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>
49 #include <linux/dax.h>
51 #include <asm/tlbflush.h>
52 #include <asm/div64.h>
54 #include <linux/swapops.h>
55 #include <linux/balloon_compaction.h>
59 #define CREATE_TRACE_POINTS
60 #include <trace/events/vmscan.h>
63 /* How many pages shrink_list() should reclaim */
64 unsigned long nr_to_reclaim;
66 /* This context's GFP mask */
69 /* Allocation order */
73 * Nodemask of nodes allowed by the caller. If NULL, all nodes
79 * The memory cgroup that hit its limit and as a result is the
80 * primary target of this reclaim invocation.
82 struct mem_cgroup *target_mem_cgroup;
84 /* Scan (total_size >> priority) pages at once */
87 /* The highest zone to isolate pages for reclaim from */
88 enum zone_type reclaim_idx;
90 unsigned int may_writepage:1;
92 /* Can mapped pages be reclaimed? */
93 unsigned int may_unmap:1;
95 /* Can pages be swapped as part of reclaim? */
96 unsigned int may_swap:1;
98 /* Can cgroups be reclaimed below their normal consumption range? */
99 unsigned int may_thrash:1;
101 unsigned int hibernation_mode:1;
103 /* One of the zones is ready for compaction */
104 unsigned int compaction_ready:1;
106 /* Incremented by the number of inactive pages that were scanned */
107 unsigned long nr_scanned;
109 /* Number of pages freed so far during a call to shrink_zones() */
110 unsigned long nr_reclaimed;
113 #ifdef ARCH_HAS_PREFETCH
114 #define prefetch_prev_lru_page(_page, _base, _field) \
116 if ((_page)->lru.prev != _base) { \
119 prev = lru_to_page(&(_page->lru)); \
120 prefetch(&prev->_field); \
124 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
127 #ifdef ARCH_HAS_PREFETCHW
128 #define prefetchw_prev_lru_page(_page, _base, _field) \
130 if ((_page)->lru.prev != _base) { \
133 prev = lru_to_page(&(_page->lru)); \
134 prefetchw(&prev->_field); \
138 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
142 * From 0 .. 100. Higher means more swappy.
144 int vm_swappiness = 60;
146 * The total number of pages which are beyond the high watermark within all
149 unsigned long vm_total_pages;
151 static LIST_HEAD(shrinker_list);
152 static DECLARE_RWSEM(shrinker_rwsem);
155 static bool global_reclaim(struct scan_control *sc)
157 return !sc->target_mem_cgroup;
161 * sane_reclaim - is the usual dirty throttling mechanism operational?
162 * @sc: scan_control in question
164 * The normal page dirty throttling mechanism in balance_dirty_pages() is
165 * completely broken with the legacy memcg and direct stalling in
166 * shrink_page_list() is used for throttling instead, which lacks all the
167 * niceties such as fairness, adaptive pausing, bandwidth proportional
168 * allocation and configurability.
170 * This function tests whether the vmscan currently in progress can assume
171 * that the normal dirty throttling mechanism is operational.
173 static bool sane_reclaim(struct scan_control *sc)
175 struct mem_cgroup *memcg = sc->target_mem_cgroup;
179 #ifdef CONFIG_CGROUP_WRITEBACK
180 if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
186 static bool global_reclaim(struct scan_control *sc)
191 static bool sane_reclaim(struct scan_control *sc)
198 * This misses isolated pages which are not accounted for to save counters.
199 * As the data only determines if reclaim or compaction continues, it is
200 * not expected that isolated pages will be a dominating factor.
202 unsigned long zone_reclaimable_pages(struct zone *zone)
206 nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
207 zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
208 if (get_nr_swap_pages() > 0)
209 nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
210 zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
215 unsigned long pgdat_reclaimable_pages(struct pglist_data *pgdat)
219 nr = node_page_state_snapshot(pgdat, NR_ACTIVE_FILE) +
220 node_page_state_snapshot(pgdat, NR_INACTIVE_FILE) +
221 node_page_state_snapshot(pgdat, NR_ISOLATED_FILE);
223 if (get_nr_swap_pages() > 0)
224 nr += node_page_state_snapshot(pgdat, NR_ACTIVE_ANON) +
225 node_page_state_snapshot(pgdat, NR_INACTIVE_ANON) +
226 node_page_state_snapshot(pgdat, NR_ISOLATED_ANON);
231 bool pgdat_reclaimable(struct pglist_data *pgdat)
233 return node_page_state_snapshot(pgdat, NR_PAGES_SCANNED) <
234 pgdat_reclaimable_pages(pgdat) * 6;
237 unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru)
239 if (!mem_cgroup_disabled())
240 return mem_cgroup_get_lru_size(lruvec, lru);
242 return node_page_state(lruvec_pgdat(lruvec), NR_LRU_BASE + lru);
245 unsigned long lruvec_zone_lru_size(struct lruvec *lruvec, enum lru_list lru,
248 if (!mem_cgroup_disabled())
249 return mem_cgroup_get_zone_lru_size(lruvec, lru, zone_idx);
251 return zone_page_state(&lruvec_pgdat(lruvec)->node_zones[zone_idx],
252 NR_ZONE_LRU_BASE + lru);
256 * Add a shrinker callback to be called from the vm.
258 int register_shrinker(struct shrinker *shrinker)
260 size_t size = sizeof(*shrinker->nr_deferred);
262 if (shrinker->flags & SHRINKER_NUMA_AWARE)
265 shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
266 if (!shrinker->nr_deferred)
269 down_write(&shrinker_rwsem);
270 list_add_tail(&shrinker->list, &shrinker_list);
271 up_write(&shrinker_rwsem);
274 EXPORT_SYMBOL(register_shrinker);
279 void unregister_shrinker(struct shrinker *shrinker)
281 down_write(&shrinker_rwsem);
282 list_del(&shrinker->list);
283 up_write(&shrinker_rwsem);
284 kfree(shrinker->nr_deferred);
286 EXPORT_SYMBOL(unregister_shrinker);
288 #define SHRINK_BATCH 128
290 static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
291 struct shrinker *shrinker,
292 unsigned long nr_scanned,
293 unsigned long nr_eligible)
295 unsigned long freed = 0;
296 unsigned long long delta;
301 int nid = shrinkctl->nid;
302 long batch_size = shrinker->batch ? shrinker->batch
304 long scanned = 0, next_deferred;
306 freeable = shrinker->count_objects(shrinker, shrinkctl);
311 * copy the current shrinker scan count into a local variable
312 * and zero it so that other concurrent shrinker invocations
313 * don't also do this scanning work.
315 nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
318 delta = (4 * nr_scanned) / shrinker->seeks;
320 do_div(delta, nr_eligible + 1);
322 if (total_scan < 0) {
323 pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n",
324 shrinker->scan_objects, total_scan);
325 total_scan = freeable;
328 next_deferred = total_scan;
331 * We need to avoid excessive windup on filesystem shrinkers
332 * due to large numbers of GFP_NOFS allocations causing the
333 * shrinkers to return -1 all the time. This results in a large
334 * nr being built up so when a shrink that can do some work
335 * comes along it empties the entire cache due to nr >>>
336 * freeable. This is bad for sustaining a working set in
339 * Hence only allow the shrinker to scan the entire cache when
340 * a large delta change is calculated directly.
342 if (delta < freeable / 4)
343 total_scan = min(total_scan, freeable / 2);
346 * Avoid risking looping forever due to too large nr value:
347 * never try to free more than twice the estimate number of
350 if (total_scan > freeable * 2)
351 total_scan = freeable * 2;
353 trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
354 nr_scanned, nr_eligible,
355 freeable, delta, total_scan);
358 * Normally, we should not scan less than batch_size objects in one
359 * pass to avoid too frequent shrinker calls, but if the slab has less
360 * than batch_size objects in total and we are really tight on memory,
361 * we will try to reclaim all available objects, otherwise we can end
362 * up failing allocations although there are plenty of reclaimable
363 * objects spread over several slabs with usage less than the
366 * We detect the "tight on memory" situations by looking at the total
367 * number of objects we want to scan (total_scan). If it is greater
368 * than the total number of objects on slab (freeable), we must be
369 * scanning at high prio and therefore should try to reclaim as much as
372 while (total_scan >= batch_size ||
373 total_scan >= freeable) {
375 unsigned long nr_to_scan = min(batch_size, total_scan);
377 shrinkctl->nr_to_scan = nr_to_scan;
378 ret = shrinker->scan_objects(shrinker, shrinkctl);
379 if (ret == SHRINK_STOP)
383 count_vm_events(SLABS_SCANNED, nr_to_scan);
384 total_scan -= nr_to_scan;
385 scanned += nr_to_scan;
390 if (next_deferred >= scanned)
391 next_deferred -= scanned;
395 * move the unused scan count back into the shrinker in a
396 * manner that handles concurrent updates. If we exhausted the
397 * scan, there is no need to do an update.
399 if (next_deferred > 0)
400 new_nr = atomic_long_add_return(next_deferred,
401 &shrinker->nr_deferred[nid]);
403 new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
405 trace_mm_shrink_slab_end(shrinker, nid, freed, nr, new_nr, total_scan);
410 * shrink_slab - shrink slab caches
411 * @gfp_mask: allocation context
412 * @nid: node whose slab caches to target
413 * @memcg: memory cgroup whose slab caches to target
414 * @nr_scanned: pressure numerator
415 * @nr_eligible: pressure denominator
417 * Call the shrink functions to age shrinkable caches.
419 * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
420 * unaware shrinkers will receive a node id of 0 instead.
422 * @memcg specifies the memory cgroup to target. If it is not NULL,
423 * only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan
424 * objects from the memory cgroup specified. Otherwise, only unaware
425 * shrinkers are called.
427 * @nr_scanned and @nr_eligible form a ratio that indicate how much of
428 * the available objects should be scanned. Page reclaim for example
429 * passes the number of pages scanned and the number of pages on the
430 * LRU lists that it considered on @nid, plus a bias in @nr_scanned
431 * when it encountered mapped pages. The ratio is further biased by
432 * the ->seeks setting of the shrink function, which indicates the
433 * cost to recreate an object relative to that of an LRU page.
435 * Returns the number of reclaimed slab objects.
437 static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
438 struct mem_cgroup *memcg,
439 unsigned long nr_scanned,
440 unsigned long nr_eligible)
442 struct shrinker *shrinker;
443 unsigned long freed = 0;
445 if (memcg && (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)))
449 nr_scanned = SWAP_CLUSTER_MAX;
451 if (!down_read_trylock(&shrinker_rwsem)) {
453 * If we would return 0, our callers would understand that we
454 * have nothing else to shrink and give up trying. By returning
455 * 1 we keep it going and assume we'll be able to shrink next
462 list_for_each_entry(shrinker, &shrinker_list, list) {
463 struct shrink_control sc = {
464 .gfp_mask = gfp_mask,
470 * If kernel memory accounting is disabled, we ignore
471 * SHRINKER_MEMCG_AWARE flag and call all shrinkers
472 * passing NULL for memcg.
474 if (memcg_kmem_enabled() &&
475 !!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
478 if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
481 freed += do_shrink_slab(&sc, shrinker, nr_scanned, nr_eligible);
484 up_read(&shrinker_rwsem);
490 void drop_slab_node(int nid)
495 struct mem_cgroup *memcg = NULL;
499 freed += shrink_slab(GFP_KERNEL, nid, memcg,
501 } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
502 } while (freed > 10);
509 for_each_online_node(nid)
513 static inline int is_page_cache_freeable(struct page *page)
516 * A freeable page cache page is referenced only by the caller
517 * that isolated the page, the page cache radix tree and
518 * optional buffer heads at page->private.
520 return page_count(page) - page_has_private(page) == 2;
523 static int may_write_to_inode(struct inode *inode, struct scan_control *sc)
525 if (current->flags & PF_SWAPWRITE)
527 if (!inode_write_congested(inode))
529 if (inode_to_bdi(inode) == current->backing_dev_info)
535 * We detected a synchronous write error writing a page out. Probably
536 * -ENOSPC. We need to propagate that into the address_space for a subsequent
537 * fsync(), msync() or close().
539 * The tricky part is that after writepage we cannot touch the mapping: nothing
540 * prevents it from being freed up. But we have a ref on the page and once
541 * that page is locked, the mapping is pinned.
543 * We're allowed to run sleeping lock_page() here because we know the caller has
546 static void handle_write_error(struct address_space *mapping,
547 struct page *page, int error)
550 if (page_mapping(page) == mapping)
551 mapping_set_error(mapping, error);
555 /* possible outcome of pageout() */
557 /* failed to write page out, page is locked */
559 /* move page to the active list, page is locked */
561 /* page has been sent to the disk successfully, page is unlocked */
563 /* page is clean and locked */
568 * pageout is called by shrink_page_list() for each dirty page.
569 * Calls ->writepage().
571 static pageout_t pageout(struct page *page, struct address_space *mapping,
572 struct scan_control *sc)
575 * If the page is dirty, only perform writeback if that write
576 * will be non-blocking. To prevent this allocation from being
577 * stalled by pagecache activity. But note that there may be
578 * stalls if we need to run get_block(). We could test
579 * PagePrivate for that.
581 * If this process is currently in __generic_file_write_iter() against
582 * this page's queue, we can perform writeback even if that
585 * If the page is swapcache, write it back even if that would
586 * block, for some throttling. This happens by accident, because
587 * swap_backing_dev_info is bust: it doesn't reflect the
588 * congestion state of the swapdevs. Easy to fix, if needed.
590 if (!is_page_cache_freeable(page))
594 * Some data journaling orphaned pages can have
595 * page->mapping == NULL while being dirty with clean buffers.
597 if (page_has_private(page)) {
598 if (try_to_free_buffers(page)) {
599 ClearPageDirty(page);
600 pr_info("%s: orphaned page\n", __func__);
606 if (mapping->a_ops->writepage == NULL)
607 return PAGE_ACTIVATE;
608 if (!may_write_to_inode(mapping->host, sc))
611 if (clear_page_dirty_for_io(page)) {
613 struct writeback_control wbc = {
614 .sync_mode = WB_SYNC_NONE,
615 .nr_to_write = SWAP_CLUSTER_MAX,
617 .range_end = LLONG_MAX,
621 SetPageReclaim(page);
622 res = mapping->a_ops->writepage(page, &wbc);
624 handle_write_error(mapping, page, res);
625 if (res == AOP_WRITEPAGE_ACTIVATE) {
626 ClearPageReclaim(page);
627 return PAGE_ACTIVATE;
630 if (!PageWriteback(page)) {
631 /* synchronous write or broken a_ops? */
632 ClearPageReclaim(page);
634 trace_mm_vmscan_writepage(page);
635 inc_node_page_state(page, NR_VMSCAN_WRITE);
643 * Same as remove_mapping, but if the page is removed from the mapping, it
644 * gets returned with a refcount of 0.
646 static int __remove_mapping(struct address_space *mapping, struct page *page,
651 BUG_ON(!PageLocked(page));
652 BUG_ON(mapping != page_mapping(page));
654 spin_lock_irqsave(&mapping->tree_lock, flags);
656 * The non racy check for a busy page.
658 * Must be careful with the order of the tests. When someone has
659 * a ref to the page, it may be possible that they dirty it then
660 * drop the reference. So if PageDirty is tested before page_count
661 * here, then the following race may occur:
663 * get_user_pages(&page);
664 * [user mapping goes away]
666 * !PageDirty(page) [good]
667 * SetPageDirty(page);
669 * !page_count(page) [good, discard it]
671 * [oops, our write_to data is lost]
673 * Reversing the order of the tests ensures such a situation cannot
674 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
675 * load is not satisfied before that of page->_refcount.
677 * Note that if SetPageDirty is always performed via set_page_dirty,
678 * and thus under tree_lock, then this ordering is not required.
680 if (!page_ref_freeze(page, 2))
682 /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
683 if (unlikely(PageDirty(page))) {
684 page_ref_unfreeze(page, 2);
688 if (PageSwapCache(page)) {
689 swp_entry_t swap = { .val = page_private(page) };
690 mem_cgroup_swapout(page, swap);
691 __delete_from_swap_cache(page);
692 spin_unlock_irqrestore(&mapping->tree_lock, flags);
693 swapcache_free(swap);
695 void (*freepage)(struct page *);
698 freepage = mapping->a_ops->freepage;
700 * Remember a shadow entry for reclaimed file cache in
701 * order to detect refaults, thus thrashing, later on.
703 * But don't store shadows in an address space that is
704 * already exiting. This is not just an optizimation,
705 * inode reclaim needs to empty out the radix tree or
706 * the nodes are lost. Don't plant shadows behind its
709 * We also don't store shadows for DAX mappings because the
710 * only page cache pages found in these are zero pages
711 * covering holes, and because we don't want to mix DAX
712 * exceptional entries and shadow exceptional entries in the
715 if (reclaimed && page_is_file_cache(page) &&
716 !mapping_exiting(mapping) && !dax_mapping(mapping))
717 shadow = workingset_eviction(mapping, page);
718 __delete_from_page_cache(page, shadow);
719 spin_unlock_irqrestore(&mapping->tree_lock, flags);
721 if (freepage != NULL)
728 spin_unlock_irqrestore(&mapping->tree_lock, flags);
733 * Attempt to detach a locked page from its ->mapping. If it is dirty or if
734 * someone else has a ref on the page, abort and return 0. If it was
735 * successfully detached, return 1. Assumes the caller has a single ref on
738 int remove_mapping(struct address_space *mapping, struct page *page)
740 if (__remove_mapping(mapping, page, false)) {
742 * Unfreezing the refcount with 1 rather than 2 effectively
743 * drops the pagecache ref for us without requiring another
746 page_ref_unfreeze(page, 1);
753 * putback_lru_page - put previously isolated page onto appropriate LRU list
754 * @page: page to be put back to appropriate lru list
756 * Add previously isolated @page to appropriate LRU list.
757 * Page may still be unevictable for other reasons.
759 * lru_lock must not be held, interrupts must be enabled.
761 void putback_lru_page(struct page *page)
764 int was_unevictable = PageUnevictable(page);
766 VM_BUG_ON_PAGE(PageLRU(page), page);
769 ClearPageUnevictable(page);
771 if (page_evictable(page)) {
773 * For evictable pages, we can use the cache.
774 * In event of a race, worst case is we end up with an
775 * unevictable page on [in]active list.
776 * We know how to handle that.
778 is_unevictable = false;
782 * Put unevictable pages directly on zone's unevictable
785 is_unevictable = true;
786 add_page_to_unevictable_list(page);
788 * When racing with an mlock or AS_UNEVICTABLE clearing
789 * (page is unlocked) make sure that if the other thread
790 * does not observe our setting of PG_lru and fails
791 * isolation/check_move_unevictable_pages,
792 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
793 * the page back to the evictable list.
795 * The other side is TestClearPageMlocked() or shmem_lock().
801 * page's status can change while we move it among lru. If an evictable
802 * page is on unevictable list, it never be freed. To avoid that,
803 * check after we added it to the list, again.
805 if (is_unevictable && page_evictable(page)) {
806 if (!isolate_lru_page(page)) {
810 /* This means someone else dropped this page from LRU
811 * So, it will be freed or putback to LRU again. There is
812 * nothing to do here.
816 if (was_unevictable && !is_unevictable)
817 count_vm_event(UNEVICTABLE_PGRESCUED);
818 else if (!was_unevictable && is_unevictable)
819 count_vm_event(UNEVICTABLE_PGCULLED);
821 put_page(page); /* drop ref from isolate */
824 enum page_references {
826 PAGEREF_RECLAIM_CLEAN,
831 static enum page_references page_check_references(struct page *page,
832 struct scan_control *sc)
834 int referenced_ptes, referenced_page;
835 unsigned long vm_flags;
837 referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
839 referenced_page = TestClearPageReferenced(page);
842 * Mlock lost the isolation race with us. Let try_to_unmap()
843 * move the page to the unevictable list.
845 if (vm_flags & VM_LOCKED)
846 return PAGEREF_RECLAIM;
848 if (referenced_ptes) {
849 if (PageSwapBacked(page))
850 return PAGEREF_ACTIVATE;
852 * All mapped pages start out with page table
853 * references from the instantiating fault, so we need
854 * to look twice if a mapped file page is used more
857 * Mark it and spare it for another trip around the
858 * inactive list. Another page table reference will
859 * lead to its activation.
861 * Note: the mark is set for activated pages as well
862 * so that recently deactivated but used pages are
865 SetPageReferenced(page);
867 if (referenced_page || referenced_ptes > 1)
868 return PAGEREF_ACTIVATE;
871 * Activate file-backed executable pages after first usage.
873 if (vm_flags & VM_EXEC)
874 return PAGEREF_ACTIVATE;
879 /* Reclaim if clean, defer dirty pages to writeback */
880 if (referenced_page && !PageSwapBacked(page))
881 return PAGEREF_RECLAIM_CLEAN;
883 return PAGEREF_RECLAIM;
886 /* Check if a page is dirty or under writeback */
887 static void page_check_dirty_writeback(struct page *page,
888 bool *dirty, bool *writeback)
890 struct address_space *mapping;
893 * Anonymous pages are not handled by flushers and must be written
894 * from reclaim context. Do not stall reclaim based on them
896 if (!page_is_file_cache(page)) {
902 /* By default assume that the page flags are accurate */
903 *dirty = PageDirty(page);
904 *writeback = PageWriteback(page);
906 /* Verify dirty/writeback state if the filesystem supports it */
907 if (!page_has_private(page))
910 mapping = page_mapping(page);
911 if (mapping && mapping->a_ops->is_dirty_writeback)
912 mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
916 * shrink_page_list() returns the number of reclaimed pages
918 static unsigned long shrink_page_list(struct list_head *page_list,
919 struct pglist_data *pgdat,
920 struct scan_control *sc,
921 enum ttu_flags ttu_flags,
922 unsigned long *ret_nr_dirty,
923 unsigned long *ret_nr_unqueued_dirty,
924 unsigned long *ret_nr_congested,
925 unsigned long *ret_nr_writeback,
926 unsigned long *ret_nr_immediate,
929 LIST_HEAD(ret_pages);
930 LIST_HEAD(free_pages);
932 unsigned long nr_unqueued_dirty = 0;
933 unsigned long nr_dirty = 0;
934 unsigned long nr_congested = 0;
935 unsigned long nr_reclaimed = 0;
936 unsigned long nr_writeback = 0;
937 unsigned long nr_immediate = 0;
941 while (!list_empty(page_list)) {
942 struct address_space *mapping;
945 enum page_references references = PAGEREF_RECLAIM_CLEAN;
946 bool dirty, writeback;
947 bool lazyfree = false;
948 int ret = SWAP_SUCCESS;
952 page = lru_to_page(page_list);
953 list_del(&page->lru);
955 if (!trylock_page(page))
958 VM_BUG_ON_PAGE(PageActive(page), page);
962 if (unlikely(!page_evictable(page)))
965 if (!sc->may_unmap && page_mapped(page))
968 /* Double the slab pressure for mapped and swapcache pages */
969 if (page_mapped(page) || PageSwapCache(page))
972 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
973 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
976 * The number of dirty pages determines if a zone is marked
977 * reclaim_congested which affects wait_iff_congested. kswapd
978 * will stall and start writing pages if the tail of the LRU
979 * is all dirty unqueued pages.
981 page_check_dirty_writeback(page, &dirty, &writeback);
982 if (dirty || writeback)
985 if (dirty && !writeback)
989 * Treat this page as congested if the underlying BDI is or if
990 * pages are cycling through the LRU so quickly that the
991 * pages marked for immediate reclaim are making it to the
992 * end of the LRU a second time.
994 mapping = page_mapping(page);
995 if (((dirty || writeback) && mapping &&
996 inode_write_congested(mapping->host)) ||
997 (writeback && PageReclaim(page)))
1001 * If a page at the tail of the LRU is under writeback, there
1002 * are three cases to consider.
1004 * 1) If reclaim is encountering an excessive number of pages
1005 * under writeback and this page is both under writeback and
1006 * PageReclaim then it indicates that pages are being queued
1007 * for IO but are being recycled through the LRU before the
1008 * IO can complete. Waiting on the page itself risks an
1009 * indefinite stall if it is impossible to writeback the
1010 * page due to IO error or disconnected storage so instead
1011 * note that the LRU is being scanned too quickly and the
1012 * caller can stall after page list has been processed.
1014 * 2) Global or new memcg reclaim encounters a page that is
1015 * not marked for immediate reclaim, or the caller does not
1016 * have __GFP_FS (or __GFP_IO if it's simply going to swap,
1017 * not to fs). In this case mark the page for immediate
1018 * reclaim and continue scanning.
1020 * Require may_enter_fs because we would wait on fs, which
1021 * may not have submitted IO yet. And the loop driver might
1022 * enter reclaim, and deadlock if it waits on a page for
1023 * which it is needed to do the write (loop masks off
1024 * __GFP_IO|__GFP_FS for this reason); but more thought
1025 * would probably show more reasons.
1027 * 3) Legacy memcg encounters a page that is already marked
1028 * PageReclaim. memcg does not have any dirty pages
1029 * throttling so we could easily OOM just because too many
1030 * pages are in writeback and there is nothing else to
1031 * reclaim. Wait for the writeback to complete.
1033 if (PageWriteback(page)) {
1035 if (current_is_kswapd() &&
1036 PageReclaim(page) &&
1037 test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
1042 } else if (sane_reclaim(sc) ||
1043 !PageReclaim(page) || !may_enter_fs) {
1045 * This is slightly racy - end_page_writeback()
1046 * might have just cleared PageReclaim, then
1047 * setting PageReclaim here end up interpreted
1048 * as PageReadahead - but that does not matter
1049 * enough to care. What we do want is for this
1050 * page to have PageReclaim set next time memcg
1051 * reclaim reaches the tests above, so it will
1052 * then wait_on_page_writeback() to avoid OOM;
1053 * and it's also appropriate in global reclaim.
1055 SetPageReclaim(page);
1062 wait_on_page_writeback(page);
1063 /* then go back and try same page again */
1064 list_add_tail(&page->lru, page_list);
1070 references = page_check_references(page, sc);
1072 switch (references) {
1073 case PAGEREF_ACTIVATE:
1074 goto activate_locked;
1077 case PAGEREF_RECLAIM:
1078 case PAGEREF_RECLAIM_CLEAN:
1079 ; /* try to reclaim the page below */
1083 * Anonymous process memory has backing store?
1084 * Try to allocate it some swap space here.
1086 if (PageAnon(page) && !PageSwapCache(page)) {
1087 if (!(sc->gfp_mask & __GFP_IO))
1089 if (!add_to_swap(page, page_list))
1090 goto activate_locked;
1094 /* Adding to swap updated mapping */
1095 mapping = page_mapping(page);
1096 } else if (unlikely(PageTransHuge(page))) {
1097 /* Split file THP */
1098 if (split_huge_page_to_list(page, page_list))
1102 VM_BUG_ON_PAGE(PageTransHuge(page), page);
1105 * The page is mapped into the page tables of one or more
1106 * processes. Try to unmap it here.
1108 if (page_mapped(page) && mapping) {
1109 switch (ret = try_to_unmap(page, lazyfree ?
1110 (ttu_flags | TTU_BATCH_FLUSH | TTU_LZFREE) :
1111 (ttu_flags | TTU_BATCH_FLUSH))) {
1113 goto activate_locked;
1121 ; /* try to free the page below */
1125 if (PageDirty(page)) {
1127 * Only kswapd can writeback filesystem pages to
1128 * avoid risk of stack overflow but only writeback
1129 * if many dirty pages have been encountered.
1131 if (page_is_file_cache(page) &&
1132 (!current_is_kswapd() ||
1133 !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
1135 * Immediately reclaim when written back.
1136 * Similar in principal to deactivate_page()
1137 * except we already have the page isolated
1138 * and know it's dirty
1140 inc_node_page_state(page, NR_VMSCAN_IMMEDIATE);
1141 SetPageReclaim(page);
1146 if (references == PAGEREF_RECLAIM_CLEAN)
1150 if (!sc->may_writepage)
1154 * Page is dirty. Flush the TLB if a writable entry
1155 * potentially exists to avoid CPU writes after IO
1156 * starts and then write it out here.
1158 try_to_unmap_flush_dirty();
1159 switch (pageout(page, mapping, sc)) {
1163 goto activate_locked;
1165 if (PageWriteback(page))
1167 if (PageDirty(page))
1171 * A synchronous write - probably a ramdisk. Go
1172 * ahead and try to reclaim the page.
1174 if (!trylock_page(page))
1176 if (PageDirty(page) || PageWriteback(page))
1178 mapping = page_mapping(page);
1180 ; /* try to free the page below */
1185 * If the page has buffers, try to free the buffer mappings
1186 * associated with this page. If we succeed we try to free
1189 * We do this even if the page is PageDirty().
1190 * try_to_release_page() does not perform I/O, but it is
1191 * possible for a page to have PageDirty set, but it is actually
1192 * clean (all its buffers are clean). This happens if the
1193 * buffers were written out directly, with submit_bh(). ext3
1194 * will do this, as well as the blockdev mapping.
1195 * try_to_release_page() will discover that cleanness and will
1196 * drop the buffers and mark the page clean - it can be freed.
1198 * Rarely, pages can have buffers and no ->mapping. These are
1199 * the pages which were not successfully invalidated in
1200 * truncate_complete_page(). We try to drop those buffers here
1201 * and if that worked, and the page is no longer mapped into
1202 * process address space (page_count == 1) it can be freed.
1203 * Otherwise, leave the page on the LRU so it is swappable.
1205 if (page_has_private(page)) {
1206 if (!try_to_release_page(page, sc->gfp_mask))
1207 goto activate_locked;
1208 if (!mapping && page_count(page) == 1) {
1210 if (put_page_testzero(page))
1214 * rare race with speculative reference.
1215 * the speculative reference will free
1216 * this page shortly, so we may
1217 * increment nr_reclaimed here (and
1218 * leave it off the LRU).
1227 if (!mapping || !__remove_mapping(mapping, page, true))
1231 * At this point, we have no other references and there is
1232 * no way to pick any more up (removed from LRU, removed
1233 * from pagecache). Can use non-atomic bitops now (and
1234 * we obviously don't have to worry about waking up a process
1235 * waiting on the page lock, because there are no references.
1237 __ClearPageLocked(page);
1239 if (ret == SWAP_LZFREE)
1240 count_vm_event(PGLAZYFREED);
1245 * Is there need to periodically free_page_list? It would
1246 * appear not as the counts should be low
1248 list_add(&page->lru, &free_pages);
1252 if (PageSwapCache(page))
1253 try_to_free_swap(page);
1255 list_add(&page->lru, &ret_pages);
1259 /* Not a candidate for swapping, so reclaim swap space. */
1260 if (PageSwapCache(page) && mem_cgroup_swap_full(page))
1261 try_to_free_swap(page);
1262 VM_BUG_ON_PAGE(PageActive(page), page);
1263 SetPageActive(page);
1268 list_add(&page->lru, &ret_pages);
1269 VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
1272 mem_cgroup_uncharge_list(&free_pages);
1273 try_to_unmap_flush();
1274 free_hot_cold_page_list(&free_pages, true);
1276 list_splice(&ret_pages, page_list);
1277 count_vm_events(PGACTIVATE, pgactivate);
1279 *ret_nr_dirty += nr_dirty;
1280 *ret_nr_congested += nr_congested;
1281 *ret_nr_unqueued_dirty += nr_unqueued_dirty;
1282 *ret_nr_writeback += nr_writeback;
1283 *ret_nr_immediate += nr_immediate;
1284 return nr_reclaimed;
1287 unsigned long reclaim_clean_pages_from_list(struct zone *zone,
1288 struct list_head *page_list)
1290 struct scan_control sc = {
1291 .gfp_mask = GFP_KERNEL,
1292 .priority = DEF_PRIORITY,
1295 unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
1296 struct page *page, *next;
1297 LIST_HEAD(clean_pages);
1299 list_for_each_entry_safe(page, next, page_list, lru) {
1300 if (page_is_file_cache(page) && !PageDirty(page) &&
1301 !__PageMovable(page)) {
1302 ClearPageActive(page);
1303 list_move(&page->lru, &clean_pages);
1307 ret = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc,
1308 TTU_UNMAP|TTU_IGNORE_ACCESS,
1309 &dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
1310 list_splice(&clean_pages, page_list);
1311 mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -ret);
1316 * Attempt to remove the specified page from its LRU. Only take this page
1317 * if it is of the appropriate PageActive status. Pages which are being
1318 * freed elsewhere are also ignored.
1320 * page: page to consider
1321 * mode: one of the LRU isolation modes defined above
1323 * returns 0 on success, -ve errno on failure.
1325 int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1329 /* Only take pages on the LRU. */
1333 /* Compaction should not handle unevictable pages but CMA can do so */
1334 if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1340 * To minimise LRU disruption, the caller can indicate that it only
1341 * wants to isolate pages it will be able to operate on without
1342 * blocking - clean pages for the most part.
1344 * ISOLATE_CLEAN means that only clean pages should be isolated. This
1345 * is used by reclaim when it is cannot write to backing storage
1347 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1348 * that it is possible to migrate without blocking
1350 if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
1351 /* All the caller can do on PageWriteback is block */
1352 if (PageWriteback(page))
1355 if (PageDirty(page)) {
1356 struct address_space *mapping;
1358 /* ISOLATE_CLEAN means only clean pages */
1359 if (mode & ISOLATE_CLEAN)
1363 * Only pages without mappings or that have a
1364 * ->migratepage callback are possible to migrate
1367 mapping = page_mapping(page);
1368 if (mapping && !mapping->a_ops->migratepage)
1373 if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1376 if (likely(get_page_unless_zero(page))) {
1378 * Be careful not to clear PageLRU until after we're
1379 * sure the page is not being freed elsewhere -- the
1380 * page release code relies on it.
1391 * Update LRU sizes after isolating pages. The LRU size updates must
1392 * be complete before mem_cgroup_update_lru_size due to a santity check.
1394 static __always_inline void update_lru_sizes(struct lruvec *lruvec,
1395 enum lru_list lru, unsigned long *nr_zone_taken)
1399 for (zid = 0; zid < MAX_NR_ZONES; zid++) {
1400 if (!nr_zone_taken[zid])
1403 __update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
1405 mem_cgroup_update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
1412 * zone_lru_lock is heavily contended. Some of the functions that
1413 * shrink the lists perform better by taking out a batch of pages
1414 * and working on them outside the LRU lock.
1416 * For pagecache intensive workloads, this function is the hottest
1417 * spot in the kernel (apart from copy_*_user functions).
1419 * Appropriate locks must be held before calling this function.
1421 * @nr_to_scan: The number of pages to look through on the list.
1422 * @lruvec: The LRU vector to pull pages from.
1423 * @dst: The temp list to put pages on to.
1424 * @nr_scanned: The number of pages that were scanned.
1425 * @sc: The scan_control struct for this reclaim session
1426 * @mode: One of the LRU isolation modes
1427 * @lru: LRU list id for isolating
1429 * returns how many pages were moved onto *@dst.
1431 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1432 struct lruvec *lruvec, struct list_head *dst,
1433 unsigned long *nr_scanned, struct scan_control *sc,
1434 isolate_mode_t mode, enum lru_list lru)
1436 struct list_head *src = &lruvec->lists[lru];
1437 unsigned long nr_taken = 0;
1438 unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
1439 unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
1440 unsigned long scan, nr_pages;
1441 LIST_HEAD(pages_skipped);
1443 for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
1444 !list_empty(src);) {
1447 page = lru_to_page(src);
1448 prefetchw_prev_lru_page(page, src, flags);
1450 VM_BUG_ON_PAGE(!PageLRU(page), page);
1452 if (page_zonenum(page) > sc->reclaim_idx) {
1453 list_move(&page->lru, &pages_skipped);
1454 nr_skipped[page_zonenum(page)]++;
1459 * Account for scanned and skipped separetly to avoid the pgdat
1460 * being prematurely marked unreclaimable by pgdat_reclaimable.
1464 switch (__isolate_lru_page(page, mode)) {
1466 nr_pages = hpage_nr_pages(page);
1467 nr_taken += nr_pages;
1468 nr_zone_taken[page_zonenum(page)] += nr_pages;
1469 list_move(&page->lru, dst);
1473 /* else it is being freed elsewhere */
1474 list_move(&page->lru, src);
1483 * Splice any skipped pages to the start of the LRU list. Note that
1484 * this disrupts the LRU order when reclaiming for lower zones but
1485 * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
1486 * scanning would soon rescan the same pages to skip and put the
1487 * system at risk of premature OOM.
1489 if (!list_empty(&pages_skipped)) {
1491 unsigned long total_skipped = 0;
1493 for (zid = 0; zid < MAX_NR_ZONES; zid++) {
1494 if (!nr_skipped[zid])
1497 __count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
1498 total_skipped += nr_skipped[zid];
1502 * Account skipped pages as a partial scan as the pgdat may be
1503 * close to unreclaimable. If the LRU list is empty, account
1504 * skipped pages as a full scan.
1506 scan += list_empty(src) ? total_skipped : total_skipped >> 2;
1508 list_splice(&pages_skipped, src);
1511 trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan, scan,
1512 nr_taken, mode, is_file_lru(lru));
1513 update_lru_sizes(lruvec, lru, nr_zone_taken);
1518 * isolate_lru_page - tries to isolate a page from its LRU list
1519 * @page: page to isolate from its LRU list
1521 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1522 * vmstat statistic corresponding to whatever LRU list the page was on.
1524 * Returns 0 if the page was removed from an LRU list.
1525 * Returns -EBUSY if the page was not on an LRU list.
1527 * The returned page will have PageLRU() cleared. If it was found on
1528 * the active list, it will have PageActive set. If it was found on
1529 * the unevictable list, it will have the PageUnevictable bit set. That flag
1530 * may need to be cleared by the caller before letting the page go.
1532 * The vmstat statistic corresponding to the list on which the page was
1533 * found will be decremented.
1536 * (1) Must be called with an elevated refcount on the page. This is a
1537 * fundamentnal difference from isolate_lru_pages (which is called
1538 * without a stable reference).
1539 * (2) the lru_lock must not be held.
1540 * (3) interrupts must be enabled.
1542 int isolate_lru_page(struct page *page)
1546 VM_BUG_ON_PAGE(!page_count(page), page);
1547 WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");
1549 if (PageLRU(page)) {
1550 struct zone *zone = page_zone(page);
1551 struct lruvec *lruvec;
1553 spin_lock_irq(zone_lru_lock(zone));
1554 lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
1555 if (PageLRU(page)) {
1556 int lru = page_lru(page);
1559 del_page_from_lru_list(page, lruvec, lru);
1562 spin_unlock_irq(zone_lru_lock(zone));
1568 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
1569 * then get resheduled. When there are massive number of tasks doing page
1570 * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
1571 * the LRU list will go small and be scanned faster than necessary, leading to
1572 * unnecessary swapping, thrashing and OOM.
1574 static int too_many_isolated(struct pglist_data *pgdat, int file,
1575 struct scan_control *sc)
1577 unsigned long inactive, isolated;
1579 if (current_is_kswapd())
1582 if (!sane_reclaim(sc))
1586 inactive = node_page_state(pgdat, NR_INACTIVE_FILE);
1587 isolated = node_page_state(pgdat, NR_ISOLATED_FILE);
1589 inactive = node_page_state(pgdat, NR_INACTIVE_ANON);
1590 isolated = node_page_state(pgdat, NR_ISOLATED_ANON);
1594 * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
1595 * won't get blocked by normal direct-reclaimers, forming a circular
1598 if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS))
1601 return isolated > inactive;
1604 static noinline_for_stack void
1605 putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1607 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1608 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1609 LIST_HEAD(pages_to_free);
1612 * Put back any unfreeable pages.
1614 while (!list_empty(page_list)) {
1615 struct page *page = lru_to_page(page_list);
1618 VM_BUG_ON_PAGE(PageLRU(page), page);
1619 list_del(&page->lru);
1620 if (unlikely(!page_evictable(page))) {
1621 spin_unlock_irq(&pgdat->lru_lock);
1622 putback_lru_page(page);
1623 spin_lock_irq(&pgdat->lru_lock);
1627 lruvec = mem_cgroup_page_lruvec(page, pgdat);
1630 lru = page_lru(page);
1631 add_page_to_lru_list(page, lruvec, lru);
1633 if (is_active_lru(lru)) {
1634 int file = is_file_lru(lru);
1635 int numpages = hpage_nr_pages(page);
1636 reclaim_stat->recent_rotated[file] += numpages;
1638 if (put_page_testzero(page)) {
1639 __ClearPageLRU(page);
1640 __ClearPageActive(page);
1641 del_page_from_lru_list(page, lruvec, lru);
1643 if (unlikely(PageCompound(page))) {
1644 spin_unlock_irq(&pgdat->lru_lock);
1645 mem_cgroup_uncharge(page);
1646 (*get_compound_page_dtor(page))(page);
1647 spin_lock_irq(&pgdat->lru_lock);
1649 list_add(&page->lru, &pages_to_free);
1654 * To save our caller's stack, now use input list for pages to free.
1656 list_splice(&pages_to_free, page_list);
1660 * If a kernel thread (such as nfsd for loop-back mounts) services
1661 * a backing device by writing to the page cache it sets PF_LESS_THROTTLE.
1662 * In that case we should only throttle if the backing device it is
1663 * writing to is congested. In other cases it is safe to throttle.
1665 static int current_may_throttle(void)
1667 return !(current->flags & PF_LESS_THROTTLE) ||
1668 current->backing_dev_info == NULL ||
1669 bdi_write_congested(current->backing_dev_info);
1672 static bool inactive_reclaimable_pages(struct lruvec *lruvec,
1673 struct scan_control *sc, enum lru_list lru)
1677 int file = is_file_lru(lru);
1678 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1680 if (!global_reclaim(sc))
1683 for (zid = sc->reclaim_idx; zid >= 0; zid--) {
1684 zone = &pgdat->node_zones[zid];
1685 if (!managed_zone(zone))
1688 if (zone_page_state_snapshot(zone, NR_ZONE_LRU_BASE +
1689 LRU_FILE * file) >= SWAP_CLUSTER_MAX)
1697 * shrink_inactive_list() is a helper for shrink_node(). It returns the number
1698 * of reclaimed pages
1700 static noinline_for_stack unsigned long
1701 shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1702 struct scan_control *sc, enum lru_list lru)
1704 LIST_HEAD(page_list);
1705 unsigned long nr_scanned;
1706 unsigned long nr_reclaimed = 0;
1707 unsigned long nr_taken;
1708 unsigned long nr_dirty = 0;
1709 unsigned long nr_congested = 0;
1710 unsigned long nr_unqueued_dirty = 0;
1711 unsigned long nr_writeback = 0;
1712 unsigned long nr_immediate = 0;
1713 isolate_mode_t isolate_mode = 0;
1714 int file = is_file_lru(lru);
1715 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1716 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1718 if (!inactive_reclaimable_pages(lruvec, sc, lru))
1721 while (unlikely(too_many_isolated(pgdat, file, sc))) {
1722 congestion_wait(BLK_RW_ASYNC, HZ/10);
1724 /* We are about to die and free our memory. Return now. */
1725 if (fatal_signal_pending(current))
1726 return SWAP_CLUSTER_MAX;
1732 isolate_mode |= ISOLATE_UNMAPPED;
1733 if (!sc->may_writepage)
1734 isolate_mode |= ISOLATE_CLEAN;
1736 spin_lock_irq(&pgdat->lru_lock);
1738 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1739 &nr_scanned, sc, isolate_mode, lru);
1741 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
1742 reclaim_stat->recent_scanned[file] += nr_taken;
1744 if (global_reclaim(sc)) {
1745 __mod_node_page_state(pgdat, NR_PAGES_SCANNED, nr_scanned);
1746 if (current_is_kswapd())
1747 __count_vm_events(PGSCAN_KSWAPD, nr_scanned);
1749 __count_vm_events(PGSCAN_DIRECT, nr_scanned);
1751 spin_unlock_irq(&pgdat->lru_lock);
1756 nr_reclaimed = shrink_page_list(&page_list, pgdat, sc, TTU_UNMAP,
1757 &nr_dirty, &nr_unqueued_dirty, &nr_congested,
1758 &nr_writeback, &nr_immediate,
1761 spin_lock_irq(&pgdat->lru_lock);
1763 if (global_reclaim(sc)) {
1764 if (current_is_kswapd())
1765 __count_vm_events(PGSTEAL_KSWAPD, nr_reclaimed);
1767 __count_vm_events(PGSTEAL_DIRECT, nr_reclaimed);
1770 putback_inactive_pages(lruvec, &page_list);
1772 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
1774 spin_unlock_irq(&pgdat->lru_lock);
1776 mem_cgroup_uncharge_list(&page_list);
1777 free_hot_cold_page_list(&page_list, true);
1780 * If reclaim is isolating dirty pages under writeback, it implies
1781 * that the long-lived page allocation rate is exceeding the page
1782 * laundering rate. Either the global limits are not being effective
1783 * at throttling processes due to the page distribution throughout
1784 * zones or there is heavy usage of a slow backing device. The
1785 * only option is to throttle from reclaim context which is not ideal
1786 * as there is no guarantee the dirtying process is throttled in the
1787 * same way balance_dirty_pages() manages.
1789 * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
1790 * of pages under pages flagged for immediate reclaim and stall if any
1791 * are encountered in the nr_immediate check below.
1793 if (nr_writeback && nr_writeback == nr_taken)
1794 set_bit(PGDAT_WRITEBACK, &pgdat->flags);
1797 * Legacy memcg will stall in page writeback so avoid forcibly
1800 if (sane_reclaim(sc)) {
1802 * Tag a zone as congested if all the dirty pages scanned were
1803 * backed by a congested BDI and wait_iff_congested will stall.
1805 if (nr_dirty && nr_dirty == nr_congested)
1806 set_bit(PGDAT_CONGESTED, &pgdat->flags);
1809 * If dirty pages are scanned that are not queued for IO, it
1810 * implies that flushers are not keeping up. In this case, flag
1811 * the pgdat PGDAT_DIRTY and kswapd will start writing pages from
1814 if (nr_unqueued_dirty == nr_taken)
1815 set_bit(PGDAT_DIRTY, &pgdat->flags);
1818 * If kswapd scans pages marked marked for immediate
1819 * reclaim and under writeback (nr_immediate), it implies
1820 * that pages are cycling through the LRU faster than
1821 * they are written so also forcibly stall.
1823 if (nr_immediate && current_may_throttle())
1824 congestion_wait(BLK_RW_ASYNC, HZ/10);
1828 * Stall direct reclaim for IO completions if underlying BDIs or zone
1829 * is congested. Allow kswapd to continue until it starts encountering
1830 * unqueued dirty pages or cycling through the LRU too quickly.
1832 if (!sc->hibernation_mode && !current_is_kswapd() &&
1833 current_may_throttle())
1834 wait_iff_congested(pgdat, BLK_RW_ASYNC, HZ/10);
1836 trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
1837 nr_scanned, nr_reclaimed,
1838 sc->priority, file);
1839 return nr_reclaimed;
1843 * This moves pages from the active list to the inactive list.
1845 * We move them the other way if the page is referenced by one or more
1846 * processes, from rmap.
1848 * If the pages are mostly unmapped, the processing is fast and it is
1849 * appropriate to hold zone_lru_lock across the whole operation. But if
1850 * the pages are mapped, the processing is slow (page_referenced()) so we
1851 * should drop zone_lru_lock around each page. It's impossible to balance
1852 * this, so instead we remove the pages from the LRU while processing them.
1853 * It is safe to rely on PG_active against the non-LRU pages in here because
1854 * nobody will play with that bit on a non-LRU page.
1856 * The downside is that we have to touch page->_refcount against each page.
1857 * But we had to alter page->flags anyway.
1859 * Returns the number of pages moved to the given lru.
1862 static unsigned move_active_pages_to_lru(struct lruvec *lruvec,
1863 struct list_head *list,
1864 struct list_head *pages_to_free,
1867 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1868 unsigned long pgmoved = 0;
1873 while (!list_empty(list)) {
1874 page = lru_to_page(list);
1875 lruvec = mem_cgroup_page_lruvec(page, pgdat);
1877 VM_BUG_ON_PAGE(PageLRU(page), page);
1880 nr_pages = hpage_nr_pages(page);
1881 update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
1882 list_move(&page->lru, &lruvec->lists[lru]);
1883 pgmoved += nr_pages;
1885 if (put_page_testzero(page)) {
1886 __ClearPageLRU(page);
1887 __ClearPageActive(page);
1888 del_page_from_lru_list(page, lruvec, lru);
1890 if (unlikely(PageCompound(page))) {
1891 spin_unlock_irq(&pgdat->lru_lock);
1892 mem_cgroup_uncharge(page);
1893 (*get_compound_page_dtor(page))(page);
1894 spin_lock_irq(&pgdat->lru_lock);
1896 list_add(&page->lru, pages_to_free);
1898 nr_moved += nr_pages;
1902 if (!is_active_lru(lru))
1903 __count_vm_events(PGDEACTIVATE, pgmoved);
1908 static void shrink_active_list(unsigned long nr_to_scan,
1909 struct lruvec *lruvec,
1910 struct scan_control *sc,
1913 unsigned long nr_taken;
1914 unsigned long nr_scanned;
1915 unsigned long vm_flags;
1916 LIST_HEAD(l_hold); /* The pages which were snipped off */
1917 LIST_HEAD(l_active);
1918 LIST_HEAD(l_inactive);
1920 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1921 unsigned nr_deactivate, nr_activate;
1922 unsigned nr_rotated = 0;
1923 isolate_mode_t isolate_mode = 0;
1924 int file = is_file_lru(lru);
1925 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1930 isolate_mode |= ISOLATE_UNMAPPED;
1931 if (!sc->may_writepage)
1932 isolate_mode |= ISOLATE_CLEAN;
1934 spin_lock_irq(&pgdat->lru_lock);
1936 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1937 &nr_scanned, sc, isolate_mode, lru);
1939 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
1940 reclaim_stat->recent_scanned[file] += nr_taken;
1942 if (global_reclaim(sc))
1943 __mod_node_page_state(pgdat, NR_PAGES_SCANNED, nr_scanned);
1944 __count_vm_events(PGREFILL, nr_scanned);
1946 spin_unlock_irq(&pgdat->lru_lock);
1948 while (!list_empty(&l_hold)) {
1950 page = lru_to_page(&l_hold);
1951 list_del(&page->lru);
1953 if (unlikely(!page_evictable(page))) {
1954 putback_lru_page(page);
1958 if (unlikely(buffer_heads_over_limit)) {
1959 if (page_has_private(page) && trylock_page(page)) {
1960 if (page_has_private(page))
1961 try_to_release_page(page, 0);
1966 if (page_referenced(page, 0, sc->target_mem_cgroup,
1968 nr_rotated += hpage_nr_pages(page);
1970 * Identify referenced, file-backed active pages and
1971 * give them one more trip around the active list. So
1972 * that executable code get better chances to stay in
1973 * memory under moderate memory pressure. Anon pages
1974 * are not likely to be evicted by use-once streaming
1975 * IO, plus JVM can create lots of anon VM_EXEC pages,
1976 * so we ignore them here.
1978 if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1979 list_add(&page->lru, &l_active);
1984 ClearPageActive(page); /* we are de-activating */
1985 list_add(&page->lru, &l_inactive);
1989 * Move pages back to the lru list.
1991 spin_lock_irq(&pgdat->lru_lock);
1993 * Count referenced pages from currently used mappings as rotated,
1994 * even though only some of them are actually re-activated. This
1995 * helps balance scan pressure between file and anonymous pages in
1998 reclaim_stat->recent_rotated[file] += nr_rotated;
2000 nr_activate = move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
2001 nr_deactivate = move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
2002 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
2003 spin_unlock_irq(&pgdat->lru_lock);
2005 mem_cgroup_uncharge_list(&l_hold);
2006 free_hot_cold_page_list(&l_hold, true);
2007 trace_mm_vmscan_lru_shrink_active(pgdat->node_id, nr_taken, nr_activate,
2008 nr_deactivate, nr_rotated, sc->priority, file);
2012 * The inactive anon list should be small enough that the VM never has
2013 * to do too much work.
2015 * The inactive file list should be small enough to leave most memory
2016 * to the established workingset on the scan-resistant active list,
2017 * but large enough to avoid thrashing the aggregate readahead window.
2019 * Both inactive lists should also be large enough that each inactive
2020 * page has a chance to be referenced again before it is reclaimed.
2022 * The inactive_ratio is the target ratio of ACTIVE to INACTIVE pages
2023 * on this LRU, maintained by the pageout code. A zone->inactive_ratio
2024 * of 3 means 3:1 or 25% of the pages are kept on the inactive list.
2027 * memory ratio inactive
2028 * -------------------------------------
2037 static bool inactive_list_is_low(struct lruvec *lruvec, bool file,
2038 struct scan_control *sc)
2040 unsigned long inactive_ratio;
2041 unsigned long inactive;
2042 unsigned long active;
2044 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2048 * If we don't have swap space, anonymous page deactivation
2051 if (!file && !total_swap_pages)
2054 inactive = lruvec_lru_size(lruvec, file * LRU_FILE);
2055 active = lruvec_lru_size(lruvec, file * LRU_FILE + LRU_ACTIVE);
2058 * For zone-constrained allocations, it is necessary to check if
2059 * deactivations are required for lowmem to be reclaimed. This
2060 * calculates the inactive/active pages available in eligible zones.
2062 for (zid = sc->reclaim_idx + 1; zid < MAX_NR_ZONES; zid++) {
2063 struct zone *zone = &pgdat->node_zones[zid];
2064 unsigned long inactive_zone, active_zone;
2066 if (!managed_zone(zone))
2069 inactive_zone = lruvec_zone_lru_size(lruvec, file * LRU_FILE, zid);
2070 active_zone = lruvec_zone_lru_size(lruvec, (file * LRU_FILE) + LRU_ACTIVE, zid);
2072 inactive -= min(inactive, inactive_zone);
2073 active -= min(active, active_zone);
2076 gb = (inactive + active) >> (30 - PAGE_SHIFT);
2078 inactive_ratio = int_sqrt(10 * gb);
2082 return inactive * inactive_ratio < active;
2085 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
2086 struct lruvec *lruvec, struct scan_control *sc)
2088 if (is_active_lru(lru)) {
2089 if (inactive_list_is_low(lruvec, is_file_lru(lru), sc))
2090 shrink_active_list(nr_to_scan, lruvec, sc, lru);
2094 return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
2105 * Determine how aggressively the anon and file LRU lists should be
2106 * scanned. The relative value of each set of LRU lists is determined
2107 * by looking at the fraction of the pages scanned we did rotate back
2108 * onto the active list instead of evict.
2110 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
2111 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
2113 static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
2114 struct scan_control *sc, unsigned long *nr,
2115 unsigned long *lru_pages)
2117 int swappiness = mem_cgroup_swappiness(memcg);
2118 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
2120 u64 denominator = 0; /* gcc */
2121 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2122 unsigned long anon_prio, file_prio;
2123 enum scan_balance scan_balance;
2124 unsigned long anon, file;
2125 bool force_scan = false;
2126 unsigned long ap, fp;
2132 * If the zone or memcg is small, nr[l] can be 0. This
2133 * results in no scanning on this priority and a potential
2134 * priority drop. Global direct reclaim can go to the next
2135 * zone and tends to have no problems. Global kswapd is for
2136 * zone balancing and it needs to scan a minimum amount. When
2137 * reclaiming for a memcg, a priority drop can cause high
2138 * latencies, so it's better to scan a minimum amount there as
2141 if (current_is_kswapd()) {
2142 if (!pgdat_reclaimable(pgdat))
2144 if (!mem_cgroup_online(memcg))
2147 if (!global_reclaim(sc))
2150 /* If we have no swap space, do not bother scanning anon pages. */
2151 if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
2152 scan_balance = SCAN_FILE;
2157 * Global reclaim will swap to prevent OOM even with no
2158 * swappiness, but memcg users want to use this knob to
2159 * disable swapping for individual groups completely when
2160 * using the memory controller's swap limit feature would be
2163 if (!global_reclaim(sc) && !swappiness) {
2164 scan_balance = SCAN_FILE;
2169 * Do not apply any pressure balancing cleverness when the
2170 * system is close to OOM, scan both anon and file equally
2171 * (unless the swappiness setting disagrees with swapping).
2173 if (!sc->priority && swappiness) {
2174 scan_balance = SCAN_EQUAL;
2179 * Prevent the reclaimer from falling into the cache trap: as
2180 * cache pages start out inactive, every cache fault will tip
2181 * the scan balance towards the file LRU. And as the file LRU
2182 * shrinks, so does the window for rotation from references.
2183 * This means we have a runaway feedback loop where a tiny
2184 * thrashing file LRU becomes infinitely more attractive than
2185 * anon pages. Try to detect this based on file LRU size.
2187 if (global_reclaim(sc)) {
2188 unsigned long pgdatfile;
2189 unsigned long pgdatfree;
2191 unsigned long total_high_wmark = 0;
2193 pgdatfree = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
2194 pgdatfile = node_page_state(pgdat, NR_ACTIVE_FILE) +
2195 node_page_state(pgdat, NR_INACTIVE_FILE);
2197 for (z = 0; z < MAX_NR_ZONES; z++) {
2198 struct zone *zone = &pgdat->node_zones[z];
2199 if (!managed_zone(zone))
2202 total_high_wmark += high_wmark_pages(zone);
2205 if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) {
2206 scan_balance = SCAN_ANON;
2212 * If there is enough inactive page cache, i.e. if the size of the
2213 * inactive list is greater than that of the active list *and* the
2214 * inactive list actually has some pages to scan on this priority, we
2215 * do not reclaim anything from the anonymous working set right now.
2216 * Without the second condition we could end up never scanning an
2217 * lruvec even if it has plenty of old anonymous pages unless the
2218 * system is under heavy pressure.
2220 if (!inactive_list_is_low(lruvec, true, sc) &&
2221 lruvec_lru_size(lruvec, LRU_INACTIVE_FILE) >> sc->priority) {
2222 scan_balance = SCAN_FILE;
2226 scan_balance = SCAN_FRACT;
2229 * With swappiness at 100, anonymous and file have the same priority.
2230 * This scanning priority is essentially the inverse of IO cost.
2232 anon_prio = swappiness;
2233 file_prio = 200 - anon_prio;
2236 * OK, so we have swap space and a fair amount of page cache
2237 * pages. We use the recently rotated / recently scanned
2238 * ratios to determine how valuable each cache is.
2240 * Because workloads change over time (and to avoid overflow)
2241 * we keep these statistics as a floating average, which ends
2242 * up weighing recent references more than old ones.
2244 * anon in [0], file in [1]
2247 anon = lruvec_lru_size(lruvec, LRU_ACTIVE_ANON) +
2248 lruvec_lru_size(lruvec, LRU_INACTIVE_ANON);
2249 file = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE) +
2250 lruvec_lru_size(lruvec, LRU_INACTIVE_FILE);
2252 spin_lock_irq(&pgdat->lru_lock);
2253 if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
2254 reclaim_stat->recent_scanned[0] /= 2;
2255 reclaim_stat->recent_rotated[0] /= 2;
2258 if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
2259 reclaim_stat->recent_scanned[1] /= 2;
2260 reclaim_stat->recent_rotated[1] /= 2;
2264 * The amount of pressure on anon vs file pages is inversely
2265 * proportional to the fraction of recently scanned pages on
2266 * each list that were recently referenced and in active use.
2268 ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
2269 ap /= reclaim_stat->recent_rotated[0] + 1;
2271 fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
2272 fp /= reclaim_stat->recent_rotated[1] + 1;
2273 spin_unlock_irq(&pgdat->lru_lock);
2277 denominator = ap + fp + 1;
2279 some_scanned = false;
2280 /* Only use force_scan on second pass. */
2281 for (pass = 0; !some_scanned && pass < 2; pass++) {
2283 for_each_evictable_lru(lru) {
2284 int file = is_file_lru(lru);
2288 size = lruvec_lru_size(lruvec, lru);
2289 scan = size >> sc->priority;
2291 if (!scan && pass && force_scan)
2292 scan = min(size, SWAP_CLUSTER_MAX);
2294 switch (scan_balance) {
2296 /* Scan lists relative to size */
2300 * Scan types proportional to swappiness and
2301 * their relative recent reclaim efficiency.
2303 scan = div64_u64(scan * fraction[file],
2308 /* Scan one type exclusively */
2309 if ((scan_balance == SCAN_FILE) != file) {
2315 /* Look ma, no brain */
2323 * Skip the second pass and don't force_scan,
2324 * if we found something to scan.
2326 some_scanned |= !!scan;
2332 * This is a basic per-node page freer. Used by both kswapd and direct reclaim.
2334 static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memcg,
2335 struct scan_control *sc, unsigned long *lru_pages)
2337 struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
2338 unsigned long nr[NR_LRU_LISTS];
2339 unsigned long targets[NR_LRU_LISTS];
2340 unsigned long nr_to_scan;
2342 unsigned long nr_reclaimed = 0;
2343 unsigned long nr_to_reclaim = sc->nr_to_reclaim;
2344 struct blk_plug plug;
2347 get_scan_count(lruvec, memcg, sc, nr, lru_pages);
2349 /* Record the original scan target for proportional adjustments later */
2350 memcpy(targets, nr, sizeof(nr));
2353 * Global reclaiming within direct reclaim at DEF_PRIORITY is a normal
2354 * event that can occur when there is little memory pressure e.g.
2355 * multiple streaming readers/writers. Hence, we do not abort scanning
2356 * when the requested number of pages are reclaimed when scanning at
2357 * DEF_PRIORITY on the assumption that the fact we are direct
2358 * reclaiming implies that kswapd is not keeping up and it is best to
2359 * do a batch of work at once. For memcg reclaim one check is made to
2360 * abort proportional reclaim if either the file or anon lru has already
2361 * dropped to zero at the first pass.
2363 scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() &&
2364 sc->priority == DEF_PRIORITY);
2366 blk_start_plug(&plug);
2367 while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
2368 nr[LRU_INACTIVE_FILE]) {
2369 unsigned long nr_anon, nr_file, percentage;
2370 unsigned long nr_scanned;
2372 for_each_evictable_lru(lru) {
2374 nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
2375 nr[lru] -= nr_to_scan;
2377 nr_reclaimed += shrink_list(lru, nr_to_scan,
2384 if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
2388 * For kswapd and memcg, reclaim at least the number of pages
2389 * requested. Ensure that the anon and file LRUs are scanned
2390 * proportionally what was requested by get_scan_count(). We
2391 * stop reclaiming one LRU and reduce the amount scanning
2392 * proportional to the original scan target.
2394 nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
2395 nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
2398 * It's just vindictive to attack the larger once the smaller
2399 * has gone to zero. And given the way we stop scanning the
2400 * smaller below, this makes sure that we only make one nudge
2401 * towards proportionality once we've got nr_to_reclaim.
2403 if (!nr_file || !nr_anon)
2406 if (nr_file > nr_anon) {
2407 unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
2408 targets[LRU_ACTIVE_ANON] + 1;
2410 percentage = nr_anon * 100 / scan_target;
2412 unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
2413 targets[LRU_ACTIVE_FILE] + 1;
2415 percentage = nr_file * 100 / scan_target;
2418 /* Stop scanning the smaller of the LRU */
2420 nr[lru + LRU_ACTIVE] = 0;
2423 * Recalculate the other LRU scan count based on its original
2424 * scan target and the percentage scanning already complete
2426 lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
2427 nr_scanned = targets[lru] - nr[lru];
2428 nr[lru] = targets[lru] * (100 - percentage) / 100;
2429 nr[lru] -= min(nr[lru], nr_scanned);
2432 nr_scanned = targets[lru] - nr[lru];
2433 nr[lru] = targets[lru] * (100 - percentage) / 100;
2434 nr[lru] -= min(nr[lru], nr_scanned);
2436 scan_adjusted = true;
2438 blk_finish_plug(&plug);
2439 sc->nr_reclaimed += nr_reclaimed;
2442 * Even if we did not try to evict anon pages at all, we want to
2443 * rebalance the anon lru active/inactive ratio.
2445 if (inactive_list_is_low(lruvec, false, sc))
2446 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2447 sc, LRU_ACTIVE_ANON);
2450 /* Use reclaim/compaction for costly allocs or under memory pressure */
2451 static bool in_reclaim_compaction(struct scan_control *sc)
2453 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2454 (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
2455 sc->priority < DEF_PRIORITY - 2))
2462 * Reclaim/compaction is used for high-order allocation requests. It reclaims
2463 * order-0 pages before compacting the zone. should_continue_reclaim() returns
2464 * true if more pages should be reclaimed such that when the page allocator
2465 * calls try_to_compact_zone() that it will have enough free pages to succeed.
2466 * It will give up earlier than that if there is difficulty reclaiming pages.
2468 static inline bool should_continue_reclaim(struct pglist_data *pgdat,
2469 unsigned long nr_reclaimed,
2470 unsigned long nr_scanned,
2471 struct scan_control *sc)
2473 unsigned long pages_for_compaction;
2474 unsigned long inactive_lru_pages;
2477 /* If not in reclaim/compaction mode, stop */
2478 if (!in_reclaim_compaction(sc))
2481 /* Consider stopping depending on scan and reclaim activity */
2482 if (sc->gfp_mask & __GFP_REPEAT) {
2484 * For __GFP_REPEAT allocations, stop reclaiming if the
2485 * full LRU list has been scanned and we are still failing
2486 * to reclaim pages. This full LRU scan is potentially
2487 * expensive but a __GFP_REPEAT caller really wants to succeed
2489 if (!nr_reclaimed && !nr_scanned)
2493 * For non-__GFP_REPEAT allocations which can presumably
2494 * fail without consequence, stop if we failed to reclaim
2495 * any pages from the last SWAP_CLUSTER_MAX number of
2496 * pages that were scanned. This will return to the
2497 * caller faster at the risk reclaim/compaction and
2498 * the resulting allocation attempt fails
2505 * If we have not reclaimed enough pages for compaction and the
2506 * inactive lists are large enough, continue reclaiming
2508 pages_for_compaction = compact_gap(sc->order);
2509 inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
2510 if (get_nr_swap_pages() > 0)
2511 inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
2512 if (sc->nr_reclaimed < pages_for_compaction &&
2513 inactive_lru_pages > pages_for_compaction)
2516 /* If compaction would go ahead or the allocation would succeed, stop */
2517 for (z = 0; z <= sc->reclaim_idx; z++) {
2518 struct zone *zone = &pgdat->node_zones[z];
2519 if (!managed_zone(zone))
2522 switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) {
2523 case COMPACT_SUCCESS:
2524 case COMPACT_CONTINUE:
2527 /* check next zone */
2534 static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
2536 struct reclaim_state *reclaim_state = current->reclaim_state;
2537 unsigned long nr_reclaimed, nr_scanned;
2538 bool reclaimable = false;
2541 struct mem_cgroup *root = sc->target_mem_cgroup;
2542 struct mem_cgroup_reclaim_cookie reclaim = {
2544 .priority = sc->priority,
2546 unsigned long node_lru_pages = 0;
2547 struct mem_cgroup *memcg;
2549 nr_reclaimed = sc->nr_reclaimed;
2550 nr_scanned = sc->nr_scanned;
2552 memcg = mem_cgroup_iter(root, NULL, &reclaim);
2554 unsigned long lru_pages;
2555 unsigned long reclaimed;
2556 unsigned long scanned;
2558 if (mem_cgroup_low(root, memcg)) {
2559 if (!sc->may_thrash)
2561 mem_cgroup_events(memcg, MEMCG_LOW, 1);
2564 reclaimed = sc->nr_reclaimed;
2565 scanned = sc->nr_scanned;
2567 shrink_node_memcg(pgdat, memcg, sc, &lru_pages);
2568 node_lru_pages += lru_pages;
2571 shrink_slab(sc->gfp_mask, pgdat->node_id,
2572 memcg, sc->nr_scanned - scanned,
2575 /* Record the group's reclaim efficiency */
2576 vmpressure(sc->gfp_mask, memcg, false,
2577 sc->nr_scanned - scanned,
2578 sc->nr_reclaimed - reclaimed);
2581 * Direct reclaim and kswapd have to scan all memory
2582 * cgroups to fulfill the overall scan target for the
2585 * Limit reclaim, on the other hand, only cares about
2586 * nr_to_reclaim pages to be reclaimed and it will
2587 * retry with decreasing priority if one round over the
2588 * whole hierarchy is not sufficient.
2590 if (!global_reclaim(sc) &&
2591 sc->nr_reclaimed >= sc->nr_to_reclaim) {
2592 mem_cgroup_iter_break(root, memcg);
2595 } while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));
2598 * Shrink the slab caches in the same proportion that
2599 * the eligible LRU pages were scanned.
2601 if (global_reclaim(sc))
2602 shrink_slab(sc->gfp_mask, pgdat->node_id, NULL,
2603 sc->nr_scanned - nr_scanned,
2606 if (reclaim_state) {
2607 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2608 reclaim_state->reclaimed_slab = 0;
2611 /* Record the subtree's reclaim efficiency */
2612 vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
2613 sc->nr_scanned - nr_scanned,
2614 sc->nr_reclaimed - nr_reclaimed);
2616 if (sc->nr_reclaimed - nr_reclaimed)
2619 } while (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
2620 sc->nr_scanned - nr_scanned, sc));
2626 * Returns true if compaction should go ahead for a costly-order request, or
2627 * the allocation would already succeed without compaction. Return false if we
2628 * should reclaim first.
2630 static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
2632 unsigned long watermark;
2633 enum compact_result suitable;
2635 suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
2636 if (suitable == COMPACT_SUCCESS)
2637 /* Allocation should succeed already. Don't reclaim. */
2639 if (suitable == COMPACT_SKIPPED)
2640 /* Compaction cannot yet proceed. Do reclaim. */
2644 * Compaction is already possible, but it takes time to run and there
2645 * are potentially other callers using the pages just freed. So proceed
2646 * with reclaim to make a buffer of free pages available to give
2647 * compaction a reasonable chance of completing and allocating the page.
2648 * Note that we won't actually reclaim the whole buffer in one attempt
2649 * as the target watermark in should_continue_reclaim() is lower. But if
2650 * we are already above the high+gap watermark, don't reclaim at all.
2652 watermark = high_wmark_pages(zone) + compact_gap(sc->order);
2654 return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
2658 * This is the direct reclaim path, for page-allocating processes. We only
2659 * try to reclaim pages from zones which will satisfy the caller's allocation
2662 * If a zone is deemed to be full of pinned pages then just give it a light
2663 * scan then give up on it.
2665 static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
2669 unsigned long nr_soft_reclaimed;
2670 unsigned long nr_soft_scanned;
2672 pg_data_t *last_pgdat = NULL;
2675 * If the number of buffer_heads in the machine exceeds the maximum
2676 * allowed level, force direct reclaim to scan the highmem zone as
2677 * highmem pages could be pinning lowmem pages storing buffer_heads
2679 orig_mask = sc->gfp_mask;
2680 if (buffer_heads_over_limit) {
2681 sc->gfp_mask |= __GFP_HIGHMEM;
2682 sc->reclaim_idx = gfp_zone(sc->gfp_mask);
2685 for_each_zone_zonelist_nodemask(zone, z, zonelist,
2686 sc->reclaim_idx, sc->nodemask) {
2688 * Take care memory controller reclaiming has small influence
2691 if (global_reclaim(sc)) {
2692 if (!cpuset_zone_allowed(zone,
2693 GFP_KERNEL | __GFP_HARDWALL))
2696 if (sc->priority != DEF_PRIORITY &&
2697 !pgdat_reclaimable(zone->zone_pgdat))
2698 continue; /* Let kswapd poll it */
2701 * If we already have plenty of memory free for
2702 * compaction in this zone, don't free any more.
2703 * Even though compaction is invoked for any
2704 * non-zero order, only frequent costly order
2705 * reclamation is disruptive enough to become a
2706 * noticeable problem, like transparent huge
2709 if (IS_ENABLED(CONFIG_COMPACTION) &&
2710 sc->order > PAGE_ALLOC_COSTLY_ORDER &&
2711 compaction_ready(zone, sc)) {
2712 sc->compaction_ready = true;
2717 * Shrink each node in the zonelist once. If the
2718 * zonelist is ordered by zone (not the default) then a
2719 * node may be shrunk multiple times but in that case
2720 * the user prefers lower zones being preserved.
2722 if (zone->zone_pgdat == last_pgdat)
2726 * This steals pages from memory cgroups over softlimit
2727 * and returns the number of reclaimed pages and
2728 * scanned pages. This works for global memory pressure
2729 * and balancing, not for a memcg's limit.
2731 nr_soft_scanned = 0;
2732 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone->zone_pgdat,
2733 sc->order, sc->gfp_mask,
2735 sc->nr_reclaimed += nr_soft_reclaimed;
2736 sc->nr_scanned += nr_soft_scanned;
2737 /* need some check for avoid more shrink_zone() */
2740 /* See comment about same check for global reclaim above */
2741 if (zone->zone_pgdat == last_pgdat)
2743 last_pgdat = zone->zone_pgdat;
2744 shrink_node(zone->zone_pgdat, sc);
2748 * Restore to original mask to avoid the impact on the caller if we
2749 * promoted it to __GFP_HIGHMEM.
2751 sc->gfp_mask = orig_mask;
2755 * This is the main entry point to direct page reclaim.
2757 * If a full scan of the inactive list fails to free enough memory then we
2758 * are "out of memory" and something needs to be killed.
2760 * If the caller is !__GFP_FS then the probability of a failure is reasonably
2761 * high - the zone may be full of dirty or under-writeback pages, which this
2762 * caller can't do much about. We kick the writeback threads and take explicit
2763 * naps in the hope that some of these pages can be written. But if the
2764 * allocating task holds filesystem locks which prevent writeout this might not
2765 * work, and the allocation attempt will fail.
2767 * returns: 0, if no pages reclaimed
2768 * else, the number of pages reclaimed
2770 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2771 struct scan_control *sc)
2773 int initial_priority = sc->priority;
2774 unsigned long total_scanned = 0;
2775 unsigned long writeback_threshold;
2777 delayacct_freepages_start();
2779 if (global_reclaim(sc))
2780 __count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
2783 vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
2786 shrink_zones(zonelist, sc);
2788 total_scanned += sc->nr_scanned;
2789 if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2792 if (sc->compaction_ready)
2796 * If we're getting trouble reclaiming, start doing
2797 * writepage even in laptop mode.
2799 if (sc->priority < DEF_PRIORITY - 2)
2800 sc->may_writepage = 1;
2803 * Try to write back as many pages as we just scanned. This
2804 * tends to cause slow streaming writers to write data to the
2805 * disk smoothly, at the dirtying rate, which is nice. But
2806 * that's undesirable in laptop mode, where we *want* lumpy
2807 * writeout. So in laptop mode, write out the whole world.
2809 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2810 if (total_scanned > writeback_threshold) {
2811 wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2812 WB_REASON_TRY_TO_FREE_PAGES);
2813 sc->may_writepage = 1;
2815 } while (--sc->priority >= 0);
2817 delayacct_freepages_end();
2819 if (sc->nr_reclaimed)
2820 return sc->nr_reclaimed;
2822 /* Aborted reclaim to try compaction? don't OOM, then */
2823 if (sc->compaction_ready)
2826 /* Untapped cgroup reserves? Don't OOM, retry. */
2827 if (!sc->may_thrash) {
2828 sc->priority = initial_priority;
2836 static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2839 unsigned long pfmemalloc_reserve = 0;
2840 unsigned long free_pages = 0;
2844 for (i = 0; i <= ZONE_NORMAL; i++) {
2845 zone = &pgdat->node_zones[i];
2846 if (!managed_zone(zone) ||
2847 pgdat_reclaimable_pages(pgdat) == 0)
2850 pfmemalloc_reserve += min_wmark_pages(zone);
2851 free_pages += zone_page_state(zone, NR_FREE_PAGES);
2854 /* If there are no reserves (unexpected config) then do not throttle */
2855 if (!pfmemalloc_reserve)
2858 wmark_ok = free_pages > pfmemalloc_reserve / 2;
2860 /* kswapd must be awake if processes are being throttled */
2861 if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2862 pgdat->kswapd_classzone_idx = min(pgdat->kswapd_classzone_idx,
2863 (enum zone_type)ZONE_NORMAL);
2864 wake_up_interruptible(&pgdat->kswapd_wait);
2871 * Throttle direct reclaimers if backing storage is backed by the network
2872 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
2873 * depleted. kswapd will continue to make progress and wake the processes
2874 * when the low watermark is reached.
2876 * Returns true if a fatal signal was delivered during throttling. If this
2877 * happens, the page allocator should not consider triggering the OOM killer.
2879 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2880 nodemask_t *nodemask)
2884 pg_data_t *pgdat = NULL;
2887 * Kernel threads should not be throttled as they may be indirectly
2888 * responsible for cleaning pages necessary for reclaim to make forward
2889 * progress. kjournald for example may enter direct reclaim while
2890 * committing a transaction where throttling it could forcing other
2891 * processes to block on log_wait_commit().
2893 if (current->flags & PF_KTHREAD)
2897 * If a fatal signal is pending, this process should not throttle.
2898 * It should return quickly so it can exit and free its memory
2900 if (fatal_signal_pending(current))
2904 * Check if the pfmemalloc reserves are ok by finding the first node
2905 * with a usable ZONE_NORMAL or lower zone. The expectation is that
2906 * GFP_KERNEL will be required for allocating network buffers when
2907 * swapping over the network so ZONE_HIGHMEM is unusable.
2909 * Throttling is based on the first usable node and throttled processes
2910 * wait on a queue until kswapd makes progress and wakes them. There
2911 * is an affinity then between processes waking up and where reclaim
2912 * progress has been made assuming the process wakes on the same node.
2913 * More importantly, processes running on remote nodes will not compete
2914 * for remote pfmemalloc reserves and processes on different nodes
2915 * should make reasonable progress.
2917 for_each_zone_zonelist_nodemask(zone, z, zonelist,
2918 gfp_zone(gfp_mask), nodemask) {
2919 if (zone_idx(zone) > ZONE_NORMAL)
2922 /* Throttle based on the first usable node */
2923 pgdat = zone->zone_pgdat;
2924 if (pfmemalloc_watermark_ok(pgdat))
2929 /* If no zone was usable by the allocation flags then do not throttle */
2933 /* Account for the throttling */
2934 count_vm_event(PGSCAN_DIRECT_THROTTLE);
2937 * If the caller cannot enter the filesystem, it's possible that it
2938 * is due to the caller holding an FS lock or performing a journal
2939 * transaction in the case of a filesystem like ext[3|4]. In this case,
2940 * it is not safe to block on pfmemalloc_wait as kswapd could be
2941 * blocked waiting on the same lock. Instead, throttle for up to a
2942 * second before continuing.
2944 if (!(gfp_mask & __GFP_FS)) {
2945 wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2946 pfmemalloc_watermark_ok(pgdat), HZ);
2951 /* Throttle until kswapd wakes the process */
2952 wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2953 pfmemalloc_watermark_ok(pgdat));
2956 if (fatal_signal_pending(current))
2963 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2964 gfp_t gfp_mask, nodemask_t *nodemask)
2966 unsigned long nr_reclaimed;
2967 struct scan_control sc = {
2968 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2969 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
2970 .reclaim_idx = gfp_zone(gfp_mask),
2972 .nodemask = nodemask,
2973 .priority = DEF_PRIORITY,
2974 .may_writepage = !laptop_mode,
2980 * Do not enter reclaim if fatal signal was delivered while throttled.
2981 * 1 is returned so that the page allocator does not OOM kill at this
2984 if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2987 trace_mm_vmscan_direct_reclaim_begin(order,
2992 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2994 trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2996 return nr_reclaimed;
3001 unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
3002 gfp_t gfp_mask, bool noswap,
3004 unsigned long *nr_scanned)
3006 struct scan_control sc = {
3007 .nr_to_reclaim = SWAP_CLUSTER_MAX,
3008 .target_mem_cgroup = memcg,
3009 .may_writepage = !laptop_mode,
3011 .reclaim_idx = MAX_NR_ZONES - 1,
3012 .may_swap = !noswap,
3014 unsigned long lru_pages;
3016 sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
3017 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
3019 trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
3025 * NOTE: Although we can get the priority field, using it
3026 * here is not a good idea, since it limits the pages we can scan.
3027 * if we don't reclaim here, the shrink_node from balance_pgdat
3028 * will pick up pages from other mem cgroup's as well. We hack
3029 * the priority and make it zero.
3031 shrink_node_memcg(pgdat, memcg, &sc, &lru_pages);
3033 trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
3035 *nr_scanned = sc.nr_scanned;
3036 return sc.nr_reclaimed;
3039 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
3040 unsigned long nr_pages,
3044 struct zonelist *zonelist;
3045 unsigned long nr_reclaimed;
3047 struct scan_control sc = {
3048 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3049 .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
3050 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
3051 .reclaim_idx = MAX_NR_ZONES - 1,
3052 .target_mem_cgroup = memcg,
3053 .priority = DEF_PRIORITY,
3054 .may_writepage = !laptop_mode,
3056 .may_swap = may_swap,
3060 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
3061 * take care of from where we get pages. So the node where we start the
3062 * scan does not need to be the current node.
3064 nid = mem_cgroup_select_victim_node(memcg);
3066 zonelist = &NODE_DATA(nid)->node_zonelists[ZONELIST_FALLBACK];
3068 trace_mm_vmscan_memcg_reclaim_begin(0,
3073 current->flags |= PF_MEMALLOC;
3074 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3075 current->flags &= ~PF_MEMALLOC;
3077 trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
3079 return nr_reclaimed;
3083 static void age_active_anon(struct pglist_data *pgdat,
3084 struct scan_control *sc)
3086 struct mem_cgroup *memcg;
3088 if (!total_swap_pages)
3091 memcg = mem_cgroup_iter(NULL, NULL, NULL);
3093 struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
3095 if (inactive_list_is_low(lruvec, false, sc))
3096 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
3097 sc, LRU_ACTIVE_ANON);
3099 memcg = mem_cgroup_iter(NULL, memcg, NULL);
3103 static bool zone_balanced(struct zone *zone, int order, int classzone_idx)
3105 unsigned long mark = high_wmark_pages(zone);
3107 if (!zone_watermark_ok_safe(zone, order, mark, classzone_idx))
3111 * If any eligible zone is balanced then the node is not considered
3112 * to be congested or dirty
3114 clear_bit(PGDAT_CONGESTED, &zone->zone_pgdat->flags);
3115 clear_bit(PGDAT_DIRTY, &zone->zone_pgdat->flags);
3121 * Prepare kswapd for sleeping. This verifies that there are no processes
3122 * waiting in throttle_direct_reclaim() and that watermarks have been met.
3124 * Returns true if kswapd is ready to sleep
3126 static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, int classzone_idx)
3131 * The throttled processes are normally woken up in balance_pgdat() as
3132 * soon as pfmemalloc_watermark_ok() is true. But there is a potential
3133 * race between when kswapd checks the watermarks and a process gets
3134 * throttled. There is also a potential race if processes get
3135 * throttled, kswapd wakes, a large process exits thereby balancing the
3136 * zones, which causes kswapd to exit balance_pgdat() before reaching
3137 * the wake up checks. If kswapd is going to sleep, no process should
3138 * be sleeping on pfmemalloc_wait, so wake them now if necessary. If
3139 * the wake up is premature, processes will wake kswapd and get
3140 * throttled again. The difference from wake ups in balance_pgdat() is
3141 * that here we are under prepare_to_wait().
3143 if (waitqueue_active(&pgdat->pfmemalloc_wait))
3144 wake_up_all(&pgdat->pfmemalloc_wait);
3146 for (i = 0; i <= classzone_idx; i++) {
3147 struct zone *zone = pgdat->node_zones + i;
3149 if (!managed_zone(zone))
3152 if (!zone_balanced(zone, order, classzone_idx))
3160 * kswapd shrinks a node of pages that are at or below the highest usable
3161 * zone that is currently unbalanced.
3163 * Returns true if kswapd scanned at least the requested number of pages to
3164 * reclaim or if the lack of progress was due to pages under writeback.
3165 * This is used to determine if the scanning priority needs to be raised.
3167 static bool kswapd_shrink_node(pg_data_t *pgdat,
3168 struct scan_control *sc)
3173 /* Reclaim a number of pages proportional to the number of zones */
3174 sc->nr_to_reclaim = 0;
3175 for (z = 0; z <= sc->reclaim_idx; z++) {
3176 zone = pgdat->node_zones + z;
3177 if (!managed_zone(zone))
3180 sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX);
3184 * Historically care was taken to put equal pressure on all zones but
3185 * now pressure is applied based on node LRU order.
3187 shrink_node(pgdat, sc);
3190 * Fragmentation may mean that the system cannot be rebalanced for
3191 * high-order allocations. If twice the allocation size has been
3192 * reclaimed then recheck watermarks only at order-0 to prevent
3193 * excessive reclaim. Assume that a process requested a high-order
3194 * can direct reclaim/compact.
3196 if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order))
3199 return sc->nr_scanned >= sc->nr_to_reclaim;
3203 * For kswapd, balance_pgdat() will reclaim pages across a node from zones
3204 * that are eligible for use by the caller until at least one zone is
3207 * Returns the order kswapd finished reclaiming at.
3209 * kswapd scans the zones in the highmem->normal->dma direction. It skips
3210 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
3211 * found to have free_pages <= high_wmark_pages(zone), any page is that zone
3212 * or lower is eligible for reclaim until at least one usable zone is
3215 static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
3218 unsigned long nr_soft_reclaimed;
3219 unsigned long nr_soft_scanned;
3221 struct scan_control sc = {
3222 .gfp_mask = GFP_KERNEL,
3224 .priority = DEF_PRIORITY,
3225 .may_writepage = !laptop_mode,
3229 count_vm_event(PAGEOUTRUN);
3232 bool raise_priority = true;
3234 sc.nr_reclaimed = 0;
3235 sc.reclaim_idx = classzone_idx;
3238 * If the number of buffer_heads exceeds the maximum allowed
3239 * then consider reclaiming from all zones. This has a dual
3240 * purpose -- on 64-bit systems it is expected that
3241 * buffer_heads are stripped during active rotation. On 32-bit
3242 * systems, highmem pages can pin lowmem memory and shrinking
3243 * buffers can relieve lowmem pressure. Reclaim may still not
3244 * go ahead if all eligible zones for the original allocation
3245 * request are balanced to avoid excessive reclaim from kswapd.
3247 if (buffer_heads_over_limit) {
3248 for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
3249 zone = pgdat->node_zones + i;
3250 if (!managed_zone(zone))
3259 * Only reclaim if there are no eligible zones. Check from
3260 * high to low zone as allocations prefer higher zones.
3261 * Scanning from low to high zone would allow congestion to be
3262 * cleared during a very small window when a small low
3263 * zone was balanced even under extreme pressure when the
3264 * overall node may be congested. Note that sc.reclaim_idx
3265 * is not used as buffer_heads_over_limit may have adjusted
3268 for (i = classzone_idx; i >= 0; i--) {
3269 zone = pgdat->node_zones + i;
3270 if (!managed_zone(zone))
3273 if (zone_balanced(zone, sc.order, classzone_idx))
3278 * Do some background aging of the anon list, to give
3279 * pages a chance to be referenced before reclaiming. All
3280 * pages are rotated regardless of classzone as this is
3281 * about consistent aging.
3283 age_active_anon(pgdat, &sc);
3286 * If we're getting trouble reclaiming, start doing writepage
3287 * even in laptop mode.
3289 if (sc.priority < DEF_PRIORITY - 2 || !pgdat_reclaimable(pgdat))
3290 sc.may_writepage = 1;
3292 /* Call soft limit reclaim before calling shrink_node. */
3294 nr_soft_scanned = 0;
3295 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(pgdat, sc.order,
3296 sc.gfp_mask, &nr_soft_scanned);
3297 sc.nr_reclaimed += nr_soft_reclaimed;
3300 * There should be no need to raise the scanning priority if
3301 * enough pages are already being scanned that that high
3302 * watermark would be met at 100% efficiency.
3304 if (kswapd_shrink_node(pgdat, &sc))
3305 raise_priority = false;
3308 * If the low watermark is met there is no need for processes
3309 * to be throttled on pfmemalloc_wait as they should not be
3310 * able to safely make forward progress. Wake them
3312 if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
3313 pfmemalloc_watermark_ok(pgdat))
3314 wake_up_all(&pgdat->pfmemalloc_wait);
3316 /* Check if kswapd should be suspending */
3317 if (try_to_freeze() || kthread_should_stop())
3321 * Raise priority if scanning rate is too low or there was no
3322 * progress in reclaiming pages
3324 if (raise_priority || !sc.nr_reclaimed)
3326 } while (sc.priority >= 1);
3330 * Return the order kswapd stopped reclaiming at as
3331 * prepare_kswapd_sleep() takes it into account. If another caller
3332 * entered the allocator slow path while kswapd was awake, order will
3333 * remain at the higher level.
3338 static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
3339 unsigned int classzone_idx)
3344 if (freezing(current) || kthread_should_stop())
3347 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3349 /* Try to sleep for a short interval */
3350 if (prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3352 * Compaction records what page blocks it recently failed to
3353 * isolate pages from and skips them in the future scanning.
3354 * When kswapd is going to sleep, it is reasonable to assume
3355 * that pages and compaction may succeed so reset the cache.
3357 reset_isolation_suitable(pgdat);
3360 * We have freed the memory, now we should compact it to make
3361 * allocation of the requested order possible.
3363 wakeup_kcompactd(pgdat, alloc_order, classzone_idx);
3365 remaining = schedule_timeout(HZ/10);
3368 * If woken prematurely then reset kswapd_classzone_idx and
3369 * order. The values will either be from a wakeup request or
3370 * the previous request that slept prematurely.
3373 pgdat->kswapd_classzone_idx = max(pgdat->kswapd_classzone_idx, classzone_idx);
3374 pgdat->kswapd_order = max(pgdat->kswapd_order, reclaim_order);
3377 finish_wait(&pgdat->kswapd_wait, &wait);
3378 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3382 * After a short sleep, check if it was a premature sleep. If not, then
3383 * go fully to sleep until explicitly woken up.
3386 prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3387 trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
3390 * vmstat counters are not perfectly accurate and the estimated
3391 * value for counters such as NR_FREE_PAGES can deviate from the
3392 * true value by nr_online_cpus * threshold. To avoid the zone
3393 * watermarks being breached while under pressure, we reduce the
3394 * per-cpu vmstat threshold while kswapd is awake and restore
3395 * them before going back to sleep.
3397 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
3399 if (!kthread_should_stop())
3402 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
3405 count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
3407 count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
3409 finish_wait(&pgdat->kswapd_wait, &wait);
3413 * The background pageout daemon, started as a kernel thread
3414 * from the init process.
3416 * This basically trickles out pages so that we have _some_
3417 * free memory available even if there is no other activity
3418 * that frees anything up. This is needed for things like routing
3419 * etc, where we otherwise might have all activity going on in
3420 * asynchronous contexts that cannot page things out.
3422 * If there are applications that are active memory-allocators
3423 * (most normal use), this basically shouldn't matter.
3425 static int kswapd(void *p)
3427 unsigned int alloc_order, reclaim_order, classzone_idx;
3428 pg_data_t *pgdat = (pg_data_t*)p;
3429 struct task_struct *tsk = current;
3431 struct reclaim_state reclaim_state = {
3432 .reclaimed_slab = 0,
3434 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
3436 lockdep_set_current_reclaim_state(GFP_KERNEL);
3438 if (!cpumask_empty(cpumask))
3439 set_cpus_allowed_ptr(tsk, cpumask);
3440 current->reclaim_state = &reclaim_state;
3443 * Tell the memory management that we're a "memory allocator",
3444 * and that if we need more memory we should get access to it
3445 * regardless (see "__alloc_pages()"). "kswapd" should
3446 * never get caught in the normal page freeing logic.
3448 * (Kswapd normally doesn't need memory anyway, but sometimes
3449 * you need a small amount of memory in order to be able to
3450 * page out something else, and this flag essentially protects
3451 * us from recursively trying to free more memory as we're
3452 * trying to free the first piece of memory in the first place).
3454 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
3457 pgdat->kswapd_order = alloc_order = reclaim_order = 0;
3458 pgdat->kswapd_classzone_idx = classzone_idx = 0;
3463 kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
3466 /* Read the new order and classzone_idx */
3467 alloc_order = reclaim_order = pgdat->kswapd_order;
3468 classzone_idx = pgdat->kswapd_classzone_idx;
3469 pgdat->kswapd_order = 0;
3470 pgdat->kswapd_classzone_idx = 0;
3472 ret = try_to_freeze();
3473 if (kthread_should_stop())
3477 * We can speed up thawing tasks if we don't call balance_pgdat
3478 * after returning from the refrigerator
3484 * Reclaim begins at the requested order but if a high-order
3485 * reclaim fails then kswapd falls back to reclaiming for
3486 * order-0. If that happens, kswapd will consider sleeping
3487 * for the order it finished reclaiming at (reclaim_order)
3488 * but kcompactd is woken to compact for the original
3489 * request (alloc_order).
3491 trace_mm_vmscan_kswapd_wake(pgdat->node_id, classzone_idx,
3493 reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx);
3494 if (reclaim_order < alloc_order)
3495 goto kswapd_try_sleep;
3497 alloc_order = reclaim_order = pgdat->kswapd_order;
3498 classzone_idx = pgdat->kswapd_classzone_idx;
3501 tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
3502 current->reclaim_state = NULL;
3503 lockdep_clear_current_reclaim_state();
3509 * A zone is low on free memory, so wake its kswapd task to service it.
3511 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
3516 if (!managed_zone(zone))
3519 if (!cpuset_zone_allowed(zone, GFP_KERNEL | __GFP_HARDWALL))
3521 pgdat = zone->zone_pgdat;
3522 pgdat->kswapd_classzone_idx = max(pgdat->kswapd_classzone_idx, classzone_idx);
3523 pgdat->kswapd_order = max(pgdat->kswapd_order, order);
3524 if (!waitqueue_active(&pgdat->kswapd_wait))
3527 /* Only wake kswapd if all zones are unbalanced */
3528 for (z = 0; z <= classzone_idx; z++) {
3529 zone = pgdat->node_zones + z;
3530 if (!managed_zone(zone))
3533 if (zone_balanced(zone, order, classzone_idx))
3537 trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3538 wake_up_interruptible(&pgdat->kswapd_wait);
3541 #ifdef CONFIG_HIBERNATION
3543 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3546 * Rather than trying to age LRUs the aim is to preserve the overall
3547 * LRU order by reclaiming preferentially
3548 * inactive > active > active referenced > active mapped
3550 unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3552 struct reclaim_state reclaim_state;
3553 struct scan_control sc = {
3554 .nr_to_reclaim = nr_to_reclaim,
3555 .gfp_mask = GFP_HIGHUSER_MOVABLE,
3556 .reclaim_idx = MAX_NR_ZONES - 1,
3557 .priority = DEF_PRIORITY,
3561 .hibernation_mode = 1,
3563 struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3564 struct task_struct *p = current;
3565 unsigned long nr_reclaimed;
3567 p->flags |= PF_MEMALLOC;
3568 lockdep_set_current_reclaim_state(sc.gfp_mask);
3569 reclaim_state.reclaimed_slab = 0;
3570 p->reclaim_state = &reclaim_state;
3572 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3574 p->reclaim_state = NULL;
3575 lockdep_clear_current_reclaim_state();
3576 p->flags &= ~PF_MEMALLOC;
3578 return nr_reclaimed;
3580 #endif /* CONFIG_HIBERNATION */
3582 /* It's optimal to keep kswapds on the same CPUs as their memory, but
3583 not required for correctness. So if the last cpu in a node goes
3584 away, we get changed to run anywhere: as the first one comes back,
3585 restore their cpu bindings. */
3586 static int kswapd_cpu_online(unsigned int cpu)
3590 for_each_node_state(nid, N_MEMORY) {
3591 pg_data_t *pgdat = NODE_DATA(nid);
3592 const struct cpumask *mask;
3594 mask = cpumask_of_node(pgdat->node_id);
3596 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3597 /* One of our CPUs online: restore mask */
3598 set_cpus_allowed_ptr(pgdat->kswapd, mask);
3604 * This kswapd start function will be called by init and node-hot-add.
3605 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3607 int kswapd_run(int nid)
3609 pg_data_t *pgdat = NODE_DATA(nid);
3615 pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3616 if (IS_ERR(pgdat->kswapd)) {
3617 /* failure at boot is fatal */
3618 BUG_ON(system_state == SYSTEM_BOOTING);
3619 pr_err("Failed to start kswapd on node %d\n", nid);
3620 ret = PTR_ERR(pgdat->kswapd);
3621 pgdat->kswapd = NULL;
3627 * Called by memory hotplug when all memory in a node is offlined. Caller must
3628 * hold mem_hotplug_begin/end().
3630 void kswapd_stop(int nid)
3632 struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3635 kthread_stop(kswapd);
3636 NODE_DATA(nid)->kswapd = NULL;
3640 static int __init kswapd_init(void)
3645 for_each_node_state(nid, N_MEMORY)
3647 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
3648 "mm/vmscan:online", kswapd_cpu_online,
3654 module_init(kswapd_init)
3660 * If non-zero call node_reclaim when the number of free pages falls below
3663 int node_reclaim_mode __read_mostly;
3665 #define RECLAIM_OFF 0
3666 #define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
3667 #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
3668 #define RECLAIM_UNMAP (1<<2) /* Unmap pages during reclaim */
3671 * Priority for NODE_RECLAIM. This determines the fraction of pages
3672 * of a node considered for each zone_reclaim. 4 scans 1/16th of
3675 #define NODE_RECLAIM_PRIORITY 4
3678 * Percentage of pages in a zone that must be unmapped for node_reclaim to
3681 int sysctl_min_unmapped_ratio = 1;
3684 * If the number of slab pages in a zone grows beyond this percentage then
3685 * slab reclaim needs to occur.
3687 int sysctl_min_slab_ratio = 5;
3689 static inline unsigned long node_unmapped_file_pages(struct pglist_data *pgdat)
3691 unsigned long file_mapped = node_page_state(pgdat, NR_FILE_MAPPED);
3692 unsigned long file_lru = node_page_state(pgdat, NR_INACTIVE_FILE) +
3693 node_page_state(pgdat, NR_ACTIVE_FILE);
3696 * It's possible for there to be more file mapped pages than
3697 * accounted for by the pages on the file LRU lists because
3698 * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3700 return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3703 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
3704 static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat)
3706 unsigned long nr_pagecache_reclaimable;
3707 unsigned long delta = 0;
3710 * If RECLAIM_UNMAP is set, then all file pages are considered
3711 * potentially reclaimable. Otherwise, we have to worry about
3712 * pages like swapcache and node_unmapped_file_pages() provides
3715 if (node_reclaim_mode & RECLAIM_UNMAP)
3716 nr_pagecache_reclaimable = node_page_state(pgdat, NR_FILE_PAGES);
3718 nr_pagecache_reclaimable = node_unmapped_file_pages(pgdat);
3720 /* If we can't clean pages, remove dirty pages from consideration */
3721 if (!(node_reclaim_mode & RECLAIM_WRITE))
3722 delta += node_page_state(pgdat, NR_FILE_DIRTY);
3724 /* Watch for any possible underflows due to delta */
3725 if (unlikely(delta > nr_pagecache_reclaimable))
3726 delta = nr_pagecache_reclaimable;
3728 return nr_pagecache_reclaimable - delta;
3732 * Try to free up some pages from this node through reclaim.
3734 static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
3736 /* Minimum pages needed in order to stay on node */
3737 const unsigned long nr_pages = 1 << order;
3738 struct task_struct *p = current;
3739 struct reclaim_state reclaim_state;
3740 int classzone_idx = gfp_zone(gfp_mask);
3741 struct scan_control sc = {
3742 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3743 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
3745 .priority = NODE_RECLAIM_PRIORITY,
3746 .may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
3747 .may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
3749 .reclaim_idx = classzone_idx,
3754 * We need to be able to allocate from the reserves for RECLAIM_UNMAP
3755 * and we also need to be able to write out pages for RECLAIM_WRITE
3756 * and RECLAIM_UNMAP.
3758 p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3759 lockdep_set_current_reclaim_state(gfp_mask);
3760 reclaim_state.reclaimed_slab = 0;
3761 p->reclaim_state = &reclaim_state;
3763 if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) {
3765 * Free memory by calling shrink zone with increasing
3766 * priorities until we have enough memory freed.
3769 shrink_node(pgdat, &sc);
3770 } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3773 p->reclaim_state = NULL;
3774 current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3775 lockdep_clear_current_reclaim_state();
3776 return sc.nr_reclaimed >= nr_pages;
3779 int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
3784 * Node reclaim reclaims unmapped file backed pages and
3785 * slab pages if we are over the defined limits.
3787 * A small portion of unmapped file backed pages is needed for
3788 * file I/O otherwise pages read by file I/O will be immediately
3789 * thrown out if the node is overallocated. So we do not reclaim
3790 * if less than a specified percentage of the node is used by
3791 * unmapped file backed pages.
3793 if (node_pagecache_reclaimable(pgdat) <= pgdat->min_unmapped_pages &&
3794 sum_zone_node_page_state(pgdat->node_id, NR_SLAB_RECLAIMABLE) <= pgdat->min_slab_pages)
3795 return NODE_RECLAIM_FULL;
3797 if (!pgdat_reclaimable(pgdat))
3798 return NODE_RECLAIM_FULL;
3801 * Do not scan if the allocation should not be delayed.
3803 if (!gfpflags_allow_blocking(gfp_mask) || (current->flags & PF_MEMALLOC))
3804 return NODE_RECLAIM_NOSCAN;
3807 * Only run node reclaim on the local node or on nodes that do not
3808 * have associated processors. This will favor the local processor
3809 * over remote processors and spread off node memory allocations
3810 * as wide as possible.
3812 if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
3813 return NODE_RECLAIM_NOSCAN;
3815 if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
3816 return NODE_RECLAIM_NOSCAN;
3818 ret = __node_reclaim(pgdat, gfp_mask, order);
3819 clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
3822 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3829 * page_evictable - test whether a page is evictable
3830 * @page: the page to test
3832 * Test whether page is evictable--i.e., should be placed on active/inactive
3833 * lists vs unevictable list.
3835 * Reasons page might not be evictable:
3836 * (1) page's mapping marked unevictable
3837 * (2) page is part of an mlocked VMA
3840 int page_evictable(struct page *page)
3842 return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
3847 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3848 * @pages: array of pages to check
3849 * @nr_pages: number of pages to check
3851 * Checks pages for evictability and moves them to the appropriate lru list.
3853 * This function is only used for SysV IPC SHM_UNLOCK.
3855 void check_move_unevictable_pages(struct page **pages, int nr_pages)
3857 struct lruvec *lruvec;
3858 struct pglist_data *pgdat = NULL;
3863 for (i = 0; i < nr_pages; i++) {
3864 struct page *page = pages[i];
3865 struct pglist_data *pagepgdat = page_pgdat(page);
3868 if (pagepgdat != pgdat) {
3870 spin_unlock_irq(&pgdat->lru_lock);
3872 spin_lock_irq(&pgdat->lru_lock);
3874 lruvec = mem_cgroup_page_lruvec(page, pgdat);
3876 if (!PageLRU(page) || !PageUnevictable(page))
3879 if (page_evictable(page)) {
3880 enum lru_list lru = page_lru_base_type(page);
3882 VM_BUG_ON_PAGE(PageActive(page), page);
3883 ClearPageUnevictable(page);
3884 del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3885 add_page_to_lru_list(page, lruvec, lru);
3891 __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3892 __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3893 spin_unlock_irq(&pgdat->lru_lock);
3896 #endif /* CONFIG_SHMEM */