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[0] = start_pfn;
93 zone->compact_cached_migrate_pfn[1] = start_pfn;
94 zone->compact_cached_free_pfn = end_pfn;
95 zone->compact_blockskip_flush = false;
97 /* Walk the zone and mark every pageblock as suitable for isolation */
98 for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
106 page = pfn_to_page(pfn);
107 if (zone != page_zone(page))
110 clear_pageblock_skip(page);
114 void reset_isolation_suitable(pg_data_t *pgdat)
118 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
119 struct zone *zone = &pgdat->node_zones[zoneid];
120 if (!populated_zone(zone))
123 /* Only flush if a full compaction finished recently */
124 if (zone->compact_blockskip_flush)
125 __reset_isolation_suitable(zone);
130 * If no pages were isolated then mark this pageblock to be skipped in the
131 * future. The information is later cleared by __reset_isolation_suitable().
133 static void update_pageblock_skip(struct compact_control *cc,
134 struct page *page, unsigned long nr_isolated,
135 bool set_unsuitable, bool migrate_scanner)
137 struct zone *zone = cc->zone;
140 if (cc->ignore_skip_hint)
150 * Only skip pageblocks when all forms of compaction will be known to
151 * fail in the near future.
154 set_pageblock_skip(page);
156 pfn = page_to_pfn(page);
158 /* Update where async and sync compaction should restart */
159 if (migrate_scanner) {
160 if (cc->finished_update_migrate)
162 if (pfn > zone->compact_cached_migrate_pfn[0])
163 zone->compact_cached_migrate_pfn[0] = pfn;
164 if (cc->mode != MIGRATE_ASYNC &&
165 pfn > zone->compact_cached_migrate_pfn[1])
166 zone->compact_cached_migrate_pfn[1] = pfn;
168 if (cc->finished_update_free)
170 if (pfn < zone->compact_cached_free_pfn)
171 zone->compact_cached_free_pfn = pfn;
175 static inline bool isolation_suitable(struct compact_control *cc,
181 static void update_pageblock_skip(struct compact_control *cc,
182 struct page *page, unsigned long nr_isolated,
183 bool set_unsuitable, bool migrate_scanner)
186 #endif /* CONFIG_COMPACTION */
188 static inline bool should_release_lock(spinlock_t *lock)
190 return need_resched() || spin_is_contended(lock);
194 * Compaction requires the taking of some coarse locks that are potentially
195 * very heavily contended. Check if the process needs to be scheduled or
196 * if the lock is contended. For async compaction, back out in the event
197 * if contention is severe. For sync compaction, schedule.
199 * Returns true if the lock is held.
200 * Returns false if the lock is released and compaction should abort
202 static bool compact_checklock_irqsave(spinlock_t *lock, unsigned long *flags,
203 bool locked, struct compact_control *cc)
205 if (should_release_lock(lock)) {
207 spin_unlock_irqrestore(lock, *flags);
211 /* async aborts if taking too long or contended */
212 if (cc->mode == MIGRATE_ASYNC) {
213 cc->contended = true;
221 spin_lock_irqsave(lock, *flags);
225 /* Returns true if the page is within a block suitable for migration to */
226 static bool suitable_migration_target(struct page *page)
228 /* If the page is a large free page, then disallow migration */
229 if (PageBuddy(page) && page_order(page) >= pageblock_order)
232 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
233 if (migrate_async_suitable(get_pageblock_migratetype(page)))
236 /* Otherwise skip the block */
241 * Isolate free pages onto a private freelist. If @strict is true, will abort
242 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
243 * (even though it may still end up isolating some pages).
245 static unsigned long isolate_freepages_block(struct compact_control *cc,
246 unsigned long blockpfn,
247 unsigned long end_pfn,
248 struct list_head *freelist,
251 int nr_scanned = 0, total_isolated = 0;
252 struct page *cursor, *valid_page = NULL;
255 bool checked_pageblock = false;
257 cursor = pfn_to_page(blockpfn);
259 /* Isolate free pages. */
260 for (; blockpfn < end_pfn; blockpfn++, cursor++) {
262 struct page *page = cursor;
265 if (!pfn_valid_within(blockpfn))
270 if (!PageBuddy(page))
274 * The zone lock must be held to isolate freepages.
275 * Unfortunately this is a very coarse lock and can be
276 * heavily contended if there are parallel allocations
277 * or parallel compactions. For async compaction do not
278 * spin on the lock and we acquire the lock as late as
281 locked = compact_checklock_irqsave(&cc->zone->lock, &flags,
286 /* Recheck this is a suitable migration target under lock */
287 if (!strict && !checked_pageblock) {
289 * We need to check suitability of pageblock only once
290 * and this isolate_freepages_block() is called with
291 * pageblock range, so just check once is sufficient.
293 checked_pageblock = true;
294 if (!suitable_migration_target(page))
298 /* Recheck this is a buddy page under lock */
299 if (!PageBuddy(page))
302 /* Found a free page, break it into order-0 pages */
303 isolated = split_free_page(page);
304 total_isolated += isolated;
305 for (i = 0; i < isolated; i++) {
306 list_add(&page->lru, freelist);
310 /* If a page was split, advance to the end of it */
312 blockpfn += isolated - 1;
313 cursor += isolated - 1;
325 trace_mm_compaction_isolate_freepages(nr_scanned, total_isolated);
328 * If strict isolation is requested by CMA then check that all the
329 * pages requested were isolated. If there were any failures, 0 is
330 * returned and CMA will fail.
332 if (strict && blockpfn < end_pfn)
336 spin_unlock_irqrestore(&cc->zone->lock, flags);
338 /* Update the pageblock-skip if the whole pageblock was scanned */
339 if (blockpfn == end_pfn)
340 update_pageblock_skip(cc, valid_page, total_isolated, true,
343 count_compact_events(COMPACTFREE_SCANNED, nr_scanned);
345 count_compact_events(COMPACTISOLATED, total_isolated);
346 return total_isolated;
350 * isolate_freepages_range() - isolate free pages.
351 * @start_pfn: The first PFN to start isolating.
352 * @end_pfn: The one-past-last PFN.
354 * Non-free pages, invalid PFNs, or zone boundaries within the
355 * [start_pfn, end_pfn) range are considered errors, cause function to
356 * undo its actions and return zero.
358 * Otherwise, function returns one-past-the-last PFN of isolated page
359 * (which may be greater then end_pfn if end fell in a middle of
363 isolate_freepages_range(struct compact_control *cc,
364 unsigned long start_pfn, unsigned long end_pfn)
366 unsigned long isolated, pfn, block_end_pfn;
369 for (pfn = start_pfn; pfn < end_pfn; pfn += isolated) {
370 if (!pfn_valid(pfn) || cc->zone != page_zone(pfn_to_page(pfn)))
374 * On subsequent iterations ALIGN() is actually not needed,
375 * but we keep it that we not to complicate the code.
377 block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
378 block_end_pfn = min(block_end_pfn, end_pfn);
380 isolated = isolate_freepages_block(cc, pfn, block_end_pfn,
384 * In strict mode, isolate_freepages_block() returns 0 if
385 * there are any holes in the block (ie. invalid PFNs or
392 * If we managed to isolate pages, it is always (1 << n) *
393 * pageblock_nr_pages for some non-negative n. (Max order
394 * page may span two pageblocks).
398 /* split_free_page does not map the pages */
399 map_pages(&freelist);
402 /* Loop terminated early, cleanup. */
403 release_freepages(&freelist);
407 /* We don't use freelists for anything. */
411 /* Update the number of anon and file isolated pages in the zone */
412 static void acct_isolated(struct zone *zone, bool locked, struct compact_control *cc)
415 unsigned int count[2] = { 0, };
417 list_for_each_entry(page, &cc->migratepages, lru)
418 count[!!page_is_file_cache(page)]++;
420 /* If locked we can use the interrupt unsafe versions */
422 __mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
423 __mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
425 mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
426 mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
430 /* Similar to reclaim, but different enough that they don't share logic */
431 static bool too_many_isolated(struct zone *zone)
433 unsigned long active, inactive, isolated;
435 inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
436 zone_page_state(zone, NR_INACTIVE_ANON);
437 active = zone_page_state(zone, NR_ACTIVE_FILE) +
438 zone_page_state(zone, NR_ACTIVE_ANON);
439 isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
440 zone_page_state(zone, NR_ISOLATED_ANON);
442 return isolated > (inactive + active) / 2;
446 * isolate_migratepages_range() - isolate all migrate-able pages in range.
447 * @zone: Zone pages are in.
448 * @cc: Compaction control structure.
449 * @low_pfn: The first PFN of the range.
450 * @end_pfn: The one-past-the-last PFN of the range.
451 * @unevictable: true if it allows to isolate unevictable pages
453 * Isolate all pages that can be migrated from the range specified by
454 * [low_pfn, end_pfn). Returns zero if there is a fatal signal
455 * pending), otherwise PFN of the first page that was not scanned
456 * (which may be both less, equal to or more then end_pfn).
458 * Assumes that cc->migratepages is empty and cc->nr_migratepages is
461 * Apart from cc->migratepages and cc->nr_migratetypes this function
462 * does not modify any cc's fields, in particular it does not modify
463 * (or read for that matter) cc->migrate_pfn.
466 isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
467 unsigned long low_pfn, unsigned long end_pfn, bool unevictable)
469 unsigned long last_pageblock_nr = 0, pageblock_nr;
470 unsigned long nr_scanned = 0, nr_isolated = 0;
471 struct list_head *migratelist = &cc->migratepages;
472 struct lruvec *lruvec;
475 struct page *page = NULL, *valid_page = NULL;
476 bool set_unsuitable = true;
477 const isolate_mode_t mode = (cc->mode == MIGRATE_ASYNC ?
478 ISOLATE_ASYNC_MIGRATE : 0) |
479 (unevictable ? ISOLATE_UNEVICTABLE : 0);
482 * Ensure that there are not too many pages isolated from the LRU
483 * list by either parallel reclaimers or compaction. If there are,
484 * delay for some time until fewer pages are isolated
486 while (unlikely(too_many_isolated(zone))) {
487 /* async migration should just abort */
488 if (cc->mode == MIGRATE_ASYNC)
491 congestion_wait(BLK_RW_ASYNC, HZ/10);
493 if (fatal_signal_pending(current))
497 /* Time to isolate some pages for migration */
499 for (; low_pfn < end_pfn; low_pfn++) {
500 /* give a chance to irqs before checking need_resched() */
501 if (locked && !(low_pfn % SWAP_CLUSTER_MAX)) {
502 if (should_release_lock(&zone->lru_lock)) {
503 spin_unlock_irqrestore(&zone->lru_lock, flags);
509 * migrate_pfn does not necessarily start aligned to a
510 * pageblock. Ensure that pfn_valid is called when moving
511 * into a new MAX_ORDER_NR_PAGES range in case of large
512 * memory holes within the zone
514 if ((low_pfn & (MAX_ORDER_NR_PAGES - 1)) == 0) {
515 if (!pfn_valid(low_pfn)) {
516 low_pfn += MAX_ORDER_NR_PAGES - 1;
521 if (!pfn_valid_within(low_pfn))
526 * Get the page and ensure the page is within the same zone.
527 * See the comment in isolate_freepages about overlapping
528 * nodes. It is deliberate that the new zone lock is not taken
529 * as memory compaction should not move pages between nodes.
531 page = pfn_to_page(low_pfn);
532 if (page_zone(page) != zone)
538 /* If isolation recently failed, do not retry */
539 pageblock_nr = low_pfn >> pageblock_order;
540 if (last_pageblock_nr != pageblock_nr) {
543 last_pageblock_nr = pageblock_nr;
544 if (!isolation_suitable(cc, page))
548 * For async migration, also only scan in MOVABLE
549 * blocks. Async migration is optimistic to see if
550 * the minimum amount of work satisfies the allocation
552 mt = get_pageblock_migratetype(page);
553 if (cc->mode == MIGRATE_ASYNC &&
554 !migrate_async_suitable(mt)) {
555 set_unsuitable = false;
561 * Skip if free. page_order cannot be used without zone->lock
562 * as nothing prevents parallel allocations or buddy merging.
568 * Check may be lockless but that's ok as we recheck later.
569 * It's possible to migrate LRU pages and balloon pages
570 * Skip any other type of page
572 if (!PageLRU(page)) {
573 if (unlikely(balloon_page_movable(page))) {
574 if (locked && balloon_page_isolate(page)) {
575 /* Successfully isolated */
576 goto isolate_success;
583 * PageLRU is set. lru_lock normally excludes isolation
584 * splitting and collapsing (collapsing has already happened
585 * if PageLRU is set) but the lock is not necessarily taken
586 * here and it is wasteful to take it just to check transhuge.
587 * Check TransHuge without lock and skip the whole pageblock if
588 * it's either a transhuge or hugetlbfs page, as calling
589 * compound_order() without preventing THP from splitting the
590 * page underneath us may return surprising results.
592 if (PageTransHuge(page)) {
595 low_pfn += (1 << compound_order(page)) - 1;
600 * Migration will fail if an anonymous page is pinned in memory,
601 * so avoid taking lru_lock and isolating it unnecessarily in an
602 * admittedly racy check.
604 if (!page_mapping(page) &&
605 page_count(page) > page_mapcount(page))
608 /* Check if it is ok to still hold the lock */
609 locked = compact_checklock_irqsave(&zone->lru_lock, &flags,
611 if (!locked || fatal_signal_pending(current))
614 /* Recheck PageLRU and PageTransHuge under lock */
617 if (PageTransHuge(page)) {
618 low_pfn += (1 << compound_order(page)) - 1;
622 lruvec = mem_cgroup_page_lruvec(page, zone);
624 /* Try isolate the page */
625 if (__isolate_lru_page(page, mode) != 0)
628 VM_BUG_ON_PAGE(PageTransCompound(page), page);
630 /* Successfully isolated */
631 del_page_from_lru_list(page, lruvec, page_lru(page));
634 cc->finished_update_migrate = true;
635 list_add(&page->lru, migratelist);
636 cc->nr_migratepages++;
639 /* Avoid isolating too much */
640 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
648 low_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages) - 1;
651 acct_isolated(zone, locked, cc);
654 spin_unlock_irqrestore(&zone->lru_lock, flags);
657 * Update the pageblock-skip information and cached scanner pfn,
658 * if the whole pageblock was scanned without isolating any page.
660 if (low_pfn == end_pfn)
661 update_pageblock_skip(cc, valid_page, nr_isolated,
662 set_unsuitable, true);
664 trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);
666 count_compact_events(COMPACTMIGRATE_SCANNED, nr_scanned);
668 count_compact_events(COMPACTISOLATED, nr_isolated);
673 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
674 #ifdef CONFIG_COMPACTION
676 * Based on information in the current compact_control, find blocks
677 * suitable for isolating free pages from and then isolate them.
679 static void isolate_freepages(struct zone *zone,
680 struct compact_control *cc)
683 unsigned long block_start_pfn; /* start of current pageblock */
684 unsigned long block_end_pfn; /* end of current pageblock */
685 unsigned long low_pfn; /* lowest pfn scanner is able to scan */
686 unsigned long next_free_pfn; /* start pfn for scaning at next round */
687 int nr_freepages = cc->nr_freepages;
688 struct list_head *freelist = &cc->freepages;
691 * Initialise the free scanner. The starting point is where we last
692 * successfully isolated from, zone-cached value, or the end of the
693 * zone when isolating for the first time. We need this aligned to
694 * the pageblock boundary, because we do
695 * block_start_pfn -= pageblock_nr_pages in the for loop.
696 * For ending point, take care when isolating in last pageblock of a
697 * a zone which ends in the middle of a pageblock.
698 * The low boundary is the end of the pageblock the migration scanner
701 block_start_pfn = cc->free_pfn & ~(pageblock_nr_pages-1);
702 block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
704 low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages);
707 * If no pages are isolated, the block_start_pfn < low_pfn check
713 * Isolate free pages until enough are available to migrate the
714 * pages on cc->migratepages. We stop searching if the migrate
715 * and free page scanners meet or enough free pages are isolated.
717 for (; block_start_pfn >= low_pfn && cc->nr_migratepages > nr_freepages;
718 block_end_pfn = block_start_pfn,
719 block_start_pfn -= pageblock_nr_pages) {
720 unsigned long isolated;
723 * This can iterate a massively long zone without finding any
724 * suitable migration targets, so periodically check if we need
729 if (!pfn_valid(block_start_pfn))
733 * Check for overlapping nodes/zones. It's possible on some
734 * configurations to have a setup like
736 * i.e. it's possible that all pages within a zones range of
737 * pages do not belong to a single zone.
739 page = pfn_to_page(block_start_pfn);
740 if (page_zone(page) != zone)
743 /* Check the block is suitable for migration */
744 if (!suitable_migration_target(page))
747 /* If isolation recently failed, do not retry */
748 if (!isolation_suitable(cc, page))
751 /* Found a block suitable for isolating free pages from */
752 isolated = isolate_freepages_block(cc, block_start_pfn,
753 block_end_pfn, freelist, false);
754 nr_freepages += isolated;
757 * Record the highest PFN we isolated pages from. When next
758 * looking for free pages, the search will restart here as
759 * page migration may have returned some pages to the allocator
761 if (isolated && next_free_pfn == 0) {
762 cc->finished_update_free = true;
763 next_free_pfn = block_start_pfn;
767 /* split_free_page does not map the pages */
771 * If we crossed the migrate scanner, we want to keep it that way
772 * so that compact_finished() may detect this
774 if (block_start_pfn < low_pfn)
775 next_free_pfn = cc->migrate_pfn;
777 cc->free_pfn = next_free_pfn;
778 cc->nr_freepages = nr_freepages;
782 * This is a migrate-callback that "allocates" freepages by taking pages
783 * from the isolated freelists in the block we are migrating to.
785 static struct page *compaction_alloc(struct page *migratepage,
789 struct compact_control *cc = (struct compact_control *)data;
790 struct page *freepage;
792 /* Isolate free pages if necessary */
793 if (list_empty(&cc->freepages)) {
794 isolate_freepages(cc->zone, cc);
796 if (list_empty(&cc->freepages))
800 freepage = list_entry(cc->freepages.next, struct page, lru);
801 list_del(&freepage->lru);
808 * This is a migrate-callback that "frees" freepages back to the isolated
809 * freelist. All pages on the freelist are from the same zone, so there is no
810 * special handling needed for NUMA.
812 static void compaction_free(struct page *page, unsigned long data)
814 struct compact_control *cc = (struct compact_control *)data;
816 list_add(&page->lru, &cc->freepages);
821 * We cannot control nr_migratepages fully when migration is running as
822 * migrate_pages() has no knowledge of of compact_control. When migration is
823 * complete, we count the number of pages on the list by hand.
825 static void update_nr_listpages(struct compact_control *cc)
827 int nr_migratepages = 0;
830 list_for_each_entry(page, &cc->migratepages, lru)
833 cc->nr_migratepages = nr_migratepages;
836 /* possible outcome of isolate_migratepages */
838 ISOLATE_ABORT, /* Abort compaction now */
839 ISOLATE_NONE, /* No pages isolated, continue scanning */
840 ISOLATE_SUCCESS, /* Pages isolated, migrate */
844 * Isolate all pages that can be migrated from the block pointed to by
845 * the migrate scanner within compact_control.
847 static isolate_migrate_t isolate_migratepages(struct zone *zone,
848 struct compact_control *cc)
850 unsigned long low_pfn, end_pfn;
852 /* Do not scan outside zone boundaries */
853 low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
855 /* Only scan within a pageblock boundary */
856 end_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages);
858 /* Do not cross the free scanner or scan within a memory hole */
859 if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
860 cc->migrate_pfn = end_pfn;
864 /* Perform the isolation */
865 low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn, false);
866 if (!low_pfn || cc->contended)
867 return ISOLATE_ABORT;
869 cc->migrate_pfn = low_pfn;
871 return ISOLATE_SUCCESS;
874 static int compact_finished(struct zone *zone,
875 struct compact_control *cc)
878 unsigned long watermark;
880 if (fatal_signal_pending(current))
881 return COMPACT_PARTIAL;
883 /* Compaction run completes if the migrate and free scanner meet */
884 if (cc->free_pfn <= cc->migrate_pfn) {
885 /* Let the next compaction start anew. */
886 zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
887 zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
888 zone->compact_cached_free_pfn = zone_end_pfn(zone);
891 * Mark that the PG_migrate_skip information should be cleared
892 * by kswapd when it goes to sleep. kswapd does not set the
893 * flag itself as the decision to be clear should be directly
894 * based on an allocation request.
896 if (!current_is_kswapd())
897 zone->compact_blockskip_flush = true;
899 return COMPACT_COMPLETE;
903 * order == -1 is expected when compacting via
904 * /proc/sys/vm/compact_memory
907 return COMPACT_CONTINUE;
909 /* Compaction run is not finished if the watermark is not met */
910 watermark = low_wmark_pages(zone);
911 watermark += (1 << cc->order);
913 if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
914 return COMPACT_CONTINUE;
916 /* Direct compactor: Is a suitable page free? */
917 for (order = cc->order; order < MAX_ORDER; order++) {
918 struct free_area *area = &zone->free_area[order];
920 /* Job done if page is free of the right migratetype */
921 if (!list_empty(&area->free_list[cc->migratetype]))
922 return COMPACT_PARTIAL;
924 /* Job done if allocation would set block type */
925 if (cc->order >= pageblock_order && area->nr_free)
926 return COMPACT_PARTIAL;
929 return COMPACT_CONTINUE;
933 * compaction_suitable: Is this suitable to run compaction on this zone now?
935 * COMPACT_SKIPPED - If there are too few free pages for compaction
936 * COMPACT_PARTIAL - If the allocation would succeed without compaction
937 * COMPACT_CONTINUE - If compaction should run now
939 unsigned long compaction_suitable(struct zone *zone, int order)
942 unsigned long watermark;
945 * order == -1 is expected when compacting via
946 * /proc/sys/vm/compact_memory
949 return COMPACT_CONTINUE;
952 * Watermarks for order-0 must be met for compaction. Note the 2UL.
953 * This is because during migration, copies of pages need to be
954 * allocated and for a short time, the footprint is higher
956 watermark = low_wmark_pages(zone) + (2UL << order);
957 if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
958 return COMPACT_SKIPPED;
961 * fragmentation index determines if allocation failures are due to
962 * low memory or external fragmentation
964 * index of -1000 implies allocations might succeed depending on
966 * index towards 0 implies failure is due to lack of memory
967 * index towards 1000 implies failure is due to fragmentation
969 * Only compact if a failure would be due to fragmentation.
971 fragindex = fragmentation_index(zone, order);
972 if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
973 return COMPACT_SKIPPED;
975 if (fragindex == -1000 && zone_watermark_ok(zone, order, watermark,
977 return COMPACT_PARTIAL;
979 return COMPACT_CONTINUE;
982 static int compact_zone(struct zone *zone, struct compact_control *cc)
985 unsigned long start_pfn = zone->zone_start_pfn;
986 unsigned long end_pfn = zone_end_pfn(zone);
987 const bool sync = cc->mode != MIGRATE_ASYNC;
989 ret = compaction_suitable(zone, cc->order);
991 case COMPACT_PARTIAL:
992 case COMPACT_SKIPPED:
993 /* Compaction is likely to fail */
995 case COMPACT_CONTINUE:
996 /* Fall through to compaction */
1001 * Clear pageblock skip if there were failures recently and compaction
1002 * is about to be retried after being deferred. kswapd does not do
1003 * this reset as it'll reset the cached information when going to sleep.
1005 if (compaction_restarting(zone, cc->order) && !current_is_kswapd())
1006 __reset_isolation_suitable(zone);
1009 * Setup to move all movable pages to the end of the zone. Used cached
1010 * information on where the scanners should start but check that it
1011 * is initialised by ensuring the values are within zone boundaries.
1013 cc->migrate_pfn = zone->compact_cached_migrate_pfn[sync];
1014 cc->free_pfn = zone->compact_cached_free_pfn;
1015 if (cc->free_pfn < start_pfn || cc->free_pfn > end_pfn) {
1016 cc->free_pfn = end_pfn & ~(pageblock_nr_pages-1);
1017 zone->compact_cached_free_pfn = cc->free_pfn;
1019 if (cc->migrate_pfn < start_pfn || cc->migrate_pfn > end_pfn) {
1020 cc->migrate_pfn = start_pfn;
1021 zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
1022 zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
1025 trace_mm_compaction_begin(start_pfn, cc->migrate_pfn, cc->free_pfn, end_pfn);
1027 migrate_prep_local();
1029 while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
1030 unsigned long nr_migrate, nr_remaining;
1033 switch (isolate_migratepages(zone, cc)) {
1035 ret = COMPACT_PARTIAL;
1036 putback_movable_pages(&cc->migratepages);
1037 cc->nr_migratepages = 0;
1041 case ISOLATE_SUCCESS:
1045 nr_migrate = cc->nr_migratepages;
1046 err = migrate_pages(&cc->migratepages, compaction_alloc,
1047 compaction_free, (unsigned long)cc, cc->mode,
1049 update_nr_listpages(cc);
1050 nr_remaining = cc->nr_migratepages;
1052 trace_mm_compaction_migratepages(nr_migrate - nr_remaining,
1055 /* Release isolated pages not migrated */
1057 putback_movable_pages(&cc->migratepages);
1058 cc->nr_migratepages = 0;
1060 * migrate_pages() may return -ENOMEM when scanners meet
1061 * and we want compact_finished() to detect it
1063 if (err == -ENOMEM && cc->free_pfn > cc->migrate_pfn) {
1064 ret = COMPACT_PARTIAL;
1071 /* Release free pages and check accounting */
1072 cc->nr_freepages -= release_freepages(&cc->freepages);
1073 VM_BUG_ON(cc->nr_freepages != 0);
1075 trace_mm_compaction_end(ret);
1080 static unsigned long compact_zone_order(struct zone *zone, int order,
1081 gfp_t gfp_mask, enum migrate_mode mode, bool *contended)
1084 struct compact_control cc = {
1086 .nr_migratepages = 0,
1088 .migratetype = allocflags_to_migratetype(gfp_mask),
1092 INIT_LIST_HEAD(&cc.freepages);
1093 INIT_LIST_HEAD(&cc.migratepages);
1095 ret = compact_zone(zone, &cc);
1097 VM_BUG_ON(!list_empty(&cc.freepages));
1098 VM_BUG_ON(!list_empty(&cc.migratepages));
1100 *contended = cc.contended;
1104 int sysctl_extfrag_threshold = 500;
1107 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1108 * @zonelist: The zonelist used for the current allocation
1109 * @order: The order of the current allocation
1110 * @gfp_mask: The GFP mask of the current allocation
1111 * @nodemask: The allowed nodes to allocate from
1112 * @mode: The migration mode for async, sync light, or sync migration
1113 * @contended: Return value that is true if compaction was aborted due to lock contention
1114 * @page: Optionally capture a free page of the requested order during compaction
1116 * This is the main entry point for direct page compaction.
1118 unsigned long try_to_compact_pages(struct zonelist *zonelist,
1119 int order, gfp_t gfp_mask, nodemask_t *nodemask,
1120 enum migrate_mode mode, bool *contended)
1122 enum zone_type high_zoneidx = gfp_zone(gfp_mask);
1123 int may_enter_fs = gfp_mask & __GFP_FS;
1124 int may_perform_io = gfp_mask & __GFP_IO;
1127 int rc = COMPACT_SKIPPED;
1128 int alloc_flags = 0;
1130 /* Check if the GFP flags allow compaction */
1131 if (!order || !may_enter_fs || !may_perform_io)
1134 count_compact_event(COMPACTSTALL);
1137 if (allocflags_to_migratetype(gfp_mask) == MIGRATE_MOVABLE)
1138 alloc_flags |= ALLOC_CMA;
1140 /* Compact each zone in the list */
1141 for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
1145 status = compact_zone_order(zone, order, gfp_mask, mode,
1147 rc = max(status, rc);
1149 /* If a normal allocation would succeed, stop compacting */
1150 if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0,
1159 /* Compact all zones within a node */
1160 static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
1165 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1167 zone = &pgdat->node_zones[zoneid];
1168 if (!populated_zone(zone))
1171 cc->nr_freepages = 0;
1172 cc->nr_migratepages = 0;
1174 INIT_LIST_HEAD(&cc->freepages);
1175 INIT_LIST_HEAD(&cc->migratepages);
1177 if (cc->order == -1 || !compaction_deferred(zone, cc->order))
1178 compact_zone(zone, cc);
1180 if (cc->order > 0) {
1181 if (zone_watermark_ok(zone, cc->order,
1182 low_wmark_pages(zone), 0, 0))
1183 compaction_defer_reset(zone, cc->order, false);
1186 VM_BUG_ON(!list_empty(&cc->freepages));
1187 VM_BUG_ON(!list_empty(&cc->migratepages));
1191 void compact_pgdat(pg_data_t *pgdat, int order)
1193 struct compact_control cc = {
1195 .mode = MIGRATE_ASYNC,
1201 __compact_pgdat(pgdat, &cc);
1204 static void compact_node(int nid)
1206 struct compact_control cc = {
1208 .mode = MIGRATE_SYNC,
1209 .ignore_skip_hint = true,
1212 __compact_pgdat(NODE_DATA(nid), &cc);
1215 /* Compact all nodes in the system */
1216 static void compact_nodes(void)
1220 /* Flush pending updates to the LRU lists */
1221 lru_add_drain_all();
1223 for_each_online_node(nid)
1227 /* The written value is actually unused, all memory is compacted */
1228 int sysctl_compact_memory;
1230 /* This is the entry point for compacting all nodes via /proc/sys/vm */
1231 int sysctl_compaction_handler(struct ctl_table *table, int write,
1232 void __user *buffer, size_t *length, loff_t *ppos)
1240 int sysctl_extfrag_handler(struct ctl_table *table, int write,
1241 void __user *buffer, size_t *length, loff_t *ppos)
1243 proc_dointvec_minmax(table, write, buffer, length, ppos);
1248 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1249 static ssize_t sysfs_compact_node(struct device *dev,
1250 struct device_attribute *attr,
1251 const char *buf, size_t count)
1255 if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
1256 /* Flush pending updates to the LRU lists */
1257 lru_add_drain_all();
1264 static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
1266 int compaction_register_node(struct node *node)
1268 return device_create_file(&node->dev, &dev_attr_compact);
1271 void compaction_unregister_node(struct node *node)
1273 return device_remove_file(&node->dev, &dev_attr_compact);
1275 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
1277 #endif /* CONFIG_COMPACTION */