cc->direct_compaction && (cc->mode == MIGRATE_ASYNC)) {
704                 skip_on_failure = true;
705                 next_skip_pfn = block_end_pfn(low_pfn, cc->order);
706         }
707 
708         /* Time to isolate some pages for migration */
709         for (; low_pfn < end_pfn; low_pfn++) {
710 
711                 if (skip_on_failure && low_pfn >= next_skip_pfn) {
712                         /*
713                          * We have isolated all migration candidates in the
714                          * previous order-aligned block, and did not skip it due
715                          * to failure. We should migrate the pages now and
716                          * hopefully succeed compaction.
717                          */
718                         if (nr_isolated)
719                                 break;
720 
721                         /*
722                          * We failed to isolate in the previous order-aligned
723                          * block. Set the new boundary to the end of the
724                          * current block. Note we can't simply increase
725                          * next_skip_pfn by 1 << order, as low_pfn might have
726                          * been incremented by a higher number due to skipping
727                          * a compound or a high-order buddy page in the
728                          * previous loop iteration.
729                          */
730                         next_skip_pfn = block_end_pfn(low_pfn, cc->order);
731                 }
732 
733                 /*
734                  * Periodically drop the lock (if held) regardless of its
735                  * contention, to give chance to IRQs. Abort async compaction
736                  * if contended.
737                  */
738                 if (!(low_pfn % SWAP_CLUSTER_MAX)
739                     && compact_unlock_should_abort(zone_lru_lock(zone), flags,
740                                                                 &locked, cc))
741                         break;
742 
743                 if (!pfn_valid_within(low_pfn))
744                         goto isolate_fail;
745                 nr_scanned++;
746 
747                 page = pfn_to_page(low_pfn);
748 
749                 if (!valid_page)
750                         valid_page = page;
751 
752                 /*
753                  * Skip if free. We read page order here without zone lock
754                  * which is generally unsafe, but the race window is small and
755                  * the worst thing that can happen is that we skip some
756                  * potential isolation targets.
757                  */
758                 if (PageBuddy(page)) {
759                         unsigned long freepage_order = page_order_unsafe(page);
760 
761                         /*
762                          * Without lock, we cannot be sure that what we got is
763                          * a valid page order. Consider only values in the
764                          * valid order range to prevent low_pfn overflow.
765                          */
766                         if (freepage_order > 0 && freepage_order < MAX_ORDER)
767                                 low_pfn += (1UL << freepage_order) - 1;
768                         continue;
769                 }
770 
771                 /*
772                  * Regardless of being on LRU, compound pages such as THP and
773                  * hugetlbfs are not to be compacted. We can potentially save
774                  * a lot of iterations if we skip them at once. The check is
775                  * racy, but we can consider only valid values and the only
776                  * danger is skipping too much.
777                  */
778                 if (PageCompound(page)) {
779                         unsigned int comp_order = compound_order(page);
780 
781                         if (likely(comp_order < MAX_ORDER))
782                                 low_pfn += (1UL << comp_order) - 1;
783 
784                         goto isolate_fail;
785                 }
786 
787                 /*
788                  * Check may be lockless but that's ok as we recheck later.
789                  * It's possible to migrate LRU and non-lru movable pages.
790                  * Skip any other type of page
791                  */
792                 if (!PageLRU(page)) {
793                         /*
794                          * __PageMovable can return false positive so we need
795                          * to verify it under page_lock.
796                          */
797                         if (unlikely(__PageMovable(page)) &&
798                                         !PageIsolated(page)) {
799                                 if (locked) {
800                                         spin_unlock_irqrestore(zone_lru_lock(zone),
801                                                                         flags);
802                                         locked = false;
803                                 }
804 
805                                 if (isolate_movable_page(page, isolate_mode))
806                                         goto isolate_success;
807                         }
808 
809                         goto isolate_fail;
810                 }
811 
812                 /*
813                  * Migration will fail if an anonymous page is pinned in memory,
814                  * so avoid taking lru_lock and isolating it unnecessarily in an
815                  * admittedly racy check.
816                  */
817                 if (!page_mapping(page) &&
818                     page_count(page) > page_mapcount(page))
819                         goto isolate_fail;
820 
821                 /*
822                  * Only allow to migrate anonymous pages in GFP_NOFS context
823                  * because those do not depend on fs locks.
824                  */
825                 if (!(cc->gfp_mask & __GFP_FS) && page_mapping(page))
826                         goto isolate_fail;
827 
828                 /* If we already hold the lock, we can skip some rechecking */
829                 if (!locked) {
830                         locked = compact_trylock_irqsave(zone_lru_lock(zone),
831                                                                 &flags, cc);
832                         if (!locked)
833                                 break;
834 
835                         /* Recheck PageLRU and PageCompound under lock */
836                         if (!PageLRU(page))
837                                 goto isolate_fail;
838 
839                         /*
840                          * Page become compound since the non-locked check,
841                          * and it's on LRU. It can only be a THP so the order
842                          * is safe to read and it's 0 for tail pages.
843                          */
844                         if (unlikely(PageCompound(page))) {
845                                 low_pfn += (1UL << compound_order(page)) - 1;
846                                 goto isolate_fail;
847                         }
848                 }
849 
850                 lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
851 
852                 /* Try isolate the page */
853                 if (__isolate_lru_page(page, isolate_mode) != 0)
854                         goto isolate_fail;
855 
856                 VM_BUG_ON_PAGE(PageCompound(page), page);
857 
858                 /* Successfully isolated */
859                 del_page_from_lru_list(page, lruvec, page_lru(page));
860                 inc_node_page_state(page,
861                                 NR_ISOLATED_ANON + page_is_file_cache(page));
862 
863 isolate_success:
864                 list_add(&page->lru, &cc->migratepages);
865                 cc->nr_migratepages++;
866                 nr_isolated++;
867 
868                 /*
869                  * Record where we could have freed pages by migration and not
870                  * yet flushed them to buddy allocator.
871                  * - this is the lowest page that was isolated and likely be
872                  * then freed by migration.
873                  */
874                 if (!cc->last_migrated_pfn)
875                         cc->last_migrated_pfn = low_pfn;
876 
877                 /* Avoid isolating too much */
878                 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
879                         ++low_pfn;
880                         break;
881                 }
882 
883                 continue;
884 isolate_fail:
885                 if (!skip_on_failure)
886                         continue;
887 
888                 /*
889                  * We have isolated some pages, but then failed. Release them
890                  * instead of migrating, as we cannot form the cc->order buddy
891                  * page anyway.
892                  */
893                 if (nr_isolated) {
894                         if (locked) {
895                                 spin_unlock_irqrestore(zone_lru_lock(zone), flags);
896                                 locked = false;
897                         }
898                         putback_movable_pages(&cc->migratepages);
899                         cc->nr_migratepages = 0;
900                         cc->last_migrated_pfn = 0;
901                         nr_isolated = 0;
902                 }
903 
904                 if (low_pfn < next_skip_pfn) {
905                         low_pfn = next_skip_pfn - 1;
906                         /*
907                          * The check near the loop beginning would have updated
908                          * next_skip_pfn too, but this is a bit simpler.
909                          */
910                         next_skip_pfn += 1UL << cc->order;
911                 }
912         }
913 
914         /*
915          * The PageBuddy() check could have potentially brought us outside
916          * the range to be scanned.
917          */
918         if (unlikely(low_pfn > end_pfn))
919                 low_pfn = end_pfn;
920 
921         if (locked)
922                 spin_unlock_irqrestore(zone_lru_lock(zone), flags);
923 
924         /*
925          * Update the pageblock-skip information and cached scanner pfn,
926          * if the whole pageblock was scanned without isolating any page.
927          */
928         if (low_pfn == end_pfn)
929                 update_pageblock_skip(cc, valid_page, nr_isolated, true);
930 
931         trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
932                                                 nr_scanned, nr_isolated);
933 
934         count_compact_events(COMPACTMIGRATE_SCANNED, nr_scanned);
935         if (nr_isolated)
936                 count_compact_events(COMPACTISOLATED, nr_isolated);
937 
938         return low_pfn;
939 }
940 
941 /**
942  * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
943  * @cc:        Compaction control structure.
944  * @start_pfn: The first PFN to start isolating.
945  * @end_pfn:   The one-past-last PFN.
946  *
947  * Returns zero if isolation fails fatally due to e.g. pending signal.
948  * Otherwise, function returns one-past-the-last PFN of isolated page
949  * (which may be greater than end_pfn if end fell in a middle of a THP page).
950  */
951 unsigned long
952 isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
953                                                         unsigned long end_pfn)
954 {
955         unsigned long pfn, block_start_pfn, block_end_pfn;
956 
957         /* Scan block by block. First and last block may be incomplete */
958         pfn = start_pfn;
959         block_start_pfn = pageblock_start_pfn(pfn);
960         if (block_start_pfn < cc->zone->zone_start_pfn)
961                 block_start_pfn = cc->zone->zone_start_pfn;
962         block_end_pfn = pageblock_end_pfn(pfn);
963 
964         for (; pfn < end_pfn; pfn = block_end_pfn,
965                                 block_start_pfn = block_end_pfn,
966                                 block_end_pfn += pageblock_nr_pages) {
967 
968                 block_end_pfn = min(block_end_pfn, end_pfn);
969 
970                 if (!pageblock_pfn_to_page(block_start_pfn,
971                                         block_end_pfn, cc->zone))
972                         continue;
973 
974                 pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
975                                                         ISOLATE_UNEVICTABLE);
976 
977                 if (!pfn)
978                         break;
979 
980                 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
981                         break;
982         }
983 
984         return pfn;
985 }
986 
987 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
988 #ifdef CONFIG_COMPACTION
989 
990 /* Returns true if the page is within a block suitable for migration to */
991 static bool suitable_migration_target(struct compact_control *cc,
992                                                         struct page *page)
993 {
994         if (cc->ignore_block_suitable)
995                 return true;
996 
997         /* If the page is a large free page, then disallow migration */
998         if (PageBuddy(page)) {
999                 /*
1000                  * We are checking page_order without zone->lock taken. But
1001                  * the only small danger is that we skip a potentially suitable
1002                  * pageblock, so it's not worth to check order for valid range.
1003                  */
1004                 if (page_order_unsafe(page) >= pageblock_order)
1005                         return false;
1006         }
1007 
1008         /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
1009         if (migrate_async_suitable(get_pageblock_migratetype(page)))
1010                 return true;
1011 
1012         /* Otherwise skip the block */
1013         return false;
1014 }
1015 
1016 /*
1017  * Test whether the free scanner has reached the same or lower pageblock than
1018  * the migration scanner, and compaction should thus terminate.
1019  */
1020 static inline bool compact_scanners_met(struct compact_control *cc)
1021 {
1022         return (cc->free_pfn >> pageblock_order)
1023                 <= (cc->migrate_pfn >> pageblock_order);
1024 }
1025 
1026 /*
1027  * Based on information in the current compact_control, find blocks
1028  * suitable for isolating free pages from and then isolate them.
1029  */
1030 static void isolate_freepages(struct compact_control *cc)
1031 {
1032         struct zone *zone = cc->zone;
1033         struct page *page;
1034         unsigned long block_start_pfn;  /* start of current pageblock */
1035         unsigned long isolate_start_pfn; /* exact pfn we start at */
1036         unsigned long block_end_pfn;    /* end of current pageblock */
1037         unsigned long low_pfn;       /* lowest pfn scanner is able to scan */
1038         struct list_head *freelist = &cc->freepages;
1039 
1040         /*
1041          * Initialise the free scanner. The starting point is where we last
1042          * successfully isolated from, zone-cached value, or the end of the
1043          * zone when isolating for the first time. For looping we also need
1044          * this pfn aligned down to the pageblock boundary, because we do
1045          * block_start_pfn -= pageblock_nr_pages in the for loop.
1046          * For ending point, take care when isolating in last pageblock of a
1047          * a zone which ends in the middle of a pageblock.
1048          * The low boundary is the end of the pageblock the migration scanner
1049          * is using.
1050          */
1051         isolate_start_pfn = cc->free_pfn;
1052         block_start_pfn = pageblock_start_pfn(cc->free_pfn);
1053         block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
1054                                                 zone_end_pfn(zone));
1055         low_pfn = pageblock_end_pfn(cc->migrate_pfn);
1056 
1057         /*
1058          * Isolate free pages until enough are available to migrate the
1059          * pages on cc->migratepages. We stop searching if the migrate
1060          * and free page scanners meet or enough free pages are isolated.
1061          */
1062         for (; block_start_pfn >= low_pfn;
1063                                 block_end_pfn = block_start_pfn,
1064                                 block_start_pfn -= pageblock_nr_pages,
1065                                 isolate_start_pfn = block_start_pfn) {
1066                 /*
1067                  * This can iterate a massively long zone without finding any
1068                  * suitable migration targets, so periodically check if we need
1069                  * to schedule, or even abort async compaction.
1070                  */
1071                 if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
1072                                                 && compact_should_abort(cc))
1073                         break;
1074 
1075                 page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1076                                                                         zone);
1077                 if (!page)
1078                         continue;
1079 
1080                 /* Check the block is suitable for migration */
1081                 if (!suitable_migration_target(cc, page))
1082                         continue;
1083 
1084                 /* If isolation recently failed, do not retry */
1085                 if (!isolation_suitable(cc, page))
1086                         continue;
1087 
1088                 /* Found a block suitable for isolating free pages from. */
1089                 isolate_freepages_block(cc, &isolate_start_pfn, block_end_pfn,
1090                                         freelist, false);
1091 
1092                 /*
1093                  * If we isolated enough freepages, or aborted due to lock
1094                  * contention, terminate.
1095                  */
1096                 if ((cc->nr_freepages >= cc->nr_migratepages)
1097                                                         || cc->contended) {
1098                         if (isolate_start_pfn >= block_end_pfn) {
1099                                 /*
1100                                  * Restart at previous pageblock if more
1101                                  * freepages can be isolated next time.
1102                                  */
1103                                 isolate_start_pfn =
1104                                         block_start_pfn - pageblock_nr_pages;
1105                         }
1106                         break;
1107                 } else if (isolate_start_pfn < block_end_pfn) {
1108                         /*
1109                          * If isolation failed early, do not continue
1110                          * needlessly.
1111                          */
1112                         break;
1113                 }
1114         }
1115 
1116         /* __isolate_free_page() does not map the pages */
1117         map_pages(freelist);
1118 
1119         /*
1120          * Record where the free scanner will restart next time. Either we
1121          * broke from the loop and set isolate_start_pfn based on the last
1122          * call to isolate_freepages_block(), or we met the migration scanner
1123          * and the loop terminated due to isolate_start_pfn < low_pfn
1124          */
1125         cc->free_pfn = isolate_start_pfn;
1126 }
1127 
1128 /*
1129  * This is a migrate-callback that "allocates" freepages by taking pages
1130  * from the isolated freelists in the block we are migrating to.
1131  */
1132 static struct page *compaction_alloc(struct page *migratepage,
1133                                         unsigned long data,
1134                                         int **result)
1135 {
1136         struct compact_control *cc = (struct compact_control *)data;
1137         struct page *freepage;
1138 
1139         /*
1140          * Isolate free pages if necessary, and if we are not aborting due to
1141          * contention.
1142          */
1143         if (list_empty(&cc->freepages)) {
1144                 if (!cc->contended)
1145                         isolate_freepages(cc);
1146 
1147                 if (list_empty(&cc->freepages))
1148                         return NULL;
1149         }
1150 
1151         freepage = list_entry(cc->freepages.next, struct page, lru);
1152         list_del(&freepage->lru);
1153         cc->nr_freepages--;
1154 
1155         return freepage;
1156 }
1157 
1158 /*
1159  * This is a migrate-callback that "frees" freepages back to the isolated
1160  * freelist.  All pages on the freelist are from the same zone, so there is no
1161  * special handling needed for NUMA.
1162  */
1163 static void compaction_free(struct page *page, unsigned long data)
1164 {
1165         struct compact_control *cc = (struct compact_control *)data;
1166 
1167         list_add(&page->lru, &cc->freepages);
1168         cc->nr_freepages++;
1169 }
1170 
1171 /* possible outcome of isolate_migratepages */
1172 typedef enum {
1173         ISOLATE_ABORT,          /* Abort compaction now */
1174         ISOLATE_NONE,           /* No pages isolated, continue scanning */
1175         ISOLATE_SUCCESS,        /* Pages isolated, migrate */
1176 } isolate_migrate_t;
1177 
1178 /*
1179  * Allow userspace to control policy on scanning the unevictable LRU for
1180  * compactable pages.
1181  */
1182 int sysctl_compact_unevictable_allowed __read_mostly = 1;
1183 
1184 /*
1185  * Isolate all pages that can be migrated from the first suitable block,
1186  * starting at the block pointed to by the migrate scanner pfn within
1187  * compact_control.
1188  */
1189 static isolate_migrate_t isolate_migratepages(struct zone *zone,
1190                                         struct compact_control *cc)
1191 {
1192         unsigned long block_start_pfn;
1193         unsigned long block_end_pfn;
1194         unsigned long low_pfn;
1195         struct page *page;
1196         const isolate_mode_t isolate_mode =
1197                 (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
1198                 (cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
1199 
1200         /*
1201          * Start at where we last stopped, or beginning of the zone as
1202          * initialized by compact_zone()
1203          */
1204         low_pfn = cc->migrate_pfn;
1205         block_start_pfn = pageblock_start_pfn(low_pfn);
1206         if (block_start_pfn < zone->zone_start_pfn)
1207                 block_start_pfn = zone->zone_start_pfn;
1208 
1209         /* Only scan within a pageblock boundary */
1210         block_end_pfn = pageblock_end_pfn(low_pfn);
1211 
1212         /*
1213          * Iterate over whole pageblocks until we find the first suitable.
1214          * Do not cross the free scanner.
1215          */
1216         for (; block_end_pfn <= cc->free_pfn;
1217                         low_pfn = block_end_pfn,
1218                         block_start_pfn = block_end_pfn,
1219                         block_end_pfn += pageblock_nr_pages) {
1220 
1221                 /*
1222                  * This can potentially iterate a massively long zone with
1223                  * many pageblocks unsuitable, so periodically check if we
1224                  * need to schedule, or even abort async compaction.
1225                  */
1226                 if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
1227                                                 && compact_should_abort(cc))
1228                         break;
1229 
1230                 page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
1231                                                                         zone);
1232                 if (!page)
1233                         continue;
1234 
1235                 /* If isolation recently failed, do not retry */
1236                 if (!isolation_suitable(cc, page))
1237                         continue;
1238 
1239                 /*
1240                  * For async compaction, also only scan in MOVABLE blocks.
1241                  * Async compaction is optimistic to see if the minimum amount
1242                  * of work satisfies the allocation.
1243                  */
1244                 if (cc->mode == MIGRATE_ASYNC &&
1245                     !migrate_async_suitable(get_pageblock_migratetype(page)))
1246                         continue;
1247 
1248                 /* Perform the isolation */
1249                 low_pfn = isolate_migratepages_block(cc, low_pfn,
1250                                                 block_end_pfn, isolate_mode);
1251 
1252                 if (!low_pfn || cc->contended)
1253                         return ISOLATE_ABORT;
1254 
1255                 /*
1256                  * Either we isolated something and proceed with migration. Or
1257                  * we failed and compact_zone should decide if we should
1258                  * continue or not.
1259                  */
1260                 break;
1261         }
1262 
1263         /* Record where migration scanner will be restarted. */
1264         cc->migrate_pfn = low_pfn;
1265 
1266         return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
1267 }
1268 
1269 /*
1270  * order == -1 is expected when compacting via
1271  * /proc/sys/vm/compact_memory
1272  */
1273 static inline bool is_via_compact_memory(int order)
1274 {
1275         return order == -1;
1276 }
1277 
1278 static enum compact_result __compact_finished(struct zone *zone, struct compact_control *cc,
1279                             const int migratetype)
1280 {
1281         unsigned int order;
1282         unsigned long watermark;
1283 
1284         if (cc->contended || fatal_signal_pending(current))
1285                 return COMPACT_CONTENDED;
1286 
1287         /* Compaction run completes if the migrate and free scanner meet */
1288         if (compact_scanners_met(cc)) {
1289                 /* Let the next compaction start anew. */
1290                 reset_cached_positions(zone);
1291 
1292                 /*
1293                  * Mark that the PG_migrate_skip information should be cleared
1294                  * by kswapd when it goes to sleep. kcompactd does not set the
1295                  * flag itself as the decision to be clear should be directly
1296                  * based on an allocation request.
1297                  */
1298                 if (cc->direct_compaction)
1299                         zone->compact_blockskip_flush = true;
1300 
1301                 if (cc->whole_zone)
1302                         return COMPACT_COMPLETE;
1303                 else
1304                         return COMPACT_PARTIAL_SKIPPED;
1305         }
1306 
1307         if (is_via_compact_memory(cc->order))
1308                 return COMPACT_CONTINUE;
1309 
1310         /* Compaction run is not finished if the watermark is not met */
1311         watermark = zone->watermark[cc->alloc_flags & ALLOC_WMARK_MASK];
1312 
1313         if (!zone_watermark_ok(zone, cc->order, watermark, cc->classzone_idx,
1314                                                         cc->alloc_flags))
1315                 return COMPACT_CONTINUE;
1316 
1317         /* Direct compactor: Is a suitable page free? */
1318         for (order = cc->order; order < MAX_ORDER; order++) {
1319                 struct free_area *area = &zone->free_area[order];
1320                 bool can_steal;
1321 
1322                 /* Job done if page is free of the right migratetype */
1323                 if (!list_empty(&area->free_list[migratetype]))
1324                         return COMPACT_SUCCESS;
1325 
1326 #ifdef CONFIG_CMA
1327                 /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
1328                 if (migratetype == MIGRATE_MOVABLE &&
1329                         !list_empty(&area->free_list[MIGRATE_CMA]))
1330                         return COMPACT_SUCCESS;
1331 #endif
1332                 /*
1333                  * Job done if allocation would steal freepages from
1334                  * other migratetype buddy lists.
1335                  */
1336                 if (find_suitable_fallback(area, order, migratetype,
1337                                                 true, &can_steal) != -1)
1338                         return COMPACT_SUCCESS;
1339         }
1340 
1341         return COMPACT_NO_SUITABLE_PAGE;
1342 }
1343 
1344 static enum compact_result compact_finished(struct zone *zone,
1345                         struct compact_control *cc,
1346                         const int migratetype)
1347 {
1348         int ret;
1349 
1350         ret = __compact_finished(zone, cc, migratetype);
1351         trace_mm_compaction_finished(zone, cc->order, ret);
1352         if (ret == COMPACT_NO_SUITABLE_PAGE)
1353                 ret = COMPACT_CONTINUE;
1354 
1355         return ret;
1356 }
1357 
1358 /*
1359  * compaction_suitable: Is this suitable to run compaction on this zone now?
1360  * Returns
1361  *   COMPACT_SKIPPED  - If there are too few free pages for compaction
1362  *   COMPACT_SUCCESS  - If the allocation would succeed without compaction
1363  *   COMPACT_CONTINUE - If compaction should run now
1364  */
1365 static enum compact_result __compaction_suitable(struct zone *zone, int order,
1366                                         unsigned int alloc_flags,
1367                                         int classzone_idx,
1368                                         unsigned long wmark_target)
1369 {
1370         unsigned long watermark;
1371 
1372         if (is_via_compact_memory(order))
1373                 return COMPACT_CONTINUE;
1374 
1375         watermark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
1376         /*
1377          * If watermarks for high-order allocation are already met, there
1378          * should be no need for compaction at all.
1379          */
1380         if (zone_watermark_ok(zone, order, watermark, classzone_idx,
1381                                                                 alloc_flags))
1382                 return COMPACT_SUCCESS;
1383 
1384         /*
1385          * Watermarks for order-0 must be met for compaction to be able to
1386          * isolate free pages for migration targets. This means that the
1387          * watermark and alloc_flags have to match, or be more pessimistic than
1388          * the check in __isolate_free_page(). We don't use the direct
1389          * compactor's alloc_flags, as they are not relevant for freepage
1390          * isolation. We however do use the direct compactor's classzone_idx to
1391          * skip over zones where lowmem reserves would prevent allocation even
1392          * if compaction succeeds.
1393          * For costly orders, we require low watermark instead of min for
1394          * compaction to proceed to increase its chances.
1395          * ALLOC_CMA is used, as pages in CMA pageblocks are considered
1396          * suitable migration targets
1397          */
1398         watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
1399                                 low_wmark_pages(zone) : min_wmark_pages(zone);
1400         watermark += compact_gap(order);
1401         if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx,
1402                                                 ALLOC_CMA, wmark_target))
1403                 return COMPACT_SKIPPED;
1404 
1405         return COMPACT_CONTINUE;
1406 }
1407 
1408 enum compact_result compaction_suitable(struct zone *zone, int order,
1409                                         unsigned int alloc_flags,
1410                                         int classzone_idx)
1411 {
1412         enum compact_result ret;
1413         int fragindex;
1414 
1415         ret = __compaction_suitable(zone, order, alloc_flags, classzone_idx,
1416                                     zone_page_state(zone, NR_FREE_PAGES));
1417         /*
1418          * fragmentation index determines if allocation failures are due to
1419          * low memory or external fragmentation
1420          *
1421          * index of -1000 would imply allocations might succeed depending on
1422          * watermarks, but we already failed the high-order watermark check
1423          * index towards 0 implies failure is due to lack of memory
1424          * index towards 1000 implies failure is due to fragmentation
1425          *
1426          * Only compact if a failure would be due to fragmentation. Also
1427          * ignore fragindex for non-costly orders where the alternative to
1428          * a successful reclaim/compaction is OOM. Fragindex and the
1429          * vm.extfrag_threshold sysctl is meant as a heuristic to prevent
1430          * excessive compaction for costly orders, but it should not be at the
1431          * expense of system stability.
1432          */
1433         if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) {
1434                 fragindex = fragmentation_index(zone, order);
1435                 if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
1436                         ret = COMPACT_NOT_SUITABLE_ZONE;
1437         }
1438 
1439         trace_mm_compaction_suitable(zone, order, ret);
1440         if (ret == COMPACT_NOT_SUITABLE_ZONE)
1441                 ret = COMPACT_SKIPPED;
1442 
1443         return ret;
1444 }
1445 
1446 bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
1447                 int alloc_flags)
1448 {
1449         struct zone *zone;
1450         struct zoneref *z;
1451 
1452         /*
1453          * Make sure at least one zone would pass __compaction_suitable if we continue
1454          * retrying the reclaim.
1455          */
1456         for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
1457                                         ac->nodemask) {
1458                 unsigned long available;
1459                 enum compact_result compact_result;
1460 
1461                 /*
1462                  * Do not consider all the reclaimable memory because we do not
1463                  * want to trash just for a single high order allocation which
1464                  * is even not guaranteed to appear even if __compaction_suitable
1465                  * is happy about the watermark check.
1466                  */
1467                 available = zone_reclaimable_pages(zone) / order;
1468                 available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
1469                 compact_result = __compaction_suitable(zone, order, alloc_flags,
1470                                 ac_classzone_idx(ac), available);
1471                 if (compact_result != COMPACT_SKIPPED)
1472                         return true;
1473         }
1474 
1475         return false;
1476 }
1477 
1478 static enum compact_result compact_zone(struct zone *zone, struct compact_control *cc)
1479 {
1480         enum compact_result ret;
1481         unsigned long start_pfn = zone->zone_start_pfn;
1482         unsigned long end_pfn = zone_end_pfn(zone);
1483         const int migratetype = gfpflags_to_migratetype(cc->gfp_mask);
1484         const bool sync = cc->mode != MIGRATE_ASYNC;
1485 
1486         ret = compaction_suitable(zone, cc->order, cc->alloc_flags,
1487                                                         cc->classzone_idx);
1488         /* Compaction is likely to fail */
1489         if (ret == COMPACT_SUCCESS || ret == COMPACT_SKIPPED)
1490                 return ret;
1491 
1492         /* huh, compaction_suitable is returning something unexpected */
1493         VM_BUG_ON(ret != COMPACT_CONTINUE);
1494 
1495         /*
1496          * Clear pageblock skip if there were failures recently and compaction
1497          * is about to be retried after being deferred.
1498          */
1499         if (compaction_restarting(zone, cc->order))
1500                 __reset_isolation_suitable(zone);
1501 
1502         /*
1503          * Setup to move all movable pages to the end of the zone. Used cached
1504          * information on where the scanners should start (unless we explicitly
1505          * want to compact the whole zone), but check that it is initialised
1506          * by ensuring the values are within zone boundaries.
1507          */
1508         if (cc->whole_zone) {
1509                 cc->migrate_pfn = start_pfn;
1510                 cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
1511         } else {
1512                 cc->migrate_pfn = zone->compact_cached_migrate_pfn[sync];
1513                 cc->free_pfn = zone->compact_cached_free_pfn;
1514                 if (cc->free_pfn < start_pfn || cc->free_pfn >= end_pfn) {
1515                         cc->free_pfn = pageblock_start_pfn(end_pfn - 1);
1516                         zone->compact_cached_free_pfn = cc->free_pfn;
1517                 }
1518                 if (cc->migrate_pfn < start_pfn || cc->migrate_pfn >= end_pfn) {
1519                         cc->migrate_pfn = start_pfn;
1520                         zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
1521                         zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
1522                 }
1523 
1524                 if (cc->migrate_pfn == start_pfn)
1525                         cc->whole_zone = true;
1526         }
1527 
1528         cc->last_migrated_pfn = 0;
1529 
1530         trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
1531                                 cc->free_pfn, end_pfn, sync);
1532 
1533         migrate_prep_local();
1534 
1535         while ((ret = compact_finished(zone, cc, migratetype)) ==
1536                                                 COMPACT_CONTINUE) {
1537                 int err;
1538 
1539                 switch (isolate_migratepages(zone, cc)) {
1540                 case ISOLATE_ABORT:
1541                         ret = COMPACT_CONTENDED;
1542                         putback_movable_pages(&cc->migratepages);
1543                         cc->nr_migratepages = 0;
1544                         goto out;
1545                 case ISOLATE_NONE:
1546                         /*
1547                          * We haven't isolated and migrated anything, but
1548                          * there might still be unflushed migrations from
1549                          * previous cc->order aligned block.
1550                          */
1551                         goto check_drain;
1552                 case ISOLATE_SUCCESS:
1553                         ;
1554                 }
1555 
1556                 err = migrate_pages(&cc->migratepages, compaction_alloc,
1557                                 compaction_free, (unsigned long)cc, cc->mode,
1558                                 MR_COMPACTION);
1559 
1560                 trace_mm_compaction_migratepages(cc->nr_migratepages, err,
1561                                                         &cc->migratepages);
1562 
1563                 /* All pages were either migrated or will be released */
1564                 cc->nr_migratepages = 0;
1565                 if (err) {
1566                         putback_movable_pages(&cc->migratepages);
1567                         /*
1568                          * migrate_pages() may return -ENOMEM when scanners meet
1569                          * and we want compact_finished() to detect it
1570                          */
1571                         if (err == -ENOMEM && !compact_scanners_met(cc)) {
1572                                 ret = COMPACT_CONTENDED;
1573                                 goto out;
1574                         }
1575                         /*
1576                          * We failed to migrate at least one page in the current
1577                          * order-aligned block, so skip the rest of it.
1578                          */
1579                         if (cc->direct_compaction &&
1580                                                 (cc->mode == MIGRATE_ASYNC)) {
1581                                 cc->migrate_pfn = block_end_pfn(
1582                                                 cc->migrate_pfn - 1, cc->order);
1583                                 /* Draining pcplists is useless in this case */
1584                                 cc->last_migrated_pfn = 0;
1585 
1586                         }
1587                 }
1588 
1589 check_drain:
1590                 /*
1591                  * Has the migration scanner moved away from the previous
1592                  * cc->order aligned block where we migrated from? If yes,
1593                  * flush the pages that were freed, so that they can merge and
1594                  * compact_finished() can detect immediately if allocation
1595                  * would succeed.
1596                  */
1597                 if (cc->order > 0 && cc->last_migrated_pfn) {
1598                         int cpu;
1599                         unsigned long current_block_start =
1600                                 block_start_pfn(cc->migrate_pfn, cc->order);
1601 
1602                         if (cc->last_migrated_pfn < current_block_start) {
1603                                 cpu = get_cpu();
1604                                 lru_add_drain_cpu(cpu);
1605                                 drain_local_pages(zone);
1606                                 put_cpu();
1607                                 /* No more flushing until we migrate again */
1608                                 cc->last_migrated_pfn = 0;
1609                         }
1610                 }
1611 
1612         }
1613 
1614 out:
1615         /*
1616          * Release free pages and update where the free scanner should restart,
1617          * so we don't leave any returned pages behind in the next attempt.
1618          */
1619         if (cc->nr_freepages > 0) {
1620                 unsigned long free_pfn = release_freepages(&cc->freepages);
1621 
1622                 cc->nr_freepages = 0;
1623                 VM_BUG_ON(free_pfn == 0);
1624                 /* The cached pfn is always the first in a pageblock */
1625                 free_pfn = pageblock_start_pfn(free_pfn);
1626                 /*
1627                  * Only go back, not forward. The cached pfn might have been
1628                  * already reset to zone end in compact_finished()
1629                  */
1630                 if (free_pfn > zone->compact_cached_free_pfn)
1631                         zone->compact_cached_free_pfn = free_pfn;
1632         }
1633 
1634         trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
1635                                 cc->free_pfn, end_pfn, sync, ret);
1636 
1637         return ret;
1638 }
1639 
1640 static enum compact_result compact_zone_order(struct zone *zone, int order,
1641                 gfp_t gfp_mask, enum compact_priority prio,
1642                 unsigned int alloc_flags, int classzone_idx)
1643 {
1644         enum compact_result ret;
1645         struct compact_control cc = {
1646                 .nr_freepages = 0,
1647                 .nr_migratepages = 0,
1648                 .order = order,
1649                 .gfp_mask = gfp_mask,
1650                 .zone = zone,
1651                 .mode = (prio == COMPACT_PRIO_ASYNC) ?
1652                                         MIGRATE_ASYNC : MIGRATE_SYNC_LIGHT,
1653                 .alloc_flags = alloc_flags,
1654                 .classzone_idx = classzone_idx,
1655                 .direct_compaction = true,
1656                 .whole_zone = (prio == MIN_COMPACT_PRIORITY),
1657                 .ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
1658                 .ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
1659         };
1660         INIT_LIST_HEAD(&cc.freepages);
1661         INIT_LIST_HEAD(&cc.migratepages);
1662 
1663         ret = compact_zone(zone, &cc);
1664 
1665         VM_BUG_ON(!list_empty(&cc.freepages));
1666         VM_BUG_ON(!list_empty(&cc.migratepages));
1667 
1668         return ret;
1669 }
1670 
1671 int sysctl_extfrag_threshold = 500;
1672 
1673 /**
1674  * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1675  * @gfp_mask: The GFP mask of the current allocation
1676  * @order: The order of the current allocation
1677  * @alloc_flags: The allocation flags of the current allocation
1678  * @ac: The context of current allocation
1679  * @mode: The migration mode for async, sync light, or sync migration
1680  *
1681  * This is the main entry point for direct page compaction.
1682  */
1683 enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
1684                 unsigned int alloc_flags, const struct alloc_context *ac,
1685                 enum compact_priority prio)
1686 {
1687         int may_perform_io = gfp_mask & __GFP_IO;
1688         struct zoneref *z;
1689         struct zone *zone;
1690         enum compact_result rc = COMPACT_SKIPPED;
1691 
1692         /*
1693          * Check if the GFP flags allow compaction - GFP_NOIO is really
1694          * tricky context because the migration might require IO
1695          */
1696         if (!may_perform_io)
1697                 return COMPACT_SKIPPED;
1698 
1699         trace_mm_compaction_try_to_compact_pages(order, gfp_mask, prio);
1700 
1701         /* Compact each zone in the list */
1702         for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
1703                                                                 ac->nodemask) {
1704                 enum compact_result status;
1705 
1706                 if (prio > MIN_COMPACT_PRIORITY
1707                                         && compaction_deferred(zone, order)) {
1708                         rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
1709                         continue;
1710                 }
1711 
1712                 status = compact_zone_order(zone, order, gfp_mask, prio,
1713                                         alloc_flags, ac_classzone_idx(ac));
1714                 rc = max(status, rc);
1715 
1716                 /* The allocation should succeed, stop compacting */
1717                 if (status == COMPACT_SUCCESS) {
1718                         /*
1719                          * We think the allocation will succeed in this zone,
1720                          * but it is not certain, hence the false. The caller
1721                          * will repeat this with true if allocation indeed
1722                          * succeeds in this zone.
1723                          */
1724                         compaction_defer_reset(zone, order, false);
1725 
1726                         break;
1727                 }
1728 
1729                 if (prio != COMPACT_PRIO_ASYNC && (status == COMPACT_COMPLETE ||
1730                                         status == COMPACT_PARTIAL_SKIPPED))
1731                         /*
1732                          * We think that allocation won't succeed in this zone
1733                          * so we defer compaction there. If it ends up
1734                          * succeeding after all, it will be reset.
1735                          */
1736                         defer_compaction(zone, order);
1737 
1738                 /*
1739                  * We might have stopped compacting due to need_resched() in
1740                  * async compaction, or due to a fatal signal detected. In that
1741                  * case do not try further zones
1742                  */
1743                 if ((prio == COMPACT_PRIO_ASYNC && need_resched())
1744                                         || fatal_signal_pending(current))
1745                         break;
1746         }
1747 
1748         return rc;
1749 }
1750 
1751 
1752 /* Compact all zones within a node */
1753 static void compact_node(int nid)
1754 {
1755         pg_data_t *pgdat = NODE_DATA(nid);
1756         int zoneid;
1757         struct zone *zone;
1758         struct compact_control cc = {
1759                 .order = -1,
1760                 .mode = MIGRATE_SYNC,
1761                 .ignore_skip_hint = true,
1762                 .whole_zone = true,
1763                 .gfp_mask = GFP_KERNEL,
1764         };
1765 
1766 
1767         for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1768 
1769                 zone = &pgdat->node_zones[zoneid];
1770                 if (!populated_zone(zone))
1771                         continue;
1772 
1773                 cc.nr_freepages = 0;
1774                 cc.nr_migratepages = 0;
1775                 cc.zone = zone;
1776                 INIT_LIST_HEAD(&cc.freepages);
1777                 INIT_LIST_HEAD(&cc.migratepages);
1778 
1779                 compact_zone(zone, &cc);
1780 
1781                 VM_BUG_ON(!list_empty(&cc.freepages));
1782                 VM_BUG_ON(!list_empty(&cc.migratepages));
1783         }
1784 }
1785 
1786 /* Compact all nodes in the system */
1787 static void compact_nodes(void)
1788 {
1789         int nid;
1790 
1791         /* Flush pending updates to the LRU lists */
1792         lru_add_drain_all();
1793 
1794         for_each_online_node(nid)
1795                 compact_node(nid);
1796 }
1797 
1798 /* The written value is actually unused, all memory is compacted */
1799 int sysctl_compact_memory;
1800 
1801 /*
1802  * This is the entry point for compacting all nodes via
1803  * /proc/sys/vm/compact_memory
1804  */
1805 int sysctl_compaction_handler(struct ctl_table *table, int write,
1806                         void __user *buffer, size_t *length, loff_t *ppos)
1807 {
1808         if (write)
1809                 compact_nodes();
1810 
1811         return 0;
1812 }
1813 
1814 int sysctl_extfrag_handler(struct ctl_table *table, int write,
1815                         void __user *buffer, size_t *length, loff_t *ppos)
1816 {
1817         proc_dointvec_minmax(table, write, buffer, length, ppos);
1818 
1819         return 0;
1820 }
1821 
1822 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1823 static ssize_t sysfs_compact_node(struct device *dev,
1824                         struct device_attribute *attr,
1825                         const char *buf, size_t count)
1826 {
1827         int nid = dev->id;
1828 
1829         if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
1830                 /* Flush pending updates to the LRU lists */
1831                 lru_add_drain_all();
1832 
1833                 compact_node(nid);
1834         }
1835 
1836         return count;
1837 }
1838 static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
1839 
1840 int compaction_register_node(struct node *node)
1841 {
1842         return device_create_file(&node->dev, &dev_attr_compact);
1843 }
1844 
1845 void compaction_unregister_node(struct node *node)
1846 {
1847         return device_remove_file(&node->dev, &dev_attr_compact);
1848 }
1849 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
1850 
1851 static inline bool kcompactd_work_requested(pg_data_t *pgdat)
1852 {
1853         return pgdat->kcompactd_max_order > 0 || kthread_should_stop();
1854 }
1855 
1856 static bool kcompactd_node_suitable(pg_data_t *pgdat)
1857 {
1858         int zoneid;
1859         struct zone *zone;
1860         enum zone_type classzone_idx = pgdat->kcompactd_classzone_idx;
1861 
1862         for (zoneid = 0; zoneid <= classzone_idx; zoneid++) {
1863                 zone = &pgdat->node_zones[zoneid];
1864 
1865                 if (!populated_zone(zone))
1866                         continue;
1867 
1868                 if (compaction_suitable(zone, pgdat->kcompactd_max_order, 0,
1869                                         classzone_idx) == COMPACT_CONTINUE)
1870                         return true;
1871         }
1872 
1873         return false;
1874 }
1875 
1876 static void kcompactd_do_work(pg_data_t *pgdat)
1877 {
1878         /*
1879          * With no special task, compact all zones so that a page of requested
1880          * order is allocatable.
1881          */
1882         int zoneid;
1883         struct zone *zone;
1884         struct compact_control cc = {
1885                 .order = pgdat->kcompactd_max_order,
1886                 .classzone_idx = pgdat->kcompactd_classzone_idx,
1887                 .mode = MIGRATE_SYNC_LIGHT,
1888                 .ignore_skip_hint = true,
1889                 .gfp_mask = GFP_KERNEL,
1890 
1891         };
1892         trace_mm_compaction_kcompactd_wake(pgdat->node_id, cc.order,
1893                                                         cc.classzone_idx);
1894         count_vm_event(KCOMPACTD_WAKE);
1895 
1896         for (zoneid = 0; zoneid <= cc.classzone_idx; zoneid++) {
1897                 int status;
1898 
1899                 zone = &pgdat->node_zones[zoneid];
1900                 if (!populated_zone(zone))
1901                         continue;
1902 
1903                 if (compaction_deferred(zone, cc.order))
1904                         continue;
1905 
1906                 if (compaction_suitable(zone, cc.order, 0, zoneid) !=
1907                                                         COMPACT_CONTINUE)
1908                         continue;
1909 
1910                 cc.nr_freepages = 0;
1911                 cc.nr_migratepages = 0;
1912                 cc.zone = zone;
1913                 INIT_LIST_HEAD(&cc.freepages);
1914                 INIT_LIST_HEAD(&cc.migratepages);
1915 
1916                 if (kthread_should_stop())
1917                         return;
1918                 status = compact_zone(zone, &cc);
1919 
1920                 if (status == COMPACT_SUCCESS) {
1921                         compaction_defer_reset(zone, cc.order, false);
1922                 } else if (status == COMPACT_PARTIAL_SKIPPED || status == COMPACT_COMPLETE) {
1923                         /*
1924                          * We use sync migration mode here, so we defer like
1925                          * sync direct compaction does.
1926                          */
1927                         defer_compaction(zone, cc.order);
1928                 }
1929 
1930                 VM_BUG_ON(!list_empty(&cc.freepages));
1931                 VM_BUG_ON(!list_empty(&cc.migratepages));
1932         }
1933 
1934         /*
1935          * Regardless of success, we are done until woken up next. But remember
1936          * the requested order/classzone_idx in case it was higher/tighter than
1937          * our current ones
1938          */
1939         if (pgdat->kcompactd_max_order <= cc.order)
1940                 pgdat->kcompactd_max_order = 0;
1941         if (pgdat->kcompactd_classzone_idx >= cc.classzone_idx)
1942                 pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
1943 }
1944 
1945 void wakeup_kcompactd(pg_data_t *pgdat, int order, int classzone_idx)
1946 {
1947         if (!order)
1948                 return;
1949 
1950         if (pgdat->kcompactd_max_order < order)
1951                 pgdat->kcompactd_max_order = order;
1952 
1953         if (pgdat->kcompactd_classzone_idx > classzone_idx)
1954                 pgdat->kcompactd_classzone_idx = classzone_idx;
1955 
1956         if (!waitqueue_active(&pgdat->kcompactd_wait))
1957                 return;
1958 
1959         if (!kcompactd_node_suitable(pgdat))
1960                 return;
1961 
1962         trace_mm_compaction_wakeup_kcompactd(pgdat->node_id, order,
1963                                                         classzone_idx);
1964         wake_up_interruptible(&pgdat->kcompactd_wait);
1965 }
1966 
1967 /*
1968  * The background compaction daemon, started as a kernel thread
1969  * from the init process.
1970  */
1971 static int kcompactd(void *p)
1972 {
1973         pg_data_t *pgdat = (pg_data_t*)p;
1974         struct task_struct *tsk = current;
1975 
1976         const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
1977 
1978         if (!cpumask_empty(cpumask))
1979                 set_cpus_allowed_ptr(tsk, cpumask);
1980 
1981         set_freezable();
1982 
1983         pgdat->kcompactd_max_order = 0;
1984         pgdat->kcompactd_classzone_idx = pgdat->nr_zones - 1;
1985 
1986         while (!kthread_should_stop()) {
1987                 trace_mm_compaction_kcompactd_sleep(pgdat->node_id);
1988                 wait_event_freezable(pgdat->kcompactd_wait,
1989                                 kcompactd_work_requested(pgdat));
1990 
1991                 kcompactd_do_work(pgdat);
1992         }
1993 
1994         return 0;
1995 }
1996 
1997 /*
1998  * This kcompactd start function will be called by init and node-hot-add.
1999  * On node-hot-add, kcompactd will moved to proper cpus if cpus are hot-added.
2000  */
2001 int kcompactd_run(int nid)
2002 {
2003         pg_data_t *pgdat = NODE_DATA(nid);
2004         int ret = 0;
2005 
2006         if (pgdat->kcompactd)
2007                 return 0;
2008 
2009         pgdat->kcompactd = kthread_run(kcompactd, pgdat, "kcompactd%d", nid);
2010         if (IS_ERR(pgdat->kcompactd)) {
2011                 pr_err("Failed to start kcompactd on node %d\n", nid);
2012                 ret = PTR_ERR(pgdat->kcompactd);
2013                 pgdat->kcompactd = NULL;
2014         }
2015         return ret;
2016 }
2017 
2018 /*
2019  * Called by memory hotplug when all memory in a node is offlined. Caller must
2020  * hold mem_hotplug_begin/end().
2021  */
2022 void kcompactd_stop(int nid)
2023 {
2024         struct task_struct *kcompactd = NODE_DATA(nid)->kcompactd;
2025 
2026         if (kcompactd) {
2027                 kthread_stop(kcompactd);
2028                 NODE_DATA(nid)->kcompactd = NULL;
2029         }
2030 }
2031 
2032 /*
2033  * It's optimal to keep kcompactd on the same CPUs as their memory, but
2034  * not required for correctness. So if the last cpu in a node goes
2035  * away, we get changed to run anywhere: as the first one comes back,
2036  * restore their cpu bindings.
2037  */
2038 static int kcompactd_cpu_online(unsigned int cpu)
2039 {
2040         int nid;
2041 
2042         for_each_node_state(nid, N_MEMORY) {
2043                 pg_data_t *pgdat = NODE_DATA(nid);
2044                 const struct cpumask *mask;
2045 
2046                 mask = cpumask_of_node(pgdat->node_id);
2047 
2048                 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2049                         /* One of our CPUs online: restore mask */
2050                         set_cpus_allowed_ptr(pgdat->kcompactd, mask);
2051         }
2052         return 0;
2053 }
2054 
2055 static int __init kcompactd_init(void)
2056 {
2057         int nid;
2058         int ret;
2059 
2060         ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
2061                                         "mm/compaction:online",
2062                                         kcompactd_cpu_online, NULL);
2063         if (ret < 0) {
2064                 pr_err("kcompactd: failed to register hotplug callbacks.\n");
2065                 return ret;
2066         }
2067 
2068         for_each_node_state(nid, N_MEMORY)
2069                 kcompactd_run(nid);
2070         return 0;
2071 }
2072 subsys_initcall(kcompactd_init)
2073 
2074 #endif /* CONFIG_COMPACTION */
2075 

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