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
->sync
&& pfn
> zone
->compact_cached_migrate_pfn
[1])
165 zone
->compact_cached_migrate_pfn
[1] = pfn
;
167 if (cc
->finished_update_free
)
169 if (pfn
< zone
->compact_cached_free_pfn
)
170 zone
->compact_cached_free_pfn
= pfn
;
174 static inline bool isolation_suitable(struct compact_control
*cc
,
180 static void update_pageblock_skip(struct compact_control
*cc
,
181 struct page
*page
, unsigned long nr_isolated
,
182 bool set_unsuitable
, bool migrate_scanner
)
185 #endif /* CONFIG_COMPACTION */
187 static inline bool should_release_lock(spinlock_t
*lock
)
189 return need_resched() || spin_is_contended(lock
);
193 * Compaction requires the taking of some coarse locks that are potentially
194 * very heavily contended. Check if the process needs to be scheduled or
195 * if the lock is contended. For async compaction, back out in the event
196 * if contention is severe. For sync compaction, schedule.
198 * Returns true if the lock is held.
199 * Returns false if the lock is released and compaction should abort
201 static bool compact_checklock_irqsave(spinlock_t
*lock
, unsigned long *flags
,
202 bool locked
, struct compact_control
*cc
)
204 if (should_release_lock(lock
)) {
206 spin_unlock_irqrestore(lock
, *flags
);
210 /* async aborts if taking too long or contended */
212 cc
->contended
= true;
220 spin_lock_irqsave(lock
, *flags
);
224 /* Returns true if the page is within a block suitable for migration to */
225 static bool suitable_migration_target(struct page
*page
)
227 /* If the page is a large free page, then disallow migration */
228 if (PageBuddy(page
) && page_order(page
) >= pageblock_order
)
231 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
232 if (migrate_async_suitable(get_pageblock_migratetype(page
)))
235 /* Otherwise skip the block */
240 * Isolate free pages onto a private freelist. If @strict is true, will abort
241 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
242 * (even though it may still end up isolating some pages).
244 static unsigned long isolate_freepages_block(struct compact_control
*cc
,
245 unsigned long blockpfn
,
246 unsigned long end_pfn
,
247 struct list_head
*freelist
,
250 int nr_scanned
= 0, total_isolated
= 0;
251 struct page
*cursor
, *valid_page
= NULL
;
254 bool checked_pageblock
= false;
256 cursor
= pfn_to_page(blockpfn
);
258 /* Isolate free pages. */
259 for (; blockpfn
< end_pfn
; blockpfn
++, cursor
++) {
261 struct page
*page
= cursor
;
264 if (!pfn_valid_within(blockpfn
))
269 if (!PageBuddy(page
))
273 * The zone lock must be held to isolate freepages.
274 * Unfortunately this is a very coarse lock and can be
275 * heavily contended if there are parallel allocations
276 * or parallel compactions. For async compaction do not
277 * spin on the lock and we acquire the lock as late as
280 locked
= compact_checklock_irqsave(&cc
->zone
->lock
, &flags
,
285 /* Recheck this is a suitable migration target under lock */
286 if (!strict
&& !checked_pageblock
) {
288 * We need to check suitability of pageblock only once
289 * and this isolate_freepages_block() is called with
290 * pageblock range, so just check once is sufficient.
292 checked_pageblock
= true;
293 if (!suitable_migration_target(page
))
297 /* Recheck this is a buddy page under lock */
298 if (!PageBuddy(page
))
301 /* Found a free page, break it into order-0 pages */
302 isolated
= split_free_page(page
);
303 total_isolated
+= isolated
;
304 for (i
= 0; i
< isolated
; i
++) {
305 list_add(&page
->lru
, freelist
);
309 /* If a page was split, advance to the end of it */
311 blockpfn
+= isolated
- 1;
312 cursor
+= isolated
- 1;
324 trace_mm_compaction_isolate_freepages(nr_scanned
, total_isolated
);
327 * If strict isolation is requested by CMA then check that all the
328 * pages requested were isolated. If there were any failures, 0 is
329 * returned and CMA will fail.
331 if (strict
&& blockpfn
< end_pfn
)
335 spin_unlock_irqrestore(&cc
->zone
->lock
, flags
);
337 /* Update the pageblock-skip if the whole pageblock was scanned */
338 if (blockpfn
== end_pfn
)
339 update_pageblock_skip(cc
, valid_page
, total_isolated
, true,
342 count_compact_events(COMPACTFREE_SCANNED
, nr_scanned
);
344 count_compact_events(COMPACTISOLATED
, total_isolated
);
345 return total_isolated
;
349 * isolate_freepages_range() - isolate free pages.
350 * @start_pfn: The first PFN to start isolating.
351 * @end_pfn: The one-past-last PFN.
353 * Non-free pages, invalid PFNs, or zone boundaries within the
354 * [start_pfn, end_pfn) range are considered errors, cause function to
355 * undo its actions and return zero.
357 * Otherwise, function returns one-past-the-last PFN of isolated page
358 * (which may be greater then end_pfn if end fell in a middle of
362 isolate_freepages_range(struct compact_control
*cc
,
363 unsigned long start_pfn
, unsigned long end_pfn
)
365 unsigned long isolated
, pfn
, block_end_pfn
;
368 for (pfn
= start_pfn
; pfn
< end_pfn
; pfn
+= isolated
) {
369 if (!pfn_valid(pfn
) || cc
->zone
!= page_zone(pfn_to_page(pfn
)))
373 * On subsequent iterations ALIGN() is actually not needed,
374 * but we keep it that we not to complicate the code.
376 block_end_pfn
= ALIGN(pfn
+ 1, pageblock_nr_pages
);
377 block_end_pfn
= min(block_end_pfn
, end_pfn
);
379 isolated
= isolate_freepages_block(cc
, pfn
, block_end_pfn
,
383 * In strict mode, isolate_freepages_block() returns 0 if
384 * there are any holes in the block (ie. invalid PFNs or
391 * If we managed to isolate pages, it is always (1 << n) *
392 * pageblock_nr_pages for some non-negative n. (Max order
393 * page may span two pageblocks).
397 /* split_free_page does not map the pages */
398 map_pages(&freelist
);
401 /* Loop terminated early, cleanup. */
402 release_freepages(&freelist
);
406 /* We don't use freelists for anything. */
410 /* Update the number of anon and file isolated pages in the zone */
411 static void acct_isolated(struct zone
*zone
, bool locked
, struct compact_control
*cc
)
414 unsigned int count
[2] = { 0, };
416 list_for_each_entry(page
, &cc
->migratepages
, lru
)
417 count
[!!page_is_file_cache(page
)]++;
419 /* If locked we can use the interrupt unsafe versions */
421 __mod_zone_page_state(zone
, NR_ISOLATED_ANON
, count
[0]);
422 __mod_zone_page_state(zone
, NR_ISOLATED_FILE
, count
[1]);
424 mod_zone_page_state(zone
, NR_ISOLATED_ANON
, count
[0]);
425 mod_zone_page_state(zone
, NR_ISOLATED_FILE
, count
[1]);
429 /* Similar to reclaim, but different enough that they don't share logic */
430 static bool too_many_isolated(struct zone
*zone
)
432 unsigned long active
, inactive
, isolated
;
434 inactive
= zone_page_state(zone
, NR_INACTIVE_FILE
) +
435 zone_page_state(zone
, NR_INACTIVE_ANON
);
436 active
= zone_page_state(zone
, NR_ACTIVE_FILE
) +
437 zone_page_state(zone
, NR_ACTIVE_ANON
);
438 isolated
= zone_page_state(zone
, NR_ISOLATED_FILE
) +
439 zone_page_state(zone
, NR_ISOLATED_ANON
);
441 return isolated
> (inactive
+ active
) / 2;
445 * isolate_migratepages_range() - isolate all migrate-able pages in range.
446 * @zone: Zone pages are in.
447 * @cc: Compaction control structure.
448 * @low_pfn: The first PFN of the range.
449 * @end_pfn: The one-past-the-last PFN of the range.
450 * @unevictable: true if it allows to isolate unevictable pages
452 * Isolate all pages that can be migrated from the range specified by
453 * [low_pfn, end_pfn). Returns zero if there is a fatal signal
454 * pending), otherwise PFN of the first page that was not scanned
455 * (which may be both less, equal to or more then end_pfn).
457 * Assumes that cc->migratepages is empty and cc->nr_migratepages is
460 * Apart from cc->migratepages and cc->nr_migratetypes this function
461 * does not modify any cc's fields, in particular it does not modify
462 * (or read for that matter) cc->migrate_pfn.
465 isolate_migratepages_range(struct zone
*zone
, struct compact_control
*cc
,
466 unsigned long low_pfn
, unsigned long end_pfn
, bool unevictable
)
468 unsigned long last_pageblock_nr
= 0, pageblock_nr
;
469 unsigned long nr_scanned
= 0, nr_isolated
= 0;
470 struct list_head
*migratelist
= &cc
->migratepages
;
471 struct lruvec
*lruvec
;
474 struct page
*page
= NULL
, *valid_page
= NULL
;
475 bool set_unsuitable
= true;
476 const isolate_mode_t mode
= (!cc
->sync
? ISOLATE_ASYNC_MIGRATE
: 0) |
477 (unevictable
? ISOLATE_UNEVICTABLE
: 0);
480 * Ensure that there are not too many pages isolated from the LRU
481 * list by either parallel reclaimers or compaction. If there are,
482 * delay for some time until fewer pages are isolated
484 while (unlikely(too_many_isolated(zone
))) {
485 /* async migration should just abort */
489 congestion_wait(BLK_RW_ASYNC
, HZ
/10);
491 if (fatal_signal_pending(current
))
495 /* Time to isolate some pages for migration */
497 for (; low_pfn
< end_pfn
; low_pfn
++) {
498 /* give a chance to irqs before checking need_resched() */
499 if (locked
&& !(low_pfn
% SWAP_CLUSTER_MAX
)) {
500 if (should_release_lock(&zone
->lru_lock
)) {
501 spin_unlock_irqrestore(&zone
->lru_lock
, flags
);
507 * migrate_pfn does not necessarily start aligned to a
508 * pageblock. Ensure that pfn_valid is called when moving
509 * into a new MAX_ORDER_NR_PAGES range in case of large
510 * memory holes within the zone
512 if ((low_pfn
& (MAX_ORDER_NR_PAGES
- 1)) == 0) {
513 if (!pfn_valid(low_pfn
)) {
514 low_pfn
+= MAX_ORDER_NR_PAGES
- 1;
519 if (!pfn_valid_within(low_pfn
))
524 * Get the page and ensure the page is within the same zone.
525 * See the comment in isolate_freepages about overlapping
526 * nodes. It is deliberate that the new zone lock is not taken
527 * as memory compaction should not move pages between nodes.
529 page
= pfn_to_page(low_pfn
);
530 if (page_zone(page
) != zone
)
536 /* If isolation recently failed, do not retry */
537 pageblock_nr
= low_pfn
>> pageblock_order
;
538 if (last_pageblock_nr
!= pageblock_nr
) {
541 last_pageblock_nr
= pageblock_nr
;
542 if (!isolation_suitable(cc
, page
))
546 * For async migration, also only scan in MOVABLE
547 * blocks. Async migration is optimistic to see if
548 * the minimum amount of work satisfies the allocation
550 mt
= get_pageblock_migratetype(page
);
551 if (!cc
->sync
&& !migrate_async_suitable(mt
)) {
552 set_unsuitable
= false;
558 * Skip if free. page_order cannot be used without zone->lock
559 * as nothing prevents parallel allocations or buddy merging.
565 * Check may be lockless but that's ok as we recheck later.
566 * It's possible to migrate LRU pages and balloon pages
567 * Skip any other type of page
569 if (!PageLRU(page
)) {
570 if (unlikely(balloon_page_movable(page
))) {
571 if (locked
&& balloon_page_isolate(page
)) {
572 /* Successfully isolated */
573 goto isolate_success
;
580 * PageLRU is set. lru_lock normally excludes isolation
581 * splitting and collapsing (collapsing has already happened
582 * if PageLRU is set) but the lock is not necessarily taken
583 * here and it is wasteful to take it just to check transhuge.
584 * Check TransHuge without lock and skip the whole pageblock if
585 * it's either a transhuge or hugetlbfs page, as calling
586 * compound_order() without preventing THP from splitting the
587 * page underneath us may return surprising results.
589 if (PageTransHuge(page
)) {
592 low_pfn
+= (1 << compound_order(page
)) - 1;
597 * Migration will fail if an anonymous page is pinned in memory,
598 * so avoid taking lru_lock and isolating it unnecessarily in an
599 * admittedly racy check.
601 if (!page_mapping(page
) &&
602 page_count(page
) > page_mapcount(page
))
605 /* Check if it is ok to still hold the lock */
606 locked
= compact_checklock_irqsave(&zone
->lru_lock
, &flags
,
608 if (!locked
|| fatal_signal_pending(current
))
611 /* Recheck PageLRU and PageTransHuge under lock */
614 if (PageTransHuge(page
)) {
615 low_pfn
+= (1 << compound_order(page
)) - 1;
619 lruvec
= mem_cgroup_page_lruvec(page
, zone
);
621 /* Try isolate the page */
622 if (__isolate_lru_page(page
, mode
) != 0)
625 VM_BUG_ON_PAGE(PageTransCompound(page
), page
);
627 /* Successfully isolated */
628 del_page_from_lru_list(page
, lruvec
, page_lru(page
));
631 cc
->finished_update_migrate
= true;
632 list_add(&page
->lru
, migratelist
);
633 cc
->nr_migratepages
++;
636 /* Avoid isolating too much */
637 if (cc
->nr_migratepages
== COMPACT_CLUSTER_MAX
) {
645 low_pfn
= ALIGN(low_pfn
+ 1, pageblock_nr_pages
) - 1;
648 acct_isolated(zone
, locked
, cc
);
651 spin_unlock_irqrestore(&zone
->lru_lock
, flags
);
654 * Update the pageblock-skip information and cached scanner pfn,
655 * if the whole pageblock was scanned without isolating any page.
657 if (low_pfn
== end_pfn
)
658 update_pageblock_skip(cc
, valid_page
, nr_isolated
,
659 set_unsuitable
, true);
661 trace_mm_compaction_isolate_migratepages(nr_scanned
, nr_isolated
);
663 count_compact_events(COMPACTMIGRATE_SCANNED
, nr_scanned
);
665 count_compact_events(COMPACTISOLATED
, nr_isolated
);
670 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
671 #ifdef CONFIG_COMPACTION
673 * Based on information in the current compact_control, find blocks
674 * suitable for isolating free pages from and then isolate them.
676 static void isolate_freepages(struct zone
*zone
,
677 struct compact_control
*cc
)
680 unsigned long block_start_pfn
; /* start of current pageblock */
681 unsigned long block_end_pfn
; /* end of current pageblock */
682 unsigned long low_pfn
; /* lowest pfn scanner is able to scan */
683 unsigned long next_free_pfn
; /* start pfn for scaning at next round */
684 int nr_freepages
= cc
->nr_freepages
;
685 struct list_head
*freelist
= &cc
->freepages
;
688 * Initialise the free scanner. The starting point is where we last
689 * successfully isolated from, zone-cached value, or the end of the
690 * zone when isolating for the first time. We need this aligned to
691 * the pageblock boundary, because we do
692 * block_start_pfn -= pageblock_nr_pages in the for loop.
693 * For ending point, take care when isolating in last pageblock of a
694 * a zone which ends in the middle of a pageblock.
695 * The low boundary is the end of the pageblock the migration scanner
698 block_start_pfn
= cc
->free_pfn
& ~(pageblock_nr_pages
-1);
699 block_end_pfn
= min(block_start_pfn
+ pageblock_nr_pages
,
701 low_pfn
= ALIGN(cc
->migrate_pfn
+ 1, pageblock_nr_pages
);
704 * If no pages are isolated, the block_start_pfn < low_pfn check
710 * Isolate free pages until enough are available to migrate the
711 * pages on cc->migratepages. We stop searching if the migrate
712 * and free page scanners meet or enough free pages are isolated.
714 for (; block_start_pfn
>= low_pfn
&& cc
->nr_migratepages
> nr_freepages
;
715 block_end_pfn
= block_start_pfn
,
716 block_start_pfn
-= pageblock_nr_pages
) {
717 unsigned long isolated
;
720 * This can iterate a massively long zone without finding any
721 * suitable migration targets, so periodically check if we need
726 if (!pfn_valid(block_start_pfn
))
730 * Check for overlapping nodes/zones. It's possible on some
731 * configurations to have a setup like
733 * i.e. it's possible that all pages within a zones range of
734 * pages do not belong to a single zone.
736 page
= pfn_to_page(block_start_pfn
);
737 if (page_zone(page
) != zone
)
740 /* Check the block is suitable for migration */
741 if (!suitable_migration_target(page
))
744 /* If isolation recently failed, do not retry */
745 if (!isolation_suitable(cc
, page
))
748 /* Found a block suitable for isolating free pages from */
749 isolated
= isolate_freepages_block(cc
, block_start_pfn
,
750 block_end_pfn
, freelist
, false);
751 nr_freepages
+= isolated
;
754 * Record the highest PFN we isolated pages from. When next
755 * looking for free pages, the search will restart here as
756 * page migration may have returned some pages to the allocator
758 if (isolated
&& next_free_pfn
== 0) {
759 cc
->finished_update_free
= true;
760 next_free_pfn
= block_start_pfn
;
764 /* split_free_page does not map the pages */
768 * If we crossed the migrate scanner, we want to keep it that way
769 * so that compact_finished() may detect this
771 if (block_start_pfn
< low_pfn
)
772 next_free_pfn
= cc
->migrate_pfn
;
774 cc
->free_pfn
= next_free_pfn
;
775 cc
->nr_freepages
= nr_freepages
;
779 * This is a migrate-callback that "allocates" freepages by taking pages
780 * from the isolated freelists in the block we are migrating to.
782 static struct page
*compaction_alloc(struct page
*migratepage
,
786 struct compact_control
*cc
= (struct compact_control
*)data
;
787 struct page
*freepage
;
789 /* Isolate free pages if necessary */
790 if (list_empty(&cc
->freepages
)) {
791 isolate_freepages(cc
->zone
, cc
);
793 if (list_empty(&cc
->freepages
))
797 freepage
= list_entry(cc
->freepages
.next
, struct page
, lru
);
798 list_del(&freepage
->lru
);
805 * This is a migrate-callback that "frees" freepages back to the isolated
806 * freelist. All pages on the freelist are from the same zone, so there is no
807 * special handling needed for NUMA.
809 static void compaction_free(struct page
*page
, unsigned long data
)
811 struct compact_control
*cc
= (struct compact_control
*)data
;
813 list_add(&page
->lru
, &cc
->freepages
);
818 * We cannot control nr_migratepages fully when migration is running as
819 * migrate_pages() has no knowledge of of compact_control. When migration is
820 * complete, we count the number of pages on the list by hand.
822 static void update_nr_listpages(struct compact_control
*cc
)
824 int nr_migratepages
= 0;
827 list_for_each_entry(page
, &cc
->migratepages
, lru
)
830 cc
->nr_migratepages
= nr_migratepages
;
833 /* possible outcome of isolate_migratepages */
835 ISOLATE_ABORT
, /* Abort compaction now */
836 ISOLATE_NONE
, /* No pages isolated, continue scanning */
837 ISOLATE_SUCCESS
, /* Pages isolated, migrate */
841 * Isolate all pages that can be migrated from the block pointed to by
842 * the migrate scanner within compact_control.
844 static isolate_migrate_t
isolate_migratepages(struct zone
*zone
,
845 struct compact_control
*cc
)
847 unsigned long low_pfn
, end_pfn
;
849 /* Do not scan outside zone boundaries */
850 low_pfn
= max(cc
->migrate_pfn
, zone
->zone_start_pfn
);
852 /* Only scan within a pageblock boundary */
853 end_pfn
= ALIGN(low_pfn
+ 1, pageblock_nr_pages
);
855 /* Do not cross the free scanner or scan within a memory hole */
856 if (end_pfn
> cc
->free_pfn
|| !pfn_valid(low_pfn
)) {
857 cc
->migrate_pfn
= end_pfn
;
861 /* Perform the isolation */
862 low_pfn
= isolate_migratepages_range(zone
, cc
, low_pfn
, end_pfn
, false);
863 if (!low_pfn
|| cc
->contended
)
864 return ISOLATE_ABORT
;
866 cc
->migrate_pfn
= low_pfn
;
868 return ISOLATE_SUCCESS
;
871 static int compact_finished(struct zone
*zone
,
872 struct compact_control
*cc
)
875 unsigned long watermark
;
877 if (fatal_signal_pending(current
))
878 return COMPACT_PARTIAL
;
880 /* Compaction run completes if the migrate and free scanner meet */
881 if (cc
->free_pfn
<= cc
->migrate_pfn
) {
882 /* Let the next compaction start anew. */
883 zone
->compact_cached_migrate_pfn
[0] = zone
->zone_start_pfn
;
884 zone
->compact_cached_migrate_pfn
[1] = zone
->zone_start_pfn
;
885 zone
->compact_cached_free_pfn
= zone_end_pfn(zone
);
888 * Mark that the PG_migrate_skip information should be cleared
889 * by kswapd when it goes to sleep. kswapd does not set the
890 * flag itself as the decision to be clear should be directly
891 * based on an allocation request.
893 if (!current_is_kswapd())
894 zone
->compact_blockskip_flush
= true;
896 return COMPACT_COMPLETE
;
900 * order == -1 is expected when compacting via
901 * /proc/sys/vm/compact_memory
904 return COMPACT_CONTINUE
;
906 /* Compaction run is not finished if the watermark is not met */
907 watermark
= low_wmark_pages(zone
);
908 watermark
+= (1 << cc
->order
);
910 if (!zone_watermark_ok(zone
, cc
->order
, watermark
, 0, 0))
911 return COMPACT_CONTINUE
;
913 /* Direct compactor: Is a suitable page free? */
914 for (order
= cc
->order
; order
< MAX_ORDER
; order
++) {
915 struct free_area
*area
= &zone
->free_area
[order
];
917 /* Job done if page is free of the right migratetype */
918 if (!list_empty(&area
->free_list
[cc
->migratetype
]))
919 return COMPACT_PARTIAL
;
921 /* Job done if allocation would set block type */
922 if (cc
->order
>= pageblock_order
&& area
->nr_free
)
923 return COMPACT_PARTIAL
;
926 return COMPACT_CONTINUE
;
930 * compaction_suitable: Is this suitable to run compaction on this zone now?
932 * COMPACT_SKIPPED - If there are too few free pages for compaction
933 * COMPACT_PARTIAL - If the allocation would succeed without compaction
934 * COMPACT_CONTINUE - If compaction should run now
936 unsigned long compaction_suitable(struct zone
*zone
, int order
)
939 unsigned long watermark
;
942 * order == -1 is expected when compacting via
943 * /proc/sys/vm/compact_memory
946 return COMPACT_CONTINUE
;
949 * Watermarks for order-0 must be met for compaction. Note the 2UL.
950 * This is because during migration, copies of pages need to be
951 * allocated and for a short time, the footprint is higher
953 watermark
= low_wmark_pages(zone
) + (2UL << order
);
954 if (!zone_watermark_ok(zone
, 0, watermark
, 0, 0))
955 return COMPACT_SKIPPED
;
958 * fragmentation index determines if allocation failures are due to
959 * low memory or external fragmentation
961 * index of -1000 implies allocations might succeed depending on
963 * index towards 0 implies failure is due to lack of memory
964 * index towards 1000 implies failure is due to fragmentation
966 * Only compact if a failure would be due to fragmentation.
968 fragindex
= fragmentation_index(zone
, order
);
969 if (fragindex
>= 0 && fragindex
<= sysctl_extfrag_threshold
)
970 return COMPACT_SKIPPED
;
972 if (fragindex
== -1000 && zone_watermark_ok(zone
, order
, watermark
,
974 return COMPACT_PARTIAL
;
976 return COMPACT_CONTINUE
;
979 static int compact_zone(struct zone
*zone
, struct compact_control
*cc
)
982 unsigned long start_pfn
= zone
->zone_start_pfn
;
983 unsigned long end_pfn
= zone_end_pfn(zone
);
985 ret
= compaction_suitable(zone
, cc
->order
);
987 case COMPACT_PARTIAL
:
988 case COMPACT_SKIPPED
:
989 /* Compaction is likely to fail */
991 case COMPACT_CONTINUE
:
992 /* Fall through to compaction */
997 * Clear pageblock skip if there were failures recently and compaction
998 * is about to be retried after being deferred. kswapd does not do
999 * this reset as it'll reset the cached information when going to sleep.
1001 if (compaction_restarting(zone
, cc
->order
) && !current_is_kswapd())
1002 __reset_isolation_suitable(zone
);
1005 * Setup to move all movable pages to the end of the zone. Used cached
1006 * information on where the scanners should start but check that it
1007 * is initialised by ensuring the values are within zone boundaries.
1009 cc
->migrate_pfn
= zone
->compact_cached_migrate_pfn
[cc
->sync
];
1010 cc
->free_pfn
= zone
->compact_cached_free_pfn
;
1011 if (cc
->free_pfn
< start_pfn
|| cc
->free_pfn
> end_pfn
) {
1012 cc
->free_pfn
= end_pfn
& ~(pageblock_nr_pages
-1);
1013 zone
->compact_cached_free_pfn
= cc
->free_pfn
;
1015 if (cc
->migrate_pfn
< start_pfn
|| cc
->migrate_pfn
> end_pfn
) {
1016 cc
->migrate_pfn
= start_pfn
;
1017 zone
->compact_cached_migrate_pfn
[0] = cc
->migrate_pfn
;
1018 zone
->compact_cached_migrate_pfn
[1] = cc
->migrate_pfn
;
1021 trace_mm_compaction_begin(start_pfn
, cc
->migrate_pfn
, cc
->free_pfn
, end_pfn
);
1023 migrate_prep_local();
1025 while ((ret
= compact_finished(zone
, cc
)) == COMPACT_CONTINUE
) {
1026 unsigned long nr_migrate
, nr_remaining
;
1029 switch (isolate_migratepages(zone
, cc
)) {
1031 ret
= COMPACT_PARTIAL
;
1032 putback_movable_pages(&cc
->migratepages
);
1033 cc
->nr_migratepages
= 0;
1037 case ISOLATE_SUCCESS
:
1041 nr_migrate
= cc
->nr_migratepages
;
1042 err
= migrate_pages(&cc
->migratepages
, compaction_alloc
,
1043 compaction_free
, (unsigned long)cc
,
1044 cc
->sync
? MIGRATE_SYNC_LIGHT
: MIGRATE_ASYNC
,
1046 update_nr_listpages(cc
);
1047 nr_remaining
= cc
->nr_migratepages
;
1049 trace_mm_compaction_migratepages(nr_migrate
- nr_remaining
,
1052 /* Release isolated pages not migrated */
1054 putback_movable_pages(&cc
->migratepages
);
1055 cc
->nr_migratepages
= 0;
1057 * migrate_pages() may return -ENOMEM when scanners meet
1058 * and we want compact_finished() to detect it
1060 if (err
== -ENOMEM
&& cc
->free_pfn
> cc
->migrate_pfn
) {
1061 ret
= COMPACT_PARTIAL
;
1068 /* Release free pages and check accounting */
1069 cc
->nr_freepages
-= release_freepages(&cc
->freepages
);
1070 VM_BUG_ON(cc
->nr_freepages
!= 0);
1072 trace_mm_compaction_end(ret
);
1077 static unsigned long compact_zone_order(struct zone
*zone
,
1078 int order
, gfp_t gfp_mask
,
1079 bool sync
, bool *contended
)
1082 struct compact_control cc
= {
1084 .nr_migratepages
= 0,
1086 .migratetype
= allocflags_to_migratetype(gfp_mask
),
1090 INIT_LIST_HEAD(&cc
.freepages
);
1091 INIT_LIST_HEAD(&cc
.migratepages
);
1093 ret
= compact_zone(zone
, &cc
);
1095 VM_BUG_ON(!list_empty(&cc
.freepages
));
1096 VM_BUG_ON(!list_empty(&cc
.migratepages
));
1098 *contended
= cc
.contended
;
1102 int sysctl_extfrag_threshold
= 500;
1105 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1106 * @zonelist: The zonelist used for the current allocation
1107 * @order: The order of the current allocation
1108 * @gfp_mask: The GFP mask of the current allocation
1109 * @nodemask: The allowed nodes to allocate from
1110 * @sync: Whether migration is synchronous or not
1111 * @contended: Return value that is true if compaction was aborted due to lock contention
1112 * @page: Optionally capture a free page of the requested order during compaction
1114 * This is the main entry point for direct page compaction.
1116 unsigned long try_to_compact_pages(struct zonelist
*zonelist
,
1117 int order
, gfp_t gfp_mask
, nodemask_t
*nodemask
,
1118 bool sync
, bool *contended
)
1120 enum zone_type high_zoneidx
= gfp_zone(gfp_mask
);
1121 int may_enter_fs
= gfp_mask
& __GFP_FS
;
1122 int may_perform_io
= gfp_mask
& __GFP_IO
;
1125 int rc
= COMPACT_SKIPPED
;
1126 int alloc_flags
= 0;
1128 /* Check if the GFP flags allow compaction */
1129 if (!order
|| !may_enter_fs
|| !may_perform_io
)
1132 count_compact_event(COMPACTSTALL
);
1135 if (allocflags_to_migratetype(gfp_mask
) == MIGRATE_MOVABLE
)
1136 alloc_flags
|= ALLOC_CMA
;
1138 /* Compact each zone in the list */
1139 for_each_zone_zonelist_nodemask(zone
, z
, zonelist
, high_zoneidx
,
1143 status
= compact_zone_order(zone
, order
, gfp_mask
, sync
,
1145 rc
= max(status
, rc
);
1147 /* If a normal allocation would succeed, stop compacting */
1148 if (zone_watermark_ok(zone
, order
, low_wmark_pages(zone
), 0,
1157 /* Compact all zones within a node */
1158 static void __compact_pgdat(pg_data_t
*pgdat
, struct compact_control
*cc
)
1163 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
1165 zone
= &pgdat
->node_zones
[zoneid
];
1166 if (!populated_zone(zone
))
1169 cc
->nr_freepages
= 0;
1170 cc
->nr_migratepages
= 0;
1172 INIT_LIST_HEAD(&cc
->freepages
);
1173 INIT_LIST_HEAD(&cc
->migratepages
);
1175 if (cc
->order
== -1 || !compaction_deferred(zone
, cc
->order
))
1176 compact_zone(zone
, cc
);
1178 if (cc
->order
> 0) {
1179 if (zone_watermark_ok(zone
, cc
->order
,
1180 low_wmark_pages(zone
), 0, 0))
1181 compaction_defer_reset(zone
, cc
->order
, false);
1184 VM_BUG_ON(!list_empty(&cc
->freepages
));
1185 VM_BUG_ON(!list_empty(&cc
->migratepages
));
1189 void compact_pgdat(pg_data_t
*pgdat
, int order
)
1191 struct compact_control cc
= {
1199 __compact_pgdat(pgdat
, &cc
);
1202 static void compact_node(int nid
)
1204 struct compact_control cc
= {
1207 .ignore_skip_hint
= true,
1210 __compact_pgdat(NODE_DATA(nid
), &cc
);
1213 /* Compact all nodes in the system */
1214 static void compact_nodes(void)
1218 /* Flush pending updates to the LRU lists */
1219 lru_add_drain_all();
1221 for_each_online_node(nid
)
1225 /* The written value is actually unused, all memory is compacted */
1226 int sysctl_compact_memory
;
1228 /* This is the entry point for compacting all nodes via /proc/sys/vm */
1229 int sysctl_compaction_handler(struct ctl_table
*table
, int write
,
1230 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
1238 int sysctl_extfrag_handler(struct ctl_table
*table
, int write
,
1239 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
1241 proc_dointvec_minmax(table
, write
, buffer
, length
, ppos
);
1246 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1247 static ssize_t
sysfs_compact_node(struct device
*dev
,
1248 struct device_attribute
*attr
,
1249 const char *buf
, size_t count
)
1253 if (nid
>= 0 && nid
< nr_node_ids
&& node_online(nid
)) {
1254 /* Flush pending updates to the LRU lists */
1255 lru_add_drain_all();
1262 static DEVICE_ATTR(compact
, S_IWUSR
, NULL
, sysfs_compact_node
);
1264 int compaction_register_node(struct node
*node
)
1266 return device_create_file(&node
->dev
, &dev_attr_compact
);
1269 void compaction_unregister_node(struct node
*node
)
1271 return device_remove_file(&node
->dev
, &dev_attr_compact
);
1273 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
1275 #endif /* CONFIG_COMPACTION */