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>
19 #include <linux/kasan.h>
22 #ifdef CONFIG_COMPACTION
23 static inline void count_compact_event(enum vm_event_item item)
28 static inline void count_compact_events(enum vm_event_item item, long delta)
30 count_vm_events(item, delta);
33 #define count_compact_event(item) do { } while (0)
34 #define count_compact_events(item, delta) do { } while (0)
37 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
39 #define CREATE_TRACE_POINTS
40 #include <trace/events/compaction.h>
42 static unsigned long release_freepages(struct list_head *freelist)
44 struct page *page, *next;
45 unsigned long high_pfn = 0;
47 list_for_each_entry_safe(page, next, freelist, lru) {
48 unsigned long pfn = page_to_pfn(page);
58 static void map_pages(struct list_head *list)
62 list_for_each_entry(page, list, lru) {
63 arch_alloc_page(page, 0);
64 kernel_map_pages(page, 1, 1);
65 kasan_alloc_pages(page, 0);
69 static inline bool migrate_async_suitable(int migratetype)
71 return is_migrate_cma(migratetype) || migratetype == MIGRATE_MOVABLE;
75 * Check that the whole (or subset of) a pageblock given by the interval of
76 * [start_pfn, end_pfn) is valid and within the same zone, before scanning it
77 * with the migration of free compaction scanner. The scanners then need to
78 * use only pfn_valid_within() check for arches that allow holes within
81 * Return struct page pointer of start_pfn, or NULL if checks were not passed.
83 * It's possible on some configurations to have a setup like node0 node1 node0
84 * i.e. it's possible that all pages within a zones range of pages do not
85 * belong to a single zone. We assume that a border between node0 and node1
86 * can occur within a single pageblock, but not a node0 node1 node0
87 * interleaving within a single pageblock. It is therefore sufficient to check
88 * the first and last page of a pageblock and avoid checking each individual
89 * page in a pageblock.
91 static struct page *pageblock_pfn_to_page(unsigned long start_pfn,
92 unsigned long end_pfn, struct zone *zone)
94 struct page *start_page;
95 struct page *end_page;
97 /* end_pfn is one past the range we are checking */
100 if (!pfn_valid(start_pfn) || !pfn_valid(end_pfn))
103 start_page = pfn_to_page(start_pfn);
105 if (page_zone(start_page) != zone)
108 end_page = pfn_to_page(end_pfn);
110 /* This gives a shorter code than deriving page_zone(end_page) */
111 if (page_zone_id(start_page) != page_zone_id(end_page))
117 #ifdef CONFIG_COMPACTION
119 /* Do not skip compaction more than 64 times */
120 #define COMPACT_MAX_DEFER_SHIFT 6
123 * Compaction is deferred when compaction fails to result in a page
124 * allocation success. 1 << compact_defer_limit compactions are skipped up
125 * to a limit of 1 << COMPACT_MAX_DEFER_SHIFT
127 void defer_compaction(struct zone *zone, int order)
129 zone->compact_considered = 0;
130 zone->compact_defer_shift++;
132 if (order < zone->compact_order_failed)
133 zone->compact_order_failed = order;
135 if (zone->compact_defer_shift > COMPACT_MAX_DEFER_SHIFT)
136 zone->compact_defer_shift = COMPACT_MAX_DEFER_SHIFT;
138 trace_mm_compaction_defer_compaction(zone, order);
141 /* Returns true if compaction should be skipped this time */
142 bool compaction_deferred(struct zone *zone, int order)
144 unsigned long defer_limit = 1UL << zone->compact_defer_shift;
146 if (order < zone->compact_order_failed)
149 /* Avoid possible overflow */
150 if (++zone->compact_considered > defer_limit)
151 zone->compact_considered = defer_limit;
153 if (zone->compact_considered >= defer_limit)
156 trace_mm_compaction_deferred(zone, order);
162 * Update defer tracking counters after successful compaction of given order,
163 * which means an allocation either succeeded (alloc_success == true) or is
164 * expected to succeed.
166 void compaction_defer_reset(struct zone *zone, int order,
170 zone->compact_considered = 0;
171 zone->compact_defer_shift = 0;
173 if (order >= zone->compact_order_failed)
174 zone->compact_order_failed = order + 1;
176 trace_mm_compaction_defer_reset(zone, order);
179 /* Returns true if restarting compaction after many failures */
180 bool compaction_restarting(struct zone *zone, int order)
182 if (order < zone->compact_order_failed)
185 return zone->compact_defer_shift == COMPACT_MAX_DEFER_SHIFT &&
186 zone->compact_considered >= 1UL << zone->compact_defer_shift;
189 /* Returns true if the pageblock should be scanned for pages to isolate. */
190 static inline bool isolation_suitable(struct compact_control *cc,
193 if (cc->ignore_skip_hint)
196 return !get_pageblock_skip(page);
199 static void reset_cached_positions(struct zone *zone)
201 zone->compact_cached_migrate_pfn[0] = zone->zone_start_pfn;
202 zone->compact_cached_migrate_pfn[1] = zone->zone_start_pfn;
203 zone->compact_cached_free_pfn = zone_end_pfn(zone);
207 * This function is called to clear all cached information on pageblocks that
208 * should be skipped for page isolation when the migrate and free page scanner
211 static void __reset_isolation_suitable(struct zone *zone)
213 unsigned long start_pfn = zone->zone_start_pfn;
214 unsigned long end_pfn = zone_end_pfn(zone);
217 zone->compact_blockskip_flush = false;
219 /* Walk the zone and mark every pageblock as suitable for isolation */
220 for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
228 page = pfn_to_page(pfn);
229 if (zone != page_zone(page))
232 clear_pageblock_skip(page);
235 reset_cached_positions(zone);
238 void reset_isolation_suitable(pg_data_t *pgdat)
242 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
243 struct zone *zone = &pgdat->node_zones[zoneid];
244 if (!populated_zone(zone))
247 /* Only flush if a full compaction finished recently */
248 if (zone->compact_blockskip_flush)
249 __reset_isolation_suitable(zone);
254 * If no pages were isolated then mark this pageblock to be skipped in the
255 * future. The information is later cleared by __reset_isolation_suitable().
257 static void update_pageblock_skip(struct compact_control *cc,
258 struct page *page, unsigned long nr_isolated,
259 bool migrate_scanner)
261 struct zone *zone = cc->zone;
264 if (cc->ignore_skip_hint)
273 set_pageblock_skip(page);
275 pfn = page_to_pfn(page);
277 /* Update where async and sync compaction should restart */
278 if (migrate_scanner) {
279 if (pfn > zone->compact_cached_migrate_pfn[0])
280 zone->compact_cached_migrate_pfn[0] = pfn;
281 if (cc->mode != MIGRATE_ASYNC &&
282 pfn > zone->compact_cached_migrate_pfn[1])
283 zone->compact_cached_migrate_pfn[1] = pfn;
285 if (pfn < zone->compact_cached_free_pfn)
286 zone->compact_cached_free_pfn = pfn;
290 static inline bool isolation_suitable(struct compact_control *cc,
296 static void update_pageblock_skip(struct compact_control *cc,
297 struct page *page, unsigned long nr_isolated,
298 bool migrate_scanner)
301 #endif /* CONFIG_COMPACTION */
304 * Compaction requires the taking of some coarse locks that are potentially
305 * very heavily contended. For async compaction, back out if the lock cannot
306 * be taken immediately. For sync compaction, spin on the lock if needed.
308 * Returns true if the lock is held
309 * Returns false if the lock is not held and compaction should abort
311 static bool compact_trylock_irqsave(spinlock_t *lock, unsigned long *flags,
312 struct compact_control *cc)
314 if (cc->mode == MIGRATE_ASYNC) {
315 if (!spin_trylock_irqsave(lock, *flags)) {
316 cc->contended = COMPACT_CONTENDED_LOCK;
320 spin_lock_irqsave(lock, *flags);
327 * Compaction requires the taking of some coarse locks that are potentially
328 * very heavily contended. The lock should be periodically unlocked to avoid
329 * having disabled IRQs for a long time, even when there is nobody waiting on
330 * the lock. It might also be that allowing the IRQs will result in
331 * need_resched() becoming true. If scheduling is needed, async compaction
332 * aborts. Sync compaction schedules.
333 * Either compaction type will also abort if a fatal signal is pending.
334 * In either case if the lock was locked, it is dropped and not regained.
336 * Returns true if compaction should abort due to fatal signal pending, or
337 * async compaction due to need_resched()
338 * Returns false when compaction can continue (sync compaction might have
341 static bool compact_unlock_should_abort(spinlock_t *lock,
342 unsigned long flags, bool *locked, struct compact_control *cc)
345 spin_unlock_irqrestore(lock, flags);
349 if (fatal_signal_pending(current)) {
350 cc->contended = COMPACT_CONTENDED_SCHED;
354 if (need_resched()) {
355 if (cc->mode == MIGRATE_ASYNC) {
356 cc->contended = COMPACT_CONTENDED_SCHED;
366 * Aside from avoiding lock contention, compaction also periodically checks
367 * need_resched() and either schedules in sync compaction or aborts async
368 * compaction. This is similar to what compact_unlock_should_abort() does, but
369 * is used where no lock is concerned.
371 * Returns false when no scheduling was needed, or sync compaction scheduled.
372 * Returns true when async compaction should abort.
374 static inline bool compact_should_abort(struct compact_control *cc)
376 /* async compaction aborts if contended */
377 if (need_resched()) {
378 if (cc->mode == MIGRATE_ASYNC) {
379 cc->contended = COMPACT_CONTENDED_SCHED;
390 * Isolate free pages onto a private freelist. If @strict is true, will abort
391 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
392 * (even though it may still end up isolating some pages).
394 static unsigned long isolate_freepages_block(struct compact_control *cc,
395 unsigned long *start_pfn,
396 unsigned long end_pfn,
397 struct list_head *freelist,
400 int nr_scanned = 0, total_isolated = 0;
401 struct page *cursor, *valid_page = NULL;
402 unsigned long flags = 0;
404 unsigned long blockpfn = *start_pfn;
406 cursor = pfn_to_page(blockpfn);
408 /* Isolate free pages. */
409 for (; blockpfn < end_pfn; blockpfn++, cursor++) {
411 struct page *page = cursor;
414 * Periodically drop the lock (if held) regardless of its
415 * contention, to give chance to IRQs. Abort if fatal signal
416 * pending or async compaction detects need_resched()
418 if (!(blockpfn % SWAP_CLUSTER_MAX)
419 && compact_unlock_should_abort(&cc->zone->lock, flags,
424 if (!pfn_valid_within(blockpfn))
431 * For compound pages such as THP and hugetlbfs, we can save
432 * potentially a lot of iterations if we skip them at once.
433 * The check is racy, but we can consider only valid values
434 * and the only danger is skipping too much.
436 if (PageCompound(page)) {
437 unsigned int comp_order = compound_order(page);
439 if (likely(comp_order < MAX_ORDER)) {
440 blockpfn += (1UL << comp_order) - 1;
441 cursor += (1UL << comp_order) - 1;
447 if (!PageBuddy(page))
451 * If we already hold the lock, we can skip some rechecking.
452 * Note that if we hold the lock now, checked_pageblock was
453 * already set in some previous iteration (or strict is true),
454 * so it is correct to skip the suitable migration target
459 * The zone lock must be held to isolate freepages.
460 * Unfortunately this is a very coarse lock and can be
461 * heavily contended if there are parallel allocations
462 * or parallel compactions. For async compaction do not
463 * spin on the lock and we acquire the lock as late as
466 locked = compact_trylock_irqsave(&cc->zone->lock,
471 /* Recheck this is a buddy page under lock */
472 if (!PageBuddy(page))
476 /* Found a free page, break it into order-0 pages */
477 isolated = split_free_page(page);
478 total_isolated += isolated;
479 for (i = 0; i < isolated; i++) {
480 list_add(&page->lru, freelist);
484 /* If a page was split, advance to the end of it */
486 cc->nr_freepages += isolated;
488 cc->nr_migratepages <= cc->nr_freepages) {
489 blockpfn += isolated;
493 blockpfn += isolated - 1;
494 cursor += isolated - 1;
507 * There is a tiny chance that we have read bogus compound_order(),
508 * so be careful to not go outside of the pageblock.
510 if (unlikely(blockpfn > end_pfn))
513 trace_mm_compaction_isolate_freepages(*start_pfn, blockpfn,
514 nr_scanned, total_isolated);
516 /* Record how far we have got within the block */
517 *start_pfn = blockpfn;
520 * If strict isolation is requested by CMA then check that all the
521 * pages requested were isolated. If there were any failures, 0 is
522 * returned and CMA will fail.
524 if (strict && blockpfn < end_pfn)
528 spin_unlock_irqrestore(&cc->zone->lock, flags);
530 /* Update the pageblock-skip if the whole pageblock was scanned */
531 if (blockpfn == end_pfn)
532 update_pageblock_skip(cc, valid_page, total_isolated, false);
534 count_compact_events(COMPACTFREE_SCANNED, nr_scanned);
536 count_compact_events(COMPACTISOLATED, total_isolated);
537 return total_isolated;
541 * isolate_freepages_range() - isolate free pages.
542 * @start_pfn: The first PFN to start isolating.
543 * @end_pfn: The one-past-last PFN.
545 * Non-free pages, invalid PFNs, or zone boundaries within the
546 * [start_pfn, end_pfn) range are considered errors, cause function to
547 * undo its actions and return zero.
549 * Otherwise, function returns one-past-the-last PFN of isolated page
550 * (which may be greater then end_pfn if end fell in a middle of
554 isolate_freepages_range(struct compact_control *cc,
555 unsigned long start_pfn, unsigned long end_pfn)
557 unsigned long isolated, pfn, block_end_pfn;
561 block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
563 for (; pfn < end_pfn; pfn += isolated,
564 block_end_pfn += pageblock_nr_pages) {
565 /* Protect pfn from changing by isolate_freepages_block */
566 unsigned long isolate_start_pfn = pfn;
568 block_end_pfn = min(block_end_pfn, end_pfn);
571 * pfn could pass the block_end_pfn if isolated freepage
572 * is more than pageblock order. In this case, we adjust
573 * scanning range to right one.
575 if (pfn >= block_end_pfn) {
576 block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
577 block_end_pfn = min(block_end_pfn, end_pfn);
580 if (!pageblock_pfn_to_page(pfn, block_end_pfn, cc->zone))
583 isolated = isolate_freepages_block(cc, &isolate_start_pfn,
584 block_end_pfn, &freelist, true);
587 * In strict mode, isolate_freepages_block() returns 0 if
588 * there are any holes in the block (ie. invalid PFNs or
595 * If we managed to isolate pages, it is always (1 << n) *
596 * pageblock_nr_pages for some non-negative n. (Max order
597 * page may span two pageblocks).
601 /* split_free_page does not map the pages */
602 map_pages(&freelist);
605 /* Loop terminated early, cleanup. */
606 release_freepages(&freelist);
610 /* We don't use freelists for anything. */
614 /* Update the number of anon and file isolated pages in the zone */
615 static void acct_isolated(struct zone *zone, struct compact_control *cc)
618 unsigned int count[2] = { 0, };
620 if (list_empty(&cc->migratepages))
623 list_for_each_entry(page, &cc->migratepages, lru)
624 count[!!page_is_file_cache(page)]++;
626 mod_zone_page_state(zone, NR_ISOLATED_ANON, count[0]);
627 mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
630 /* Similar to reclaim, but different enough that they don't share logic */
631 static bool too_many_isolated(struct zone *zone)
633 unsigned long active, inactive, isolated;
635 inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
636 zone_page_state(zone, NR_INACTIVE_ANON);
637 active = zone_page_state(zone, NR_ACTIVE_FILE) +
638 zone_page_state(zone, NR_ACTIVE_ANON);
639 isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
640 zone_page_state(zone, NR_ISOLATED_ANON);
642 return isolated > (inactive + active) / 2;
646 * isolate_migratepages_block() - isolate all migrate-able pages within
648 * @cc: Compaction control structure.
649 * @low_pfn: The first PFN to isolate
650 * @end_pfn: The one-past-the-last PFN to isolate, within same pageblock
651 * @isolate_mode: Isolation mode to be used.
653 * Isolate all pages that can be migrated from the range specified by
654 * [low_pfn, end_pfn). The range is expected to be within same pageblock.
655 * Returns zero if there is a fatal signal pending, otherwise PFN of the
656 * first page that was not scanned (which may be both less, equal to or more
659 * The pages are isolated on cc->migratepages list (not required to be empty),
660 * and cc->nr_migratepages is updated accordingly. The cc->migrate_pfn field
661 * is neither read nor updated.
664 isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
665 unsigned long end_pfn, isolate_mode_t isolate_mode)
667 struct zone *zone = cc->zone;
668 unsigned long nr_scanned = 0, nr_isolated = 0;
669 struct list_head *migratelist = &cc->migratepages;
670 struct lruvec *lruvec;
671 unsigned long flags = 0;
673 struct page *page = NULL, *valid_page = NULL;
674 unsigned long start_pfn = low_pfn;
677 * Ensure that there are not too many pages isolated from the LRU
678 * list by either parallel reclaimers or compaction. If there are,
679 * delay for some time until fewer pages are isolated
681 while (unlikely(too_many_isolated(zone))) {
682 /* async migration should just abort */
683 if (cc->mode == MIGRATE_ASYNC)
686 congestion_wait(BLK_RW_ASYNC, HZ/10);
688 if (fatal_signal_pending(current))
692 if (compact_should_abort(cc))
695 /* Time to isolate some pages for migration */
696 for (; low_pfn < end_pfn; low_pfn++) {
700 * Periodically drop the lock (if held) regardless of its
701 * contention, to give chance to IRQs. Abort async compaction
704 if (!(low_pfn % SWAP_CLUSTER_MAX)
705 && compact_unlock_should_abort(&zone->lru_lock, flags,
709 if (!pfn_valid_within(low_pfn))
713 page = pfn_to_page(low_pfn);
719 * Skip if free. We read page order here without zone lock
720 * which is generally unsafe, but the race window is small and
721 * the worst thing that can happen is that we skip some
722 * potential isolation targets.
724 if (PageBuddy(page)) {
725 unsigned long freepage_order = page_order_unsafe(page);
728 * Without lock, we cannot be sure that what we got is
729 * a valid page order. Consider only values in the
730 * valid order range to prevent low_pfn overflow.
732 if (freepage_order > 0 && freepage_order < MAX_ORDER)
733 low_pfn += (1UL << freepage_order) - 1;
738 * Check may be lockless but that's ok as we recheck later.
739 * It's possible to migrate LRU pages and balloon pages
740 * Skip any other type of page
742 is_lru = PageLRU(page);
744 if (unlikely(balloon_page_movable(page))) {
745 if (balloon_page_isolate(page)) {
746 /* Successfully isolated */
747 goto isolate_success;
753 * Regardless of being on LRU, compound pages such as THP and
754 * hugetlbfs are not to be compacted. We can potentially save
755 * a lot of iterations if we skip them at once. The check is
756 * racy, but we can consider only valid values and the only
757 * danger is skipping too much.
759 if (PageCompound(page)) {
760 unsigned int comp_order = compound_order(page);
762 if (likely(comp_order < MAX_ORDER))
763 low_pfn += (1UL << comp_order) - 1;
772 * Migration will fail if an anonymous page is pinned in memory,
773 * so avoid taking lru_lock and isolating it unnecessarily in an
774 * admittedly racy check.
776 if (!page_mapping(page) &&
777 page_count(page) > page_mapcount(page))
780 /* If we already hold the lock, we can skip some rechecking */
782 locked = compact_trylock_irqsave(&zone->lru_lock,
787 /* Recheck PageLRU and PageCompound under lock */
792 * Page become compound since the non-locked check,
793 * and it's on LRU. It can only be a THP so the order
794 * is safe to read and it's 0 for tail pages.
796 if (unlikely(PageCompound(page))) {
797 low_pfn += (1UL << compound_order(page)) - 1;
802 lruvec = mem_cgroup_page_lruvec(page, zone);
804 /* Try isolate the page */
805 if (__isolate_lru_page(page, isolate_mode) != 0)
808 VM_BUG_ON_PAGE(PageCompound(page), page);
810 /* Successfully isolated */
811 del_page_from_lru_list(page, lruvec, page_lru(page));
814 list_add(&page->lru, migratelist);
815 cc->nr_migratepages++;
818 /* Avoid isolating too much */
819 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX) {
826 * The PageBuddy() check could have potentially brought us outside
827 * the range to be scanned.
829 if (unlikely(low_pfn > end_pfn))
833 spin_unlock_irqrestore(&zone->lru_lock, flags);
836 * Update the pageblock-skip information and cached scanner pfn,
837 * if the whole pageblock was scanned without isolating any page.
839 if (low_pfn == end_pfn)
840 update_pageblock_skip(cc, valid_page, nr_isolated, true);
842 trace_mm_compaction_isolate_migratepages(start_pfn, low_pfn,
843 nr_scanned, nr_isolated);
845 count_compact_events(COMPACTMIGRATE_SCANNED, nr_scanned);
847 count_compact_events(COMPACTISOLATED, nr_isolated);
853 * isolate_migratepages_range() - isolate migrate-able pages in a PFN range
854 * @cc: Compaction control structure.
855 * @start_pfn: The first PFN to start isolating.
856 * @end_pfn: The one-past-last PFN.
858 * Returns zero if isolation fails fatally due to e.g. pending signal.
859 * Otherwise, function returns one-past-the-last PFN of isolated page
860 * (which may be greater than end_pfn if end fell in a middle of a THP page).
863 isolate_migratepages_range(struct compact_control *cc, unsigned long start_pfn,
864 unsigned long end_pfn)
866 unsigned long pfn, block_end_pfn;
868 /* Scan block by block. First and last block may be incomplete */
870 block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages);
872 for (; pfn < end_pfn; pfn = block_end_pfn,
873 block_end_pfn += pageblock_nr_pages) {
875 block_end_pfn = min(block_end_pfn, end_pfn);
877 if (!pageblock_pfn_to_page(pfn, block_end_pfn, cc->zone))
880 pfn = isolate_migratepages_block(cc, pfn, block_end_pfn,
881 ISOLATE_UNEVICTABLE);
886 if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
889 acct_isolated(cc->zone, cc);
894 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
895 #ifdef CONFIG_COMPACTION
897 /* Returns true if the page is within a block suitable for migration to */
898 static bool suitable_migration_target(struct page *page)
900 /* If the page is a large free page, then disallow migration */
901 if (PageBuddy(page)) {
903 * We are checking page_order without zone->lock taken. But
904 * the only small danger is that we skip a potentially suitable
905 * pageblock, so it's not worth to check order for valid range.
907 if (page_order_unsafe(page) >= pageblock_order)
911 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
912 if (migrate_async_suitable(get_pageblock_migratetype(page)))
915 /* Otherwise skip the block */
920 * Test whether the free scanner has reached the same or lower pageblock than
921 * the migration scanner, and compaction should thus terminate.
923 static inline bool compact_scanners_met(struct compact_control *cc)
925 return (cc->free_pfn >> pageblock_order)
926 <= (cc->migrate_pfn >> pageblock_order);
930 * Based on information in the current compact_control, find blocks
931 * suitable for isolating free pages from and then isolate them.
933 static void isolate_freepages(struct compact_control *cc)
935 struct zone *zone = cc->zone;
937 unsigned long block_start_pfn; /* start of current pageblock */
938 unsigned long isolate_start_pfn; /* exact pfn we start at */
939 unsigned long block_end_pfn; /* end of current pageblock */
940 unsigned long low_pfn; /* lowest pfn scanner is able to scan */
941 struct list_head *freelist = &cc->freepages;
944 * Initialise the free scanner. The starting point is where we last
945 * successfully isolated from, zone-cached value, or the end of the
946 * zone when isolating for the first time. For looping we also need
947 * this pfn aligned down to the pageblock boundary, because we do
948 * block_start_pfn -= pageblock_nr_pages in the for loop.
949 * For ending point, take care when isolating in last pageblock of a
950 * a zone which ends in the middle of a pageblock.
951 * The low boundary is the end of the pageblock the migration scanner
954 isolate_start_pfn = cc->free_pfn;
955 block_start_pfn = cc->free_pfn & ~(pageblock_nr_pages-1);
956 block_end_pfn = min(block_start_pfn + pageblock_nr_pages,
958 low_pfn = ALIGN(cc->migrate_pfn + 1, pageblock_nr_pages);
961 * Isolate free pages until enough are available to migrate the
962 * pages on cc->migratepages. We stop searching if the migrate
963 * and free page scanners meet or enough free pages are isolated.
965 for (; block_start_pfn >= low_pfn;
966 block_end_pfn = block_start_pfn,
967 block_start_pfn -= pageblock_nr_pages,
968 isolate_start_pfn = block_start_pfn) {
971 * This can iterate a massively long zone without finding any
972 * suitable migration targets, so periodically check if we need
973 * to schedule, or even abort async compaction.
975 if (!(block_start_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
976 && compact_should_abort(cc))
979 page = pageblock_pfn_to_page(block_start_pfn, block_end_pfn,
984 /* Check the block is suitable for migration */
985 if (!suitable_migration_target(page))
988 /* If isolation recently failed, do not retry */
989 if (!isolation_suitable(cc, page))
992 /* Found a block suitable for isolating free pages from. */
993 isolate_freepages_block(cc, &isolate_start_pfn,
994 block_end_pfn, freelist, false);
997 * If we isolated enough freepages, or aborted due to async
998 * compaction being contended, terminate the loop.
999 * Remember where the free scanner should restart next time,
1000 * which is where isolate_freepages_block() left off.
1001 * But if it scanned the whole pageblock, isolate_start_pfn
1002 * now points at block_end_pfn, which is the start of the next
1004 * In that case we will however want to restart at the start
1005 * of the previous pageblock.
1007 if ((cc->nr_freepages >= cc->nr_migratepages)
1009 if (isolate_start_pfn >= block_end_pfn)
1011 block_start_pfn - pageblock_nr_pages;
1015 * isolate_freepages_block() should not terminate
1016 * prematurely unless contended, or isolated enough
1018 VM_BUG_ON(isolate_start_pfn < block_end_pfn);
1022 /* split_free_page does not map the pages */
1023 map_pages(freelist);
1026 * Record where the free scanner will restart next time. Either we
1027 * broke from the loop and set isolate_start_pfn based on the last
1028 * call to isolate_freepages_block(), or we met the migration scanner
1029 * and the loop terminated due to isolate_start_pfn < low_pfn
1031 cc->free_pfn = isolate_start_pfn;
1035 * This is a migrate-callback that "allocates" freepages by taking pages
1036 * from the isolated freelists in the block we are migrating to.
1038 static struct page *compaction_alloc(struct page *migratepage,
1042 struct compact_control *cc = (struct compact_control *)data;
1043 struct page *freepage;
1046 * Isolate free pages if necessary, and if we are not aborting due to
1049 if (list_empty(&cc->freepages)) {
1051 isolate_freepages(cc);
1053 if (list_empty(&cc->freepages))
1057 freepage = list_entry(cc->freepages.next, struct page, lru);
1058 list_del(&freepage->lru);
1065 * This is a migrate-callback that "frees" freepages back to the isolated
1066 * freelist. All pages on the freelist are from the same zone, so there is no
1067 * special handling needed for NUMA.
1069 static void compaction_free(struct page *page, unsigned long data)
1071 struct compact_control *cc = (struct compact_control *)data;
1073 list_add(&page->lru, &cc->freepages);
1077 /* possible outcome of isolate_migratepages */
1079 ISOLATE_ABORT, /* Abort compaction now */
1080 ISOLATE_NONE, /* No pages isolated, continue scanning */
1081 ISOLATE_SUCCESS, /* Pages isolated, migrate */
1082 } isolate_migrate_t;
1085 * Allow userspace to control policy on scanning the unevictable LRU for
1086 * compactable pages.
1088 int sysctl_compact_unevictable_allowed __read_mostly = 1;
1091 * Isolate all pages that can be migrated from the first suitable block,
1092 * starting at the block pointed to by the migrate scanner pfn within
1095 static isolate_migrate_t isolate_migratepages(struct zone *zone,
1096 struct compact_control *cc)
1098 unsigned long low_pfn, end_pfn;
1099 unsigned long isolate_start_pfn;
1101 const isolate_mode_t isolate_mode =
1102 (sysctl_compact_unevictable_allowed ? ISOLATE_UNEVICTABLE : 0) |
1103 (cc->mode == MIGRATE_ASYNC ? ISOLATE_ASYNC_MIGRATE : 0);
1106 * Start at where we last stopped, or beginning of the zone as
1107 * initialized by compact_zone()
1109 low_pfn = cc->migrate_pfn;
1111 /* Only scan within a pageblock boundary */
1112 end_pfn = ALIGN(low_pfn + 1, pageblock_nr_pages);
1115 * Iterate over whole pageblocks until we find the first suitable.
1116 * Do not cross the free scanner.
1118 for (; end_pfn <= cc->free_pfn;
1119 low_pfn = end_pfn, end_pfn += pageblock_nr_pages) {
1122 * This can potentially iterate a massively long zone with
1123 * many pageblocks unsuitable, so periodically check if we
1124 * need to schedule, or even abort async compaction.
1126 if (!(low_pfn % (SWAP_CLUSTER_MAX * pageblock_nr_pages))
1127 && compact_should_abort(cc))
1130 page = pageblock_pfn_to_page(low_pfn, end_pfn, zone);
1134 /* If isolation recently failed, do not retry */
1135 if (!isolation_suitable(cc, page))
1139 * For async compaction, also only scan in MOVABLE blocks.
1140 * Async compaction is optimistic to see if the minimum amount
1141 * of work satisfies the allocation.
1143 if (cc->mode == MIGRATE_ASYNC &&
1144 !migrate_async_suitable(get_pageblock_migratetype(page)))
1147 /* Perform the isolation */
1148 isolate_start_pfn = low_pfn;
1149 low_pfn = isolate_migratepages_block(cc, low_pfn, end_pfn,
1152 if (!low_pfn || cc->contended) {
1153 acct_isolated(zone, cc);
1154 return ISOLATE_ABORT;
1158 * Record where we could have freed pages by migration and not
1159 * yet flushed them to buddy allocator.
1160 * - this is the lowest page that could have been isolated and
1161 * then freed by migration.
1163 if (cc->nr_migratepages && !cc->last_migrated_pfn)
1164 cc->last_migrated_pfn = isolate_start_pfn;
1167 * Either we isolated something and proceed with migration. Or
1168 * we failed and compact_zone should decide if we should
1174 acct_isolated(zone, cc);
1175 /* Record where migration scanner will be restarted. */
1176 cc->migrate_pfn = low_pfn;
1178 return cc->nr_migratepages ? ISOLATE_SUCCESS : ISOLATE_NONE;
1182 * order == -1 is expected when compacting via
1183 * /proc/sys/vm/compact_memory
1185 static inline bool is_via_compact_memory(int order)
1190 static int __compact_finished(struct zone *zone, struct compact_control *cc,
1191 const int migratetype)
1194 unsigned long watermark;
1196 if (cc->contended || fatal_signal_pending(current))
1197 return COMPACT_CONTENDED;
1199 /* Compaction run completes if the migrate and free scanner meet */
1200 if (compact_scanners_met(cc)) {
1201 /* Let the next compaction start anew. */
1202 reset_cached_positions(zone);
1205 * Mark that the PG_migrate_skip information should be cleared
1206 * by kswapd when it goes to sleep. kswapd does not set the
1207 * flag itself as the decision to be clear should be directly
1208 * based on an allocation request.
1210 if (!current_is_kswapd())
1211 zone->compact_blockskip_flush = true;
1213 return COMPACT_COMPLETE;
1216 if (is_via_compact_memory(cc->order))
1217 return COMPACT_CONTINUE;
1219 /* Compaction run is not finished if the watermark is not met */
1220 watermark = low_wmark_pages(zone);
1222 if (!zone_watermark_ok(zone, cc->order, watermark, cc->classzone_idx,
1224 return COMPACT_CONTINUE;
1226 /* Direct compactor: Is a suitable page free? */
1227 for (order = cc->order; order < MAX_ORDER; order++) {
1228 struct free_area *area = &zone->free_area[order];
1231 /* Job done if page is free of the right migratetype */
1232 if (!list_empty(&area->free_list[migratetype]))
1233 return COMPACT_PARTIAL;
1236 /* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
1237 if (migratetype == MIGRATE_MOVABLE &&
1238 !list_empty(&area->free_list[MIGRATE_CMA]))
1239 return COMPACT_PARTIAL;
1242 * Job done if allocation would steal freepages from
1243 * other migratetype buddy lists.
1245 if (find_suitable_fallback(area, order, migratetype,
1246 true, &can_steal) != -1)
1247 return COMPACT_PARTIAL;
1250 return COMPACT_NO_SUITABLE_PAGE;
1253 static int compact_finished(struct zone *zone, struct compact_control *cc,
1254 const int migratetype)
1258 ret = __compact_finished(zone, cc, migratetype);
1259 trace_mm_compaction_finished(zone, cc->order, ret);
1260 if (ret == COMPACT_NO_SUITABLE_PAGE)
1261 ret = COMPACT_CONTINUE;
1267 * compaction_suitable: Is this suitable to run compaction on this zone now?
1269 * COMPACT_SKIPPED - If there are too few free pages for compaction
1270 * COMPACT_PARTIAL - If the allocation would succeed without compaction
1271 * COMPACT_CONTINUE - If compaction should run now
1273 static unsigned long __compaction_suitable(struct zone *zone, int order,
1274 int alloc_flags, int classzone_idx)
1277 unsigned long watermark;
1279 if (is_via_compact_memory(order))
1280 return COMPACT_CONTINUE;
1282 watermark = low_wmark_pages(zone);
1284 * If watermarks for high-order allocation are already met, there
1285 * should be no need for compaction at all.
1287 if (zone_watermark_ok(zone, order, watermark, classzone_idx,
1289 return COMPACT_PARTIAL;
1292 * Watermarks for order-0 must be met for compaction. Note the 2UL.
1293 * This is because during migration, copies of pages need to be
1294 * allocated and for a short time, the footprint is higher
1296 watermark += (2UL << order);
1297 if (!zone_watermark_ok(zone, 0, watermark, classzone_idx, alloc_flags))
1298 return COMPACT_SKIPPED;
1301 * fragmentation index determines if allocation failures are due to
1302 * low memory or external fragmentation
1304 * index of -1000 would imply allocations might succeed depending on
1305 * watermarks, but we already failed the high-order watermark check
1306 * index towards 0 implies failure is due to lack of memory
1307 * index towards 1000 implies failure is due to fragmentation
1309 * Only compact if a failure would be due to fragmentation.
1311 fragindex = fragmentation_index(zone, order);
1312 if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
1313 return COMPACT_NOT_SUITABLE_ZONE;
1315 return COMPACT_CONTINUE;
1318 unsigned long compaction_suitable(struct zone *zone, int order,
1319 int alloc_flags, int classzone_idx)
1323 ret = __compaction_suitable(zone, order, alloc_flags, classzone_idx);
1324 trace_mm_compaction_suitable(zone, order, ret);
1325 if (ret == COMPACT_NOT_SUITABLE_ZONE)
1326 ret = COMPACT_SKIPPED;
1331 static int compact_zone(struct zone *zone, struct compact_control *cc)
1334 unsigned long start_pfn = zone->zone_start_pfn;
1335 unsigned long end_pfn = zone_end_pfn(zone);
1336 const int migratetype = gfpflags_to_migratetype(cc->gfp_mask);
1337 const bool sync = cc->mode != MIGRATE_ASYNC;
1339 ret = compaction_suitable(zone, cc->order, cc->alloc_flags,
1342 case COMPACT_PARTIAL:
1343 case COMPACT_SKIPPED:
1344 /* Compaction is likely to fail */
1346 case COMPACT_CONTINUE:
1347 /* Fall through to compaction */
1352 * Clear pageblock skip if there were failures recently and compaction
1353 * is about to be retried after being deferred. kswapd does not do
1354 * this reset as it'll reset the cached information when going to sleep.
1356 if (compaction_restarting(zone, cc->order) && !current_is_kswapd())
1357 __reset_isolation_suitable(zone);
1360 * Setup to move all movable pages to the end of the zone. Used cached
1361 * information on where the scanners should start but check that it
1362 * is initialised by ensuring the values are within zone boundaries.
1364 cc->migrate_pfn = zone->compact_cached_migrate_pfn[sync];
1365 cc->free_pfn = zone->compact_cached_free_pfn;
1366 if (cc->free_pfn < start_pfn || cc->free_pfn > end_pfn) {
1367 cc->free_pfn = end_pfn & ~(pageblock_nr_pages-1);
1368 zone->compact_cached_free_pfn = cc->free_pfn;
1370 if (cc->migrate_pfn < start_pfn || cc->migrate_pfn > end_pfn) {
1371 cc->migrate_pfn = start_pfn;
1372 zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
1373 zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
1375 cc->last_migrated_pfn = 0;
1377 trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
1378 cc->free_pfn, end_pfn, sync);
1380 migrate_prep_local();
1382 while ((ret = compact_finished(zone, cc, migratetype)) ==
1386 switch (isolate_migratepages(zone, cc)) {
1388 ret = COMPACT_CONTENDED;
1389 putback_movable_pages(&cc->migratepages);
1390 cc->nr_migratepages = 0;
1394 * We haven't isolated and migrated anything, but
1395 * there might still be unflushed migrations from
1396 * previous cc->order aligned block.
1399 case ISOLATE_SUCCESS:
1403 err = migrate_pages(&cc->migratepages, compaction_alloc,
1404 compaction_free, (unsigned long)cc, cc->mode,
1407 trace_mm_compaction_migratepages(cc->nr_migratepages, err,
1410 /* All pages were either migrated or will be released */
1411 cc->nr_migratepages = 0;
1413 putback_movable_pages(&cc->migratepages);
1415 * migrate_pages() may return -ENOMEM when scanners meet
1416 * and we want compact_finished() to detect it
1418 if (err == -ENOMEM && !compact_scanners_met(cc)) {
1419 ret = COMPACT_CONTENDED;
1426 * Has the migration scanner moved away from the previous
1427 * cc->order aligned block where we migrated from? If yes,
1428 * flush the pages that were freed, so that they can merge and
1429 * compact_finished() can detect immediately if allocation
1432 if (cc->order > 0 && cc->last_migrated_pfn) {
1434 unsigned long current_block_start =
1435 cc->migrate_pfn & ~((1UL << cc->order) - 1);
1437 if (cc->last_migrated_pfn < current_block_start) {
1439 lru_add_drain_cpu(cpu);
1440 drain_local_pages(zone);
1442 /* No more flushing until we migrate again */
1443 cc->last_migrated_pfn = 0;
1451 * Release free pages and update where the free scanner should restart,
1452 * so we don't leave any returned pages behind in the next attempt.
1454 if (cc->nr_freepages > 0) {
1455 unsigned long free_pfn = release_freepages(&cc->freepages);
1457 cc->nr_freepages = 0;
1458 VM_BUG_ON(free_pfn == 0);
1459 /* The cached pfn is always the first in a pageblock */
1460 free_pfn &= ~(pageblock_nr_pages-1);
1462 * Only go back, not forward. The cached pfn might have been
1463 * already reset to zone end in compact_finished()
1465 if (free_pfn > zone->compact_cached_free_pfn)
1466 zone->compact_cached_free_pfn = free_pfn;
1469 trace_mm_compaction_end(start_pfn, cc->migrate_pfn,
1470 cc->free_pfn, end_pfn, sync, ret);
1472 if (ret == COMPACT_CONTENDED)
1473 ret = COMPACT_PARTIAL;
1478 static unsigned long compact_zone_order(struct zone *zone, int order,
1479 gfp_t gfp_mask, enum migrate_mode mode, int *contended,
1480 int alloc_flags, int classzone_idx)
1483 struct compact_control cc = {
1485 .nr_migratepages = 0,
1487 .gfp_mask = gfp_mask,
1490 .alloc_flags = alloc_flags,
1491 .classzone_idx = classzone_idx,
1493 INIT_LIST_HEAD(&cc.freepages);
1494 INIT_LIST_HEAD(&cc.migratepages);
1496 ret = compact_zone(zone, &cc);
1498 VM_BUG_ON(!list_empty(&cc.freepages));
1499 VM_BUG_ON(!list_empty(&cc.migratepages));
1501 *contended = cc.contended;
1505 int sysctl_extfrag_threshold = 500;
1508 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1509 * @gfp_mask: The GFP mask of the current allocation
1510 * @order: The order of the current allocation
1511 * @alloc_flags: The allocation flags of the current allocation
1512 * @ac: The context of current allocation
1513 * @mode: The migration mode for async, sync light, or sync migration
1514 * @contended: Return value that determines if compaction was aborted due to
1515 * need_resched() or lock contention
1517 * This is the main entry point for direct page compaction.
1519 unsigned long try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
1520 int alloc_flags, const struct alloc_context *ac,
1521 enum migrate_mode mode, int *contended)
1523 int may_enter_fs = gfp_mask & __GFP_FS;
1524 int may_perform_io = gfp_mask & __GFP_IO;
1527 int rc = COMPACT_DEFERRED;
1528 int all_zones_contended = COMPACT_CONTENDED_LOCK; /* init for &= op */
1530 *contended = COMPACT_CONTENDED_NONE;
1532 /* Check if the GFP flags allow compaction */
1533 if (!order || !may_enter_fs || !may_perform_io)
1534 return COMPACT_SKIPPED;
1536 trace_mm_compaction_try_to_compact_pages(order, gfp_mask, mode);
1538 /* Compact each zone in the list */
1539 for_each_zone_zonelist_nodemask(zone, z, ac->zonelist, ac->high_zoneidx,
1544 if (compaction_deferred(zone, order))
1547 status = compact_zone_order(zone, order, gfp_mask, mode,
1548 &zone_contended, alloc_flags,
1550 rc = max(status, rc);
1552 * It takes at least one zone that wasn't lock contended
1553 * to clear all_zones_contended.
1555 all_zones_contended &= zone_contended;
1557 /* If a normal allocation would succeed, stop compacting */
1558 if (zone_watermark_ok(zone, order, low_wmark_pages(zone),
1559 ac->classzone_idx, alloc_flags)) {
1561 * We think the allocation will succeed in this zone,
1562 * but it is not certain, hence the false. The caller
1563 * will repeat this with true if allocation indeed
1564 * succeeds in this zone.
1566 compaction_defer_reset(zone, order, false);
1568 * It is possible that async compaction aborted due to
1569 * need_resched() and the watermarks were ok thanks to
1570 * somebody else freeing memory. The allocation can
1571 * however still fail so we better signal the
1572 * need_resched() contention anyway (this will not
1573 * prevent the allocation attempt).
1575 if (zone_contended == COMPACT_CONTENDED_SCHED)
1576 *contended = COMPACT_CONTENDED_SCHED;
1581 if (mode != MIGRATE_ASYNC && status == COMPACT_COMPLETE) {
1583 * We think that allocation won't succeed in this zone
1584 * so we defer compaction there. If it ends up
1585 * succeeding after all, it will be reset.
1587 defer_compaction(zone, order);
1591 * We might have stopped compacting due to need_resched() in
1592 * async compaction, or due to a fatal signal detected. In that
1593 * case do not try further zones and signal need_resched()
1596 if ((zone_contended == COMPACT_CONTENDED_SCHED)
1597 || fatal_signal_pending(current)) {
1598 *contended = COMPACT_CONTENDED_SCHED;
1605 * We might not have tried all the zones, so be conservative
1606 * and assume they are not all lock contended.
1608 all_zones_contended = 0;
1613 * If at least one zone wasn't deferred or skipped, we report if all
1614 * zones that were tried were lock contended.
1616 if (rc > COMPACT_SKIPPED && all_zones_contended)
1617 *contended = COMPACT_CONTENDED_LOCK;
1623 /* Compact all zones within a node */
1624 static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
1629 for (zoneid = 0; zoneid < MAX_NR_ZONES; zoneid++) {
1631 zone = &pgdat->node_zones[zoneid];
1632 if (!populated_zone(zone))
1635 cc->nr_freepages = 0;
1636 cc->nr_migratepages = 0;
1638 INIT_LIST_HEAD(&cc->freepages);
1639 INIT_LIST_HEAD(&cc->migratepages);
1642 * When called via /proc/sys/vm/compact_memory
1643 * this makes sure we compact the whole zone regardless of
1644 * cached scanner positions.
1646 if (is_via_compact_memory(cc->order))
1647 __reset_isolation_suitable(zone);
1649 if (is_via_compact_memory(cc->order) ||
1650 !compaction_deferred(zone, cc->order))
1651 compact_zone(zone, cc);
1653 if (cc->order > 0) {
1654 if (zone_watermark_ok(zone, cc->order,
1655 low_wmark_pages(zone), 0, 0))
1656 compaction_defer_reset(zone, cc->order, false);
1659 VM_BUG_ON(!list_empty(&cc->freepages));
1660 VM_BUG_ON(!list_empty(&cc->migratepages));
1664 void compact_pgdat(pg_data_t *pgdat, int order)
1666 struct compact_control cc = {
1668 .mode = MIGRATE_ASYNC,
1674 __compact_pgdat(pgdat, &cc);
1677 static void compact_node(int nid)
1679 struct compact_control cc = {
1681 .mode = MIGRATE_SYNC,
1682 .ignore_skip_hint = true,
1685 __compact_pgdat(NODE_DATA(nid), &cc);
1688 /* Compact all nodes in the system */
1689 static void compact_nodes(void)
1693 /* Flush pending updates to the LRU lists */
1694 lru_add_drain_all();
1696 for_each_online_node(nid)
1700 /* The written value is actually unused, all memory is compacted */
1701 int sysctl_compact_memory;
1703 /* This is the entry point for compacting all nodes via /proc/sys/vm */
1704 int sysctl_compaction_handler(struct ctl_table *table, int write,
1705 void __user *buffer, size_t *length, loff_t *ppos)
1713 int sysctl_extfrag_handler(struct ctl_table *table, int write,
1714 void __user *buffer, size_t *length, loff_t *ppos)
1716 proc_dointvec_minmax(table, write, buffer, length, ppos);
1721 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1722 static ssize_t sysfs_compact_node(struct device *dev,
1723 struct device_attribute *attr,
1724 const char *buf, size_t count)
1728 if (nid >= 0 && nid < nr_node_ids && node_online(nid)) {
1729 /* Flush pending updates to the LRU lists */
1730 lru_add_drain_all();
1737 static DEVICE_ATTR(compact, S_IWUSR, NULL, sysfs_compact_node);
1739 int compaction_register_node(struct node *node)
1741 return device_create_file(&node->dev, &dev_attr_compact);
1744 void compaction_unregister_node(struct node *node)
1746 return device_remove_file(&node->dev, &dev_attr_compact);
1748 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
1750 #endif /* CONFIG_COMPACTION */