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.
14 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
17 #include <linux/module.h>
18 #include <linux/gfp.h>
19 #include <linux/kernel_stat.h>
20 #include <linux/swap.h>
21 #include <linux/pagemap.h>
22 #include <linux/init.h>
23 #include <linux/highmem.h>
24 #include <linux/vmpressure.h>
25 #include <linux/vmstat.h>
26 #include <linux/file.h>
27 #include <linux/writeback.h>
28 #include <linux/blkdev.h>
29 #include <linux/buffer_head.h> /* for try_to_release_page(),
30 buffer_heads_over_limit */
31 #include <linux/mm_inline.h>
32 #include <linux/backing-dev.h>
33 #include <linux/rmap.h>
34 #include <linux/topology.h>
35 #include <linux/cpu.h>
36 #include <linux/cpuset.h>
37 #include <linux/compaction.h>
38 #include <linux/notifier.h>
39 #include <linux/rwsem.h>
40 #include <linux/delay.h>
41 #include <linux/kthread.h>
42 #include <linux/freezer.h>
43 #include <linux/memcontrol.h>
44 #include <linux/delayacct.h>
45 #include <linux/sysctl.h>
46 #include <linux/oom.h>
47 #include <linux/prefetch.h>
48 #include <linux/printk.h>
50 #include <asm/tlbflush.h>
51 #include <asm/div64.h>
53 #include <linux/swapops.h>
54 #include <linux/balloon_compaction.h>
58 #define CREATE_TRACE_POINTS
59 #include <trace/events/vmscan.h>
62 /* How many pages shrink_list() should reclaim */
63 unsigned long nr_to_reclaim;
65 /* This context's GFP mask */
68 /* Allocation order */
72 * Nodemask of nodes allowed by the caller. If NULL, all nodes
78 * The memory cgroup that hit its limit and as a result is the
79 * primary target of this reclaim invocation.
81 struct mem_cgroup *target_mem_cgroup;
83 /* Scan (total_size >> priority) pages at once */
86 unsigned int may_writepage:1;
88 /* Can mapped pages be reclaimed? */
89 unsigned int may_unmap:1;
91 /* Can pages be swapped as part of reclaim? */
92 unsigned int may_swap:1;
94 unsigned int hibernation_mode:1;
96 /* One of the zones is ready for compaction */
97 unsigned int compaction_ready:1;
99 /* Incremented by the number of inactive pages that were scanned */
100 unsigned long nr_scanned;
102 /* Number of pages freed so far during a call to shrink_zones() */
103 unsigned long nr_reclaimed;
106 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
108 #ifdef ARCH_HAS_PREFETCH
109 #define prefetch_prev_lru_page(_page, _base, _field) \
111 if ((_page)->lru.prev != _base) { \
114 prev = lru_to_page(&(_page->lru)); \
115 prefetch(&prev->_field); \
119 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
122 #ifdef ARCH_HAS_PREFETCHW
123 #define prefetchw_prev_lru_page(_page, _base, _field) \
125 if ((_page)->lru.prev != _base) { \
128 prev = lru_to_page(&(_page->lru)); \
129 prefetchw(&prev->_field); \
133 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
137 * From 0 .. 100. Higher means more swappy.
139 int vm_swappiness = 60;
141 * The total number of pages which are beyond the high watermark within all
144 unsigned long vm_total_pages;
146 static LIST_HEAD(shrinker_list);
147 static DECLARE_RWSEM(shrinker_rwsem);
150 static bool global_reclaim(struct scan_control *sc)
152 return !sc->target_mem_cgroup;
155 static bool global_reclaim(struct scan_control *sc)
161 static 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_page_state(zone, NR_PAGES_SCANNED) <
178 zone_reclaimable_pages(zone) * 6;
181 static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
183 if (!mem_cgroup_disabled())
184 return mem_cgroup_get_lru_size(lruvec, lru);
186 return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);
190 * Add a shrinker callback to be called from the vm.
192 int register_shrinker(struct shrinker *shrinker)
194 size_t size = sizeof(*shrinker->nr_deferred);
197 * If we only have one possible node in the system anyway, save
198 * ourselves the trouble and disable NUMA aware behavior. This way we
199 * will save memory and some small loop time later.
201 if (nr_node_ids == 1)
202 shrinker->flags &= ~SHRINKER_NUMA_AWARE;
204 if (shrinker->flags & SHRINKER_NUMA_AWARE)
207 shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
208 if (!shrinker->nr_deferred)
211 down_write(&shrinker_rwsem);
212 list_add_tail(&shrinker->list, &shrinker_list);
213 up_write(&shrinker_rwsem);
216 EXPORT_SYMBOL(register_shrinker);
221 void unregister_shrinker(struct shrinker *shrinker)
223 down_write(&shrinker_rwsem);
224 list_del(&shrinker->list);
225 up_write(&shrinker_rwsem);
226 kfree(shrinker->nr_deferred);
228 EXPORT_SYMBOL(unregister_shrinker);
230 #define SHRINK_BATCH 128
233 shrink_slab_node(struct shrink_control *shrinkctl, struct shrinker *shrinker,
234 unsigned long nr_pages_scanned, unsigned long lru_pages)
236 unsigned long freed = 0;
237 unsigned long long delta;
242 int nid = shrinkctl->nid;
243 long batch_size = shrinker->batch ? shrinker->batch
246 freeable = shrinker->count_objects(shrinker, shrinkctl);
251 * copy the current shrinker scan count into a local variable
252 * and zero it so that other concurrent shrinker invocations
253 * don't also do this scanning work.
255 nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
258 delta = (4 * nr_pages_scanned) / shrinker->seeks;
260 do_div(delta, lru_pages + 1);
262 if (total_scan < 0) {
264 "shrink_slab: %pF negative objects to delete nr=%ld\n",
265 shrinker->scan_objects, total_scan);
266 total_scan = freeable;
270 * We need to avoid excessive windup on filesystem shrinkers
271 * due to large numbers of GFP_NOFS allocations causing the
272 * shrinkers to return -1 all the time. This results in a large
273 * nr being built up so when a shrink that can do some work
274 * comes along it empties the entire cache due to nr >>>
275 * freeable. This is bad for sustaining a working set in
278 * Hence only allow the shrinker to scan the entire cache when
279 * a large delta change is calculated directly.
281 if (delta < freeable / 4)
282 total_scan = min(total_scan, freeable / 2);
285 * Avoid risking looping forever due to too large nr value:
286 * never try to free more than twice the estimate number of
289 if (total_scan > freeable * 2)
290 total_scan = freeable * 2;
292 trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
293 nr_pages_scanned, lru_pages,
294 freeable, delta, total_scan);
297 * Normally, we should not scan less than batch_size objects in one
298 * pass to avoid too frequent shrinker calls, but if the slab has less
299 * than batch_size objects in total and we are really tight on memory,
300 * we will try to reclaim all available objects, otherwise we can end
301 * up failing allocations although there are plenty of reclaimable
302 * objects spread over several slabs with usage less than the
305 * We detect the "tight on memory" situations by looking at the total
306 * number of objects we want to scan (total_scan). If it is greater
307 * than the total number of objects on slab (freeable), we must be
308 * scanning at high prio and therefore should try to reclaim as much as
311 while (total_scan >= batch_size ||
312 total_scan >= freeable) {
314 unsigned long nr_to_scan = min(batch_size, total_scan);
316 shrinkctl->nr_to_scan = nr_to_scan;
317 ret = shrinker->scan_objects(shrinker, shrinkctl);
318 if (ret == SHRINK_STOP)
322 count_vm_events(SLABS_SCANNED, nr_to_scan);
323 total_scan -= nr_to_scan;
329 * move the unused scan count back into the shrinker in a
330 * manner that handles concurrent updates. If we exhausted the
331 * scan, there is no need to do an update.
334 new_nr = atomic_long_add_return(total_scan,
335 &shrinker->nr_deferred[nid]);
337 new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
339 trace_mm_shrink_slab_end(shrinker, nid, freed, nr, new_nr, total_scan);
344 * Call the shrink functions to age shrinkable caches
346 * Here we assume it costs one seek to replace a lru page and that it also
347 * takes a seek to recreate a cache object. With this in mind we age equal
348 * percentages of the lru and ageable caches. This should balance the seeks
349 * generated by these structures.
351 * If the vm encountered mapped pages on the LRU it increase the pressure on
352 * slab to avoid swapping.
354 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
356 * `lru_pages' represents the number of on-LRU pages in all the zones which
357 * are eligible for the caller's allocation attempt. It is used for balancing
358 * slab reclaim versus page reclaim.
360 * Returns the number of slab objects which we shrunk.
362 unsigned long shrink_slab(struct shrink_control *shrinkctl,
363 unsigned long nr_pages_scanned,
364 unsigned long lru_pages)
366 struct shrinker *shrinker;
367 unsigned long freed = 0;
369 if (nr_pages_scanned == 0)
370 nr_pages_scanned = SWAP_CLUSTER_MAX;
372 if (!down_read_trylock(&shrinker_rwsem)) {
374 * If we would return 0, our callers would understand that we
375 * have nothing else to shrink and give up trying. By returning
376 * 1 we keep it going and assume we'll be able to shrink next
383 list_for_each_entry(shrinker, &shrinker_list, list) {
384 if (!(shrinker->flags & SHRINKER_NUMA_AWARE)) {
386 freed += shrink_slab_node(shrinkctl, shrinker,
387 nr_pages_scanned, lru_pages);
391 for_each_node_mask(shrinkctl->nid, shrinkctl->nodes_to_scan) {
392 if (node_online(shrinkctl->nid))
393 freed += shrink_slab_node(shrinkctl, shrinker,
394 nr_pages_scanned, lru_pages);
398 up_read(&shrinker_rwsem);
404 static inline int is_page_cache_freeable(struct page *page)
407 * A freeable page cache page is referenced only by the caller
408 * that isolated the page, the page cache radix tree and
409 * optional buffer heads at page->private.
411 return page_count(page) - page_has_private(page) == 2;
414 static int may_write_to_queue(struct backing_dev_info *bdi,
415 struct scan_control *sc)
417 if (current->flags & PF_SWAPWRITE)
419 if (!bdi_write_congested(bdi))
421 if (bdi == current->backing_dev_info)
427 * We detected a synchronous write error writing a page out. Probably
428 * -ENOSPC. We need to propagate that into the address_space for a subsequent
429 * fsync(), msync() or close().
431 * The tricky part is that after writepage we cannot touch the mapping: nothing
432 * prevents it from being freed up. But we have a ref on the page and once
433 * that page is locked, the mapping is pinned.
435 * We're allowed to run sleeping lock_page() here because we know the caller has
438 static void handle_write_error(struct address_space *mapping,
439 struct page *page, int error)
442 if (page_mapping(page) == mapping)
443 mapping_set_error(mapping, error);
447 /* possible outcome of pageout() */
449 /* failed to write page out, page is locked */
451 /* move page to the active list, page is locked */
453 /* page has been sent to the disk successfully, page is unlocked */
455 /* page is clean and locked */
460 * pageout is called by shrink_page_list() for each dirty page.
461 * Calls ->writepage().
463 static pageout_t pageout(struct page *page, struct address_space *mapping,
464 struct scan_control *sc)
467 * If the page is dirty, only perform writeback if that write
468 * will be non-blocking. To prevent this allocation from being
469 * stalled by pagecache activity. But note that there may be
470 * stalls if we need to run get_block(). We could test
471 * PagePrivate for that.
473 * If this process is currently in __generic_file_write_iter() against
474 * this page's queue, we can perform writeback even if that
477 * If the page is swapcache, write it back even if that would
478 * block, for some throttling. This happens by accident, because
479 * swap_backing_dev_info is bust: it doesn't reflect the
480 * congestion state of the swapdevs. Easy to fix, if needed.
482 if (!is_page_cache_freeable(page))
486 * Some data journaling orphaned pages can have
487 * page->mapping == NULL while being dirty with clean buffers.
489 if (page_has_private(page)) {
490 if (try_to_free_buffers(page)) {
491 ClearPageDirty(page);
492 pr_info("%s: orphaned page\n", __func__);
498 if (mapping->a_ops->writepage == NULL)
499 return PAGE_ACTIVATE;
500 if (!may_write_to_queue(mapping->backing_dev_info, sc))
503 if (clear_page_dirty_for_io(page)) {
505 struct writeback_control wbc = {
506 .sync_mode = WB_SYNC_NONE,
507 .nr_to_write = SWAP_CLUSTER_MAX,
509 .range_end = LLONG_MAX,
513 SetPageReclaim(page);
514 res = mapping->a_ops->writepage(page, &wbc);
516 handle_write_error(mapping, page, res);
517 if (res == AOP_WRITEPAGE_ACTIVATE) {
518 ClearPageReclaim(page);
519 return PAGE_ACTIVATE;
522 if (!PageWriteback(page)) {
523 /* synchronous write or broken a_ops? */
524 ClearPageReclaim(page);
526 trace_mm_vmscan_writepage(page, trace_reclaim_flags(page));
527 inc_zone_page_state(page, NR_VMSCAN_WRITE);
535 * Same as remove_mapping, but if the page is removed from the mapping, it
536 * gets returned with a refcount of 0.
538 static int __remove_mapping(struct address_space *mapping, struct page *page,
541 BUG_ON(!PageLocked(page));
542 BUG_ON(mapping != page_mapping(page));
544 spin_lock_irq(&mapping->tree_lock);
546 * The non racy check for a busy page.
548 * Must be careful with the order of the tests. When someone has
549 * a ref to the page, it may be possible that they dirty it then
550 * drop the reference. So if PageDirty is tested before page_count
551 * here, then the following race may occur:
553 * get_user_pages(&page);
554 * [user mapping goes away]
556 * !PageDirty(page) [good]
557 * SetPageDirty(page);
559 * !page_count(page) [good, discard it]
561 * [oops, our write_to data is lost]
563 * Reversing the order of the tests ensures such a situation cannot
564 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
565 * load is not satisfied before that of page->_count.
567 * Note that if SetPageDirty is always performed via set_page_dirty,
568 * and thus under tree_lock, then this ordering is not required.
570 if (!page_freeze_refs(page, 2))
572 /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
573 if (unlikely(PageDirty(page))) {
574 page_unfreeze_refs(page, 2);
578 if (PageSwapCache(page)) {
579 swp_entry_t swap = { .val = page_private(page) };
580 mem_cgroup_swapout(page, swap);
581 __delete_from_swap_cache(page);
582 spin_unlock_irq(&mapping->tree_lock);
583 swapcache_free(swap);
585 void (*freepage)(struct page *);
588 freepage = mapping->a_ops->freepage;
590 * Remember a shadow entry for reclaimed file cache in
591 * order to detect refaults, thus thrashing, later on.
593 * But don't store shadows in an address space that is
594 * already exiting. This is not just an optizimation,
595 * inode reclaim needs to empty out the radix tree or
596 * the nodes are lost. Don't plant shadows behind its
599 if (reclaimed && page_is_file_cache(page) &&
600 !mapping_exiting(mapping))
601 shadow = workingset_eviction(mapping, page);
602 __delete_from_page_cache(page, shadow);
603 spin_unlock_irq(&mapping->tree_lock);
605 if (freepage != NULL)
612 spin_unlock_irq(&mapping->tree_lock);
617 * Attempt to detach a locked page from its ->mapping. If it is dirty or if
618 * someone else has a ref on the page, abort and return 0. If it was
619 * successfully detached, return 1. Assumes the caller has a single ref on
622 int remove_mapping(struct address_space *mapping, struct page *page)
624 if (__remove_mapping(mapping, page, false)) {
626 * Unfreezing the refcount with 1 rather than 2 effectively
627 * drops the pagecache ref for us without requiring another
630 page_unfreeze_refs(page, 1);
637 * putback_lru_page - put previously isolated page onto appropriate LRU list
638 * @page: page to be put back to appropriate lru list
640 * Add previously isolated @page to appropriate LRU list.
641 * Page may still be unevictable for other reasons.
643 * lru_lock must not be held, interrupts must be enabled.
645 void putback_lru_page(struct page *page)
648 int was_unevictable = PageUnevictable(page);
650 VM_BUG_ON_PAGE(PageLRU(page), page);
653 ClearPageUnevictable(page);
655 if (page_evictable(page)) {
657 * For evictable pages, we can use the cache.
658 * In event of a race, worst case is we end up with an
659 * unevictable page on [in]active list.
660 * We know how to handle that.
662 is_unevictable = false;
666 * Put unevictable pages directly on zone's unevictable
669 is_unevictable = true;
670 add_page_to_unevictable_list(page);
672 * When racing with an mlock or AS_UNEVICTABLE clearing
673 * (page is unlocked) make sure that if the other thread
674 * does not observe our setting of PG_lru and fails
675 * isolation/check_move_unevictable_pages,
676 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
677 * the page back to the evictable list.
679 * The other side is TestClearPageMlocked() or shmem_lock().
685 * page's status can change while we move it among lru. If an evictable
686 * page is on unevictable list, it never be freed. To avoid that,
687 * check after we added it to the list, again.
689 if (is_unevictable && page_evictable(page)) {
690 if (!isolate_lru_page(page)) {
694 /* This means someone else dropped this page from LRU
695 * So, it will be freed or putback to LRU again. There is
696 * nothing to do here.
700 if (was_unevictable && !is_unevictable)
701 count_vm_event(UNEVICTABLE_PGRESCUED);
702 else if (!was_unevictable && is_unevictable)
703 count_vm_event(UNEVICTABLE_PGCULLED);
705 put_page(page); /* drop ref from isolate */
708 enum page_references {
710 PAGEREF_RECLAIM_CLEAN,
715 static enum page_references page_check_references(struct page *page,
716 struct scan_control *sc)
718 int referenced_ptes, referenced_page;
719 unsigned long vm_flags;
721 referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
723 referenced_page = TestClearPageReferenced(page);
726 * Mlock lost the isolation race with us. Let try_to_unmap()
727 * move the page to the unevictable list.
729 if (vm_flags & VM_LOCKED)
730 return PAGEREF_RECLAIM;
732 if (referenced_ptes) {
733 if (PageSwapBacked(page))
734 return PAGEREF_ACTIVATE;
736 * All mapped pages start out with page table
737 * references from the instantiating fault, so we need
738 * to look twice if a mapped file page is used more
741 * Mark it and spare it for another trip around the
742 * inactive list. Another page table reference will
743 * lead to its activation.
745 * Note: the mark is set for activated pages as well
746 * so that recently deactivated but used pages are
749 SetPageReferenced(page);
751 if (referenced_page || referenced_ptes > 1)
752 return PAGEREF_ACTIVATE;
755 * Activate file-backed executable pages after first usage.
757 if (vm_flags & VM_EXEC)
758 return PAGEREF_ACTIVATE;
763 /* Reclaim if clean, defer dirty pages to writeback */
764 if (referenced_page && !PageSwapBacked(page))
765 return PAGEREF_RECLAIM_CLEAN;
767 return PAGEREF_RECLAIM;
770 /* Check if a page is dirty or under writeback */
771 static void page_check_dirty_writeback(struct page *page,
772 bool *dirty, bool *writeback)
774 struct address_space *mapping;
777 * Anonymous pages are not handled by flushers and must be written
778 * from reclaim context. Do not stall reclaim based on them
780 if (!page_is_file_cache(page)) {
786 /* By default assume that the page flags are accurate */
787 *dirty = PageDirty(page);
788 *writeback = PageWriteback(page);
790 /* Verify dirty/writeback state if the filesystem supports it */
791 if (!page_has_private(page))
794 mapping = page_mapping(page);
795 if (mapping && mapping->a_ops->is_dirty_writeback)
796 mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
800 * shrink_page_list() returns the number of reclaimed pages
802 static unsigned long shrink_page_list(struct list_head *page_list,
804 struct scan_control *sc,
805 enum ttu_flags ttu_flags,
806 unsigned long *ret_nr_dirty,
807 unsigned long *ret_nr_unqueued_dirty,
808 unsigned long *ret_nr_congested,
809 unsigned long *ret_nr_writeback,
810 unsigned long *ret_nr_immediate,
813 LIST_HEAD(ret_pages);
814 LIST_HEAD(free_pages);
816 unsigned long nr_unqueued_dirty = 0;
817 unsigned long nr_dirty = 0;
818 unsigned long nr_congested = 0;
819 unsigned long nr_reclaimed = 0;
820 unsigned long nr_writeback = 0;
821 unsigned long nr_immediate = 0;
825 while (!list_empty(page_list)) {
826 struct address_space *mapping;
829 enum page_references references = PAGEREF_RECLAIM_CLEAN;
830 bool dirty, writeback;
834 page = lru_to_page(page_list);
835 list_del(&page->lru);
837 if (!trylock_page(page))
840 VM_BUG_ON_PAGE(PageActive(page), page);
841 VM_BUG_ON_PAGE(page_zone(page) != zone, page);
845 if (unlikely(!page_evictable(page)))
848 if (!sc->may_unmap && page_mapped(page))
851 /* Double the slab pressure for mapped and swapcache pages */
852 if (page_mapped(page) || PageSwapCache(page))
855 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
856 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
859 * The number of dirty pages determines if a zone is marked
860 * reclaim_congested which affects wait_iff_congested. kswapd
861 * will stall and start writing pages if the tail of the LRU
862 * is all dirty unqueued pages.
864 page_check_dirty_writeback(page, &dirty, &writeback);
865 if (dirty || writeback)
868 if (dirty && !writeback)
872 * Treat this page as congested if the underlying BDI is or if
873 * pages are cycling through the LRU so quickly that the
874 * pages marked for immediate reclaim are making it to the
875 * end of the LRU a second time.
877 mapping = page_mapping(page);
878 if ((mapping && bdi_write_congested(mapping->backing_dev_info)) ||
879 (writeback && PageReclaim(page)))
883 * If a page at the tail of the LRU is under writeback, there
884 * are three cases to consider.
886 * 1) If reclaim is encountering an excessive number of pages
887 * under writeback and this page is both under writeback and
888 * PageReclaim then it indicates that pages are being queued
889 * for IO but are being recycled through the LRU before the
890 * IO can complete. Waiting on the page itself risks an
891 * indefinite stall if it is impossible to writeback the
892 * page due to IO error or disconnected storage so instead
893 * note that the LRU is being scanned too quickly and the
894 * caller can stall after page list has been processed.
896 * 2) Global reclaim encounters a page, memcg encounters a
897 * page that is not marked for immediate reclaim or
898 * the caller does not have __GFP_IO. In this case mark
899 * the page for immediate reclaim and continue scanning.
901 * __GFP_IO is checked because a loop driver thread might
902 * enter reclaim, and deadlock if it waits on a page for
903 * which it is needed to do the write (loop masks off
904 * __GFP_IO|__GFP_FS for this reason); but more thought
905 * would probably show more reasons.
907 * Don't require __GFP_FS, since we're not going into the
908 * FS, just waiting on its writeback completion. Worryingly,
909 * ext4 gfs2 and xfs allocate pages with
910 * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so testing
911 * may_enter_fs here is liable to OOM on them.
913 * 3) memcg encounters a page that is not already marked
914 * PageReclaim. memcg does not have any dirty pages
915 * throttling so we could easily OOM just because too many
916 * pages are in writeback and there is nothing else to
917 * reclaim. Wait for the writeback to complete.
919 if (PageWriteback(page)) {
921 if (current_is_kswapd() &&
923 zone_is_reclaim_writeback(zone)) {
928 } else if (global_reclaim(sc) ||
929 !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
931 * This is slightly racy - end_page_writeback()
932 * might have just cleared PageReclaim, then
933 * setting PageReclaim here end up interpreted
934 * as PageReadahead - but that does not matter
935 * enough to care. What we do want is for this
936 * page to have PageReclaim set next time memcg
937 * reclaim reaches the tests above, so it will
938 * then wait_on_page_writeback() to avoid OOM;
939 * and it's also appropriate in global reclaim.
941 SetPageReclaim(page);
948 wait_on_page_writeback(page);
953 references = page_check_references(page, sc);
955 switch (references) {
956 case PAGEREF_ACTIVATE:
957 goto activate_locked;
960 case PAGEREF_RECLAIM:
961 case PAGEREF_RECLAIM_CLEAN:
962 ; /* try to reclaim the page below */
966 * Anonymous process memory has backing store?
967 * Try to allocate it some swap space here.
969 if (PageAnon(page) && !PageSwapCache(page)) {
970 if (!(sc->gfp_mask & __GFP_IO))
972 if (!add_to_swap(page, page_list))
973 goto activate_locked;
976 /* Adding to swap updated mapping */
977 mapping = page_mapping(page);
981 * The page is mapped into the page tables of one or more
982 * processes. Try to unmap it here.
984 if (page_mapped(page) && mapping) {
985 switch (try_to_unmap(page, ttu_flags)) {
987 goto activate_locked;
993 ; /* try to free the page below */
997 if (PageDirty(page)) {
999 * Only kswapd can writeback filesystem pages to
1000 * avoid risk of stack overflow but only writeback
1001 * if many dirty pages have been encountered.
1003 if (page_is_file_cache(page) &&
1004 (!current_is_kswapd() ||
1005 !zone_is_reclaim_dirty(zone))) {
1007 * Immediately reclaim when written back.
1008 * Similar in principal to deactivate_page()
1009 * except we already have the page isolated
1010 * and know it's dirty
1012 inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
1013 SetPageReclaim(page);
1018 if (references == PAGEREF_RECLAIM_CLEAN)
1022 if (!sc->may_writepage)
1025 /* Page is dirty, try to write it out here */
1026 switch (pageout(page, mapping, sc)) {
1030 goto activate_locked;
1032 if (PageWriteback(page))
1034 if (PageDirty(page))
1038 * A synchronous write - probably a ramdisk. Go
1039 * ahead and try to reclaim the page.
1041 if (!trylock_page(page))
1043 if (PageDirty(page) || PageWriteback(page))
1045 mapping = page_mapping(page);
1047 ; /* try to free the page below */
1052 * If the page has buffers, try to free the buffer mappings
1053 * associated with this page. If we succeed we try to free
1056 * We do this even if the page is PageDirty().
1057 * try_to_release_page() does not perform I/O, but it is
1058 * possible for a page to have PageDirty set, but it is actually
1059 * clean (all its buffers are clean). This happens if the
1060 * buffers were written out directly, with submit_bh(). ext3
1061 * will do this, as well as the blockdev mapping.
1062 * try_to_release_page() will discover that cleanness and will
1063 * drop the buffers and mark the page clean - it can be freed.
1065 * Rarely, pages can have buffers and no ->mapping. These are
1066 * the pages which were not successfully invalidated in
1067 * truncate_complete_page(). We try to drop those buffers here
1068 * and if that worked, and the page is no longer mapped into
1069 * process address space (page_count == 1) it can be freed.
1070 * Otherwise, leave the page on the LRU so it is swappable.
1072 if (page_has_private(page)) {
1073 if (!try_to_release_page(page, sc->gfp_mask))
1074 goto activate_locked;
1075 if (!mapping && page_count(page) == 1) {
1077 if (put_page_testzero(page))
1081 * rare race with speculative reference.
1082 * the speculative reference will free
1083 * this page shortly, so we may
1084 * increment nr_reclaimed here (and
1085 * leave it off the LRU).
1093 if (!mapping || !__remove_mapping(mapping, page, true))
1097 * At this point, we have no other references and there is
1098 * no way to pick any more up (removed from LRU, removed
1099 * from pagecache). Can use non-atomic bitops now (and
1100 * we obviously don't have to worry about waking up a process
1101 * waiting on the page lock, because there are no references.
1103 __clear_page_locked(page);
1108 * Is there need to periodically free_page_list? It would
1109 * appear not as the counts should be low
1111 list_add(&page->lru, &free_pages);
1115 if (PageSwapCache(page))
1116 try_to_free_swap(page);
1118 putback_lru_page(page);
1122 /* Not a candidate for swapping, so reclaim swap space. */
1123 if (PageSwapCache(page) && vm_swap_full())
1124 try_to_free_swap(page);
1125 VM_BUG_ON_PAGE(PageActive(page), page);
1126 SetPageActive(page);
1131 list_add(&page->lru, &ret_pages);
1132 VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
1135 mem_cgroup_uncharge_list(&free_pages);
1136 free_hot_cold_page_list(&free_pages, true);
1138 list_splice(&ret_pages, page_list);
1139 count_vm_events(PGACTIVATE, pgactivate);
1141 *ret_nr_dirty += nr_dirty;
1142 *ret_nr_congested += nr_congested;
1143 *ret_nr_unqueued_dirty += nr_unqueued_dirty;
1144 *ret_nr_writeback += nr_writeback;
1145 *ret_nr_immediate += nr_immediate;
1146 return nr_reclaimed;
1149 unsigned long reclaim_clean_pages_from_list(struct zone *zone,
1150 struct list_head *page_list)
1152 struct scan_control sc = {
1153 .gfp_mask = GFP_KERNEL,
1154 .priority = DEF_PRIORITY,
1157 unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
1158 struct page *page, *next;
1159 LIST_HEAD(clean_pages);
1161 list_for_each_entry_safe(page, next, page_list, lru) {
1162 if (page_is_file_cache(page) && !PageDirty(page) &&
1163 !isolated_balloon_page(page)) {
1164 ClearPageActive(page);
1165 list_move(&page->lru, &clean_pages);
1169 ret = shrink_page_list(&clean_pages, zone, &sc,
1170 TTU_UNMAP|TTU_IGNORE_ACCESS,
1171 &dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
1172 list_splice(&clean_pages, page_list);
1173 mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
1178 * Attempt to remove the specified page from its LRU. Only take this page
1179 * if it is of the appropriate PageActive status. Pages which are being
1180 * freed elsewhere are also ignored.
1182 * page: page to consider
1183 * mode: one of the LRU isolation modes defined above
1185 * returns 0 on success, -ve errno on failure.
1187 int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1191 /* Only take pages on the LRU. */
1195 /* Compaction should not handle unevictable pages but CMA can do so */
1196 if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1202 * To minimise LRU disruption, the caller can indicate that it only
1203 * wants to isolate pages it will be able to operate on without
1204 * blocking - clean pages for the most part.
1206 * ISOLATE_CLEAN means that only clean pages should be isolated. This
1207 * is used by reclaim when it is cannot write to backing storage
1209 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1210 * that it is possible to migrate without blocking
1212 if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
1213 /* All the caller can do on PageWriteback is block */
1214 if (PageWriteback(page))
1217 if (PageDirty(page)) {
1218 struct address_space *mapping;
1220 /* ISOLATE_CLEAN means only clean pages */
1221 if (mode & ISOLATE_CLEAN)
1225 * Only pages without mappings or that have a
1226 * ->migratepage callback are possible to migrate
1229 mapping = page_mapping(page);
1230 if (mapping && !mapping->a_ops->migratepage)
1235 if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1238 if (likely(get_page_unless_zero(page))) {
1240 * Be careful not to clear PageLRU until after we're
1241 * sure the page is not being freed elsewhere -- the
1242 * page release code relies on it.
1252 * zone->lru_lock is heavily contended. Some of the functions that
1253 * shrink the lists perform better by taking out a batch of pages
1254 * and working on them outside the LRU lock.
1256 * For pagecache intensive workloads, this function is the hottest
1257 * spot in the kernel (apart from copy_*_user functions).
1259 * Appropriate locks must be held before calling this function.
1261 * @nr_to_scan: The number of pages to look through on the list.
1262 * @lruvec: The LRU vector to pull pages from.
1263 * @dst: The temp list to put pages on to.
1264 * @nr_scanned: The number of pages that were scanned.
1265 * @sc: The scan_control struct for this reclaim session
1266 * @mode: One of the LRU isolation modes
1267 * @lru: LRU list id for isolating
1269 * returns how many pages were moved onto *@dst.
1271 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1272 struct lruvec *lruvec, struct list_head *dst,
1273 unsigned long *nr_scanned, struct scan_control *sc,
1274 isolate_mode_t mode, enum lru_list lru)
1276 struct list_head *src = &lruvec->lists[lru];
1277 unsigned long nr_taken = 0;
1280 for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1284 page = lru_to_page(src);
1285 prefetchw_prev_lru_page(page, src, flags);
1287 VM_BUG_ON_PAGE(!PageLRU(page), page);
1289 switch (__isolate_lru_page(page, mode)) {
1291 nr_pages = hpage_nr_pages(page);
1292 mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
1293 list_move(&page->lru, dst);
1294 nr_taken += nr_pages;
1298 /* else it is being freed elsewhere */
1299 list_move(&page->lru, src);
1308 trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
1309 nr_taken, mode, is_file_lru(lru));
1314 * isolate_lru_page - tries to isolate a page from its LRU list
1315 * @page: page to isolate from its LRU list
1317 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1318 * vmstat statistic corresponding to whatever LRU list the page was on.
1320 * Returns 0 if the page was removed from an LRU list.
1321 * Returns -EBUSY if the page was not on an LRU list.
1323 * The returned page will have PageLRU() cleared. If it was found on
1324 * the active list, it will have PageActive set. If it was found on
1325 * the unevictable list, it will have the PageUnevictable bit set. That flag
1326 * may need to be cleared by the caller before letting the page go.
1328 * The vmstat statistic corresponding to the list on which the page was
1329 * found will be decremented.
1332 * (1) Must be called with an elevated refcount on the page. This is a
1333 * fundamentnal difference from isolate_lru_pages (which is called
1334 * without a stable reference).
1335 * (2) the lru_lock must not be held.
1336 * (3) interrupts must be enabled.
1338 int isolate_lru_page(struct page *page)
1342 VM_BUG_ON_PAGE(!page_count(page), page);
1344 if (PageLRU(page)) {
1345 struct zone *zone = page_zone(page);
1346 struct lruvec *lruvec;
1348 spin_lock_irq(&zone->lru_lock);
1349 lruvec = mem_cgroup_page_lruvec(page, zone);
1350 if (PageLRU(page)) {
1351 int lru = page_lru(page);
1354 del_page_from_lru_list(page, lruvec, lru);
1357 spin_unlock_irq(&zone->lru_lock);
1363 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
1364 * then get resheduled. When there are massive number of tasks doing page
1365 * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
1366 * the LRU list will go small and be scanned faster than necessary, leading to
1367 * unnecessary swapping, thrashing and OOM.
1369 static int too_many_isolated(struct zone *zone, int file,
1370 struct scan_control *sc)
1372 unsigned long inactive, isolated;
1374 if (current_is_kswapd())
1377 if (!global_reclaim(sc))
1381 inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1382 isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1384 inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1385 isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1389 * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
1390 * won't get blocked by normal direct-reclaimers, forming a circular
1393 if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS)
1396 return isolated > inactive;
1399 static noinline_for_stack void
1400 putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1402 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1403 struct zone *zone = lruvec_zone(lruvec);
1404 LIST_HEAD(pages_to_free);
1407 * Put back any unfreeable pages.
1409 while (!list_empty(page_list)) {
1410 struct page *page = lru_to_page(page_list);
1413 VM_BUG_ON_PAGE(PageLRU(page), page);
1414 list_del(&page->lru);
1415 if (unlikely(!page_evictable(page))) {
1416 spin_unlock_irq(&zone->lru_lock);
1417 putback_lru_page(page);
1418 spin_lock_irq(&zone->lru_lock);
1422 lruvec = mem_cgroup_page_lruvec(page, zone);
1425 lru = page_lru(page);
1426 add_page_to_lru_list(page, lruvec, lru);
1428 if (is_active_lru(lru)) {
1429 int file = is_file_lru(lru);
1430 int numpages = hpage_nr_pages(page);
1431 reclaim_stat->recent_rotated[file] += numpages;
1433 if (put_page_testzero(page)) {
1434 __ClearPageLRU(page);
1435 __ClearPageActive(page);
1436 del_page_from_lru_list(page, lruvec, lru);
1438 if (unlikely(PageCompound(page))) {
1439 spin_unlock_irq(&zone->lru_lock);
1440 mem_cgroup_uncharge(page);
1441 (*get_compound_page_dtor(page))(page);
1442 spin_lock_irq(&zone->lru_lock);
1444 list_add(&page->lru, &pages_to_free);
1449 * To save our caller's stack, now use input list for pages to free.
1451 list_splice(&pages_to_free, page_list);
1455 * If a kernel thread (such as nfsd for loop-back mounts) services
1456 * a backing device by writing to the page cache it sets PF_LESS_THROTTLE.
1457 * In that case we should only throttle if the backing device it is
1458 * writing to is congested. In other cases it is safe to throttle.
1460 static int current_may_throttle(void)
1462 return !(current->flags & PF_LESS_THROTTLE) ||
1463 current->backing_dev_info == NULL ||
1464 bdi_write_congested(current->backing_dev_info);
1468 * shrink_inactive_list() is a helper for shrink_zone(). It returns the number
1469 * of reclaimed pages
1471 static noinline_for_stack unsigned long
1472 shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1473 struct scan_control *sc, enum lru_list lru)
1475 LIST_HEAD(page_list);
1476 unsigned long nr_scanned;
1477 unsigned long nr_reclaimed = 0;
1478 unsigned long nr_taken;
1479 unsigned long nr_dirty = 0;
1480 unsigned long nr_congested = 0;
1481 unsigned long nr_unqueued_dirty = 0;
1482 unsigned long nr_writeback = 0;
1483 unsigned long nr_immediate = 0;
1484 isolate_mode_t isolate_mode = 0;
1485 int file = is_file_lru(lru);
1486 struct zone *zone = lruvec_zone(lruvec);
1487 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1489 while (unlikely(too_many_isolated(zone, file, sc))) {
1490 congestion_wait(BLK_RW_ASYNC, HZ/10);
1492 /* We are about to die and free our memory. Return now. */
1493 if (fatal_signal_pending(current))
1494 return SWAP_CLUSTER_MAX;
1500 isolate_mode |= ISOLATE_UNMAPPED;
1501 if (!sc->may_writepage)
1502 isolate_mode |= ISOLATE_CLEAN;
1504 spin_lock_irq(&zone->lru_lock);
1506 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1507 &nr_scanned, sc, isolate_mode, lru);
1509 __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1510 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1512 if (global_reclaim(sc)) {
1513 __mod_zone_page_state(zone, NR_PAGES_SCANNED, nr_scanned);
1514 if (current_is_kswapd())
1515 __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1517 __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1519 spin_unlock_irq(&zone->lru_lock);
1524 nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
1525 &nr_dirty, &nr_unqueued_dirty, &nr_congested,
1526 &nr_writeback, &nr_immediate,
1529 spin_lock_irq(&zone->lru_lock);
1531 reclaim_stat->recent_scanned[file] += nr_taken;
1533 if (global_reclaim(sc)) {
1534 if (current_is_kswapd())
1535 __count_zone_vm_events(PGSTEAL_KSWAPD, zone,
1538 __count_zone_vm_events(PGSTEAL_DIRECT, zone,
1542 putback_inactive_pages(lruvec, &page_list);
1544 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1546 spin_unlock_irq(&zone->lru_lock);
1548 mem_cgroup_uncharge_list(&page_list);
1549 free_hot_cold_page_list(&page_list, true);
1552 * If reclaim is isolating dirty pages under writeback, it implies
1553 * that the long-lived page allocation rate is exceeding the page
1554 * laundering rate. Either the global limits are not being effective
1555 * at throttling processes due to the page distribution throughout
1556 * zones or there is heavy usage of a slow backing device. The
1557 * only option is to throttle from reclaim context which is not ideal
1558 * as there is no guarantee the dirtying process is throttled in the
1559 * same way balance_dirty_pages() manages.
1561 * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
1562 * of pages under pages flagged for immediate reclaim and stall if any
1563 * are encountered in the nr_immediate check below.
1565 if (nr_writeback && nr_writeback == nr_taken)
1566 zone_set_flag(zone, ZONE_WRITEBACK);
1569 * memcg will stall in page writeback so only consider forcibly
1570 * stalling for global reclaim
1572 if (global_reclaim(sc)) {
1574 * Tag a zone as congested if all the dirty pages scanned were
1575 * backed by a congested BDI and wait_iff_congested will stall.
1577 if (nr_dirty && nr_dirty == nr_congested)
1578 zone_set_flag(zone, ZONE_CONGESTED);
1581 * If dirty pages are scanned that are not queued for IO, it
1582 * implies that flushers are not keeping up. In this case, flag
1583 * the zone ZONE_TAIL_LRU_DIRTY and kswapd will start writing
1584 * pages from reclaim context.
1586 if (nr_unqueued_dirty == nr_taken)
1587 zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY);
1590 * If kswapd scans pages marked marked for immediate
1591 * reclaim and under writeback (nr_immediate), it implies
1592 * that pages are cycling through the LRU faster than
1593 * they are written so also forcibly stall.
1595 if (nr_immediate && current_may_throttle())
1596 congestion_wait(BLK_RW_ASYNC, HZ/10);
1600 * Stall direct reclaim for IO completions if underlying BDIs or zone
1601 * is congested. Allow kswapd to continue until it starts encountering
1602 * unqueued dirty pages or cycling through the LRU too quickly.
1604 if (!sc->hibernation_mode && !current_is_kswapd() &&
1605 current_may_throttle())
1606 wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
1608 trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1610 nr_scanned, nr_reclaimed,
1612 trace_shrink_flags(file));
1613 return nr_reclaimed;
1617 * This moves pages from the active list to the inactive list.
1619 * We move them the other way if the page is referenced by one or more
1620 * processes, from rmap.
1622 * If the pages are mostly unmapped, the processing is fast and it is
1623 * appropriate to hold zone->lru_lock across the whole operation. But if
1624 * the pages are mapped, the processing is slow (page_referenced()) so we
1625 * should drop zone->lru_lock around each page. It's impossible to balance
1626 * this, so instead we remove the pages from the LRU while processing them.
1627 * It is safe to rely on PG_active against the non-LRU pages in here because
1628 * nobody will play with that bit on a non-LRU page.
1630 * The downside is that we have to touch page->_count against each page.
1631 * But we had to alter page->flags anyway.
1634 static void move_active_pages_to_lru(struct lruvec *lruvec,
1635 struct list_head *list,
1636 struct list_head *pages_to_free,
1639 struct zone *zone = lruvec_zone(lruvec);
1640 unsigned long pgmoved = 0;
1644 while (!list_empty(list)) {
1645 page = lru_to_page(list);
1646 lruvec = mem_cgroup_page_lruvec(page, zone);
1648 VM_BUG_ON_PAGE(PageLRU(page), page);
1651 nr_pages = hpage_nr_pages(page);
1652 mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1653 list_move(&page->lru, &lruvec->lists[lru]);
1654 pgmoved += nr_pages;
1656 if (put_page_testzero(page)) {
1657 __ClearPageLRU(page);
1658 __ClearPageActive(page);
1659 del_page_from_lru_list(page, lruvec, lru);
1661 if (unlikely(PageCompound(page))) {
1662 spin_unlock_irq(&zone->lru_lock);
1663 mem_cgroup_uncharge(page);
1664 (*get_compound_page_dtor(page))(page);
1665 spin_lock_irq(&zone->lru_lock);
1667 list_add(&page->lru, pages_to_free);
1670 __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1671 if (!is_active_lru(lru))
1672 __count_vm_events(PGDEACTIVATE, pgmoved);
1675 static void shrink_active_list(unsigned long nr_to_scan,
1676 struct lruvec *lruvec,
1677 struct scan_control *sc,
1680 unsigned long nr_taken;
1681 unsigned long nr_scanned;
1682 unsigned long vm_flags;
1683 LIST_HEAD(l_hold); /* The pages which were snipped off */
1684 LIST_HEAD(l_active);
1685 LIST_HEAD(l_inactive);
1687 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1688 unsigned long nr_rotated = 0;
1689 isolate_mode_t isolate_mode = 0;
1690 int file = is_file_lru(lru);
1691 struct zone *zone = lruvec_zone(lruvec);
1696 isolate_mode |= ISOLATE_UNMAPPED;
1697 if (!sc->may_writepage)
1698 isolate_mode |= ISOLATE_CLEAN;
1700 spin_lock_irq(&zone->lru_lock);
1702 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1703 &nr_scanned, sc, isolate_mode, lru);
1704 if (global_reclaim(sc))
1705 __mod_zone_page_state(zone, NR_PAGES_SCANNED, nr_scanned);
1707 reclaim_stat->recent_scanned[file] += nr_taken;
1709 __count_zone_vm_events(PGREFILL, zone, nr_scanned);
1710 __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1711 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1712 spin_unlock_irq(&zone->lru_lock);
1714 while (!list_empty(&l_hold)) {
1716 page = lru_to_page(&l_hold);
1717 list_del(&page->lru);
1719 if (unlikely(!page_evictable(page))) {
1720 putback_lru_page(page);
1724 if (unlikely(buffer_heads_over_limit)) {
1725 if (page_has_private(page) && trylock_page(page)) {
1726 if (page_has_private(page))
1727 try_to_release_page(page, 0);
1732 if (page_referenced(page, 0, sc->target_mem_cgroup,
1734 nr_rotated += hpage_nr_pages(page);
1736 * Identify referenced, file-backed active pages and
1737 * give them one more trip around the active list. So
1738 * that executable code get better chances to stay in
1739 * memory under moderate memory pressure. Anon pages
1740 * are not likely to be evicted by use-once streaming
1741 * IO, plus JVM can create lots of anon VM_EXEC pages,
1742 * so we ignore them here.
1744 if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1745 list_add(&page->lru, &l_active);
1750 ClearPageActive(page); /* we are de-activating */
1751 list_add(&page->lru, &l_inactive);
1755 * Move pages back to the lru list.
1757 spin_lock_irq(&zone->lru_lock);
1759 * Count referenced pages from currently used mappings as rotated,
1760 * even though only some of them are actually re-activated. This
1761 * helps balance scan pressure between file and anonymous pages in
1764 reclaim_stat->recent_rotated[file] += nr_rotated;
1766 move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1767 move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1768 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1769 spin_unlock_irq(&zone->lru_lock);
1771 mem_cgroup_uncharge_list(&l_hold);
1772 free_hot_cold_page_list(&l_hold, true);
1776 static int inactive_anon_is_low_global(struct zone *zone)
1778 unsigned long active, inactive;
1780 active = zone_page_state(zone, NR_ACTIVE_ANON);
1781 inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1783 if (inactive * zone->inactive_ratio < active)
1790 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1791 * @lruvec: LRU vector to check
1793 * Returns true if the zone does not have enough inactive anon pages,
1794 * meaning some active anon pages need to be deactivated.
1796 static int inactive_anon_is_low(struct lruvec *lruvec)
1799 * If we don't have swap space, anonymous page deactivation
1802 if (!total_swap_pages)
1805 if (!mem_cgroup_disabled())
1806 return mem_cgroup_inactive_anon_is_low(lruvec);
1808 return inactive_anon_is_low_global(lruvec_zone(lruvec));
1811 static inline int inactive_anon_is_low(struct lruvec *lruvec)
1818 * inactive_file_is_low - check if file pages need to be deactivated
1819 * @lruvec: LRU vector to check
1821 * When the system is doing streaming IO, memory pressure here
1822 * ensures that active file pages get deactivated, until more
1823 * than half of the file pages are on the inactive list.
1825 * Once we get to that situation, protect the system's working
1826 * set from being evicted by disabling active file page aging.
1828 * This uses a different ratio than the anonymous pages, because
1829 * the page cache uses a use-once replacement algorithm.
1831 static int inactive_file_is_low(struct lruvec *lruvec)
1833 unsigned long inactive;
1834 unsigned long active;
1836 inactive = get_lru_size(lruvec, LRU_INACTIVE_FILE);
1837 active = get_lru_size(lruvec, LRU_ACTIVE_FILE);
1839 return active > inactive;
1842 static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1844 if (is_file_lru(lru))
1845 return inactive_file_is_low(lruvec);
1847 return inactive_anon_is_low(lruvec);
1850 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1851 struct lruvec *lruvec, struct scan_control *sc)
1853 if (is_active_lru(lru)) {
1854 if (inactive_list_is_low(lruvec, lru))
1855 shrink_active_list(nr_to_scan, lruvec, sc, lru);
1859 return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1870 * Determine how aggressively the anon and file LRU lists should be
1871 * scanned. The relative value of each set of LRU lists is determined
1872 * by looking at the fraction of the pages scanned we did rotate back
1873 * onto the active list instead of evict.
1875 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
1876 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
1878 static void get_scan_count(struct lruvec *lruvec, int swappiness,
1879 struct scan_control *sc, unsigned long *nr)
1881 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1883 u64 denominator = 0; /* gcc */
1884 struct zone *zone = lruvec_zone(lruvec);
1885 unsigned long anon_prio, file_prio;
1886 enum scan_balance scan_balance;
1887 unsigned long anon, file;
1888 bool force_scan = false;
1889 unsigned long ap, fp;
1895 * If the zone or memcg is small, nr[l] can be 0. This
1896 * results in no scanning on this priority and a potential
1897 * priority drop. Global direct reclaim can go to the next
1898 * zone and tends to have no problems. Global kswapd is for
1899 * zone balancing and it needs to scan a minimum amount. When
1900 * reclaiming for a memcg, a priority drop can cause high
1901 * latencies, so it's better to scan a minimum amount there as
1904 if (current_is_kswapd() && !zone_reclaimable(zone))
1906 if (!global_reclaim(sc))
1909 /* If we have no swap space, do not bother scanning anon pages. */
1910 if (!sc->may_swap || (get_nr_swap_pages() <= 0)) {
1911 scan_balance = SCAN_FILE;
1916 * Global reclaim will swap to prevent OOM even with no
1917 * swappiness, but memcg users want to use this knob to
1918 * disable swapping for individual groups completely when
1919 * using the memory controller's swap limit feature would be
1922 if (!global_reclaim(sc) && !swappiness) {
1923 scan_balance = SCAN_FILE;
1928 * Do not apply any pressure balancing cleverness when the
1929 * system is close to OOM, scan both anon and file equally
1930 * (unless the swappiness setting disagrees with swapping).
1932 if (!sc->priority && swappiness) {
1933 scan_balance = SCAN_EQUAL;
1938 * Prevent the reclaimer from falling into the cache trap: as
1939 * cache pages start out inactive, every cache fault will tip
1940 * the scan balance towards the file LRU. And as the file LRU
1941 * shrinks, so does the window for rotation from references.
1942 * This means we have a runaway feedback loop where a tiny
1943 * thrashing file LRU becomes infinitely more attractive than
1944 * anon pages. Try to detect this based on file LRU size.
1946 if (global_reclaim(sc)) {
1947 unsigned long zonefile;
1948 unsigned long zonefree;
1950 zonefree = zone_page_state(zone, NR_FREE_PAGES);
1951 zonefile = zone_page_state(zone, NR_ACTIVE_FILE) +
1952 zone_page_state(zone, NR_INACTIVE_FILE);
1954 if (unlikely(zonefile + zonefree <= high_wmark_pages(zone))) {
1955 scan_balance = SCAN_ANON;
1961 * There is enough inactive page cache, do not reclaim
1962 * anything from the anonymous working set right now.
1964 if (!inactive_file_is_low(lruvec)) {
1965 scan_balance = SCAN_FILE;
1969 scan_balance = SCAN_FRACT;
1972 * With swappiness at 100, anonymous and file have the same priority.
1973 * This scanning priority is essentially the inverse of IO cost.
1975 anon_prio = swappiness;
1976 file_prio = 200 - anon_prio;
1979 * OK, so we have swap space and a fair amount of page cache
1980 * pages. We use the recently rotated / recently scanned
1981 * ratios to determine how valuable each cache is.
1983 * Because workloads change over time (and to avoid overflow)
1984 * we keep these statistics as a floating average, which ends
1985 * up weighing recent references more than old ones.
1987 * anon in [0], file in [1]
1990 anon = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
1991 get_lru_size(lruvec, LRU_INACTIVE_ANON);
1992 file = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
1993 get_lru_size(lruvec, LRU_INACTIVE_FILE);
1995 spin_lock_irq(&zone->lru_lock);
1996 if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1997 reclaim_stat->recent_scanned[0] /= 2;
1998 reclaim_stat->recent_rotated[0] /= 2;
2001 if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
2002 reclaim_stat->recent_scanned[1] /= 2;
2003 reclaim_stat->recent_rotated[1] /= 2;
2007 * The amount of pressure on anon vs file pages is inversely
2008 * proportional to the fraction of recently scanned pages on
2009 * each list that were recently referenced and in active use.
2011 ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
2012 ap /= reclaim_stat->recent_rotated[0] + 1;
2014 fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
2015 fp /= reclaim_stat->recent_rotated[1] + 1;
2016 spin_unlock_irq(&zone->lru_lock);
2020 denominator = ap + fp + 1;
2022 some_scanned = false;
2023 /* Only use force_scan on second pass. */
2024 for (pass = 0; !some_scanned && pass < 2; pass++) {
2025 for_each_evictable_lru(lru) {
2026 int file = is_file_lru(lru);
2030 size = get_lru_size(lruvec, lru);
2031 scan = size >> sc->priority;
2033 if (!scan && pass && force_scan)
2034 scan = min(size, SWAP_CLUSTER_MAX);
2036 switch (scan_balance) {
2038 /* Scan lists relative to size */
2042 * Scan types proportional to swappiness and
2043 * their relative recent reclaim efficiency.
2045 scan = div64_u64(scan * fraction[file],
2050 /* Scan one type exclusively */
2051 if ((scan_balance == SCAN_FILE) != file)
2055 /* Look ma, no brain */
2060 * Skip the second pass and don't force_scan,
2061 * if we found something to scan.
2063 some_scanned |= !!scan;
2069 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
2071 static void shrink_lruvec(struct lruvec *lruvec, int swappiness,
2072 struct scan_control *sc)
2074 unsigned long nr[NR_LRU_LISTS];
2075 unsigned long targets[NR_LRU_LISTS];
2076 unsigned long nr_to_scan;
2078 unsigned long nr_reclaimed = 0;
2079 unsigned long nr_to_reclaim = sc->nr_to_reclaim;
2080 struct blk_plug plug;
2083 get_scan_count(lruvec, swappiness, sc, nr);
2085 /* Record the original scan target for proportional adjustments later */
2086 memcpy(targets, nr, sizeof(nr));
2089 * Global reclaiming within direct reclaim at DEF_PRIORITY is a normal
2090 * event that can occur when there is little memory pressure e.g.
2091 * multiple streaming readers/writers. Hence, we do not abort scanning
2092 * when the requested number of pages are reclaimed when scanning at
2093 * DEF_PRIORITY on the assumption that the fact we are direct
2094 * reclaiming implies that kswapd is not keeping up and it is best to
2095 * do a batch of work at once. For memcg reclaim one check is made to
2096 * abort proportional reclaim if either the file or anon lru has already
2097 * dropped to zero at the first pass.
2099 scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() &&
2100 sc->priority == DEF_PRIORITY);
2102 blk_start_plug(&plug);
2103 while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
2104 nr[LRU_INACTIVE_FILE]) {
2105 unsigned long nr_anon, nr_file, percentage;
2106 unsigned long nr_scanned;
2108 for_each_evictable_lru(lru) {
2110 nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
2111 nr[lru] -= nr_to_scan;
2113 nr_reclaimed += shrink_list(lru, nr_to_scan,
2118 if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
2122 * For kswapd and memcg, reclaim at least the number of pages
2123 * requested. Ensure that the anon and file LRUs are scanned
2124 * proportionally what was requested by get_scan_count(). We
2125 * stop reclaiming one LRU and reduce the amount scanning
2126 * proportional to the original scan target.
2128 nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
2129 nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
2132 * It's just vindictive to attack the larger once the smaller
2133 * has gone to zero. And given the way we stop scanning the
2134 * smaller below, this makes sure that we only make one nudge
2135 * towards proportionality once we've got nr_to_reclaim.
2137 if (!nr_file || !nr_anon)
2140 if (nr_file > nr_anon) {
2141 unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
2142 targets[LRU_ACTIVE_ANON] + 1;
2144 percentage = nr_anon * 100 / scan_target;
2146 unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
2147 targets[LRU_ACTIVE_FILE] + 1;
2149 percentage = nr_file * 100 / scan_target;
2152 /* Stop scanning the smaller of the LRU */
2154 nr[lru + LRU_ACTIVE] = 0;
2157 * Recalculate the other LRU scan count based on its original
2158 * scan target and the percentage scanning already complete
2160 lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
2161 nr_scanned = targets[lru] - nr[lru];
2162 nr[lru] = targets[lru] * (100 - percentage) / 100;
2163 nr[lru] -= min(nr[lru], nr_scanned);
2166 nr_scanned = targets[lru] - nr[lru];
2167 nr[lru] = targets[lru] * (100 - percentage) / 100;
2168 nr[lru] -= min(nr[lru], nr_scanned);
2170 scan_adjusted = true;
2172 blk_finish_plug(&plug);
2173 sc->nr_reclaimed += nr_reclaimed;
2176 * Even if we did not try to evict anon pages at all, we want to
2177 * rebalance the anon lru active/inactive ratio.
2179 if (inactive_anon_is_low(lruvec))
2180 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2181 sc, LRU_ACTIVE_ANON);
2183 throttle_vm_writeout(sc->gfp_mask);
2186 /* Use reclaim/compaction for costly allocs or under memory pressure */
2187 static bool in_reclaim_compaction(struct scan_control *sc)
2189 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2190 (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
2191 sc->priority < DEF_PRIORITY - 2))
2198 * Reclaim/compaction is used for high-order allocation requests. It reclaims
2199 * order-0 pages before compacting the zone. should_continue_reclaim() returns
2200 * true if more pages should be reclaimed such that when the page allocator
2201 * calls try_to_compact_zone() that it will have enough free pages to succeed.
2202 * It will give up earlier than that if there is difficulty reclaiming pages.
2204 static inline bool should_continue_reclaim(struct zone *zone,
2205 unsigned long nr_reclaimed,
2206 unsigned long nr_scanned,
2207 struct scan_control *sc)
2209 unsigned long pages_for_compaction;
2210 unsigned long inactive_lru_pages;
2212 /* If not in reclaim/compaction mode, stop */
2213 if (!in_reclaim_compaction(sc))
2216 /* Consider stopping depending on scan and reclaim activity */
2217 if (sc->gfp_mask & __GFP_REPEAT) {
2219 * For __GFP_REPEAT allocations, stop reclaiming if the
2220 * full LRU list has been scanned and we are still failing
2221 * to reclaim pages. This full LRU scan is potentially
2222 * expensive but a __GFP_REPEAT caller really wants to succeed
2224 if (!nr_reclaimed && !nr_scanned)
2228 * For non-__GFP_REPEAT allocations which can presumably
2229 * fail without consequence, stop if we failed to reclaim
2230 * any pages from the last SWAP_CLUSTER_MAX number of
2231 * pages that were scanned. This will return to the
2232 * caller faster at the risk reclaim/compaction and
2233 * the resulting allocation attempt fails
2240 * If we have not reclaimed enough pages for compaction and the
2241 * inactive lists are large enough, continue reclaiming
2243 pages_for_compaction = (2UL << sc->order);
2244 inactive_lru_pages = zone_page_state(zone, NR_INACTIVE_FILE);
2245 if (get_nr_swap_pages() > 0)
2246 inactive_lru_pages += zone_page_state(zone, NR_INACTIVE_ANON);
2247 if (sc->nr_reclaimed < pages_for_compaction &&
2248 inactive_lru_pages > pages_for_compaction)
2251 /* If compaction would go ahead or the allocation would succeed, stop */
2252 switch (compaction_suitable(zone, sc->order)) {
2253 case COMPACT_PARTIAL:
2254 case COMPACT_CONTINUE:
2261 static bool shrink_zone(struct zone *zone, struct scan_control *sc)
2263 unsigned long nr_reclaimed, nr_scanned;
2264 bool reclaimable = false;
2267 struct mem_cgroup *root = sc->target_mem_cgroup;
2268 struct mem_cgroup_reclaim_cookie reclaim = {
2270 .priority = sc->priority,
2272 struct mem_cgroup *memcg;
2274 nr_reclaimed = sc->nr_reclaimed;
2275 nr_scanned = sc->nr_scanned;
2277 memcg = mem_cgroup_iter(root, NULL, &reclaim);
2279 struct lruvec *lruvec;
2282 lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2283 swappiness = mem_cgroup_swappiness(memcg);
2285 shrink_lruvec(lruvec, swappiness, sc);
2288 * Direct reclaim and kswapd have to scan all memory
2289 * cgroups to fulfill the overall scan target for the
2292 * Limit reclaim, on the other hand, only cares about
2293 * nr_to_reclaim pages to be reclaimed and it will
2294 * retry with decreasing priority if one round over the
2295 * whole hierarchy is not sufficient.
2297 if (!global_reclaim(sc) &&
2298 sc->nr_reclaimed >= sc->nr_to_reclaim) {
2299 mem_cgroup_iter_break(root, memcg);
2302 memcg = mem_cgroup_iter(root, memcg, &reclaim);
2305 vmpressure(sc->gfp_mask, sc->target_mem_cgroup,
2306 sc->nr_scanned - nr_scanned,
2307 sc->nr_reclaimed - nr_reclaimed);
2309 if (sc->nr_reclaimed - nr_reclaimed)
2312 } while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed,
2313 sc->nr_scanned - nr_scanned, sc));
2319 * Returns true if compaction should go ahead for a high-order request, or
2320 * the high-order allocation would succeed without compaction.
2322 static inline bool compaction_ready(struct zone *zone, int order)
2324 unsigned long balance_gap, watermark;
2328 * Compaction takes time to run and there are potentially other
2329 * callers using the pages just freed. Continue reclaiming until
2330 * there is a buffer of free pages available to give compaction
2331 * a reasonable chance of completing and allocating the page
2333 balance_gap = min(low_wmark_pages(zone), DIV_ROUND_UP(
2334 zone->managed_pages, KSWAPD_ZONE_BALANCE_GAP_RATIO));
2335 watermark = high_wmark_pages(zone) + balance_gap + (2UL << order);
2336 watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
2339 * If compaction is deferred, reclaim up to a point where
2340 * compaction will have a chance of success when re-enabled
2342 if (compaction_deferred(zone, order))
2343 return watermark_ok;
2346 * If compaction is not ready to start and allocation is not likely
2347 * to succeed without it, then keep reclaiming.
2349 if (compaction_suitable(zone, order) == COMPACT_SKIPPED)
2352 return watermark_ok;
2356 * This is the direct reclaim path, for page-allocating processes. We only
2357 * try to reclaim pages from zones which will satisfy the caller's allocation
2360 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
2362 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
2364 * b) The target zone may be at high_wmark_pages(zone) but the lower zones
2365 * must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
2366 * zone defense algorithm.
2368 * If a zone is deemed to be full of pinned pages then just give it a light
2369 * scan then give up on it.
2371 * Returns true if a zone was reclaimable.
2373 static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
2377 unsigned long nr_soft_reclaimed;
2378 unsigned long nr_soft_scanned;
2379 unsigned long lru_pages = 0;
2380 struct reclaim_state *reclaim_state = current->reclaim_state;
2382 struct shrink_control shrink = {
2383 .gfp_mask = sc->gfp_mask,
2385 enum zone_type requested_highidx = gfp_zone(sc->gfp_mask);
2386 bool reclaimable = false;
2389 * If the number of buffer_heads in the machine exceeds the maximum
2390 * allowed level, force direct reclaim to scan the highmem zone as
2391 * highmem pages could be pinning lowmem pages storing buffer_heads
2393 orig_mask = sc->gfp_mask;
2394 if (buffer_heads_over_limit)
2395 sc->gfp_mask |= __GFP_HIGHMEM;
2397 nodes_clear(shrink.nodes_to_scan);
2399 for_each_zone_zonelist_nodemask(zone, z, zonelist,
2400 gfp_zone(sc->gfp_mask), sc->nodemask) {
2401 if (!populated_zone(zone))
2404 * Take care memory controller reclaiming has small influence
2407 if (global_reclaim(sc)) {
2408 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2411 lru_pages += zone_reclaimable_pages(zone);
2412 node_set(zone_to_nid(zone), shrink.nodes_to_scan);
2414 if (sc->priority != DEF_PRIORITY &&
2415 !zone_reclaimable(zone))
2416 continue; /* Let kswapd poll it */
2419 * If we already have plenty of memory free for
2420 * compaction in this zone, don't free any more.
2421 * Even though compaction is invoked for any
2422 * non-zero order, only frequent costly order
2423 * reclamation is disruptive enough to become a
2424 * noticeable problem, like transparent huge
2427 if (IS_ENABLED(CONFIG_COMPACTION) &&
2428 sc->order > PAGE_ALLOC_COSTLY_ORDER &&
2429 zonelist_zone_idx(z) <= requested_highidx &&
2430 compaction_ready(zone, sc->order)) {
2431 sc->compaction_ready = true;
2436 * This steals pages from memory cgroups over softlimit
2437 * and returns the number of reclaimed pages and
2438 * scanned pages. This works for global memory pressure
2439 * and balancing, not for a memcg's limit.
2441 nr_soft_scanned = 0;
2442 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2443 sc->order, sc->gfp_mask,
2445 sc->nr_reclaimed += nr_soft_reclaimed;
2446 sc->nr_scanned += nr_soft_scanned;
2447 if (nr_soft_reclaimed)
2449 /* need some check for avoid more shrink_zone() */
2452 if (shrink_zone(zone, sc))
2455 if (global_reclaim(sc) &&
2456 !reclaimable && zone_reclaimable(zone))
2461 * Don't shrink slabs when reclaiming memory from over limit cgroups
2462 * but do shrink slab at least once when aborting reclaim for
2463 * compaction to avoid unevenly scanning file/anon LRU pages over slab
2466 if (global_reclaim(sc)) {
2467 shrink_slab(&shrink, sc->nr_scanned, lru_pages);
2468 if (reclaim_state) {
2469 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2470 reclaim_state->reclaimed_slab = 0;
2475 * Restore to original mask to avoid the impact on the caller if we
2476 * promoted it to __GFP_HIGHMEM.
2478 sc->gfp_mask = orig_mask;
2484 * This is the main entry point to direct page reclaim.
2486 * If a full scan of the inactive list fails to free enough memory then we
2487 * are "out of memory" and something needs to be killed.
2489 * If the caller is !__GFP_FS then the probability of a failure is reasonably
2490 * high - the zone may be full of dirty or under-writeback pages, which this
2491 * caller can't do much about. We kick the writeback threads and take explicit
2492 * naps in the hope that some of these pages can be written. But if the
2493 * allocating task holds filesystem locks which prevent writeout this might not
2494 * work, and the allocation attempt will fail.
2496 * returns: 0, if no pages reclaimed
2497 * else, the number of pages reclaimed
2499 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2500 struct scan_control *sc)
2502 unsigned long total_scanned = 0;
2503 unsigned long writeback_threshold;
2504 bool zones_reclaimable;
2506 delayacct_freepages_start();
2508 if (global_reclaim(sc))
2509 count_vm_event(ALLOCSTALL);
2512 vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
2515 zones_reclaimable = shrink_zones(zonelist, sc);
2517 total_scanned += sc->nr_scanned;
2518 if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2521 if (sc->compaction_ready)
2525 * If we're getting trouble reclaiming, start doing
2526 * writepage even in laptop mode.
2528 if (sc->priority < DEF_PRIORITY - 2)
2529 sc->may_writepage = 1;
2532 * Try to write back as many pages as we just scanned. This
2533 * tends to cause slow streaming writers to write data to the
2534 * disk smoothly, at the dirtying rate, which is nice. But
2535 * that's undesirable in laptop mode, where we *want* lumpy
2536 * writeout. So in laptop mode, write out the whole world.
2538 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2539 if (total_scanned > writeback_threshold) {
2540 wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2541 WB_REASON_TRY_TO_FREE_PAGES);
2542 sc->may_writepage = 1;
2544 } while (--sc->priority >= 0);
2546 delayacct_freepages_end();
2548 if (sc->nr_reclaimed)
2549 return sc->nr_reclaimed;
2551 /* Aborted reclaim to try compaction? don't OOM, then */
2552 if (sc->compaction_ready)
2555 /* Any of the zones still reclaimable? Don't OOM. */
2556 if (zones_reclaimable)
2562 static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2565 unsigned long pfmemalloc_reserve = 0;
2566 unsigned long free_pages = 0;
2570 for (i = 0; i <= ZONE_NORMAL; i++) {
2571 zone = &pgdat->node_zones[i];
2572 if (!populated_zone(zone))
2575 pfmemalloc_reserve += min_wmark_pages(zone);
2576 free_pages += zone_page_state(zone, NR_FREE_PAGES);
2579 /* If there are no reserves (unexpected config) then do not throttle */
2580 if (!pfmemalloc_reserve)
2583 wmark_ok = free_pages > pfmemalloc_reserve / 2;
2585 /* kswapd must be awake if processes are being throttled */
2586 if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2587 pgdat->classzone_idx = min(pgdat->classzone_idx,
2588 (enum zone_type)ZONE_NORMAL);
2589 wake_up_interruptible(&pgdat->kswapd_wait);
2596 * Throttle direct reclaimers if backing storage is backed by the network
2597 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
2598 * depleted. kswapd will continue to make progress and wake the processes
2599 * when the low watermark is reached.
2601 * Returns true if a fatal signal was delivered during throttling. If this
2602 * happens, the page allocator should not consider triggering the OOM killer.
2604 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2605 nodemask_t *nodemask)
2609 pg_data_t *pgdat = NULL;
2612 * Kernel threads should not be throttled as they may be indirectly
2613 * responsible for cleaning pages necessary for reclaim to make forward
2614 * progress. kjournald for example may enter direct reclaim while
2615 * committing a transaction where throttling it could forcing other
2616 * processes to block on log_wait_commit().
2618 if (current->flags & PF_KTHREAD)
2622 * If a fatal signal is pending, this process should not throttle.
2623 * It should return quickly so it can exit and free its memory
2625 if (fatal_signal_pending(current))
2629 * Check if the pfmemalloc reserves are ok by finding the first node
2630 * with a usable ZONE_NORMAL or lower zone. The expectation is that
2631 * GFP_KERNEL will be required for allocating network buffers when
2632 * swapping over the network so ZONE_HIGHMEM is unusable.
2634 * Throttling is based on the first usable node and throttled processes
2635 * wait on a queue until kswapd makes progress and wakes them. There
2636 * is an affinity then between processes waking up and where reclaim
2637 * progress has been made assuming the process wakes on the same node.
2638 * More importantly, processes running on remote nodes will not compete
2639 * for remote pfmemalloc reserves and processes on different nodes
2640 * should make reasonable progress.
2642 for_each_zone_zonelist_nodemask(zone, z, zonelist,
2643 gfp_mask, nodemask) {
2644 if (zone_idx(zone) > ZONE_NORMAL)
2647 /* Throttle based on the first usable node */
2648 pgdat = zone->zone_pgdat;
2649 if (pfmemalloc_watermark_ok(pgdat))
2654 /* If no zone was usable by the allocation flags then do not throttle */
2658 /* Account for the throttling */
2659 count_vm_event(PGSCAN_DIRECT_THROTTLE);
2662 * If the caller cannot enter the filesystem, it's possible that it
2663 * is due to the caller holding an FS lock or performing a journal
2664 * transaction in the case of a filesystem like ext[3|4]. In this case,
2665 * it is not safe to block on pfmemalloc_wait as kswapd could be
2666 * blocked waiting on the same lock. Instead, throttle for up to a
2667 * second before continuing.
2669 if (!(gfp_mask & __GFP_FS)) {
2670 wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2671 pfmemalloc_watermark_ok(pgdat), HZ);
2676 /* Throttle until kswapd wakes the process */
2677 wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2678 pfmemalloc_watermark_ok(pgdat));
2681 if (fatal_signal_pending(current))
2688 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2689 gfp_t gfp_mask, nodemask_t *nodemask)
2691 unsigned long nr_reclaimed;
2692 struct scan_control sc = {
2693 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2694 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
2696 .nodemask = nodemask,
2697 .priority = DEF_PRIORITY,
2698 .may_writepage = !laptop_mode,
2704 * Do not enter reclaim if fatal signal was delivered while throttled.
2705 * 1 is returned so that the page allocator does not OOM kill at this
2708 if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2711 trace_mm_vmscan_direct_reclaim_begin(order,
2715 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2717 trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2719 return nr_reclaimed;
2724 unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2725 gfp_t gfp_mask, bool noswap,
2727 unsigned long *nr_scanned)
2729 struct scan_control sc = {
2730 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2731 .target_mem_cgroup = memcg,
2732 .may_writepage = !laptop_mode,
2734 .may_swap = !noswap,
2736 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2737 int swappiness = mem_cgroup_swappiness(memcg);
2739 sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2740 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2742 trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2747 * NOTE: Although we can get the priority field, using it
2748 * here is not a good idea, since it limits the pages we can scan.
2749 * if we don't reclaim here, the shrink_zone from balance_pgdat
2750 * will pick up pages from other mem cgroup's as well. We hack
2751 * the priority and make it zero.
2753 shrink_lruvec(lruvec, swappiness, &sc);
2755 trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2757 *nr_scanned = sc.nr_scanned;
2758 return sc.nr_reclaimed;
2761 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
2765 struct zonelist *zonelist;
2766 unsigned long nr_reclaimed;
2768 struct scan_control sc = {
2769 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2770 .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2771 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2772 .target_mem_cgroup = memcg,
2773 .priority = DEF_PRIORITY,
2774 .may_writepage = !laptop_mode,
2776 .may_swap = !noswap,
2780 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2781 * take care of from where we get pages. So the node where we start the
2782 * scan does not need to be the current node.
2784 nid = mem_cgroup_select_victim_node(memcg);
2786 zonelist = NODE_DATA(nid)->node_zonelists;
2788 trace_mm_vmscan_memcg_reclaim_begin(0,
2792 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2794 trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2796 return nr_reclaimed;
2800 static void age_active_anon(struct zone *zone, struct scan_control *sc)
2802 struct mem_cgroup *memcg;
2804 if (!total_swap_pages)
2807 memcg = mem_cgroup_iter(NULL, NULL, NULL);
2809 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2811 if (inactive_anon_is_low(lruvec))
2812 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2813 sc, LRU_ACTIVE_ANON);
2815 memcg = mem_cgroup_iter(NULL, memcg, NULL);
2819 static bool zone_balanced(struct zone *zone, int order,
2820 unsigned long balance_gap, int classzone_idx)
2822 if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) +
2823 balance_gap, classzone_idx, 0))
2826 if (IS_ENABLED(CONFIG_COMPACTION) && order &&
2827 compaction_suitable(zone, order) == COMPACT_SKIPPED)
2834 * pgdat_balanced() is used when checking if a node is balanced.
2836 * For order-0, all zones must be balanced!
2838 * For high-order allocations only zones that meet watermarks and are in a
2839 * zone allowed by the callers classzone_idx are added to balanced_pages. The
2840 * total of balanced pages must be at least 25% of the zones allowed by
2841 * classzone_idx for the node to be considered balanced. Forcing all zones to
2842 * be balanced for high orders can cause excessive reclaim when there are
2844 * The choice of 25% is due to
2845 * o a 16M DMA zone that is balanced will not balance a zone on any
2846 * reasonable sized machine
2847 * o On all other machines, the top zone must be at least a reasonable
2848 * percentage of the middle zones. For example, on 32-bit x86, highmem
2849 * would need to be at least 256M for it to be balance a whole node.
2850 * Similarly, on x86-64 the Normal zone would need to be at least 1G
2851 * to balance a node on its own. These seemed like reasonable ratios.
2853 static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
2855 unsigned long managed_pages = 0;
2856 unsigned long balanced_pages = 0;
2859 /* Check the watermark levels */
2860 for (i = 0; i <= classzone_idx; i++) {
2861 struct zone *zone = pgdat->node_zones + i;
2863 if (!populated_zone(zone))
2866 managed_pages += zone->managed_pages;
2869 * A special case here:
2871 * balance_pgdat() skips over all_unreclaimable after
2872 * DEF_PRIORITY. Effectively, it considers them balanced so
2873 * they must be considered balanced here as well!
2875 if (!zone_reclaimable(zone)) {
2876 balanced_pages += zone->managed_pages;
2880 if (zone_balanced(zone, order, 0, i))
2881 balanced_pages += zone->managed_pages;
2887 return balanced_pages >= (managed_pages >> 2);
2893 * Prepare kswapd for sleeping. This verifies that there are no processes
2894 * waiting in throttle_direct_reclaim() and that watermarks have been met.
2896 * Returns true if kswapd is ready to sleep
2898 static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
2901 /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2906 * There is a potential race between when kswapd checks its watermarks
2907 * and a process gets throttled. There is also a potential race if
2908 * processes get throttled, kswapd wakes, a large process exits therby
2909 * balancing the zones that causes kswapd to miss a wakeup. If kswapd
2910 * is going to sleep, no process should be sleeping on pfmemalloc_wait
2911 * so wake them now if necessary. If necessary, processes will wake
2912 * kswapd and get throttled again
2914 if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
2915 wake_up(&pgdat->pfmemalloc_wait);
2919 return pgdat_balanced(pgdat, order, classzone_idx);
2923 * kswapd shrinks the zone by the number of pages required to reach
2924 * the high watermark.
2926 * Returns true if kswapd scanned at least the requested number of pages to
2927 * reclaim or if the lack of progress was due to pages under writeback.
2928 * This is used to determine if the scanning priority needs to be raised.
2930 static bool kswapd_shrink_zone(struct zone *zone,
2932 struct scan_control *sc,
2933 unsigned long lru_pages,
2934 unsigned long *nr_attempted)
2936 int testorder = sc->order;
2937 unsigned long balance_gap;
2938 struct reclaim_state *reclaim_state = current->reclaim_state;
2939 struct shrink_control shrink = {
2940 .gfp_mask = sc->gfp_mask,
2942 bool lowmem_pressure;
2944 /* Reclaim above the high watermark. */
2945 sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
2948 * Kswapd reclaims only single pages with compaction enabled. Trying
2949 * too hard to reclaim until contiguous free pages have become
2950 * available can hurt performance by evicting too much useful data
2951 * from memory. Do not reclaim more than needed for compaction.
2953 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2954 compaction_suitable(zone, sc->order) !=
2959 * We put equal pressure on every zone, unless one zone has way too
2960 * many pages free already. The "too many pages" is defined as the
2961 * high wmark plus a "gap" where the gap is either the low
2962 * watermark or 1% of the zone, whichever is smaller.
2964 balance_gap = min(low_wmark_pages(zone), DIV_ROUND_UP(
2965 zone->managed_pages, KSWAPD_ZONE_BALANCE_GAP_RATIO));
2968 * If there is no low memory pressure or the zone is balanced then no
2969 * reclaim is necessary
2971 lowmem_pressure = (buffer_heads_over_limit && is_highmem(zone));
2972 if (!lowmem_pressure && zone_balanced(zone, testorder,
2973 balance_gap, classzone_idx))
2976 shrink_zone(zone, sc);
2977 nodes_clear(shrink.nodes_to_scan);
2978 node_set(zone_to_nid(zone), shrink.nodes_to_scan);
2980 reclaim_state->reclaimed_slab = 0;
2981 shrink_slab(&shrink, sc->nr_scanned, lru_pages);
2982 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2984 /* Account for the number of pages attempted to reclaim */
2985 *nr_attempted += sc->nr_to_reclaim;
2987 zone_clear_flag(zone, ZONE_WRITEBACK);
2990 * If a zone reaches its high watermark, consider it to be no longer
2991 * congested. It's possible there are dirty pages backed by congested
2992 * BDIs but as pressure is relieved, speculatively avoid congestion
2995 if (zone_reclaimable(zone) &&
2996 zone_balanced(zone, testorder, 0, classzone_idx)) {
2997 zone_clear_flag(zone, ZONE_CONGESTED);
2998 zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY);
3001 return sc->nr_scanned >= sc->nr_to_reclaim;
3005 * For kswapd, balance_pgdat() will work across all this node's zones until
3006 * they are all at high_wmark_pages(zone).
3008 * Returns the final order kswapd was reclaiming at
3010 * There is special handling here for zones which are full of pinned pages.
3011 * This can happen if the pages are all mlocked, or if they are all used by
3012 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
3013 * What we do is to detect the case where all pages in the zone have been
3014 * scanned twice and there has been zero successful reclaim. Mark the zone as
3015 * dead and from now on, only perform a short scan. Basically we're polling
3016 * the zone for when the problem goes away.
3018 * kswapd scans the zones in the highmem->normal->dma direction. It skips
3019 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
3020 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
3021 * lower zones regardless of the number of free pages in the lower zones. This
3022 * interoperates with the page allocator fallback scheme to ensure that aging
3023 * of pages is balanced across the zones.
3025 static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
3029 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
3030 unsigned long nr_soft_reclaimed;
3031 unsigned long nr_soft_scanned;
3032 struct scan_control sc = {
3033 .gfp_mask = GFP_KERNEL,
3035 .priority = DEF_PRIORITY,
3036 .may_writepage = !laptop_mode,
3040 count_vm_event(PAGEOUTRUN);
3043 unsigned long lru_pages = 0;
3044 unsigned long nr_attempted = 0;
3045 bool raise_priority = true;
3046 bool pgdat_needs_compaction = (order > 0);
3048 sc.nr_reclaimed = 0;
3051 * Scan in the highmem->dma direction for the highest
3052 * zone which needs scanning
3054 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
3055 struct zone *zone = pgdat->node_zones + i;
3057 if (!populated_zone(zone))
3060 if (sc.priority != DEF_PRIORITY &&
3061 !zone_reclaimable(zone))
3065 * Do some background aging of the anon list, to give
3066 * pages a chance to be referenced before reclaiming.
3068 age_active_anon(zone, &sc);
3071 * If the number of buffer_heads in the machine
3072 * exceeds the maximum allowed level and this node
3073 * has a highmem zone, force kswapd to reclaim from
3074 * it to relieve lowmem pressure.
3076 if (buffer_heads_over_limit && is_highmem_idx(i)) {
3081 if (!zone_balanced(zone, order, 0, 0)) {
3086 * If balanced, clear the dirty and congested
3089 zone_clear_flag(zone, ZONE_CONGESTED);
3090 zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY);
3097 for (i = 0; i <= end_zone; i++) {
3098 struct zone *zone = pgdat->node_zones + i;
3100 if (!populated_zone(zone))
3103 lru_pages += zone_reclaimable_pages(zone);
3106 * If any zone is currently balanced then kswapd will
3107 * not call compaction as it is expected that the
3108 * necessary pages are already available.
3110 if (pgdat_needs_compaction &&
3111 zone_watermark_ok(zone, order,
3112 low_wmark_pages(zone),
3114 pgdat_needs_compaction = false;
3118 * If we're getting trouble reclaiming, start doing writepage
3119 * even in laptop mode.
3121 if (sc.priority < DEF_PRIORITY - 2)
3122 sc.may_writepage = 1;
3125 * Now scan the zone in the dma->highmem direction, stopping
3126 * at the last zone which needs scanning.
3128 * We do this because the page allocator works in the opposite
3129 * direction. This prevents the page allocator from allocating
3130 * pages behind kswapd's direction of progress, which would
3131 * cause too much scanning of the lower zones.
3133 for (i = 0; i <= end_zone; i++) {
3134 struct zone *zone = pgdat->node_zones + i;
3136 if (!populated_zone(zone))
3139 if (sc.priority != DEF_PRIORITY &&
3140 !zone_reclaimable(zone))
3145 nr_soft_scanned = 0;
3147 * Call soft limit reclaim before calling shrink_zone.
3149 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
3152 sc.nr_reclaimed += nr_soft_reclaimed;
3155 * There should be no need to raise the scanning
3156 * priority if enough pages are already being scanned
3157 * that that high watermark would be met at 100%
3160 if (kswapd_shrink_zone(zone, end_zone, &sc,
3161 lru_pages, &nr_attempted))
3162 raise_priority = false;
3166 * If the low watermark is met there is no need for processes
3167 * to be throttled on pfmemalloc_wait as they should not be
3168 * able to safely make forward progress. Wake them
3170 if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
3171 pfmemalloc_watermark_ok(pgdat))
3172 wake_up(&pgdat->pfmemalloc_wait);
3175 * Fragmentation may mean that the system cannot be rebalanced
3176 * for high-order allocations in all zones. If twice the
3177 * allocation size has been reclaimed and the zones are still
3178 * not balanced then recheck the watermarks at order-0 to
3179 * prevent kswapd reclaiming excessively. Assume that a
3180 * process requested a high-order can direct reclaim/compact.
3182 if (order && sc.nr_reclaimed >= 2UL << order)
3183 order = sc.order = 0;
3185 /* Check if kswapd should be suspending */
3186 if (try_to_freeze() || kthread_should_stop())
3190 * Compact if necessary and kswapd is reclaiming at least the
3191 * high watermark number of pages as requsted
3193 if (pgdat_needs_compaction && sc.nr_reclaimed > nr_attempted)
3194 compact_pgdat(pgdat, order);
3197 * Raise priority if scanning rate is too low or there was no
3198 * progress in reclaiming pages
3200 if (raise_priority || !sc.nr_reclaimed)
3202 } while (sc.priority >= 1 &&
3203 !pgdat_balanced(pgdat, order, *classzone_idx));
3207 * Return the order we were reclaiming at so prepare_kswapd_sleep()
3208 * makes a decision on the order we were last reclaiming at. However,
3209 * if another caller entered the allocator slow path while kswapd
3210 * was awake, order will remain at the higher level
3212 *classzone_idx = end_zone;
3216 static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
3221 if (freezing(current) || kthread_should_stop())
3224 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3226 /* Try to sleep for a short interval */
3227 if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
3228 remaining = schedule_timeout(HZ/10);
3229 finish_wait(&pgdat->kswapd_wait, &wait);
3230 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3234 * After a short sleep, check if it was a premature sleep. If not, then
3235 * go fully to sleep until explicitly woken up.
3237 if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
3238 trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
3241 * vmstat counters are not perfectly accurate and the estimated
3242 * value for counters such as NR_FREE_PAGES can deviate from the
3243 * true value by nr_online_cpus * threshold. To avoid the zone
3244 * watermarks being breached while under pressure, we reduce the
3245 * per-cpu vmstat threshold while kswapd is awake and restore
3246 * them before going back to sleep.
3248 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
3251 * Compaction records what page blocks it recently failed to
3252 * isolate pages from and skips them in the future scanning.
3253 * When kswapd is going to sleep, it is reasonable to assume
3254 * that pages and compaction may succeed so reset the cache.
3256 reset_isolation_suitable(pgdat);
3258 if (!kthread_should_stop())
3261 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
3264 count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
3266 count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
3268 finish_wait(&pgdat->kswapd_wait, &wait);
3272 * The background pageout daemon, started as a kernel thread
3273 * from the init process.
3275 * This basically trickles out pages so that we have _some_
3276 * free memory available even if there is no other activity
3277 * that frees anything up. This is needed for things like routing
3278 * etc, where we otherwise might have all activity going on in
3279 * asynchronous contexts that cannot page things out.
3281 * If there are applications that are active memory-allocators
3282 * (most normal use), this basically shouldn't matter.
3284 static int kswapd(void *p)
3286 unsigned long order, new_order;
3287 unsigned balanced_order;
3288 int classzone_idx, new_classzone_idx;
3289 int balanced_classzone_idx;
3290 pg_data_t *pgdat = (pg_data_t*)p;
3291 struct task_struct *tsk = current;
3293 struct reclaim_state reclaim_state = {
3294 .reclaimed_slab = 0,
3296 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
3298 lockdep_set_current_reclaim_state(GFP_KERNEL);
3300 if (!cpumask_empty(cpumask))
3301 set_cpus_allowed_ptr(tsk, cpumask);
3302 current->reclaim_state = &reclaim_state;
3305 * Tell the memory management that we're a "memory allocator",
3306 * and that if we need more memory we should get access to it
3307 * regardless (see "__alloc_pages()"). "kswapd" should
3308 * never get caught in the normal page freeing logic.
3310 * (Kswapd normally doesn't need memory anyway, but sometimes
3311 * you need a small amount of memory in order to be able to
3312 * page out something else, and this flag essentially protects
3313 * us from recursively trying to free more memory as we're
3314 * trying to free the first piece of memory in the first place).
3316 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
3319 order = new_order = 0;
3321 classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
3322 balanced_classzone_idx = classzone_idx;
3327 * If the last balance_pgdat was unsuccessful it's unlikely a
3328 * new request of a similar or harder type will succeed soon
3329 * so consider going to sleep on the basis we reclaimed at
3331 if (balanced_classzone_idx >= new_classzone_idx &&
3332 balanced_order == new_order) {
3333 new_order = pgdat->kswapd_max_order;
3334 new_classzone_idx = pgdat->classzone_idx;
3335 pgdat->kswapd_max_order = 0;
3336 pgdat->classzone_idx = pgdat->nr_zones - 1;
3339 if (order < new_order || classzone_idx > new_classzone_idx) {
3341 * Don't sleep if someone wants a larger 'order'
3342 * allocation or has tigher zone constraints
3345 classzone_idx = new_classzone_idx;
3347 kswapd_try_to_sleep(pgdat, balanced_order,
3348 balanced_classzone_idx);
3349 order = pgdat->kswapd_max_order;
3350 classzone_idx = pgdat->classzone_idx;
3352 new_classzone_idx = classzone_idx;
3353 pgdat->kswapd_max_order = 0;
3354 pgdat->classzone_idx = pgdat->nr_zones - 1;
3357 ret = try_to_freeze();
3358 if (kthread_should_stop())
3362 * We can speed up thawing tasks if we don't call balance_pgdat
3363 * after returning from the refrigerator
3366 trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
3367 balanced_classzone_idx = classzone_idx;
3368 balanced_order = balance_pgdat(pgdat, order,
3369 &balanced_classzone_idx);
3373 tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
3374 current->reclaim_state = NULL;
3375 lockdep_clear_current_reclaim_state();
3381 * A zone is low on free memory, so wake its kswapd task to service it.
3383 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
3387 if (!populated_zone(zone))
3390 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
3392 pgdat = zone->zone_pgdat;
3393 if (pgdat->kswapd_max_order < order) {
3394 pgdat->kswapd_max_order = order;
3395 pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
3397 if (!waitqueue_active(&pgdat->kswapd_wait))
3399 if (zone_balanced(zone, order, 0, 0))
3402 trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3403 wake_up_interruptible(&pgdat->kswapd_wait);
3406 #ifdef CONFIG_HIBERNATION
3408 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3411 * Rather than trying to age LRUs the aim is to preserve the overall
3412 * LRU order by reclaiming preferentially
3413 * inactive > active > active referenced > active mapped
3415 unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3417 struct reclaim_state reclaim_state;
3418 struct scan_control sc = {
3419 .nr_to_reclaim = nr_to_reclaim,
3420 .gfp_mask = GFP_HIGHUSER_MOVABLE,
3421 .priority = DEF_PRIORITY,
3425 .hibernation_mode = 1,
3427 struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3428 struct task_struct *p = current;
3429 unsigned long nr_reclaimed;
3431 p->flags |= PF_MEMALLOC;
3432 lockdep_set_current_reclaim_state(sc.gfp_mask);
3433 reclaim_state.reclaimed_slab = 0;
3434 p->reclaim_state = &reclaim_state;
3436 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3438 p->reclaim_state = NULL;
3439 lockdep_clear_current_reclaim_state();
3440 p->flags &= ~PF_MEMALLOC;
3442 return nr_reclaimed;
3444 #endif /* CONFIG_HIBERNATION */
3446 /* It's optimal to keep kswapds on the same CPUs as their memory, but
3447 not required for correctness. So if the last cpu in a node goes
3448 away, we get changed to run anywhere: as the first one comes back,
3449 restore their cpu bindings. */
3450 static int cpu_callback(struct notifier_block *nfb, unsigned long action,
3455 if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
3456 for_each_node_state(nid, N_MEMORY) {
3457 pg_data_t *pgdat = NODE_DATA(nid);
3458 const struct cpumask *mask;
3460 mask = cpumask_of_node(pgdat->node_id);
3462 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3463 /* One of our CPUs online: restore mask */
3464 set_cpus_allowed_ptr(pgdat->kswapd, mask);
3471 * This kswapd start function will be called by init and node-hot-add.
3472 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3474 int kswapd_run(int nid)
3476 pg_data_t *pgdat = NODE_DATA(nid);
3482 pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3483 if (IS_ERR(pgdat->kswapd)) {
3484 /* failure at boot is fatal */
3485 BUG_ON(system_state == SYSTEM_BOOTING);
3486 pr_err("Failed to start kswapd on node %d\n", nid);
3487 ret = PTR_ERR(pgdat->kswapd);
3488 pgdat->kswapd = NULL;
3494 * Called by memory hotplug when all memory in a node is offlined. Caller must
3495 * hold mem_hotplug_begin/end().
3497 void kswapd_stop(int nid)
3499 struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3502 kthread_stop(kswapd);
3503 NODE_DATA(nid)->kswapd = NULL;
3507 static int __init kswapd_init(void)
3512 for_each_node_state(nid, N_MEMORY)
3514 hotcpu_notifier(cpu_callback, 0);
3518 module_init(kswapd_init)
3524 * If non-zero call zone_reclaim when the number of free pages falls below
3527 int zone_reclaim_mode __read_mostly;
3529 #define RECLAIM_OFF 0
3530 #define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
3531 #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
3532 #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
3535 * Priority for ZONE_RECLAIM. This determines the fraction of pages
3536 * of a node considered for each zone_reclaim. 4 scans 1/16th of
3539 #define ZONE_RECLAIM_PRIORITY 4
3542 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
3545 int sysctl_min_unmapped_ratio = 1;
3548 * If the number of slab pages in a zone grows beyond this percentage then
3549 * slab reclaim needs to occur.
3551 int sysctl_min_slab_ratio = 5;
3553 static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3555 unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3556 unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3557 zone_page_state(zone, NR_ACTIVE_FILE);
3560 * It's possible for there to be more file mapped pages than
3561 * accounted for by the pages on the file LRU lists because
3562 * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3564 return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3567 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
3568 static long zone_pagecache_reclaimable(struct zone *zone)
3570 long nr_pagecache_reclaimable;
3574 * If RECLAIM_SWAP is set, then all file pages are considered
3575 * potentially reclaimable. Otherwise, we have to worry about
3576 * pages like swapcache and zone_unmapped_file_pages() provides
3579 if (zone_reclaim_mode & RECLAIM_SWAP)
3580 nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3582 nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3584 /* If we can't clean pages, remove dirty pages from consideration */
3585 if (!(zone_reclaim_mode & RECLAIM_WRITE))
3586 delta += zone_page_state(zone, NR_FILE_DIRTY);
3588 /* Watch for any possible underflows due to delta */
3589 if (unlikely(delta > nr_pagecache_reclaimable))
3590 delta = nr_pagecache_reclaimable;
3592 return nr_pagecache_reclaimable - delta;
3596 * Try to free up some pages from this zone through reclaim.
3598 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3600 /* Minimum pages needed in order to stay on node */
3601 const unsigned long nr_pages = 1 << order;
3602 struct task_struct *p = current;
3603 struct reclaim_state reclaim_state;
3604 struct scan_control sc = {
3605 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3606 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
3608 .priority = ZONE_RECLAIM_PRIORITY,
3609 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3610 .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3613 struct shrink_control shrink = {
3614 .gfp_mask = sc.gfp_mask,
3616 unsigned long nr_slab_pages0, nr_slab_pages1;
3620 * We need to be able to allocate from the reserves for RECLAIM_SWAP
3621 * and we also need to be able to write out pages for RECLAIM_WRITE
3624 p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3625 lockdep_set_current_reclaim_state(gfp_mask);
3626 reclaim_state.reclaimed_slab = 0;
3627 p->reclaim_state = &reclaim_state;
3629 if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3631 * Free memory by calling shrink zone with increasing
3632 * priorities until we have enough memory freed.
3635 shrink_zone(zone, &sc);
3636 } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3639 nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3640 if (nr_slab_pages0 > zone->min_slab_pages) {
3642 * shrink_slab() does not currently allow us to determine how
3643 * many pages were freed in this zone. So we take the current
3644 * number of slab pages and shake the slab until it is reduced
3645 * by the same nr_pages that we used for reclaiming unmapped
3648 nodes_clear(shrink.nodes_to_scan);
3649 node_set(zone_to_nid(zone), shrink.nodes_to_scan);
3651 unsigned long lru_pages = zone_reclaimable_pages(zone);
3653 /* No reclaimable slab or very low memory pressure */
3654 if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3657 /* Freed enough memory */
3658 nr_slab_pages1 = zone_page_state(zone,
3659 NR_SLAB_RECLAIMABLE);
3660 if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3665 * Update nr_reclaimed by the number of slab pages we
3666 * reclaimed from this zone.
3668 nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3669 if (nr_slab_pages1 < nr_slab_pages0)
3670 sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3673 p->reclaim_state = NULL;
3674 current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3675 lockdep_clear_current_reclaim_state();
3676 return sc.nr_reclaimed >= nr_pages;
3679 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3685 * Zone reclaim reclaims unmapped file backed pages and
3686 * slab pages if we are over the defined limits.
3688 * A small portion of unmapped file backed pages is needed for
3689 * file I/O otherwise pages read by file I/O will be immediately
3690 * thrown out if the zone is overallocated. So we do not reclaim
3691 * if less than a specified percentage of the zone is used by
3692 * unmapped file backed pages.
3694 if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3695 zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3696 return ZONE_RECLAIM_FULL;
3698 if (!zone_reclaimable(zone))
3699 return ZONE_RECLAIM_FULL;
3702 * Do not scan if the allocation should not be delayed.
3704 if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3705 return ZONE_RECLAIM_NOSCAN;
3708 * Only run zone reclaim on the local zone or on zones that do not
3709 * have associated processors. This will favor the local processor
3710 * over remote processors and spread off node memory allocations
3711 * as wide as possible.
3713 node_id = zone_to_nid(zone);
3714 if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3715 return ZONE_RECLAIM_NOSCAN;
3717 if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3718 return ZONE_RECLAIM_NOSCAN;
3720 ret = __zone_reclaim(zone, gfp_mask, order);
3721 zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3724 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3731 * page_evictable - test whether a page is evictable
3732 * @page: the page to test
3734 * Test whether page is evictable--i.e., should be placed on active/inactive
3735 * lists vs unevictable list.
3737 * Reasons page might not be evictable:
3738 * (1) page's mapping marked unevictable
3739 * (2) page is part of an mlocked VMA
3742 int page_evictable(struct page *page)
3744 return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
3749 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3750 * @pages: array of pages to check
3751 * @nr_pages: number of pages to check
3753 * Checks pages for evictability and moves them to the appropriate lru list.
3755 * This function is only used for SysV IPC SHM_UNLOCK.
3757 void check_move_unevictable_pages(struct page **pages, int nr_pages)
3759 struct lruvec *lruvec;
3760 struct zone *zone = NULL;
3765 for (i = 0; i < nr_pages; i++) {
3766 struct page *page = pages[i];
3767 struct zone *pagezone;
3770 pagezone = page_zone(page);
3771 if (pagezone != zone) {
3773 spin_unlock_irq(&zone->lru_lock);
3775 spin_lock_irq(&zone->lru_lock);
3777 lruvec = mem_cgroup_page_lruvec(page, zone);
3779 if (!PageLRU(page) || !PageUnevictable(page))
3782 if (page_evictable(page)) {
3783 enum lru_list lru = page_lru_base_type(page);
3785 VM_BUG_ON_PAGE(PageActive(page), page);
3786 ClearPageUnevictable(page);
3787 del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3788 add_page_to_lru_list(page, lruvec, lru);
3794 __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3795 __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3796 spin_unlock_irq(&zone->lru_lock);
3799 #endif /* CONFIG_SHMEM */