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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/swap.h>
 11 #include <linux/migrate.h>
 12 #include <linux/compaction.h>
 13 #include <linux/mm_inline.h>
 14 #include <linux/backing-dev.h>
 15 #include <linux/sysctl.h>
 16 #include <linux/sysfs.h>
 17 #include "internal.h"
 18 
 19 /*
 20  * compact_control is used to track pages being migrated and the free pages
 21  * they are being migrated to during memory compaction. The free_pfn starts
 22  * at the end of a zone and migrate_pfn begins at the start. Movable pages
 23  * are moved to the end of a zone during a compaction run and the run
 24  * completes when free_pfn <= migrate_pfn
 25  */
 26 struct compact_control {
 27         struct list_head freepages;     /* List of free pages to migrate to */
 28         struct list_head migratepages;  /* List of pages being migrated */
 29         unsigned long nr_freepages;     /* Number of isolated free pages */
 30         unsigned long nr_migratepages;  /* Number of pages to migrate */
 31         unsigned long free_pfn;         /* isolate_freepages search base */
 32         unsigned long migrate_pfn;      /* isolate_migratepages search base */
 33 
 34         /* Account for isolated anon and file pages */
 35         unsigned long nr_anon;
 36         unsigned long nr_file;
 37 
 38         unsigned int order;             /* order a direct compactor needs */
 39         int migratetype;                /* MOVABLE, RECLAIMABLE etc */
 40         struct zone *zone;
 41 };
 42 
 43 static unsigned long release_freepages(struct list_head *freelist)
 44 {
 45         struct page *page, *next;
 46         unsigned long count = 0;
 47 
 48         list_for_each_entry_safe(page, next, freelist, lru) {
 49                 list_del(&page->lru);
 50                 __free_page(page);
 51                 count++;
 52         }
 53 
 54         return count;
 55 }
 56 
 57 /* Isolate free pages onto a private freelist. Must hold zone->lock */
 58 static unsigned long isolate_freepages_block(struct zone *zone,
 59                                 unsigned long blockpfn,
 60                                 struct list_head *freelist)
 61 {
 62         unsigned long zone_end_pfn, end_pfn;
 63         int total_isolated = 0;
 64         struct page *cursor;
 65 
 66         /* Get the last PFN we should scan for free pages at */
 67         zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
 68         end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);
 69 
 70         /* Find the first usable PFN in the block to initialse page cursor */
 71         for (; blockpfn < end_pfn; blockpfn++) {
 72                 if (pfn_valid_within(blockpfn))
 73                         break;
 74         }
 75         cursor = pfn_to_page(blockpfn);
 76 
 77         /* Isolate free pages. This assumes the block is valid */
 78         for (; blockpfn < end_pfn; blockpfn++, cursor++) {
 79                 int isolated, i;
 80                 struct page *page = cursor;
 81 
 82                 if (!pfn_valid_within(blockpfn))
 83                         continue;
 84 
 85                 if (!PageBuddy(page))
 86                         continue;
 87 
 88                 /* Found a free page, break it into order-0 pages */
 89                 isolated = split_free_page(page);
 90                 total_isolated += isolated;
 91                 for (i = 0; i < isolated; i++) {
 92                         list_add(&page->lru, freelist);
 93                         page++;
 94                 }
 95 
 96                 /* If a page was split, advance to the end of it */
 97                 if (isolated) {
 98                         blockpfn += isolated - 1;
 99                         cursor += isolated - 1;
100                 }
101         }
102 
103         return total_isolated;
104 }
105 
106 /* Returns true if the page is within a block suitable for migration to */
107 static bool suitable_migration_target(struct page *page)
108 {
109 
110         int migratetype = get_pageblock_migratetype(page);
111 
112         /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
113         if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
114                 return false;
115 
116         /* If the page is a large free page, then allow migration */
117         if (PageBuddy(page) && page_order(page) >= pageblock_order)
118                 return true;
119 
120         /* If the block is MIGRATE_MOVABLE, allow migration */
121         if (migratetype == MIGRATE_MOVABLE)
122                 return true;
123 
124         /* Otherwise skip the block */
125         return false;
126 }
127 
128 /*
129  * Based on information in the current compact_control, find blocks
130  * suitable for isolating free pages from and then isolate them.
131  */
132 static void isolate_freepages(struct zone *zone,
133                                 struct compact_control *cc)
134 {
135         struct page *page;
136         unsigned long high_pfn, low_pfn, pfn;
137         unsigned long flags;
138         int nr_freepages = cc->nr_freepages;
139         struct list_head *freelist = &cc->freepages;
140 
141         pfn = cc->free_pfn;
142         low_pfn = cc->migrate_pfn + pageblock_nr_pages;
143         high_pfn = low_pfn;
144 
145         /*
146          * Isolate free pages until enough are available to migrate the
147          * pages on cc->migratepages. We stop searching if the migrate
148          * and free page scanners meet or enough free pages are isolated.
149          */
150         spin_lock_irqsave(&zone->lock, flags);
151         for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
152                                         pfn -= pageblock_nr_pages) {
153                 unsigned long isolated;
154 
155                 if (!pfn_valid(pfn))
156                         continue;
157 
158                 /*
159                  * Check for overlapping nodes/zones. It's possible on some
160                  * configurations to have a setup like
161                  * node0 node1 node0
162                  * i.e. it's possible that all pages within a zones range of
163                  * pages do not belong to a single zone.
164                  */
165                 page = pfn_to_page(pfn);
166                 if (page_zone(page) != zone)
167                         continue;
168 
169                 /* Check the block is suitable for migration */
170                 if (!suitable_migration_target(page))
171                         continue;
172 
173                 /* Found a block suitable for isolating free pages from */
174                 isolated = isolate_freepages_block(zone, pfn, freelist);
175                 nr_freepages += isolated;
176 
177                 /*
178                  * Record the highest PFN we isolated pages from. When next
179                  * looking for free pages, the search will restart here as
180                  * page migration may have returned some pages to the allocator
181                  */
182                 if (isolated)
183                         high_pfn = max(high_pfn, pfn);
184         }
185         spin_unlock_irqrestore(&zone->lock, flags);
186 
187         /* split_free_page does not map the pages */
188         list_for_each_entry(page, freelist, lru) {
189                 arch_alloc_page(page, 0);
190                 kernel_map_pages(page, 1, 1);
191         }
192 
193         cc->free_pfn = high_pfn;
194         cc->nr_freepages = nr_freepages;
195 }
196 
197 /* Update the number of anon and file isolated pages in the zone */
198 static void acct_isolated(struct zone *zone, struct compact_control *cc)
199 {
200         struct page *page;
201         unsigned int count[NR_LRU_LISTS] = { 0, };
202 
203         list_for_each_entry(page, &cc->migratepages, lru) {
204                 int lru = page_lru_base_type(page);
205                 count[lru]++;
206         }
207 
208         cc->nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
209         cc->nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
210         __mod_zone_page_state(zone, NR_ISOLATED_ANON, cc->nr_anon);
211         __mod_zone_page_state(zone, NR_ISOLATED_FILE, cc->nr_file);
212 }
213 
214 /* Similar to reclaim, but different enough that they don't share logic */
215 static bool too_many_isolated(struct zone *zone)
216 {
217         unsigned long active, inactive, isolated;
218 
219         inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
220                                         zone_page_state(zone, NR_INACTIVE_ANON);
221         active = zone_page_state(zone, NR_ACTIVE_FILE) +
222                                         zone_page_state(zone, NR_ACTIVE_ANON);
223         isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
224                                         zone_page_state(zone, NR_ISOLATED_ANON);
225 
226         return isolated > (inactive + active) / 2;
227 }
228 
229 /*
230  * Isolate all pages that can be migrated from the block pointed to by
231  * the migrate scanner within compact_control.
232  */
233 static unsigned long isolate_migratepages(struct zone *zone,
234                                         struct compact_control *cc)
235 {
236         unsigned long low_pfn, end_pfn;
237         struct list_head *migratelist = &cc->migratepages;
238 
239         /* Do not scan outside zone boundaries */
240         low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
241 
242         /* Only scan within a pageblock boundary */
243         end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
244 
245         /* Do not cross the free scanner or scan within a memory hole */
246         if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
247                 cc->migrate_pfn = end_pfn;
248                 return 0;
249         }
250 
251         /*
252          * Ensure that there are not too many pages isolated from the LRU
253          * list by either parallel reclaimers or compaction. If there are,
254          * delay for some time until fewer pages are isolated
255          */
256         while (unlikely(too_many_isolated(zone))) {
257                 congestion_wait(BLK_RW_ASYNC, HZ/10);
258 
259                 if (fatal_signal_pending(current))
260                         return 0;
261         }
262 
263         /* Time to isolate some pages for migration */
264         spin_lock_irq(&zone->lru_lock);
265         for (; low_pfn < end_pfn; low_pfn++) {
266                 struct page *page;
267                 if (!pfn_valid_within(low_pfn))
268                         continue;
269 
270                 /* Get the page and skip if free */
271                 page = pfn_to_page(low_pfn);
272                 if (PageBuddy(page))
273                         continue;
274 
275                 /* Try isolate the page */
276                 if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
277                         continue;
278 
279                 /* Successfully isolated */
280                 del_page_from_lru_list(zone, page, page_lru(page));
281                 list_add(&page->lru, migratelist);
282                 mem_cgroup_del_lru(page);
283                 cc->nr_migratepages++;
284 
285                 /* Avoid isolating too much */
286                 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
287                         break;
288         }
289 
290         acct_isolated(zone, cc);
291 
292         spin_unlock_irq(&zone->lru_lock);
293         cc->migrate_pfn = low_pfn;
294 
295         return cc->nr_migratepages;
296 }
297 
298 /*
299  * This is a migrate-callback that "allocates" freepages by taking pages
300  * from the isolated freelists in the block we are migrating to.
301  */
302 static struct page *compaction_alloc(struct page *migratepage,
303                                         unsigned long data,
304                                         int **result)
305 {
306         struct compact_control *cc = (struct compact_control *)data;
307         struct page *freepage;
308 
309         /* Isolate free pages if necessary */
310         if (list_empty(&cc->freepages)) {
311                 isolate_freepages(cc->zone, cc);
312 
313                 if (list_empty(&cc->freepages))
314                         return NULL;
315         }
316 
317         freepage = list_entry(cc->freepages.next, struct page, lru);
318         list_del(&freepage->lru);
319         cc->nr_freepages--;
320 
321         return freepage;
322 }
323 
324 /*
325  * We cannot control nr_migratepages and nr_freepages fully when migration is
326  * running as migrate_pages() has no knowledge of compact_control. When
327  * migration is complete, we count the number of pages on the lists by hand.
328  */
329 static void update_nr_listpages(struct compact_control *cc)
330 {
331         int nr_migratepages = 0;
332         int nr_freepages = 0;
333         struct page *page;
334 
335         list_for_each_entry(page, &cc->migratepages, lru)
336                 nr_migratepages++;
337         list_for_each_entry(page, &cc->freepages, lru)
338                 nr_freepages++;
339 
340         cc->nr_migratepages = nr_migratepages;
341         cc->nr_freepages = nr_freepages;
342 }
343 
344 static int compact_finished(struct zone *zone,
345                                                 struct compact_control *cc)
346 {
347         unsigned int order;
348         unsigned long watermark = low_wmark_pages(zone) + (1 << cc->order);
349 
350         if (fatal_signal_pending(current))
351                 return COMPACT_PARTIAL;
352 
353         /* Compaction run completes if the migrate and free scanner meet */
354         if (cc->free_pfn <= cc->migrate_pfn)
355                 return COMPACT_COMPLETE;
356 
357         /* Compaction run is not finished if the watermark is not met */
358         if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
359                 return COMPACT_CONTINUE;
360 
361         if (cc->order == -1)
362                 return COMPACT_CONTINUE;
363 
364         /* Direct compactor: Is a suitable page free? */
365         for (order = cc->order; order < MAX_ORDER; order++) {
366                 /* Job done if page is free of the right migratetype */
367                 if (!list_empty(&zone->free_area[order].free_list[cc->migratetype]))
368                         return COMPACT_PARTIAL;
369 
370                 /* Job done if allocation would set block type */
371                 if (order >= pageblock_order && zone->free_area[order].nr_free)
372                         return COMPACT_PARTIAL;
373         }
374 
375         return COMPACT_CONTINUE;
376 }
377 
378 static int compact_zone(struct zone *zone, struct compact_control *cc)
379 {
380         int ret;
381 
382         /* Setup to move all movable pages to the end of the zone */
383         cc->migrate_pfn = zone->zone_start_pfn;
384         cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
385         cc->free_pfn &= ~(pageblock_nr_pages-1);
386 
387         migrate_prep_local();
388 
389         while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
390                 unsigned long nr_migrate, nr_remaining;
391 
392                 if (!isolate_migratepages(zone, cc))
393                         continue;
394 
395                 nr_migrate = cc->nr_migratepages;
396                 migrate_pages(&cc->migratepages, compaction_alloc,
397                                                 (unsigned long)cc, 0);
398                 update_nr_listpages(cc);
399                 nr_remaining = cc->nr_migratepages;
400 
401                 count_vm_event(COMPACTBLOCKS);
402                 count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
403                 if (nr_remaining)
404                         count_vm_events(COMPACTPAGEFAILED, nr_remaining);
405 
406                 /* Release LRU pages not migrated */
407                 if (!list_empty(&cc->migratepages)) {
408                         putback_lru_pages(&cc->migratepages);
409                         cc->nr_migratepages = 0;
410                 }
411 
412         }
413 
414         /* Release free pages and check accounting */
415         cc->nr_freepages -= release_freepages(&cc->freepages);
416         VM_BUG_ON(cc->nr_freepages != 0);
417 
418         return ret;
419 }
420 
421 static unsigned long compact_zone_order(struct zone *zone,
422                                                 int order, gfp_t gfp_mask)
423 {
424         struct compact_control cc = {
425                 .nr_freepages = 0,
426                 .nr_migratepages = 0,
427                 .order = order,
428                 .migratetype = allocflags_to_migratetype(gfp_mask),
429                 .zone = zone,
430         };
431         INIT_LIST_HEAD(&cc.freepages);
432         INIT_LIST_HEAD(&cc.migratepages);
433 
434         return compact_zone(zone, &cc);
435 }
436 
437 int sysctl_extfrag_threshold = 500;
438 
439 /**
440  * try_to_compact_pages - Direct compact to satisfy a high-order allocation
441  * @zonelist: The zonelist used for the current allocation
442  * @order: The order of the current allocation
443  * @gfp_mask: The GFP mask of the current allocation
444  * @nodemask: The allowed nodes to allocate from
445  *
446  * This is the main entry point for direct page compaction.
447  */
448 unsigned long try_to_compact_pages(struct zonelist *zonelist,
449                         int order, gfp_t gfp_mask, nodemask_t *nodemask)
450 {
451         enum zone_type high_zoneidx = gfp_zone(gfp_mask);
452         int may_enter_fs = gfp_mask & __GFP_FS;
453         int may_perform_io = gfp_mask & __GFP_IO;
454         unsigned long watermark;
455         struct zoneref *z;
456         struct zone *zone;
457         int rc = COMPACT_SKIPPED;
458 
459         /*
460          * Check whether it is worth even starting compaction. The order check is
461          * made because an assumption is made that the page allocator can satisfy
462          * the "cheaper" orders without taking special steps
463          */
464         if (order <= PAGE_ALLOC_COSTLY_ORDER || !may_enter_fs || !may_perform_io)
465                 return rc;
466 
467         count_vm_event(COMPACTSTALL);
468 
469         /* Compact each zone in the list */
470         for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
471                                                                 nodemask) {
472                 int fragindex;
473                 int status;
474 
475                 /*
476                  * Watermarks for order-0 must be met for compaction. Note
477                  * the 2UL. This is because during migration, copies of
478                  * pages need to be allocated and for a short time, the
479                  * footprint is higher
480                  */
481                 watermark = low_wmark_pages(zone) + (2UL << order);
482                 if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
483                         continue;
484 
485                 /*
486                  * fragmentation index determines if allocation failures are
487                  * due to low memory or external fragmentation
488                  *
489                  * index of -1 implies allocations might succeed depending
490                  *      on watermarks
491                  * index towards 0 implies failure is due to lack of memory
492                  * index towards 1000 implies failure is due to fragmentation
493                  *
494                  * Only compact if a failure would be due to fragmentation.
495                  */
496                 fragindex = fragmentation_index(zone, order);
497                 if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
498                         continue;
499 
500                 if (fragindex == -1 && zone_watermark_ok(zone, order, watermark, 0, 0)) {
501                         rc = COMPACT_PARTIAL;
502                         break;
503                 }
504 
505                 status = compact_zone_order(zone, order, gfp_mask);
506                 rc = max(status, rc);
507 
508                 if (zone_watermark_ok(zone, order, watermark, 0, 0))
509                         break;
510         }
511 
512         return rc;
513 }
514 
515 
516 /* Compact all zones within a node */
517 static int compact_node(int nid)
518 {
519         int zoneid;
520         pg_data_t *pgdat;
521         struct zone *zone;
522 
523         if (nid < 0 || nid >= nr_node_ids || !node_online(nid))
524                 return -EINVAL;
525         pgdat = NODE_DATA(nid);
526 
527         /* Flush pending updates to the LRU lists */
528         lru_add_drain_all();
529 
530         for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
531                 struct compact_control cc = {
532                         .nr_freepages = 0,
533                         .nr_migratepages = 0,
534                         .order = -1,
535                 };
536 
537                 zone = &pgdat->node_zones[zoneid];
538                 if (!populated_zone(zone))
539                         continue;
540 
541                 cc.zone = zone;
542                 INIT_LIST_HEAD(&cc.freepages);
543                 INIT_LIST_HEAD(&cc.migratepages);
544 
545                 compact_zone(zone, &cc);
546 
547                 VM_BUG_ON(!list_empty(&cc.freepages));
548                 VM_BUG_ON(!list_empty(&cc.migratepages));
549         }
550 
551         return 0;
552 }
553 
554 /* Compact all nodes in the system */
555 static int compact_nodes(void)
556 {
557         int nid;
558 
559         for_each_online_node(nid)
560                 compact_node(nid);
561 
562         return COMPACT_COMPLETE;
563 }
564 
565 /* The written value is actually unused, all memory is compacted */
566 int sysctl_compact_memory;
567 
568 /* This is the entry point for compacting all nodes via /proc/sys/vm */
569 int sysctl_compaction_handler(struct ctl_table *table, int write,
570                         void __user *buffer, size_t *length, loff_t *ppos)
571 {
572         if (write)
573                 return compact_nodes();
574 
575         return 0;
576 }
577 
578 int sysctl_extfrag_handler(struct ctl_table *table, int write,
579                         void __user *buffer, size_t *length, loff_t *ppos)
580 {
581         proc_dointvec_minmax(table, write, buffer, length, ppos);
582 
583         return 0;
584 }
585 
586 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
587 ssize_t sysfs_compact_node(struct sys_device *dev,
588                         struct sysdev_attribute *attr,
589                         const char *buf, size_t count)
590 {
591         compact_node(dev->id);
592 
593         return count;
594 }
595 static SYSDEV_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
596 
597 int compaction_register_node(struct node *node)
598 {
599         return sysdev_create_file(&node->sysdev, &attr_compact);
600 }
601 
602 void compaction_unregister_node(struct node *node)
603 {
604         return sysdev_remove_file(&node->sysdev, &attr_compact);
605 }
606 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
607 

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