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>
20 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
22 #define CREATE_TRACE_POINTS
23 #include <trace/events/compaction.h>
25 static unsigned long release_freepages(struct list_head
*freelist
)
27 struct page
*page
, *next
;
28 unsigned long count
= 0;
30 list_for_each_entry_safe(page
, next
, freelist
, lru
) {
39 static void map_pages(struct list_head
*list
)
43 list_for_each_entry(page
, list
, lru
) {
44 arch_alloc_page(page
, 0);
45 kernel_map_pages(page
, 1, 1);
49 static inline bool migrate_async_suitable(int migratetype
)
51 return is_migrate_cma(migratetype
) || migratetype
== MIGRATE_MOVABLE
;
54 #ifdef CONFIG_COMPACTION
55 /* Returns true if the pageblock should be scanned for pages to isolate. */
56 static inline bool isolation_suitable(struct compact_control
*cc
,
59 if (cc
->ignore_skip_hint
)
62 return !get_pageblock_skip(page
);
66 * This function is called to clear all cached information on pageblocks that
67 * should be skipped for page isolation when the migrate and free page scanner
70 static void __reset_isolation_suitable(struct zone
*zone
)
72 unsigned long start_pfn
= zone
->zone_start_pfn
;
73 unsigned long end_pfn
= zone
->zone_start_pfn
+ zone
->spanned_pages
;
76 zone
->compact_cached_migrate_pfn
= start_pfn
;
77 zone
->compact_cached_free_pfn
= end_pfn
;
78 zone
->compact_blockskip_flush
= false;
80 /* Walk the zone and mark every pageblock as suitable for isolation */
81 for (pfn
= start_pfn
; pfn
< end_pfn
; pfn
+= pageblock_nr_pages
) {
89 page
= pfn_to_page(pfn
);
90 if (zone
!= page_zone(page
))
93 clear_pageblock_skip(page
);
97 void reset_isolation_suitable(pg_data_t
*pgdat
)
101 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
102 struct zone
*zone
= &pgdat
->node_zones
[zoneid
];
103 if (!populated_zone(zone
))
106 /* Only flush if a full compaction finished recently */
107 if (zone
->compact_blockskip_flush
)
108 __reset_isolation_suitable(zone
);
113 * If no pages were isolated then mark this pageblock to be skipped in the
114 * future. The information is later cleared by __reset_isolation_suitable().
116 static void update_pageblock_skip(struct compact_control
*cc
,
117 struct page
*page
, unsigned long nr_isolated
,
118 bool migrate_scanner
)
120 struct zone
*zone
= cc
->zone
;
125 unsigned long pfn
= page_to_pfn(page
);
126 set_pageblock_skip(page
);
128 /* Update where compaction should restart */
129 if (migrate_scanner
) {
130 if (!cc
->finished_update_migrate
&&
131 pfn
> zone
->compact_cached_migrate_pfn
)
132 zone
->compact_cached_migrate_pfn
= pfn
;
134 if (!cc
->finished_update_free
&&
135 pfn
< zone
->compact_cached_free_pfn
)
136 zone
->compact_cached_free_pfn
= pfn
;
141 static inline bool isolation_suitable(struct compact_control
*cc
,
147 static void update_pageblock_skip(struct compact_control
*cc
,
148 struct page
*page
, unsigned long nr_isolated
,
149 bool migrate_scanner
)
152 #endif /* CONFIG_COMPACTION */
154 static inline bool should_release_lock(spinlock_t
*lock
)
156 return need_resched() || spin_is_contended(lock
);
160 * Compaction requires the taking of some coarse locks that are potentially
161 * very heavily contended. Check if the process needs to be scheduled or
162 * if the lock is contended. For async compaction, back out in the event
163 * if contention is severe. For sync compaction, schedule.
165 * Returns true if the lock is held.
166 * Returns false if the lock is released and compaction should abort
168 static bool compact_checklock_irqsave(spinlock_t
*lock
, unsigned long *flags
,
169 bool locked
, struct compact_control
*cc
)
171 if (should_release_lock(lock
)) {
173 spin_unlock_irqrestore(lock
, *flags
);
177 /* async aborts if taking too long or contended */
179 cc
->contended
= true;
187 spin_lock_irqsave(lock
, *flags
);
191 static inline bool compact_trylock_irqsave(spinlock_t
*lock
,
192 unsigned long *flags
, struct compact_control
*cc
)
194 return compact_checklock_irqsave(lock
, flags
, false, cc
);
197 /* Returns true if the page is within a block suitable for migration to */
198 static bool suitable_migration_target(struct page
*page
)
200 int migratetype
= get_pageblock_migratetype(page
);
202 /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
203 if (migratetype
== MIGRATE_ISOLATE
|| migratetype
== MIGRATE_RESERVE
)
206 /* If the page is a large free page, then allow migration */
207 if (PageBuddy(page
) && page_order(page
) >= pageblock_order
)
210 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
211 if (migrate_async_suitable(migratetype
))
214 /* Otherwise skip the block */
219 * Isolate free pages onto a private freelist. Caller must hold zone->lock.
220 * If @strict is true, will abort returning 0 on any invalid PFNs or non-free
221 * pages inside of the pageblock (even though it may still end up isolating
224 static unsigned long isolate_freepages_block(struct compact_control
*cc
,
225 unsigned long blockpfn
,
226 unsigned long end_pfn
,
227 struct list_head
*freelist
,
230 int nr_scanned
= 0, total_isolated
= 0;
231 struct page
*cursor
, *valid_page
= NULL
;
232 unsigned long nr_strict_required
= end_pfn
- blockpfn
;
236 cursor
= pfn_to_page(blockpfn
);
238 /* Isolate free pages. */
239 for (; blockpfn
< end_pfn
; blockpfn
++, cursor
++) {
241 struct page
*page
= cursor
;
244 if (!pfn_valid_within(blockpfn
))
248 if (!PageBuddy(page
))
252 * The zone lock must be held to isolate freepages.
253 * Unfortunately this is a very coarse lock and can be
254 * heavily contended if there are parallel allocations
255 * or parallel compactions. For async compaction do not
256 * spin on the lock and we acquire the lock as late as
259 locked
= compact_checklock_irqsave(&cc
->zone
->lock
, &flags
,
264 /* Recheck this is a suitable migration target under lock */
265 if (!strict
&& !suitable_migration_target(page
))
268 /* Recheck this is a buddy page under lock */
269 if (!PageBuddy(page
))
272 /* Found a free page, break it into order-0 pages */
273 isolated
= split_free_page(page
);
274 if (!isolated
&& strict
)
276 total_isolated
+= isolated
;
277 for (i
= 0; i
< isolated
; i
++) {
278 list_add(&page
->lru
, freelist
);
282 /* If a page was split, advance to the end of it */
284 blockpfn
+= isolated
- 1;
285 cursor
+= isolated
- 1;
289 trace_mm_compaction_isolate_freepages(nr_scanned
, total_isolated
);
292 * If strict isolation is requested by CMA then check that all the
293 * pages requested were isolated. If there were any failures, 0 is
294 * returned and CMA will fail.
296 if (strict
&& nr_strict_required
> total_isolated
)
300 spin_unlock_irqrestore(&cc
->zone
->lock
, flags
);
302 /* Update the pageblock-skip if the whole pageblock was scanned */
303 if (blockpfn
== end_pfn
)
304 update_pageblock_skip(cc
, valid_page
, total_isolated
, false);
306 count_vm_events(COMPACTFREE_SCANNED
, nr_scanned
);
308 count_vm_events(COMPACTISOLATED
, total_isolated
);
310 return total_isolated
;
314 * isolate_freepages_range() - isolate free pages.
315 * @start_pfn: The first PFN to start isolating.
316 * @end_pfn: The one-past-last PFN.
318 * Non-free pages, invalid PFNs, or zone boundaries within the
319 * [start_pfn, end_pfn) range are considered errors, cause function to
320 * undo its actions and return zero.
322 * Otherwise, function returns one-past-the-last PFN of isolated page
323 * (which may be greater then end_pfn if end fell in a middle of
327 isolate_freepages_range(struct compact_control
*cc
,
328 unsigned long start_pfn
, unsigned long end_pfn
)
330 unsigned long isolated
, pfn
, block_end_pfn
;
333 for (pfn
= start_pfn
; pfn
< end_pfn
; pfn
+= isolated
) {
334 if (!pfn_valid(pfn
) || cc
->zone
!= page_zone(pfn_to_page(pfn
)))
338 * On subsequent iterations ALIGN() is actually not needed,
339 * but we keep it that we not to complicate the code.
341 block_end_pfn
= ALIGN(pfn
+ 1, pageblock_nr_pages
);
342 block_end_pfn
= min(block_end_pfn
, end_pfn
);
344 isolated
= isolate_freepages_block(cc
, pfn
, block_end_pfn
,
348 * In strict mode, isolate_freepages_block() returns 0 if
349 * there are any holes in the block (ie. invalid PFNs or
356 * If we managed to isolate pages, it is always (1 << n) *
357 * pageblock_nr_pages for some non-negative n. (Max order
358 * page may span two pageblocks).
362 /* split_free_page does not map the pages */
363 map_pages(&freelist
);
366 /* Loop terminated early, cleanup. */
367 release_freepages(&freelist
);
371 /* We don't use freelists for anything. */
375 /* Update the number of anon and file isolated pages in the zone */
376 static void acct_isolated(struct zone
*zone
, bool locked
, struct compact_control
*cc
)
379 unsigned int count
[2] = { 0, };
381 list_for_each_entry(page
, &cc
->migratepages
, lru
)
382 count
[!!page_is_file_cache(page
)]++;
384 /* If locked we can use the interrupt unsafe versions */
386 __mod_zone_page_state(zone
, NR_ISOLATED_ANON
, count
[0]);
387 __mod_zone_page_state(zone
, NR_ISOLATED_FILE
, count
[1]);
389 mod_zone_page_state(zone
, NR_ISOLATED_ANON
, count
[0]);
390 mod_zone_page_state(zone
, NR_ISOLATED_FILE
, count
[1]);
394 /* Similar to reclaim, but different enough that they don't share logic */
395 static bool too_many_isolated(struct zone
*zone
)
397 unsigned long active
, inactive
, isolated
;
399 inactive
= zone_page_state(zone
, NR_INACTIVE_FILE
) +
400 zone_page_state(zone
, NR_INACTIVE_ANON
);
401 active
= zone_page_state(zone
, NR_ACTIVE_FILE
) +
402 zone_page_state(zone
, NR_ACTIVE_ANON
);
403 isolated
= zone_page_state(zone
, NR_ISOLATED_FILE
) +
404 zone_page_state(zone
, NR_ISOLATED_ANON
);
406 return isolated
> (inactive
+ active
) / 2;
410 * isolate_migratepages_range() - isolate all migrate-able pages in range.
411 * @zone: Zone pages are in.
412 * @cc: Compaction control structure.
413 * @low_pfn: The first PFN of the range.
414 * @end_pfn: The one-past-the-last PFN of the range.
415 * @unevictable: true if it allows to isolate unevictable pages
417 * Isolate all pages that can be migrated from the range specified by
418 * [low_pfn, end_pfn). Returns zero if there is a fatal signal
419 * pending), otherwise PFN of the first page that was not scanned
420 * (which may be both less, equal to or more then end_pfn).
422 * Assumes that cc->migratepages is empty and cc->nr_migratepages is
425 * Apart from cc->migratepages and cc->nr_migratetypes this function
426 * does not modify any cc's fields, in particular it does not modify
427 * (or read for that matter) cc->migrate_pfn.
430 isolate_migratepages_range(struct zone
*zone
, struct compact_control
*cc
,
431 unsigned long low_pfn
, unsigned long end_pfn
, bool unevictable
)
433 unsigned long last_pageblock_nr
= 0, pageblock_nr
;
434 unsigned long nr_scanned
= 0, nr_isolated
= 0;
435 struct list_head
*migratelist
= &cc
->migratepages
;
436 isolate_mode_t mode
= 0;
437 struct lruvec
*lruvec
;
440 struct page
*page
= NULL
, *valid_page
= NULL
;
443 * Ensure that there are not too many pages isolated from the LRU
444 * list by either parallel reclaimers or compaction. If there are,
445 * delay for some time until fewer pages are isolated
447 while (unlikely(too_many_isolated(zone
))) {
448 /* async migration should just abort */
452 congestion_wait(BLK_RW_ASYNC
, HZ
/10);
454 if (fatal_signal_pending(current
))
458 /* Time to isolate some pages for migration */
460 for (; low_pfn
< end_pfn
; low_pfn
++) {
461 /* give a chance to irqs before checking need_resched() */
462 if (locked
&& !((low_pfn
+1) % SWAP_CLUSTER_MAX
)) {
463 if (should_release_lock(&zone
->lru_lock
)) {
464 spin_unlock_irqrestore(&zone
->lru_lock
, flags
);
470 * migrate_pfn does not necessarily start aligned to a
471 * pageblock. Ensure that pfn_valid is called when moving
472 * into a new MAX_ORDER_NR_PAGES range in case of large
473 * memory holes within the zone
475 if ((low_pfn
& (MAX_ORDER_NR_PAGES
- 1)) == 0) {
476 if (!pfn_valid(low_pfn
)) {
477 low_pfn
+= MAX_ORDER_NR_PAGES
- 1;
482 if (!pfn_valid_within(low_pfn
))
487 * Get the page and ensure the page is within the same zone.
488 * See the comment in isolate_freepages about overlapping
489 * nodes. It is deliberate that the new zone lock is not taken
490 * as memory compaction should not move pages between nodes.
492 page
= pfn_to_page(low_pfn
);
493 if (page_zone(page
) != zone
)
499 /* If isolation recently failed, do not retry */
500 pageblock_nr
= low_pfn
>> pageblock_order
;
501 if (!isolation_suitable(cc
, page
))
509 * For async migration, also only scan in MOVABLE blocks. Async
510 * migration is optimistic to see if the minimum amount of work
511 * satisfies the allocation
513 if (!cc
->sync
&& last_pageblock_nr
!= pageblock_nr
&&
514 !migrate_async_suitable(get_pageblock_migratetype(page
))) {
515 cc
->finished_update_migrate
= true;
520 * Check may be lockless but that's ok as we recheck later.
521 * It's possible to migrate LRU pages and balloon pages
522 * Skip any other type of page
524 if (!PageLRU(page
)) {
525 if (unlikely(balloon_page_movable(page
))) {
526 if (locked
&& balloon_page_isolate(page
)) {
527 /* Successfully isolated */
528 cc
->finished_update_migrate
= true;
529 list_add(&page
->lru
, migratelist
);
530 cc
->nr_migratepages
++;
532 goto check_compact_cluster
;
539 * PageLRU is set. lru_lock normally excludes isolation
540 * splitting and collapsing (collapsing has already happened
541 * if PageLRU is set) but the lock is not necessarily taken
542 * here and it is wasteful to take it just to check transhuge.
543 * Check TransHuge without lock and skip the whole pageblock if
544 * it's either a transhuge or hugetlbfs page, as calling
545 * compound_order() without preventing THP from splitting the
546 * page underneath us may return surprising results.
548 if (PageTransHuge(page
)) {
551 low_pfn
+= (1 << compound_order(page
)) - 1;
555 /* Check if it is ok to still hold the lock */
556 locked
= compact_checklock_irqsave(&zone
->lru_lock
, &flags
,
558 if (!locked
|| fatal_signal_pending(current
))
561 /* Recheck PageLRU and PageTransHuge under lock */
564 if (PageTransHuge(page
)) {
565 low_pfn
+= (1 << compound_order(page
)) - 1;
570 mode
|= ISOLATE_ASYNC_MIGRATE
;
573 mode
|= ISOLATE_UNEVICTABLE
;
575 lruvec
= mem_cgroup_page_lruvec(page
, zone
);
577 /* Try isolate the page */
578 if (__isolate_lru_page(page
, mode
) != 0)
581 VM_BUG_ON(PageTransCompound(page
));
583 /* Successfully isolated */
584 cc
->finished_update_migrate
= true;
585 del_page_from_lru_list(page
, lruvec
, page_lru(page
));
586 list_add(&page
->lru
, migratelist
);
587 cc
->nr_migratepages
++;
590 check_compact_cluster
:
591 /* Avoid isolating too much */
592 if (cc
->nr_migratepages
== COMPACT_CLUSTER_MAX
) {
600 low_pfn
+= pageblock_nr_pages
;
601 low_pfn
= ALIGN(low_pfn
, pageblock_nr_pages
) - 1;
602 last_pageblock_nr
= pageblock_nr
;
605 acct_isolated(zone
, locked
, cc
);
608 spin_unlock_irqrestore(&zone
->lru_lock
, flags
);
610 /* Update the pageblock-skip if the whole pageblock was scanned */
611 if (low_pfn
== end_pfn
)
612 update_pageblock_skip(cc
, valid_page
, nr_isolated
, true);
614 trace_mm_compaction_isolate_migratepages(nr_scanned
, nr_isolated
);
616 count_vm_events(COMPACTMIGRATE_SCANNED
, nr_scanned
);
618 count_vm_events(COMPACTISOLATED
, nr_isolated
);
623 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
624 #ifdef CONFIG_COMPACTION
626 * Based on information in the current compact_control, find blocks
627 * suitable for isolating free pages from and then isolate them.
629 static void isolate_freepages(struct zone
*zone
,
630 struct compact_control
*cc
)
633 unsigned long high_pfn
, low_pfn
, pfn
, zone_end_pfn
, end_pfn
;
634 int nr_freepages
= cc
->nr_freepages
;
635 struct list_head
*freelist
= &cc
->freepages
;
638 * Initialise the free scanner. The starting point is where we last
639 * scanned from (or the end of the zone if starting). The low point
640 * is the end of the pageblock the migration scanner is using.
643 low_pfn
= cc
->migrate_pfn
+ pageblock_nr_pages
;
646 * Take care that if the migration scanner is at the end of the zone
647 * that the free scanner does not accidentally move to the next zone
648 * in the next isolation cycle.
650 high_pfn
= min(low_pfn
, pfn
);
652 zone_end_pfn
= zone
->zone_start_pfn
+ zone
->spanned_pages
;
655 * Isolate free pages until enough are available to migrate the
656 * pages on cc->migratepages. We stop searching if the migrate
657 * and free page scanners meet or enough free pages are isolated.
659 for (; pfn
> low_pfn
&& cc
->nr_migratepages
> nr_freepages
;
660 pfn
-= pageblock_nr_pages
) {
661 unsigned long isolated
;
667 * Check for overlapping nodes/zones. It's possible on some
668 * configurations to have a setup like
670 * i.e. it's possible that all pages within a zones range of
671 * pages do not belong to a single zone.
673 page
= pfn_to_page(pfn
);
674 if (page_zone(page
) != zone
)
677 /* Check the block is suitable for migration */
678 if (!suitable_migration_target(page
))
681 /* If isolation recently failed, do not retry */
682 if (!isolation_suitable(cc
, page
))
685 /* Found a block suitable for isolating free pages from */
689 * As pfn may not start aligned, pfn+pageblock_nr_page
690 * may cross a MAX_ORDER_NR_PAGES boundary and miss
691 * a pfn_valid check. Ensure isolate_freepages_block()
692 * only scans within a pageblock
694 end_pfn
= ALIGN(pfn
+ 1, pageblock_nr_pages
);
695 end_pfn
= min(end_pfn
, zone_end_pfn
);
696 isolated
= isolate_freepages_block(cc
, pfn
, end_pfn
,
698 nr_freepages
+= isolated
;
701 * Record the highest PFN we isolated pages from. When next
702 * looking for free pages, the search will restart here as
703 * page migration may have returned some pages to the allocator
706 cc
->finished_update_free
= true;
707 high_pfn
= max(high_pfn
, pfn
);
711 /* split_free_page does not map the pages */
714 cc
->free_pfn
= high_pfn
;
715 cc
->nr_freepages
= nr_freepages
;
719 * This is a migrate-callback that "allocates" freepages by taking pages
720 * from the isolated freelists in the block we are migrating to.
722 static struct page
*compaction_alloc(struct page
*migratepage
,
726 struct compact_control
*cc
= (struct compact_control
*)data
;
727 struct page
*freepage
;
729 /* Isolate free pages if necessary */
730 if (list_empty(&cc
->freepages
)) {
731 isolate_freepages(cc
->zone
, cc
);
733 if (list_empty(&cc
->freepages
))
737 freepage
= list_entry(cc
->freepages
.next
, struct page
, lru
);
738 list_del(&freepage
->lru
);
745 * We cannot control nr_migratepages and nr_freepages fully when migration is
746 * running as migrate_pages() has no knowledge of compact_control. When
747 * migration is complete, we count the number of pages on the lists by hand.
749 static void update_nr_listpages(struct compact_control
*cc
)
751 int nr_migratepages
= 0;
752 int nr_freepages
= 0;
755 list_for_each_entry(page
, &cc
->migratepages
, lru
)
757 list_for_each_entry(page
, &cc
->freepages
, lru
)
760 cc
->nr_migratepages
= nr_migratepages
;
761 cc
->nr_freepages
= nr_freepages
;
764 /* possible outcome of isolate_migratepages */
766 ISOLATE_ABORT
, /* Abort compaction now */
767 ISOLATE_NONE
, /* No pages isolated, continue scanning */
768 ISOLATE_SUCCESS
, /* Pages isolated, migrate */
772 * Isolate all pages that can be migrated from the block pointed to by
773 * the migrate scanner within compact_control.
775 static isolate_migrate_t
isolate_migratepages(struct zone
*zone
,
776 struct compact_control
*cc
)
778 unsigned long low_pfn
, end_pfn
;
780 /* Do not scan outside zone boundaries */
781 low_pfn
= max(cc
->migrate_pfn
, zone
->zone_start_pfn
);
783 /* Only scan within a pageblock boundary */
784 end_pfn
= ALIGN(low_pfn
+ pageblock_nr_pages
, pageblock_nr_pages
);
786 /* Do not cross the free scanner or scan within a memory hole */
787 if (end_pfn
> cc
->free_pfn
|| !pfn_valid(low_pfn
)) {
788 cc
->migrate_pfn
= end_pfn
;
792 /* Perform the isolation */
793 low_pfn
= isolate_migratepages_range(zone
, cc
, low_pfn
, end_pfn
, false);
794 if (!low_pfn
|| cc
->contended
)
795 return ISOLATE_ABORT
;
797 cc
->migrate_pfn
= low_pfn
;
799 return ISOLATE_SUCCESS
;
802 static int compact_finished(struct zone
*zone
,
803 struct compact_control
*cc
)
805 unsigned long watermark
;
807 if (fatal_signal_pending(current
))
808 return COMPACT_PARTIAL
;
810 /* Compaction run completes if the migrate and free scanner meet */
811 if (cc
->free_pfn
<= cc
->migrate_pfn
) {
813 * Mark that the PG_migrate_skip information should be cleared
814 * by kswapd when it goes to sleep. kswapd does not set the
815 * flag itself as the decision to be clear should be directly
816 * based on an allocation request.
818 if (!current_is_kswapd())
819 zone
->compact_blockskip_flush
= true;
821 return COMPACT_COMPLETE
;
825 * order == -1 is expected when compacting via
826 * /proc/sys/vm/compact_memory
829 return COMPACT_CONTINUE
;
831 /* Compaction run is not finished if the watermark is not met */
832 watermark
= low_wmark_pages(zone
);
833 watermark
+= (1 << cc
->order
);
835 if (!zone_watermark_ok(zone
, cc
->order
, watermark
, 0, 0))
836 return COMPACT_CONTINUE
;
838 /* Direct compactor: Is a suitable page free? */
840 /* Was a suitable page captured? */
842 return COMPACT_PARTIAL
;
845 for (order
= cc
->order
; order
< MAX_ORDER
; order
++) {
846 struct free_area
*area
= &zone
->free_area
[cc
->order
];
847 /* Job done if page is free of the right migratetype */
848 if (!list_empty(&area
->free_list
[cc
->migratetype
]))
849 return COMPACT_PARTIAL
;
851 /* Job done if allocation would set block type */
852 if (cc
->order
>= pageblock_order
&& area
->nr_free
)
853 return COMPACT_PARTIAL
;
857 return COMPACT_CONTINUE
;
861 * compaction_suitable: Is this suitable to run compaction on this zone now?
863 * COMPACT_SKIPPED - If there are too few free pages for compaction
864 * COMPACT_PARTIAL - If the allocation would succeed without compaction
865 * COMPACT_CONTINUE - If compaction should run now
867 unsigned long compaction_suitable(struct zone
*zone
, int order
)
870 unsigned long watermark
;
873 * order == -1 is expected when compacting via
874 * /proc/sys/vm/compact_memory
877 return COMPACT_CONTINUE
;
880 * Watermarks for order-0 must be met for compaction. Note the 2UL.
881 * This is because during migration, copies of pages need to be
882 * allocated and for a short time, the footprint is higher
884 watermark
= low_wmark_pages(zone
) + (2UL << order
);
885 if (!zone_watermark_ok(zone
, 0, watermark
, 0, 0))
886 return COMPACT_SKIPPED
;
889 * fragmentation index determines if allocation failures are due to
890 * low memory or external fragmentation
892 * index of -1000 implies allocations might succeed depending on
894 * index towards 0 implies failure is due to lack of memory
895 * index towards 1000 implies failure is due to fragmentation
897 * Only compact if a failure would be due to fragmentation.
899 fragindex
= fragmentation_index(zone
, order
);
900 if (fragindex
>= 0 && fragindex
<= sysctl_extfrag_threshold
)
901 return COMPACT_SKIPPED
;
903 if (fragindex
== -1000 && zone_watermark_ok(zone
, order
, watermark
,
905 return COMPACT_PARTIAL
;
907 return COMPACT_CONTINUE
;
910 static void compact_capture_page(struct compact_control
*cc
)
913 int mtype
, mtype_low
, mtype_high
;
915 if (!cc
->page
|| *cc
->page
)
919 * For MIGRATE_MOVABLE allocations we capture a suitable page ASAP
920 * regardless of the migratetype of the freelist is is captured from.
921 * This is fine because the order for a high-order MIGRATE_MOVABLE
922 * allocation is typically at least a pageblock size and overall
923 * fragmentation is not impaired. Other allocation types must
924 * capture pages from their own migratelist because otherwise they
925 * could pollute other pageblocks like MIGRATE_MOVABLE with
926 * difficult to move pages and making fragmentation worse overall.
928 if (cc
->migratetype
== MIGRATE_MOVABLE
) {
930 mtype_high
= MIGRATE_PCPTYPES
;
932 mtype_low
= cc
->migratetype
;
933 mtype_high
= cc
->migratetype
+ 1;
936 /* Speculatively examine the free lists without zone lock */
937 for (mtype
= mtype_low
; mtype
< mtype_high
; mtype
++) {
939 for (order
= cc
->order
; order
< MAX_ORDER
; order
++) {
941 struct free_area
*area
;
942 area
= &(cc
->zone
->free_area
[order
]);
943 if (list_empty(&area
->free_list
[mtype
]))
946 /* Take the lock and attempt capture of the page */
947 if (!compact_trylock_irqsave(&cc
->zone
->lock
, &flags
, cc
))
949 if (!list_empty(&area
->free_list
[mtype
])) {
950 page
= list_entry(area
->free_list
[mtype
].next
,
952 if (capture_free_page(page
, cc
->order
, mtype
)) {
953 spin_unlock_irqrestore(&cc
->zone
->lock
,
959 spin_unlock_irqrestore(&cc
->zone
->lock
, flags
);
964 static int compact_zone(struct zone
*zone
, struct compact_control
*cc
)
967 unsigned long start_pfn
= zone
->zone_start_pfn
;
968 unsigned long end_pfn
= zone
->zone_start_pfn
+ zone
->spanned_pages
;
970 ret
= compaction_suitable(zone
, cc
->order
);
972 case COMPACT_PARTIAL
:
973 case COMPACT_SKIPPED
:
974 /* Compaction is likely to fail */
976 case COMPACT_CONTINUE
:
977 /* Fall through to compaction */
982 * Setup to move all movable pages to the end of the zone. Used cached
983 * information on where the scanners should start but check that it
984 * is initialised by ensuring the values are within zone boundaries.
986 cc
->migrate_pfn
= zone
->compact_cached_migrate_pfn
;
987 cc
->free_pfn
= zone
->compact_cached_free_pfn
;
988 if (cc
->free_pfn
< start_pfn
|| cc
->free_pfn
> end_pfn
) {
989 cc
->free_pfn
= end_pfn
& ~(pageblock_nr_pages
-1);
990 zone
->compact_cached_free_pfn
= cc
->free_pfn
;
992 if (cc
->migrate_pfn
< start_pfn
|| cc
->migrate_pfn
> end_pfn
) {
993 cc
->migrate_pfn
= start_pfn
;
994 zone
->compact_cached_migrate_pfn
= cc
->migrate_pfn
;
998 * Clear pageblock skip if there were failures recently and compaction
999 * is about to be retried after being deferred. kswapd does not do
1000 * this reset as it'll reset the cached information when going to sleep.
1002 if (compaction_restarting(zone
, cc
->order
) && !current_is_kswapd())
1003 __reset_isolation_suitable(zone
);
1005 migrate_prep_local();
1007 while ((ret
= compact_finished(zone
, cc
)) == COMPACT_CONTINUE
) {
1008 unsigned long nr_migrate
, nr_remaining
;
1011 switch (isolate_migratepages(zone
, cc
)) {
1013 ret
= COMPACT_PARTIAL
;
1014 putback_movable_pages(&cc
->migratepages
);
1015 cc
->nr_migratepages
= 0;
1019 case ISOLATE_SUCCESS
:
1023 nr_migrate
= cc
->nr_migratepages
;
1024 err
= migrate_pages(&cc
->migratepages
, compaction_alloc
,
1025 (unsigned long)cc
, false,
1026 cc
->sync
? MIGRATE_SYNC_LIGHT
: MIGRATE_ASYNC
,
1028 update_nr_listpages(cc
);
1029 nr_remaining
= cc
->nr_migratepages
;
1031 trace_mm_compaction_migratepages(nr_migrate
- nr_remaining
,
1034 /* Release isolated pages not migrated */
1036 putback_movable_pages(&cc
->migratepages
);
1037 cc
->nr_migratepages
= 0;
1038 if (err
== -ENOMEM
) {
1039 ret
= COMPACT_PARTIAL
;
1044 /* Capture a page now if it is a suitable size */
1045 compact_capture_page(cc
);
1049 /* Release free pages and check accounting */
1050 cc
->nr_freepages
-= release_freepages(&cc
->freepages
);
1051 VM_BUG_ON(cc
->nr_freepages
!= 0);
1056 static unsigned long compact_zone_order(struct zone
*zone
,
1057 int order
, gfp_t gfp_mask
,
1058 bool sync
, bool *contended
,
1062 struct compact_control cc
= {
1064 .nr_migratepages
= 0,
1066 .migratetype
= allocflags_to_migratetype(gfp_mask
),
1071 INIT_LIST_HEAD(&cc
.freepages
);
1072 INIT_LIST_HEAD(&cc
.migratepages
);
1074 ret
= compact_zone(zone
, &cc
);
1076 VM_BUG_ON(!list_empty(&cc
.freepages
));
1077 VM_BUG_ON(!list_empty(&cc
.migratepages
));
1079 *contended
= cc
.contended
;
1083 int sysctl_extfrag_threshold
= 500;
1086 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1087 * @zonelist: The zonelist used for the current allocation
1088 * @order: The order of the current allocation
1089 * @gfp_mask: The GFP mask of the current allocation
1090 * @nodemask: The allowed nodes to allocate from
1091 * @sync: Whether migration is synchronous or not
1092 * @contended: Return value that is true if compaction was aborted due to lock contention
1093 * @page: Optionally capture a free page of the requested order during compaction
1095 * This is the main entry point for direct page compaction.
1097 unsigned long try_to_compact_pages(struct zonelist
*zonelist
,
1098 int order
, gfp_t gfp_mask
, nodemask_t
*nodemask
,
1099 bool sync
, bool *contended
, struct page
**page
)
1101 enum zone_type high_zoneidx
= gfp_zone(gfp_mask
);
1102 int may_enter_fs
= gfp_mask
& __GFP_FS
;
1103 int may_perform_io
= gfp_mask
& __GFP_IO
;
1106 int rc
= COMPACT_SKIPPED
;
1107 int alloc_flags
= 0;
1109 /* Check if the GFP flags allow compaction */
1110 if (!order
|| !may_enter_fs
|| !may_perform_io
)
1113 count_vm_event(COMPACTSTALL
);
1116 if (allocflags_to_migratetype(gfp_mask
) == MIGRATE_MOVABLE
)
1117 alloc_flags
|= ALLOC_CMA
;
1119 /* Compact each zone in the list */
1120 for_each_zone_zonelist_nodemask(zone
, z
, zonelist
, high_zoneidx
,
1124 status
= compact_zone_order(zone
, order
, gfp_mask
, sync
,
1126 rc
= max(status
, rc
);
1128 /* If a normal allocation would succeed, stop compacting */
1129 if (zone_watermark_ok(zone
, order
, low_wmark_pages(zone
), 0,
1138 /* Compact all zones within a node */
1139 static int __compact_pgdat(pg_data_t
*pgdat
, struct compact_control
*cc
)
1144 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
1146 zone
= &pgdat
->node_zones
[zoneid
];
1147 if (!populated_zone(zone
))
1150 cc
->nr_freepages
= 0;
1151 cc
->nr_migratepages
= 0;
1153 INIT_LIST_HEAD(&cc
->freepages
);
1154 INIT_LIST_HEAD(&cc
->migratepages
);
1156 if (cc
->order
== -1 || !compaction_deferred(zone
, cc
->order
))
1157 compact_zone(zone
, cc
);
1159 if (cc
->order
> 0) {
1160 int ok
= zone_watermark_ok(zone
, cc
->order
,
1161 low_wmark_pages(zone
), 0, 0);
1162 if (ok
&& cc
->order
>= zone
->compact_order_failed
)
1163 zone
->compact_order_failed
= cc
->order
+ 1;
1164 /* Currently async compaction is never deferred. */
1165 else if (!ok
&& cc
->sync
)
1166 defer_compaction(zone
, cc
->order
);
1169 VM_BUG_ON(!list_empty(&cc
->freepages
));
1170 VM_BUG_ON(!list_empty(&cc
->migratepages
));
1176 int compact_pgdat(pg_data_t
*pgdat
, int order
)
1178 struct compact_control cc
= {
1184 return __compact_pgdat(pgdat
, &cc
);
1187 static int compact_node(int nid
)
1189 struct compact_control cc
= {
1195 return __compact_pgdat(NODE_DATA(nid
), &cc
);
1198 /* Compact all nodes in the system */
1199 static int compact_nodes(void)
1203 /* Flush pending updates to the LRU lists */
1204 lru_add_drain_all();
1206 for_each_online_node(nid
)
1209 return COMPACT_COMPLETE
;
1212 /* The written value is actually unused, all memory is compacted */
1213 int sysctl_compact_memory
;
1215 /* This is the entry point for compacting all nodes via /proc/sys/vm */
1216 int sysctl_compaction_handler(struct ctl_table
*table
, int write
,
1217 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
1220 return compact_nodes();
1225 int sysctl_extfrag_handler(struct ctl_table
*table
, int write
,
1226 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
1228 proc_dointvec_minmax(table
, write
, buffer
, length
, ppos
);
1233 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1234 ssize_t
sysfs_compact_node(struct device
*dev
,
1235 struct device_attribute
*attr
,
1236 const char *buf
, size_t count
)
1240 if (nid
>= 0 && nid
< nr_node_ids
&& node_online(nid
)) {
1241 /* Flush pending updates to the LRU lists */
1242 lru_add_drain_all();
1249 static DEVICE_ATTR(compact
, S_IWUSR
, NULL
, sysfs_compact_node
);
1251 int compaction_register_node(struct node
*node
)
1253 return device_create_file(&node
->dev
, &dev_attr_compact
);
1256 void compaction_unregister_node(struct node
*node
)
1258 return device_remove_file(&node
->dev
, &dev_attr_compact
);
1260 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
1262 #endif /* CONFIG_COMPACTION */