4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
6 * Swap reorganised 29.12.95, Stephen Tweedie.
7 * kswapd added: 7.1.96 sct
8 * Removed kswapd_ctl limits, and swap out as many pages as needed
9 * to bring the system back to freepages.high: 2.4.97, Rik van Riel.
10 * Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
11 * Multiqueue VM started 5.8.00, Rik van Riel.
15 #include <linux/module.h>
16 #include <linux/gfp.h>
17 #include <linux/kernel_stat.h>
18 #include <linux/swap.h>
19 #include <linux/pagemap.h>
20 #include <linux/init.h>
21 #include <linux/highmem.h>
22 #include <linux/vmpressure.h>
23 #include <linux/vmstat.h>
24 #include <linux/file.h>
25 #include <linux/writeback.h>
26 #include <linux/blkdev.h>
27 #include <linux/buffer_head.h> /* for try_to_release_page(),
28 buffer_heads_over_limit */
29 #include <linux/mm_inline.h>
30 #include <linux/backing-dev.h>
31 #include <linux/rmap.h>
32 #include <linux/topology.h>
33 #include <linux/cpu.h>
34 #include <linux/cpuset.h>
35 #include <linux/compaction.h>
36 #include <linux/notifier.h>
37 #include <linux/rwsem.h>
38 #include <linux/delay.h>
39 #include <linux/kthread.h>
40 #include <linux/freezer.h>
41 #include <linux/memcontrol.h>
42 #include <linux/delayacct.h>
43 #include <linux/sysctl.h>
44 #include <linux/oom.h>
45 #include <linux/prefetch.h>
47 #include <asm/tlbflush.h>
48 #include <asm/div64.h>
50 #include <linux/swapops.h>
54 #define CREATE_TRACE_POINTS
55 #include <trace/events/vmscan.h>
58 /* Incremented by the number of inactive pages that were scanned */
59 unsigned long nr_scanned;
61 /* Number of pages freed so far during a call to shrink_zones() */
62 unsigned long nr_reclaimed;
64 /* How many pages shrink_list() should reclaim */
65 unsigned long nr_to_reclaim;
67 unsigned long hibernation_mode;
69 /* This context's GFP mask */
74 /* Can mapped pages be reclaimed? */
77 /* Can pages be swapped as part of reclaim? */
82 /* Scan (total_size >> priority) pages at once */
86 * The memory cgroup that hit its limit and as a result is the
87 * primary target of this reclaim invocation.
89 struct mem_cgroup *target_mem_cgroup;
92 * Nodemask of nodes allowed by the caller. If NULL, all nodes
98 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
100 #ifdef ARCH_HAS_PREFETCH
101 #define prefetch_prev_lru_page(_page, _base, _field) \
103 if ((_page)->lru.prev != _base) { \
106 prev = lru_to_page(&(_page->lru)); \
107 prefetch(&prev->_field); \
111 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
114 #ifdef ARCH_HAS_PREFETCHW
115 #define prefetchw_prev_lru_page(_page, _base, _field) \
117 if ((_page)->lru.prev != _base) { \
120 prev = lru_to_page(&(_page->lru)); \
121 prefetchw(&prev->_field); \
125 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
129 * From 0 .. 100. Higher means more swappy.
131 int vm_swappiness = 60;
132 unsigned long vm_total_pages; /* The total number of pages which the VM controls */
134 static LIST_HEAD(shrinker_list);
135 static DECLARE_RWSEM(shrinker_rwsem);
138 static bool global_reclaim(struct scan_control *sc)
140 return !sc->target_mem_cgroup;
143 static bool mem_cgroup_should_soft_reclaim(struct scan_control *sc)
145 struct mem_cgroup *root = sc->target_mem_cgroup;
146 return !mem_cgroup_disabled() &&
147 mem_cgroup_soft_reclaim_eligible(root, root) != SKIP_TREE;
150 static bool global_reclaim(struct scan_control *sc)
155 static bool mem_cgroup_should_soft_reclaim(struct scan_control *sc)
161 unsigned long zone_reclaimable_pages(struct zone *zone)
165 nr = zone_page_state(zone, NR_ACTIVE_FILE) +
166 zone_page_state(zone, NR_INACTIVE_FILE);
168 if (get_nr_swap_pages() > 0)
169 nr += zone_page_state(zone, NR_ACTIVE_ANON) +
170 zone_page_state(zone, NR_INACTIVE_ANON);
175 bool zone_reclaimable(struct zone *zone)
177 return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
180 static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
182 if (!mem_cgroup_disabled())
183 return mem_cgroup_get_lru_size(lruvec, lru);
185 return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);
189 * Add a shrinker callback to be called from the vm
191 void register_shrinker(struct shrinker *shrinker)
193 atomic_long_set(&shrinker->nr_in_batch, 0);
194 down_write(&shrinker_rwsem);
195 list_add_tail(&shrinker->list, &shrinker_list);
196 up_write(&shrinker_rwsem);
198 EXPORT_SYMBOL(register_shrinker);
203 void unregister_shrinker(struct shrinker *shrinker)
205 down_write(&shrinker_rwsem);
206 list_del(&shrinker->list);
207 up_write(&shrinker_rwsem);
209 EXPORT_SYMBOL(unregister_shrinker);
211 static inline int do_shrinker_shrink(struct shrinker *shrinker,
212 struct shrink_control *sc,
213 unsigned long nr_to_scan)
215 sc->nr_to_scan = nr_to_scan;
216 return (*shrinker->shrink)(shrinker, sc);
219 #define SHRINK_BATCH 128
221 * Call the shrink functions to age shrinkable caches
223 * Here we assume it costs one seek to replace a lru page and that it also
224 * takes a seek to recreate a cache object. With this in mind we age equal
225 * percentages of the lru and ageable caches. This should balance the seeks
226 * generated by these structures.
228 * If the vm encountered mapped pages on the LRU it increase the pressure on
229 * slab to avoid swapping.
231 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
233 * `lru_pages' represents the number of on-LRU pages in all the zones which
234 * are eligible for the caller's allocation attempt. It is used for balancing
235 * slab reclaim versus page reclaim.
237 * Returns the number of slab objects which we shrunk.
239 unsigned long shrink_slab(struct shrink_control *shrink,
240 unsigned long nr_pages_scanned,
241 unsigned long lru_pages)
243 struct shrinker *shrinker;
244 unsigned long ret = 0;
246 if (nr_pages_scanned == 0)
247 nr_pages_scanned = SWAP_CLUSTER_MAX;
249 if (!down_read_trylock(&shrinker_rwsem)) {
250 /* Assume we'll be able to shrink next time */
255 list_for_each_entry(shrinker, &shrinker_list, list) {
256 unsigned long long delta;
262 long batch_size = shrinker->batch ? shrinker->batch
265 max_pass = do_shrinker_shrink(shrinker, shrink, 0);
270 * copy the current shrinker scan count into a local variable
271 * and zero it so that other concurrent shrinker invocations
272 * don't also do this scanning work.
274 nr = atomic_long_xchg(&shrinker->nr_in_batch, 0);
277 delta = (4 * nr_pages_scanned) / shrinker->seeks;
279 do_div(delta, lru_pages + 1);
281 if (total_scan < 0) {
282 printk(KERN_ERR "shrink_slab: %pF negative objects to "
284 shrinker->shrink, total_scan);
285 total_scan = max_pass;
289 * We need to avoid excessive windup on filesystem shrinkers
290 * due to large numbers of GFP_NOFS allocations causing the
291 * shrinkers to return -1 all the time. This results in a large
292 * nr being built up so when a shrink that can do some work
293 * comes along it empties the entire cache due to nr >>>
294 * max_pass. This is bad for sustaining a working set in
297 * Hence only allow the shrinker to scan the entire cache when
298 * a large delta change is calculated directly.
300 if (delta < max_pass / 4)
301 total_scan = min(total_scan, max_pass / 2);
304 * Avoid risking looping forever due to too large nr value:
305 * never try to free more than twice the estimate number of
308 if (total_scan > max_pass * 2)
309 total_scan = max_pass * 2;
311 trace_mm_shrink_slab_start(shrinker, shrink, nr,
312 nr_pages_scanned, lru_pages,
313 max_pass, delta, total_scan);
315 while (total_scan >= batch_size) {
318 nr_before = do_shrinker_shrink(shrinker, shrink, 0);
319 shrink_ret = do_shrinker_shrink(shrinker, shrink,
321 if (shrink_ret == -1)
323 if (shrink_ret < nr_before)
324 ret += nr_before - shrink_ret;
325 count_vm_events(SLABS_SCANNED, batch_size);
326 total_scan -= batch_size;
332 * move the unused scan count back into the shrinker in a
333 * manner that handles concurrent updates. If we exhausted the
334 * scan, there is no need to do an update.
337 new_nr = atomic_long_add_return(total_scan,
338 &shrinker->nr_in_batch);
340 new_nr = atomic_long_read(&shrinker->nr_in_batch);
342 trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
344 up_read(&shrinker_rwsem);
350 static inline int is_page_cache_freeable(struct page *page)
353 * A freeable page cache page is referenced only by the caller
354 * that isolated the page, the page cache radix tree and
355 * optional buffer heads at page->private.
357 return page_count(page) - page_has_private(page) == 2;
360 static int may_write_to_queue(struct backing_dev_info *bdi,
361 struct scan_control *sc)
363 if (current->flags & PF_SWAPWRITE)
365 if (!bdi_write_congested(bdi))
367 if (bdi == current->backing_dev_info)
373 * We detected a synchronous write error writing a page out. Probably
374 * -ENOSPC. We need to propagate that into the address_space for a subsequent
375 * fsync(), msync() or close().
377 * The tricky part is that after writepage we cannot touch the mapping: nothing
378 * prevents it from being freed up. But we have a ref on the page and once
379 * that page is locked, the mapping is pinned.
381 * We're allowed to run sleeping lock_page() here because we know the caller has
384 static void handle_write_error(struct address_space *mapping,
385 struct page *page, int error)
388 if (page_mapping(page) == mapping)
389 mapping_set_error(mapping, error);
393 /* possible outcome of pageout() */
395 /* failed to write page out, page is locked */
397 /* move page to the active list, page is locked */
399 /* page has been sent to the disk successfully, page is unlocked */
401 /* page is clean and locked */
406 * pageout is called by shrink_page_list() for each dirty page.
407 * Calls ->writepage().
409 static pageout_t pageout(struct page *page, struct address_space *mapping,
410 struct scan_control *sc)
413 * If the page is dirty, only perform writeback if that write
414 * will be non-blocking. To prevent this allocation from being
415 * stalled by pagecache activity. But note that there may be
416 * stalls if we need to run get_block(). We could test
417 * PagePrivate for that.
419 * If this process is currently in __generic_file_aio_write() against
420 * this page's queue, we can perform writeback even if that
423 * If the page is swapcache, write it back even if that would
424 * block, for some throttling. This happens by accident, because
425 * swap_backing_dev_info is bust: it doesn't reflect the
426 * congestion state of the swapdevs. Easy to fix, if needed.
428 if (!is_page_cache_freeable(page))
432 * Some data journaling orphaned pages can have
433 * page->mapping == NULL while being dirty with clean buffers.
435 if (page_has_private(page)) {
436 if (try_to_free_buffers(page)) {
437 ClearPageDirty(page);
438 printk("%s: orphaned page\n", __func__);
444 if (mapping->a_ops->writepage == NULL)
445 return PAGE_ACTIVATE;
446 if (!may_write_to_queue(mapping->backing_dev_info, sc))
449 if (clear_page_dirty_for_io(page)) {
451 struct writeback_control wbc = {
452 .sync_mode = WB_SYNC_NONE,
453 .nr_to_write = SWAP_CLUSTER_MAX,
455 .range_end = LLONG_MAX,
459 SetPageReclaim(page);
460 res = mapping->a_ops->writepage(page, &wbc);
462 handle_write_error(mapping, page, res);
463 if (res == AOP_WRITEPAGE_ACTIVATE) {
464 ClearPageReclaim(page);
465 return PAGE_ACTIVATE;
468 if (!PageWriteback(page)) {
469 /* synchronous write or broken a_ops? */
470 ClearPageReclaim(page);
472 trace_mm_vmscan_writepage(page, trace_reclaim_flags(page));
473 inc_zone_page_state(page, NR_VMSCAN_WRITE);
481 * Same as remove_mapping, but if the page is removed from the mapping, it
482 * gets returned with a refcount of 0.
484 static int __remove_mapping(struct address_space *mapping, struct page *page)
486 BUG_ON(!PageLocked(page));
487 BUG_ON(mapping != page_mapping(page));
489 spin_lock_irq(&mapping->tree_lock);
491 * The non racy check for a busy page.
493 * Must be careful with the order of the tests. When someone has
494 * a ref to the page, it may be possible that they dirty it then
495 * drop the reference. So if PageDirty is tested before page_count
496 * here, then the following race may occur:
498 * get_user_pages(&page);
499 * [user mapping goes away]
501 * !PageDirty(page) [good]
502 * SetPageDirty(page);
504 * !page_count(page) [good, discard it]
506 * [oops, our write_to data is lost]
508 * Reversing the order of the tests ensures such a situation cannot
509 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
510 * load is not satisfied before that of page->_count.
512 * Note that if SetPageDirty is always performed via set_page_dirty,
513 * and thus under tree_lock, then this ordering is not required.
515 if (!page_freeze_refs(page, 2))
517 /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
518 if (unlikely(PageDirty(page))) {
519 page_unfreeze_refs(page, 2);
523 if (PageSwapCache(page)) {
524 swp_entry_t swap = { .val = page_private(page) };
525 __delete_from_swap_cache(page);
526 spin_unlock_irq(&mapping->tree_lock);
527 swapcache_free(swap, page);
529 void (*freepage)(struct page *);
531 freepage = mapping->a_ops->freepage;
533 __delete_from_page_cache(page);
534 spin_unlock_irq(&mapping->tree_lock);
535 mem_cgroup_uncharge_cache_page(page);
537 if (freepage != NULL)
544 spin_unlock_irq(&mapping->tree_lock);
549 * Attempt to detach a locked page from its ->mapping. If it is dirty or if
550 * someone else has a ref on the page, abort and return 0. If it was
551 * successfully detached, return 1. Assumes the caller has a single ref on
554 int remove_mapping(struct address_space *mapping, struct page *page)
556 if (__remove_mapping(mapping, page)) {
558 * Unfreezing the refcount with 1 rather than 2 effectively
559 * drops the pagecache ref for us without requiring another
562 page_unfreeze_refs(page, 1);
569 * putback_lru_page - put previously isolated page onto appropriate LRU list
570 * @page: page to be put back to appropriate lru list
572 * Add previously isolated @page to appropriate LRU list.
573 * Page may still be unevictable for other reasons.
575 * lru_lock must not be held, interrupts must be enabled.
577 void putback_lru_page(struct page *page)
580 int was_unevictable = PageUnevictable(page);
582 VM_BUG_ON(PageLRU(page));
585 ClearPageUnevictable(page);
587 if (page_evictable(page)) {
589 * For evictable pages, we can use the cache.
590 * In event of a race, worst case is we end up with an
591 * unevictable page on [in]active list.
592 * We know how to handle that.
594 is_unevictable = false;
598 * Put unevictable pages directly on zone's unevictable
601 is_unevictable = true;
602 add_page_to_unevictable_list(page);
604 * When racing with an mlock or AS_UNEVICTABLE clearing
605 * (page is unlocked) make sure that if the other thread
606 * does not observe our setting of PG_lru and fails
607 * isolation/check_move_unevictable_pages,
608 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
609 * the page back to the evictable list.
611 * The other side is TestClearPageMlocked() or shmem_lock().
617 * page's status can change while we move it among lru. If an evictable
618 * page is on unevictable list, it never be freed. To avoid that,
619 * check after we added it to the list, again.
621 if (is_unevictable && page_evictable(page)) {
622 if (!isolate_lru_page(page)) {
626 /* This means someone else dropped this page from LRU
627 * So, it will be freed or putback to LRU again. There is
628 * nothing to do here.
632 if (was_unevictable && !is_unevictable)
633 count_vm_event(UNEVICTABLE_PGRESCUED);
634 else if (!was_unevictable && is_unevictable)
635 count_vm_event(UNEVICTABLE_PGCULLED);
637 put_page(page); /* drop ref from isolate */
640 enum page_references {
642 PAGEREF_RECLAIM_CLEAN,
647 static enum page_references page_check_references(struct page *page,
648 struct scan_control *sc)
650 int referenced_ptes, referenced_page;
651 unsigned long vm_flags;
653 referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
655 referenced_page = TestClearPageReferenced(page);
658 * Mlock lost the isolation race with us. Let try_to_unmap()
659 * move the page to the unevictable list.
661 if (vm_flags & VM_LOCKED)
662 return PAGEREF_RECLAIM;
664 if (referenced_ptes) {
665 if (PageSwapBacked(page))
666 return PAGEREF_ACTIVATE;
668 * All mapped pages start out with page table
669 * references from the instantiating fault, so we need
670 * to look twice if a mapped file page is used more
673 * Mark it and spare it for another trip around the
674 * inactive list. Another page table reference will
675 * lead to its activation.
677 * Note: the mark is set for activated pages as well
678 * so that recently deactivated but used pages are
681 SetPageReferenced(page);
683 if (referenced_page || referenced_ptes > 1)
684 return PAGEREF_ACTIVATE;
687 * Activate file-backed executable pages after first usage.
689 if (vm_flags & VM_EXEC)
690 return PAGEREF_ACTIVATE;
695 /* Reclaim if clean, defer dirty pages to writeback */
696 if (referenced_page && !PageSwapBacked(page))
697 return PAGEREF_RECLAIM_CLEAN;
699 return PAGEREF_RECLAIM;
702 /* Check if a page is dirty or under writeback */
703 static void page_check_dirty_writeback(struct page *page,
704 bool *dirty, bool *writeback)
706 struct address_space *mapping;
709 * Anonymous pages are not handled by flushers and must be written
710 * from reclaim context. Do not stall reclaim based on them
712 if (!page_is_file_cache(page)) {
718 /* By default assume that the page flags are accurate */
719 *dirty = PageDirty(page);
720 *writeback = PageWriteback(page);
722 /* Verify dirty/writeback state if the filesystem supports it */
723 if (!page_has_private(page))
726 mapping = page_mapping(page);
727 if (mapping && mapping->a_ops->is_dirty_writeback)
728 mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
732 * shrink_page_list() returns the number of reclaimed pages
734 static unsigned long shrink_page_list(struct list_head *page_list,
736 struct scan_control *sc,
737 enum ttu_flags ttu_flags,
738 unsigned long *ret_nr_dirty,
739 unsigned long *ret_nr_unqueued_dirty,
740 unsigned long *ret_nr_congested,
741 unsigned long *ret_nr_writeback,
742 unsigned long *ret_nr_immediate,
745 LIST_HEAD(ret_pages);
746 LIST_HEAD(free_pages);
748 unsigned long nr_unqueued_dirty = 0;
749 unsigned long nr_dirty = 0;
750 unsigned long nr_congested = 0;
751 unsigned long nr_reclaimed = 0;
752 unsigned long nr_writeback = 0;
753 unsigned long nr_immediate = 0;
757 mem_cgroup_uncharge_start();
758 while (!list_empty(page_list)) {
759 struct address_space *mapping;
762 enum page_references references = PAGEREF_RECLAIM_CLEAN;
763 bool dirty, writeback;
767 page = lru_to_page(page_list);
768 list_del(&page->lru);
770 if (!trylock_page(page))
773 VM_BUG_ON(PageActive(page));
774 VM_BUG_ON(page_zone(page) != zone);
778 if (unlikely(!page_evictable(page)))
781 if (!sc->may_unmap && page_mapped(page))
784 /* Double the slab pressure for mapped and swapcache pages */
785 if (page_mapped(page) || PageSwapCache(page))
788 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
789 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
792 * The number of dirty pages determines if a zone is marked
793 * reclaim_congested which affects wait_iff_congested. kswapd
794 * will stall and start writing pages if the tail of the LRU
795 * is all dirty unqueued pages.
797 page_check_dirty_writeback(page, &dirty, &writeback);
798 if (dirty || writeback)
801 if (dirty && !writeback)
805 * Treat this page as congested if the underlying BDI is or if
806 * pages are cycling through the LRU so quickly that the
807 * pages marked for immediate reclaim are making it to the
808 * end of the LRU a second time.
810 mapping = page_mapping(page);
811 if ((mapping && bdi_write_congested(mapping->backing_dev_info)) ||
812 (writeback && PageReclaim(page)))
816 * If a page at the tail of the LRU is under writeback, there
817 * are three cases to consider.
819 * 1) If reclaim is encountering an excessive number of pages
820 * under writeback and this page is both under writeback and
821 * PageReclaim then it indicates that pages are being queued
822 * for IO but are being recycled through the LRU before the
823 * IO can complete. Waiting on the page itself risks an
824 * indefinite stall if it is impossible to writeback the
825 * page due to IO error or disconnected storage so instead
826 * note that the LRU is being scanned too quickly and the
827 * caller can stall after page list has been processed.
829 * 2) Global reclaim encounters a page, memcg encounters a
830 * page that is not marked for immediate reclaim or
831 * the caller does not have __GFP_IO. In this case mark
832 * the page for immediate reclaim and continue scanning.
834 * __GFP_IO is checked because a loop driver thread might
835 * enter reclaim, and deadlock if it waits on a page for
836 * which it is needed to do the write (loop masks off
837 * __GFP_IO|__GFP_FS for this reason); but more thought
838 * would probably show more reasons.
840 * Don't require __GFP_FS, since we're not going into the
841 * FS, just waiting on its writeback completion. Worryingly,
842 * ext4 gfs2 and xfs allocate pages with
843 * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so testing
844 * may_enter_fs here is liable to OOM on them.
846 * 3) memcg encounters a page that is not already marked
847 * PageReclaim. memcg does not have any dirty pages
848 * throttling so we could easily OOM just because too many
849 * pages are in writeback and there is nothing else to
850 * reclaim. Wait for the writeback to complete.
852 if (PageWriteback(page)) {
854 if (current_is_kswapd() &&
856 zone_is_reclaim_writeback(zone)) {
861 } else if (global_reclaim(sc) ||
862 !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
864 * This is slightly racy - end_page_writeback()
865 * might have just cleared PageReclaim, then
866 * setting PageReclaim here end up interpreted
867 * as PageReadahead - but that does not matter
868 * enough to care. What we do want is for this
869 * page to have PageReclaim set next time memcg
870 * reclaim reaches the tests above, so it will
871 * then wait_on_page_writeback() to avoid OOM;
872 * and it's also appropriate in global reclaim.
874 SetPageReclaim(page);
881 wait_on_page_writeback(page);
886 references = page_check_references(page, sc);
888 switch (references) {
889 case PAGEREF_ACTIVATE:
890 goto activate_locked;
893 case PAGEREF_RECLAIM:
894 case PAGEREF_RECLAIM_CLEAN:
895 ; /* try to reclaim the page below */
899 * Anonymous process memory has backing store?
900 * Try to allocate it some swap space here.
902 if (PageAnon(page) && !PageSwapCache(page)) {
903 if (!(sc->gfp_mask & __GFP_IO))
905 if (!add_to_swap(page, page_list))
906 goto activate_locked;
909 /* Adding to swap updated mapping */
910 mapping = page_mapping(page);
914 * The page is mapped into the page tables of one or more
915 * processes. Try to unmap it here.
917 if (page_mapped(page) && mapping) {
918 switch (try_to_unmap(page, ttu_flags)) {
920 goto activate_locked;
926 ; /* try to free the page below */
930 if (PageDirty(page)) {
932 * Only kswapd can writeback filesystem pages to
933 * avoid risk of stack overflow but only writeback
934 * if many dirty pages have been encountered.
936 if (page_is_file_cache(page) &&
937 (!current_is_kswapd() ||
938 !zone_is_reclaim_dirty(zone))) {
940 * Immediately reclaim when written back.
941 * Similar in principal to deactivate_page()
942 * except we already have the page isolated
943 * and know it's dirty
945 inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
946 SetPageReclaim(page);
951 if (references == PAGEREF_RECLAIM_CLEAN)
955 if (!sc->may_writepage)
958 /* Page is dirty, try to write it out here */
959 switch (pageout(page, mapping, sc)) {
963 goto activate_locked;
965 if (PageWriteback(page))
971 * A synchronous write - probably a ramdisk. Go
972 * ahead and try to reclaim the page.
974 if (!trylock_page(page))
976 if (PageDirty(page) || PageWriteback(page))
978 mapping = page_mapping(page);
980 ; /* try to free the page below */
985 * If the page has buffers, try to free the buffer mappings
986 * associated with this page. If we succeed we try to free
989 * We do this even if the page is PageDirty().
990 * try_to_release_page() does not perform I/O, but it is
991 * possible for a page to have PageDirty set, but it is actually
992 * clean (all its buffers are clean). This happens if the
993 * buffers were written out directly, with submit_bh(). ext3
994 * will do this, as well as the blockdev mapping.
995 * try_to_release_page() will discover that cleanness and will
996 * drop the buffers and mark the page clean - it can be freed.
998 * Rarely, pages can have buffers and no ->mapping. These are
999 * the pages which were not successfully invalidated in
1000 * truncate_complete_page(). We try to drop those buffers here
1001 * and if that worked, and the page is no longer mapped into
1002 * process address space (page_count == 1) it can be freed.
1003 * Otherwise, leave the page on the LRU so it is swappable.
1005 if (page_has_private(page)) {
1006 if (!try_to_release_page(page, sc->gfp_mask))
1007 goto activate_locked;
1008 if (!mapping && page_count(page) == 1) {
1010 if (put_page_testzero(page))
1014 * rare race with speculative reference.
1015 * the speculative reference will free
1016 * this page shortly, so we may
1017 * increment nr_reclaimed here (and
1018 * leave it off the LRU).
1026 if (!mapping || !__remove_mapping(mapping, page))
1030 * At this point, we have no other references and there is
1031 * no way to pick any more up (removed from LRU, removed
1032 * from pagecache). Can use non-atomic bitops now (and
1033 * we obviously don't have to worry about waking up a process
1034 * waiting on the page lock, because there are no references.
1036 __clear_page_locked(page);
1041 * Is there need to periodically free_page_list? It would
1042 * appear not as the counts should be low
1044 list_add(&page->lru, &free_pages);
1048 if (PageSwapCache(page))
1049 try_to_free_swap(page);
1051 putback_lru_page(page);
1055 /* Not a candidate for swapping, so reclaim swap space. */
1056 if (PageSwapCache(page) && vm_swap_full())
1057 try_to_free_swap(page);
1058 VM_BUG_ON(PageActive(page));
1059 SetPageActive(page);
1064 list_add(&page->lru, &ret_pages);
1065 VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
1068 free_hot_cold_page_list(&free_pages, 1);
1070 list_splice(&ret_pages, page_list);
1071 count_vm_events(PGACTIVATE, pgactivate);
1072 mem_cgroup_uncharge_end();
1073 *ret_nr_dirty += nr_dirty;
1074 *ret_nr_congested += nr_congested;
1075 *ret_nr_unqueued_dirty += nr_unqueued_dirty;
1076 *ret_nr_writeback += nr_writeback;
1077 *ret_nr_immediate += nr_immediate;
1078 return nr_reclaimed;
1081 unsigned long reclaim_clean_pages_from_list(struct zone *zone,
1082 struct list_head *page_list)
1084 struct scan_control sc = {
1085 .gfp_mask = GFP_KERNEL,
1086 .priority = DEF_PRIORITY,
1089 unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
1090 struct page *page, *next;
1091 LIST_HEAD(clean_pages);
1093 list_for_each_entry_safe(page, next, page_list, lru) {
1094 if (page_is_file_cache(page) && !PageDirty(page)) {
1095 ClearPageActive(page);
1096 list_move(&page->lru, &clean_pages);
1100 ret = shrink_page_list(&clean_pages, zone, &sc,
1101 TTU_UNMAP|TTU_IGNORE_ACCESS,
1102 &dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
1103 list_splice(&clean_pages, page_list);
1104 __mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
1109 * Attempt to remove the specified page from its LRU. Only take this page
1110 * if it is of the appropriate PageActive status. Pages which are being
1111 * freed elsewhere are also ignored.
1113 * page: page to consider
1114 * mode: one of the LRU isolation modes defined above
1116 * returns 0 on success, -ve errno on failure.
1118 int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1122 /* Only take pages on the LRU. */
1126 /* Compaction should not handle unevictable pages but CMA can do so */
1127 if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1133 * To minimise LRU disruption, the caller can indicate that it only
1134 * wants to isolate pages it will be able to operate on without
1135 * blocking - clean pages for the most part.
1137 * ISOLATE_CLEAN means that only clean pages should be isolated. This
1138 * is used by reclaim when it is cannot write to backing storage
1140 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1141 * that it is possible to migrate without blocking
1143 if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
1144 /* All the caller can do on PageWriteback is block */
1145 if (PageWriteback(page))
1148 if (PageDirty(page)) {
1149 struct address_space *mapping;
1151 /* ISOLATE_CLEAN means only clean pages */
1152 if (mode & ISOLATE_CLEAN)
1156 * Only pages without mappings or that have a
1157 * ->migratepage callback are possible to migrate
1160 mapping = page_mapping(page);
1161 if (mapping && !mapping->a_ops->migratepage)
1166 if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1169 if (likely(get_page_unless_zero(page))) {
1171 * Be careful not to clear PageLRU until after we're
1172 * sure the page is not being freed elsewhere -- the
1173 * page release code relies on it.
1183 * zone->lru_lock is heavily contended. Some of the functions that
1184 * shrink the lists perform better by taking out a batch of pages
1185 * and working on them outside the LRU lock.
1187 * For pagecache intensive workloads, this function is the hottest
1188 * spot in the kernel (apart from copy_*_user functions).
1190 * Appropriate locks must be held before calling this function.
1192 * @nr_to_scan: The number of pages to look through on the list.
1193 * @lruvec: The LRU vector to pull pages from.
1194 * @dst: The temp list to put pages on to.
1195 * @nr_scanned: The number of pages that were scanned.
1196 * @sc: The scan_control struct for this reclaim session
1197 * @mode: One of the LRU isolation modes
1198 * @lru: LRU list id for isolating
1200 * returns how many pages were moved onto *@dst.
1202 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1203 struct lruvec *lruvec, struct list_head *dst,
1204 unsigned long *nr_scanned, struct scan_control *sc,
1205 isolate_mode_t mode, enum lru_list lru)
1207 struct list_head *src = &lruvec->lists[lru];
1208 unsigned long nr_taken = 0;
1211 for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1215 page = lru_to_page(src);
1216 prefetchw_prev_lru_page(page, src, flags);
1218 VM_BUG_ON(!PageLRU(page));
1220 switch (__isolate_lru_page(page, mode)) {
1222 nr_pages = hpage_nr_pages(page);
1223 mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
1224 list_move(&page->lru, dst);
1225 nr_taken += nr_pages;
1229 /* else it is being freed elsewhere */
1230 list_move(&page->lru, src);
1239 trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
1240 nr_taken, mode, is_file_lru(lru));
1245 * isolate_lru_page - tries to isolate a page from its LRU list
1246 * @page: page to isolate from its LRU list
1248 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1249 * vmstat statistic corresponding to whatever LRU list the page was on.
1251 * Returns 0 if the page was removed from an LRU list.
1252 * Returns -EBUSY if the page was not on an LRU list.
1254 * The returned page will have PageLRU() cleared. If it was found on
1255 * the active list, it will have PageActive set. If it was found on
1256 * the unevictable list, it will have the PageUnevictable bit set. That flag
1257 * may need to be cleared by the caller before letting the page go.
1259 * The vmstat statistic corresponding to the list on which the page was
1260 * found will be decremented.
1263 * (1) Must be called with an elevated refcount on the page. This is a
1264 * fundamentnal difference from isolate_lru_pages (which is called
1265 * without a stable reference).
1266 * (2) the lru_lock must not be held.
1267 * (3) interrupts must be enabled.
1269 int isolate_lru_page(struct page *page)
1273 VM_BUG_ON(!page_count(page));
1275 if (PageLRU(page)) {
1276 struct zone *zone = page_zone(page);
1277 struct lruvec *lruvec;
1279 spin_lock_irq(&zone->lru_lock);
1280 lruvec = mem_cgroup_page_lruvec(page, zone);
1281 if (PageLRU(page)) {
1282 int lru = page_lru(page);
1285 del_page_from_lru_list(page, lruvec, lru);
1288 spin_unlock_irq(&zone->lru_lock);
1294 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
1295 * then get resheduled. When there are massive number of tasks doing page
1296 * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
1297 * the LRU list will go small and be scanned faster than necessary, leading to
1298 * unnecessary swapping, thrashing and OOM.
1300 static int too_many_isolated(struct zone *zone, int file,
1301 struct scan_control *sc)
1303 unsigned long inactive, isolated;
1305 if (current_is_kswapd())
1308 if (!global_reclaim(sc))
1312 inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1313 isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1315 inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1316 isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1320 * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
1321 * won't get blocked by normal direct-reclaimers, forming a circular
1324 if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS)
1327 return isolated > inactive;
1330 static noinline_for_stack void
1331 putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1333 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1334 struct zone *zone = lruvec_zone(lruvec);
1335 LIST_HEAD(pages_to_free);
1338 * Put back any unfreeable pages.
1340 while (!list_empty(page_list)) {
1341 struct page *page = lru_to_page(page_list);
1344 VM_BUG_ON(PageLRU(page));
1345 list_del(&page->lru);
1346 if (unlikely(!page_evictable(page))) {
1347 spin_unlock_irq(&zone->lru_lock);
1348 putback_lru_page(page);
1349 spin_lock_irq(&zone->lru_lock);
1353 lruvec = mem_cgroup_page_lruvec(page, zone);
1356 lru = page_lru(page);
1357 add_page_to_lru_list(page, lruvec, lru);
1359 if (is_active_lru(lru)) {
1360 int file = is_file_lru(lru);
1361 int numpages = hpage_nr_pages(page);
1362 reclaim_stat->recent_rotated[file] += numpages;
1364 if (put_page_testzero(page)) {
1365 __ClearPageLRU(page);
1366 __ClearPageActive(page);
1367 del_page_from_lru_list(page, lruvec, lru);
1369 if (unlikely(PageCompound(page))) {
1370 spin_unlock_irq(&zone->lru_lock);
1371 (*get_compound_page_dtor(page))(page);
1372 spin_lock_irq(&zone->lru_lock);
1374 list_add(&page->lru, &pages_to_free);
1379 * To save our caller's stack, now use input list for pages to free.
1381 list_splice(&pages_to_free, page_list);
1385 * shrink_inactive_list() is a helper for shrink_zone(). It returns the number
1386 * of reclaimed pages
1388 static noinline_for_stack unsigned long
1389 shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1390 struct scan_control *sc, enum lru_list lru)
1392 LIST_HEAD(page_list);
1393 unsigned long nr_scanned;
1394 unsigned long nr_reclaimed = 0;
1395 unsigned long nr_taken;
1396 unsigned long nr_dirty = 0;
1397 unsigned long nr_congested = 0;
1398 unsigned long nr_unqueued_dirty = 0;
1399 unsigned long nr_writeback = 0;
1400 unsigned long nr_immediate = 0;
1401 isolate_mode_t isolate_mode = 0;
1402 int file = is_file_lru(lru);
1403 struct zone *zone = lruvec_zone(lruvec);
1404 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1406 while (unlikely(too_many_isolated(zone, file, sc))) {
1407 congestion_wait(BLK_RW_ASYNC, HZ/10);
1409 /* We are about to die and free our memory. Return now. */
1410 if (fatal_signal_pending(current))
1411 return SWAP_CLUSTER_MAX;
1417 isolate_mode |= ISOLATE_UNMAPPED;
1418 if (!sc->may_writepage)
1419 isolate_mode |= ISOLATE_CLEAN;
1421 spin_lock_irq(&zone->lru_lock);
1423 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1424 &nr_scanned, sc, isolate_mode, lru);
1426 __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1427 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1429 if (global_reclaim(sc)) {
1430 zone->pages_scanned += nr_scanned;
1431 if (current_is_kswapd())
1432 __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1434 __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1436 spin_unlock_irq(&zone->lru_lock);
1441 nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
1442 &nr_dirty, &nr_unqueued_dirty, &nr_congested,
1443 &nr_writeback, &nr_immediate,
1446 spin_lock_irq(&zone->lru_lock);
1448 reclaim_stat->recent_scanned[file] += nr_taken;
1450 if (global_reclaim(sc)) {
1451 if (current_is_kswapd())
1452 __count_zone_vm_events(PGSTEAL_KSWAPD, zone,
1455 __count_zone_vm_events(PGSTEAL_DIRECT, zone,
1459 putback_inactive_pages(lruvec, &page_list);
1461 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1463 spin_unlock_irq(&zone->lru_lock);
1465 free_hot_cold_page_list(&page_list, 1);
1468 * If reclaim is isolating dirty pages under writeback, it implies
1469 * that the long-lived page allocation rate is exceeding the page
1470 * laundering rate. Either the global limits are not being effective
1471 * at throttling processes due to the page distribution throughout
1472 * zones or there is heavy usage of a slow backing device. The
1473 * only option is to throttle from reclaim context which is not ideal
1474 * as there is no guarantee the dirtying process is throttled in the
1475 * same way balance_dirty_pages() manages.
1477 * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
1478 * of pages under pages flagged for immediate reclaim and stall if any
1479 * are encountered in the nr_immediate check below.
1481 if (nr_writeback && nr_writeback == nr_taken)
1482 zone_set_flag(zone, ZONE_WRITEBACK);
1485 * memcg will stall in page writeback so only consider forcibly
1486 * stalling for global reclaim
1488 if (global_reclaim(sc)) {
1490 * Tag a zone as congested if all the dirty pages scanned were
1491 * backed by a congested BDI and wait_iff_congested will stall.
1493 if (nr_dirty && nr_dirty == nr_congested)
1494 zone_set_flag(zone, ZONE_CONGESTED);
1497 * If dirty pages are scanned that are not queued for IO, it
1498 * implies that flushers are not keeping up. In this case, flag
1499 * the zone ZONE_TAIL_LRU_DIRTY and kswapd will start writing
1500 * pages from reclaim context. It will forcibly stall in the
1503 if (nr_unqueued_dirty == nr_taken)
1504 zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY);
1507 * In addition, if kswapd scans pages marked marked for
1508 * immediate reclaim and under writeback (nr_immediate), it
1509 * implies that pages are cycling through the LRU faster than
1510 * they are written so also forcibly stall.
1512 if (nr_unqueued_dirty == nr_taken || nr_immediate)
1513 congestion_wait(BLK_RW_ASYNC, HZ/10);
1517 * Stall direct reclaim for IO completions if underlying BDIs or zone
1518 * is congested. Allow kswapd to continue until it starts encountering
1519 * unqueued dirty pages or cycling through the LRU too quickly.
1521 if (!sc->hibernation_mode && !current_is_kswapd())
1522 wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
1524 trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1526 nr_scanned, nr_reclaimed,
1528 trace_shrink_flags(file));
1529 return nr_reclaimed;
1533 * This moves pages from the active list to the inactive list.
1535 * We move them the other way if the page is referenced by one or more
1536 * processes, from rmap.
1538 * If the pages are mostly unmapped, the processing is fast and it is
1539 * appropriate to hold zone->lru_lock across the whole operation. But if
1540 * the pages are mapped, the processing is slow (page_referenced()) so we
1541 * should drop zone->lru_lock around each page. It's impossible to balance
1542 * this, so instead we remove the pages from the LRU while processing them.
1543 * It is safe to rely on PG_active against the non-LRU pages in here because
1544 * nobody will play with that bit on a non-LRU page.
1546 * The downside is that we have to touch page->_count against each page.
1547 * But we had to alter page->flags anyway.
1550 static void move_active_pages_to_lru(struct lruvec *lruvec,
1551 struct list_head *list,
1552 struct list_head *pages_to_free,
1555 struct zone *zone = lruvec_zone(lruvec);
1556 unsigned long pgmoved = 0;
1560 while (!list_empty(list)) {
1561 page = lru_to_page(list);
1562 lruvec = mem_cgroup_page_lruvec(page, zone);
1564 VM_BUG_ON(PageLRU(page));
1567 nr_pages = hpage_nr_pages(page);
1568 mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1569 list_move(&page->lru, &lruvec->lists[lru]);
1570 pgmoved += nr_pages;
1572 if (put_page_testzero(page)) {
1573 __ClearPageLRU(page);
1574 __ClearPageActive(page);
1575 del_page_from_lru_list(page, lruvec, lru);
1577 if (unlikely(PageCompound(page))) {
1578 spin_unlock_irq(&zone->lru_lock);
1579 (*get_compound_page_dtor(page))(page);
1580 spin_lock_irq(&zone->lru_lock);
1582 list_add(&page->lru, pages_to_free);
1585 __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1586 if (!is_active_lru(lru))
1587 __count_vm_events(PGDEACTIVATE, pgmoved);
1590 static void shrink_active_list(unsigned long nr_to_scan,
1591 struct lruvec *lruvec,
1592 struct scan_control *sc,
1595 unsigned long nr_taken;
1596 unsigned long nr_scanned;
1597 unsigned long vm_flags;
1598 LIST_HEAD(l_hold); /* The pages which were snipped off */
1599 LIST_HEAD(l_active);
1600 LIST_HEAD(l_inactive);
1602 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1603 unsigned long nr_rotated = 0;
1604 isolate_mode_t isolate_mode = 0;
1605 int file = is_file_lru(lru);
1606 struct zone *zone = lruvec_zone(lruvec);
1611 isolate_mode |= ISOLATE_UNMAPPED;
1612 if (!sc->may_writepage)
1613 isolate_mode |= ISOLATE_CLEAN;
1615 spin_lock_irq(&zone->lru_lock);
1617 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1618 &nr_scanned, sc, isolate_mode, lru);
1619 if (global_reclaim(sc))
1620 zone->pages_scanned += nr_scanned;
1622 reclaim_stat->recent_scanned[file] += nr_taken;
1624 __count_zone_vm_events(PGREFILL, zone, nr_scanned);
1625 __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1626 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1627 spin_unlock_irq(&zone->lru_lock);
1629 while (!list_empty(&l_hold)) {
1631 page = lru_to_page(&l_hold);
1632 list_del(&page->lru);
1634 if (unlikely(!page_evictable(page))) {
1635 putback_lru_page(page);
1639 if (unlikely(buffer_heads_over_limit)) {
1640 if (page_has_private(page) && trylock_page(page)) {
1641 if (page_has_private(page))
1642 try_to_release_page(page, 0);
1647 if (page_referenced(page, 0, sc->target_mem_cgroup,
1649 nr_rotated += hpage_nr_pages(page);
1651 * Identify referenced, file-backed active pages and
1652 * give them one more trip around the active list. So
1653 * that executable code get better chances to stay in
1654 * memory under moderate memory pressure. Anon pages
1655 * are not likely to be evicted by use-once streaming
1656 * IO, plus JVM can create lots of anon VM_EXEC pages,
1657 * so we ignore them here.
1659 if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1660 list_add(&page->lru, &l_active);
1665 ClearPageActive(page); /* we are de-activating */
1666 list_add(&page->lru, &l_inactive);
1670 * Move pages back to the lru list.
1672 spin_lock_irq(&zone->lru_lock);
1674 * Count referenced pages from currently used mappings as rotated,
1675 * even though only some of them are actually re-activated. This
1676 * helps balance scan pressure between file and anonymous pages in
1679 reclaim_stat->recent_rotated[file] += nr_rotated;
1681 move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1682 move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1683 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1684 spin_unlock_irq(&zone->lru_lock);
1686 free_hot_cold_page_list(&l_hold, 1);
1690 static int inactive_anon_is_low_global(struct zone *zone)
1692 unsigned long active, inactive;
1694 active = zone_page_state(zone, NR_ACTIVE_ANON);
1695 inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1697 if (inactive * zone->inactive_ratio < active)
1704 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1705 * @lruvec: LRU vector to check
1707 * Returns true if the zone does not have enough inactive anon pages,
1708 * meaning some active anon pages need to be deactivated.
1710 static int inactive_anon_is_low(struct lruvec *lruvec)
1713 * If we don't have swap space, anonymous page deactivation
1716 if (!total_swap_pages)
1719 if (!mem_cgroup_disabled())
1720 return mem_cgroup_inactive_anon_is_low(lruvec);
1722 return inactive_anon_is_low_global(lruvec_zone(lruvec));
1725 static inline int inactive_anon_is_low(struct lruvec *lruvec)
1732 * inactive_file_is_low - check if file pages need to be deactivated
1733 * @lruvec: LRU vector to check
1735 * When the system is doing streaming IO, memory pressure here
1736 * ensures that active file pages get deactivated, until more
1737 * than half of the file pages are on the inactive list.
1739 * Once we get to that situation, protect the system's working
1740 * set from being evicted by disabling active file page aging.
1742 * This uses a different ratio than the anonymous pages, because
1743 * the page cache uses a use-once replacement algorithm.
1745 static int inactive_file_is_low(struct lruvec *lruvec)
1747 unsigned long inactive;
1748 unsigned long active;
1750 inactive = get_lru_size(lruvec, LRU_INACTIVE_FILE);
1751 active = get_lru_size(lruvec, LRU_ACTIVE_FILE);
1753 return active > inactive;
1756 static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1758 if (is_file_lru(lru))
1759 return inactive_file_is_low(lruvec);
1761 return inactive_anon_is_low(lruvec);
1764 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1765 struct lruvec *lruvec, struct scan_control *sc)
1767 if (is_active_lru(lru)) {
1768 if (inactive_list_is_low(lruvec, lru))
1769 shrink_active_list(nr_to_scan, lruvec, sc, lru);
1773 return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1776 static int vmscan_swappiness(struct scan_control *sc)
1778 if (global_reclaim(sc))
1779 return vm_swappiness;
1780 return mem_cgroup_swappiness(sc->target_mem_cgroup);
1791 * Determine how aggressively the anon and file LRU lists should be
1792 * scanned. The relative value of each set of LRU lists is determined
1793 * by looking at the fraction of the pages scanned we did rotate back
1794 * onto the active list instead of evict.
1796 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
1797 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
1799 static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
1802 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1804 u64 denominator = 0; /* gcc */
1805 struct zone *zone = lruvec_zone(lruvec);
1806 unsigned long anon_prio, file_prio;
1807 enum scan_balance scan_balance;
1808 unsigned long anon, file, free;
1809 bool force_scan = false;
1810 unsigned long ap, fp;
1814 * If the zone or memcg is small, nr[l] can be 0. This
1815 * results in no scanning on this priority and a potential
1816 * priority drop. Global direct reclaim can go to the next
1817 * zone and tends to have no problems. Global kswapd is for
1818 * zone balancing and it needs to scan a minimum amount. When
1819 * reclaiming for a memcg, a priority drop can cause high
1820 * latencies, so it's better to scan a minimum amount there as
1823 if (current_is_kswapd() && !zone_reclaimable(zone))
1825 if (!global_reclaim(sc))
1828 /* If we have no swap space, do not bother scanning anon pages. */
1829 if (!sc->may_swap || (get_nr_swap_pages() <= 0)) {
1830 scan_balance = SCAN_FILE;
1835 * Global reclaim will swap to prevent OOM even with no
1836 * swappiness, but memcg users want to use this knob to
1837 * disable swapping for individual groups completely when
1838 * using the memory controller's swap limit feature would be
1841 if (!global_reclaim(sc) && !vmscan_swappiness(sc)) {
1842 scan_balance = SCAN_FILE;
1847 * Do not apply any pressure balancing cleverness when the
1848 * system is close to OOM, scan both anon and file equally
1849 * (unless the swappiness setting disagrees with swapping).
1851 if (!sc->priority && vmscan_swappiness(sc)) {
1852 scan_balance = SCAN_EQUAL;
1856 anon = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
1857 get_lru_size(lruvec, LRU_INACTIVE_ANON);
1858 file = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
1859 get_lru_size(lruvec, LRU_INACTIVE_FILE);
1862 * If it's foreseeable that reclaiming the file cache won't be
1863 * enough to get the zone back into a desirable shape, we have
1864 * to swap. Better start now and leave the - probably heavily
1865 * thrashing - remaining file pages alone.
1867 if (global_reclaim(sc)) {
1868 free = zone_page_state(zone, NR_FREE_PAGES);
1869 if (unlikely(file + free <= high_wmark_pages(zone))) {
1870 scan_balance = SCAN_ANON;
1876 * There is enough inactive page cache, do not reclaim
1877 * anything from the anonymous working set right now.
1879 if (!inactive_file_is_low(lruvec)) {
1880 scan_balance = SCAN_FILE;
1884 scan_balance = SCAN_FRACT;
1887 * With swappiness at 100, anonymous and file have the same priority.
1888 * This scanning priority is essentially the inverse of IO cost.
1890 anon_prio = vmscan_swappiness(sc);
1891 file_prio = 200 - anon_prio;
1894 * OK, so we have swap space and a fair amount of page cache
1895 * pages. We use the recently rotated / recently scanned
1896 * ratios to determine how valuable each cache is.
1898 * Because workloads change over time (and to avoid overflow)
1899 * we keep these statistics as a floating average, which ends
1900 * up weighing recent references more than old ones.
1902 * anon in [0], file in [1]
1904 spin_lock_irq(&zone->lru_lock);
1905 if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1906 reclaim_stat->recent_scanned[0] /= 2;
1907 reclaim_stat->recent_rotated[0] /= 2;
1910 if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1911 reclaim_stat->recent_scanned[1] /= 2;
1912 reclaim_stat->recent_rotated[1] /= 2;
1916 * The amount of pressure on anon vs file pages is inversely
1917 * proportional to the fraction of recently scanned pages on
1918 * each list that were recently referenced and in active use.
1920 ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1921 ap /= reclaim_stat->recent_rotated[0] + 1;
1923 fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
1924 fp /= reclaim_stat->recent_rotated[1] + 1;
1925 spin_unlock_irq(&zone->lru_lock);
1929 denominator = ap + fp + 1;
1931 for_each_evictable_lru(lru) {
1932 int file = is_file_lru(lru);
1936 size = get_lru_size(lruvec, lru);
1937 scan = size >> sc->priority;
1939 if (!scan && force_scan)
1940 scan = min(size, SWAP_CLUSTER_MAX);
1942 switch (scan_balance) {
1944 /* Scan lists relative to size */
1948 * Scan types proportional to swappiness and
1949 * their relative recent reclaim efficiency.
1951 scan = div64_u64(scan * fraction[file], denominator);
1955 /* Scan one type exclusively */
1956 if ((scan_balance == SCAN_FILE) != file)
1960 /* Look ma, no brain */
1968 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
1970 static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
1972 unsigned long nr[NR_LRU_LISTS];
1973 unsigned long targets[NR_LRU_LISTS];
1974 unsigned long nr_to_scan;
1976 unsigned long nr_reclaimed = 0;
1977 unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1978 struct blk_plug plug;
1979 bool scan_adjusted = false;
1981 get_scan_count(lruvec, sc, nr);
1983 /* Record the original scan target for proportional adjustments later */
1984 memcpy(targets, nr, sizeof(nr));
1986 blk_start_plug(&plug);
1987 while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1988 nr[LRU_INACTIVE_FILE]) {
1989 unsigned long nr_anon, nr_file, percentage;
1990 unsigned long nr_scanned;
1992 for_each_evictable_lru(lru) {
1994 nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
1995 nr[lru] -= nr_to_scan;
1997 nr_reclaimed += shrink_list(lru, nr_to_scan,
2002 if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
2006 * For global direct reclaim, reclaim only the number of pages
2007 * requested. Less care is taken to scan proportionally as it
2008 * is more important to minimise direct reclaim stall latency
2009 * than it is to properly age the LRU lists.
2011 if (global_reclaim(sc) && !current_is_kswapd())
2015 * For kswapd and memcg, reclaim at least the number of pages
2016 * requested. Ensure that the anon and file LRUs shrink
2017 * proportionally what was requested by get_scan_count(). We
2018 * stop reclaiming one LRU and reduce the amount scanning
2019 * proportional to the original scan target.
2021 nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
2022 nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
2024 if (nr_file > nr_anon) {
2025 unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
2026 targets[LRU_ACTIVE_ANON] + 1;
2028 percentage = nr_anon * 100 / scan_target;
2030 unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
2031 targets[LRU_ACTIVE_FILE] + 1;
2033 percentage = nr_file * 100 / scan_target;
2036 /* Stop scanning the smaller of the LRU */
2038 nr[lru + LRU_ACTIVE] = 0;
2041 * Recalculate the other LRU scan count based on its original
2042 * scan target and the percentage scanning already complete
2044 lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
2045 nr_scanned = targets[lru] - nr[lru];
2046 nr[lru] = targets[lru] * (100 - percentage) / 100;
2047 nr[lru] -= min(nr[lru], nr_scanned);
2050 nr_scanned = targets[lru] - nr[lru];
2051 nr[lru] = targets[lru] * (100 - percentage) / 100;
2052 nr[lru] -= min(nr[lru], nr_scanned);
2054 scan_adjusted = true;
2056 blk_finish_plug(&plug);
2057 sc->nr_reclaimed += nr_reclaimed;
2060 * Even if we did not try to evict anon pages at all, we want to
2061 * rebalance the anon lru active/inactive ratio.
2063 if (inactive_anon_is_low(lruvec))
2064 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2065 sc, LRU_ACTIVE_ANON);
2067 throttle_vm_writeout(sc->gfp_mask);
2070 /* Use reclaim/compaction for costly allocs or under memory pressure */
2071 static bool in_reclaim_compaction(struct scan_control *sc)
2073 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2074 (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
2075 sc->priority < DEF_PRIORITY - 2))
2082 * Reclaim/compaction is used for high-order allocation requests. It reclaims
2083 * order-0 pages before compacting the zone. should_continue_reclaim() returns
2084 * true if more pages should be reclaimed such that when the page allocator
2085 * calls try_to_compact_zone() that it will have enough free pages to succeed.
2086 * It will give up earlier than that if there is difficulty reclaiming pages.
2088 static inline bool should_continue_reclaim(struct zone *zone,
2089 unsigned long nr_reclaimed,
2090 unsigned long nr_scanned,
2091 struct scan_control *sc)
2093 unsigned long pages_for_compaction;
2094 unsigned long inactive_lru_pages;
2096 /* If not in reclaim/compaction mode, stop */
2097 if (!in_reclaim_compaction(sc))
2100 /* Consider stopping depending on scan and reclaim activity */
2101 if (sc->gfp_mask & __GFP_REPEAT) {
2103 * For __GFP_REPEAT allocations, stop reclaiming if the
2104 * full LRU list has been scanned and we are still failing
2105 * to reclaim pages. This full LRU scan is potentially
2106 * expensive but a __GFP_REPEAT caller really wants to succeed
2108 if (!nr_reclaimed && !nr_scanned)
2112 * For non-__GFP_REPEAT allocations which can presumably
2113 * fail without consequence, stop if we failed to reclaim
2114 * any pages from the last SWAP_CLUSTER_MAX number of
2115 * pages that were scanned. This will return to the
2116 * caller faster at the risk reclaim/compaction and
2117 * the resulting allocation attempt fails
2124 * If we have not reclaimed enough pages for compaction and the
2125 * inactive lists are large enough, continue reclaiming
2127 pages_for_compaction = (2UL << sc->order);
2128 inactive_lru_pages = zone_page_state(zone, NR_INACTIVE_FILE);
2129 if (get_nr_swap_pages() > 0)
2130 inactive_lru_pages += zone_page_state(zone, NR_INACTIVE_ANON);
2131 if (sc->nr_reclaimed < pages_for_compaction &&
2132 inactive_lru_pages > pages_for_compaction)
2135 /* If compaction would go ahead or the allocation would succeed, stop */
2136 switch (compaction_suitable(zone, sc->order)) {
2137 case COMPACT_PARTIAL:
2138 case COMPACT_CONTINUE:
2146 __shrink_zone(struct zone *zone, struct scan_control *sc, bool soft_reclaim)
2148 unsigned long nr_reclaimed, nr_scanned;
2151 struct mem_cgroup *root = sc->target_mem_cgroup;
2152 struct mem_cgroup_reclaim_cookie reclaim = {
2154 .priority = sc->priority,
2156 struct mem_cgroup *memcg = NULL;
2157 mem_cgroup_iter_filter filter = (soft_reclaim) ?
2158 mem_cgroup_soft_reclaim_eligible : NULL;
2160 nr_reclaimed = sc->nr_reclaimed;
2161 nr_scanned = sc->nr_scanned;
2163 while ((memcg = mem_cgroup_iter_cond(root, memcg, &reclaim, filter))) {
2164 struct lruvec *lruvec;
2166 lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2168 shrink_lruvec(lruvec, sc);
2171 * Direct reclaim and kswapd have to scan all memory
2172 * cgroups to fulfill the overall scan target for the
2175 * Limit reclaim, on the other hand, only cares about
2176 * nr_to_reclaim pages to be reclaimed and it will
2177 * retry with decreasing priority if one round over the
2178 * whole hierarchy is not sufficient.
2180 if (!global_reclaim(sc) &&
2181 sc->nr_reclaimed >= sc->nr_to_reclaim) {
2182 mem_cgroup_iter_break(root, memcg);
2187 vmpressure(sc->gfp_mask, sc->target_mem_cgroup,
2188 sc->nr_scanned - nr_scanned,
2189 sc->nr_reclaimed - nr_reclaimed);
2191 } while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed,
2192 sc->nr_scanned - nr_scanned, sc));
2196 static void shrink_zone(struct zone *zone, struct scan_control *sc)
2198 bool do_soft_reclaim = mem_cgroup_should_soft_reclaim(sc);
2199 unsigned long nr_scanned = sc->nr_scanned;
2201 __shrink_zone(zone, sc, do_soft_reclaim);
2204 * No group is over the soft limit or those that are do not have
2205 * pages in the zone we are reclaiming so we have to reclaim everybody
2207 if (do_soft_reclaim && (sc->nr_scanned == nr_scanned)) {
2208 __shrink_zone(zone, sc, false);
2213 /* Returns true if compaction should go ahead for a high-order request */
2214 static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
2216 unsigned long balance_gap, watermark;
2219 /* Do not consider compaction for orders reclaim is meant to satisfy */
2220 if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
2224 * Compaction takes time to run and there are potentially other
2225 * callers using the pages just freed. Continue reclaiming until
2226 * there is a buffer of free pages available to give compaction
2227 * a reasonable chance of completing and allocating the page
2229 balance_gap = min(low_wmark_pages(zone),
2230 (zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2231 KSWAPD_ZONE_BALANCE_GAP_RATIO);
2232 watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
2233 watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
2236 * If compaction is deferred, reclaim up to a point where
2237 * compaction will have a chance of success when re-enabled
2239 if (compaction_deferred(zone, sc->order))
2240 return watermark_ok;
2242 /* If compaction is not ready to start, keep reclaiming */
2243 if (!compaction_suitable(zone, sc->order))
2246 return watermark_ok;
2250 * This is the direct reclaim path, for page-allocating processes. We only
2251 * try to reclaim pages from zones which will satisfy the caller's allocation
2254 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
2256 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
2258 * b) The target zone may be at high_wmark_pages(zone) but the lower zones
2259 * must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
2260 * zone defense algorithm.
2262 * If a zone is deemed to be full of pinned pages then just give it a light
2263 * scan then give up on it.
2265 * This function returns true if a zone is being reclaimed for a costly
2266 * high-order allocation and compaction is ready to begin. This indicates to
2267 * the caller that it should consider retrying the allocation instead of
2270 static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
2274 bool aborted_reclaim = false;
2277 * If the number of buffer_heads in the machine exceeds the maximum
2278 * allowed level, force direct reclaim to scan the highmem zone as
2279 * highmem pages could be pinning lowmem pages storing buffer_heads
2281 if (buffer_heads_over_limit)
2282 sc->gfp_mask |= __GFP_HIGHMEM;
2284 for_each_zone_zonelist_nodemask(zone, z, zonelist,
2285 gfp_zone(sc->gfp_mask), sc->nodemask) {
2286 if (!populated_zone(zone))
2289 * Take care memory controller reclaiming has small influence
2292 if (global_reclaim(sc)) {
2293 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2295 if (sc->priority != DEF_PRIORITY &&
2296 !zone_reclaimable(zone))
2297 continue; /* Let kswapd poll it */
2298 if (IS_ENABLED(CONFIG_COMPACTION)) {
2300 * If we already have plenty of memory free for
2301 * compaction in this zone, don't free any more.
2302 * Even though compaction is invoked for any
2303 * non-zero order, only frequent costly order
2304 * reclamation is disruptive enough to become a
2305 * noticeable problem, like transparent huge
2308 if (compaction_ready(zone, sc)) {
2309 aborted_reclaim = true;
2313 /* need some check for avoid more shrink_zone() */
2316 shrink_zone(zone, sc);
2319 return aborted_reclaim;
2322 /* All zones in zonelist are unreclaimable? */
2323 static bool all_unreclaimable(struct zonelist *zonelist,
2324 struct scan_control *sc)
2329 for_each_zone_zonelist_nodemask(zone, z, zonelist,
2330 gfp_zone(sc->gfp_mask), sc->nodemask) {
2331 if (!populated_zone(zone))
2333 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2335 if (zone_reclaimable(zone))
2343 * This is the main entry point to direct page reclaim.
2345 * If a full scan of the inactive list fails to free enough memory then we
2346 * are "out of memory" and something needs to be killed.
2348 * If the caller is !__GFP_FS then the probability of a failure is reasonably
2349 * high - the zone may be full of dirty or under-writeback pages, which this
2350 * caller can't do much about. We kick the writeback threads and take explicit
2351 * naps in the hope that some of these pages can be written. But if the
2352 * allocating task holds filesystem locks which prevent writeout this might not
2353 * work, and the allocation attempt will fail.
2355 * returns: 0, if no pages reclaimed
2356 * else, the number of pages reclaimed
2358 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2359 struct scan_control *sc,
2360 struct shrink_control *shrink)
2362 unsigned long total_scanned = 0;
2363 struct reclaim_state *reclaim_state = current->reclaim_state;
2366 unsigned long writeback_threshold;
2367 bool aborted_reclaim;
2369 delayacct_freepages_start();
2371 if (global_reclaim(sc))
2372 count_vm_event(ALLOCSTALL);
2375 vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
2378 aborted_reclaim = shrink_zones(zonelist, sc);
2381 * Don't shrink slabs when reclaiming memory from over limit
2382 * cgroups but do shrink slab at least once when aborting
2383 * reclaim for compaction to avoid unevenly scanning file/anon
2384 * LRU pages over slab pages.
2386 if (global_reclaim(sc)) {
2387 unsigned long lru_pages = 0;
2388 for_each_zone_zonelist(zone, z, zonelist,
2389 gfp_zone(sc->gfp_mask)) {
2390 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2393 lru_pages += zone_reclaimable_pages(zone);
2396 shrink_slab(shrink, sc->nr_scanned, lru_pages);
2397 if (reclaim_state) {
2398 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2399 reclaim_state->reclaimed_slab = 0;
2402 total_scanned += sc->nr_scanned;
2403 if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2407 * If we're getting trouble reclaiming, start doing
2408 * writepage even in laptop mode.
2410 if (sc->priority < DEF_PRIORITY - 2)
2411 sc->may_writepage = 1;
2414 * Try to write back as many pages as we just scanned. This
2415 * tends to cause slow streaming writers to write data to the
2416 * disk smoothly, at the dirtying rate, which is nice. But
2417 * that's undesirable in laptop mode, where we *want* lumpy
2418 * writeout. So in laptop mode, write out the whole world.
2420 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2421 if (total_scanned > writeback_threshold) {
2422 wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2423 WB_REASON_TRY_TO_FREE_PAGES);
2424 sc->may_writepage = 1;
2426 } while (--sc->priority >= 0 && !aborted_reclaim);
2429 delayacct_freepages_end();
2431 if (sc->nr_reclaimed)
2432 return sc->nr_reclaimed;
2435 * As hibernation is going on, kswapd is freezed so that it can't mark
2436 * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2439 if (oom_killer_disabled)
2442 /* Aborted reclaim to try compaction? don't OOM, then */
2443 if (aborted_reclaim)
2446 /* top priority shrink_zones still had more to do? don't OOM, then */
2447 if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2453 static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2456 unsigned long pfmemalloc_reserve = 0;
2457 unsigned long free_pages = 0;
2461 for (i = 0; i <= ZONE_NORMAL; i++) {
2462 zone = &pgdat->node_zones[i];
2463 pfmemalloc_reserve += min_wmark_pages(zone);
2464 free_pages += zone_page_state(zone, NR_FREE_PAGES);
2467 wmark_ok = free_pages > pfmemalloc_reserve / 2;
2469 /* kswapd must be awake if processes are being throttled */
2470 if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2471 pgdat->classzone_idx = min(pgdat->classzone_idx,
2472 (enum zone_type)ZONE_NORMAL);
2473 wake_up_interruptible(&pgdat->kswapd_wait);
2480 * Throttle direct reclaimers if backing storage is backed by the network
2481 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
2482 * depleted. kswapd will continue to make progress and wake the processes
2483 * when the low watermark is reached.
2485 * Returns true if a fatal signal was delivered during throttling. If this
2486 * happens, the page allocator should not consider triggering the OOM killer.
2488 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2489 nodemask_t *nodemask)
2492 int high_zoneidx = gfp_zone(gfp_mask);
2496 * Kernel threads should not be throttled as they may be indirectly
2497 * responsible for cleaning pages necessary for reclaim to make forward
2498 * progress. kjournald for example may enter direct reclaim while
2499 * committing a transaction where throttling it could forcing other
2500 * processes to block on log_wait_commit().
2502 if (current->flags & PF_KTHREAD)
2506 * If a fatal signal is pending, this process should not throttle.
2507 * It should return quickly so it can exit and free its memory
2509 if (fatal_signal_pending(current))
2512 /* Check if the pfmemalloc reserves are ok */
2513 first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
2514 pgdat = zone->zone_pgdat;
2515 if (pfmemalloc_watermark_ok(pgdat))
2518 /* Account for the throttling */
2519 count_vm_event(PGSCAN_DIRECT_THROTTLE);
2522 * If the caller cannot enter the filesystem, it's possible that it
2523 * is due to the caller holding an FS lock or performing a journal
2524 * transaction in the case of a filesystem like ext[3|4]. In this case,
2525 * it is not safe to block on pfmemalloc_wait as kswapd could be
2526 * blocked waiting on the same lock. Instead, throttle for up to a
2527 * second before continuing.
2529 if (!(gfp_mask & __GFP_FS)) {
2530 wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2531 pfmemalloc_watermark_ok(pgdat), HZ);
2536 /* Throttle until kswapd wakes the process */
2537 wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2538 pfmemalloc_watermark_ok(pgdat));
2541 if (fatal_signal_pending(current))
2548 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2549 gfp_t gfp_mask, nodemask_t *nodemask)
2551 unsigned long nr_reclaimed;
2552 struct scan_control sc = {
2553 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
2554 .may_writepage = !laptop_mode,
2555 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2559 .priority = DEF_PRIORITY,
2560 .target_mem_cgroup = NULL,
2561 .nodemask = nodemask,
2563 struct shrink_control shrink = {
2564 .gfp_mask = sc.gfp_mask,
2568 * Do not enter reclaim if fatal signal was delivered while throttled.
2569 * 1 is returned so that the page allocator does not OOM kill at this
2572 if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2575 trace_mm_vmscan_direct_reclaim_begin(order,
2579 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2581 trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2583 return nr_reclaimed;
2588 unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2589 gfp_t gfp_mask, bool noswap,
2591 unsigned long *nr_scanned)
2593 struct scan_control sc = {
2595 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2596 .may_writepage = !laptop_mode,
2598 .may_swap = !noswap,
2601 .target_mem_cgroup = memcg,
2603 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2605 sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2606 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2608 trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2613 * NOTE: Although we can get the priority field, using it
2614 * here is not a good idea, since it limits the pages we can scan.
2615 * if we don't reclaim here, the shrink_zone from balance_pgdat
2616 * will pick up pages from other mem cgroup's as well. We hack
2617 * the priority and make it zero.
2619 shrink_lruvec(lruvec, &sc);
2621 trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2623 *nr_scanned = sc.nr_scanned;
2624 return sc.nr_reclaimed;
2627 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
2631 struct zonelist *zonelist;
2632 unsigned long nr_reclaimed;
2634 struct scan_control sc = {
2635 .may_writepage = !laptop_mode,
2637 .may_swap = !noswap,
2638 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2640 .priority = DEF_PRIORITY,
2641 .target_mem_cgroup = memcg,
2642 .nodemask = NULL, /* we don't care the placement */
2643 .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2644 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2646 struct shrink_control shrink = {
2647 .gfp_mask = sc.gfp_mask,
2651 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2652 * take care of from where we get pages. So the node where we start the
2653 * scan does not need to be the current node.
2655 nid = mem_cgroup_select_victim_node(memcg);
2657 zonelist = NODE_DATA(nid)->node_zonelists;
2659 trace_mm_vmscan_memcg_reclaim_begin(0,
2663 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2665 trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2667 return nr_reclaimed;
2671 static void age_active_anon(struct zone *zone, struct scan_control *sc)
2673 struct mem_cgroup *memcg;
2675 if (!total_swap_pages)
2678 memcg = mem_cgroup_iter(NULL, NULL, NULL);
2680 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2682 if (inactive_anon_is_low(lruvec))
2683 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2684 sc, LRU_ACTIVE_ANON);
2686 memcg = mem_cgroup_iter(NULL, memcg, NULL);
2690 static bool zone_balanced(struct zone *zone, int order,
2691 unsigned long balance_gap, int classzone_idx)
2693 if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) +
2694 balance_gap, classzone_idx, 0))
2697 if (IS_ENABLED(CONFIG_COMPACTION) && order &&
2698 !compaction_suitable(zone, order))
2705 * pgdat_balanced() is used when checking if a node is balanced.
2707 * For order-0, all zones must be balanced!
2709 * For high-order allocations only zones that meet watermarks and are in a
2710 * zone allowed by the callers classzone_idx are added to balanced_pages. The
2711 * total of balanced pages must be at least 25% of the zones allowed by
2712 * classzone_idx for the node to be considered balanced. Forcing all zones to
2713 * be balanced for high orders can cause excessive reclaim when there are
2715 * The choice of 25% is due to
2716 * o a 16M DMA zone that is balanced will not balance a zone on any
2717 * reasonable sized machine
2718 * o On all other machines, the top zone must be at least a reasonable
2719 * percentage of the middle zones. For example, on 32-bit x86, highmem
2720 * would need to be at least 256M for it to be balance a whole node.
2721 * Similarly, on x86-64 the Normal zone would need to be at least 1G
2722 * to balance a node on its own. These seemed like reasonable ratios.
2724 static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
2726 unsigned long managed_pages = 0;
2727 unsigned long balanced_pages = 0;
2730 /* Check the watermark levels */
2731 for (i = 0; i <= classzone_idx; i++) {
2732 struct zone *zone = pgdat->node_zones + i;
2734 if (!populated_zone(zone))
2737 managed_pages += zone->managed_pages;
2740 * A special case here:
2742 * balance_pgdat() skips over all_unreclaimable after
2743 * DEF_PRIORITY. Effectively, it considers them balanced so
2744 * they must be considered balanced here as well!
2746 if (!zone_reclaimable(zone)) {
2747 balanced_pages += zone->managed_pages;
2751 if (zone_balanced(zone, order, 0, i))
2752 balanced_pages += zone->managed_pages;
2758 return balanced_pages >= (managed_pages >> 2);
2764 * Prepare kswapd for sleeping. This verifies that there are no processes
2765 * waiting in throttle_direct_reclaim() and that watermarks have been met.
2767 * Returns true if kswapd is ready to sleep
2769 static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
2772 /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2777 * There is a potential race between when kswapd checks its watermarks
2778 * and a process gets throttled. There is also a potential race if
2779 * processes get throttled, kswapd wakes, a large process exits therby
2780 * balancing the zones that causes kswapd to miss a wakeup. If kswapd
2781 * is going to sleep, no process should be sleeping on pfmemalloc_wait
2782 * so wake them now if necessary. If necessary, processes will wake
2783 * kswapd and get throttled again
2785 if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
2786 wake_up(&pgdat->pfmemalloc_wait);
2790 return pgdat_balanced(pgdat, order, classzone_idx);
2794 * kswapd shrinks the zone by the number of pages required to reach
2795 * the high watermark.
2797 * Returns true if kswapd scanned at least the requested number of pages to
2798 * reclaim or if the lack of progress was due to pages under writeback.
2799 * This is used to determine if the scanning priority needs to be raised.
2801 static bool kswapd_shrink_zone(struct zone *zone,
2803 struct scan_control *sc,
2804 unsigned long lru_pages,
2805 unsigned long *nr_attempted)
2807 int testorder = sc->order;
2808 unsigned long balance_gap;
2809 struct reclaim_state *reclaim_state = current->reclaim_state;
2810 struct shrink_control shrink = {
2811 .gfp_mask = sc->gfp_mask,
2813 bool lowmem_pressure;
2815 /* Reclaim above the high watermark. */
2816 sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
2819 * Kswapd reclaims only single pages with compaction enabled. Trying
2820 * too hard to reclaim until contiguous free pages have become
2821 * available can hurt performance by evicting too much useful data
2822 * from memory. Do not reclaim more than needed for compaction.
2824 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2825 compaction_suitable(zone, sc->order) !=
2830 * We put equal pressure on every zone, unless one zone has way too
2831 * many pages free already. The "too many pages" is defined as the
2832 * high wmark plus a "gap" where the gap is either the low
2833 * watermark or 1% of the zone, whichever is smaller.
2835 balance_gap = min(low_wmark_pages(zone),
2836 (zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2837 KSWAPD_ZONE_BALANCE_GAP_RATIO);
2840 * If there is no low memory pressure or the zone is balanced then no
2841 * reclaim is necessary
2843 lowmem_pressure = (buffer_heads_over_limit && is_highmem(zone));
2844 if (!lowmem_pressure && zone_balanced(zone, testorder,
2845 balance_gap, classzone_idx))
2848 shrink_zone(zone, sc);
2850 reclaim_state->reclaimed_slab = 0;
2851 shrink_slab(&shrink, sc->nr_scanned, lru_pages);
2852 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2854 /* Account for the number of pages attempted to reclaim */
2855 *nr_attempted += sc->nr_to_reclaim;
2857 zone_clear_flag(zone, ZONE_WRITEBACK);
2860 * If a zone reaches its high watermark, consider it to be no longer
2861 * congested. It's possible there are dirty pages backed by congested
2862 * BDIs but as pressure is relieved, speculatively avoid congestion
2865 if (zone_reclaimable(zone) &&
2866 zone_balanced(zone, testorder, 0, classzone_idx)) {
2867 zone_clear_flag(zone, ZONE_CONGESTED);
2868 zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY);
2871 return sc->nr_scanned >= sc->nr_to_reclaim;
2875 * For kswapd, balance_pgdat() will work across all this node's zones until
2876 * they are all at high_wmark_pages(zone).
2878 * Returns the final order kswapd was reclaiming at
2880 * There is special handling here for zones which are full of pinned pages.
2881 * This can happen if the pages are all mlocked, or if they are all used by
2882 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
2883 * What we do is to detect the case where all pages in the zone have been
2884 * scanned twice and there has been zero successful reclaim. Mark the zone as
2885 * dead and from now on, only perform a short scan. Basically we're polling
2886 * the zone for when the problem goes away.
2888 * kswapd scans the zones in the highmem->normal->dma direction. It skips
2889 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2890 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2891 * lower zones regardless of the number of free pages in the lower zones. This
2892 * interoperates with the page allocator fallback scheme to ensure that aging
2893 * of pages is balanced across the zones.
2895 static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2899 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
2900 struct scan_control sc = {
2901 .gfp_mask = GFP_KERNEL,
2902 .priority = DEF_PRIORITY,
2905 .may_writepage = !laptop_mode,
2907 .target_mem_cgroup = NULL,
2909 count_vm_event(PAGEOUTRUN);
2912 unsigned long lru_pages = 0;
2913 unsigned long nr_attempted = 0;
2914 bool raise_priority = true;
2915 bool pgdat_needs_compaction = (order > 0);
2917 sc.nr_reclaimed = 0;
2920 * Scan in the highmem->dma direction for the highest
2921 * zone which needs scanning
2923 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2924 struct zone *zone = pgdat->node_zones + i;
2926 if (!populated_zone(zone))
2929 if (sc.priority != DEF_PRIORITY &&
2930 !zone_reclaimable(zone))
2934 * Do some background aging of the anon list, to give
2935 * pages a chance to be referenced before reclaiming.
2937 age_active_anon(zone, &sc);
2940 * If the number of buffer_heads in the machine
2941 * exceeds the maximum allowed level and this node
2942 * has a highmem zone, force kswapd to reclaim from
2943 * it to relieve lowmem pressure.
2945 if (buffer_heads_over_limit && is_highmem_idx(i)) {
2950 if (!zone_balanced(zone, order, 0, 0)) {
2955 * If balanced, clear the dirty and congested
2958 zone_clear_flag(zone, ZONE_CONGESTED);
2959 zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY);
2966 for (i = 0; i <= end_zone; i++) {
2967 struct zone *zone = pgdat->node_zones + i;
2969 if (!populated_zone(zone))
2972 lru_pages += zone_reclaimable_pages(zone);
2975 * If any zone is currently balanced then kswapd will
2976 * not call compaction as it is expected that the
2977 * necessary pages are already available.
2979 if (pgdat_needs_compaction &&
2980 zone_watermark_ok(zone, order,
2981 low_wmark_pages(zone),
2983 pgdat_needs_compaction = false;
2987 * If we're getting trouble reclaiming, start doing writepage
2988 * even in laptop mode.
2990 if (sc.priority < DEF_PRIORITY - 2)
2991 sc.may_writepage = 1;
2994 * Now scan the zone in the dma->highmem direction, stopping
2995 * at the last zone which needs scanning.
2997 * We do this because the page allocator works in the opposite
2998 * direction. This prevents the page allocator from allocating
2999 * pages behind kswapd's direction of progress, which would
3000 * cause too much scanning of the lower zones.
3002 for (i = 0; i <= end_zone; i++) {
3003 struct zone *zone = pgdat->node_zones + i;
3005 if (!populated_zone(zone))
3008 if (sc.priority != DEF_PRIORITY &&
3009 !zone_reclaimable(zone))
3015 * There should be no need to raise the scanning
3016 * priority if enough pages are already being scanned
3017 * that that high watermark would be met at 100%
3020 if (kswapd_shrink_zone(zone, end_zone, &sc,
3021 lru_pages, &nr_attempted))
3022 raise_priority = false;
3026 * If the low watermark is met there is no need for processes
3027 * to be throttled on pfmemalloc_wait as they should not be
3028 * able to safely make forward progress. Wake them
3030 if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
3031 pfmemalloc_watermark_ok(pgdat))
3032 wake_up(&pgdat->pfmemalloc_wait);
3035 * Fragmentation may mean that the system cannot be rebalanced
3036 * for high-order allocations in all zones. If twice the
3037 * allocation size has been reclaimed and the zones are still
3038 * not balanced then recheck the watermarks at order-0 to
3039 * prevent kswapd reclaiming excessively. Assume that a
3040 * process requested a high-order can direct reclaim/compact.
3042 if (order && sc.nr_reclaimed >= 2UL << order)
3043 order = sc.order = 0;
3045 /* Check if kswapd should be suspending */
3046 if (try_to_freeze() || kthread_should_stop())
3050 * Compact if necessary and kswapd is reclaiming at least the
3051 * high watermark number of pages as requsted
3053 if (pgdat_needs_compaction && sc.nr_reclaimed > nr_attempted)
3054 compact_pgdat(pgdat, order);
3057 * Raise priority if scanning rate is too low or there was no
3058 * progress in reclaiming pages
3060 if (raise_priority || !sc.nr_reclaimed)
3062 } while (sc.priority >= 1 &&
3063 !pgdat_balanced(pgdat, order, *classzone_idx));
3067 * Return the order we were reclaiming at so prepare_kswapd_sleep()
3068 * makes a decision on the order we were last reclaiming at. However,
3069 * if another caller entered the allocator slow path while kswapd
3070 * was awake, order will remain at the higher level
3072 *classzone_idx = end_zone;
3076 static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
3081 if (freezing(current) || kthread_should_stop())
3084 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3086 /* Try to sleep for a short interval */
3087 if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
3088 remaining = schedule_timeout(HZ/10);
3089 finish_wait(&pgdat->kswapd_wait, &wait);
3090 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3094 * After a short sleep, check if it was a premature sleep. If not, then
3095 * go fully to sleep until explicitly woken up.
3097 if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
3098 trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
3101 * vmstat counters are not perfectly accurate and the estimated
3102 * value for counters such as NR_FREE_PAGES can deviate from the
3103 * true value by nr_online_cpus * threshold. To avoid the zone
3104 * watermarks being breached while under pressure, we reduce the
3105 * per-cpu vmstat threshold while kswapd is awake and restore
3106 * them before going back to sleep.
3108 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
3111 * Compaction records what page blocks it recently failed to
3112 * isolate pages from and skips them in the future scanning.
3113 * When kswapd is going to sleep, it is reasonable to assume
3114 * that pages and compaction may succeed so reset the cache.
3116 reset_isolation_suitable(pgdat);
3118 if (!kthread_should_stop())
3121 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
3124 count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
3126 count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
3128 finish_wait(&pgdat->kswapd_wait, &wait);
3132 * The background pageout daemon, started as a kernel thread
3133 * from the init process.
3135 * This basically trickles out pages so that we have _some_
3136 * free memory available even if there is no other activity
3137 * that frees anything up. This is needed for things like routing
3138 * etc, where we otherwise might have all activity going on in
3139 * asynchronous contexts that cannot page things out.
3141 * If there are applications that are active memory-allocators
3142 * (most normal use), this basically shouldn't matter.
3144 static int kswapd(void *p)
3146 unsigned long order, new_order;
3147 unsigned balanced_order;
3148 int classzone_idx, new_classzone_idx;
3149 int balanced_classzone_idx;
3150 pg_data_t *pgdat = (pg_data_t*)p;
3151 struct task_struct *tsk = current;
3153 struct reclaim_state reclaim_state = {
3154 .reclaimed_slab = 0,
3156 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
3158 lockdep_set_current_reclaim_state(GFP_KERNEL);
3160 if (!cpumask_empty(cpumask))
3161 set_cpus_allowed_ptr(tsk, cpumask);
3162 current->reclaim_state = &reclaim_state;
3165 * Tell the memory management that we're a "memory allocator",
3166 * and that if we need more memory we should get access to it
3167 * regardless (see "__alloc_pages()"). "kswapd" should
3168 * never get caught in the normal page freeing logic.
3170 * (Kswapd normally doesn't need memory anyway, but sometimes
3171 * you need a small amount of memory in order to be able to
3172 * page out something else, and this flag essentially protects
3173 * us from recursively trying to free more memory as we're
3174 * trying to free the first piece of memory in the first place).
3176 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
3179 order = new_order = 0;
3181 classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
3182 balanced_classzone_idx = classzone_idx;
3187 * If the last balance_pgdat was unsuccessful it's unlikely a
3188 * new request of a similar or harder type will succeed soon
3189 * so consider going to sleep on the basis we reclaimed at
3191 if (balanced_classzone_idx >= new_classzone_idx &&
3192 balanced_order == new_order) {
3193 new_order = pgdat->kswapd_max_order;
3194 new_classzone_idx = pgdat->classzone_idx;
3195 pgdat->kswapd_max_order = 0;
3196 pgdat->classzone_idx = pgdat->nr_zones - 1;
3199 if (order < new_order || classzone_idx > new_classzone_idx) {
3201 * Don't sleep if someone wants a larger 'order'
3202 * allocation or has tigher zone constraints
3205 classzone_idx = new_classzone_idx;
3207 kswapd_try_to_sleep(pgdat, balanced_order,
3208 balanced_classzone_idx);
3209 order = pgdat->kswapd_max_order;
3210 classzone_idx = pgdat->classzone_idx;
3212 new_classzone_idx = classzone_idx;
3213 pgdat->kswapd_max_order = 0;
3214 pgdat->classzone_idx = pgdat->nr_zones - 1;
3217 ret = try_to_freeze();
3218 if (kthread_should_stop())
3222 * We can speed up thawing tasks if we don't call balance_pgdat
3223 * after returning from the refrigerator
3226 trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
3227 balanced_classzone_idx = classzone_idx;
3228 balanced_order = balance_pgdat(pgdat, order,
3229 &balanced_classzone_idx);
3233 current->reclaim_state = NULL;
3238 * A zone is low on free memory, so wake its kswapd task to service it.
3240 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
3244 if (!populated_zone(zone))
3247 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
3249 pgdat = zone->zone_pgdat;
3250 if (pgdat->kswapd_max_order < order) {
3251 pgdat->kswapd_max_order = order;
3252 pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
3254 if (!waitqueue_active(&pgdat->kswapd_wait))
3256 if (zone_balanced(zone, order, 0, 0))
3259 trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3260 wake_up_interruptible(&pgdat->kswapd_wait);
3264 * The reclaimable count would be mostly accurate.
3265 * The less reclaimable pages may be
3266 * - mlocked pages, which will be moved to unevictable list when encountered
3267 * - mapped pages, which may require several travels to be reclaimed
3268 * - dirty pages, which is not "instantly" reclaimable
3270 unsigned long global_reclaimable_pages(void)
3274 nr = global_page_state(NR_ACTIVE_FILE) +
3275 global_page_state(NR_INACTIVE_FILE);
3277 if (get_nr_swap_pages() > 0)
3278 nr += global_page_state(NR_ACTIVE_ANON) +
3279 global_page_state(NR_INACTIVE_ANON);
3284 #ifdef CONFIG_HIBERNATION
3286 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3289 * Rather than trying to age LRUs the aim is to preserve the overall
3290 * LRU order by reclaiming preferentially
3291 * inactive > active > active referenced > active mapped
3293 unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3295 struct reclaim_state reclaim_state;
3296 struct scan_control sc = {
3297 .gfp_mask = GFP_HIGHUSER_MOVABLE,
3301 .nr_to_reclaim = nr_to_reclaim,
3302 .hibernation_mode = 1,
3304 .priority = DEF_PRIORITY,
3306 struct shrink_control shrink = {
3307 .gfp_mask = sc.gfp_mask,
3309 struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3310 struct task_struct *p = current;
3311 unsigned long nr_reclaimed;
3313 p->flags |= PF_MEMALLOC;
3314 lockdep_set_current_reclaim_state(sc.gfp_mask);
3315 reclaim_state.reclaimed_slab = 0;
3316 p->reclaim_state = &reclaim_state;
3318 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
3320 p->reclaim_state = NULL;
3321 lockdep_clear_current_reclaim_state();
3322 p->flags &= ~PF_MEMALLOC;
3324 return nr_reclaimed;
3326 #endif /* CONFIG_HIBERNATION */
3328 /* It's optimal to keep kswapds on the same CPUs as their memory, but
3329 not required for correctness. So if the last cpu in a node goes
3330 away, we get changed to run anywhere: as the first one comes back,
3331 restore their cpu bindings. */
3332 static int cpu_callback(struct notifier_block *nfb, unsigned long action,
3337 if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
3338 for_each_node_state(nid, N_MEMORY) {
3339 pg_data_t *pgdat = NODE_DATA(nid);
3340 const struct cpumask *mask;
3342 mask = cpumask_of_node(pgdat->node_id);
3344 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3345 /* One of our CPUs online: restore mask */
3346 set_cpus_allowed_ptr(pgdat->kswapd, mask);
3353 * This kswapd start function will be called by init and node-hot-add.
3354 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3356 int kswapd_run(int nid)
3358 pg_data_t *pgdat = NODE_DATA(nid);
3364 pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3365 if (IS_ERR(pgdat->kswapd)) {
3366 /* failure at boot is fatal */
3367 BUG_ON(system_state == SYSTEM_BOOTING);
3368 pr_err("Failed to start kswapd on node %d\n", nid);
3369 ret = PTR_ERR(pgdat->kswapd);
3370 pgdat->kswapd = NULL;
3376 * Called by memory hotplug when all memory in a node is offlined. Caller must
3377 * hold lock_memory_hotplug().
3379 void kswapd_stop(int nid)
3381 struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3384 kthread_stop(kswapd);
3385 NODE_DATA(nid)->kswapd = NULL;
3389 static int __init kswapd_init(void)
3394 for_each_node_state(nid, N_MEMORY)
3396 hotcpu_notifier(cpu_callback, 0);
3400 module_init(kswapd_init)
3406 * If non-zero call zone_reclaim when the number of free pages falls below
3409 int zone_reclaim_mode __read_mostly;
3411 #define RECLAIM_OFF 0
3412 #define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
3413 #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
3414 #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
3417 * Priority for ZONE_RECLAIM. This determines the fraction of pages
3418 * of a node considered for each zone_reclaim. 4 scans 1/16th of
3421 #define ZONE_RECLAIM_PRIORITY 4
3424 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
3427 int sysctl_min_unmapped_ratio = 1;
3430 * If the number of slab pages in a zone grows beyond this percentage then
3431 * slab reclaim needs to occur.
3433 int sysctl_min_slab_ratio = 5;
3435 static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3437 unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3438 unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3439 zone_page_state(zone, NR_ACTIVE_FILE);
3442 * It's possible for there to be more file mapped pages than
3443 * accounted for by the pages on the file LRU lists because
3444 * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3446 return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3449 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
3450 static long zone_pagecache_reclaimable(struct zone *zone)
3452 long nr_pagecache_reclaimable;
3456 * If RECLAIM_SWAP is set, then all file pages are considered
3457 * potentially reclaimable. Otherwise, we have to worry about
3458 * pages like swapcache and zone_unmapped_file_pages() provides
3461 if (zone_reclaim_mode & RECLAIM_SWAP)
3462 nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3464 nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3466 /* If we can't clean pages, remove dirty pages from consideration */
3467 if (!(zone_reclaim_mode & RECLAIM_WRITE))
3468 delta += zone_page_state(zone, NR_FILE_DIRTY);
3470 /* Watch for any possible underflows due to delta */
3471 if (unlikely(delta > nr_pagecache_reclaimable))
3472 delta = nr_pagecache_reclaimable;
3474 return nr_pagecache_reclaimable - delta;
3478 * Try to free up some pages from this zone through reclaim.
3480 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3482 /* Minimum pages needed in order to stay on node */
3483 const unsigned long nr_pages = 1 << order;
3484 struct task_struct *p = current;
3485 struct reclaim_state reclaim_state;
3486 struct scan_control sc = {
3487 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3488 .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3490 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3491 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
3493 .priority = ZONE_RECLAIM_PRIORITY,
3495 struct shrink_control shrink = {
3496 .gfp_mask = sc.gfp_mask,
3498 unsigned long nr_slab_pages0, nr_slab_pages1;
3502 * We need to be able to allocate from the reserves for RECLAIM_SWAP
3503 * and we also need to be able to write out pages for RECLAIM_WRITE
3506 p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3507 lockdep_set_current_reclaim_state(gfp_mask);
3508 reclaim_state.reclaimed_slab = 0;
3509 p->reclaim_state = &reclaim_state;
3511 if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3513 * Free memory by calling shrink zone with increasing
3514 * priorities until we have enough memory freed.
3517 shrink_zone(zone, &sc);
3518 } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3521 nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3522 if (nr_slab_pages0 > zone->min_slab_pages) {
3524 * shrink_slab() does not currently allow us to determine how
3525 * many pages were freed in this zone. So we take the current
3526 * number of slab pages and shake the slab until it is reduced
3527 * by the same nr_pages that we used for reclaiming unmapped
3530 * Note that shrink_slab will free memory on all zones and may
3534 unsigned long lru_pages = zone_reclaimable_pages(zone);
3536 /* No reclaimable slab or very low memory pressure */
3537 if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3540 /* Freed enough memory */
3541 nr_slab_pages1 = zone_page_state(zone,
3542 NR_SLAB_RECLAIMABLE);
3543 if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3548 * Update nr_reclaimed by the number of slab pages we
3549 * reclaimed from this zone.
3551 nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3552 if (nr_slab_pages1 < nr_slab_pages0)
3553 sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3556 p->reclaim_state = NULL;
3557 current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3558 lockdep_clear_current_reclaim_state();
3559 return sc.nr_reclaimed >= nr_pages;
3562 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3568 * Zone reclaim reclaims unmapped file backed pages and
3569 * slab pages if we are over the defined limits.
3571 * A small portion of unmapped file backed pages is needed for
3572 * file I/O otherwise pages read by file I/O will be immediately
3573 * thrown out if the zone is overallocated. So we do not reclaim
3574 * if less than a specified percentage of the zone is used by
3575 * unmapped file backed pages.
3577 if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3578 zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3579 return ZONE_RECLAIM_FULL;
3581 if (!zone_reclaimable(zone))
3582 return ZONE_RECLAIM_FULL;
3585 * Do not scan if the allocation should not be delayed.
3587 if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3588 return ZONE_RECLAIM_NOSCAN;
3591 * Only run zone reclaim on the local zone or on zones that do not
3592 * have associated processors. This will favor the local processor
3593 * over remote processors and spread off node memory allocations
3594 * as wide as possible.
3596 node_id = zone_to_nid(zone);
3597 if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3598 return ZONE_RECLAIM_NOSCAN;
3600 if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3601 return ZONE_RECLAIM_NOSCAN;
3603 ret = __zone_reclaim(zone, gfp_mask, order);
3604 zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3607 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3614 * page_evictable - test whether a page is evictable
3615 * @page: the page to test
3617 * Test whether page is evictable--i.e., should be placed on active/inactive
3618 * lists vs unevictable list.
3620 * Reasons page might not be evictable:
3621 * (1) page's mapping marked unevictable
3622 * (2) page is part of an mlocked VMA
3625 int page_evictable(struct page *page)
3627 return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
3632 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3633 * @pages: array of pages to check
3634 * @nr_pages: number of pages to check
3636 * Checks pages for evictability and moves them to the appropriate lru list.
3638 * This function is only used for SysV IPC SHM_UNLOCK.
3640 void check_move_unevictable_pages(struct page **pages, int nr_pages)
3642 struct lruvec *lruvec;
3643 struct zone *zone = NULL;
3648 for (i = 0; i < nr_pages; i++) {
3649 struct page *page = pages[i];
3650 struct zone *pagezone;
3653 pagezone = page_zone(page);
3654 if (pagezone != zone) {
3656 spin_unlock_irq(&zone->lru_lock);
3658 spin_lock_irq(&zone->lru_lock);
3660 lruvec = mem_cgroup_page_lruvec(page, zone);
3662 if (!PageLRU(page) || !PageUnevictable(page))
3665 if (page_evictable(page)) {
3666 enum lru_list lru = page_lru_base_type(page);
3668 VM_BUG_ON(PageActive(page));
3669 ClearPageUnevictable(page);
3670 del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3671 add_page_to_lru_list(page, lruvec, lru);
3677 __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3678 __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3679 spin_unlock_irq(&zone->lru_lock);
3682 #endif /* CONFIG_SHMEM */
3684 static void warn_scan_unevictable_pages(void)
3686 printk_once(KERN_WARNING
3687 "%s: The scan_unevictable_pages sysctl/node-interface has been "
3688 "disabled for lack of a legitimate use case. If you have "
3689 "one, please send an email to linux-mm@kvack.org.\n",
3694 * scan_unevictable_pages [vm] sysctl handler. On demand re-scan of
3695 * all nodes' unevictable lists for evictable pages
3697 unsigned long scan_unevictable_pages;
3699 int scan_unevictable_handler(struct ctl_table *table, int write,
3700 void __user *buffer,
3701 size_t *length, loff_t *ppos)
3703 warn_scan_unevictable_pages();
3704 proc_doulongvec_minmax(table, write, buffer, length, ppos);
3705 scan_unevictable_pages = 0;
3711 * per node 'scan_unevictable_pages' attribute. On demand re-scan of
3712 * a specified node's per zone unevictable lists for evictable pages.
3715 static ssize_t read_scan_unevictable_node(struct device *dev,
3716 struct device_attribute *attr,
3719 warn_scan_unevictable_pages();
3720 return sprintf(buf, "0\n"); /* always zero; should fit... */
3723 static ssize_t write_scan_unevictable_node(struct device *dev,
3724 struct device_attribute *attr,
3725 const char *buf, size_t count)
3727 warn_scan_unevictable_pages();
3732 static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3733 read_scan_unevictable_node,
3734 write_scan_unevictable_node);
3736 int scan_unevictable_register_node(struct node *node)
3738 return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages);
3741 void scan_unevictable_unregister_node(struct node *node)
3743 device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages);