2 * linux/mm/compaction.c
4 * Memory compaction for the reduction of external fragmentation. Note that
5 * this heavily depends upon page migration to do all the real heavy
8 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
10 #include <linux/swap.h>
11 #include <linux/migrate.h>
12 #include <linux/compaction.h>
13 #include <linux/mm_inline.h>
14 #include <linux/backing-dev.h>
15 #include <linux/sysctl.h>
16 #include <linux/sysfs.h>
17 #include <linux/balloon_compaction.h>
18 #include <linux/page-isolation.h>
21 #ifdef CONFIG_COMPACTION
22 static inline void count_compact_event(enum vm_event_item item
)
27 static inline void count_compact_events(enum vm_event_item item
, long delta
)
29 count_vm_events(item
, delta
);
32 #define count_compact_event(item) do { } while (0)
33 #define count_compact_events(item, delta) do { } while (0)
36 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
38 #define CREATE_TRACE_POINTS
39 #include <trace/events/compaction.h>
41 static unsigned long release_freepages(struct list_head
*freelist
)
43 struct page
*page
, *next
;
44 unsigned long count
= 0;
46 list_for_each_entry_safe(page
, next
, freelist
, lru
) {
55 static void map_pages(struct list_head
*list
)
59 list_for_each_entry(page
, list
, lru
) {
60 arch_alloc_page(page
, 0);
61 kernel_map_pages(page
, 1, 1);
65 static inline bool migrate_async_suitable(int migratetype
)
67 return is_migrate_cma(migratetype
) || migratetype
== MIGRATE_MOVABLE
;
70 #ifdef CONFIG_COMPACTION
71 /* Returns true if the pageblock should be scanned for pages to isolate. */
72 static inline bool isolation_suitable(struct compact_control
*cc
,
75 if (cc
->ignore_skip_hint
)
78 return !get_pageblock_skip(page
);
82 * This function is called to clear all cached information on pageblocks that
83 * should be skipped for page isolation when the migrate and free page scanner
86 static void __reset_isolation_suitable(struct zone
*zone
)
88 unsigned long start_pfn
= zone
->zone_start_pfn
;
89 unsigned long end_pfn
= zone_end_pfn(zone
);
92 zone
->compact_cached_migrate_pfn
= start_pfn
;
93 zone
->compact_cached_free_pfn
= end_pfn
;
94 zone
->compact_blockskip_flush
= false;
96 /* Walk the zone and mark every pageblock as suitable for isolation */
97 for (pfn
= start_pfn
; pfn
< end_pfn
; pfn
+= pageblock_nr_pages
) {
105 page
= pfn_to_page(pfn
);
106 if (zone
!= page_zone(page
))
109 clear_pageblock_skip(page
);
113 void reset_isolation_suitable(pg_data_t
*pgdat
)
117 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
118 struct zone
*zone
= &pgdat
->node_zones
[zoneid
];
119 if (!populated_zone(zone
))
122 /* Only flush if a full compaction finished recently */
123 if (zone
->compact_blockskip_flush
)
124 __reset_isolation_suitable(zone
);
129 * If no pages were isolated then mark this pageblock to be skipped in the
130 * future. The information is later cleared by __reset_isolation_suitable().
132 static void update_pageblock_skip(struct compact_control
*cc
,
133 struct page
*page
, unsigned long nr_isolated
,
134 bool migrate_scanner
)
136 struct zone
*zone
= cc
->zone
;
138 if (cc
->ignore_skip_hint
)
145 unsigned long pfn
= page_to_pfn(page
);
146 set_pageblock_skip(page
);
148 /* Update where compaction should restart */
149 if (migrate_scanner
) {
150 if (!cc
->finished_update_migrate
&&
151 pfn
> zone
->compact_cached_migrate_pfn
)
152 zone
->compact_cached_migrate_pfn
= pfn
;
154 if (!cc
->finished_update_free
&&
155 pfn
< zone
->compact_cached_free_pfn
)
156 zone
->compact_cached_free_pfn
= pfn
;
161 static inline bool isolation_suitable(struct compact_control
*cc
,
167 static void update_pageblock_skip(struct compact_control
*cc
,
168 struct page
*page
, unsigned long nr_isolated
,
169 bool migrate_scanner
)
172 #endif /* CONFIG_COMPACTION */
174 static inline bool should_release_lock(spinlock_t
*lock
)
176 return need_resched() || spin_is_contended(lock
);
180 * Compaction requires the taking of some coarse locks that are potentially
181 * very heavily contended. Check if the process needs to be scheduled or
182 * if the lock is contended. For async compaction, back out in the event
183 * if contention is severe. For sync compaction, schedule.
185 * Returns true if the lock is held.
186 * Returns false if the lock is released and compaction should abort
188 static bool compact_checklock_irqsave(spinlock_t
*lock
, unsigned long *flags
,
189 bool locked
, struct compact_control
*cc
)
191 if (should_release_lock(lock
)) {
193 spin_unlock_irqrestore(lock
, *flags
);
197 /* async aborts if taking too long or contended */
199 cc
->contended
= true;
207 spin_lock_irqsave(lock
, *flags
);
211 static inline bool compact_trylock_irqsave(spinlock_t
*lock
,
212 unsigned long *flags
, struct compact_control
*cc
)
214 return compact_checklock_irqsave(lock
, flags
, false, cc
);
217 /* Returns true if the page is within a block suitable for migration to */
218 static bool suitable_migration_target(struct page
*page
)
220 int migratetype
= get_pageblock_migratetype(page
);
222 /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
223 if (migratetype
== MIGRATE_RESERVE
)
226 if (is_migrate_isolate(migratetype
))
229 /* If the page is a large free page, then allow migration */
230 if (PageBuddy(page
) && page_order(page
) >= pageblock_order
)
233 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
234 if (migrate_async_suitable(migratetype
))
237 /* Otherwise skip the block */
242 * Isolate free pages onto a private freelist. If @strict is true, will abort
243 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
244 * (even though it may still end up isolating some pages).
246 static unsigned long isolate_freepages_block(struct compact_control
*cc
,
247 unsigned long blockpfn
,
248 unsigned long end_pfn
,
249 struct list_head
*freelist
,
252 int nr_scanned
= 0, total_isolated
= 0;
253 struct page
*cursor
, *valid_page
= NULL
;
254 unsigned long nr_strict_required
= end_pfn
- blockpfn
;
258 cursor
= pfn_to_page(blockpfn
);
260 /* Isolate free pages. */
261 for (; blockpfn
< end_pfn
; blockpfn
++, cursor
++) {
263 struct page
*page
= cursor
;
266 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
&& !suitable_migration_target(page
))
290 /* Recheck this is a buddy page under lock */
291 if (!PageBuddy(page
))
294 /* Found a free page, break it into order-0 pages */
295 isolated
= split_free_page(page
);
296 if (!isolated
&& strict
)
298 total_isolated
+= isolated
;
299 for (i
= 0; i
< isolated
; i
++) {
300 list_add(&page
->lru
, freelist
);
304 /* If a page was split, advance to the end of it */
306 blockpfn
+= isolated
- 1;
307 cursor
+= isolated
- 1;
311 trace_mm_compaction_isolate_freepages(nr_scanned
, total_isolated
);
314 * If strict isolation is requested by CMA then check that all the
315 * pages requested were isolated. If there were any failures, 0 is
316 * returned and CMA will fail.
318 if (strict
&& nr_strict_required
> total_isolated
)
322 spin_unlock_irqrestore(&cc
->zone
->lock
, flags
);
324 /* Update the pageblock-skip if the whole pageblock was scanned */
325 if (blockpfn
== end_pfn
)
326 update_pageblock_skip(cc
, valid_page
, total_isolated
, false);
328 count_compact_events(COMPACTFREE_SCANNED
, nr_scanned
);
330 count_compact_events(COMPACTISOLATED
, total_isolated
);
331 return total_isolated
;
335 * isolate_freepages_range() - isolate free pages.
336 * @start_pfn: The first PFN to start isolating.
337 * @end_pfn: The one-past-last PFN.
339 * Non-free pages, invalid PFNs, or zone boundaries within the
340 * [start_pfn, end_pfn) range are considered errors, cause function to
341 * undo its actions and return zero.
343 * Otherwise, function returns one-past-the-last PFN of isolated page
344 * (which may be greater then end_pfn if end fell in a middle of
348 isolate_freepages_range(struct compact_control
*cc
,
349 unsigned long start_pfn
, unsigned long end_pfn
)
351 unsigned long isolated
, pfn
, block_end_pfn
;
354 for (pfn
= start_pfn
; pfn
< end_pfn
; pfn
+= isolated
) {
355 if (!pfn_valid(pfn
) || cc
->zone
!= page_zone(pfn_to_page(pfn
)))
359 * On subsequent iterations ALIGN() is actually not needed,
360 * but we keep it that we not to complicate the code.
362 block_end_pfn
= ALIGN(pfn
+ 1, pageblock_nr_pages
);
363 block_end_pfn
= min(block_end_pfn
, end_pfn
);
365 isolated
= isolate_freepages_block(cc
, pfn
, block_end_pfn
,
369 * In strict mode, isolate_freepages_block() returns 0 if
370 * there are any holes in the block (ie. invalid PFNs or
377 * If we managed to isolate pages, it is always (1 << n) *
378 * pageblock_nr_pages for some non-negative n. (Max order
379 * page may span two pageblocks).
383 /* split_free_page does not map the pages */
384 map_pages(&freelist
);
387 /* Loop terminated early, cleanup. */
388 release_freepages(&freelist
);
392 /* We don't use freelists for anything. */
396 /* Update the number of anon and file isolated pages in the zone */
397 static void acct_isolated(struct zone
*zone
, bool locked
, struct compact_control
*cc
)
400 unsigned int count
[2] = { 0, };
402 list_for_each_entry(page
, &cc
->migratepages
, lru
)
403 count
[!!page_is_file_cache(page
)]++;
405 /* If locked we can use the interrupt unsafe versions */
407 __mod_zone_page_state(zone
, NR_ISOLATED_ANON
, count
[0]);
408 __mod_zone_page_state(zone
, NR_ISOLATED_FILE
, count
[1]);
410 mod_zone_page_state(zone
, NR_ISOLATED_ANON
, count
[0]);
411 mod_zone_page_state(zone
, NR_ISOLATED_FILE
, count
[1]);
415 /* Similar to reclaim, but different enough that they don't share logic */
416 static bool too_many_isolated(struct zone
*zone
)
418 unsigned long active
, inactive
, isolated
;
420 inactive
= zone_page_state(zone
, NR_INACTIVE_FILE
) +
421 zone_page_state(zone
, NR_INACTIVE_ANON
);
422 active
= zone_page_state(zone
, NR_ACTIVE_FILE
) +
423 zone_page_state(zone
, NR_ACTIVE_ANON
);
424 isolated
= zone_page_state(zone
, NR_ISOLATED_FILE
) +
425 zone_page_state(zone
, NR_ISOLATED_ANON
);
427 return isolated
> (inactive
+ active
) / 2;
431 * isolate_migratepages_range() - isolate all migrate-able pages in range.
432 * @zone: Zone pages are in.
433 * @cc: Compaction control structure.
434 * @low_pfn: The first PFN of the range.
435 * @end_pfn: The one-past-the-last PFN of the range.
436 * @unevictable: true if it allows to isolate unevictable pages
438 * Isolate all pages that can be migrated from the range specified by
439 * [low_pfn, end_pfn). Returns zero if there is a fatal signal
440 * pending), otherwise PFN of the first page that was not scanned
441 * (which may be both less, equal to or more then end_pfn).
443 * Assumes that cc->migratepages is empty and cc->nr_migratepages is
446 * Apart from cc->migratepages and cc->nr_migratetypes this function
447 * does not modify any cc's fields, in particular it does not modify
448 * (or read for that matter) cc->migrate_pfn.
451 isolate_migratepages_range(struct zone
*zone
, struct compact_control
*cc
,
452 unsigned long low_pfn
, unsigned long end_pfn
, bool unevictable
)
454 unsigned long last_pageblock_nr
= 0, pageblock_nr
;
455 unsigned long nr_scanned
= 0, nr_isolated
= 0;
456 struct list_head
*migratelist
= &cc
->migratepages
;
457 isolate_mode_t mode
= 0;
458 struct lruvec
*lruvec
;
461 struct page
*page
= NULL
, *valid_page
= NULL
;
462 bool skipped_async_unsuitable
= false;
465 * Ensure that there are not too many pages isolated from the LRU
466 * list by either parallel reclaimers or compaction. If there are,
467 * delay for some time until fewer pages are isolated
469 while (unlikely(too_many_isolated(zone
))) {
470 /* async migration should just abort */
474 congestion_wait(BLK_RW_ASYNC
, HZ
/10);
476 if (fatal_signal_pending(current
))
480 /* Time to isolate some pages for migration */
482 for (; low_pfn
< end_pfn
; low_pfn
++) {
483 /* give a chance to irqs before checking need_resched() */
484 if (locked
&& !((low_pfn
+1) % SWAP_CLUSTER_MAX
)) {
485 if (should_release_lock(&zone
->lru_lock
)) {
486 spin_unlock_irqrestore(&zone
->lru_lock
, flags
);
492 * migrate_pfn does not necessarily start aligned to a
493 * pageblock. Ensure that pfn_valid is called when moving
494 * into a new MAX_ORDER_NR_PAGES range in case of large
495 * memory holes within the zone
497 if ((low_pfn
& (MAX_ORDER_NR_PAGES
- 1)) == 0) {
498 if (!pfn_valid(low_pfn
)) {
499 low_pfn
+= MAX_ORDER_NR_PAGES
- 1;
504 if (!pfn_valid_within(low_pfn
))
509 * Get the page and ensure the page is within the same zone.
510 * See the comment in isolate_freepages about overlapping
511 * nodes. It is deliberate that the new zone lock is not taken
512 * as memory compaction should not move pages between nodes.
514 page
= pfn_to_page(low_pfn
);
515 if (page_zone(page
) != zone
)
521 /* If isolation recently failed, do not retry */
522 pageblock_nr
= low_pfn
>> pageblock_order
;
523 if (!isolation_suitable(cc
, page
))
531 * For async migration, also only scan in MOVABLE blocks. Async
532 * migration is optimistic to see if the minimum amount of work
533 * satisfies the allocation
535 if (!cc
->sync
&& last_pageblock_nr
!= pageblock_nr
&&
536 !migrate_async_suitable(get_pageblock_migratetype(page
))) {
537 cc
->finished_update_migrate
= true;
538 skipped_async_unsuitable
= true;
543 * Check may be lockless but that's ok as we recheck later.
544 * It's possible to migrate LRU pages and balloon pages
545 * Skip any other type of page
547 if (!PageLRU(page
)) {
548 if (unlikely(balloon_page_movable(page
))) {
549 if (locked
&& balloon_page_isolate(page
)) {
550 /* Successfully isolated */
551 cc
->finished_update_migrate
= true;
552 list_add(&page
->lru
, migratelist
);
553 cc
->nr_migratepages
++;
555 goto check_compact_cluster
;
562 * PageLRU is set. lru_lock normally excludes isolation
563 * splitting and collapsing (collapsing has already happened
564 * if PageLRU is set) but the lock is not necessarily taken
565 * here and it is wasteful to take it just to check transhuge.
566 * Check TransHuge without lock and skip the whole pageblock if
567 * it's either a transhuge or hugetlbfs page, as calling
568 * compound_order() without preventing THP from splitting the
569 * page underneath us may return surprising results.
571 if (PageTransHuge(page
)) {
574 low_pfn
+= (1 << compound_order(page
)) - 1;
578 /* Check if it is ok to still hold the lock */
579 locked
= compact_checklock_irqsave(&zone
->lru_lock
, &flags
,
581 if (!locked
|| fatal_signal_pending(current
))
584 /* Recheck PageLRU and PageTransHuge under lock */
587 if (PageTransHuge(page
)) {
588 low_pfn
+= (1 << compound_order(page
)) - 1;
593 mode
|= ISOLATE_ASYNC_MIGRATE
;
596 mode
|= ISOLATE_UNEVICTABLE
;
598 lruvec
= mem_cgroup_page_lruvec(page
, zone
);
600 /* Try isolate the page */
601 if (__isolate_lru_page(page
, mode
) != 0)
604 VM_BUG_ON(PageTransCompound(page
));
606 /* Successfully isolated */
607 cc
->finished_update_migrate
= true;
608 del_page_from_lru_list(page
, lruvec
, page_lru(page
));
609 list_add(&page
->lru
, migratelist
);
610 cc
->nr_migratepages
++;
613 check_compact_cluster
:
614 /* Avoid isolating too much */
615 if (cc
->nr_migratepages
== COMPACT_CLUSTER_MAX
) {
623 low_pfn
= ALIGN(low_pfn
+ 1, pageblock_nr_pages
) - 1;
624 last_pageblock_nr
= pageblock_nr
;
627 acct_isolated(zone
, locked
, cc
);
630 spin_unlock_irqrestore(&zone
->lru_lock
, flags
);
633 * Update the pageblock-skip information and cached scanner pfn,
634 * if the whole pageblock was scanned without isolating any page.
635 * This is not done when pageblock was skipped due to being unsuitable
636 * for async compaction, so that eventual sync compaction can try.
638 if (low_pfn
== end_pfn
&& !skipped_async_unsuitable
)
639 update_pageblock_skip(cc
, valid_page
, nr_isolated
, true);
641 trace_mm_compaction_isolate_migratepages(nr_scanned
, nr_isolated
);
643 count_compact_events(COMPACTMIGRATE_SCANNED
, nr_scanned
);
645 count_compact_events(COMPACTISOLATED
, nr_isolated
);
650 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
651 #ifdef CONFIG_COMPACTION
653 * Based on information in the current compact_control, find blocks
654 * suitable for isolating free pages from and then isolate them.
656 static void isolate_freepages(struct zone
*zone
,
657 struct compact_control
*cc
)
660 unsigned long high_pfn
, low_pfn
, pfn
, z_end_pfn
, end_pfn
;
661 int nr_freepages
= cc
->nr_freepages
;
662 struct list_head
*freelist
= &cc
->freepages
;
665 * Initialise the free scanner. The starting point is where we last
666 * scanned from (or the end of the zone if starting). The low point
667 * is the end of the pageblock the migration scanner is using.
670 low_pfn
= ALIGN(cc
->migrate_pfn
+ 1, pageblock_nr_pages
);
673 * Take care that if the migration scanner is at the end of the zone
674 * that the free scanner does not accidentally move to the next zone
675 * in the next isolation cycle.
677 high_pfn
= min(low_pfn
, pfn
);
679 z_end_pfn
= zone_end_pfn(zone
);
682 * Isolate free pages until enough are available to migrate the
683 * pages on cc->migratepages. We stop searching if the migrate
684 * and free page scanners meet or enough free pages are isolated.
686 for (; pfn
>= low_pfn
&& cc
->nr_migratepages
> nr_freepages
;
687 pfn
-= pageblock_nr_pages
) {
688 unsigned long isolated
;
691 * This can iterate a massively long zone without finding any
692 * suitable migration targets, so periodically check if we need
701 * Check for overlapping nodes/zones. It's possible on some
702 * configurations to have a setup like
704 * i.e. it's possible that all pages within a zones range of
705 * pages do not belong to a single zone.
707 page
= pfn_to_page(pfn
);
708 if (page_zone(page
) != zone
)
711 /* Check the block is suitable for migration */
712 if (!suitable_migration_target(page
))
715 /* If isolation recently failed, do not retry */
716 if (!isolation_suitable(cc
, page
))
719 /* Found a block suitable for isolating free pages from */
723 * As pfn may not start aligned, pfn+pageblock_nr_page
724 * may cross a MAX_ORDER_NR_PAGES boundary and miss
725 * a pfn_valid check. Ensure isolate_freepages_block()
726 * only scans within a pageblock
728 end_pfn
= ALIGN(pfn
+ 1, pageblock_nr_pages
);
729 end_pfn
= min(end_pfn
, z_end_pfn
);
730 isolated
= isolate_freepages_block(cc
, pfn
, end_pfn
,
732 nr_freepages
+= isolated
;
735 * Record the highest PFN we isolated pages from. When next
736 * looking for free pages, the search will restart here as
737 * page migration may have returned some pages to the allocator
740 cc
->finished_update_free
= true;
741 high_pfn
= max(high_pfn
, pfn
);
745 /* split_free_page does not map the pages */
749 * If we crossed the migrate scanner, we want to keep it that way
750 * so that compact_finished() may detect this
753 cc
->free_pfn
= max(pfn
, zone
->zone_start_pfn
);
755 cc
->free_pfn
= high_pfn
;
756 cc
->nr_freepages
= nr_freepages
;
760 * This is a migrate-callback that "allocates" freepages by taking pages
761 * from the isolated freelists in the block we are migrating to.
763 static struct page
*compaction_alloc(struct page
*migratepage
,
767 struct compact_control
*cc
= (struct compact_control
*)data
;
768 struct page
*freepage
;
770 /* Isolate free pages if necessary */
771 if (list_empty(&cc
->freepages
)) {
772 isolate_freepages(cc
->zone
, cc
);
774 if (list_empty(&cc
->freepages
))
778 freepage
= list_entry(cc
->freepages
.next
, struct page
, lru
);
779 list_del(&freepage
->lru
);
786 * We cannot control nr_migratepages and nr_freepages fully when migration is
787 * running as migrate_pages() has no knowledge of compact_control. When
788 * migration is complete, we count the number of pages on the lists by hand.
790 static void update_nr_listpages(struct compact_control
*cc
)
792 int nr_migratepages
= 0;
793 int nr_freepages
= 0;
796 list_for_each_entry(page
, &cc
->migratepages
, lru
)
798 list_for_each_entry(page
, &cc
->freepages
, lru
)
801 cc
->nr_migratepages
= nr_migratepages
;
802 cc
->nr_freepages
= nr_freepages
;
805 /* possible outcome of isolate_migratepages */
807 ISOLATE_ABORT
, /* Abort compaction now */
808 ISOLATE_NONE
, /* No pages isolated, continue scanning */
809 ISOLATE_SUCCESS
, /* Pages isolated, migrate */
813 * Isolate all pages that can be migrated from the block pointed to by
814 * the migrate scanner within compact_control.
816 static isolate_migrate_t
isolate_migratepages(struct zone
*zone
,
817 struct compact_control
*cc
)
819 unsigned long low_pfn
, end_pfn
;
821 /* Do not scan outside zone boundaries */
822 low_pfn
= max(cc
->migrate_pfn
, zone
->zone_start_pfn
);
824 /* Only scan within a pageblock boundary */
825 end_pfn
= ALIGN(low_pfn
+ 1, pageblock_nr_pages
);
827 /* Do not cross the free scanner or scan within a memory hole */
828 if (end_pfn
> cc
->free_pfn
|| !pfn_valid(low_pfn
)) {
829 cc
->migrate_pfn
= end_pfn
;
833 /* Perform the isolation */
834 low_pfn
= isolate_migratepages_range(zone
, cc
, low_pfn
, end_pfn
, false);
835 if (!low_pfn
|| cc
->contended
)
836 return ISOLATE_ABORT
;
838 cc
->migrate_pfn
= low_pfn
;
840 return ISOLATE_SUCCESS
;
843 static int compact_finished(struct zone
*zone
,
844 struct compact_control
*cc
)
847 unsigned long watermark
;
849 if (fatal_signal_pending(current
))
850 return COMPACT_PARTIAL
;
852 /* Compaction run completes if the migrate and free scanner meet */
853 if (cc
->free_pfn
<= cc
->migrate_pfn
) {
854 /* Let the next compaction start anew. */
855 zone
->compact_cached_migrate_pfn
= zone
->zone_start_pfn
;
856 zone
->compact_cached_free_pfn
= zone_end_pfn(zone
);
859 * Mark that the PG_migrate_skip information should be cleared
860 * by kswapd when it goes to sleep. kswapd does not set the
861 * flag itself as the decision to be clear should be directly
862 * based on an allocation request.
864 if (!current_is_kswapd())
865 zone
->compact_blockskip_flush
= true;
867 return COMPACT_COMPLETE
;
871 * order == -1 is expected when compacting via
872 * /proc/sys/vm/compact_memory
875 return COMPACT_CONTINUE
;
877 /* Compaction run is not finished if the watermark is not met */
878 watermark
= low_wmark_pages(zone
);
879 watermark
+= (1 << cc
->order
);
881 if (!zone_watermark_ok(zone
, cc
->order
, watermark
, 0, 0))
882 return COMPACT_CONTINUE
;
884 /* Direct compactor: Is a suitable page free? */
885 for (order
= cc
->order
; order
< MAX_ORDER
; order
++) {
886 struct free_area
*area
= &zone
->free_area
[order
];
888 /* Job done if page is free of the right migratetype */
889 if (!list_empty(&area
->free_list
[cc
->migratetype
]))
890 return COMPACT_PARTIAL
;
892 /* Job done if allocation would set block type */
893 if (cc
->order
>= pageblock_order
&& area
->nr_free
)
894 return COMPACT_PARTIAL
;
897 return COMPACT_CONTINUE
;
901 * compaction_suitable: Is this suitable to run compaction on this zone now?
903 * COMPACT_SKIPPED - If there are too few free pages for compaction
904 * COMPACT_PARTIAL - If the allocation would succeed without compaction
905 * COMPACT_CONTINUE - If compaction should run now
907 unsigned long compaction_suitable(struct zone
*zone
, int order
)
910 unsigned long watermark
;
913 * order == -1 is expected when compacting via
914 * /proc/sys/vm/compact_memory
917 return COMPACT_CONTINUE
;
920 * Watermarks for order-0 must be met for compaction. Note the 2UL.
921 * This is because during migration, copies of pages need to be
922 * allocated and for a short time, the footprint is higher
924 watermark
= low_wmark_pages(zone
) + (2UL << order
);
925 if (!zone_watermark_ok(zone
, 0, watermark
, 0, 0))
926 return COMPACT_SKIPPED
;
929 * fragmentation index determines if allocation failures are due to
930 * low memory or external fragmentation
932 * index of -1000 implies allocations might succeed depending on
934 * index towards 0 implies failure is due to lack of memory
935 * index towards 1000 implies failure is due to fragmentation
937 * Only compact if a failure would be due to fragmentation.
939 fragindex
= fragmentation_index(zone
, order
);
940 if (fragindex
>= 0 && fragindex
<= sysctl_extfrag_threshold
)
941 return COMPACT_SKIPPED
;
943 if (fragindex
== -1000 && zone_watermark_ok(zone
, order
, watermark
,
945 return COMPACT_PARTIAL
;
947 return COMPACT_CONTINUE
;
950 static int compact_zone(struct zone
*zone
, struct compact_control
*cc
)
953 unsigned long start_pfn
= zone
->zone_start_pfn
;
954 unsigned long end_pfn
= zone_end_pfn(zone
);
956 ret
= compaction_suitable(zone
, cc
->order
);
958 case COMPACT_PARTIAL
:
959 case COMPACT_SKIPPED
:
960 /* Compaction is likely to fail */
962 case COMPACT_CONTINUE
:
963 /* Fall through to compaction */
968 * Clear pageblock skip if there were failures recently and compaction
969 * is about to be retried after being deferred. kswapd does not do
970 * this reset as it'll reset the cached information when going to sleep.
972 if (compaction_restarting(zone
, cc
->order
) && !current_is_kswapd())
973 __reset_isolation_suitable(zone
);
976 * Setup to move all movable pages to the end of the zone. Used cached
977 * information on where the scanners should start but check that it
978 * is initialised by ensuring the values are within zone boundaries.
980 cc
->migrate_pfn
= zone
->compact_cached_migrate_pfn
;
981 cc
->free_pfn
= zone
->compact_cached_free_pfn
;
982 if (cc
->free_pfn
< start_pfn
|| cc
->free_pfn
> end_pfn
) {
983 cc
->free_pfn
= end_pfn
& ~(pageblock_nr_pages
-1);
984 zone
->compact_cached_free_pfn
= cc
->free_pfn
;
986 if (cc
->migrate_pfn
< start_pfn
|| cc
->migrate_pfn
> end_pfn
) {
987 cc
->migrate_pfn
= start_pfn
;
988 zone
->compact_cached_migrate_pfn
= cc
->migrate_pfn
;
991 trace_mm_compaction_begin(start_pfn
, cc
->migrate_pfn
, cc
->free_pfn
, end_pfn
);
993 migrate_prep_local();
995 while ((ret
= compact_finished(zone
, cc
)) == COMPACT_CONTINUE
) {
996 unsigned long nr_migrate
, nr_remaining
;
999 switch (isolate_migratepages(zone
, cc
)) {
1001 ret
= COMPACT_PARTIAL
;
1002 putback_movable_pages(&cc
->migratepages
);
1003 cc
->nr_migratepages
= 0;
1007 case ISOLATE_SUCCESS
:
1011 nr_migrate
= cc
->nr_migratepages
;
1012 err
= migrate_pages(&cc
->migratepages
, compaction_alloc
,
1014 cc
->sync
? MIGRATE_SYNC_LIGHT
: MIGRATE_ASYNC
,
1016 update_nr_listpages(cc
);
1017 nr_remaining
= cc
->nr_migratepages
;
1019 trace_mm_compaction_migratepages(nr_migrate
- nr_remaining
,
1022 /* Release isolated pages not migrated */
1024 putback_movable_pages(&cc
->migratepages
);
1025 cc
->nr_migratepages
= 0;
1027 * migrate_pages() may return -ENOMEM when scanners meet
1028 * and we want compact_finished() to detect it
1030 if (err
== -ENOMEM
&& cc
->free_pfn
> cc
->migrate_pfn
) {
1031 ret
= COMPACT_PARTIAL
;
1038 /* Release free pages and check accounting */
1039 cc
->nr_freepages
-= release_freepages(&cc
->freepages
);
1040 VM_BUG_ON(cc
->nr_freepages
!= 0);
1042 trace_mm_compaction_end(ret
);
1047 static unsigned long compact_zone_order(struct zone
*zone
,
1048 int order
, gfp_t gfp_mask
,
1049 bool sync
, bool *contended
)
1052 struct compact_control cc
= {
1054 .nr_migratepages
= 0,
1056 .migratetype
= allocflags_to_migratetype(gfp_mask
),
1060 INIT_LIST_HEAD(&cc
.freepages
);
1061 INIT_LIST_HEAD(&cc
.migratepages
);
1063 ret
= compact_zone(zone
, &cc
);
1065 VM_BUG_ON(!list_empty(&cc
.freepages
));
1066 VM_BUG_ON(!list_empty(&cc
.migratepages
));
1068 *contended
= cc
.contended
;
1072 int sysctl_extfrag_threshold
= 500;
1075 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1076 * @zonelist: The zonelist used for the current allocation
1077 * @order: The order of the current allocation
1078 * @gfp_mask: The GFP mask of the current allocation
1079 * @nodemask: The allowed nodes to allocate from
1080 * @sync: Whether migration is synchronous or not
1081 * @contended: Return value that is true if compaction was aborted due to lock contention
1082 * @page: Optionally capture a free page of the requested order during compaction
1084 * This is the main entry point for direct page compaction.
1086 unsigned long try_to_compact_pages(struct zonelist
*zonelist
,
1087 int order
, gfp_t gfp_mask
, nodemask_t
*nodemask
,
1088 bool sync
, bool *contended
)
1090 enum zone_type high_zoneidx
= gfp_zone(gfp_mask
);
1091 int may_enter_fs
= gfp_mask
& __GFP_FS
;
1092 int may_perform_io
= gfp_mask
& __GFP_IO
;
1095 int rc
= COMPACT_SKIPPED
;
1096 int alloc_flags
= 0;
1098 /* Check if the GFP flags allow compaction */
1099 if (!order
|| !may_enter_fs
|| !may_perform_io
)
1102 count_compact_event(COMPACTSTALL
);
1105 if (allocflags_to_migratetype(gfp_mask
) == MIGRATE_MOVABLE
)
1106 alloc_flags
|= ALLOC_CMA
;
1108 /* Compact each zone in the list */
1109 for_each_zone_zonelist_nodemask(zone
, z
, zonelist
, high_zoneidx
,
1113 status
= compact_zone_order(zone
, order
, gfp_mask
, sync
,
1115 rc
= max(status
, rc
);
1117 /* If a normal allocation would succeed, stop compacting */
1118 if (zone_watermark_ok(zone
, order
, low_wmark_pages(zone
), 0,
1127 /* Compact all zones within a node */
1128 static void __compact_pgdat(pg_data_t
*pgdat
, struct compact_control
*cc
)
1133 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
1135 zone
= &pgdat
->node_zones
[zoneid
];
1136 if (!populated_zone(zone
))
1139 cc
->nr_freepages
= 0;
1140 cc
->nr_migratepages
= 0;
1142 INIT_LIST_HEAD(&cc
->freepages
);
1143 INIT_LIST_HEAD(&cc
->migratepages
);
1145 if (cc
->order
== -1 || !compaction_deferred(zone
, cc
->order
))
1146 compact_zone(zone
, cc
);
1148 if (cc
->order
> 0) {
1149 if (zone_watermark_ok(zone
, cc
->order
,
1150 low_wmark_pages(zone
), 0, 0))
1151 compaction_defer_reset(zone
, cc
->order
, false);
1152 /* Currently async compaction is never deferred. */
1154 defer_compaction(zone
, cc
->order
);
1157 VM_BUG_ON(!list_empty(&cc
->freepages
));
1158 VM_BUG_ON(!list_empty(&cc
->migratepages
));
1162 void compact_pgdat(pg_data_t
*pgdat
, int order
)
1164 struct compact_control cc
= {
1172 __compact_pgdat(pgdat
, &cc
);
1175 static void compact_node(int nid
)
1177 struct compact_control cc
= {
1182 __compact_pgdat(NODE_DATA(nid
), &cc
);
1185 /* Compact all nodes in the system */
1186 static void compact_nodes(void)
1190 /* Flush pending updates to the LRU lists */
1191 lru_add_drain_all();
1193 for_each_online_node(nid
)
1197 /* The written value is actually unused, all memory is compacted */
1198 int sysctl_compact_memory
;
1200 /* This is the entry point for compacting all nodes via /proc/sys/vm */
1201 int sysctl_compaction_handler(struct ctl_table
*table
, int write
,
1202 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
1210 int sysctl_extfrag_handler(struct ctl_table
*table
, int write
,
1211 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
1213 proc_dointvec_minmax(table
, write
, buffer
, length
, ppos
);
1218 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1219 ssize_t
sysfs_compact_node(struct device
*dev
,
1220 struct device_attribute
*attr
,
1221 const char *buf
, size_t count
)
1225 if (nid
>= 0 && nid
< nr_node_ids
&& node_online(nid
)) {
1226 /* Flush pending updates to the LRU lists */
1227 lru_add_drain_all();
1234 static DEVICE_ATTR(compact
, S_IWUSR
, NULL
, sysfs_compact_node
);
1236 int compaction_register_node(struct node
*node
)
1238 return device_create_file(&node
->dev
, &dev_attr_compact
);
1241 void compaction_unregister_node(struct node
*node
)
1243 return device_remove_file(&node
->dev
, &dev_attr_compact
);
1245 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
1247 #endif /* CONFIG_COMPACTION */