1 /*
2 * linux/mm/vmscan.c
3 *
4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
5 *
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.
12 */
14 #include <linux/mm.h>
15 #include <linux/module.h>
16 #include <linux/gfp.h>
17 #include <linux/kernel_stat.h>
18 #include <linux/swap.h>
19 #include <linux/pagemap.h>
20 #include <linux/init.h>
21 #include <linux/highmem.h>
22 #include <linux/vmpressure.h>
23 #include <linux/vmstat.h>
24 #include <linux/file.h>
25 #include <linux/writeback.h>
26 #include <linux/blkdev.h>
27 #include <linux/buffer_head.h> /* for try_to_release_page(),
28 buffer_heads_over_limit */
29 #include <linux/mm_inline.h>
30 #include <linux/backing-dev.h>
31 #include <linux/rmap.h>
32 #include <linux/topology.h>
33 #include <linux/cpu.h>
34 #include <linux/cpuset.h>
35 #include <linux/compaction.h>
36 #include <linux/notifier.h>
37 #include <linux/rwsem.h>
38 #include <linux/delay.h>
39 #include <linux/kthread.h>
40 #include <linux/freezer.h>
41 #include <linux/memcontrol.h>
42 #include <linux/delayacct.h>
43 #include <linux/sysctl.h>
44 #include <linux/oom.h>
45 #include <linux/prefetch.h>
47 #include <asm/tlbflush.h>
48 #include <asm/div64.h>
50 #include <linux/swapops.h>
51 #include <linux/balloon_compaction.h>
53 #include "internal.h"
55 #define CREATE_TRACE_POINTS
56 #include <trace/events/vmscan.h>
58 struct scan_control {
59 /* Incremented by the number of inactive pages that were scanned */
60 unsigned long nr_scanned;
62 /* Number of pages freed so far during a call to shrink_zones() */
63 unsigned long nr_reclaimed;
65 /* How many pages shrink_list() should reclaim */
66 unsigned long nr_to_reclaim;
68 unsigned long hibernation_mode;
70 /* This context's GFP mask */
71 gfp_t gfp_mask;
73 int may_writepage;
75 /* Can mapped pages be reclaimed? */
76 int may_unmap;
78 /* Can pages be swapped as part of reclaim? */
79 int may_swap;
81 int order;
83 /* Scan (total_size >> priority) pages at once */
84 int priority;
86 /*
87 * The memory cgroup that hit its limit and as a result is the
88 * primary target of this reclaim invocation.
89 */
90 struct mem_cgroup *target_mem_cgroup;
92 /*
93 * Nodemask of nodes allowed by the caller. If NULL, all nodes
94 * are scanned.
95 */
96 nodemask_t *nodemask;
97 };
99 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
101 #ifdef ARCH_HAS_PREFETCH
102 #define prefetch_prev_lru_page(_page, _base, _field) \
103 do { \
104 if ((_page)->lru.prev != _base) { \
105 struct page *prev; \
106 \
107 prev = lru_to_page(&(_page->lru)); \
108 prefetch(&prev->_field); \
109 } \
110 } while (0)
111 #else
112 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
113 #endif
115 #ifdef ARCH_HAS_PREFETCHW
116 #define prefetchw_prev_lru_page(_page, _base, _field) \
117 do { \
118 if ((_page)->lru.prev != _base) { \
119 struct page *prev; \
120 \
121 prev = lru_to_page(&(_page->lru)); \
122 prefetchw(&prev->_field); \
123 } \
124 } while (0)
125 #else
126 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
127 #endif
129 /*
130 * From 0 .. 100. Higher means more swappy.
131 */
132 int vm_swappiness = 60;
133 unsigned long vm_total_pages; /* The total number of pages which the VM controls */
135 static LIST_HEAD(shrinker_list);
136 static DECLARE_RWSEM(shrinker_rwsem);
138 #ifdef CONFIG_MEMCG
139 static bool global_reclaim(struct scan_control *sc)
140 {
141 return !sc->target_mem_cgroup;
142 }
143 #else
144 static bool global_reclaim(struct scan_control *sc)
145 {
146 return true;
147 }
148 #endif
150 static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
151 {
152 if (!mem_cgroup_disabled())
153 return mem_cgroup_get_lru_size(lruvec, lru);
155 return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);
156 }
158 /*
159 * Add a shrinker callback to be called from the vm
160 */
161 void register_shrinker(struct shrinker *shrinker)
162 {
163 atomic_long_set(&shrinker->nr_in_batch, 0);
164 down_write(&shrinker_rwsem);
165 list_add_tail(&shrinker->list, &shrinker_list);
166 up_write(&shrinker_rwsem);
167 }
168 EXPORT_SYMBOL(register_shrinker);
170 /*
171 * Remove one
172 */
173 void unregister_shrinker(struct shrinker *shrinker)
174 {
175 down_write(&shrinker_rwsem);
176 list_del(&shrinker->list);
177 up_write(&shrinker_rwsem);
178 }
179 EXPORT_SYMBOL(unregister_shrinker);
181 static inline int do_shrinker_shrink(struct shrinker *shrinker,
182 struct shrink_control *sc,
183 unsigned long nr_to_scan)
184 {
185 sc->nr_to_scan = nr_to_scan;
186 return (*shrinker->shrink)(shrinker, sc);
187 }
189 #define SHRINK_BATCH 128
190 /*
191 * Call the shrink functions to age shrinkable caches
192 *
193 * Here we assume it costs one seek to replace a lru page and that it also
194 * takes a seek to recreate a cache object. With this in mind we age equal
195 * percentages of the lru and ageable caches. This should balance the seeks
196 * generated by these structures.
197 *
198 * If the vm encountered mapped pages on the LRU it increase the pressure on
199 * slab to avoid swapping.
200 *
201 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
202 *
203 * `lru_pages' represents the number of on-LRU pages in all the zones which
204 * are eligible for the caller's allocation attempt. It is used for balancing
205 * slab reclaim versus page reclaim.
206 *
207 * Returns the number of slab objects which we shrunk.
208 */
209 unsigned long shrink_slab(struct shrink_control *shrink,
210 unsigned long nr_pages_scanned,
211 unsigned long lru_pages)
212 {
213 struct shrinker *shrinker;
214 unsigned long ret = 0;
216 if (nr_pages_scanned == 0)
217 nr_pages_scanned = SWAP_CLUSTER_MAX;
219 if (!down_read_trylock(&shrinker_rwsem)) {
220 /* Assume we'll be able to shrink next time */
221 ret = 1;
222 goto out;
223 }
225 list_for_each_entry(shrinker, &shrinker_list, list) {
226 unsigned long long delta;
227 long total_scan;
228 long max_pass;
229 int shrink_ret = 0;
230 long nr;
231 long new_nr;
232 long batch_size = shrinker->batch ? shrinker->batch
233 : SHRINK_BATCH;
235 max_pass = do_shrinker_shrink(shrinker, shrink, 0);
236 if (max_pass <= 0)
237 continue;
239 /*
240 * copy the current shrinker scan count into a local variable
241 * and zero it so that other concurrent shrinker invocations
242 * don't also do this scanning work.
243 */
244 nr = atomic_long_xchg(&shrinker->nr_in_batch, 0);
246 total_scan = nr;
247 delta = (4 * nr_pages_scanned) / shrinker->seeks;
248 delta *= max_pass;
249 do_div(delta, lru_pages + 1);
250 total_scan += delta;
251 if (total_scan < 0) {
252 printk(KERN_ERR "shrink_slab: %pF negative objects to "
253 "delete nr=%ld\n",
254 shrinker->shrink, total_scan);
255 total_scan = max_pass;
256 }
258 /*
259 * We need to avoid excessive windup on filesystem shrinkers
260 * due to large numbers of GFP_NOFS allocations causing the
261 * shrinkers to return -1 all the time. This results in a large
262 * nr being built up so when a shrink that can do some work
263 * comes along it empties the entire cache due to nr >>>
264 * max_pass. This is bad for sustaining a working set in
265 * memory.
266 *
267 * Hence only allow the shrinker to scan the entire cache when
268 * a large delta change is calculated directly.
269 */
270 if (delta < max_pass / 4)
271 total_scan = min(total_scan, max_pass / 2);
273 /*
274 * Avoid risking looping forever due to too large nr value:
275 * never try to free more than twice the estimate number of
276 * freeable entries.
277 */
278 if (total_scan > max_pass * 2)
279 total_scan = max_pass * 2;
281 trace_mm_shrink_slab_start(shrinker, shrink, nr,
282 nr_pages_scanned, lru_pages,
283 max_pass, delta, total_scan);
285 while (total_scan >= batch_size) {
286 int nr_before;
288 nr_before = do_shrinker_shrink(shrinker, shrink, 0);
289 shrink_ret = do_shrinker_shrink(shrinker, shrink,
290 batch_size);
291 if (shrink_ret == -1)
292 break;
293 if (shrink_ret < nr_before)
294 ret += nr_before - shrink_ret;
295 count_vm_events(SLABS_SCANNED, batch_size);
296 total_scan -= batch_size;
298 cond_resched();
299 }
301 /*
302 * move the unused scan count back into the shrinker in a
303 * manner that handles concurrent updates. If we exhausted the
304 * scan, there is no need to do an update.
305 */
306 if (total_scan > 0)
307 new_nr = atomic_long_add_return(total_scan,
308 &shrinker->nr_in_batch);
309 else
310 new_nr = atomic_long_read(&shrinker->nr_in_batch);
312 trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
313 }
314 up_read(&shrinker_rwsem);
315 out:
316 cond_resched();
317 return ret;
318 }
320 static inline int is_page_cache_freeable(struct page *page)
321 {
322 /*
323 * A freeable page cache page is referenced only by the caller
324 * that isolated the page, the page cache radix tree and
325 * optional buffer heads at page->private.
326 */
327 return page_count(page) - page_has_private(page) == 2;
328 }
330 static int may_write_to_queue(struct backing_dev_info *bdi,
331 struct scan_control *sc)
332 {
333 if (current->flags & PF_SWAPWRITE)
334 return 1;
335 if (!bdi_write_congested(bdi))
336 return 1;
337 if (bdi == current->backing_dev_info)
338 return 1;
339 return 0;
340 }
342 /*
343 * We detected a synchronous write error writing a page out. Probably
344 * -ENOSPC. We need to propagate that into the address_space for a subsequent
345 * fsync(), msync() or close().
346 *
347 * The tricky part is that after writepage we cannot touch the mapping: nothing
348 * prevents it from being freed up. But we have a ref on the page and once
349 * that page is locked, the mapping is pinned.
350 *
351 * We're allowed to run sleeping lock_page() here because we know the caller has
352 * __GFP_FS.
353 */
354 static void handle_write_error(struct address_space *mapping,
355 struct page *page, int error)
356 {
357 lock_page(page);
358 if (page_mapping(page) == mapping)
359 mapping_set_error(mapping, error);
360 unlock_page(page);
361 }
363 /* possible outcome of pageout() */
364 typedef enum {
365 /* failed to write page out, page is locked */
366 PAGE_KEEP,
367 /* move page to the active list, page is locked */
368 PAGE_ACTIVATE,
369 /* page has been sent to the disk successfully, page is unlocked */
370 PAGE_SUCCESS,
371 /* page is clean and locked */
372 PAGE_CLEAN,
373 } pageout_t;
375 /*
376 * pageout is called by shrink_page_list() for each dirty page.
377 * Calls ->writepage().
378 */
379 static pageout_t pageout(struct page *page, struct address_space *mapping,
380 struct scan_control *sc)
381 {
382 /*
383 * If the page is dirty, only perform writeback if that write
384 * will be non-blocking. To prevent this allocation from being
385 * stalled by pagecache activity. But note that there may be
386 * stalls if we need to run get_block(). We could test
387 * PagePrivate for that.
388 *
389 * If this process is currently in __generic_file_aio_write() against
390 * this page's queue, we can perform writeback even if that
391 * will block.
392 *
393 * If the page is swapcache, write it back even if that would
394 * block, for some throttling. This happens by accident, because
395 * swap_backing_dev_info is bust: it doesn't reflect the
396 * congestion state of the swapdevs. Easy to fix, if needed.
397 */
398 if (!is_page_cache_freeable(page))
399 return PAGE_KEEP;
400 if (!mapping) {
401 /*
402 * Some data journaling orphaned pages can have
403 * page->mapping == NULL while being dirty with clean buffers.
404 */
405 if (page_has_private(page)) {
406 if (try_to_free_buffers(page)) {
407 ClearPageDirty(page);
408 printk("%s: orphaned page\n", __func__);
409 return PAGE_CLEAN;
410 }
411 }
412 return PAGE_KEEP;
413 }
414 if (mapping->a_ops->writepage == NULL)
415 return PAGE_ACTIVATE;
416 if (!may_write_to_queue(mapping->backing_dev_info, sc))
417 return PAGE_KEEP;
419 if (clear_page_dirty_for_io(page)) {
420 int res;
421 struct writeback_control wbc = {
422 .sync_mode = WB_SYNC_NONE,
423 .nr_to_write = SWAP_CLUSTER_MAX,
424 .range_start = 0,
425 .range_end = LLONG_MAX,
426 .for_reclaim = 1,
427 };
429 SetPageReclaim(page);
430 res = mapping->a_ops->writepage(page, &wbc);
431 if (res < 0)
432 handle_write_error(mapping, page, res);
433 if (res == AOP_WRITEPAGE_ACTIVATE) {
434 ClearPageReclaim(page);
435 return PAGE_ACTIVATE;
436 }
438 if (!PageWriteback(page)) {
439 /* synchronous write or broken a_ops? */
440 ClearPageReclaim(page);
441 }
442 trace_mm_vmscan_writepage(page, trace_reclaim_flags(page));
443 inc_zone_page_state(page, NR_VMSCAN_WRITE);
444 return PAGE_SUCCESS;
445 }
447 return PAGE_CLEAN;
448 }
450 /*
451 * Same as remove_mapping, but if the page is removed from the mapping, it
452 * gets returned with a refcount of 0.
453 */
454 static int __remove_mapping(struct address_space *mapping, struct page *page)
455 {
456 BUG_ON(!PageLocked(page));
457 BUG_ON(mapping != page_mapping(page));
459 spin_lock_irq(&mapping->tree_lock);
460 /*
461 * The non racy check for a busy page.
462 *
463 * Must be careful with the order of the tests. When someone has
464 * a ref to the page, it may be possible that they dirty it then
465 * drop the reference. So if PageDirty is tested before page_count
466 * here, then the following race may occur:
467 *
468 * get_user_pages(&page);
469 * [user mapping goes away]
470 * write_to(page);
471 * !PageDirty(page) [good]
472 * SetPageDirty(page);
473 * put_page(page);
474 * !page_count(page) [good, discard it]
475 *
476 * [oops, our write_to data is lost]
477 *
478 * Reversing the order of the tests ensures such a situation cannot
479 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
480 * load is not satisfied before that of page->_count.
481 *
482 * Note that if SetPageDirty is always performed via set_page_dirty,
483 * and thus under tree_lock, then this ordering is not required.
484 */
485 if (!page_freeze_refs(page, 2))
486 goto cannot_free;
487 /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
488 if (unlikely(PageDirty(page))) {
489 page_unfreeze_refs(page, 2);
490 goto cannot_free;
491 }
493 if (PageSwapCache(page)) {
494 swp_entry_t swap = { .val = page_private(page) };
495 __delete_from_swap_cache(page);
496 spin_unlock_irq(&mapping->tree_lock);
497 swapcache_free(swap, page);
498 } else {
499 void (*freepage)(struct page *);
501 freepage = mapping->a_ops->freepage;
503 __delete_from_page_cache(page);
504 spin_unlock_irq(&mapping->tree_lock);
505 mem_cgroup_uncharge_cache_page(page);
507 if (freepage != NULL)
508 freepage(page);
509 }
511 return 1;
513 cannot_free:
514 spin_unlock_irq(&mapping->tree_lock);
515 return 0;
516 }
518 /*
519 * Attempt to detach a locked page from its ->mapping. If it is dirty or if
520 * someone else has a ref on the page, abort and return 0. If it was
521 * successfully detached, return 1. Assumes the caller has a single ref on
522 * this page.
523 */
524 int remove_mapping(struct address_space *mapping, struct page *page)
525 {
526 if (__remove_mapping(mapping, page)) {
527 /*
528 * Unfreezing the refcount with 1 rather than 2 effectively
529 * drops the pagecache ref for us without requiring another
530 * atomic operation.
531 */
532 page_unfreeze_refs(page, 1);
533 return 1;
534 }
535 return 0;
536 }
538 /**
539 * putback_lru_page - put previously isolated page onto appropriate LRU list
540 * @page: page to be put back to appropriate lru list
541 *
542 * Add previously isolated @page to appropriate LRU list.
543 * Page may still be unevictable for other reasons.
544 *
545 * lru_lock must not be held, interrupts must be enabled.
546 */
547 void putback_lru_page(struct page *page)
548 {
549 int lru;
550 int active = !!TestClearPageActive(page);
551 int was_unevictable = PageUnevictable(page);
553 VM_BUG_ON(PageLRU(page));
555 redo:
556 ClearPageUnevictable(page);
558 if (page_evictable(page)) {
559 /*
560 * For evictable pages, we can use the cache.
561 * In event of a race, worst case is we end up with an
562 * unevictable page on [in]active list.
563 * We know how to handle that.
564 */
565 lru = active + page_lru_base_type(page);
566 lru_cache_add_lru(page, lru);
567 } else {
568 /*
569 * Put unevictable pages directly on zone's unevictable
570 * list.
571 */
572 lru = LRU_UNEVICTABLE;
573 add_page_to_unevictable_list(page);
574 /*
575 * When racing with an mlock or AS_UNEVICTABLE clearing
576 * (page is unlocked) make sure that if the other thread
577 * does not observe our setting of PG_lru and fails
578 * isolation/check_move_unevictable_pages,
579 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
580 * the page back to the evictable list.
581 *
582 * The other side is TestClearPageMlocked() or shmem_lock().
583 */
584 smp_mb();
585 }
587 /*
588 * page's status can change while we move it among lru. If an evictable
589 * page is on unevictable list, it never be freed. To avoid that,
590 * check after we added it to the list, again.
591 */
592 if (lru == LRU_UNEVICTABLE && page_evictable(page)) {
593 if (!isolate_lru_page(page)) {
594 put_page(page);
595 goto redo;
596 }
597 /* This means someone else dropped this page from LRU
598 * So, it will be freed or putback to LRU again. There is
599 * nothing to do here.
600 */
601 }
603 if (was_unevictable && lru != LRU_UNEVICTABLE)
604 count_vm_event(UNEVICTABLE_PGRESCUED);
605 else if (!was_unevictable && lru == LRU_UNEVICTABLE)
606 count_vm_event(UNEVICTABLE_PGCULLED);
608 put_page(page); /* drop ref from isolate */
609 }
611 enum page_references {
612 PAGEREF_RECLAIM,
613 PAGEREF_RECLAIM_CLEAN,
614 PAGEREF_KEEP,
615 PAGEREF_ACTIVATE,
616 };
618 static enum page_references page_check_references(struct page *page,
619 struct scan_control *sc)
620 {
621 int referenced_ptes, referenced_page;
622 unsigned long vm_flags;
624 referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
625 &vm_flags);
626 referenced_page = TestClearPageReferenced(page);
628 /*
629 * Mlock lost the isolation race with us. Let try_to_unmap()
630 * move the page to the unevictable list.
631 */
632 if (vm_flags & VM_LOCKED)
633 return PAGEREF_RECLAIM;
635 if (referenced_ptes) {
636 if (PageSwapBacked(page))
637 return PAGEREF_ACTIVATE;
638 /*
639 * All mapped pages start out with page table
640 * references from the instantiating fault, so we need
641 * to look twice if a mapped file page is used more
642 * than once.
643 *
644 * Mark it and spare it for another trip around the
645 * inactive list. Another page table reference will
646 * lead to its activation.
647 *
648 * Note: the mark is set for activated pages as well
649 * so that recently deactivated but used pages are
650 * quickly recovered.
651 */
652 SetPageReferenced(page);
654 if (referenced_page || referenced_ptes > 1)
655 return PAGEREF_ACTIVATE;
657 /*
658 * Activate file-backed executable pages after first usage.
659 */
660 if (vm_flags & VM_EXEC)
661 return PAGEREF_ACTIVATE;
663 return PAGEREF_KEEP;
664 }
666 /* Reclaim if clean, defer dirty pages to writeback */
667 if (referenced_page && !PageSwapBacked(page))
668 return PAGEREF_RECLAIM_CLEAN;
670 return PAGEREF_RECLAIM;
671 }
673 /*
674 * shrink_page_list() returns the number of reclaimed pages
675 */
676 static unsigned long shrink_page_list(struct list_head *page_list,
677 struct zone *zone,
678 struct scan_control *sc,
679 enum ttu_flags ttu_flags,
680 unsigned long *ret_nr_dirty,
681 unsigned long *ret_nr_writeback,
682 bool force_reclaim)
683 {
684 LIST_HEAD(ret_pages);
685 LIST_HEAD(free_pages);
686 int pgactivate = 0;
687 unsigned long nr_dirty = 0;
688 unsigned long nr_congested = 0;
689 unsigned long nr_reclaimed = 0;
690 unsigned long nr_writeback = 0;
692 cond_resched();
694 mem_cgroup_uncharge_start();
695 while (!list_empty(page_list)) {
696 struct address_space *mapping;
697 struct page *page;
698 int may_enter_fs;
699 enum page_references references = PAGEREF_RECLAIM_CLEAN;
701 cond_resched();
703 page = lru_to_page(page_list);
704 list_del(&page->lru);
706 if (!trylock_page(page))
707 goto keep;
709 VM_BUG_ON(PageActive(page));
710 VM_BUG_ON(page_zone(page) != zone);
712 sc->nr_scanned++;
714 if (unlikely(!page_evictable(page)))
715 goto cull_mlocked;
717 if (!sc->may_unmap && page_mapped(page))
718 goto keep_locked;
720 /* Double the slab pressure for mapped and swapcache pages */
721 if (page_mapped(page) || PageSwapCache(page))
722 sc->nr_scanned++;
724 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
725 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
727 if (PageWriteback(page)) {
728 /*
729 * memcg doesn't have any dirty pages throttling so we
730 * could easily OOM just because too many pages are in
731 * writeback and there is nothing else to reclaim.
732 *
733 * Check __GFP_IO, certainly because a loop driver
734 * thread might enter reclaim, and deadlock if it waits
735 * on a page for which it is needed to do the write
736 * (loop masks off __GFP_IO|__GFP_FS for this reason);
737 * but more thought would probably show more reasons.
738 *
739 * Don't require __GFP_FS, since we're not going into
740 * the FS, just waiting on its writeback completion.
741 * Worryingly, ext4 gfs2 and xfs allocate pages with
742 * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so
743 * testing may_enter_fs here is liable to OOM on them.
744 */
745 if (global_reclaim(sc) ||
746 !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
747 /*
748 * This is slightly racy - end_page_writeback()
749 * might have just cleared PageReclaim, then
750 * setting PageReclaim here end up interpreted
751 * as PageReadahead - but that does not matter
752 * enough to care. What we do want is for this
753 * page to have PageReclaim set next time memcg
754 * reclaim reaches the tests above, so it will
755 * then wait_on_page_writeback() to avoid OOM;
756 * and it's also appropriate in global reclaim.
757 */
758 SetPageReclaim(page);
759 nr_writeback++;
760 goto keep_locked;
761 }
762 wait_on_page_writeback(page);
763 }
765 if (!force_reclaim)
766 references = page_check_references(page, sc);
768 switch (references) {
769 case PAGEREF_ACTIVATE:
770 goto activate_locked;
771 case PAGEREF_KEEP:
772 goto keep_locked;
773 case PAGEREF_RECLAIM:
774 case PAGEREF_RECLAIM_CLEAN:
775 ; /* try to reclaim the page below */
776 }
778 /*
779 * Anonymous process memory has backing store?
780 * Try to allocate it some swap space here.
781 */
782 if (PageAnon(page) && !PageSwapCache(page)) {
783 if (!(sc->gfp_mask & __GFP_IO))
784 goto keep_locked;
785 if (!add_to_swap(page, page_list))
786 goto activate_locked;
787 may_enter_fs = 1;
788 }
790 mapping = page_mapping(page);
792 /*
793 * The page is mapped into the page tables of one or more
794 * processes. Try to unmap it here.
795 */
796 if (page_mapped(page) && mapping) {
797 switch (try_to_unmap(page, ttu_flags)) {
798 case SWAP_FAIL:
799 goto activate_locked;
800 case SWAP_AGAIN:
801 goto keep_locked;
802 case SWAP_MLOCK:
803 goto cull_mlocked;
804 case SWAP_SUCCESS:
805 ; /* try to free the page below */
806 }
807 }
809 if (PageDirty(page)) {
810 nr_dirty++;
812 /*
813 * Only kswapd can writeback filesystem pages to
814 * avoid risk of stack overflow but do not writeback
815 * unless under significant pressure.
816 */
817 if (page_is_file_cache(page) &&
818 (!current_is_kswapd() ||
819 sc->priority >= DEF_PRIORITY - 2)) {
820 /*
821 * Immediately reclaim when written back.
822 * Similar in principal to deactivate_page()
823 * except we already have the page isolated
824 * and know it's dirty
825 */
826 inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
827 SetPageReclaim(page);
829 goto keep_locked;
830 }
832 if (references == PAGEREF_RECLAIM_CLEAN)
833 goto keep_locked;
834 if (!may_enter_fs)
835 goto keep_locked;
836 if (!sc->may_writepage)
837 goto keep_locked;
839 /* Page is dirty, try to write it out here */
840 switch (pageout(page, mapping, sc)) {
841 case PAGE_KEEP:
842 nr_congested++;
843 goto keep_locked;
844 case PAGE_ACTIVATE:
845 goto activate_locked;
846 case PAGE_SUCCESS:
847 if (PageWriteback(page))
848 goto keep;
849 if (PageDirty(page))
850 goto keep;
852 /*
853 * A synchronous write - probably a ramdisk. Go
854 * ahead and try to reclaim the page.
855 */
856 if (!trylock_page(page))
857 goto keep;
858 if (PageDirty(page) || PageWriteback(page))
859 goto keep_locked;
860 mapping = page_mapping(page);
861 case PAGE_CLEAN:
862 ; /* try to free the page below */
863 }
864 }
866 /*
867 * If the page has buffers, try to free the buffer mappings
868 * associated with this page. If we succeed we try to free
869 * the page as well.
870 *
871 * We do this even if the page is PageDirty().
872 * try_to_release_page() does not perform I/O, but it is
873 * possible for a page to have PageDirty set, but it is actually
874 * clean (all its buffers are clean). This happens if the
875 * buffers were written out directly, with submit_bh(). ext3
876 * will do this, as well as the blockdev mapping.
877 * try_to_release_page() will discover that cleanness and will
878 * drop the buffers and mark the page clean - it can be freed.
879 *
880 * Rarely, pages can have buffers and no ->mapping. These are
881 * the pages which were not successfully invalidated in
882 * truncate_complete_page(). We try to drop those buffers here
883 * and if that worked, and the page is no longer mapped into
884 * process address space (page_count == 1) it can be freed.
885 * Otherwise, leave the page on the LRU so it is swappable.
886 */
887 if (page_has_private(page)) {
888 if (!try_to_release_page(page, sc->gfp_mask))
889 goto activate_locked;
890 if (!mapping && page_count(page) == 1) {
891 unlock_page(page);
892 if (put_page_testzero(page))
893 goto free_it;
894 else {
895 /*
896 * rare race with speculative reference.
897 * the speculative reference will free
898 * this page shortly, so we may
899 * increment nr_reclaimed here (and
900 * leave it off the LRU).
901 */
902 nr_reclaimed++;
903 continue;
904 }
905 }
906 }
908 if (!mapping || !__remove_mapping(mapping, page))
909 goto keep_locked;
911 /*
912 * At this point, we have no other references and there is
913 * no way to pick any more up (removed from LRU, removed
914 * from pagecache). Can use non-atomic bitops now (and
915 * we obviously don't have to worry about waking up a process
916 * waiting on the page lock, because there are no references.
917 */
918 __clear_page_locked(page);
919 free_it:
920 nr_reclaimed++;
922 /*
923 * Is there need to periodically free_page_list? It would
924 * appear not as the counts should be low
925 */
926 list_add(&page->lru, &free_pages);
927 continue;
929 cull_mlocked:
930 if (PageSwapCache(page))
931 try_to_free_swap(page);
932 unlock_page(page);
933 putback_lru_page(page);
934 continue;
936 activate_locked:
937 /* Not a candidate for swapping, so reclaim swap space. */
938 if (PageSwapCache(page) && vm_swap_full())
939 try_to_free_swap(page);
940 VM_BUG_ON(PageActive(page));
941 SetPageActive(page);
942 pgactivate++;
943 keep_locked:
944 unlock_page(page);
945 keep:
946 list_add(&page->lru, &ret_pages);
947 VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
948 }
950 /*
951 * Tag a zone as congested if all the dirty pages encountered were
952 * backed by a congested BDI. In this case, reclaimers should just
953 * back off and wait for congestion to clear because further reclaim
954 * will encounter the same problem
955 */
956 if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
957 zone_set_flag(zone, ZONE_CONGESTED);
959 free_hot_cold_page_list(&free_pages, 1);
961 list_splice(&ret_pages, page_list);
962 count_vm_events(PGACTIVATE, pgactivate);
963 mem_cgroup_uncharge_end();
964 *ret_nr_dirty += nr_dirty;
965 *ret_nr_writeback += nr_writeback;
966 return nr_reclaimed;
967 }
969 unsigned long reclaim_clean_pages_from_list(struct zone *zone,
970 struct list_head *page_list)
971 {
972 struct scan_control sc = {
973 .gfp_mask = GFP_KERNEL,
974 .priority = DEF_PRIORITY,
975 .may_unmap = 1,
976 };
977 unsigned long ret, dummy1, dummy2;
978 struct page *page, *next;
979 LIST_HEAD(clean_pages);
981 list_for_each_entry_safe(page, next, page_list, lru) {
982 if (page_is_file_cache(page) && !PageDirty(page) &&
983 !isolated_balloon_page(page)) {
984 ClearPageActive(page);
985 list_move(&page->lru, &clean_pages);
986 }
987 }
989 ret = shrink_page_list(&clean_pages, zone, &sc,
990 TTU_UNMAP|TTU_IGNORE_ACCESS,
991 &dummy1, &dummy2, true);
992 list_splice(&clean_pages, page_list);
993 __mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
994 return ret;
995 }
997 /*
998 * Attempt to remove the specified page from its LRU. Only take this page
999 * if it is of the appropriate PageActive status. Pages which are being
1000 * freed elsewhere are also ignored.
1001 *
1002 * page: page to consider
1003 * mode: one of the LRU isolation modes defined above
1004 *
1005 * returns 0 on success, -ve errno on failure.
1006 */
1007 int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1008 {
1009 int ret = -EINVAL;
1011 /* Only take pages on the LRU. */
1012 if (!PageLRU(page))
1013 return ret;
1015 /* Compaction should not handle unevictable pages but CMA can do so */
1016 if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1017 return ret;
1019 ret = -EBUSY;
1021 /*
1022 * To minimise LRU disruption, the caller can indicate that it only
1023 * wants to isolate pages it will be able to operate on without
1024 * blocking - clean pages for the most part.
1025 *
1026 * ISOLATE_CLEAN means that only clean pages should be isolated. This
1027 * is used by reclaim when it is cannot write to backing storage
1028 *
1029 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1030 * that it is possible to migrate without blocking
1031 */
1032 if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
1033 /* All the caller can do on PageWriteback is block */
1034 if (PageWriteback(page))
1035 return ret;
1037 if (PageDirty(page)) {
1038 struct address_space *mapping;
1040 /* ISOLATE_CLEAN means only clean pages */
1041 if (mode & ISOLATE_CLEAN)
1042 return ret;
1044 /*
1045 * Only pages without mappings or that have a
1046 * ->migratepage callback are possible to migrate
1047 * without blocking
1048 */
1049 mapping = page_mapping(page);
1050 if (mapping && !mapping->a_ops->migratepage)
1051 return ret;
1052 }
1053 }
1055 if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1056 return ret;
1058 if (likely(get_page_unless_zero(page))) {
1059 /*
1060 * Be careful not to clear PageLRU until after we're
1061 * sure the page is not being freed elsewhere -- the
1062 * page release code relies on it.
1063 */
1064 ClearPageLRU(page);
1065 ret = 0;
1066 }
1068 return ret;
1069 }
1071 /*
1072 * zone->lru_lock is heavily contended. Some of the functions that
1073 * shrink the lists perform better by taking out a batch of pages
1074 * and working on them outside the LRU lock.
1075 *
1076 * For pagecache intensive workloads, this function is the hottest
1077 * spot in the kernel (apart from copy_*_user functions).
1078 *
1079 * Appropriate locks must be held before calling this function.
1080 *
1081 * @nr_to_scan: The number of pages to look through on the list.
1082 * @lruvec: The LRU vector to pull pages from.
1083 * @dst: The temp list to put pages on to.
1084 * @nr_scanned: The number of pages that were scanned.
1085 * @sc: The scan_control struct for this reclaim session
1086 * @mode: One of the LRU isolation modes
1087 * @lru: LRU list id for isolating
1088 *
1089 * returns how many pages were moved onto *@dst.
1090 */
1091 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1092 struct lruvec *lruvec, struct list_head *dst,
1093 unsigned long *nr_scanned, struct scan_control *sc,
1094 isolate_mode_t mode, enum lru_list lru)
1095 {
1096 struct list_head *src = &lruvec->lists[lru];
1097 unsigned long nr_taken = 0;
1098 unsigned long scan;
1100 for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1101 struct page *page;
1102 int nr_pages;
1104 page = lru_to_page(src);
1105 prefetchw_prev_lru_page(page, src, flags);
1107 VM_BUG_ON(!PageLRU(page));
1109 switch (__isolate_lru_page(page, mode)) {
1110 case 0:
1111 nr_pages = hpage_nr_pages(page);
1112 mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
1113 list_move(&page->lru, dst);
1114 nr_taken += nr_pages;
1115 break;
1117 case -EBUSY:
1118 /* else it is being freed elsewhere */
1119 list_move(&page->lru, src);
1120 continue;
1122 default:
1123 BUG();
1124 }
1125 }
1127 *nr_scanned = scan;
1128 trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
1129 nr_taken, mode, is_file_lru(lru));
1130 return nr_taken;
1131 }
1133 /**
1134 * isolate_lru_page - tries to isolate a page from its LRU list
1135 * @page: page to isolate from its LRU list
1136 *
1137 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1138 * vmstat statistic corresponding to whatever LRU list the page was on.
1139 *
1140 * Returns 0 if the page was removed from an LRU list.
1141 * Returns -EBUSY if the page was not on an LRU list.
1142 *
1143 * The returned page will have PageLRU() cleared. If it was found on
1144 * the active list, it will have PageActive set. If it was found on
1145 * the unevictable list, it will have the PageUnevictable bit set. That flag
1146 * may need to be cleared by the caller before letting the page go.
1147 *
1148 * The vmstat statistic corresponding to the list on which the page was
1149 * found will be decremented.
1150 *
1151 * Restrictions:
1152 * (1) Must be called with an elevated refcount on the page. This is a
1153 * fundamentnal difference from isolate_lru_pages (which is called
1154 * without a stable reference).
1155 * (2) the lru_lock must not be held.
1156 * (3) interrupts must be enabled.
1157 */
1158 int isolate_lru_page(struct page *page)
1159 {
1160 int ret = -EBUSY;
1162 VM_BUG_ON(!page_count(page));
1164 if (PageLRU(page)) {
1165 struct zone *zone = page_zone(page);
1166 struct lruvec *lruvec;
1168 spin_lock_irq(&zone->lru_lock);
1169 lruvec = mem_cgroup_page_lruvec(page, zone);
1170 if (PageLRU(page)) {
1171 int lru = page_lru(page);
1172 get_page(page);
1173 ClearPageLRU(page);
1174 del_page_from_lru_list(page, lruvec, lru);
1175 ret = 0;
1176 }
1177 spin_unlock_irq(&zone->lru_lock);
1178 }
1179 return ret;
1180 }
1182 /*
1183 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
1184 * then get resheduled. When there are massive number of tasks doing page
1185 * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
1186 * the LRU list will go small and be scanned faster than necessary, leading to
1187 * unnecessary swapping, thrashing and OOM.
1188 */
1189 static int too_many_isolated(struct zone *zone, int file,
1190 struct scan_control *sc)
1191 {
1192 unsigned long inactive, isolated;
1194 if (current_is_kswapd())
1195 return 0;
1197 if (!global_reclaim(sc))
1198 return 0;
1200 if (file) {
1201 inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1202 isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1203 } else {
1204 inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1205 isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1206 }
1208 /*
1209 * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
1210 * won't get blocked by normal direct-reclaimers, forming a circular
1211 * deadlock.
1212 */
1213 if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS)
1214 inactive >>= 3;
1216 return isolated > inactive;
1217 }
1219 static noinline_for_stack void
1220 putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1221 {
1222 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1223 struct zone *zone = lruvec_zone(lruvec);
1224 LIST_HEAD(pages_to_free);
1226 /*
1227 * Put back any unfreeable pages.
1228 */
1229 while (!list_empty(page_list)) {
1230 struct page *page = lru_to_page(page_list);
1231 int lru;
1233 VM_BUG_ON(PageLRU(page));
1234 list_del(&page->lru);
1235 if (unlikely(!page_evictable(page))) {
1236 spin_unlock_irq(&zone->lru_lock);
1237 putback_lru_page(page);
1238 spin_lock_irq(&zone->lru_lock);
1239 continue;
1240 }
1242 lruvec = mem_cgroup_page_lruvec(page, zone);
1244 SetPageLRU(page);
1245 lru = page_lru(page);
1246 add_page_to_lru_list(page, lruvec, lru);
1248 if (is_active_lru(lru)) {
1249 int file = is_file_lru(lru);
1250 int numpages = hpage_nr_pages(page);
1251 reclaim_stat->recent_rotated[file] += numpages;
1252 }
1253 if (put_page_testzero(page)) {
1254 __ClearPageLRU(page);
1255 __ClearPageActive(page);
1256 del_page_from_lru_list(page, lruvec, lru);
1258 if (unlikely(PageCompound(page))) {
1259 spin_unlock_irq(&zone->lru_lock);
1260 (*get_compound_page_dtor(page))(page);
1261 spin_lock_irq(&zone->lru_lock);
1262 } else
1263 list_add(&page->lru, &pages_to_free);
1264 }
1265 }
1267 /*
1268 * To save our caller's stack, now use input list for pages to free.
1269 */
1270 list_splice(&pages_to_free, page_list);
1271 }
1273 /*
1274 * shrink_inactive_list() is a helper for shrink_zone(). It returns the number
1275 * of reclaimed pages
1276 */
1277 static noinline_for_stack unsigned long
1278 shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1279 struct scan_control *sc, enum lru_list lru)
1280 {
1281 LIST_HEAD(page_list);
1282 unsigned long nr_scanned;
1283 unsigned long nr_reclaimed = 0;
1284 unsigned long nr_taken;
1285 unsigned long nr_dirty = 0;
1286 unsigned long nr_writeback = 0;
1287 isolate_mode_t isolate_mode = 0;
1288 int file = is_file_lru(lru);
1289 struct zone *zone = lruvec_zone(lruvec);
1290 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1292 while (unlikely(too_many_isolated(zone, file, sc))) {
1293 congestion_wait(BLK_RW_ASYNC, HZ/10);
1295 /* We are about to die and free our memory. Return now. */
1296 if (fatal_signal_pending(current))
1297 return SWAP_CLUSTER_MAX;
1298 }
1300 lru_add_drain();
1302 if (!sc->may_unmap)
1303 isolate_mode |= ISOLATE_UNMAPPED;
1304 if (!sc->may_writepage)
1305 isolate_mode |= ISOLATE_CLEAN;
1307 spin_lock_irq(&zone->lru_lock);
1309 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1310 &nr_scanned, sc, isolate_mode, lru);
1312 __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1313 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1315 if (global_reclaim(sc)) {
1316 zone->pages_scanned += nr_scanned;
1317 if (current_is_kswapd())
1318 __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1319 else
1320 __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1321 }
1322 spin_unlock_irq(&zone->lru_lock);
1324 if (nr_taken == 0)
1325 return 0;
1327 nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
1328 &nr_dirty, &nr_writeback, false);
1330 spin_lock_irq(&zone->lru_lock);
1332 reclaim_stat->recent_scanned[file] += nr_taken;
1334 if (global_reclaim(sc)) {
1335 if (current_is_kswapd())
1336 __count_zone_vm_events(PGSTEAL_KSWAPD, zone,
1337 nr_reclaimed);
1338 else
1339 __count_zone_vm_events(PGSTEAL_DIRECT, zone,
1340 nr_reclaimed);
1341 }
1343 putback_inactive_pages(lruvec, &page_list);
1345 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1347 spin_unlock_irq(&zone->lru_lock);
1349 free_hot_cold_page_list(&page_list, 1);
1351 /*
1352 * If reclaim is isolating dirty pages under writeback, it implies
1353 * that the long-lived page allocation rate is exceeding the page
1354 * laundering rate. Either the global limits are not being effective
1355 * at throttling processes due to the page distribution throughout
1356 * zones or there is heavy usage of a slow backing device. The
1357 * only option is to throttle from reclaim context which is not ideal
1358 * as there is no guarantee the dirtying process is throttled in the
1359 * same way balance_dirty_pages() manages.
1360 *
1361 * This scales the number of dirty pages that must be under writeback
1362 * before throttling depending on priority. It is a simple backoff
1363 * function that has the most effect in the range DEF_PRIORITY to
1364 * DEF_PRIORITY-2 which is the priority reclaim is considered to be
1365 * in trouble and reclaim is considered to be in trouble.
1366 *
1367 * DEF_PRIORITY 100% isolated pages must be PageWriteback to throttle
1368 * DEF_PRIORITY-1 50% must be PageWriteback
1369 * DEF_PRIORITY-2 25% must be PageWriteback, kswapd in trouble
1370 * ...
1371 * DEF_PRIORITY-6 For SWAP_CLUSTER_MAX isolated pages, throttle if any
1372 * isolated page is PageWriteback
1373 */
1374 if (nr_writeback && nr_writeback >=
1375 (nr_taken >> (DEF_PRIORITY - sc->priority)))
1376 wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
1378 trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1379 zone_idx(zone),
1380 nr_scanned, nr_reclaimed,
1381 sc->priority,
1382 trace_shrink_flags(file));
1383 return nr_reclaimed;
1384 }
1386 /*
1387 * This moves pages from the active list to the inactive list.
1388 *
1389 * We move them the other way if the page is referenced by one or more
1390 * processes, from rmap.
1391 *
1392 * If the pages are mostly unmapped, the processing is fast and it is
1393 * appropriate to hold zone->lru_lock across the whole operation. But if
1394 * the pages are mapped, the processing is slow (page_referenced()) so we
1395 * should drop zone->lru_lock around each page. It's impossible to balance
1396 * this, so instead we remove the pages from the LRU while processing them.
1397 * It is safe to rely on PG_active against the non-LRU pages in here because
1398 * nobody will play with that bit on a non-LRU page.
1399 *
1400 * The downside is that we have to touch page->_count against each page.
1401 * But we had to alter page->flags anyway.
1402 */
1404 static void move_active_pages_to_lru(struct lruvec *lruvec,
1405 struct list_head *list,
1406 struct list_head *pages_to_free,
1407 enum lru_list lru)
1408 {
1409 struct zone *zone = lruvec_zone(lruvec);
1410 unsigned long pgmoved = 0;
1411 struct page *page;
1412 int nr_pages;
1414 while (!list_empty(list)) {
1415 page = lru_to_page(list);
1416 lruvec = mem_cgroup_page_lruvec(page, zone);
1418 VM_BUG_ON(PageLRU(page));
1419 SetPageLRU(page);
1421 nr_pages = hpage_nr_pages(page);
1422 mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1423 list_move(&page->lru, &lruvec->lists[lru]);
1424 pgmoved += nr_pages;
1426 if (put_page_testzero(page)) {
1427 __ClearPageLRU(page);
1428 __ClearPageActive(page);
1429 del_page_from_lru_list(page, lruvec, lru);
1431 if (unlikely(PageCompound(page))) {
1432 spin_unlock_irq(&zone->lru_lock);
1433 (*get_compound_page_dtor(page))(page);
1434 spin_lock_irq(&zone->lru_lock);
1435 } else
1436 list_add(&page->lru, pages_to_free);
1437 }
1438 }
1439 __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1440 if (!is_active_lru(lru))
1441 __count_vm_events(PGDEACTIVATE, pgmoved);
1442 }
1444 static void shrink_active_list(unsigned long nr_to_scan,
1445 struct lruvec *lruvec,
1446 struct scan_control *sc,
1447 enum lru_list lru)
1448 {
1449 unsigned long nr_taken;
1450 unsigned long nr_scanned;
1451 unsigned long vm_flags;
1452 LIST_HEAD(l_hold); /* The pages which were snipped off */
1453 LIST_HEAD(l_active);
1454 LIST_HEAD(l_inactive);
1455 struct page *page;
1456 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1457 unsigned long nr_rotated = 0;
1458 isolate_mode_t isolate_mode = 0;
1459 int file = is_file_lru(lru);
1460 struct zone *zone = lruvec_zone(lruvec);
1462 lru_add_drain();
1464 if (!sc->may_unmap)
1465 isolate_mode |= ISOLATE_UNMAPPED;
1466 if (!sc->may_writepage)
1467 isolate_mode |= ISOLATE_CLEAN;
1469 spin_lock_irq(&zone->lru_lock);
1471 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1472 &nr_scanned, sc, isolate_mode, lru);
1473 if (global_reclaim(sc))
1474 zone->pages_scanned += nr_scanned;
1476 reclaim_stat->recent_scanned[file] += nr_taken;
1478 __count_zone_vm_events(PGREFILL, zone, nr_scanned);
1479 __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1480 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1481 spin_unlock_irq(&zone->lru_lock);
1483 while (!list_empty(&l_hold)) {
1484 cond_resched();
1485 page = lru_to_page(&l_hold);
1486 list_del(&page->lru);
1488 if (unlikely(!page_evictable(page))) {
1489 putback_lru_page(page);
1490 continue;
1491 }
1493 if (unlikely(buffer_heads_over_limit)) {
1494 if (page_has_private(page) && trylock_page(page)) {
1495 if (page_has_private(page))
1496 try_to_release_page(page, 0);
1497 unlock_page(page);
1498 }
1499 }
1501 if (page_referenced(page, 0, sc->target_mem_cgroup,
1502 &vm_flags)) {
1503 nr_rotated += hpage_nr_pages(page);
1504 /*
1505 * Identify referenced, file-backed active pages and
1506 * give them one more trip around the active list. So
1507 * that executable code get better chances to stay in
1508 * memory under moderate memory pressure. Anon pages
1509 * are not likely to be evicted by use-once streaming
1510 * IO, plus JVM can create lots of anon VM_EXEC pages,
1511 * so we ignore them here.
1512 */
1513 if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1514 list_add(&page->lru, &l_active);
1515 continue;
1516 }
1517 }
1519 ClearPageActive(page); /* we are de-activating */
1520 list_add(&page->lru, &l_inactive);
1521 }
1523 /*
1524 * Move pages back to the lru list.
1525 */
1526 spin_lock_irq(&zone->lru_lock);
1527 /*
1528 * Count referenced pages from currently used mappings as rotated,
1529 * even though only some of them are actually re-activated. This
1530 * helps balance scan pressure between file and anonymous pages in
1531 * get_scan_ratio.
1532 */
1533 reclaim_stat->recent_rotated[file] += nr_rotated;
1535 move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1536 move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1537 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1538 spin_unlock_irq(&zone->lru_lock);
1540 free_hot_cold_page_list(&l_hold, 1);
1541 }
1543 #ifdef CONFIG_SWAP
1544 static int inactive_anon_is_low_global(struct zone *zone)
1545 {
1546 unsigned long active, inactive;
1548 active = zone_page_state(zone, NR_ACTIVE_ANON);
1549 inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1551 if (inactive * zone->inactive_ratio < active)
1552 return 1;
1554 return 0;
1555 }
1557 /**
1558 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1559 * @lruvec: LRU vector to check
1560 *
1561 * Returns true if the zone does not have enough inactive anon pages,
1562 * meaning some active anon pages need to be deactivated.
1563 */
1564 static int inactive_anon_is_low(struct lruvec *lruvec)
1565 {
1566 /*
1567 * If we don't have swap space, anonymous page deactivation
1568 * is pointless.
1569 */
1570 if (!total_swap_pages)
1571 return 0;
1573 if (!mem_cgroup_disabled())
1574 return mem_cgroup_inactive_anon_is_low(lruvec);
1576 return inactive_anon_is_low_global(lruvec_zone(lruvec));
1577 }
1578 #else
1579 static inline int inactive_anon_is_low(struct lruvec *lruvec)
1580 {
1581 return 0;
1582 }
1583 #endif
1585 /**
1586 * inactive_file_is_low - check if file pages need to be deactivated
1587 * @lruvec: LRU vector to check
1588 *
1589 * When the system is doing streaming IO, memory pressure here
1590 * ensures that active file pages get deactivated, until more
1591 * than half of the file pages are on the inactive list.
1592 *
1593 * Once we get to that situation, protect the system's working
1594 * set from being evicted by disabling active file page aging.
1595 *
1596 * This uses a different ratio than the anonymous pages, because
1597 * the page cache uses a use-once replacement algorithm.
1598 */
1599 static int inactive_file_is_low(struct lruvec *lruvec)
1600 {
1601 unsigned long inactive;
1602 unsigned long active;
1604 inactive = get_lru_size(lruvec, LRU_INACTIVE_FILE);
1605 active = get_lru_size(lruvec, LRU_ACTIVE_FILE);
1607 return active > inactive;
1608 }
1610 static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1611 {
1612 if (is_file_lru(lru))
1613 return inactive_file_is_low(lruvec);
1614 else
1615 return inactive_anon_is_low(lruvec);
1616 }
1618 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1619 struct lruvec *lruvec, struct scan_control *sc)
1620 {
1621 if (is_active_lru(lru)) {
1622 if (inactive_list_is_low(lruvec, lru))
1623 shrink_active_list(nr_to_scan, lruvec, sc, lru);
1624 return 0;
1625 }
1627 return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1628 }
1630 static int vmscan_swappiness(struct scan_control *sc)
1631 {
1632 if (global_reclaim(sc))
1633 return vm_swappiness;
1634 return mem_cgroup_swappiness(sc->target_mem_cgroup);
1635 }
1637 enum scan_balance {
1638 SCAN_EQUAL,
1639 SCAN_FRACT,
1640 SCAN_ANON,
1641 SCAN_FILE,
1642 };
1644 /*
1645 * Determine how aggressively the anon and file LRU lists should be
1646 * scanned. The relative value of each set of LRU lists is determined
1647 * by looking at the fraction of the pages scanned we did rotate back
1648 * onto the active list instead of evict.
1649 *
1650 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
1651 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
1652 */
1653 static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
1654 unsigned long *nr)
1655 {
1656 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1657 u64 fraction[2];
1658 u64 denominator = 0; /* gcc */
1659 struct zone *zone = lruvec_zone(lruvec);
1660 unsigned long anon_prio, file_prio;
1661 enum scan_balance scan_balance;
1662 unsigned long anon, file, free;
1663 bool force_scan = false;
1664 unsigned long ap, fp;
1665 enum lru_list lru;
1667 /*
1668 * If the zone or memcg is small, nr[l] can be 0. This
1669 * results in no scanning on this priority and a potential
1670 * priority drop. Global direct reclaim can go to the next
1671 * zone and tends to have no problems. Global kswapd is for
1672 * zone balancing and it needs to scan a minimum amount. When
1673 * reclaiming for a memcg, a priority drop can cause high
1674 * latencies, so it's better to scan a minimum amount there as
1675 * well.
1676 */
1677 if (current_is_kswapd() && zone->all_unreclaimable)
1678 force_scan = true;
1679 if (!global_reclaim(sc))
1680 force_scan = true;
1682 /* If we have no swap space, do not bother scanning anon pages. */
1683 if (!sc->may_swap || (get_nr_swap_pages() <= 0)) {
1684 scan_balance = SCAN_FILE;
1685 goto out;
1686 }
1688 /*
1689 * Global reclaim will swap to prevent OOM even with no
1690 * swappiness, but memcg users want to use this knob to
1691 * disable swapping for individual groups completely when
1692 * using the memory controller's swap limit feature would be
1693 * too expensive.
1694 */
1695 if (!global_reclaim(sc) && !vmscan_swappiness(sc)) {
1696 scan_balance = SCAN_FILE;
1697 goto out;
1698 }
1700 /*
1701 * Do not apply any pressure balancing cleverness when the
1702 * system is close to OOM, scan both anon and file equally
1703 * (unless the swappiness setting disagrees with swapping).
1704 */
1705 if (!sc->priority && vmscan_swappiness(sc)) {
1706 scan_balance = SCAN_EQUAL;
1707 goto out;
1708 }
1710 anon = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
1711 get_lru_size(lruvec, LRU_INACTIVE_ANON);
1712 file = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
1713 get_lru_size(lruvec, LRU_INACTIVE_FILE);
1715 /*
1716 * If it's foreseeable that reclaiming the file cache won't be
1717 * enough to get the zone back into a desirable shape, we have
1718 * to swap. Better start now and leave the - probably heavily
1719 * thrashing - remaining file pages alone.
1720 */
1721 if (global_reclaim(sc)) {
1722 free = zone_page_state(zone, NR_FREE_PAGES);
1723 if (unlikely(file + free <= high_wmark_pages(zone))) {
1724 scan_balance = SCAN_ANON;
1725 goto out;
1726 }
1727 }
1729 /*
1730 * There is enough inactive page cache, do not reclaim
1731 * anything from the anonymous working set right now.
1732 */
1733 if (!inactive_file_is_low(lruvec)) {
1734 scan_balance = SCAN_FILE;
1735 goto out;
1736 }
1738 scan_balance = SCAN_FRACT;
1740 /*
1741 * With swappiness at 100, anonymous and file have the same priority.
1742 * This scanning priority is essentially the inverse of IO cost.
1743 */
1744 anon_prio = vmscan_swappiness(sc);
1745 file_prio = 200 - anon_prio;
1747 /*
1748 * OK, so we have swap space and a fair amount of page cache
1749 * pages. We use the recently rotated / recently scanned
1750 * ratios to determine how valuable each cache is.
1751 *
1752 * Because workloads change over time (and to avoid overflow)
1753 * we keep these statistics as a floating average, which ends
1754 * up weighing recent references more than old ones.
1755 *
1756 * anon in [0], file in [1]
1757 */
1758 spin_lock_irq(&zone->lru_lock);
1759 if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1760 reclaim_stat->recent_scanned[0] /= 2;
1761 reclaim_stat->recent_rotated[0] /= 2;
1762 }
1764 if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1765 reclaim_stat->recent_scanned[1] /= 2;
1766 reclaim_stat->recent_rotated[1] /= 2;
1767 }
1769 /*
1770 * The amount of pressure on anon vs file pages is inversely
1771 * proportional to the fraction of recently scanned pages on
1772 * each list that were recently referenced and in active use.
1773 */
1774 ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1775 ap /= reclaim_stat->recent_rotated[0] + 1;
1777 fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
1778 fp /= reclaim_stat->recent_rotated[1] + 1;
1779 spin_unlock_irq(&zone->lru_lock);
1781 fraction[0] = ap;
1782 fraction[1] = fp;
1783 denominator = ap + fp + 1;
1784 out:
1785 for_each_evictable_lru(lru) {
1786 int file = is_file_lru(lru);
1787 unsigned long size;
1788 unsigned long scan;
1790 size = get_lru_size(lruvec, lru);
1791 scan = size >> sc->priority;
1793 if (!scan && force_scan)
1794 scan = min(size, SWAP_CLUSTER_MAX);
1796 switch (scan_balance) {
1797 case SCAN_EQUAL:
1798 /* Scan lists relative to size */
1799 break;
1800 case SCAN_FRACT:
1801 /*
1802 * Scan types proportional to swappiness and
1803 * their relative recent reclaim efficiency.
1804 */
1805 scan = div64_u64(scan * fraction[file], denominator);
1806 break;
1807 case SCAN_FILE:
1808 case SCAN_ANON:
1809 /* Scan one type exclusively */
1810 if ((scan_balance == SCAN_FILE) != file)
1811 scan = 0;
1812 break;
1813 default:
1814 /* Look ma, no brain */
1815 BUG();
1816 }
1817 nr[lru] = scan;
1818 }
1819 }
1821 /*
1822 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
1823 */
1824 static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
1825 {
1826 unsigned long nr[NR_LRU_LISTS];
1827 unsigned long nr_to_scan;
1828 enum lru_list lru;
1829 unsigned long nr_reclaimed = 0;
1830 unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1831 struct blk_plug plug;
1833 get_scan_count(lruvec, sc, nr);
1835 blk_start_plug(&plug);
1836 while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1837 nr[LRU_INACTIVE_FILE]) {
1838 for_each_evictable_lru(lru) {
1839 if (nr[lru]) {
1840 nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
1841 nr[lru] -= nr_to_scan;
1843 nr_reclaimed += shrink_list(lru, nr_to_scan,
1844 lruvec, sc);
1845 }
1846 }
1847 /*
1848 * On large memory systems, scan >> priority can become
1849 * really large. This is fine for the starting priority;
1850 * we want to put equal scanning pressure on each zone.
1851 * However, if the VM has a harder time of freeing pages,
1852 * with multiple processes reclaiming pages, the total
1853 * freeing target can get unreasonably large.
1854 */
1855 if (nr_reclaimed >= nr_to_reclaim &&
1856 sc->priority < DEF_PRIORITY)
1857 break;
1858 }
1859 blk_finish_plug(&plug);
1860 sc->nr_reclaimed += nr_reclaimed;
1862 /*
1863 * Even if we did not try to evict anon pages at all, we want to
1864 * rebalance the anon lru active/inactive ratio.
1865 */
1866 if (inactive_anon_is_low(lruvec))
1867 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
1868 sc, LRU_ACTIVE_ANON);
1870 throttle_vm_writeout(sc->gfp_mask);
1871 }
1873 /* Use reclaim/compaction for costly allocs or under memory pressure */
1874 static bool in_reclaim_compaction(struct scan_control *sc)
1875 {
1876 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
1877 (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
1878 sc->priority < DEF_PRIORITY - 2))
1879 return true;
1881 return false;
1882 }
1884 /*
1885 * Reclaim/compaction is used for high-order allocation requests. It reclaims
1886 * order-0 pages before compacting the zone. should_continue_reclaim() returns
1887 * true if more pages should be reclaimed such that when the page allocator
1888 * calls try_to_compact_zone() that it will have enough free pages to succeed.
1889 * It will give up earlier than that if there is difficulty reclaiming pages.
1890 */
1891 static inline bool should_continue_reclaim(struct zone *zone,
1892 unsigned long nr_reclaimed,
1893 unsigned long nr_scanned,
1894 struct scan_control *sc)
1895 {
1896 unsigned long pages_for_compaction;
1897 unsigned long inactive_lru_pages;
1899 /* If not in reclaim/compaction mode, stop */
1900 if (!in_reclaim_compaction(sc))
1901 return false;
1903 /* Consider stopping depending on scan and reclaim activity */
1904 if (sc->gfp_mask & __GFP_REPEAT) {
1905 /*
1906 * For __GFP_REPEAT allocations, stop reclaiming if the
1907 * full LRU list has been scanned and we are still failing
1908 * to reclaim pages. This full LRU scan is potentially
1909 * expensive but a __GFP_REPEAT caller really wants to succeed
1910 */
1911 if (!nr_reclaimed && !nr_scanned)
1912 return false;
1913 } else {
1914 /*
1915 * For non-__GFP_REPEAT allocations which can presumably
1916 * fail without consequence, stop if we failed to reclaim
1917 * any pages from the last SWAP_CLUSTER_MAX number of
1918 * pages that were scanned. This will return to the
1919 * caller faster at the risk reclaim/compaction and
1920 * the resulting allocation attempt fails
1921 */
1922 if (!nr_reclaimed)
1923 return false;
1924 }
1926 /*
1927 * If we have not reclaimed enough pages for compaction and the
1928 * inactive lists are large enough, continue reclaiming
1929 */
1930 pages_for_compaction = (2UL << sc->order);
1931 inactive_lru_pages = zone_page_state(zone, NR_INACTIVE_FILE);
1932 if (get_nr_swap_pages() > 0)
1933 inactive_lru_pages += zone_page_state(zone, NR_INACTIVE_ANON);
1934 if (sc->nr_reclaimed < pages_for_compaction &&
1935 inactive_lru_pages > pages_for_compaction)
1936 return true;
1938 /* If compaction would go ahead or the allocation would succeed, stop */
1939 switch (compaction_suitable(zone, sc->order)) {
1940 case COMPACT_PARTIAL:
1941 case COMPACT_CONTINUE:
1942 return false;
1943 default:
1944 return true;
1945 }
1946 }
1948 static void shrink_zone(struct zone *zone, struct scan_control *sc)
1949 {
1950 unsigned long nr_reclaimed, nr_scanned;
1952 do {
1953 struct mem_cgroup *root = sc->target_mem_cgroup;
1954 struct mem_cgroup_reclaim_cookie reclaim = {
1955 .zone = zone,
1956 .priority = sc->priority,
1957 };
1958 struct mem_cgroup *memcg;
1960 nr_reclaimed = sc->nr_reclaimed;
1961 nr_scanned = sc->nr_scanned;
1963 memcg = mem_cgroup_iter(root, NULL, &reclaim);
1964 do {
1965 struct lruvec *lruvec;
1967 lruvec = mem_cgroup_zone_lruvec(zone, memcg);
1969 shrink_lruvec(lruvec, sc);
1971 /*
1972 * Direct reclaim and kswapd have to scan all memory
1973 * cgroups to fulfill the overall scan target for the
1974 * zone.
1975 *
1976 * Limit reclaim, on the other hand, only cares about
1977 * nr_to_reclaim pages to be reclaimed and it will
1978 * retry with decreasing priority if one round over the
1979 * whole hierarchy is not sufficient.
1980 */
1981 if (!global_reclaim(sc) &&
1982 sc->nr_reclaimed >= sc->nr_to_reclaim) {
1983 mem_cgroup_iter_break(root, memcg);
1984 break;
1985 }
1986 memcg = mem_cgroup_iter(root, memcg, &reclaim);
1987 } while (memcg);
1989 vmpressure(sc->gfp_mask, sc->target_mem_cgroup,
1990 sc->nr_scanned - nr_scanned,
1991 sc->nr_reclaimed - nr_reclaimed);
1993 } while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed,
1994 sc->nr_scanned - nr_scanned, sc));
1995 }
1997 /* Returns true if compaction should go ahead for a high-order request */
1998 static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
1999 {
2000 unsigned long balance_gap, watermark;
2001 bool watermark_ok;
2003 /* Do not consider compaction for orders reclaim is meant to satisfy */
2004 if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
2005 return false;
2007 /*
2008 * Compaction takes time to run and there are potentially other
2009 * callers using the pages just freed. Continue reclaiming until
2010 * there is a buffer of free pages available to give compaction
2011 * a reasonable chance of completing and allocating the page
2012 */
2013 balance_gap = min(low_wmark_pages(zone),
2014 (zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2015 KSWAPD_ZONE_BALANCE_GAP_RATIO);
2016 watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
2017 watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
2019 /*
2020 * If compaction is deferred, reclaim up to a point where
2021 * compaction will have a chance of success when re-enabled
2022 */
2023 if (compaction_deferred(zone, sc->order))
2024 return watermark_ok;
2026 /* If compaction is not ready to start, keep reclaiming */
2027 if (!compaction_suitable(zone, sc->order))
2028 return false;
2030 return watermark_ok;
2031 }
2033 /*
2034 * This is the direct reclaim path, for page-allocating processes. We only
2035 * try to reclaim pages from zones which will satisfy the caller's allocation
2036 * request.
2037 *
2038 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
2039 * Because:
2040 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
2041 * allocation or
2042 * b) The target zone may be at high_wmark_pages(zone) but the lower zones
2043 * must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
2044 * zone defense algorithm.
2045 *
2046 * If a zone is deemed to be full of pinned pages then just give it a light
2047 * scan then give up on it.
2048 *
2049 * This function returns true if a zone is being reclaimed for a costly
2050 * high-order allocation and compaction is ready to begin. This indicates to
2051 * the caller that it should consider retrying the allocation instead of
2052 * further reclaim.
2053 */
2054 static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
2055 {
2056 struct zoneref *z;
2057 struct zone *zone;
2058 unsigned long nr_soft_reclaimed;
2059 unsigned long nr_soft_scanned;
2060 bool aborted_reclaim = false;
2062 /*
2063 * If the number of buffer_heads in the machine exceeds the maximum
2064 * allowed level, force direct reclaim to scan the highmem zone as
2065 * highmem pages could be pinning lowmem pages storing buffer_heads
2066 */
2067 if (buffer_heads_over_limit)
2068 sc->gfp_mask |= __GFP_HIGHMEM;
2070 for_each_zone_zonelist_nodemask(zone, z, zonelist,
2071 gfp_zone(sc->gfp_mask), sc->nodemask) {
2072 if (!populated_zone(zone))
2073 continue;
2074 /*
2075 * Take care memory controller reclaiming has small influence
2076 * to global LRU.
2077 */
2078 if (global_reclaim(sc)) {
2079 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2080 continue;
2081 if (zone->all_unreclaimable &&
2082 sc->priority != DEF_PRIORITY)
2083 continue; /* Let kswapd poll it */
2084 if (IS_ENABLED(CONFIG_COMPACTION)) {
2085 /*
2086 * If we already have plenty of memory free for
2087 * compaction in this zone, don't free any more.
2088 * Even though compaction is invoked for any
2089 * non-zero order, only frequent costly order
2090 * reclamation is disruptive enough to become a
2091 * noticeable problem, like transparent huge
2092 * page allocations.
2093 */
2094 if (compaction_ready(zone, sc)) {
2095 aborted_reclaim = true;
2096 continue;
2097 }
2098 }
2099 /*
2100 * This steals pages from memory cgroups over softlimit
2101 * and returns the number of reclaimed pages and
2102 * scanned pages. This works for global memory pressure
2103 * and balancing, not for a memcg's limit.
2104 */
2105 nr_soft_scanned = 0;
2106 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2107 sc->order, sc->gfp_mask,
2108 &nr_soft_scanned);
2109 sc->nr_reclaimed += nr_soft_reclaimed;
2110 sc->nr_scanned += nr_soft_scanned;
2111 /* need some check for avoid more shrink_zone() */
2112 }
2114 shrink_zone(zone, sc);
2115 }
2117 return aborted_reclaim;
2118 }
2120 static unsigned long zone_reclaimable_pages(struct zone *zone)
2121 {
2122 int nr;
2124 nr = zone_page_state(zone, NR_ACTIVE_FILE) +
2125 zone_page_state(zone, NR_INACTIVE_FILE);
2127 if (get_nr_swap_pages() > 0)
2128 nr += zone_page_state(zone, NR_ACTIVE_ANON) +
2129 zone_page_state(zone, NR_INACTIVE_ANON);
2131 return nr;
2132 }
2134 static bool zone_reclaimable(struct zone *zone)
2135 {
2136 return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
2137 }
2139 /* All zones in zonelist are unreclaimable? */
2140 static bool all_unreclaimable(struct zonelist *zonelist,
2141 struct scan_control *sc)
2142 {
2143 struct zoneref *z;
2144 struct zone *zone;
2146 for_each_zone_zonelist_nodemask(zone, z, zonelist,
2147 gfp_zone(sc->gfp_mask), sc->nodemask) {
2148 if (!populated_zone(zone))
2149 continue;
2150 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2151 continue;
2152 if (!zone->all_unreclaimable)
2153 return false;
2154 }
2156 return true;
2157 }
2159 /*
2160 * This is the main entry point to direct page reclaim.
2161 *
2162 * If a full scan of the inactive list fails to free enough memory then we
2163 * are "out of memory" and something needs to be killed.
2164 *
2165 * If the caller is !__GFP_FS then the probability of a failure is reasonably
2166 * high - the zone may be full of dirty or under-writeback pages, which this
2167 * caller can't do much about. We kick the writeback threads and take explicit
2168 * naps in the hope that some of these pages can be written. But if the
2169 * allocating task holds filesystem locks which prevent writeout this might not
2170 * work, and the allocation attempt will fail.
2171 *
2172 * returns: 0, if no pages reclaimed
2173 * else, the number of pages reclaimed
2174 */
2175 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2176 struct scan_control *sc,
2177 struct shrink_control *shrink)
2178 {
2179 unsigned long total_scanned = 0;
2180 struct reclaim_state *reclaim_state = current->reclaim_state;
2181 struct zoneref *z;
2182 struct zone *zone;
2183 unsigned long writeback_threshold;
2184 bool aborted_reclaim;
2186 delayacct_freepages_start();
2188 if (global_reclaim(sc))
2189 count_vm_event(ALLOCSTALL);
2191 do {
2192 vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
2193 sc->priority);
2194 sc->nr_scanned = 0;
2195 aborted_reclaim = shrink_zones(zonelist, sc);
2197 /*
2198 * Don't shrink slabs when reclaiming memory from
2199 * over limit cgroups
2200 */
2201 if (global_reclaim(sc)) {
2202 unsigned long lru_pages = 0;
2203 for_each_zone_zonelist(zone, z, zonelist,
2204 gfp_zone(sc->gfp_mask)) {
2205 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2206 continue;
2208 lru_pages += zone_reclaimable_pages(zone);
2209 }
2211 shrink_slab(shrink, sc->nr_scanned, lru_pages);
2212 if (reclaim_state) {
2213 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2214 reclaim_state->reclaimed_slab = 0;
2215 }
2216 }
2217 total_scanned += sc->nr_scanned;
2218 if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2219 goto out;
2221 /*
2222 * If we're getting trouble reclaiming, start doing
2223 * writepage even in laptop mode.
2224 */
2225 if (sc->priority < DEF_PRIORITY - 2)
2226 sc->may_writepage = 1;
2228 /*
2229 * Try to write back as many pages as we just scanned. This
2230 * tends to cause slow streaming writers to write data to the
2231 * disk smoothly, at the dirtying rate, which is nice. But
2232 * that's undesirable in laptop mode, where we *want* lumpy
2233 * writeout. So in laptop mode, write out the whole world.
2234 */
2235 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2236 if (total_scanned > writeback_threshold) {
2237 wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2238 WB_REASON_TRY_TO_FREE_PAGES);
2239 sc->may_writepage = 1;
2240 }
2242 /* Take a nap, wait for some writeback to complete */
2243 if (!sc->hibernation_mode && sc->nr_scanned &&
2244 sc->priority < DEF_PRIORITY - 2) {
2245 struct zone *preferred_zone;
2247 first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
2248 &cpuset_current_mems_allowed,
2249 &preferred_zone);
2250 wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
2251 }
2252 } while (--sc->priority >= 0);
2254 out:
2255 delayacct_freepages_end();
2257 if (sc->nr_reclaimed)
2258 return sc->nr_reclaimed;
2260 /*
2261 * As hibernation is going on, kswapd is freezed so that it can't mark
2262 * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2263 * check.
2264 */
2265 if (oom_killer_disabled)
2266 return 0;
2268 /* Aborted reclaim to try compaction? don't OOM, then */
2269 if (aborted_reclaim)
2270 return 1;
2272 /* top priority shrink_zones still had more to do? don't OOM, then */
2273 if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2274 return 1;
2276 return 0;
2277 }
2279 static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2280 {
2281 struct zone *zone;
2282 unsigned long pfmemalloc_reserve = 0;
2283 unsigned long free_pages = 0;
2284 int i;
2285 bool wmark_ok;
2287 for (i = 0; i <= ZONE_NORMAL; i++) {
2288 zone = &pgdat->node_zones[i];
2289 if (!populated_zone(zone))
2290 continue;
2292 pfmemalloc_reserve += min_wmark_pages(zone);
2293 free_pages += zone_page_state(zone, NR_FREE_PAGES);
2294 }
2296 /* If there are no reserves (unexpected config) then do not throttle */
2297 if (!pfmemalloc_reserve)
2298 return true;
2300 wmark_ok = free_pages > pfmemalloc_reserve / 2;
2302 /* kswapd must be awake if processes are being throttled */
2303 if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2304 pgdat->classzone_idx = min(pgdat->classzone_idx,
2305 (enum zone_type)ZONE_NORMAL);
2306 wake_up_interruptible(&pgdat->kswapd_wait);
2307 }
2309 return wmark_ok;
2310 }
2312 /*
2313 * Throttle direct reclaimers if backing storage is backed by the network
2314 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
2315 * depleted. kswapd will continue to make progress and wake the processes
2316 * when the low watermark is reached.
2317 *
2318 * Returns true if a fatal signal was delivered during throttling. If this
2319 * happens, the page allocator should not consider triggering the OOM killer.
2320 */
2321 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2322 nodemask_t *nodemask)
2323 {
2324 struct zoneref *z;
2325 struct zone *zone;
2326 pg_data_t *pgdat = NULL;
2328 /*
2329 * Kernel threads should not be throttled as they may be indirectly
2330 * responsible for cleaning pages necessary for reclaim to make forward
2331 * progress. kjournald for example may enter direct reclaim while
2332 * committing a transaction where throttling it could forcing other
2333 * processes to block on log_wait_commit().
2334 */
2335 if (current->flags & PF_KTHREAD)
2336 goto out;
2338 /*
2339 * If a fatal signal is pending, this process should not throttle.
2340 * It should return quickly so it can exit and free its memory
2341 */
2342 if (fatal_signal_pending(current))
2343 goto out;
2345 /*
2346 * Check if the pfmemalloc reserves are ok by finding the first node
2347 * with a usable ZONE_NORMAL or lower zone. The expectation is that
2348 * GFP_KERNEL will be required for allocating network buffers when
2349 * swapping over the network so ZONE_HIGHMEM is unusable.
2350 *
2351 * Throttling is based on the first usable node and throttled processes
2352 * wait on a queue until kswapd makes progress and wakes them. There
2353 * is an affinity then between processes waking up and where reclaim
2354 * progress has been made assuming the process wakes on the same node.
2355 * More importantly, processes running on remote nodes will not compete
2356 * for remote pfmemalloc reserves and processes on different nodes
2357 * should make reasonable progress.
2358 */
2359 for_each_zone_zonelist_nodemask(zone, z, zonelist,
2360 gfp_mask, nodemask) {
2361 if (zone_idx(zone) > ZONE_NORMAL)
2362 continue;
2364 /* Throttle based on the first usable node */
2365 pgdat = zone->zone_pgdat;
2366 if (pfmemalloc_watermark_ok(pgdat))
2367 goto out;
2368 break;
2369 }
2371 /* If no zone was usable by the allocation flags then do not throttle */
2372 if (!pgdat)
2373 goto out;
2375 /* Account for the throttling */
2376 count_vm_event(PGSCAN_DIRECT_THROTTLE);
2378 /*
2379 * If the caller cannot enter the filesystem, it's possible that it
2380 * is due to the caller holding an FS lock or performing a journal
2381 * transaction in the case of a filesystem like ext[3|4]. In this case,
2382 * it is not safe to block on pfmemalloc_wait as kswapd could be
2383 * blocked waiting on the same lock. Instead, throttle for up to a
2384 * second before continuing.
2385 */
2386 if (!(gfp_mask & __GFP_FS)) {
2387 wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2388 pfmemalloc_watermark_ok(pgdat), HZ);
2390 goto check_pending;
2391 }
2393 /* Throttle until kswapd wakes the process */
2394 wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2395 pfmemalloc_watermark_ok(pgdat));
2397 check_pending:
2398 if (fatal_signal_pending(current))
2399 return true;
2401 out:
2402 return false;
2403 }
2405 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2406 gfp_t gfp_mask, nodemask_t *nodemask)
2407 {
2408 unsigned long nr_reclaimed;
2409 struct scan_control sc = {
2410 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
2411 .may_writepage = !laptop_mode,
2412 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2413 .may_unmap = 1,
2414 .may_swap = 1,
2415 .order = order,
2416 .priority = DEF_PRIORITY,
2417 .target_mem_cgroup = NULL,
2418 .nodemask = nodemask,
2419 };
2420 struct shrink_control shrink = {
2421 .gfp_mask = sc.gfp_mask,
2422 };
2424 /*
2425 * Do not enter reclaim if fatal signal was delivered while throttled.
2426 * 1 is returned so that the page allocator does not OOM kill at this
2427 * point.
2428 */
2429 if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2430 return 1;
2432 trace_mm_vmscan_direct_reclaim_begin(order,
2433 sc.may_writepage,
2434 gfp_mask);
2436 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2438 trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2440 return nr_reclaimed;
2441 }
2443 #ifdef CONFIG_MEMCG
2445 unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2446 gfp_t gfp_mask, bool noswap,
2447 struct zone *zone,
2448 unsigned long *nr_scanned)
2449 {
2450 struct scan_control sc = {
2451 .nr_scanned = 0,
2452 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2453 .may_writepage = !laptop_mode,
2454 .may_unmap = 1,
2455 .may_swap = !noswap,
2456 .order = 0,
2457 .priority = 0,
2458 .target_mem_cgroup = memcg,
2459 };
2460 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2462 sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2463 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2465 trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2466 sc.may_writepage,
2467 sc.gfp_mask);
2469 /*
2470 * NOTE: Although we can get the priority field, using it
2471 * here is not a good idea, since it limits the pages we can scan.
2472 * if we don't reclaim here, the shrink_zone from balance_pgdat
2473 * will pick up pages from other mem cgroup's as well. We hack
2474 * the priority and make it zero.
2475 */
2476 shrink_lruvec(lruvec, &sc);
2478 trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2480 *nr_scanned = sc.nr_scanned;
2481 return sc.nr_reclaimed;
2482 }
2484 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
2485 gfp_t gfp_mask,
2486 bool noswap)
2487 {
2488 struct zonelist *zonelist;
2489 unsigned long nr_reclaimed;
2490 int nid;
2491 struct scan_control sc = {
2492 .may_writepage = !laptop_mode,
2493 .may_unmap = 1,
2494 .may_swap = !noswap,
2495 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2496 .order = 0,
2497 .priority = DEF_PRIORITY,
2498 .target_mem_cgroup = memcg,
2499 .nodemask = NULL, /* we don't care the placement */
2500 .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2501 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2502 };
2503 struct shrink_control shrink = {
2504 .gfp_mask = sc.gfp_mask,
2505 };
2507 /*
2508 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2509 * take care of from where we get pages. So the node where we start the
2510 * scan does not need to be the current node.
2511 */
2512 nid = mem_cgroup_select_victim_node(memcg);
2514 zonelist = NODE_DATA(nid)->node_zonelists;
2516 trace_mm_vmscan_memcg_reclaim_begin(0,
2517 sc.may_writepage,
2518 sc.gfp_mask);
2520 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2522 trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2524 return nr_reclaimed;
2525 }
2526 #endif
2528 static void age_active_anon(struct zone *zone, struct scan_control *sc)
2529 {
2530 struct mem_cgroup *memcg;
2532 if (!total_swap_pages)
2533 return;
2535 memcg = mem_cgroup_iter(NULL, NULL, NULL);
2536 do {
2537 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2539 if (inactive_anon_is_low(lruvec))
2540 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2541 sc, LRU_ACTIVE_ANON);
2543 memcg = mem_cgroup_iter(NULL, memcg, NULL);
2544 } while (memcg);
2545 }
2547 static bool zone_balanced(struct zone *zone, int order,
2548 unsigned long balance_gap, int classzone_idx)
2549 {
2550 if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) +
2551 balance_gap, classzone_idx, 0))
2552 return false;
2554 if (IS_ENABLED(CONFIG_COMPACTION) && order &&
2555 !compaction_suitable(zone, order))
2556 return false;
2558 return true;
2559 }
2561 /*
2562 * pgdat_balanced() is used when checking if a node is balanced.
2563 *
2564 * For order-0, all zones must be balanced!
2565 *
2566 * For high-order allocations only zones that meet watermarks and are in a
2567 * zone allowed by the callers classzone_idx are added to balanced_pages. The
2568 * total of balanced pages must be at least 25% of the zones allowed by
2569 * classzone_idx for the node to be considered balanced. Forcing all zones to
2570 * be balanced for high orders can cause excessive reclaim when there are
2571 * imbalanced zones.
2572 * The choice of 25% is due to
2573 * o a 16M DMA zone that is balanced will not balance a zone on any
2574 * reasonable sized machine
2575 * o On all other machines, the top zone must be at least a reasonable
2576 * percentage of the middle zones. For example, on 32-bit x86, highmem
2577 * would need to be at least 256M for it to be balance a whole node.
2578 * Similarly, on x86-64 the Normal zone would need to be at least 1G
2579 * to balance a node on its own. These seemed like reasonable ratios.
2580 */
2581 static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
2582 {
2583 unsigned long managed_pages = 0;
2584 unsigned long balanced_pages = 0;
2585 int i;
2587 /* Check the watermark levels */
2588 for (i = 0; i <= classzone_idx; i++) {
2589 struct zone *zone = pgdat->node_zones + i;
2591 if (!populated_zone(zone))
2592 continue;
2594 managed_pages += zone->managed_pages;
2596 /*
2597 * A special case here:
2598 *
2599 * balance_pgdat() skips over all_unreclaimable after
2600 * DEF_PRIORITY. Effectively, it considers them balanced so
2601 * they must be considered balanced here as well!
2602 */
2603 if (zone->all_unreclaimable) {
2604 balanced_pages += zone->managed_pages;
2605 continue;
2606 }
2608 if (zone_balanced(zone, order, 0, i))
2609 balanced_pages += zone->managed_pages;
2610 else if (!order)
2611 return false;
2612 }
2614 if (order)
2615 return balanced_pages >= (managed_pages >> 2);
2616 else
2617 return true;
2618 }
2620 /*
2621 * Prepare kswapd for sleeping. This verifies that there are no processes
2622 * waiting in throttle_direct_reclaim() and that watermarks have been met.
2623 *
2624 * Returns true if kswapd is ready to sleep
2625 */
2626 static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
2627 int classzone_idx)
2628 {
2629 /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2630 if (remaining)
2631 return false;
2633 /*
2634 * There is a potential race between when kswapd checks its watermarks
2635 * and a process gets throttled. There is also a potential race if
2636 * processes get throttled, kswapd wakes, a large process exits therby
2637 * balancing the zones that causes kswapd to miss a wakeup. If kswapd
2638 * is going to sleep, no process should be sleeping on pfmemalloc_wait
2639 * so wake them now if necessary. If necessary, processes will wake
2640 * kswapd and get throttled again
2641 */
2642 if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
2643 wake_up(&pgdat->pfmemalloc_wait);
2644 return false;
2645 }
2647 return pgdat_balanced(pgdat, order, classzone_idx);
2648 }
2650 /*
2651 * For kswapd, balance_pgdat() will work across all this node's zones until
2652 * they are all at high_wmark_pages(zone).
2653 *
2654 * Returns the final order kswapd was reclaiming at
2655 *
2656 * There is special handling here for zones which are full of pinned pages.
2657 * This can happen if the pages are all mlocked, or if they are all used by
2658 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
2659 * What we do is to detect the case where all pages in the zone have been
2660 * scanned twice and there has been zero successful reclaim. Mark the zone as
2661 * dead and from now on, only perform a short scan. Basically we're polling
2662 * the zone for when the problem goes away.
2663 *
2664 * kswapd scans the zones in the highmem->normal->dma direction. It skips
2665 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2666 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2667 * lower zones regardless of the number of free pages in the lower zones. This
2668 * interoperates with the page allocator fallback scheme to ensure that aging
2669 * of pages is balanced across the zones.
2670 */
2671 static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2672 int *classzone_idx)
2673 {
2674 bool pgdat_is_balanced = false;
2675 int i;
2676 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
2677 struct reclaim_state *reclaim_state = current->reclaim_state;
2678 unsigned long nr_soft_reclaimed;
2679 unsigned long nr_soft_scanned;
2680 struct scan_control sc = {
2681 .gfp_mask = GFP_KERNEL,
2682 .may_unmap = 1,
2683 .may_swap = 1,
2684 /*
2685 * kswapd doesn't want to be bailed out while reclaim. because
2686 * we want to put equal scanning pressure on each zone.
2687 */
2688 .nr_to_reclaim = ULONG_MAX,
2689 .order = order,
2690 .target_mem_cgroup = NULL,
2691 };
2692 struct shrink_control shrink = {
2693 .gfp_mask = sc.gfp_mask,
2694 };
2695 loop_again:
2696 sc.priority = DEF_PRIORITY;
2697 sc.nr_reclaimed = 0;
2698 sc.may_writepage = !laptop_mode;
2699 count_vm_event(PAGEOUTRUN);
2701 do {
2702 unsigned long lru_pages = 0;
2704 /*
2705 * Scan in the highmem->dma direction for the highest
2706 * zone which needs scanning
2707 */
2708 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2709 struct zone *zone = pgdat->node_zones + i;
2711 if (!populated_zone(zone))
2712 continue;
2714 if (zone->all_unreclaimable &&
2715 sc.priority != DEF_PRIORITY)
2716 continue;
2718 /*
2719 * Do some background aging of the anon list, to give
2720 * pages a chance to be referenced before reclaiming.
2721 */
2722 age_active_anon(zone, &sc);
2724 /*
2725 * If the number of buffer_heads in the machine
2726 * exceeds the maximum allowed level and this node
2727 * has a highmem zone, force kswapd to reclaim from
2728 * it to relieve lowmem pressure.
2729 */
2730 if (buffer_heads_over_limit && is_highmem_idx(i)) {
2731 end_zone = i;
2732 break;
2733 }
2735 if (!zone_balanced(zone, order, 0, 0)) {
2736 end_zone = i;
2737 break;
2738 } else {
2739 /* If balanced, clear the congested flag */
2740 zone_clear_flag(zone, ZONE_CONGESTED);
2741 }
2742 }
2744 if (i < 0) {
2745 pgdat_is_balanced = true;
2746 goto out;
2747 }
2749 for (i = 0; i <= end_zone; i++) {
2750 struct zone *zone = pgdat->node_zones + i;
2752 lru_pages += zone_reclaimable_pages(zone);
2753 }
2755 /*
2756 * Now scan the zone in the dma->highmem direction, stopping
2757 * at the last zone which needs scanning.
2758 *
2759 * We do this because the page allocator works in the opposite
2760 * direction. This prevents the page allocator from allocating
2761 * pages behind kswapd's direction of progress, which would
2762 * cause too much scanning of the lower zones.
2763 */
2764 for (i = 0; i <= end_zone; i++) {
2765 struct zone *zone = pgdat->node_zones + i;
2766 int nr_slab, testorder;
2767 unsigned long balance_gap;
2769 if (!populated_zone(zone))
2770 continue;
2772 if (zone->all_unreclaimable &&
2773 sc.priority != DEF_PRIORITY)
2774 continue;
2776 sc.nr_scanned = 0;
2778 nr_soft_scanned = 0;
2779 /*
2780 * Call soft limit reclaim before calling shrink_zone.
2781 */
2782 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2783 order, sc.gfp_mask,
2784 &nr_soft_scanned);
2785 sc.nr_reclaimed += nr_soft_reclaimed;
2787 /*
2788 * We put equal pressure on every zone, unless
2789 * one zone has way too many pages free
2790 * already. The "too many pages" is defined
2791 * as the high wmark plus a "gap" where the
2792 * gap is either the low watermark or 1%
2793 * of the zone, whichever is smaller.
2794 */
2795 balance_gap = min(low_wmark_pages(zone),
2796 (zone->managed_pages +
2797 KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2798 KSWAPD_ZONE_BALANCE_GAP_RATIO);
2799 /*
2800 * Kswapd reclaims only single pages with compaction
2801 * enabled. Trying too hard to reclaim until contiguous
2802 * free pages have become available can hurt performance
2803 * by evicting too much useful data from memory.
2804 * Do not reclaim more than needed for compaction.
2805 */
2806 testorder = order;
2807 if (IS_ENABLED(CONFIG_COMPACTION) && order &&
2808 compaction_suitable(zone, order) !=
2809 COMPACT_SKIPPED)
2810 testorder = 0;
2812 if ((buffer_heads_over_limit && is_highmem_idx(i)) ||
2813 !zone_balanced(zone, testorder,
2814 balance_gap, end_zone)) {
2815 shrink_zone(zone, &sc);
2817 reclaim_state->reclaimed_slab = 0;
2818 nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages);
2819 sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2821 if (nr_slab == 0 && !zone_reclaimable(zone))
2822 zone->all_unreclaimable = 1;
2823 }
2825 /*
2826 * If we're getting trouble reclaiming, start doing
2827 * writepage even in laptop mode.
2828 */
2829 if (sc.priority < DEF_PRIORITY - 2)
2830 sc.may_writepage = 1;
2832 if (zone->all_unreclaimable) {
2833 if (end_zone && end_zone == i)
2834 end_zone--;
2835 continue;
2836 }
2838 if (zone_balanced(zone, testorder, 0, end_zone))
2839 /*
2840 * If a zone reaches its high watermark,
2841 * consider it to be no longer congested. It's
2842 * possible there are dirty pages backed by
2843 * congested BDIs but as pressure is relieved,
2844 * speculatively avoid congestion waits
2845 */
2846 zone_clear_flag(zone, ZONE_CONGESTED);
2847 }
2849 /*
2850 * If the low watermark is met there is no need for processes
2851 * to be throttled on pfmemalloc_wait as they should not be
2852 * able to safely make forward progress. Wake them
2853 */
2854 if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
2855 pfmemalloc_watermark_ok(pgdat))
2856 wake_up(&pgdat->pfmemalloc_wait);
2858 if (pgdat_balanced(pgdat, order, *classzone_idx)) {
2859 pgdat_is_balanced = true;
2860 break; /* kswapd: all done */
2861 }
2863 /*
2864 * We do this so kswapd doesn't build up large priorities for
2865 * example when it is freeing in parallel with allocators. It
2866 * matches the direct reclaim path behaviour in terms of impact
2867 * on zone->*_priority.
2868 */
2869 if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2870 break;
2871 } while (--sc.priority >= 0);
2873 out:
2874 if (!pgdat_is_balanced) {
2875 cond_resched();
2877 try_to_freeze();
2879 /*
2880 * Fragmentation may mean that the system cannot be
2881 * rebalanced for high-order allocations in all zones.
2882 * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2883 * it means the zones have been fully scanned and are still
2884 * not balanced. For high-order allocations, there is
2885 * little point trying all over again as kswapd may
2886 * infinite loop.
2887 *
2888 * Instead, recheck all watermarks at order-0 as they
2889 * are the most important. If watermarks are ok, kswapd will go
2890 * back to sleep. High-order users can still perform direct
2891 * reclaim if they wish.
2892 */
2893 if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2894 order = sc.order = 0;
2896 goto loop_again;
2897 }
2899 /*
2900 * If kswapd was reclaiming at a higher order, it has the option of
2901 * sleeping without all zones being balanced. Before it does, it must
2902 * ensure that the watermarks for order-0 on *all* zones are met and
2903 * that the congestion flags are cleared. The congestion flag must
2904 * be cleared as kswapd is the only mechanism that clears the flag
2905 * and it is potentially going to sleep here.
2906 */
2907 if (order) {
2908 int zones_need_compaction = 1;
2910 for (i = 0; i <= end_zone; i++) {
2911 struct zone *zone = pgdat->node_zones + i;
2913 if (!populated_zone(zone))
2914 continue;
2916 /* Check if the memory needs to be defragmented. */
2917 if (zone_watermark_ok(zone, order,
2918 low_wmark_pages(zone), *classzone_idx, 0))
2919 zones_need_compaction = 0;
2920 }
2922 if (zones_need_compaction)
2923 compact_pgdat(pgdat, order);
2924 }
2926 /*
2927 * Return the order we were reclaiming at so prepare_kswapd_sleep()
2928 * makes a decision on the order we were last reclaiming at. However,
2929 * if another caller entered the allocator slow path while kswapd
2930 * was awake, order will remain at the higher level
2931 */
2932 *classzone_idx = end_zone;
2933 return order;
2934 }
2936 static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
2937 {
2938 long remaining = 0;
2939 DEFINE_WAIT(wait);
2941 if (freezing(current) || kthread_should_stop())
2942 return;
2944 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2946 /* Try to sleep for a short interval */
2947 if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2948 remaining = schedule_timeout(HZ/10);
2949 finish_wait(&pgdat->kswapd_wait, &wait);
2950 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2951 }
2953 /*
2954 * After a short sleep, check if it was a premature sleep. If not, then
2955 * go fully to sleep until explicitly woken up.
2956 */
2957 if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2958 trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
2960 /*
2961 * vmstat counters are not perfectly accurate and the estimated
2962 * value for counters such as NR_FREE_PAGES can deviate from the
2963 * true value by nr_online_cpus * threshold. To avoid the zone
2964 * watermarks being breached while under pressure, we reduce the
2965 * per-cpu vmstat threshold while kswapd is awake and restore
2966 * them before going back to sleep.
2967 */
2968 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
2970 /*
2971 * Compaction records what page blocks it recently failed to
2972 * isolate pages from and skips them in the future scanning.
2973 * When kswapd is going to sleep, it is reasonable to assume
2974 * that pages and compaction may succeed so reset the cache.
2975 */
2976 reset_isolation_suitable(pgdat);
2978 if (!kthread_should_stop())
2979 schedule();
2981 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
2982 } else {
2983 if (remaining)
2984 count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2985 else
2986 count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2987 }
2988 finish_wait(&pgdat->kswapd_wait, &wait);
2989 }
2991 /*
2992 * The background pageout daemon, started as a kernel thread
2993 * from the init process.
2994 *
2995 * This basically trickles out pages so that we have _some_
2996 * free memory available even if there is no other activity
2997 * that frees anything up. This is needed for things like routing
2998 * etc, where we otherwise might have all activity going on in
2999 * asynchronous contexts that cannot page things out.
3000 *
3001 * If there are applications that are active memory-allocators
3002 * (most normal use), this basically shouldn't matter.
3003 */
3004 static int kswapd(void *p)
3005 {
3006 unsigned long order, new_order;
3007 unsigned balanced_order;
3008 int classzone_idx, new_classzone_idx;
3009 int balanced_classzone_idx;
3010 pg_data_t *pgdat = (pg_data_t*)p;
3011 struct task_struct *tsk = current;
3013 struct reclaim_state reclaim_state = {
3014 .reclaimed_slab = 0,
3015 };
3016 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
3018 lockdep_set_current_reclaim_state(GFP_KERNEL);
3020 if (!cpumask_empty(cpumask))
3021 set_cpus_allowed_ptr(tsk, cpumask);
3022 current->reclaim_state = &reclaim_state;
3024 /*
3025 * Tell the memory management that we're a "memory allocator",
3026 * and that if we need more memory we should get access to it
3027 * regardless (see "__alloc_pages()"). "kswapd" should
3028 * never get caught in the normal page freeing logic.
3029 *
3030 * (Kswapd normally doesn't need memory anyway, but sometimes
3031 * you need a small amount of memory in order to be able to
3032 * page out something else, and this flag essentially protects
3033 * us from recursively trying to free more memory as we're
3034 * trying to free the first piece of memory in the first place).
3035 */
3036 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
3037 set_freezable();
3039 order = new_order = 0;
3040 balanced_order = 0;
3041 classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
3042 balanced_classzone_idx = classzone_idx;
3043 for ( ; ; ) {
3044 bool ret;
3046 /*
3047 * If the last balance_pgdat was unsuccessful it's unlikely a
3048 * new request of a similar or harder type will succeed soon
3049 * so consider going to sleep on the basis we reclaimed at
3050 */
3051 if (balanced_classzone_idx >= new_classzone_idx &&
3052 balanced_order == new_order) {
3053 new_order = pgdat->kswapd_max_order;
3054 new_classzone_idx = pgdat->classzone_idx;
3055 pgdat->kswapd_max_order = 0;
3056 pgdat->classzone_idx = pgdat->nr_zones - 1;
3057 }
3059 if (order < new_order || classzone_idx > new_classzone_idx) {
3060 /*
3061 * Don't sleep if someone wants a larger 'order'
3062 * allocation or has tigher zone constraints
3063 */
3064 order = new_order;
3065 classzone_idx = new_classzone_idx;
3066 } else {
3067 kswapd_try_to_sleep(pgdat, balanced_order,
3068 balanced_classzone_idx);
3069 order = pgdat->kswapd_max_order;
3070 classzone_idx = pgdat->classzone_idx;
3071 new_order = order;
3072 new_classzone_idx = classzone_idx;
3073 pgdat->kswapd_max_order = 0;
3074 pgdat->classzone_idx = pgdat->nr_zones - 1;
3075 }
3077 ret = try_to_freeze();
3078 if (kthread_should_stop())
3079 break;
3081 /*
3082 * We can speed up thawing tasks if we don't call balance_pgdat
3083 * after returning from the refrigerator
3084 */
3085 if (!ret) {
3086 trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
3087 balanced_classzone_idx = classzone_idx;
3088 balanced_order = balance_pgdat(pgdat, order,
3089 &balanced_classzone_idx);
3090 }
3091 }
3093 tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
3094 current->reclaim_state = NULL;
3095 lockdep_clear_current_reclaim_state();
3097 return 0;
3098 }
3100 /*
3101 * A zone is low on free memory, so wake its kswapd task to service it.
3102 */
3103 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
3104 {
3105 pg_data_t *pgdat;
3107 if (!populated_zone(zone))
3108 return;
3110 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
3111 return;
3112 pgdat = zone->zone_pgdat;
3113 if (pgdat->kswapd_max_order < order) {
3114 pgdat->kswapd_max_order = order;
3115 pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
3116 }
3117 if (!waitqueue_active(&pgdat->kswapd_wait))
3118 return;
3119 if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
3120 return;
3122 trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3123 wake_up_interruptible(&pgdat->kswapd_wait);
3124 }
3126 #ifdef CONFIG_HIBERNATION
3127 /*
3128 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3129 * freed pages.
3130 *
3131 * Rather than trying to age LRUs the aim is to preserve the overall
3132 * LRU order by reclaiming preferentially
3133 * inactive > active > active referenced > active mapped
3134 */
3135 unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3136 {
3137 struct reclaim_state reclaim_state;
3138 struct scan_control sc = {
3139 .gfp_mask = GFP_HIGHUSER_MOVABLE,
3140 .may_swap = 1,
3141 .may_unmap = 1,
3142 .may_writepage = 1,
3143 .nr_to_reclaim = nr_to_reclaim,
3144 .hibernation_mode = 1,
3145 .order = 0,
3146 .priority = DEF_PRIORITY,
3147 };
3148 struct shrink_control shrink = {
3149 .gfp_mask = sc.gfp_mask,
3150 };
3151 struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3152 struct task_struct *p = current;
3153 unsigned long nr_reclaimed;
3155 p->flags |= PF_MEMALLOC;
3156 lockdep_set_current_reclaim_state(sc.gfp_mask);
3157 reclaim_state.reclaimed_slab = 0;
3158 p->reclaim_state = &reclaim_state;
3160 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
3162 p->reclaim_state = NULL;
3163 lockdep_clear_current_reclaim_state();
3164 p->flags &= ~PF_MEMALLOC;
3166 return nr_reclaimed;
3167 }
3168 #endif /* CONFIG_HIBERNATION */
3170 /* It's optimal to keep kswapds on the same CPUs as their memory, but
3171 not required for correctness. So if the last cpu in a node goes
3172 away, we get changed to run anywhere: as the first one comes back,
3173 restore their cpu bindings. */
3174 static int cpu_callback(struct notifier_block *nfb, unsigned long action,
3175 void *hcpu)
3176 {
3177 int nid;
3179 if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
3180 for_each_node_state(nid, N_MEMORY) {
3181 pg_data_t *pgdat = NODE_DATA(nid);
3182 const struct cpumask *mask;
3184 mask = cpumask_of_node(pgdat->node_id);
3186 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3187 /* One of our CPUs online: restore mask */
3188 set_cpus_allowed_ptr(pgdat->kswapd, mask);
3189 }
3190 }
3191 return NOTIFY_OK;
3192 }
3194 /*
3195 * This kswapd start function will be called by init and node-hot-add.
3196 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3197 */
3198 int kswapd_run(int nid)
3199 {
3200 pg_data_t *pgdat = NODE_DATA(nid);
3201 int ret = 0;
3203 if (pgdat->kswapd)
3204 return 0;
3206 pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3207 if (IS_ERR(pgdat->kswapd)) {
3208 /* failure at boot is fatal */
3209 BUG_ON(system_state == SYSTEM_BOOTING);
3210 pr_err("Failed to start kswapd on node %d\n", nid);
3211 ret = PTR_ERR(pgdat->kswapd);
3212 pgdat->kswapd = NULL;
3213 }
3214 return ret;
3215 }
3217 /*
3218 * Called by memory hotplug when all memory in a node is offlined. Caller must
3219 * hold lock_memory_hotplug().
3220 */
3221 void kswapd_stop(int nid)
3222 {
3223 struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3225 if (kswapd) {
3226 kthread_stop(kswapd);
3227 NODE_DATA(nid)->kswapd = NULL;
3228 }
3229 }
3231 static int __init kswapd_init(void)
3232 {
3233 int nid;
3235 swap_setup();
3236 for_each_node_state(nid, N_MEMORY)
3237 kswapd_run(nid);
3238 hotcpu_notifier(cpu_callback, 0);
3239 return 0;
3240 }
3242 module_init(kswapd_init)
3244 #ifdef CONFIG_NUMA
3245 /*
3246 * Zone reclaim mode
3247 *
3248 * If non-zero call zone_reclaim when the number of free pages falls below
3249 * the watermarks.
3250 */
3251 int zone_reclaim_mode __read_mostly;
3253 #define RECLAIM_OFF 0
3254 #define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
3255 #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
3256 #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
3258 /*
3259 * Priority for ZONE_RECLAIM. This determines the fraction of pages
3260 * of a node considered for each zone_reclaim. 4 scans 1/16th of
3261 * a zone.
3262 */
3263 #define ZONE_RECLAIM_PRIORITY 4
3265 /*
3266 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
3267 * occur.
3268 */
3269 int sysctl_min_unmapped_ratio = 1;
3271 /*
3272 * If the number of slab pages in a zone grows beyond this percentage then
3273 * slab reclaim needs to occur.
3274 */
3275 int sysctl_min_slab_ratio = 5;
3277 static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3278 {
3279 unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3280 unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3281 zone_page_state(zone, NR_ACTIVE_FILE);
3283 /*
3284 * It's possible for there to be more file mapped pages than
3285 * accounted for by the pages on the file LRU lists because
3286 * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3287 */
3288 return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3289 }
3291 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
3292 static long zone_pagecache_reclaimable(struct zone *zone)
3293 {
3294 long nr_pagecache_reclaimable;
3295 long delta = 0;
3297 /*
3298 * If RECLAIM_SWAP is set, then all file pages are considered
3299 * potentially reclaimable. Otherwise, we have to worry about
3300 * pages like swapcache and zone_unmapped_file_pages() provides
3301 * a better estimate
3302 */
3303 if (zone_reclaim_mode & RECLAIM_SWAP)
3304 nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3305 else
3306 nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3308 /* If we can't clean pages, remove dirty pages from consideration */
3309 if (!(zone_reclaim_mode & RECLAIM_WRITE))
3310 delta += zone_page_state(zone, NR_FILE_DIRTY);
3312 /* Watch for any possible underflows due to delta */
3313 if (unlikely(delta > nr_pagecache_reclaimable))
3314 delta = nr_pagecache_reclaimable;
3316 return nr_pagecache_reclaimable - delta;
3317 }
3319 /*
3320 * Try to free up some pages from this zone through reclaim.
3321 */
3322 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3323 {
3324 /* Minimum pages needed in order to stay on node */
3325 const unsigned long nr_pages = 1 << order;
3326 struct task_struct *p = current;
3327 struct reclaim_state reclaim_state;
3328 struct scan_control sc = {
3329 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3330 .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3331 .may_swap = 1,
3332 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3333 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
3334 .order = order,
3335 .priority = ZONE_RECLAIM_PRIORITY,
3336 };
3337 struct shrink_control shrink = {
3338 .gfp_mask = sc.gfp_mask,
3339 };
3340 unsigned long nr_slab_pages0, nr_slab_pages1;
3342 cond_resched();
3343 /*
3344 * We need to be able to allocate from the reserves for RECLAIM_SWAP
3345 * and we also need to be able to write out pages for RECLAIM_WRITE
3346 * and RECLAIM_SWAP.
3347 */
3348 p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3349 lockdep_set_current_reclaim_state(gfp_mask);
3350 reclaim_state.reclaimed_slab = 0;
3351 p->reclaim_state = &reclaim_state;
3353 if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3354 /*
3355 * Free memory by calling shrink zone with increasing
3356 * priorities until we have enough memory freed.
3357 */
3358 do {
3359 shrink_zone(zone, &sc);
3360 } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3361 }
3363 nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3364 if (nr_slab_pages0 > zone->min_slab_pages) {
3365 /*
3366 * shrink_slab() does not currently allow us to determine how
3367 * many pages were freed in this zone. So we take the current
3368 * number of slab pages and shake the slab until it is reduced
3369 * by the same nr_pages that we used for reclaiming unmapped
3370 * pages.
3371 *
3372 * Note that shrink_slab will free memory on all zones and may
3373 * take a long time.
3374 */
3375 for (;;) {
3376 unsigned long lru_pages = zone_reclaimable_pages(zone);
3378 /* No reclaimable slab or very low memory pressure */
3379 if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3380 break;
3382 /* Freed enough memory */
3383 nr_slab_pages1 = zone_page_state(zone,
3384 NR_SLAB_RECLAIMABLE);
3385 if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3386 break;
3387 }
3389 /*
3390 * Update nr_reclaimed by the number of slab pages we
3391 * reclaimed from this zone.
3392 */
3393 nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3394 if (nr_slab_pages1 < nr_slab_pages0)
3395 sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3396 }
3398 p->reclaim_state = NULL;
3399 current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3400 lockdep_clear_current_reclaim_state();
3401 return sc.nr_reclaimed >= nr_pages;
3402 }
3404 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3405 {
3406 int node_id;
3407 int ret;
3409 /*
3410 * Zone reclaim reclaims unmapped file backed pages and
3411 * slab pages if we are over the defined limits.
3412 *
3413 * A small portion of unmapped file backed pages is needed for
3414 * file I/O otherwise pages read by file I/O will be immediately
3415 * thrown out if the zone is overallocated. So we do not reclaim
3416 * if less than a specified percentage of the zone is used by
3417 * unmapped file backed pages.
3418 */
3419 if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3420 zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3421 return ZONE_RECLAIM_FULL;
3423 if (zone->all_unreclaimable)
3424 return ZONE_RECLAIM_FULL;
3426 /*
3427 * Do not scan if the allocation should not be delayed.
3428 */
3429 if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3430 return ZONE_RECLAIM_NOSCAN;
3432 /*
3433 * Only run zone reclaim on the local zone or on zones that do not
3434 * have associated processors. This will favor the local processor
3435 * over remote processors and spread off node memory allocations
3436 * as wide as possible.
3437 */
3438 node_id = zone_to_nid(zone);
3439 if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3440 return ZONE_RECLAIM_NOSCAN;
3442 if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3443 return ZONE_RECLAIM_NOSCAN;
3445 ret = __zone_reclaim(zone, gfp_mask, order);
3446 zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3448 if (!ret)
3449 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3451 return ret;
3452 }
3453 #endif
3455 /*
3456 * page_evictable - test whether a page is evictable
3457 * @page: the page to test
3458 *
3459 * Test whether page is evictable--i.e., should be placed on active/inactive
3460 * lists vs unevictable list.
3461 *
3462 * Reasons page might not be evictable:
3463 * (1) page's mapping marked unevictable
3464 * (2) page is part of an mlocked VMA
3465 *
3466 */
3467 int page_evictable(struct page *page)
3468 {
3469 return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
3470 }
3472 #ifdef CONFIG_SHMEM
3473 /**
3474 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3475 * @pages: array of pages to check
3476 * @nr_pages: number of pages to check
3477 *
3478 * Checks pages for evictability and moves them to the appropriate lru list.
3479 *
3480 * This function is only used for SysV IPC SHM_UNLOCK.
3481 */
3482 void check_move_unevictable_pages(struct page **pages, int nr_pages)
3483 {
3484 struct lruvec *lruvec;
3485 struct zone *zone = NULL;
3486 int pgscanned = 0;
3487 int pgrescued = 0;
3488 int i;
3490 for (i = 0; i < nr_pages; i++) {
3491 struct page *page = pages[i];
3492 struct zone *pagezone;
3494 pgscanned++;
3495 pagezone = page_zone(page);
3496 if (pagezone != zone) {
3497 if (zone)
3498 spin_unlock_irq(&zone->lru_lock);
3499 zone = pagezone;
3500 spin_lock_irq(&zone->lru_lock);
3501 }
3502 lruvec = mem_cgroup_page_lruvec(page, zone);
3504 if (!PageLRU(page) || !PageUnevictable(page))
3505 continue;
3507 if (page_evictable(page)) {
3508 enum lru_list lru = page_lru_base_type(page);
3510 VM_BUG_ON(PageActive(page));
3511 ClearPageUnevictable(page);
3512 del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3513 add_page_to_lru_list(page, lruvec, lru);
3514 pgrescued++;
3515 }
3516 }
3518 if (zone) {
3519 __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3520 __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3521 spin_unlock_irq(&zone->lru_lock);
3522 }
3523 }
3524 #endif /* CONFIG_SHMEM */
3526 static void warn_scan_unevictable_pages(void)
3527 {
3528 printk_once(KERN_WARNING
3529 "%s: The scan_unevictable_pages sysctl/node-interface has been "
3530 "disabled for lack of a legitimate use case. If you have "
3531 "one, please send an email to linux-mm@kvack.org.\n",
3532 current->comm);
3533 }
3535 /*
3536 * scan_unevictable_pages [vm] sysctl handler. On demand re-scan of
3537 * all nodes' unevictable lists for evictable pages
3538 */
3539 unsigned long scan_unevictable_pages;
3541 int scan_unevictable_handler(struct ctl_table *table, int write,
3542 void __user *buffer,
3543 size_t *length, loff_t *ppos)
3544 {
3545 warn_scan_unevictable_pages();
3546 proc_doulongvec_minmax(table, write, buffer, length, ppos);
3547 scan_unevictable_pages = 0;
3548 return 0;
3549 }
3551 #ifdef CONFIG_NUMA
3552 /*
3553 * per node 'scan_unevictable_pages' attribute. On demand re-scan of
3554 * a specified node's per zone unevictable lists for evictable pages.
3555 */
3557 static ssize_t read_scan_unevictable_node(struct device *dev,
3558 struct device_attribute *attr,
3559 char *buf)
3560 {
3561 warn_scan_unevictable_pages();
3562 return sprintf(buf, "0\n"); /* always zero; should fit... */
3563 }
3565 static ssize_t write_scan_unevictable_node(struct device *dev,
3566 struct device_attribute *attr,
3567 const char *buf, size_t count)
3568 {
3569 warn_scan_unevictable_pages();
3570 return 1;
3571 }
3574 static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3575 read_scan_unevictable_node,
3576 write_scan_unevictable_node);
3578 int scan_unevictable_register_node(struct node *node)
3579 {
3580 return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages);
3581 }
3583 void scan_unevictable_unregister_node(struct node *node)
3584 {
3585 device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages);
3586 }
3587 #endif