2 * linux/mm/compaction.c
4 * Memory compaction for the reduction of external fragmentation. Note that
5 * this heavily depends upon page migration to do all the real heavy
8 * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
10 #include <linux/swap.h>
11 #include <linux/migrate.h>
12 #include <linux/compaction.h>
13 #include <linux/mm_inline.h>
14 #include <linux/backing-dev.h>
15 #include <linux/sysctl.h>
16 #include <linux/sysfs.h>
17 #include <linux/balloon_compaction.h>
18 #include <linux/page-isolation.h>
21 #ifdef CONFIG_COMPACTION
22 static inline void count_compact_event(enum vm_event_item item
)
27 static inline void count_compact_events(enum vm_event_item item
, long delta
)
29 count_vm_events(item
, delta
);
32 #define count_compact_event(item) do { } while (0)
33 #define count_compact_events(item, delta) do { } while (0)
36 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
38 #define CREATE_TRACE_POINTS
39 #include <trace/events/compaction.h>
41 static unsigned long release_freepages(struct list_head
*freelist
)
43 struct page
*page
, *next
;
44 unsigned long count
= 0;
46 list_for_each_entry_safe(page
, next
, freelist
, lru
) {
55 static void map_pages(struct list_head
*list
)
59 list_for_each_entry(page
, list
, lru
) {
60 arch_alloc_page(page
, 0);
61 kernel_map_pages(page
, 1, 1);
65 static inline bool migrate_async_suitable(int migratetype
)
67 return is_migrate_cma(migratetype
) || migratetype
== MIGRATE_MOVABLE
;
70 #ifdef CONFIG_COMPACTION
71 /* Returns true if the pageblock should be scanned for pages to isolate. */
72 static inline bool isolation_suitable(struct compact_control
*cc
,
75 if (cc
->ignore_skip_hint
)
78 return !get_pageblock_skip(page
);
82 * This function is called to clear all cached information on pageblocks that
83 * should be skipped for page isolation when the migrate and free page scanner
86 static void __reset_isolation_suitable(struct zone
*zone
)
88 unsigned long start_pfn
= zone
->zone_start_pfn
;
89 unsigned long end_pfn
= zone_end_pfn(zone
);
92 zone
->compact_cached_migrate_pfn
[0] = start_pfn
;
93 zone
->compact_cached_migrate_pfn
[1] = start_pfn
;
94 zone
->compact_cached_free_pfn
= end_pfn
;
95 zone
->compact_blockskip_flush
= false;
97 /* Walk the zone and mark every pageblock as suitable for isolation */
98 for (pfn
= start_pfn
; pfn
< end_pfn
; pfn
+= pageblock_nr_pages
) {
106 page
= pfn_to_page(pfn
);
107 if (zone
!= page_zone(page
))
110 clear_pageblock_skip(page
);
114 void reset_isolation_suitable(pg_data_t
*pgdat
)
118 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
119 struct zone
*zone
= &pgdat
->node_zones
[zoneid
];
120 if (!populated_zone(zone
))
123 /* Only flush if a full compaction finished recently */
124 if (zone
->compact_blockskip_flush
)
125 __reset_isolation_suitable(zone
);
130 * If no pages were isolated then mark this pageblock to be skipped in the
131 * future. The information is later cleared by __reset_isolation_suitable().
133 static void update_pageblock_skip(struct compact_control
*cc
,
134 struct page
*page
, unsigned long nr_isolated
,
135 bool set_unsuitable
, bool migrate_scanner
)
137 struct zone
*zone
= cc
->zone
;
140 if (cc
->ignore_skip_hint
)
150 * Only skip pageblocks when all forms of compaction will be known to
151 * fail in the near future.
154 set_pageblock_skip(page
);
156 pfn
= page_to_pfn(page
);
158 /* Update where async and sync compaction should restart */
159 if (migrate_scanner
) {
160 if (cc
->finished_update_migrate
)
162 if (pfn
> zone
->compact_cached_migrate_pfn
[0])
163 zone
->compact_cached_migrate_pfn
[0] = pfn
;
164 if (cc
->mode
!= MIGRATE_ASYNC
&&
165 pfn
> zone
->compact_cached_migrate_pfn
[1])
166 zone
->compact_cached_migrate_pfn
[1] = pfn
;
168 if (cc
->finished_update_free
)
170 if (pfn
< zone
->compact_cached_free_pfn
)
171 zone
->compact_cached_free_pfn
= pfn
;
175 static inline bool isolation_suitable(struct compact_control
*cc
,
181 static void update_pageblock_skip(struct compact_control
*cc
,
182 struct page
*page
, unsigned long nr_isolated
,
183 bool set_unsuitable
, bool migrate_scanner
)
186 #endif /* CONFIG_COMPACTION */
188 static inline bool should_release_lock(spinlock_t
*lock
)
190 return need_resched() || spin_is_contended(lock
);
194 * Compaction requires the taking of some coarse locks that are potentially
195 * very heavily contended. Check if the process needs to be scheduled or
196 * if the lock is contended. For async compaction, back out in the event
197 * if contention is severe. For sync compaction, schedule.
199 * Returns true if the lock is held.
200 * Returns false if the lock is released and compaction should abort
202 static bool compact_checklock_irqsave(spinlock_t
*lock
, unsigned long *flags
,
203 bool locked
, struct compact_control
*cc
)
205 if (should_release_lock(lock
)) {
207 spin_unlock_irqrestore(lock
, *flags
);
211 /* async aborts if taking too long or contended */
212 if (cc
->mode
== MIGRATE_ASYNC
) {
213 cc
->contended
= true;
221 spin_lock_irqsave(lock
, *flags
);
225 /* Returns true if the page is within a block suitable for migration to */
226 static bool suitable_migration_target(struct page
*page
)
228 /* If the page is a large free page, then disallow migration */
229 if (PageBuddy(page
) && page_order(page
) >= pageblock_order
)
232 /* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
233 if (migrate_async_suitable(get_pageblock_migratetype(page
)))
236 /* Otherwise skip the block */
241 * Isolate free pages onto a private freelist. If @strict is true, will abort
242 * returning 0 on any invalid PFNs or non-free pages inside of the pageblock
243 * (even though it may still end up isolating some pages).
245 static unsigned long isolate_freepages_block(struct compact_control
*cc
,
246 unsigned long blockpfn
,
247 unsigned long end_pfn
,
248 struct list_head
*freelist
,
251 int nr_scanned
= 0, total_isolated
= 0;
252 struct page
*cursor
, *valid_page
= NULL
;
255 bool checked_pageblock
= false;
257 cursor
= pfn_to_page(blockpfn
);
259 /* Isolate free pages. */
260 for (; blockpfn
< end_pfn
; blockpfn
++, cursor
++) {
262 struct page
*page
= cursor
;
265 if (!pfn_valid_within(blockpfn
))
270 if (!PageBuddy(page
))
274 * The zone lock must be held to isolate freepages.
275 * Unfortunately this is a very coarse lock and can be
276 * heavily contended if there are parallel allocations
277 * or parallel compactions. For async compaction do not
278 * spin on the lock and we acquire the lock as late as
281 locked
= compact_checklock_irqsave(&cc
->zone
->lock
, &flags
,
286 /* Recheck this is a suitable migration target under lock */
287 if (!strict
&& !checked_pageblock
) {
289 * We need to check suitability of pageblock only once
290 * and this isolate_freepages_block() is called with
291 * pageblock range, so just check once is sufficient.
293 checked_pageblock
= true;
294 if (!suitable_migration_target(page
))
298 /* Recheck this is a buddy page under lock */
299 if (!PageBuddy(page
))
302 /* Found a free page, break it into order-0 pages */
303 isolated
= split_free_page(page
);
304 total_isolated
+= isolated
;
305 for (i
= 0; i
< isolated
; i
++) {
306 list_add(&page
->lru
, freelist
);
310 /* If a page was split, advance to the end of it */
312 blockpfn
+= isolated
- 1;
313 cursor
+= isolated
- 1;
325 trace_mm_compaction_isolate_freepages(nr_scanned
, total_isolated
);
328 * If strict isolation is requested by CMA then check that all the
329 * pages requested were isolated. If there were any failures, 0 is
330 * returned and CMA will fail.
332 if (strict
&& blockpfn
< end_pfn
)
336 spin_unlock_irqrestore(&cc
->zone
->lock
, flags
);
338 /* Update the pageblock-skip if the whole pageblock was scanned */
339 if (blockpfn
== end_pfn
)
340 update_pageblock_skip(cc
, valid_page
, total_isolated
, true,
343 count_compact_events(COMPACTFREE_SCANNED
, nr_scanned
);
345 count_compact_events(COMPACTISOLATED
, total_isolated
);
346 return total_isolated
;
350 * isolate_freepages_range() - isolate free pages.
351 * @start_pfn: The first PFN to start isolating.
352 * @end_pfn: The one-past-last PFN.
354 * Non-free pages, invalid PFNs, or zone boundaries within the
355 * [start_pfn, end_pfn) range are considered errors, cause function to
356 * undo its actions and return zero.
358 * Otherwise, function returns one-past-the-last PFN of isolated page
359 * (which may be greater then end_pfn if end fell in a middle of
363 isolate_freepages_range(struct compact_control
*cc
,
364 unsigned long start_pfn
, unsigned long end_pfn
)
366 unsigned long isolated
, pfn
, block_end_pfn
;
369 for (pfn
= start_pfn
; pfn
< end_pfn
; pfn
+= isolated
) {
370 if (!pfn_valid(pfn
) || cc
->zone
!= page_zone(pfn_to_page(pfn
)))
374 * On subsequent iterations ALIGN() is actually not needed,
375 * but we keep it that we not to complicate the code.
377 block_end_pfn
= ALIGN(pfn
+ 1, pageblock_nr_pages
);
378 block_end_pfn
= min(block_end_pfn
, end_pfn
);
380 isolated
= isolate_freepages_block(cc
, pfn
, block_end_pfn
,
384 * In strict mode, isolate_freepages_block() returns 0 if
385 * there are any holes in the block (ie. invalid PFNs or
392 * If we managed to isolate pages, it is always (1 << n) *
393 * pageblock_nr_pages for some non-negative n. (Max order
394 * page may span two pageblocks).
398 /* split_free_page does not map the pages */
399 map_pages(&freelist
);
402 /* Loop terminated early, cleanup. */
403 release_freepages(&freelist
);
407 /* We don't use freelists for anything. */
411 /* Update the number of anon and file isolated pages in the zone */
412 static void acct_isolated(struct zone
*zone
, bool locked
, struct compact_control
*cc
)
415 unsigned int count
[2] = { 0, };
417 list_for_each_entry(page
, &cc
->migratepages
, lru
)
418 count
[!!page_is_file_cache(page
)]++;
420 /* If locked we can use the interrupt unsafe versions */
422 __mod_zone_page_state(zone
, NR_ISOLATED_ANON
, count
[0]);
423 __mod_zone_page_state(zone
, NR_ISOLATED_FILE
, count
[1]);
425 mod_zone_page_state(zone
, NR_ISOLATED_ANON
, count
[0]);
426 mod_zone_page_state(zone
, NR_ISOLATED_FILE
, count
[1]);
430 /* Similar to reclaim, but different enough that they don't share logic */
431 static bool too_many_isolated(struct zone
*zone
)
433 unsigned long active
, inactive
, isolated
;
435 inactive
= zone_page_state(zone
, NR_INACTIVE_FILE
) +
436 zone_page_state(zone
, NR_INACTIVE_ANON
);
437 active
= zone_page_state(zone
, NR_ACTIVE_FILE
) +
438 zone_page_state(zone
, NR_ACTIVE_ANON
);
439 isolated
= zone_page_state(zone
, NR_ISOLATED_FILE
) +
440 zone_page_state(zone
, NR_ISOLATED_ANON
);
442 return isolated
> (inactive
+ active
) / 2;
446 * isolate_migratepages_range() - isolate all migrate-able pages in range.
447 * @zone: Zone pages are in.
448 * @cc: Compaction control structure.
449 * @low_pfn: The first PFN of the range.
450 * @end_pfn: The one-past-the-last PFN of the range.
451 * @unevictable: true if it allows to isolate unevictable pages
453 * Isolate all pages that can be migrated from the range specified by
454 * [low_pfn, end_pfn). Returns zero if there is a fatal signal
455 * pending), otherwise PFN of the first page that was not scanned
456 * (which may be both less, equal to or more then end_pfn).
458 * Assumes that cc->migratepages is empty and cc->nr_migratepages is
461 * Apart from cc->migratepages and cc->nr_migratetypes this function
462 * does not modify any cc's fields, in particular it does not modify
463 * (or read for that matter) cc->migrate_pfn.
466 isolate_migratepages_range(struct zone
*zone
, struct compact_control
*cc
,
467 unsigned long low_pfn
, unsigned long end_pfn
, bool unevictable
)
469 unsigned long last_pageblock_nr
= 0, pageblock_nr
;
470 unsigned long nr_scanned
= 0, nr_isolated
= 0;
471 struct list_head
*migratelist
= &cc
->migratepages
;
472 struct lruvec
*lruvec
;
475 struct page
*page
= NULL
, *valid_page
= NULL
;
476 bool set_unsuitable
= true;
477 const isolate_mode_t mode
= (cc
->mode
== MIGRATE_ASYNC
?
478 ISOLATE_ASYNC_MIGRATE
: 0) |
479 (unevictable
? ISOLATE_UNEVICTABLE
: 0);
482 * Ensure that there are not too many pages isolated from the LRU
483 * list by either parallel reclaimers or compaction. If there are,
484 * delay for some time until fewer pages are isolated
486 while (unlikely(too_many_isolated(zone
))) {
487 /* async migration should just abort */
488 if (cc
->mode
== MIGRATE_ASYNC
)
491 congestion_wait(BLK_RW_ASYNC
, HZ
/10);
493 if (fatal_signal_pending(current
))
497 if (cond_resched()) {
498 /* Async terminates prematurely on need_resched() */
499 if (cc
->mode
== MIGRATE_ASYNC
)
503 /* Time to isolate some pages for migration */
504 for (; low_pfn
< end_pfn
; low_pfn
++) {
505 /* give a chance to irqs before checking need_resched() */
506 if (locked
&& !(low_pfn
% SWAP_CLUSTER_MAX
)) {
507 if (should_release_lock(&zone
->lru_lock
)) {
508 spin_unlock_irqrestore(&zone
->lru_lock
, flags
);
514 * migrate_pfn does not necessarily start aligned to a
515 * pageblock. Ensure that pfn_valid is called when moving
516 * into a new MAX_ORDER_NR_PAGES range in case of large
517 * memory holes within the zone
519 if ((low_pfn
& (MAX_ORDER_NR_PAGES
- 1)) == 0) {
520 if (!pfn_valid(low_pfn
)) {
521 low_pfn
+= MAX_ORDER_NR_PAGES
- 1;
526 if (!pfn_valid_within(low_pfn
))
531 * Get the page and ensure the page is within the same zone.
532 * See the comment in isolate_freepages about overlapping
533 * nodes. It is deliberate that the new zone lock is not taken
534 * as memory compaction should not move pages between nodes.
536 page
= pfn_to_page(low_pfn
);
537 if (page_zone(page
) != zone
)
543 /* If isolation recently failed, do not retry */
544 pageblock_nr
= low_pfn
>> pageblock_order
;
545 if (last_pageblock_nr
!= pageblock_nr
) {
548 last_pageblock_nr
= pageblock_nr
;
549 if (!isolation_suitable(cc
, page
))
553 * For async migration, also only scan in MOVABLE
554 * blocks. Async migration is optimistic to see if
555 * the minimum amount of work satisfies the allocation
557 mt
= get_pageblock_migratetype(page
);
558 if (cc
->mode
== MIGRATE_ASYNC
&&
559 !migrate_async_suitable(mt
)) {
560 set_unsuitable
= false;
566 * Skip if free. page_order cannot be used without zone->lock
567 * as nothing prevents parallel allocations or buddy merging.
573 * Check may be lockless but that's ok as we recheck later.
574 * It's possible to migrate LRU pages and balloon pages
575 * Skip any other type of page
577 if (!PageLRU(page
)) {
578 if (unlikely(balloon_page_movable(page
))) {
579 if (locked
&& balloon_page_isolate(page
)) {
580 /* Successfully isolated */
581 goto isolate_success
;
588 * PageLRU is set. lru_lock normally excludes isolation
589 * splitting and collapsing (collapsing has already happened
590 * if PageLRU is set) but the lock is not necessarily taken
591 * here and it is wasteful to take it just to check transhuge.
592 * Check TransHuge without lock and skip the whole pageblock if
593 * it's either a transhuge or hugetlbfs page, as calling
594 * compound_order() without preventing THP from splitting the
595 * page underneath us may return surprising results.
597 if (PageTransHuge(page
)) {
600 low_pfn
+= (1 << compound_order(page
)) - 1;
605 * Migration will fail if an anonymous page is pinned in memory,
606 * so avoid taking lru_lock and isolating it unnecessarily in an
607 * admittedly racy check.
609 if (!page_mapping(page
) &&
610 page_count(page
) > page_mapcount(page
))
613 /* Check if it is ok to still hold the lock */
614 locked
= compact_checklock_irqsave(&zone
->lru_lock
, &flags
,
616 if (!locked
|| fatal_signal_pending(current
))
619 /* Recheck PageLRU and PageTransHuge under lock */
622 if (PageTransHuge(page
)) {
623 low_pfn
+= (1 << compound_order(page
)) - 1;
627 lruvec
= mem_cgroup_page_lruvec(page
, zone
);
629 /* Try isolate the page */
630 if (__isolate_lru_page(page
, mode
) != 0)
633 VM_BUG_ON_PAGE(PageTransCompound(page
), page
);
635 /* Successfully isolated */
636 del_page_from_lru_list(page
, lruvec
, page_lru(page
));
639 cc
->finished_update_migrate
= true;
640 list_add(&page
->lru
, migratelist
);
641 cc
->nr_migratepages
++;
644 /* Avoid isolating too much */
645 if (cc
->nr_migratepages
== COMPACT_CLUSTER_MAX
) {
653 low_pfn
= ALIGN(low_pfn
+ 1, pageblock_nr_pages
) - 1;
656 acct_isolated(zone
, locked
, cc
);
659 spin_unlock_irqrestore(&zone
->lru_lock
, flags
);
662 * Update the pageblock-skip information and cached scanner pfn,
663 * if the whole pageblock was scanned without isolating any page.
665 if (low_pfn
== end_pfn
)
666 update_pageblock_skip(cc
, valid_page
, nr_isolated
,
667 set_unsuitable
, true);
669 trace_mm_compaction_isolate_migratepages(nr_scanned
, nr_isolated
);
671 count_compact_events(COMPACTMIGRATE_SCANNED
, nr_scanned
);
673 count_compact_events(COMPACTISOLATED
, nr_isolated
);
678 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
679 #ifdef CONFIG_COMPACTION
681 * Based on information in the current compact_control, find blocks
682 * suitable for isolating free pages from and then isolate them.
684 static void isolate_freepages(struct zone
*zone
,
685 struct compact_control
*cc
)
688 unsigned long block_start_pfn
; /* start of current pageblock */
689 unsigned long block_end_pfn
; /* end of current pageblock */
690 unsigned long low_pfn
; /* lowest pfn scanner is able to scan */
691 unsigned long next_free_pfn
; /* start pfn for scaning at next round */
692 int nr_freepages
= cc
->nr_freepages
;
693 struct list_head
*freelist
= &cc
->freepages
;
696 * Initialise the free scanner. The starting point is where we last
697 * successfully isolated from, zone-cached value, or the end of the
698 * zone when isolating for the first time. We need this aligned to
699 * the pageblock boundary, because we do
700 * block_start_pfn -= pageblock_nr_pages in the for loop.
701 * For ending point, take care when isolating in last pageblock of a
702 * a zone which ends in the middle of a pageblock.
703 * The low boundary is the end of the pageblock the migration scanner
706 block_start_pfn
= cc
->free_pfn
& ~(pageblock_nr_pages
-1);
707 block_end_pfn
= min(block_start_pfn
+ pageblock_nr_pages
,
709 low_pfn
= ALIGN(cc
->migrate_pfn
+ 1, pageblock_nr_pages
);
712 * If no pages are isolated, the block_start_pfn < low_pfn check
718 * Isolate free pages until enough are available to migrate the
719 * pages on cc->migratepages. We stop searching if the migrate
720 * and free page scanners meet or enough free pages are isolated.
722 for (; block_start_pfn
>= low_pfn
&& cc
->nr_migratepages
> nr_freepages
;
723 block_end_pfn
= block_start_pfn
,
724 block_start_pfn
-= pageblock_nr_pages
) {
725 unsigned long isolated
;
728 * This can iterate a massively long zone without finding any
729 * suitable migration targets, so periodically check if we need
734 if (!pfn_valid(block_start_pfn
))
738 * Check for overlapping nodes/zones. It's possible on some
739 * configurations to have a setup like
741 * i.e. it's possible that all pages within a zones range of
742 * pages do not belong to a single zone.
744 page
= pfn_to_page(block_start_pfn
);
745 if (page_zone(page
) != zone
)
748 /* Check the block is suitable for migration */
749 if (!suitable_migration_target(page
))
752 /* If isolation recently failed, do not retry */
753 if (!isolation_suitable(cc
, page
))
756 /* Found a block suitable for isolating free pages from */
757 isolated
= isolate_freepages_block(cc
, block_start_pfn
,
758 block_end_pfn
, freelist
, false);
759 nr_freepages
+= isolated
;
762 * Record the highest PFN we isolated pages from. When next
763 * looking for free pages, the search will restart here as
764 * page migration may have returned some pages to the allocator
766 if (isolated
&& next_free_pfn
== 0) {
767 cc
->finished_update_free
= true;
768 next_free_pfn
= block_start_pfn
;
772 /* split_free_page does not map the pages */
776 * If we crossed the migrate scanner, we want to keep it that way
777 * so that compact_finished() may detect this
779 if (block_start_pfn
< low_pfn
)
780 next_free_pfn
= cc
->migrate_pfn
;
782 cc
->free_pfn
= next_free_pfn
;
783 cc
->nr_freepages
= nr_freepages
;
787 * This is a migrate-callback that "allocates" freepages by taking pages
788 * from the isolated freelists in the block we are migrating to.
790 static struct page
*compaction_alloc(struct page
*migratepage
,
794 struct compact_control
*cc
= (struct compact_control
*)data
;
795 struct page
*freepage
;
797 /* Isolate free pages if necessary */
798 if (list_empty(&cc
->freepages
)) {
799 isolate_freepages(cc
->zone
, cc
);
801 if (list_empty(&cc
->freepages
))
805 freepage
= list_entry(cc
->freepages
.next
, struct page
, lru
);
806 list_del(&freepage
->lru
);
813 * This is a migrate-callback that "frees" freepages back to the isolated
814 * freelist. All pages on the freelist are from the same zone, so there is no
815 * special handling needed for NUMA.
817 static void compaction_free(struct page
*page
, unsigned long data
)
819 struct compact_control
*cc
= (struct compact_control
*)data
;
821 list_add(&page
->lru
, &cc
->freepages
);
825 /* possible outcome of isolate_migratepages */
827 ISOLATE_ABORT
, /* Abort compaction now */
828 ISOLATE_NONE
, /* No pages isolated, continue scanning */
829 ISOLATE_SUCCESS
, /* Pages isolated, migrate */
833 * Isolate all pages that can be migrated from the block pointed to by
834 * the migrate scanner within compact_control.
836 static isolate_migrate_t
isolate_migratepages(struct zone
*zone
,
837 struct compact_control
*cc
)
839 unsigned long low_pfn
, end_pfn
;
841 /* Do not scan outside zone boundaries */
842 low_pfn
= max(cc
->migrate_pfn
, zone
->zone_start_pfn
);
844 /* Only scan within a pageblock boundary */
845 end_pfn
= ALIGN(low_pfn
+ 1, pageblock_nr_pages
);
847 /* Do not cross the free scanner or scan within a memory hole */
848 if (end_pfn
> cc
->free_pfn
|| !pfn_valid(low_pfn
)) {
849 cc
->migrate_pfn
= end_pfn
;
853 /* Perform the isolation */
854 low_pfn
= isolate_migratepages_range(zone
, cc
, low_pfn
, end_pfn
, false);
855 if (!low_pfn
|| cc
->contended
)
856 return ISOLATE_ABORT
;
858 cc
->migrate_pfn
= low_pfn
;
860 return ISOLATE_SUCCESS
;
863 static int compact_finished(struct zone
*zone
,
864 struct compact_control
*cc
)
867 unsigned long watermark
;
869 if (fatal_signal_pending(current
))
870 return COMPACT_PARTIAL
;
872 /* Compaction run completes if the migrate and free scanner meet */
873 if (cc
->free_pfn
<= cc
->migrate_pfn
) {
874 /* Let the next compaction start anew. */
875 zone
->compact_cached_migrate_pfn
[0] = zone
->zone_start_pfn
;
876 zone
->compact_cached_migrate_pfn
[1] = zone
->zone_start_pfn
;
877 zone
->compact_cached_free_pfn
= zone_end_pfn(zone
);
880 * Mark that the PG_migrate_skip information should be cleared
881 * by kswapd when it goes to sleep. kswapd does not set the
882 * flag itself as the decision to be clear should be directly
883 * based on an allocation request.
885 if (!current_is_kswapd())
886 zone
->compact_blockskip_flush
= true;
888 return COMPACT_COMPLETE
;
892 * order == -1 is expected when compacting via
893 * /proc/sys/vm/compact_memory
896 return COMPACT_CONTINUE
;
898 /* Compaction run is not finished if the watermark is not met */
899 watermark
= low_wmark_pages(zone
);
900 watermark
+= (1 << cc
->order
);
902 if (!zone_watermark_ok(zone
, cc
->order
, watermark
, 0, 0))
903 return COMPACT_CONTINUE
;
905 /* Direct compactor: Is a suitable page free? */
906 for (order
= cc
->order
; order
< MAX_ORDER
; order
++) {
907 struct free_area
*area
= &zone
->free_area
[order
];
909 /* Job done if page is free of the right migratetype */
910 if (!list_empty(&area
->free_list
[cc
->migratetype
]))
911 return COMPACT_PARTIAL
;
913 /* Job done if allocation would set block type */
914 if (cc
->order
>= pageblock_order
&& area
->nr_free
)
915 return COMPACT_PARTIAL
;
918 return COMPACT_CONTINUE
;
922 * compaction_suitable: Is this suitable to run compaction on this zone now?
924 * COMPACT_SKIPPED - If there are too few free pages for compaction
925 * COMPACT_PARTIAL - If the allocation would succeed without compaction
926 * COMPACT_CONTINUE - If compaction should run now
928 unsigned long compaction_suitable(struct zone
*zone
, int order
)
931 unsigned long watermark
;
934 * order == -1 is expected when compacting via
935 * /proc/sys/vm/compact_memory
938 return COMPACT_CONTINUE
;
941 * Watermarks for order-0 must be met for compaction. Note the 2UL.
942 * This is because during migration, copies of pages need to be
943 * allocated and for a short time, the footprint is higher
945 watermark
= low_wmark_pages(zone
) + (2UL << order
);
946 if (!zone_watermark_ok(zone
, 0, watermark
, 0, 0))
947 return COMPACT_SKIPPED
;
950 * fragmentation index determines if allocation failures are due to
951 * low memory or external fragmentation
953 * index of -1000 implies allocations might succeed depending on
955 * index towards 0 implies failure is due to lack of memory
956 * index towards 1000 implies failure is due to fragmentation
958 * Only compact if a failure would be due to fragmentation.
960 fragindex
= fragmentation_index(zone
, order
);
961 if (fragindex
>= 0 && fragindex
<= sysctl_extfrag_threshold
)
962 return COMPACT_SKIPPED
;
964 if (fragindex
== -1000 && zone_watermark_ok(zone
, order
, watermark
,
966 return COMPACT_PARTIAL
;
968 return COMPACT_CONTINUE
;
971 static int compact_zone(struct zone
*zone
, struct compact_control
*cc
)
974 unsigned long start_pfn
= zone
->zone_start_pfn
;
975 unsigned long end_pfn
= zone_end_pfn(zone
);
976 const bool sync
= cc
->mode
!= MIGRATE_ASYNC
;
978 ret
= compaction_suitable(zone
, cc
->order
);
980 case COMPACT_PARTIAL
:
981 case COMPACT_SKIPPED
:
982 /* Compaction is likely to fail */
984 case COMPACT_CONTINUE
:
985 /* Fall through to compaction */
990 * Clear pageblock skip if there were failures recently and compaction
991 * is about to be retried after being deferred. kswapd does not do
992 * this reset as it'll reset the cached information when going to sleep.
994 if (compaction_restarting(zone
, cc
->order
) && !current_is_kswapd())
995 __reset_isolation_suitable(zone
);
998 * Setup to move all movable pages to the end of the zone. Used cached
999 * information on where the scanners should start but check that it
1000 * is initialised by ensuring the values are within zone boundaries.
1002 cc
->migrate_pfn
= zone
->compact_cached_migrate_pfn
[sync
];
1003 cc
->free_pfn
= zone
->compact_cached_free_pfn
;
1004 if (cc
->free_pfn
< start_pfn
|| cc
->free_pfn
> end_pfn
) {
1005 cc
->free_pfn
= end_pfn
& ~(pageblock_nr_pages
-1);
1006 zone
->compact_cached_free_pfn
= cc
->free_pfn
;
1008 if (cc
->migrate_pfn
< start_pfn
|| cc
->migrate_pfn
> end_pfn
) {
1009 cc
->migrate_pfn
= start_pfn
;
1010 zone
->compact_cached_migrate_pfn
[0] = cc
->migrate_pfn
;
1011 zone
->compact_cached_migrate_pfn
[1] = cc
->migrate_pfn
;
1014 trace_mm_compaction_begin(start_pfn
, cc
->migrate_pfn
, cc
->free_pfn
, end_pfn
);
1016 migrate_prep_local();
1018 while ((ret
= compact_finished(zone
, cc
)) == COMPACT_CONTINUE
) {
1021 switch (isolate_migratepages(zone
, cc
)) {
1023 ret
= COMPACT_PARTIAL
;
1024 putback_movable_pages(&cc
->migratepages
);
1025 cc
->nr_migratepages
= 0;
1029 case ISOLATE_SUCCESS
:
1033 if (!cc
->nr_migratepages
)
1036 err
= migrate_pages(&cc
->migratepages
, compaction_alloc
,
1037 compaction_free
, (unsigned long)cc
, cc
->mode
,
1040 trace_mm_compaction_migratepages(cc
->nr_migratepages
, err
,
1043 /* All pages were either migrated or will be released */
1044 cc
->nr_migratepages
= 0;
1046 putback_movable_pages(&cc
->migratepages
);
1048 * migrate_pages() may return -ENOMEM when scanners meet
1049 * and we want compact_finished() to detect it
1051 if (err
== -ENOMEM
&& cc
->free_pfn
> cc
->migrate_pfn
) {
1052 ret
= COMPACT_PARTIAL
;
1059 /* Release free pages and check accounting */
1060 cc
->nr_freepages
-= release_freepages(&cc
->freepages
);
1061 VM_BUG_ON(cc
->nr_freepages
!= 0);
1063 trace_mm_compaction_end(ret
);
1068 static unsigned long compact_zone_order(struct zone
*zone
, int order
,
1069 gfp_t gfp_mask
, enum migrate_mode mode
, bool *contended
)
1072 struct compact_control cc
= {
1074 .nr_migratepages
= 0,
1076 .migratetype
= allocflags_to_migratetype(gfp_mask
),
1080 INIT_LIST_HEAD(&cc
.freepages
);
1081 INIT_LIST_HEAD(&cc
.migratepages
);
1083 ret
= compact_zone(zone
, &cc
);
1085 VM_BUG_ON(!list_empty(&cc
.freepages
));
1086 VM_BUG_ON(!list_empty(&cc
.migratepages
));
1088 *contended
= cc
.contended
;
1092 int sysctl_extfrag_threshold
= 500;
1095 * try_to_compact_pages - Direct compact to satisfy a high-order allocation
1096 * @zonelist: The zonelist used for the current allocation
1097 * @order: The order of the current allocation
1098 * @gfp_mask: The GFP mask of the current allocation
1099 * @nodemask: The allowed nodes to allocate from
1100 * @mode: The migration mode for async, sync light, or sync migration
1101 * @contended: Return value that is true if compaction was aborted due to lock contention
1102 * @page: Optionally capture a free page of the requested order during compaction
1104 * This is the main entry point for direct page compaction.
1106 unsigned long try_to_compact_pages(struct zonelist
*zonelist
,
1107 int order
, gfp_t gfp_mask
, nodemask_t
*nodemask
,
1108 enum migrate_mode mode
, bool *contended
)
1110 enum zone_type high_zoneidx
= gfp_zone(gfp_mask
);
1111 int may_enter_fs
= gfp_mask
& __GFP_FS
;
1112 int may_perform_io
= gfp_mask
& __GFP_IO
;
1115 int rc
= COMPACT_SKIPPED
;
1116 int alloc_flags
= 0;
1118 /* Check if the GFP flags allow compaction */
1119 if (!order
|| !may_enter_fs
|| !may_perform_io
)
1122 count_compact_event(COMPACTSTALL
);
1125 if (allocflags_to_migratetype(gfp_mask
) == MIGRATE_MOVABLE
)
1126 alloc_flags
|= ALLOC_CMA
;
1128 /* Compact each zone in the list */
1129 for_each_zone_zonelist_nodemask(zone
, z
, zonelist
, high_zoneidx
,
1133 status
= compact_zone_order(zone
, order
, gfp_mask
, mode
,
1135 rc
= max(status
, rc
);
1137 /* If a normal allocation would succeed, stop compacting */
1138 if (zone_watermark_ok(zone
, order
, low_wmark_pages(zone
), 0,
1147 /* Compact all zones within a node */
1148 static void __compact_pgdat(pg_data_t
*pgdat
, struct compact_control
*cc
)
1153 for (zoneid
= 0; zoneid
< MAX_NR_ZONES
; zoneid
++) {
1155 zone
= &pgdat
->node_zones
[zoneid
];
1156 if (!populated_zone(zone
))
1159 cc
->nr_freepages
= 0;
1160 cc
->nr_migratepages
= 0;
1162 INIT_LIST_HEAD(&cc
->freepages
);
1163 INIT_LIST_HEAD(&cc
->migratepages
);
1165 if (cc
->order
== -1 || !compaction_deferred(zone
, cc
->order
))
1166 compact_zone(zone
, cc
);
1168 if (cc
->order
> 0) {
1169 if (zone_watermark_ok(zone
, cc
->order
,
1170 low_wmark_pages(zone
), 0, 0))
1171 compaction_defer_reset(zone
, cc
->order
, false);
1174 VM_BUG_ON(!list_empty(&cc
->freepages
));
1175 VM_BUG_ON(!list_empty(&cc
->migratepages
));
1179 void compact_pgdat(pg_data_t
*pgdat
, int order
)
1181 struct compact_control cc
= {
1183 .mode
= MIGRATE_ASYNC
,
1189 __compact_pgdat(pgdat
, &cc
);
1192 static void compact_node(int nid
)
1194 struct compact_control cc
= {
1196 .mode
= MIGRATE_SYNC
,
1197 .ignore_skip_hint
= true,
1200 __compact_pgdat(NODE_DATA(nid
), &cc
);
1203 /* Compact all nodes in the system */
1204 static void compact_nodes(void)
1208 /* Flush pending updates to the LRU lists */
1209 lru_add_drain_all();
1211 for_each_online_node(nid
)
1215 /* The written value is actually unused, all memory is compacted */
1216 int sysctl_compact_memory
;
1218 /* This is the entry point for compacting all nodes via /proc/sys/vm */
1219 int sysctl_compaction_handler(struct ctl_table
*table
, int write
,
1220 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
1228 int sysctl_extfrag_handler(struct ctl_table
*table
, int write
,
1229 void __user
*buffer
, size_t *length
, loff_t
*ppos
)
1231 proc_dointvec_minmax(table
, write
, buffer
, length
, ppos
);
1236 #if defined(CONFIG_SYSFS) && defined(CONFIG_NUMA)
1237 static ssize_t
sysfs_compact_node(struct device
*dev
,
1238 struct device_attribute
*attr
,
1239 const char *buf
, size_t count
)
1243 if (nid
>= 0 && nid
< nr_node_ids
&& node_online(nid
)) {
1244 /* Flush pending updates to the LRU lists */
1245 lru_add_drain_all();
1252 static DEVICE_ATTR(compact
, S_IWUSR
, NULL
, sysfs_compact_node
);
1254 int compaction_register_node(struct node
*node
)
1256 return device_create_file(&node
->dev
, &dev_attr_compact
);
1259 void compaction_unregister_node(struct node
*node
)
1261 return device_remove_file(&node
->dev
, &dev_attr_compact
);
1263 #endif /* CONFIG_SYSFS && CONFIG_NUMA */
1265 #endif /* CONFIG_COMPACTION */