2 * linux/mm/compaction.c
4 * Memory compaction for the reduction of external fragmentation. Note that
5 * this heavily depends upon page migration to do all the real heavy
8 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
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 <linux/balloon_compaction.h>
18 #include <linux/page-isolation.h>
21 #ifdef CONFIG_COMPACTION
22 static inline void count_compact_event(enum vm_event_item item)
27 static inline void count_compact_events(enum vm_event_item item, long delta)
29 count_vm_events(item, delta);
32 #define count_compact_event(item) do { } while (0)
33 #define count_compact_events(item, delta) do { } while (0)
36 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
38 #define CREATE_TRACE_POINTS
39 #include <trace/events/compaction.h>
41 static unsigned long release_freepages(struct list_head *freelist)
43 struct page *page, *next;
44 unsigned long count = 0;
46 list_for_each_entry_safe(page, next, freelist, lru) {
55 static void map_pages(struct list_head *list)
59 list_for_each_entry(page, list, lru) {
60 arch_alloc_page(page, 0);
61 kernel_map_pages(page, 1, 1);
65 static inline bool migrate_async_suitable(int migratetype)
67 return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
70 #ifdef CONFIG_COMPACTION
71 /* Returns true if the pageblock should be scanned for pages to isolate. */
72 static inline bool isolation_suitable(struct compact_control *cc,
75 if (cc->ignore_skip_hint)
78 return !get_pageblock_skip(page);
82 * This function is called to clear all cached information on pageblocks that
83 * should be skipped for page isolation when the migrate and free page scanner
86 static void __reset_isolation_suitable(struct zone *zone)
88 unsigned long start_pfn = zone->zone_start_pfn;
89 unsigned long end_pfn = zone_end_pfn(zone);
92 zone->compact_cached_migrate_pfn = start_pfn;
93 zone->compact_cached_free_pfn = end_pfn;
94 zone->compact_blockskip_flush = false;
96 /* Walk the zone and mark every pageblock as suitable for isolation */
97 for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
105 page = pfn_to_page(pfn);
106 if (zone != page_zone(page))
109 clear_pageblock_skip(page);
113 void reset_isolation_suitable(pg_data_t *pgdat)
117 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
118 struct zone *zone = &pgdat->node_zones[zoneid];
119 if (!populated_zone(zone))
122 /* Only flush if a full compaction finished recently */
123 if (zone->compact_blockskip_flush)
124 __reset_isolation_suitable(zone);
129 * If no pages were isolated then mark this pageblock to be skipped in the
130 * future. The information is later cleared by __reset_isolation_suitable().
132 static void update_pageblock_skip(struct compact_control *cc,
133 struct page *page, unsigned long nr_isolated,
134 bool migrate_scanner)
136 struct zone *zone = cc->zone;
138 if (cc->ignore_skip_hint)
145 unsigned long pfn = page_to_pfn(page);
146 set_pageblock_skip(page);
148 /* Update where compaction should restart */
149 if (migrate_scanner) {
150 if (!cc->finished_update_migrate &&
151 pfn > zone->compact_cached_migrate_pfn)
152 zone->compact_cached_migrate_pfn = pfn;
154 if (!cc->finished_update_free &&
155 pfn < zone->compact_cached_free_pfn)
156 zone->compact_cached_free_pfn = pfn;
161 static inline bool isolation_suitable(struct compact_control *cc,
167 static void update_pageblock_skip(struct compact_control *cc,
168 struct page *page, unsigned long nr_isolated,
169 bool migrate_scanner)
172 #endif /* CONFIG_COMPACTION */
174 static inline bool should_release_lock(spinlock_t *lock)
176 return need_resched() || spin_is_contended(lock);
180 * Compaction requires the taking of some coarse locks that are potentially
181 * very heavily contended. Check if the process needs to be scheduled or
182 * if the lock is contended. For async compaction, back out in the event
183 * if contention is severe. For sync compaction, schedule.
185 * Returns true if the lock is held.
186 * Returns false if the lock is released and compaction should abort
188 static bool compact_checklock_irqsave(spinlock_t *lock, unsigned long *flags,
189 bool locked, struct compact_control *cc)
191 if (should_release_lock(lock)) {
193 spin_unlock_irqrestore(lock, *flags);
197 /* async aborts if taking too long or contended */
199 cc->contended = true;
207 spin_lock_irqsave(lock, *flags);
211 static inline bool compact_trylock_irqsave(spinlock_t *lock,
212 unsigned long *flags, struct compact_control *cc)
214 return compact_checklock_irqsave(lock, flags, false, cc);
217 /* Returns true if the page is within a block suitable for migration to */
218 static bool suitable_migration_target(struct page *page)
220 /* If the page is a large free page, then disallow migration */
221 if (PageBuddy(page) && page_order(page) >= pageblock_order)
224 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
225 if (migrate_async_suitable(get_pageblock_migratetype(page)))
228 /* Otherwise skip the block */
233 * Isolate free pages onto a private freelist. If @strict is true, will abort
234 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
235 * (even though it may still end up isolating some pages).
237 static unsigned long isolate_freepages_block(struct compact_control *cc,
238 unsigned long blockpfn,
239 unsigned long end_pfn,
240 struct list_head *freelist,
243 int nr_scanned = 0, total_isolated = 0;
244 struct page *cursor, *valid_page = NULL;
247 bool checked_pageblock = false;
249 cursor = pfn_to_page(blockpfn);
251 /* Isolate free pages. */
252 for (; blockpfn < end_pfn; blockpfn++, cursor++) {
254 struct page *page = cursor;
257 if (!pfn_valid_within(blockpfn))
262 if (!PageBuddy(page))
266 * The zone lock must be held to isolate freepages.
267 * Unfortunately this is a very coarse lock and can be
268 * heavily contended if there are parallel allocations
269 * or parallel compactions. For async compaction do not
270 * spin on the lock and we acquire the lock as late as
273 locked = compact_checklock_irqsave(&cc->zone->lock, &flags,
278 /* Recheck this is a suitable migration target under lock */
279 if (!strict && !checked_pageblock) {
281 * We need to check suitability of pageblock only once
282 * and this isolate_freepages_block() is called with
283 * pageblock range, so just check once is sufficient.
285 checked_pageblock = true;
286 if (!suitable_migration_target(page))
290 /* Recheck this is a buddy page under lock */
291 if (!PageBuddy(page))
294 /* Found a free page, break it into order-0 pages */
295 isolated = split_free_page(page);
296 total_isolated += isolated;
297 for (i = 0; i < isolated; i++) {
298 list_add(&page->lru, freelist);
302 /* If a page was split, advance to the end of it */
304 blockpfn += isolated - 1;
305 cursor += isolated - 1;
317 trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
320 * If strict isolation is requested by CMA then check that all the
321 * pages requested were isolated. If there were any failures, 0 is
322 * returned and CMA will fail.
324 if (strict && blockpfn < end_pfn)
328 spin_unlock_irqrestore(&cc->zone->lock, flags);
330 /* Update the pageblock-skip if the whole pageblock was scanned */
331 if (blockpfn == end_pfn)
332 update_pageblock_skip(cc, valid_page, total_isolated, false);
334 count_compact_events(COMPACTFREE_SCANNED, nr_scanned);
336 count_compact_events(COMPACTISOLATED, total_isolated);
337 return total_isolated;
341 * isolate_freepages_range() - isolate free pages.
342 * @start_pfn: The first PFN to start isolating.
343 * @end_pfn: The one-past-last PFN.
345 * Non-free pages, invalid PFNs, or zone boundaries within the
346 * [start_pfn, end_pfn) range are considered errors, cause function to
347 * undo its actions and return zero.
349 * Otherwise, function returns one-past-the-last PFN of isolated page
350 * (which may be greater then end_pfn if end fell in a middle of
354 isolate_freepages_range(struct compact_control *cc,
355 unsigned long start_pfn, unsigned long end_pfn)
357 unsigned long isolated, pfn, block_end_pfn;
360 for (pfn = start_pfn; pfn < end_pfn; pfn += isolated) {
361 if (!pfn_valid(pfn) || cc->zone != page_zone(pfn_to_page(pfn)))
365 * On subsequent iterations ALIGN() is actually not needed,
366 * but we keep it that we not to complicate the code.
368 block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
369 block_end_pfn = min(block_end_pfn, end_pfn);
371 isolated = isolate_freepages_block(cc, pfn, block_end_pfn,
375 * In strict mode, isolate_freepages_block() returns 0 if
376 * there are any holes in the block (ie. invalid PFNs or
383 * If we managed to isolate pages, it is always (1 << n) *
384 * pageblock_nr_pages for some non-negative n. (Max order
385 * page may span two pageblocks).
389 /* split_free_page does not map the pages */
390 map_pages(&freelist);
393 /* Loop terminated early, cleanup. */
394 release_freepages(&freelist);
398 /* We don't use freelists for anything. */
402 /* Update the number of anon and file isolated pages in the zone */
403 static void acct_isolated(struct zone *zone, bool locked, struct compact_control *cc)
406 unsigned int count[2] = { 0, };
408 list_for_each_entry(page, &cc->migratepages, lru)
409 count[!!page_is_file_cache(page)]++;
411 /* If locked we can use the interrupt unsafe versions */
413 __mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
414 __mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
416 mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
417 mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
421 /* Similar to reclaim, but different enough that they don't share logic */
422 static bool too_many_isolated(struct zone *zone)
424 unsigned long active, inactive, isolated;
426 inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
427 zone_page_state(zone, NR_INACTIVE_ANON);
428 active = zone_page_state(zone, NR_ACTIVE_FILE) +
429 zone_page_state(zone, NR_ACTIVE_ANON);
430 isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
431 zone_page_state(zone, NR_ISOLATED_ANON);
433 return isolated > (inactive + active) / 2;
437 * isolate_migratepages_range() - isolate all migrate-able pages in range.
438 * @zone: Zone pages are in.
439 * @cc: Compaction control structure.
440 * @low_pfn: The first PFN of the range.
441 * @end_pfn: The one-past-the-last PFN of the range.
442 * @unevictable: true if it allows to isolate unevictable pages
444 * Isolate all pages that can be migrated from the range specified by
445 * [low_pfn, end_pfn). Returns zero if there is a fatal signal
446 * pending), otherwise PFN of the first page that was not scanned
447 * (which may be both less, equal to or more then end_pfn).
449 * Assumes that cc->migratepages is empty and cc->nr_migratepages is
452 * Apart from cc->migratepages and cc->nr_migratetypes this function
453 * does not modify any cc's fields, in particular it does not modify
454 * (or read for that matter) cc->migrate_pfn.
457 isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
458 unsigned long low_pfn, unsigned long end_pfn, bool unevictable)
460 unsigned long last_pageblock_nr = 0, pageblock_nr;
461 unsigned long nr_scanned = 0, nr_isolated = 0;
462 struct list_head *migratelist = &cc->migratepages;
463 isolate_mode_t mode = 0;
464 struct lruvec *lruvec;
467 struct page *page = NULL, *valid_page = NULL;
468 bool skipped_async_unsuitable = false;
471 * Ensure that there are not too many pages isolated from the LRU
472 * list by either parallel reclaimers or compaction. If there are,
473 * delay for some time until fewer pages are isolated
475 while (unlikely(too_many_isolated(zone))) {
476 /* async migration should just abort */
480 congestion_wait(BLK_RW_ASYNC, HZ/10);
482 if (fatal_signal_pending(current))
486 /* Time to isolate some pages for migration */
488 for (; low_pfn < end_pfn; low_pfn++) {
489 /* give a chance to irqs before checking need_resched() */
490 if (locked && !(low_pfn % SWAP_CLUSTER_MAX)) {
491 if (should_release_lock(&zone->lru_lock)) {
492 spin_unlock_irqrestore(&zone->lru_lock, flags);
498 * migrate_pfn does not necessarily start aligned to a
499 * pageblock. Ensure that pfn_valid is called when moving
500 * into a new MAX_ORDER_NR_PAGES range in case of large
501 * memory holes within the zone
503 if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
504 if (!pfn_valid(low_pfn)) {
505 low_pfn += MAX_ORDER_NR_PAGES - 1;
510 if (!pfn_valid_within(low_pfn))
515 * Get the page and ensure the page is within the same zone.
516 * See the comment in isolate_freepages about overlapping
517 * nodes. It is deliberate that the new zone lock is not taken
518 * as memory compaction should not move pages between nodes.
520 page = pfn_to_page(low_pfn);
521 if (page_zone(page) != zone)
527 /* If isolation recently failed, do not retry */
528 pageblock_nr = low_pfn >> pageblock_order;
529 if (last_pageblock_nr != pageblock_nr) {
532 last_pageblock_nr = pageblock_nr;
533 if (!isolation_suitable(cc, page))
537 * For async migration, also only scan in MOVABLE
538 * blocks. Async migration is optimistic to see if
539 * the minimum amount of work satisfies the allocation
541 mt = get_pageblock_migratetype(page);
542 if (!cc->sync && !migrate_async_suitable(mt)) {
543 cc->finished_update_migrate = true;
544 skipped_async_unsuitable = true;
550 * Skip if free. page_order cannot be used without zone->lock
551 * as nothing prevents parallel allocations or buddy merging.
557 * Check may be lockless but that's ok as we recheck later.
558 * It's possible to migrate LRU pages and balloon pages
559 * Skip any other type of page
561 if (!PageLRU(page)) {
562 if (unlikely(balloon_page_movable(page))) {
563 if (locked && balloon_page_isolate(page)) {
564 /* Successfully isolated */
565 goto isolate_success;
572 * PageLRU is set. lru_lock normally excludes isolation
573 * splitting and collapsing (collapsing has already happened
574 * if PageLRU is set) but the lock is not necessarily taken
575 * here and it is wasteful to take it just to check transhuge.
576 * Check TransHuge without lock and skip the whole pageblock if
577 * it's either a transhuge or hugetlbfs page, as calling
578 * compound_order() without preventing THP from splitting the
579 * page underneath us may return surprising results.
581 if (PageTransHuge(page)) {
584 low_pfn += (1 << compound_order(page)) - 1;
589 * Migration will fail if an anonymous page is pinned in memory,
590 * so avoid taking lru_lock and isolating it unnecessarily in an
591 * admittedly racy check.
593 if (!page_mapping(page) &&
594 page_count(page) > page_mapcount(page))
597 /* Check if it is ok to still hold the lock */
598 locked = compact_checklock_irqsave(&zone->lru_lock, &flags,
600 if (!locked || fatal_signal_pending(current))
603 /* Recheck PageLRU and PageTransHuge under lock */
606 if (PageTransHuge(page)) {
607 low_pfn += (1 << compound_order(page)) - 1;
612 mode |= ISOLATE_ASYNC_MIGRATE;
615 mode |= ISOLATE_UNEVICTABLE;
617 lruvec = mem_cgroup_page_lruvec(page, zone);
619 /* Try isolate the page */
620 if (__isolate_lru_page(page, mode) != 0)
623 VM_BUG_ON_PAGE(PageTransCompound(page), page);
625 /* Successfully isolated */
626 del_page_from_lru_list(page, lruvec, page_lru(page));
629 cc->finished_update_migrate = true;
630 list_add(&page->lru, migratelist);
631 cc->nr_migratepages++;
634 /* Avoid isolating too much */
635 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
643 low_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages) - 1;
646 acct_isolated(zone, locked, cc);
649 spin_unlock_irqrestore(&zone->lru_lock, flags);
652 * Update the pageblock-skip information and cached scanner pfn,
653 * if the whole pageblock was scanned without isolating any page.
654 * This is not done when pageblock was skipped due to being unsuitable
655 * for async compaction, so that eventual sync compaction can try.
657 if (low_pfn == end_pfn && !skipped_async_unsuitable)
658 update_pageblock_skip(cc, valid_page, nr_isolated, true);
660 trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
662 count_compact_events(COMPACTMIGRATE_SCANNED, nr_scanned);
664 count_compact_events(COMPACTISOLATED, nr_isolated);
669 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
670 #ifdef CONFIG_COMPACTION
672 * Based on information in the current compact_control, find blocks
673 * suitable for isolating free pages from and then isolate them.
675 static void isolate_freepages(struct zone *zone,
676 struct compact_control *cc)
679 unsigned long high_pfn, low_pfn, pfn, z_end_pfn;
680 int nr_freepages = cc->nr_freepages;
681 struct list_head *freelist = &cc->freepages;
684 * Initialise the free scanner. The starting point is where we last
685 * successfully isolated from, zone-cached value, or the end of the
686 * zone when isolating for the first time. We need this aligned to
687 * the pageblock boundary, because we do pfn -= pageblock_nr_pages
689 * The low boundary is the end of the pageblock the migration scanner
692 pfn = cc->free_pfn & ~(pageblock_nr_pages-1);
693 low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages);
696 * Take care that if the migration scanner is at the end of the zone
697 * that the free scanner does not accidentally move to the next zone
698 * in the next isolation cycle.
700 high_pfn = min(low_pfn, pfn);
702 z_end_pfn = zone_end_pfn(zone);
705 * Isolate free pages until enough are available to migrate the
706 * pages on cc->migratepages. We stop searching if the migrate
707 * and free page scanners meet or enough free pages are isolated.
709 for (; pfn >= low_pfn && cc->nr_migratepages > nr_freepages;
710 pfn -= pageblock_nr_pages) {
711 unsigned long isolated;
712 unsigned long end_pfn;
715 * This can iterate a massively long zone without finding any
716 * suitable migration targets, so periodically check if we need
725 * Check for overlapping nodes/zones. It's possible on some
726 * configurations to have a setup like
728 * i.e. it's possible that all pages within a zones range of
729 * pages do not belong to a single zone.
731 page = pfn_to_page(pfn);
732 if (page_zone(page) != zone)
735 /* Check the block is suitable for migration */
736 if (!suitable_migration_target(page))
739 /* If isolation recently failed, do not retry */
740 if (!isolation_suitable(cc, page))
743 /* Found a block suitable for isolating free pages from */
747 * Take care when isolating in last pageblock of a zone which
748 * ends in the middle of a pageblock.
750 end_pfn = min(pfn + pageblock_nr_pages, z_end_pfn);
751 isolated = isolate_freepages_block(cc, pfn, end_pfn,
753 nr_freepages += isolated;
756 * Record the highest PFN we isolated pages from. When next
757 * looking for free pages, the search will restart here as
758 * page migration may have returned some pages to the allocator
761 cc->finished_update_free = true;
762 high_pfn = max(high_pfn, pfn);
766 /* split_free_page does not map the pages */
770 * If we crossed the migrate scanner, we want to keep it that way
771 * so that compact_finished() may detect this
774 cc->free_pfn = max(pfn, zone->zone_start_pfn);
776 cc->free_pfn = high_pfn;
777 cc->nr_freepages = nr_freepages;
781 * This is a migrate-callback that "allocates" freepages by taking pages
782 * from the isolated freelists in the block we are migrating to.
784 static struct page *compaction_alloc(struct page *migratepage,
788 struct compact_control *cc = (struct compact_control *)data;
789 struct page *freepage;
791 /* Isolate free pages if necessary */
792 if (list_empty(&cc->freepages)) {
793 isolate_freepages(cc->zone, cc);
795 if (list_empty(&cc->freepages))
799 freepage = list_entry(cc->freepages.next, struct page, lru);
800 list_del(&freepage->lru);
807 * We cannot control nr_migratepages and nr_freepages fully when migration is
808 * running as migrate_pages() has no knowledge of compact_control. When
809 * migration is complete, we count the number of pages on the lists by hand.
811 static void update_nr_listpages(struct compact_control *cc)
813 int nr_migratepages = 0;
814 int nr_freepages = 0;
817 list_for_each_entry(page, &cc->migratepages, lru)
819 list_for_each_entry(page, &cc->freepages, lru)
822 cc->nr_migratepages = nr_migratepages;
823 cc->nr_freepages = nr_freepages;
826 /* possible outcome of isolate_migratepages */
828 ISOLATE_ABORT, /* Abort compaction now */
829 ISOLATE_NONE, /* No pages isolated, continue scanning */
830 ISOLATE_SUCCESS, /* Pages isolated, migrate */
834 * Isolate all pages that can be migrated from the block pointed to by
835 * the migrate scanner within compact_control.
837 static isolate_migrate_t isolate_migratepages(struct zone *zone,
838 struct compact_control *cc)
840 unsigned long low_pfn, end_pfn;
842 /* Do not scan outside zone boundaries */
843 low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
845 /* Only scan within a pageblock boundary */
846 end_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages);
848 /* Do not cross the free scanner or scan within a memory hole */
849 if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
850 cc->migrate_pfn = end_pfn;
854 /* Perform the isolation */
855 low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn, false);
856 if (!low_pfn || cc->contended)
857 return ISOLATE_ABORT;
859 cc->migrate_pfn = low_pfn;
861 return ISOLATE_SUCCESS;
864 static int compact_finished(struct zone *zone,
865 struct compact_control *cc)
868 unsigned long watermark;
870 if (fatal_signal_pending(current))
871 return COMPACT_PARTIAL;
873 /* Compaction run completes if the migrate and free scanner meet */
874 if (cc->free_pfn <= cc->migrate_pfn) {
875 /* Let the next compaction start anew. */
876 zone->compact_cached_migrate_pfn = zone->zone_start_pfn;
877 zone->compact_cached_free_pfn = zone_end_pfn(zone);
880 * Mark that the PG_migrate_skip information should be cleared
881 * by kswapd when it goes to sleep. kswapd does not set the
882 * flag itself as the decision to be clear should be directly
883 * based on an allocation request.
885 if (!current_is_kswapd())
886 zone->compact_blockskip_flush = true;
888 return COMPACT_COMPLETE;
892 * order == -1 is expected when compacting via
893 * /proc/sys/vm/compact_memory
896 return COMPACT_CONTINUE;
898 /* Compaction run is not finished if the watermark is not met */
899 watermark = low_wmark_pages(zone);
900 watermark += (1 << cc->order);
902 if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
903 return COMPACT_CONTINUE;
905 /* Direct compactor: Is a suitable page free? */
906 for (order = cc->order; order < MAX_ORDER; order++) {
907 struct free_area *area = &zone->free_area[order];
909 /* Job done if page is free of the right migratetype */
910 if (!list_empty(&area->free_list[cc->migratetype]))
911 return COMPACT_PARTIAL;
913 /* Job done if allocation would set block type */
914 if (cc->order >= pageblock_order && area->nr_free)
915 return COMPACT_PARTIAL;
918 return COMPACT_CONTINUE;
922 * compaction_suitable: Is this suitable to run compaction on this zone now?
924 * COMPACT_SKIPPED - If there are too few free pages for compaction
925 * COMPACT_PARTIAL - If the allocation would succeed without compaction
926 * COMPACT_CONTINUE - If compaction should run now
928 unsigned long compaction_suitable(struct zone *zone, int order)
931 unsigned long watermark;
934 * order == -1 is expected when compacting via
935 * /proc/sys/vm/compact_memory
938 return COMPACT_CONTINUE;
941 * Watermarks for order-0 must be met for compaction. Note the 2UL.
942 * This is because during migration, copies of pages need to be
943 * allocated and for a short time, the footprint is higher
945 watermark = low_wmark_pages(zone) + (2UL << order);
946 if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
947 return COMPACT_SKIPPED;
950 * fragmentation index determines if allocation failures are due to
951 * low memory or external fragmentation
953 * index of -1000 implies allocations might succeed depending on
955 * index towards 0 implies failure is due to lack of memory
956 * index towards 1000 implies failure is due to fragmentation
958 * Only compact if a failure would be due to fragmentation.
960 fragindex = fragmentation_index(zone, order);
961 if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
962 return COMPACT_SKIPPED;
964 if (fragindex == -1000 && zone_watermark_ok(zone, order, watermark,
966 return COMPACT_PARTIAL;
968 return COMPACT_CONTINUE;
971 static int compact_zone(struct zone *zone, struct compact_control *cc)
974 unsigned long start_pfn = zone->zone_start_pfn;
975 unsigned long end_pfn = zone_end_pfn(zone);
977 ret = compaction_suitable(zone, cc->order);
979 case COMPACT_PARTIAL:
980 case COMPACT_SKIPPED:
981 /* Compaction is likely to fail */
983 case COMPACT_CONTINUE:
984 /* Fall through to compaction */
989 * Clear pageblock skip if there were failures recently and compaction
990 * is about to be retried after being deferred. kswapd does not do
991 * this reset as it'll reset the cached information when going to sleep.
993 if (compaction_restarting(zone, cc->order) && !current_is_kswapd())
994 __reset_isolation_suitable(zone);
997 * Setup to move all movable pages to the end of the zone. Used cached
998 * information on where the scanners should start but check that it
999 * is initialised by ensuring the values are within zone boundaries.
1001 cc->migrate_pfn = zone->compact_cached_migrate_pfn;
1002 cc->free_pfn = zone->compact_cached_free_pfn;
1003 if (cc->free_pfn < start_pfn || cc->free_pfn > end_pfn) {
1004 cc->free_pfn = end_pfn & ~(pageblock_nr_pages-1);
1005 zone->compact_cached_free_pfn = cc->free_pfn;
1007 if (cc->migrate_pfn < start_pfn || cc->migrate_pfn > end_pfn) {
1008 cc->migrate_pfn = start_pfn;
1009 zone->compact_cached_migrate_pfn = cc->migrate_pfn;
1012 trace_mm_compaction_begin(start_pfn, cc->migrate_pfn, cc->free_pfn, end_pfn);
1014 migrate_prep_local();
1016 while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
1017 unsigned long nr_migrate, nr_remaining;
1020 switch (isolate_migratepages(zone, cc)) {
1022 ret = COMPACT_PARTIAL;
1023 putback_movable_pages(&cc->migratepages);
1024 cc->nr_migratepages = 0;
1028 case ISOLATE_SUCCESS:
1032 nr_migrate = cc->nr_migratepages;
1033 err = migrate_pages(&cc->migratepages, compaction_alloc,
1035 cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC,
1037 update_nr_listpages(cc);
1038 nr_remaining = cc->nr_migratepages;
1040 trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
1043 /* Release isolated pages not migrated */
1045 putback_movable_pages(&cc->migratepages);
1046 cc->nr_migratepages = 0;
1048 * migrate_pages() may return -ENOMEM when scanners meet
1049 * and we want compact_finished() to detect it
1051 if (err == -ENOMEM && cc->free_pfn > cc->migrate_pfn) {
1052 ret = COMPACT_PARTIAL;
1059 /* Release free pages and check accounting */
1060 cc->nr_freepages -= release_freepages(&cc->freepages);
1061 VM_BUG_ON(cc->nr_freepages != 0);
1063 trace_mm_compaction_end(ret);
1068 static unsigned long compact_zone_order(struct zone *zone,
1069 int order, gfp_t gfp_mask,
1070 bool sync, bool *contended)
1073 struct compact_control cc = {
1075 .nr_migratepages = 0,
1077 .migratetype = allocflags_to_migratetype(gfp_mask),
1081 INIT_LIST_HEAD(&cc.freepages);
1082 INIT_LIST_HEAD(&cc.migratepages);
1084 ret = compact_zone(zone, &cc);
1086 VM_BUG_ON(!list_empty(&cc.freepages));
1087 VM_BUG_ON(!list_empty(&cc.migratepages));
1089 *contended = cc.contended;
1093 int sysctl_extfrag_threshold = 500;
1096 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1097 * @zonelist: The zonelist used for the current allocation
1098 * @order: The order of the current allocation
1099 * @gfp_mask: The GFP mask of the current allocation
1100 * @nodemask: The allowed nodes to allocate from
1101 * @sync: Whether migration is synchronous or not
1102 * @contended: Return value that is true if compaction was aborted due to lock contention
1103 * @page: Optionally capture a free page of the requested order during compaction
1105 * This is the main entry point for direct page compaction.
1107 unsigned long try_to_compact_pages(struct zonelist *zonelist,
1108 int order, gfp_t gfp_mask, nodemask_t *nodemask,
1109 bool sync, bool *contended)
1111 enum zone_type high_zoneidx = gfp_zone(gfp_mask);
1112 int may_enter_fs = gfp_mask & __GFP_FS;
1113 int may_perform_io = gfp_mask & __GFP_IO;
1116 int rc = COMPACT_SKIPPED;
1117 int alloc_flags = 0;
1119 /* Check if the GFP flags allow compaction */
1120 if (!order || !may_enter_fs || !may_perform_io)
1123 count_compact_event(COMPACTSTALL);
1126 if (allocflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE)
1127 alloc_flags |= ALLOC_CMA;
1129 /* Compact each zone in the list */
1130 for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
1134 status = compact_zone_order(zone, order, gfp_mask, sync,
1136 rc = max(status, rc);
1138 /* If a normal allocation would succeed, stop compacting */
1139 if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0,
1148 /* Compact all zones within a node */
1149 static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
1154 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1156 zone = &pgdat->node_zones[zoneid];
1157 if (!populated_zone(zone))
1160 cc->nr_freepages = 0;
1161 cc->nr_migratepages = 0;
1163 INIT_LIST_HEAD(&cc->freepages);
1164 INIT_LIST_HEAD(&cc->migratepages);
1166 if (cc->order == -1 || !compaction_deferred(zone, cc->order))
1167 compact_zone(zone, cc);
1169 if (cc->order > 0) {
1170 if (zone_watermark_ok(zone, cc->order,
1171 low_wmark_pages(zone), 0, 0))
1172 compaction_defer_reset(zone, cc->order, false);
1173 /* Currently async compaction is never deferred. */
1175 defer_compaction(zone, cc->order);
1178 VM_BUG_ON(!list_empty(&cc->freepages));
1179 VM_BUG_ON(!list_empty(&cc->migratepages));
1183 void compact_pgdat(pg_data_t *pgdat, int order)
1185 struct compact_control cc = {
1193 __compact_pgdat(pgdat, &cc);
1196 static void compact_node(int nid)
1198 struct compact_control cc = {
1203 __compact_pgdat(NODE_DATA(nid), &cc);
1206 /* Compact all nodes in the system */
1207 static void compact_nodes(void)
1211 /* Flush pending updates to the LRU lists */
1212 lru_add_drain_all();
1214 for_each_online_node(nid)
1218 /* The written value is actually unused, all memory is compacted */
1219 int sysctl_compact_memory;
1221 /* This is the entry point for compacting all nodes via /proc/sys/vm */
1222 int sysctl_compaction_handler(struct ctl_table *table, int write,
1223 void __user *buffer, size_t *length, loff_t *ppos)
1231 int sysctl_extfrag_handler(struct ctl_table *table, int write,
1232 void __user *buffer, size_t *length, loff_t *ppos)
1234 proc_dointvec_minmax(table, write, buffer, length, ppos);
1239 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1240 ssize_t sysfs_compact_node(struct device *dev,
1241 struct device_attribute *attr,
1242 const char *buf, size_t count)
1246 if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
1247 /* Flush pending updates to the LRU lists */
1248 lru_add_drain_all();
1255 static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
1257 int compaction_register_node(struct node *node)
1259 return device_create_file(&node->dev, &dev_attr_compact);
1262 void compaction_unregister_node(struct node *node)
1264 return device_remove_file(&node->dev, &dev_attr_compact);
1266 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
1268 #endif /* CONFIG_COMPACTION */