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1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * linux/mm/vmscan.c
4 *
5 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
6 *
7 * Swap reorganised 29.12.95, Stephen Tweedie.
8 * kswapd added: 7.1.96 sct
9 * Removed kswapd_ctl limits, and swap out as many pages as needed
10 * to bring the system back to freepages.high: 2.4.97, Rik van Riel.
11 * Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
12 * Multiqueue VM started 5.8.00, Rik van Riel.
13 */
14
15 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
16
17 #include <linux/mm.h>
18 #include <linux/sched/mm.h>
19 #include <linux/module.h>
20 #include <linux/gfp.h>
21 #include <linux/kernel_stat.h>
22 #include <linux/swap.h>
23 #include <linux/pagemap.h>
24 #include <linux/init.h>
25 #include <linux/highmem.h>
26 #include <linux/vmpressure.h>
27 #include <linux/vmstat.h>
28 #include <linux/file.h>
29 #include <linux/writeback.h>
30 #include <linux/blkdev.h>
31 #include <linux/buffer_head.h> /* for try_to_release_page(),
32 buffer_heads_over_limit */
33 #include <linux/mm_inline.h>
34 #include <linux/backing-dev.h>
35 #include <linux/rmap.h>
36 #include <linux/topology.h>
37 #include <linux/cpu.h>
38 #include <linux/cpuset.h>
39 #include <linux/compaction.h>
40 #include <linux/notifier.h>
41 #include <linux/rwsem.h>
42 #include <linux/delay.h>
43 #include <linux/kthread.h>
44 #include <linux/freezer.h>
45 #include <linux/memcontrol.h>
46 #include <linux/delayacct.h>
47 #include <linux/sysctl.h>
48 #include <linux/oom.h>
49 #include <linux/prefetch.h>
50 #include <linux/printk.h>
51 #include <linux/dax.h>
52
53 #include <asm/tlbflush.h>
54 #include <asm/div64.h>
55
56 #include <linux/swapops.h>
57 #include <linux/balloon_compaction.h>
58
59 #include "internal.h"
60
61 #define CREATE_TRACE_POINTS
62 #include <trace/events/vmscan.h>
63
64 struct scan_control {
65 /* How many pages shrink_list() should reclaim */
66 unsigned long nr_to_reclaim;
67
68 /* This context's GFP mask */
69 gfp_t gfp_mask;
70
71 /* Allocation order */
72 int order;
73
74 /*
75 * Nodemask of nodes allowed by the caller. If NULL, all nodes
76 * are scanned.
77 */
78 nodemask_t *nodemask;
79
80 /*
81 * The memory cgroup that hit its limit and as a result is the
82 * primary target of this reclaim invocation.
83 */
84 struct mem_cgroup *target_mem_cgroup;
85
86 /* Scan (total_size >> priority) pages at once */
87 int priority;
88
89 /* The highest zone to isolate pages for reclaim from */
90 enum zone_type reclaim_idx;
91
92 /* Writepage batching in laptop mode; RECLAIM_WRITE */
93 unsigned int may_writepage:1;
94
95 /* Can mapped pages be reclaimed? */
96 unsigned int may_unmap:1;
97
98 /* Can pages be swapped as part of reclaim? */
99 unsigned int may_swap:1;
100
101 /*
102 * Cgroups are not reclaimed below their configured memory.low,
103 * unless we threaten to OOM. If any cgroups are skipped due to
104 * memory.low and nothing was reclaimed, go back for memory.low.
105 */
106 unsigned int memcg_low_reclaim:1;
107 unsigned int memcg_low_skipped:1;
108
109 unsigned int hibernation_mode:1;
110
111 /* One of the zones is ready for compaction */
112 unsigned int compaction_ready:1;
113
114 /* Incremented by the number of inactive pages that were scanned */
115 unsigned long nr_scanned;
116
117 /* Number of pages freed so far during a call to shrink_zones() */
118 unsigned long nr_reclaimed;
119 };
120
121 #ifdef ARCH_HAS_PREFETCH
122 #define prefetch_prev_lru_page(_page, _base, _field) \
123 do { \
124 if ((_page)->lru.prev != _base) { \
125 struct page *prev; \
126 \
127 prev = lru_to_page(&(_page->lru)); \
128 prefetch(&prev->_field); \
129 } \
130 } while (0)
131 #else
132 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
133 #endif
134
135 #ifdef ARCH_HAS_PREFETCHW
136 #define prefetchw_prev_lru_page(_page, _base, _field) \
137 do { \
138 if ((_page)->lru.prev != _base) { \
139 struct page *prev; \
140 \
141 prev = lru_to_page(&(_page->lru)); \
142 prefetchw(&prev->_field); \
143 } \
144 } while (0)
145 #else
146 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
147 #endif
148
149 /*
150 * From 0 .. 100. Higher means more swappy.
151 */
152 int vm_swappiness = 60;
153 /*
154 * The total number of pages which are beyond the high watermark within all
155 * zones.
156 */
157 unsigned long vm_total_pages;
158
159 static LIST_HEAD(shrinker_list);
160 static DECLARE_RWSEM(shrinker_rwsem);
161
162 #ifdef CONFIG_MEMCG
163 static bool global_reclaim(struct scan_control *sc)
164 {
165 return !sc->target_mem_cgroup;
166 }
167
168 /**
169 * sane_reclaim - is the usual dirty throttling mechanism operational?
170 * @sc: scan_control in question
171 *
172 * The normal page dirty throttling mechanism in balance_dirty_pages() is
173 * completely broken with the legacy memcg and direct stalling in
174 * shrink_page_list() is used for throttling instead, which lacks all the
175 * niceties such as fairness, adaptive pausing, bandwidth proportional
176 * allocation and configurability.
177 *
178 * This function tests whether the vmscan currently in progress can assume
179 * that the normal dirty throttling mechanism is operational.
180 */
181 static bool sane_reclaim(struct scan_control *sc)
182 {
183 struct mem_cgroup *memcg = sc->target_mem_cgroup;
184
185 if (!memcg)
186 return true;
187 #ifdef CONFIG_CGROUP_WRITEBACK
188 if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
189 return true;
190 #endif
191 return false;
192 }
193 #else
194 static bool global_reclaim(struct scan_control *sc)
195 {
196 return true;
197 }
198
199 static bool sane_reclaim(struct scan_control *sc)
200 {
201 return true;
202 }
203 #endif
204
205 /*
206 * This misses isolated pages which are not accounted for to save counters.
207 * As the data only determines if reclaim or compaction continues, it is
208 * not expected that isolated pages will be a dominating factor.
209 */
210 unsigned long zone_reclaimable_pages(struct zone *zone)
211 {
212 unsigned long nr;
213
214 nr = zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_FILE) +
215 zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_FILE);
216 if (get_nr_swap_pages() > 0)
217 nr += zone_page_state_snapshot(zone, NR_ZONE_INACTIVE_ANON) +
218 zone_page_state_snapshot(zone, NR_ZONE_ACTIVE_ANON);
219
220 return nr;
221 }
222
223 unsigned long pgdat_reclaimable_pages(struct pglist_data *pgdat)
224 {
225 unsigned long nr;
226
227 nr = node_page_state_snapshot(pgdat, NR_ACTIVE_FILE) +
228 node_page_state_snapshot(pgdat, NR_INACTIVE_FILE) +
229 node_page_state_snapshot(pgdat, NR_ISOLATED_FILE);
230
231 if (get_nr_swap_pages() > 0)
232 nr += node_page_state_snapshot(pgdat, NR_ACTIVE_ANON) +
233 node_page_state_snapshot(pgdat, NR_INACTIVE_ANON) +
234 node_page_state_snapshot(pgdat, NR_ISOLATED_ANON);
235
236 return nr;
237 }
238
239 /**
240 * lruvec_lru_size - Returns the number of pages on the given LRU list.
241 * @lruvec: lru vector
242 * @lru: lru to use
243 * @zone_idx: zones to consider (use MAX_NR_ZONES for the whole LRU list)
244 */
245 unsigned long lruvec_lru_size(struct lruvec *lruvec, enum lru_list lru, int zone_idx)
246 {
247 unsigned long lru_size;
248 int zid;
249
250 if (!mem_cgroup_disabled())
251 lru_size = mem_cgroup_get_lru_size(lruvec, lru);
252 else
253 lru_size = node_page_state(lruvec_pgdat(lruvec), NR_LRU_BASE + lru);
254
255 for (zid = zone_idx + 1; zid < MAX_NR_ZONES; zid++) {
256 struct zone *zone = &lruvec_pgdat(lruvec)->node_zones[zid];
257 unsigned long size;
258
259 if (!managed_zone(zone))
260 continue;
261
262 if (!mem_cgroup_disabled())
263 size = mem_cgroup_get_zone_lru_size(lruvec, lru, zid);
264 else
265 size = zone_page_state(&lruvec_pgdat(lruvec)->node_zones[zid],
266 NR_ZONE_LRU_BASE + lru);
267 lru_size -= min(size, lru_size);
268 }
269
270 return lru_size;
271
272 }
273
274 /*
275 * Add a shrinker callback to be called from the vm.
276 */
277 int register_shrinker(struct shrinker *shrinker)
278 {
279 size_t size = sizeof(*shrinker->nr_deferred);
280
281 if (shrinker->flags & SHRINKER_NUMA_AWARE)
282 size *= nr_node_ids;
283
284 shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
285 if (!shrinker->nr_deferred)
286 return -ENOMEM;
287
288 down_write(&shrinker_rwsem);
289 list_add_tail(&shrinker->list, &shrinker_list);
290 up_write(&shrinker_rwsem);
291 return 0;
292 }
293 EXPORT_SYMBOL(register_shrinker);
294
295 /*
296 * Remove one
297 */
298 void unregister_shrinker(struct shrinker *shrinker)
299 {
300 down_write(&shrinker_rwsem);
301 list_del(&shrinker->list);
302 up_write(&shrinker_rwsem);
303 kfree(shrinker->nr_deferred);
304 }
305 EXPORT_SYMBOL(unregister_shrinker);
306
307 #define SHRINK_BATCH 128
308
309 static unsigned long do_shrink_slab(struct shrink_control *shrinkctl,
310 struct shrinker *shrinker,
311 unsigned long nr_scanned,
312 unsigned long nr_eligible)
313 {
314 unsigned long freed = 0;
315 unsigned long long delta;
316 long total_scan;
317 long freeable;
318 long nr;
319 long new_nr;
320 int nid = shrinkctl->nid;
321 long batch_size = shrinker->batch ? shrinker->batch
322 : SHRINK_BATCH;
323 long scanned = 0, next_deferred;
324
325 freeable = shrinker->count_objects(shrinker, shrinkctl);
326 if (freeable == 0)
327 return 0;
328
329 /*
330 * copy the current shrinker scan count into a local variable
331 * and zero it so that other concurrent shrinker invocations
332 * don't also do this scanning work.
333 */
334 nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
335
336 total_scan = nr;
337 delta = (4 * nr_scanned) / shrinker->seeks;
338 delta *= freeable;
339 do_div(delta, nr_eligible + 1);
340 total_scan += delta;
341 if (total_scan < 0) {
342 pr_err("shrink_slab: %pF negative objects to delete nr=%ld\n",
343 shrinker->scan_objects, total_scan);
344 total_scan = freeable;
345 next_deferred = nr;
346 } else
347 next_deferred = total_scan;
348
349 /*
350 * We need to avoid excessive windup on filesystem shrinkers
351 * due to large numbers of GFP_NOFS allocations causing the
352 * shrinkers to return -1 all the time. This results in a large
353 * nr being built up so when a shrink that can do some work
354 * comes along it empties the entire cache due to nr >>>
355 * freeable. This is bad for sustaining a working set in
356 * memory.
357 *
358 * Hence only allow the shrinker to scan the entire cache when
359 * a large delta change is calculated directly.
360 */
361 if (delta < freeable / 4)
362 total_scan = min(total_scan, freeable / 2);
363
364 /*
365 * Avoid risking looping forever due to too large nr value:
366 * never try to free more than twice the estimate number of
367 * freeable entries.
368 */
369 if (total_scan > freeable * 2)
370 total_scan = freeable * 2;
371
372 trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
373 nr_scanned, nr_eligible,
374 freeable, delta, total_scan);
375
376 /*
377 * Normally, we should not scan less than batch_size objects in one
378 * pass to avoid too frequent shrinker calls, but if the slab has less
379 * than batch_size objects in total and we are really tight on memory,
380 * we will try to reclaim all available objects, otherwise we can end
381 * up failing allocations although there are plenty of reclaimable
382 * objects spread over several slabs with usage less than the
383 * batch_size.
384 *
385 * We detect the "tight on memory" situations by looking at the total
386 * number of objects we want to scan (total_scan). If it is greater
387 * than the total number of objects on slab (freeable), we must be
388 * scanning at high prio and therefore should try to reclaim as much as
389 * possible.
390 */
391 while (total_scan >= batch_size ||
392 total_scan >= freeable) {
393 unsigned long ret;
394 unsigned long nr_to_scan = min(batch_size, total_scan);
395
396 shrinkctl->nr_to_scan = nr_to_scan;
397 shrinkctl->nr_scanned = nr_to_scan;
398 ret = shrinker->scan_objects(shrinker, shrinkctl);
399 if (ret == SHRINK_STOP)
400 break;
401 freed += ret;
402
403 count_vm_events(SLABS_SCANNED, shrinkctl->nr_scanned);
404 total_scan -= shrinkctl->nr_scanned;
405 scanned += shrinkctl->nr_scanned;
406
407 cond_resched();
408 }
409
410 if (next_deferred >= scanned)
411 next_deferred -= scanned;
412 else
413 next_deferred = 0;
414 /*
415 * move the unused scan count back into the shrinker in a
416 * manner that handles concurrent updates. If we exhausted the
417 * scan, there is no need to do an update.
418 */
419 if (next_deferred > 0)
420 new_nr = atomic_long_add_return(next_deferred,
421 &shrinker->nr_deferred[nid]);
422 else
423 new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
424
425 trace_mm_shrink_slab_end(shrinker, nid, freed, nr, new_nr, total_scan);
426 return freed;
427 }
428
429 /**
430 * shrink_slab - shrink slab caches
431 * @gfp_mask: allocation context
432 * @nid: node whose slab caches to target
433 * @memcg: memory cgroup whose slab caches to target
434 * @nr_scanned: pressure numerator
435 * @nr_eligible: pressure denominator
436 *
437 * Call the shrink functions to age shrinkable caches.
438 *
439 * @nid is passed along to shrinkers with SHRINKER_NUMA_AWARE set,
440 * unaware shrinkers will receive a node id of 0 instead.
441 *
442 * @memcg specifies the memory cgroup to target. If it is not NULL,
443 * only shrinkers with SHRINKER_MEMCG_AWARE set will be called to scan
444 * objects from the memory cgroup specified. Otherwise, only unaware
445 * shrinkers are called.
446 *
447 * @nr_scanned and @nr_eligible form a ratio that indicate how much of
448 * the available objects should be scanned. Page reclaim for example
449 * passes the number of pages scanned and the number of pages on the
450 * LRU lists that it considered on @nid, plus a bias in @nr_scanned
451 * when it encountered mapped pages. The ratio is further biased by
452 * the ->seeks setting of the shrink function, which indicates the
453 * cost to recreate an object relative to that of an LRU page.
454 *
455 * Returns the number of reclaimed slab objects.
456 */
457 static unsigned long shrink_slab(gfp_t gfp_mask, int nid,
458 struct mem_cgroup *memcg,
459 unsigned long nr_scanned,
460 unsigned long nr_eligible)
461 {
462 struct shrinker *shrinker;
463 unsigned long freed = 0;
464
465 if (memcg && (!memcg_kmem_enabled() || !mem_cgroup_online(memcg)))
466 return 0;
467
468 if (nr_scanned == 0)
469 nr_scanned = SWAP_CLUSTER_MAX;
470
471 if (!down_read_trylock(&shrinker_rwsem)) {
472 /*
473 * If we would return 0, our callers would understand that we
474 * have nothing else to shrink and give up trying. By returning
475 * 1 we keep it going and assume we'll be able to shrink next
476 * time.
477 */
478 freed = 1;
479 goto out;
480 }
481
482 list_for_each_entry(shrinker, &shrinker_list, list) {
483 struct shrink_control sc = {
484 .gfp_mask = gfp_mask,
485 .nid = nid,
486 .memcg = memcg,
487 };
488
489 /*
490 * If kernel memory accounting is disabled, we ignore
491 * SHRINKER_MEMCG_AWARE flag and call all shrinkers
492 * passing NULL for memcg.
493 */
494 if (memcg_kmem_enabled() &&
495 !!memcg != !!(shrinker->flags & SHRINKER_MEMCG_AWARE))
496 continue;
497
498 if (!(shrinker->flags & SHRINKER_NUMA_AWARE))
499 sc.nid = 0;
500
501 freed += do_shrink_slab(&sc, shrinker, nr_scanned, nr_eligible);
502 }
503
504 up_read(&shrinker_rwsem);
505 out:
506 cond_resched();
507 return freed;
508 }
509
510 void drop_slab_node(int nid)
511 {
512 unsigned long freed;
513
514 do {
515 struct mem_cgroup *memcg = NULL;
516
517 freed = 0;
518 do {
519 freed += shrink_slab(GFP_KERNEL, nid, memcg,
520 1000, 1000);
521 } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)) != NULL);
522 } while (freed > 10);
523 }
524
525 void drop_slab(void)
526 {
527 int nid;
528
529 for_each_online_node(nid)
530 drop_slab_node(nid);
531 }
532
533 static inline int is_page_cache_freeable(struct page *page)
534 {
535 /*
536 * A freeable page cache page is referenced only by the caller
537 * that isolated the page, the page cache radix tree and
538 * optional buffer heads at page->private.
539 */
540 int radix_pins = PageTransHuge(page) && PageSwapCache(page) ?
541 HPAGE_PMD_NR : 1;
542 return page_count(page) - page_has_private(page) == 1 + radix_pins;
543 }
544
545 static int may_write_to_inode(struct inode *inode, struct scan_control *sc)
546 {
547 if (current->flags & PF_SWAPWRITE)
548 return 1;
549 if (!inode_write_congested(inode))
550 return 1;
551 if (inode_to_bdi(inode) == current->backing_dev_info)
552 return 1;
553 return 0;
554 }
555
556 /*
557 * We detected a synchronous write error writing a page out. Probably
558 * -ENOSPC. We need to propagate that into the address_space for a subsequent
559 * fsync(), msync() or close().
560 *
561 * The tricky part is that after writepage we cannot touch the mapping: nothing
562 * prevents it from being freed up. But we have a ref on the page and once
563 * that page is locked, the mapping is pinned.
564 *
565 * We're allowed to run sleeping lock_page() here because we know the caller has
566 * __GFP_FS.
567 */
568 static void handle_write_error(struct address_space *mapping,
569 struct page *page, int error)
570 {
571 lock_page(page);
572 if (page_mapping(page) == mapping)
573 mapping_set_error(mapping, error);
574 unlock_page(page);
575 }
576
577 /* possible outcome of pageout() */
578 typedef enum {
579 /* failed to write page out, page is locked */
580 PAGE_KEEP,
581 /* move page to the active list, page is locked */
582 PAGE_ACTIVATE,
583 /* page has been sent to the disk successfully, page is unlocked */
584 PAGE_SUCCESS,
585 /* page is clean and locked */
586 PAGE_CLEAN,
587 } pageout_t;
588
589 /*
590 * pageout is called by shrink_page_list() for each dirty page.
591 * Calls ->writepage().
592 */
593 static pageout_t pageout(struct page *page, struct address_space *mapping,
594 struct scan_control *sc)
595 {
596 /*
597 * If the page is dirty, only perform writeback if that write
598 * will be non-blocking. To prevent this allocation from being
599 * stalled by pagecache activity. But note that there may be
600 * stalls if we need to run get_block(). We could test
601 * PagePrivate for that.
602 *
603 * If this process is currently in __generic_file_write_iter() against
604 * this page's queue, we can perform writeback even if that
605 * will block.
606 *
607 * If the page is swapcache, write it back even if that would
608 * block, for some throttling. This happens by accident, because
609 * swap_backing_dev_info is bust: it doesn't reflect the
610 * congestion state of the swapdevs. Easy to fix, if needed.
611 */
612 if (!is_page_cache_freeable(page))
613 return PAGE_KEEP;
614 if (!mapping) {
615 /*
616 * Some data journaling orphaned pages can have
617 * page->mapping == NULL while being dirty with clean buffers.
618 */
619 if (page_has_private(page)) {
620 if (try_to_free_buffers(page)) {
621 ClearPageDirty(page);
622 pr_info("%s: orphaned page\n", __func__);
623 return PAGE_CLEAN;
624 }
625 }
626 return PAGE_KEEP;
627 }
628 if (mapping->a_ops->writepage == NULL)
629 return PAGE_ACTIVATE;
630 if (!may_write_to_inode(mapping->host, sc))
631 return PAGE_KEEP;
632
633 if (clear_page_dirty_for_io(page)) {
634 int res;
635 struct writeback_control wbc = {
636 .sync_mode = WB_SYNC_NONE,
637 .nr_to_write = SWAP_CLUSTER_MAX,
638 .range_start = 0,
639 .range_end = LLONG_MAX,
640 .for_reclaim = 1,
641 };
642
643 SetPageReclaim(page);
644 res = mapping->a_ops->writepage(page, &wbc);
645 if (res < 0)
646 handle_write_error(mapping, page, res);
647 if (res == AOP_WRITEPAGE_ACTIVATE) {
648 ClearPageReclaim(page);
649 return PAGE_ACTIVATE;
650 }
651
652 if (!PageWriteback(page)) {
653 /* synchronous write or broken a_ops? */
654 ClearPageReclaim(page);
655 }
656 trace_mm_vmscan_writepage(page);
657 inc_node_page_state(page, NR_VMSCAN_WRITE);
658 return PAGE_SUCCESS;
659 }
660
661 return PAGE_CLEAN;
662 }
663
664 /*
665 * Same as remove_mapping, but if the page is removed from the mapping, it
666 * gets returned with a refcount of 0.
667 */
668 static int __remove_mapping(struct address_space *mapping, struct page *page,
669 bool reclaimed)
670 {
671 unsigned long flags;
672 int refcount;
673
674 BUG_ON(!PageLocked(page));
675 BUG_ON(mapping != page_mapping(page));
676
677 spin_lock_irqsave(&mapping->tree_lock, flags);
678 /*
679 * The non racy check for a busy page.
680 *
681 * Must be careful with the order of the tests. When someone has
682 * a ref to the page, it may be possible that they dirty it then
683 * drop the reference. So if PageDirty is tested before page_count
684 * here, then the following race may occur:
685 *
686 * get_user_pages(&page);
687 * [user mapping goes away]
688 * write_to(page);
689 * !PageDirty(page) [good]
690 * SetPageDirty(page);
691 * put_page(page);
692 * !page_count(page) [good, discard it]
693 *
694 * [oops, our write_to data is lost]
695 *
696 * Reversing the order of the tests ensures such a situation cannot
697 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
698 * load is not satisfied before that of page->_refcount.
699 *
700 * Note that if SetPageDirty is always performed via set_page_dirty,
701 * and thus under tree_lock, then this ordering is not required.
702 */
703 if (unlikely(PageTransHuge(page)) && PageSwapCache(page))
704 refcount = 1 + HPAGE_PMD_NR;
705 else
706 refcount = 2;
707 if (!page_ref_freeze(page, refcount))
708 goto cannot_free;
709 /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
710 if (unlikely(PageDirty(page))) {
711 page_ref_unfreeze(page, refcount);
712 goto cannot_free;
713 }
714
715 if (PageSwapCache(page)) {
716 swp_entry_t swap = { .val = page_private(page) };
717 mem_cgroup_swapout(page, swap);
718 __delete_from_swap_cache(page);
719 spin_unlock_irqrestore(&mapping->tree_lock, flags);
720 put_swap_page(page, swap);
721 } else {
722 void (*freepage)(struct page *);
723 void *shadow = NULL;
724
725 freepage = mapping->a_ops->freepage;
726 /*
727 * Remember a shadow entry for reclaimed file cache in
728 * order to detect refaults, thus thrashing, later on.
729 *
730 * But don't store shadows in an address space that is
731 * already exiting. This is not just an optizimation,
732 * inode reclaim needs to empty out the radix tree or
733 * the nodes are lost. Don't plant shadows behind its
734 * back.
735 *
736 * We also don't store shadows for DAX mappings because the
737 * only page cache pages found in these are zero pages
738 * covering holes, and because we don't want to mix DAX
739 * exceptional entries and shadow exceptional entries in the
740 * same page_tree.
741 */
742 if (reclaimed && page_is_file_cache(page) &&
743 !mapping_exiting(mapping) && !dax_mapping(mapping))
744 shadow = workingset_eviction(mapping, page);
745 __delete_from_page_cache(page, shadow);
746 spin_unlock_irqrestore(&mapping->tree_lock, flags);
747
748 if (freepage != NULL)
749 freepage(page);
750 }
751
752 return 1;
753
754 cannot_free:
755 spin_unlock_irqrestore(&mapping->tree_lock, flags);
756 return 0;
757 }
758
759 /*
760 * Attempt to detach a locked page from its ->mapping. If it is dirty or if
761 * someone else has a ref on the page, abort and return 0. If it was
762 * successfully detached, return 1. Assumes the caller has a single ref on
763 * this page.
764 */
765 int remove_mapping(struct address_space *mapping, struct page *page)
766 {
767 if (__remove_mapping(mapping, page, false)) {
768 /*
769 * Unfreezing the refcount with 1 rather than 2 effectively
770 * drops the pagecache ref for us without requiring another
771 * atomic operation.
772 */
773 page_ref_unfreeze(page, 1);
774 return 1;
775 }
776 return 0;
777 }
778
779 /**
780 * putback_lru_page - put previously isolated page onto appropriate LRU list
781 * @page: page to be put back to appropriate lru list
782 *
783 * Add previously isolated @page to appropriate LRU list.
784 * Page may still be unevictable for other reasons.
785 *
786 * lru_lock must not be held, interrupts must be enabled.
787 */
788 void putback_lru_page(struct page *page)
789 {
790 bool is_unevictable;
791 int was_unevictable = PageUnevictable(page);
792
793 VM_BUG_ON_PAGE(PageLRU(page), page);
794
795 redo:
796 ClearPageUnevictable(page);
797
798 if (page_evictable(page)) {
799 /*
800 * For evictable pages, we can use the cache.
801 * In event of a race, worst case is we end up with an
802 * unevictable page on [in]active list.
803 * We know how to handle that.
804 */
805 is_unevictable = false;
806 lru_cache_add(page);
807 } else {
808 /*
809 * Put unevictable pages directly on zone's unevictable
810 * list.
811 */
812 is_unevictable = true;
813 add_page_to_unevictable_list(page);
814 /*
815 * When racing with an mlock or AS_UNEVICTABLE clearing
816 * (page is unlocked) make sure that if the other thread
817 * does not observe our setting of PG_lru and fails
818 * isolation/check_move_unevictable_pages,
819 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
820 * the page back to the evictable list.
821 *
822 * The other side is TestClearPageMlocked() or shmem_lock().
823 */
824 smp_mb();
825 }
826
827 /*
828 * page's status can change while we move it among lru. If an evictable
829 * page is on unevictable list, it never be freed. To avoid that,
830 * check after we added it to the list, again.
831 */
832 if (is_unevictable && page_evictable(page)) {
833 if (!isolate_lru_page(page)) {
834 put_page(page);
835 goto redo;
836 }
837 /* This means someone else dropped this page from LRU
838 * So, it will be freed or putback to LRU again. There is
839 * nothing to do here.
840 */
841 }
842
843 if (was_unevictable && !is_unevictable)
844 count_vm_event(UNEVICTABLE_PGRESCUED);
845 else if (!was_unevictable && is_unevictable)
846 count_vm_event(UNEVICTABLE_PGCULLED);
847
848 put_page(page); /* drop ref from isolate */
849 }
850
851 enum page_references {
852 PAGEREF_RECLAIM,
853 PAGEREF_RECLAIM_CLEAN,
854 PAGEREF_KEEP,
855 PAGEREF_ACTIVATE,
856 };
857
858 static enum page_references page_check_references(struct page *page,
859 struct scan_control *sc)
860 {
861 int referenced_ptes, referenced_page;
862 unsigned long vm_flags;
863
864 referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
865 &vm_flags);
866 referenced_page = TestClearPageReferenced(page);
867
868 /*
869 * Mlock lost the isolation race with us. Let try_to_unmap()
870 * move the page to the unevictable list.
871 */
872 if (vm_flags & VM_LOCKED)
873 return PAGEREF_RECLAIM;
874
875 if (referenced_ptes) {
876 if (PageSwapBacked(page))
877 return PAGEREF_ACTIVATE;
878 /*
879 * All mapped pages start out with page table
880 * references from the instantiating fault, so we need
881 * to look twice if a mapped file page is used more
882 * than once.
883 *
884 * Mark it and spare it for another trip around the
885 * inactive list. Another page table reference will
886 * lead to its activation.
887 *
888 * Note: the mark is set for activated pages as well
889 * so that recently deactivated but used pages are
890 * quickly recovered.
891 */
892 SetPageReferenced(page);
893
894 if (referenced_page || referenced_ptes > 1)
895 return PAGEREF_ACTIVATE;
896
897 /*
898 * Activate file-backed executable pages after first usage.
899 */
900 if (vm_flags & VM_EXEC)
901 return PAGEREF_ACTIVATE;
902
903 return PAGEREF_KEEP;
904 }
905
906 /* Reclaim if clean, defer dirty pages to writeback */
907 if (referenced_page && !PageSwapBacked(page))
908 return PAGEREF_RECLAIM_CLEAN;
909
910 return PAGEREF_RECLAIM;
911 }
912
913 /* Check if a page is dirty or under writeback */
914 static void page_check_dirty_writeback(struct page *page,
915 bool *dirty, bool *writeback)
916 {
917 struct address_space *mapping;
918
919 /*
920 * Anonymous pages are not handled by flushers and must be written
921 * from reclaim context. Do not stall reclaim based on them
922 */
923 if (!page_is_file_cache(page) ||
924 (PageAnon(page) && !PageSwapBacked(page))) {
925 *dirty = false;
926 *writeback = false;
927 return;
928 }
929
930 /* By default assume that the page flags are accurate */
931 *dirty = PageDirty(page);
932 *writeback = PageWriteback(page);
933
934 /* Verify dirty/writeback state if the filesystem supports it */
935 if (!page_has_private(page))
936 return;
937
938 mapping = page_mapping(page);
939 if (mapping && mapping->a_ops->is_dirty_writeback)
940 mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
941 }
942
943 struct reclaim_stat {
944 unsigned nr_dirty;
945 unsigned nr_unqueued_dirty;
946 unsigned nr_congested;
947 unsigned nr_writeback;
948 unsigned nr_immediate;
949 unsigned nr_activate;
950 unsigned nr_ref_keep;
951 unsigned nr_unmap_fail;
952 };
953
954 /*
955 * shrink_page_list() returns the number of reclaimed pages
956 */
957 static unsigned long shrink_page_list(struct list_head *page_list,
958 struct pglist_data *pgdat,
959 struct scan_control *sc,
960 enum ttu_flags ttu_flags,
961 struct reclaim_stat *stat,
962 bool force_reclaim)
963 {
964 LIST_HEAD(ret_pages);
965 LIST_HEAD(free_pages);
966 int pgactivate = 0;
967 unsigned nr_unqueued_dirty = 0;
968 unsigned nr_dirty = 0;
969 unsigned nr_congested = 0;
970 unsigned nr_reclaimed = 0;
971 unsigned nr_writeback = 0;
972 unsigned nr_immediate = 0;
973 unsigned nr_ref_keep = 0;
974 unsigned nr_unmap_fail = 0;
975
976 cond_resched();
977
978 while (!list_empty(page_list)) {
979 struct address_space *mapping;
980 struct page *page;
981 int may_enter_fs;
982 enum page_references references = PAGEREF_RECLAIM_CLEAN;
983 bool dirty, writeback;
984
985 cond_resched();
986
987 page = lru_to_page(page_list);
988 list_del(&page->lru);
989
990 if (!trylock_page(page))
991 goto keep;
992
993 VM_BUG_ON_PAGE(PageActive(page), page);
994
995 sc->nr_scanned++;
996
997 if (unlikely(!page_evictable(page)))
998 goto activate_locked;
999
1000 if (!sc->may_unmap && page_mapped(page))
1001 goto keep_locked;
1002
1003 /* Double the slab pressure for mapped and swapcache pages */
1004 if ((page_mapped(page) || PageSwapCache(page)) &&
1005 !(PageAnon(page) && !PageSwapBacked(page)))
1006 sc->nr_scanned++;
1007
1008 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
1009 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
1010
1011 /*
1012 * The number of dirty pages determines if a zone is marked
1013 * reclaim_congested which affects wait_iff_congested. kswapd
1014 * will stall and start writing pages if the tail of the LRU
1015 * is all dirty unqueued pages.
1016 */
1017 page_check_dirty_writeback(page, &dirty, &writeback);
1018 if (dirty || writeback)
1019 nr_dirty++;
1020
1021 if (dirty && !writeback)
1022 nr_unqueued_dirty++;
1023
1024 /*
1025 * Treat this page as congested if the underlying BDI is or if
1026 * pages are cycling through the LRU so quickly that the
1027 * pages marked for immediate reclaim are making it to the
1028 * end of the LRU a second time.
1029 */
1030 mapping = page_mapping(page);
1031 if (((dirty || writeback) && mapping &&
1032 inode_write_congested(mapping->host)) ||
1033 (writeback && PageReclaim(page)))
1034 nr_congested++;
1035
1036 /*
1037 * If a page at the tail of the LRU is under writeback, there
1038 * are three cases to consider.
1039 *
1040 * 1) If reclaim is encountering an excessive number of pages
1041 * under writeback and this page is both under writeback and
1042 * PageReclaim then it indicates that pages are being queued
1043 * for IO but are being recycled through the LRU before the
1044 * IO can complete. Waiting on the page itself risks an
1045 * indefinite stall if it is impossible to writeback the
1046 * page due to IO error or disconnected storage so instead
1047 * note that the LRU is being scanned too quickly and the
1048 * caller can stall after page list has been processed.
1049 *
1050 * 2) Global or new memcg reclaim encounters a page that is
1051 * not marked for immediate reclaim, or the caller does not
1052 * have __GFP_FS (or __GFP_IO if it's simply going to swap,
1053 * not to fs). In this case mark the page for immediate
1054 * reclaim and continue scanning.
1055 *
1056 * Require may_enter_fs because we would wait on fs, which
1057 * may not have submitted IO yet. And the loop driver might
1058 * enter reclaim, and deadlock if it waits on a page for
1059 * which it is needed to do the write (loop masks off
1060 * __GFP_IO|__GFP_FS for this reason); but more thought
1061 * would probably show more reasons.
1062 *
1063 * 3) Legacy memcg encounters a page that is already marked
1064 * PageReclaim. memcg does not have any dirty pages
1065 * throttling so we could easily OOM just because too many
1066 * pages are in writeback and there is nothing else to
1067 * reclaim. Wait for the writeback to complete.
1068 *
1069 * In cases 1) and 2) we activate the pages to get them out of
1070 * the way while we continue scanning for clean pages on the
1071 * inactive list and refilling from the active list. The
1072 * observation here is that waiting for disk writes is more
1073 * expensive than potentially causing reloads down the line.
1074 * Since they're marked for immediate reclaim, they won't put
1075 * memory pressure on the cache working set any longer than it
1076 * takes to write them to disk.
1077 */
1078 if (PageWriteback(page)) {
1079 /* Case 1 above */
1080 if (current_is_kswapd() &&
1081 PageReclaim(page) &&
1082 test_bit(PGDAT_WRITEBACK, &pgdat->flags)) {
1083 nr_immediate++;
1084 goto activate_locked;
1085
1086 /* Case 2 above */
1087 } else if (sane_reclaim(sc) ||
1088 !PageReclaim(page) || !may_enter_fs) {
1089 /*
1090 * This is slightly racy - end_page_writeback()
1091 * might have just cleared PageReclaim, then
1092 * setting PageReclaim here end up interpreted
1093 * as PageReadahead - but that does not matter
1094 * enough to care. What we do want is for this
1095 * page to have PageReclaim set next time memcg
1096 * reclaim reaches the tests above, so it will
1097 * then wait_on_page_writeback() to avoid OOM;
1098 * and it's also appropriate in global reclaim.
1099 */
1100 SetPageReclaim(page);
1101 nr_writeback++;
1102 goto activate_locked;
1103
1104 /* Case 3 above */
1105 } else {
1106 unlock_page(page);
1107 wait_on_page_writeback(page);
1108 /* then go back and try same page again */
1109 list_add_tail(&page->lru, page_list);
1110 continue;
1111 }
1112 }
1113
1114 if (!force_reclaim)
1115 references = page_check_references(page, sc);
1116
1117 switch (references) {
1118 case PAGEREF_ACTIVATE:
1119 goto activate_locked;
1120 case PAGEREF_KEEP:
1121 nr_ref_keep++;
1122 goto keep_locked;
1123 case PAGEREF_RECLAIM:
1124 case PAGEREF_RECLAIM_CLEAN:
1125 ; /* try to reclaim the page below */
1126 }
1127
1128 /*
1129 * Anonymous process memory has backing store?
1130 * Try to allocate it some swap space here.
1131 * Lazyfree page could be freed directly
1132 */
1133 if (PageAnon(page) && PageSwapBacked(page)) {
1134 if (!PageSwapCache(page)) {
1135 if (!(sc->gfp_mask & __GFP_IO))
1136 goto keep_locked;
1137 if (PageTransHuge(page)) {
1138 /* cannot split THP, skip it */
1139 if (!can_split_huge_page(page, NULL))
1140 goto activate_locked;
1141 /*
1142 * Split pages without a PMD map right
1143 * away. Chances are some or all of the
1144 * tail pages can be freed without IO.
1145 */
1146 if (!compound_mapcount(page) &&
1147 split_huge_page_to_list(page,
1148 page_list))
1149 goto activate_locked;
1150 }
1151 if (!add_to_swap(page)) {
1152 if (!PageTransHuge(page))
1153 goto activate_locked;
1154 /* Fallback to swap normal pages */
1155 if (split_huge_page_to_list(page,
1156 page_list))
1157 goto activate_locked;
1158 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
1159 count_vm_event(THP_SWPOUT_FALLBACK);
1160 #endif
1161 if (!add_to_swap(page))
1162 goto activate_locked;
1163 }
1164
1165 may_enter_fs = 1;
1166
1167 /* Adding to swap updated mapping */
1168 mapping = page_mapping(page);
1169 }
1170 } else if (unlikely(PageTransHuge(page))) {
1171 /* Split file THP */
1172 if (split_huge_page_to_list(page, page_list))
1173 goto keep_locked;
1174 }
1175
1176 /*
1177 * The page is mapped into the page tables of one or more
1178 * processes. Try to unmap it here.
1179 */
1180 if (page_mapped(page)) {
1181 enum ttu_flags flags = ttu_flags | TTU_BATCH_FLUSH;
1182
1183 if (unlikely(PageTransHuge(page)))
1184 flags |= TTU_SPLIT_HUGE_PMD;
1185 if (!try_to_unmap(page, flags)) {
1186 nr_unmap_fail++;
1187 goto activate_locked;
1188 }
1189 }
1190
1191 if (PageDirty(page)) {
1192 /*
1193 * Only kswapd can writeback filesystem pages
1194 * to avoid risk of stack overflow. But avoid
1195 * injecting inefficient single-page IO into
1196 * flusher writeback as much as possible: only
1197 * write pages when we've encountered many
1198 * dirty pages, and when we've already scanned
1199 * the rest of the LRU for clean pages and see
1200 * the same dirty pages again (PageReclaim).
1201 */
1202 if (page_is_file_cache(page) &&
1203 (!current_is_kswapd() || !PageReclaim(page) ||
1204 !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
1205 /*
1206 * Immediately reclaim when written back.
1207 * Similar in principal to deactivate_page()
1208 * except we already have the page isolated
1209 * and know it's dirty
1210 */
1211 inc_node_page_state(page, NR_VMSCAN_IMMEDIATE);
1212 SetPageReclaim(page);
1213
1214 goto activate_locked;
1215 }
1216
1217 if (references == PAGEREF_RECLAIM_CLEAN)
1218 goto keep_locked;
1219 if (!may_enter_fs)
1220 goto keep_locked;
1221 if (!sc->may_writepage)
1222 goto keep_locked;
1223
1224 /*
1225 * Page is dirty. Flush the TLB if a writable entry
1226 * potentially exists to avoid CPU writes after IO
1227 * starts and then write it out here.
1228 */
1229 try_to_unmap_flush_dirty();
1230 switch (pageout(page, mapping, sc)) {
1231 case PAGE_KEEP:
1232 goto keep_locked;
1233 case PAGE_ACTIVATE:
1234 goto activate_locked;
1235 case PAGE_SUCCESS:
1236 if (PageWriteback(page))
1237 goto keep;
1238 if (PageDirty(page))
1239 goto keep;
1240
1241 /*
1242 * A synchronous write - probably a ramdisk. Go
1243 * ahead and try to reclaim the page.
1244 */
1245 if (!trylock_page(page))
1246 goto keep;
1247 if (PageDirty(page) || PageWriteback(page))
1248 goto keep_locked;
1249 mapping = page_mapping(page);
1250 case PAGE_CLEAN:
1251 ; /* try to free the page below */
1252 }
1253 }
1254
1255 /*
1256 * If the page has buffers, try to free the buffer mappings
1257 * associated with this page. If we succeed we try to free
1258 * the page as well.
1259 *
1260 * We do this even if the page is PageDirty().
1261 * try_to_release_page() does not perform I/O, but it is
1262 * possible for a page to have PageDirty set, but it is actually
1263 * clean (all its buffers are clean). This happens if the
1264 * buffers were written out directly, with submit_bh(). ext3
1265 * will do this, as well as the blockdev mapping.
1266 * try_to_release_page() will discover that cleanness and will
1267 * drop the buffers and mark the page clean - it can be freed.
1268 *
1269 * Rarely, pages can have buffers and no ->mapping. These are
1270 * the pages which were not successfully invalidated in
1271 * truncate_complete_page(). We try to drop those buffers here
1272 * and if that worked, and the page is no longer mapped into
1273 * process address space (page_count == 1) it can be freed.
1274 * Otherwise, leave the page on the LRU so it is swappable.
1275 */
1276 if (page_has_private(page)) {
1277 if (!try_to_release_page(page, sc->gfp_mask))
1278 goto activate_locked;
1279 if (!mapping && page_count(page) == 1) {
1280 unlock_page(page);
1281 if (put_page_testzero(page))
1282 goto free_it;
1283 else {
1284 /*
1285 * rare race with speculative reference.
1286 * the speculative reference will free
1287 * this page shortly, so we may
1288 * increment nr_reclaimed here (and
1289 * leave it off the LRU).
1290 */
1291 nr_reclaimed++;
1292 continue;
1293 }
1294 }
1295 }
1296
1297 if (PageAnon(page) && !PageSwapBacked(page)) {
1298 /* follow __remove_mapping for reference */
1299 if (!page_ref_freeze(page, 1))
1300 goto keep_locked;
1301 if (PageDirty(page)) {
1302 page_ref_unfreeze(page, 1);
1303 goto keep_locked;
1304 }
1305
1306 count_vm_event(PGLAZYFREED);
1307 count_memcg_page_event(page, PGLAZYFREED);
1308 } else if (!mapping || !__remove_mapping(mapping, page, true))
1309 goto keep_locked;
1310 /*
1311 * At this point, we have no other references and there is
1312 * no way to pick any more up (removed from LRU, removed
1313 * from pagecache). Can use non-atomic bitops now (and
1314 * we obviously don't have to worry about waking up a process
1315 * waiting on the page lock, because there are no references.
1316 */
1317 __ClearPageLocked(page);
1318 free_it:
1319 nr_reclaimed++;
1320
1321 /*
1322 * Is there need to periodically free_page_list? It would
1323 * appear not as the counts should be low
1324 */
1325 if (unlikely(PageTransHuge(page))) {
1326 mem_cgroup_uncharge(page);
1327 (*get_compound_page_dtor(page))(page);
1328 } else
1329 list_add(&page->lru, &free_pages);
1330 continue;
1331
1332 activate_locked:
1333 /* Not a candidate for swapping, so reclaim swap space. */
1334 if (PageSwapCache(page) && (mem_cgroup_swap_full(page) ||
1335 PageMlocked(page)))
1336 try_to_free_swap(page);
1337 VM_BUG_ON_PAGE(PageActive(page), page);
1338 if (!PageMlocked(page)) {
1339 SetPageActive(page);
1340 pgactivate++;
1341 count_memcg_page_event(page, PGACTIVATE);
1342 }
1343 keep_locked:
1344 unlock_page(page);
1345 keep:
1346 list_add(&page->lru, &ret_pages);
1347 VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
1348 }
1349
1350 mem_cgroup_uncharge_list(&free_pages);
1351 try_to_unmap_flush();
1352 free_unref_page_list(&free_pages);
1353
1354 list_splice(&ret_pages, page_list);
1355 count_vm_events(PGACTIVATE, pgactivate);
1356
1357 if (stat) {
1358 stat->nr_dirty = nr_dirty;
1359 stat->nr_congested = nr_congested;
1360 stat->nr_unqueued_dirty = nr_unqueued_dirty;
1361 stat->nr_writeback = nr_writeback;
1362 stat->nr_immediate = nr_immediate;
1363 stat->nr_activate = pgactivate;
1364 stat->nr_ref_keep = nr_ref_keep;
1365 stat->nr_unmap_fail = nr_unmap_fail;
1366 }
1367 return nr_reclaimed;
1368 }
1369
1370 unsigned long reclaim_clean_pages_from_list(struct zone *zone,
1371 struct list_head *page_list)
1372 {
1373 struct scan_control sc = {
1374 .gfp_mask = GFP_KERNEL,
1375 .priority = DEF_PRIORITY,
1376 .may_unmap = 1,
1377 };
1378 unsigned long ret;
1379 struct page *page, *next;
1380 LIST_HEAD(clean_pages);
1381
1382 list_for_each_entry_safe(page, next, page_list, lru) {
1383 if (page_is_file_cache(page) && !PageDirty(page) &&
1384 !__PageMovable(page)) {
1385 ClearPageActive(page);
1386 list_move(&page->lru, &clean_pages);
1387 }
1388 }
1389
1390 ret = shrink_page_list(&clean_pages, zone->zone_pgdat, &sc,
1391 TTU_IGNORE_ACCESS, NULL, true);
1392 list_splice(&clean_pages, page_list);
1393 mod_node_page_state(zone->zone_pgdat, NR_ISOLATED_FILE, -ret);
1394 return ret;
1395 }
1396
1397 /*
1398 * Attempt to remove the specified page from its LRU. Only take this page
1399 * if it is of the appropriate PageActive status. Pages which are being
1400 * freed elsewhere are also ignored.
1401 *
1402 * page: page to consider
1403 * mode: one of the LRU isolation modes defined above
1404 *
1405 * returns 0 on success, -ve errno on failure.
1406 */
1407 int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1408 {
1409 int ret = -EINVAL;
1410
1411 /* Only take pages on the LRU. */
1412 if (!PageLRU(page))
1413 return ret;
1414
1415 /* Compaction should not handle unevictable pages but CMA can do so */
1416 if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1417 return ret;
1418
1419 ret = -EBUSY;
1420
1421 /*
1422 * To minimise LRU disruption, the caller can indicate that it only
1423 * wants to isolate pages it will be able to operate on without
1424 * blocking - clean pages for the most part.
1425 *
1426 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1427 * that it is possible to migrate without blocking
1428 */
1429 if (mode & ISOLATE_ASYNC_MIGRATE) {
1430 /* All the caller can do on PageWriteback is block */
1431 if (PageWriteback(page))
1432 return ret;
1433
1434 if (PageDirty(page)) {
1435 struct address_space *mapping;
1436
1437 /*
1438 * Only pages without mappings or that have a
1439 * ->migratepage callback are possible to migrate
1440 * without blocking
1441 */
1442 mapping = page_mapping(page);
1443 if (mapping && !mapping->a_ops->migratepage)
1444 return ret;
1445 }
1446 }
1447
1448 if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1449 return ret;
1450
1451 if (likely(get_page_unless_zero(page))) {
1452 /*
1453 * Be careful not to clear PageLRU until after we're
1454 * sure the page is not being freed elsewhere -- the
1455 * page release code relies on it.
1456 */
1457 ClearPageLRU(page);
1458 ret = 0;
1459 }
1460
1461 return ret;
1462 }
1463
1464
1465 /*
1466 * Update LRU sizes after isolating pages. The LRU size updates must
1467 * be complete before mem_cgroup_update_lru_size due to a santity check.
1468 */
1469 static __always_inline void update_lru_sizes(struct lruvec *lruvec,
1470 enum lru_list lru, unsigned long *nr_zone_taken)
1471 {
1472 int zid;
1473
1474 for (zid = 0; zid < MAX_NR_ZONES; zid++) {
1475 if (!nr_zone_taken[zid])
1476 continue;
1477
1478 __update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
1479 #ifdef CONFIG_MEMCG
1480 mem_cgroup_update_lru_size(lruvec, lru, zid, -nr_zone_taken[zid]);
1481 #endif
1482 }
1483
1484 }
1485
1486 /*
1487 * zone_lru_lock is heavily contended. Some of the functions that
1488 * shrink the lists perform better by taking out a batch of pages
1489 * and working on them outside the LRU lock.
1490 *
1491 * For pagecache intensive workloads, this function is the hottest
1492 * spot in the kernel (apart from copy_*_user functions).
1493 *
1494 * Appropriate locks must be held before calling this function.
1495 *
1496 * @nr_to_scan: The number of eligible pages to look through on the list.
1497 * @lruvec: The LRU vector to pull pages from.
1498 * @dst: The temp list to put pages on to.
1499 * @nr_scanned: The number of pages that were scanned.
1500 * @sc: The scan_control struct for this reclaim session
1501 * @mode: One of the LRU isolation modes
1502 * @lru: LRU list id for isolating
1503 *
1504 * returns how many pages were moved onto *@dst.
1505 */
1506 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1507 struct lruvec *lruvec, struct list_head *dst,
1508 unsigned long *nr_scanned, struct scan_control *sc,
1509 isolate_mode_t mode, enum lru_list lru)
1510 {
1511 struct list_head *src = &lruvec->lists[lru];
1512 unsigned long nr_taken = 0;
1513 unsigned long nr_zone_taken[MAX_NR_ZONES] = { 0 };
1514 unsigned long nr_skipped[MAX_NR_ZONES] = { 0, };
1515 unsigned long skipped = 0;
1516 unsigned long scan, total_scan, nr_pages;
1517 LIST_HEAD(pages_skipped);
1518
1519 scan = 0;
1520 for (total_scan = 0;
1521 scan < nr_to_scan && nr_taken < nr_to_scan && !list_empty(src);
1522 total_scan++) {
1523 struct page *page;
1524
1525 page = lru_to_page(src);
1526 prefetchw_prev_lru_page(page, src, flags);
1527
1528 VM_BUG_ON_PAGE(!PageLRU(page), page);
1529
1530 if (page_zonenum(page) > sc->reclaim_idx) {
1531 list_move(&page->lru, &pages_skipped);
1532 nr_skipped[page_zonenum(page)]++;
1533 continue;
1534 }
1535
1536 /*
1537 * Do not count skipped pages because that makes the function
1538 * return with no isolated pages if the LRU mostly contains
1539 * ineligible pages. This causes the VM to not reclaim any
1540 * pages, triggering a premature OOM.
1541 */
1542 scan++;
1543 switch (__isolate_lru_page(page, mode)) {
1544 case 0:
1545 nr_pages = hpage_nr_pages(page);
1546 nr_taken += nr_pages;
1547 nr_zone_taken[page_zonenum(page)] += nr_pages;
1548 list_move(&page->lru, dst);
1549 break;
1550
1551 case -EBUSY:
1552 /* else it is being freed elsewhere */
1553 list_move(&page->lru, src);
1554 continue;
1555
1556 default:
1557 BUG();
1558 }
1559 }
1560
1561 /*
1562 * Splice any skipped pages to the start of the LRU list. Note that
1563 * this disrupts the LRU order when reclaiming for lower zones but
1564 * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
1565 * scanning would soon rescan the same pages to skip and put the
1566 * system at risk of premature OOM.
1567 */
1568 if (!list_empty(&pages_skipped)) {
1569 int zid;
1570
1571 list_splice(&pages_skipped, src);
1572 for (zid = 0; zid < MAX_NR_ZONES; zid++) {
1573 if (!nr_skipped[zid])
1574 continue;
1575
1576 __count_zid_vm_events(PGSCAN_SKIP, zid, nr_skipped[zid]);
1577 skipped += nr_skipped[zid];
1578 }
1579 }
1580 *nr_scanned = total_scan;
1581 trace_mm_vmscan_lru_isolate(sc->reclaim_idx, sc->order, nr_to_scan,
1582 total_scan, skipped, nr_taken, mode, lru);
1583 update_lru_sizes(lruvec, lru, nr_zone_taken);
1584 return nr_taken;
1585 }
1586
1587 /**
1588 * isolate_lru_page - tries to isolate a page from its LRU list
1589 * @page: page to isolate from its LRU list
1590 *
1591 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1592 * vmstat statistic corresponding to whatever LRU list the page was on.
1593 *
1594 * Returns 0 if the page was removed from an LRU list.
1595 * Returns -EBUSY if the page was not on an LRU list.
1596 *
1597 * The returned page will have PageLRU() cleared. If it was found on
1598 * the active list, it will have PageActive set. If it was found on
1599 * the unevictable list, it will have the PageUnevictable bit set. That flag
1600 * may need to be cleared by the caller before letting the page go.
1601 *
1602 * The vmstat statistic corresponding to the list on which the page was
1603 * found will be decremented.
1604 *
1605 * Restrictions:
1606 * (1) Must be called with an elevated refcount on the page. This is a
1607 * fundamentnal difference from isolate_lru_pages (which is called
1608 * without a stable reference).
1609 * (2) the lru_lock must not be held.
1610 * (3) interrupts must be enabled.
1611 */
1612 int isolate_lru_page(struct page *page)
1613 {
1614 int ret = -EBUSY;
1615
1616 VM_BUG_ON_PAGE(!page_count(page), page);
1617 WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");
1618
1619 if (PageLRU(page)) {
1620 struct zone *zone = page_zone(page);
1621 struct lruvec *lruvec;
1622
1623 spin_lock_irq(zone_lru_lock(zone));
1624 lruvec = mem_cgroup_page_lruvec(page, zone->zone_pgdat);
1625 if (PageLRU(page)) {
1626 int lru = page_lru(page);
1627 get_page(page);
1628 ClearPageLRU(page);
1629 del_page_from_lru_list(page, lruvec, lru);
1630 ret = 0;
1631 }
1632 spin_unlock_irq(zone_lru_lock(zone));
1633 }
1634 return ret;
1635 }
1636
1637 /*
1638 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
1639 * then get resheduled. When there are massive number of tasks doing page
1640 * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
1641 * the LRU list will go small and be scanned faster than necessary, leading to
1642 * unnecessary swapping, thrashing and OOM.
1643 */
1644 static int too_many_isolated(struct pglist_data *pgdat, int file,
1645 struct scan_control *sc)
1646 {
1647 unsigned long inactive, isolated;
1648
1649 if (current_is_kswapd())
1650 return 0;
1651
1652 if (!sane_reclaim(sc))
1653 return 0;
1654
1655 if (file) {
1656 inactive = node_page_state(pgdat, NR_INACTIVE_FILE);
1657 isolated = node_page_state(pgdat, NR_ISOLATED_FILE);
1658 } else {
1659 inactive = node_page_state(pgdat, NR_INACTIVE_ANON);
1660 isolated = node_page_state(pgdat, NR_ISOLATED_ANON);
1661 }
1662
1663 /*
1664 * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
1665 * won't get blocked by normal direct-reclaimers, forming a circular
1666 * deadlock.
1667 */
1668 if ((sc->gfp_mask & (__GFP_IO | __GFP_FS)) == (__GFP_IO | __GFP_FS))
1669 inactive >>= 3;
1670
1671 return isolated > inactive;
1672 }
1673
1674 static noinline_for_stack void
1675 putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1676 {
1677 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1678 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1679 LIST_HEAD(pages_to_free);
1680
1681 /*
1682 * Put back any unfreeable pages.
1683 */
1684 while (!list_empty(page_list)) {
1685 struct page *page = lru_to_page(page_list);
1686 int lru;
1687
1688 VM_BUG_ON_PAGE(PageLRU(page), page);
1689 list_del(&page->lru);
1690 if (unlikely(!page_evictable(page))) {
1691 spin_unlock_irq(&pgdat->lru_lock);
1692 putback_lru_page(page);
1693 spin_lock_irq(&pgdat->lru_lock);
1694 continue;
1695 }
1696
1697 lruvec = mem_cgroup_page_lruvec(page, pgdat);
1698
1699 SetPageLRU(page);
1700 lru = page_lru(page);
1701 add_page_to_lru_list(page, lruvec, lru);
1702
1703 if (is_active_lru(lru)) {
1704 int file = is_file_lru(lru);
1705 int numpages = hpage_nr_pages(page);
1706 reclaim_stat->recent_rotated[file] += numpages;
1707 }
1708 if (put_page_testzero(page)) {
1709 __ClearPageLRU(page);
1710 __ClearPageActive(page);
1711 del_page_from_lru_list(page, lruvec, lru);
1712
1713 if (unlikely(PageCompound(page))) {
1714 spin_unlock_irq(&pgdat->lru_lock);
1715 mem_cgroup_uncharge(page);
1716 (*get_compound_page_dtor(page))(page);
1717 spin_lock_irq(&pgdat->lru_lock);
1718 } else
1719 list_add(&page->lru, &pages_to_free);
1720 }
1721 }
1722
1723 /*
1724 * To save our caller's stack, now use input list for pages to free.
1725 */
1726 list_splice(&pages_to_free, page_list);
1727 }
1728
1729 /*
1730 * If a kernel thread (such as nfsd for loop-back mounts) services
1731 * a backing device by writing to the page cache it sets PF_LESS_THROTTLE.
1732 * In that case we should only throttle if the backing device it is
1733 * writing to is congested. In other cases it is safe to throttle.
1734 */
1735 static int current_may_throttle(void)
1736 {
1737 return !(current->flags & PF_LESS_THROTTLE) ||
1738 current->backing_dev_info == NULL ||
1739 bdi_write_congested(current->backing_dev_info);
1740 }
1741
1742 /*
1743 * shrink_inactive_list() is a helper for shrink_node(). It returns the number
1744 * of reclaimed pages
1745 */
1746 static noinline_for_stack unsigned long
1747 shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1748 struct scan_control *sc, enum lru_list lru)
1749 {
1750 LIST_HEAD(page_list);
1751 unsigned long nr_scanned;
1752 unsigned long nr_reclaimed = 0;
1753 unsigned long nr_taken;
1754 struct reclaim_stat stat = {};
1755 isolate_mode_t isolate_mode = 0;
1756 int file = is_file_lru(lru);
1757 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1758 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1759 bool stalled = false;
1760
1761 while (unlikely(too_many_isolated(pgdat, file, sc))) {
1762 if (stalled)
1763 return 0;
1764
1765 /* wait a bit for the reclaimer. */
1766 msleep(100);
1767 stalled = true;
1768
1769 /* We are about to die and free our memory. Return now. */
1770 if (fatal_signal_pending(current))
1771 return SWAP_CLUSTER_MAX;
1772 }
1773
1774 lru_add_drain();
1775
1776 if (!sc->may_unmap)
1777 isolate_mode |= ISOLATE_UNMAPPED;
1778
1779 spin_lock_irq(&pgdat->lru_lock);
1780
1781 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1782 &nr_scanned, sc, isolate_mode, lru);
1783
1784 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
1785 reclaim_stat->recent_scanned[file] += nr_taken;
1786
1787 if (current_is_kswapd()) {
1788 if (global_reclaim(sc))
1789 __count_vm_events(PGSCAN_KSWAPD, nr_scanned);
1790 count_memcg_events(lruvec_memcg(lruvec), PGSCAN_KSWAPD,
1791 nr_scanned);
1792 } else {
1793 if (global_reclaim(sc))
1794 __count_vm_events(PGSCAN_DIRECT, nr_scanned);
1795 count_memcg_events(lruvec_memcg(lruvec), PGSCAN_DIRECT,
1796 nr_scanned);
1797 }
1798 spin_unlock_irq(&pgdat->lru_lock);
1799
1800 if (nr_taken == 0)
1801 return 0;
1802
1803 nr_reclaimed = shrink_page_list(&page_list, pgdat, sc, 0,
1804 &stat, false);
1805
1806 spin_lock_irq(&pgdat->lru_lock);
1807
1808 if (current_is_kswapd()) {
1809 if (global_reclaim(sc))
1810 __count_vm_events(PGSTEAL_KSWAPD, nr_reclaimed);
1811 count_memcg_events(lruvec_memcg(lruvec), PGSTEAL_KSWAPD,
1812 nr_reclaimed);
1813 } else {
1814 if (global_reclaim(sc))
1815 __count_vm_events(PGSTEAL_DIRECT, nr_reclaimed);
1816 count_memcg_events(lruvec_memcg(lruvec), PGSTEAL_DIRECT,
1817 nr_reclaimed);
1818 }
1819
1820 putback_inactive_pages(lruvec, &page_list);
1821
1822 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
1823
1824 spin_unlock_irq(&pgdat->lru_lock);
1825
1826 mem_cgroup_uncharge_list(&page_list);
1827 free_unref_page_list(&page_list);
1828
1829 /*
1830 * If reclaim is isolating dirty pages under writeback, it implies
1831 * that the long-lived page allocation rate is exceeding the page
1832 * laundering rate. Either the global limits are not being effective
1833 * at throttling processes due to the page distribution throughout
1834 * zones or there is heavy usage of a slow backing device. The
1835 * only option is to throttle from reclaim context which is not ideal
1836 * as there is no guarantee the dirtying process is throttled in the
1837 * same way balance_dirty_pages() manages.
1838 *
1839 * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
1840 * of pages under pages flagged for immediate reclaim and stall if any
1841 * are encountered in the nr_immediate check below.
1842 */
1843 if (stat.nr_writeback && stat.nr_writeback == nr_taken)
1844 set_bit(PGDAT_WRITEBACK, &pgdat->flags);
1845
1846 /*
1847 * Legacy memcg will stall in page writeback so avoid forcibly
1848 * stalling here.
1849 */
1850 if (sane_reclaim(sc)) {
1851 /*
1852 * Tag a zone as congested if all the dirty pages scanned were
1853 * backed by a congested BDI and wait_iff_congested will stall.
1854 */
1855 if (stat.nr_dirty && stat.nr_dirty == stat.nr_congested)
1856 set_bit(PGDAT_CONGESTED, &pgdat->flags);
1857
1858 /*
1859 * If dirty pages are scanned that are not queued for IO, it
1860 * implies that flushers are not doing their job. This can
1861 * happen when memory pressure pushes dirty pages to the end of
1862 * the LRU before the dirty limits are breached and the dirty
1863 * data has expired. It can also happen when the proportion of
1864 * dirty pages grows not through writes but through memory
1865 * pressure reclaiming all the clean cache. And in some cases,
1866 * the flushers simply cannot keep up with the allocation
1867 * rate. Nudge the flusher threads in case they are asleep, but
1868 * also allow kswapd to start writing pages during reclaim.
1869 */
1870 if (stat.nr_unqueued_dirty == nr_taken) {
1871 wakeup_flusher_threads(WB_REASON_VMSCAN);
1872 set_bit(PGDAT_DIRTY, &pgdat->flags);
1873 }
1874
1875 /*
1876 * If kswapd scans pages marked marked for immediate
1877 * reclaim and under writeback (nr_immediate), it implies
1878 * that pages are cycling through the LRU faster than
1879 * they are written so also forcibly stall.
1880 */
1881 if (stat.nr_immediate && current_may_throttle())
1882 congestion_wait(BLK_RW_ASYNC, HZ/10);
1883 }
1884
1885 /*
1886 * Stall direct reclaim for IO completions if underlying BDIs or zone
1887 * is congested. Allow kswapd to continue until it starts encountering
1888 * unqueued dirty pages or cycling through the LRU too quickly.
1889 */
1890 if (!sc->hibernation_mode && !current_is_kswapd() &&
1891 current_may_throttle())
1892 wait_iff_congested(pgdat, BLK_RW_ASYNC, HZ/10);
1893
1894 trace_mm_vmscan_lru_shrink_inactive(pgdat->node_id,
1895 nr_scanned, nr_reclaimed,
1896 stat.nr_dirty, stat.nr_writeback,
1897 stat.nr_congested, stat.nr_immediate,
1898 stat.nr_activate, stat.nr_ref_keep,
1899 stat.nr_unmap_fail,
1900 sc->priority, file);
1901 return nr_reclaimed;
1902 }
1903
1904 /*
1905 * This moves pages from the active list to the inactive list.
1906 *
1907 * We move them the other way if the page is referenced by one or more
1908 * processes, from rmap.
1909 *
1910 * If the pages are mostly unmapped, the processing is fast and it is
1911 * appropriate to hold zone_lru_lock across the whole operation. But if
1912 * the pages are mapped, the processing is slow (page_referenced()) so we
1913 * should drop zone_lru_lock around each page. It's impossible to balance
1914 * this, so instead we remove the pages from the LRU while processing them.
1915 * It is safe to rely on PG_active against the non-LRU pages in here because
1916 * nobody will play with that bit on a non-LRU page.
1917 *
1918 * The downside is that we have to touch page->_refcount against each page.
1919 * But we had to alter page->flags anyway.
1920 *
1921 * Returns the number of pages moved to the given lru.
1922 */
1923
1924 static unsigned move_active_pages_to_lru(struct lruvec *lruvec,
1925 struct list_head *list,
1926 struct list_head *pages_to_free,
1927 enum lru_list lru)
1928 {
1929 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1930 struct page *page;
1931 int nr_pages;
1932 int nr_moved = 0;
1933
1934 while (!list_empty(list)) {
1935 page = lru_to_page(list);
1936 lruvec = mem_cgroup_page_lruvec(page, pgdat);
1937
1938 VM_BUG_ON_PAGE(PageLRU(page), page);
1939 SetPageLRU(page);
1940
1941 nr_pages = hpage_nr_pages(page);
1942 update_lru_size(lruvec, lru, page_zonenum(page), nr_pages);
1943 list_move(&page->lru, &lruvec->lists[lru]);
1944
1945 if (put_page_testzero(page)) {
1946 __ClearPageLRU(page);
1947 __ClearPageActive(page);
1948 del_page_from_lru_list(page, lruvec, lru);
1949
1950 if (unlikely(PageCompound(page))) {
1951 spin_unlock_irq(&pgdat->lru_lock);
1952 mem_cgroup_uncharge(page);
1953 (*get_compound_page_dtor(page))(page);
1954 spin_lock_irq(&pgdat->lru_lock);
1955 } else
1956 list_add(&page->lru, pages_to_free);
1957 } else {
1958 nr_moved += nr_pages;
1959 }
1960 }
1961
1962 if (!is_active_lru(lru)) {
1963 __count_vm_events(PGDEACTIVATE, nr_moved);
1964 count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE,
1965 nr_moved);
1966 }
1967
1968 return nr_moved;
1969 }
1970
1971 static void shrink_active_list(unsigned long nr_to_scan,
1972 struct lruvec *lruvec,
1973 struct scan_control *sc,
1974 enum lru_list lru)
1975 {
1976 unsigned long nr_taken;
1977 unsigned long nr_scanned;
1978 unsigned long vm_flags;
1979 LIST_HEAD(l_hold); /* The pages which were snipped off */
1980 LIST_HEAD(l_active);
1981 LIST_HEAD(l_inactive);
1982 struct page *page;
1983 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1984 unsigned nr_deactivate, nr_activate;
1985 unsigned nr_rotated = 0;
1986 isolate_mode_t isolate_mode = 0;
1987 int file = is_file_lru(lru);
1988 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
1989
1990 lru_add_drain();
1991
1992 if (!sc->may_unmap)
1993 isolate_mode |= ISOLATE_UNMAPPED;
1994
1995 spin_lock_irq(&pgdat->lru_lock);
1996
1997 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1998 &nr_scanned, sc, isolate_mode, lru);
1999
2000 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
2001 reclaim_stat->recent_scanned[file] += nr_taken;
2002
2003 __count_vm_events(PGREFILL, nr_scanned);
2004 count_memcg_events(lruvec_memcg(lruvec), PGREFILL, nr_scanned);
2005
2006 spin_unlock_irq(&pgdat->lru_lock);
2007
2008 while (!list_empty(&l_hold)) {
2009 cond_resched();
2010 page = lru_to_page(&l_hold);
2011 list_del(&page->lru);
2012
2013 if (unlikely(!page_evictable(page))) {
2014 putback_lru_page(page);
2015 continue;
2016 }
2017
2018 if (unlikely(buffer_heads_over_limit)) {
2019 if (page_has_private(page) && trylock_page(page)) {
2020 if (page_has_private(page))
2021 try_to_release_page(page, 0);
2022 unlock_page(page);
2023 }
2024 }
2025
2026 if (page_referenced(page, 0, sc->target_mem_cgroup,
2027 &vm_flags)) {
2028 nr_rotated += hpage_nr_pages(page);
2029 /*
2030 * Identify referenced, file-backed active pages and
2031 * give them one more trip around the active list. So
2032 * that executable code get better chances to stay in
2033 * memory under moderate memory pressure. Anon pages
2034 * are not likely to be evicted by use-once streaming
2035 * IO, plus JVM can create lots of anon VM_EXEC pages,
2036 * so we ignore them here.
2037 */
2038 if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
2039 list_add(&page->lru, &l_active);
2040 continue;
2041 }
2042 }
2043
2044 ClearPageActive(page); /* we are de-activating */
2045 list_add(&page->lru, &l_inactive);
2046 }
2047
2048 /*
2049 * Move pages back to the lru list.
2050 */
2051 spin_lock_irq(&pgdat->lru_lock);
2052 /*
2053 * Count referenced pages from currently used mappings as rotated,
2054 * even though only some of them are actually re-activated. This
2055 * helps balance scan pressure between file and anonymous pages in
2056 * get_scan_count.
2057 */
2058 reclaim_stat->recent_rotated[file] += nr_rotated;
2059
2060 nr_activate = move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
2061 nr_deactivate = move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
2062 __mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, -nr_taken);
2063 spin_unlock_irq(&pgdat->lru_lock);
2064
2065 mem_cgroup_uncharge_list(&l_hold);
2066 free_unref_page_list(&l_hold);
2067 trace_mm_vmscan_lru_shrink_active(pgdat->node_id, nr_taken, nr_activate,
2068 nr_deactivate, nr_rotated, sc->priority, file);
2069 }
2070
2071 /*
2072 * The inactive anon list should be small enough that the VM never has
2073 * to do too much work.
2074 *
2075 * The inactive file list should be small enough to leave most memory
2076 * to the established workingset on the scan-resistant active list,
2077 * but large enough to avoid thrashing the aggregate readahead window.
2078 *
2079 * Both inactive lists should also be large enough that each inactive
2080 * page has a chance to be referenced again before it is reclaimed.
2081 *
2082 * If that fails and refaulting is observed, the inactive list grows.
2083 *
2084 * The inactive_ratio is the target ratio of ACTIVE to INACTIVE pages
2085 * on this LRU, maintained by the pageout code. An inactive_ratio
2086 * of 3 means 3:1 or 25% of the pages are kept on the inactive list.
2087 *
2088 * total target max
2089 * memory ratio inactive
2090 * -------------------------------------
2091 * 10MB 1 5MB
2092 * 100MB 1 50MB
2093 * 1GB 3 250MB
2094 * 10GB 10 0.9GB
2095 * 100GB 31 3GB
2096 * 1TB 101 10GB
2097 * 10TB 320 32GB
2098 */
2099 static bool inactive_list_is_low(struct lruvec *lruvec, bool file,
2100 struct mem_cgroup *memcg,
2101 struct scan_control *sc, bool actual_reclaim)
2102 {
2103 enum lru_list active_lru = file * LRU_FILE + LRU_ACTIVE;
2104 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2105 enum lru_list inactive_lru = file * LRU_FILE;
2106 unsigned long inactive, active;
2107 unsigned long inactive_ratio;
2108 unsigned long refaults;
2109 unsigned long gb;
2110
2111 /*
2112 * If we don't have swap space, anonymous page deactivation
2113 * is pointless.
2114 */
2115 if (!file && !total_swap_pages)
2116 return false;
2117
2118 inactive = lruvec_lru_size(lruvec, inactive_lru, sc->reclaim_idx);
2119 active = lruvec_lru_size(lruvec, active_lru, sc->reclaim_idx);
2120
2121 if (memcg)
2122 refaults = memcg_page_state(memcg, WORKINGSET_ACTIVATE);
2123 else
2124 refaults = node_page_state(pgdat, WORKINGSET_ACTIVATE);
2125
2126 /*
2127 * When refaults are being observed, it means a new workingset
2128 * is being established. Disable active list protection to get
2129 * rid of the stale workingset quickly.
2130 */
2131 if (file && actual_reclaim && lruvec->refaults != refaults) {
2132 inactive_ratio = 0;
2133 } else {
2134 gb = (inactive + active) >> (30 - PAGE_SHIFT);
2135 if (gb)
2136 inactive_ratio = int_sqrt(10 * gb);
2137 else
2138 inactive_ratio = 1;
2139 }
2140
2141 if (actual_reclaim)
2142 trace_mm_vmscan_inactive_list_is_low(pgdat->node_id, sc->reclaim_idx,
2143 lruvec_lru_size(lruvec, inactive_lru, MAX_NR_ZONES), inactive,
2144 lruvec_lru_size(lruvec, active_lru, MAX_NR_ZONES), active,
2145 inactive_ratio, file);
2146
2147 return inactive * inactive_ratio < active;
2148 }
2149
2150 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
2151 struct lruvec *lruvec, struct mem_cgroup *memcg,
2152 struct scan_control *sc)
2153 {
2154 if (is_active_lru(lru)) {
2155 if (inactive_list_is_low(lruvec, is_file_lru(lru),
2156 memcg, sc, true))
2157 shrink_active_list(nr_to_scan, lruvec, sc, lru);
2158 return 0;
2159 }
2160
2161 return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
2162 }
2163
2164 enum scan_balance {
2165 SCAN_EQUAL,
2166 SCAN_FRACT,
2167 SCAN_ANON,
2168 SCAN_FILE,
2169 };
2170
2171 /*
2172 * Determine how aggressively the anon and file LRU lists should be
2173 * scanned. The relative value of each set of LRU lists is determined
2174 * by looking at the fraction of the pages scanned we did rotate back
2175 * onto the active list instead of evict.
2176 *
2177 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
2178 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
2179 */
2180 static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
2181 struct scan_control *sc, unsigned long *nr,
2182 unsigned long *lru_pages)
2183 {
2184 int swappiness = mem_cgroup_swappiness(memcg);
2185 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
2186 u64 fraction[2];
2187 u64 denominator = 0; /* gcc */
2188 struct pglist_data *pgdat = lruvec_pgdat(lruvec);
2189 unsigned long anon_prio, file_prio;
2190 enum scan_balance scan_balance;
2191 unsigned long anon, file;
2192 unsigned long ap, fp;
2193 enum lru_list lru;
2194
2195 /* If we have no swap space, do not bother scanning anon pages. */
2196 if (!sc->may_swap || mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
2197 scan_balance = SCAN_FILE;
2198 goto out;
2199 }
2200
2201 /*
2202 * Global reclaim will swap to prevent OOM even with no
2203 * swappiness, but memcg users want to use this knob to
2204 * disable swapping for individual groups completely when
2205 * using the memory controller's swap limit feature would be
2206 * too expensive.
2207 */
2208 if (!global_reclaim(sc) && !swappiness) {
2209 scan_balance = SCAN_FILE;
2210 goto out;
2211 }
2212
2213 /*
2214 * Do not apply any pressure balancing cleverness when the
2215 * system is close to OOM, scan both anon and file equally
2216 * (unless the swappiness setting disagrees with swapping).
2217 */
2218 if (!sc->priority && swappiness) {
2219 scan_balance = SCAN_EQUAL;
2220 goto out;
2221 }
2222
2223 /*
2224 * Prevent the reclaimer from falling into the cache trap: as
2225 * cache pages start out inactive, every cache fault will tip
2226 * the scan balance towards the file LRU. And as the file LRU
2227 * shrinks, so does the window for rotation from references.
2228 * This means we have a runaway feedback loop where a tiny
2229 * thrashing file LRU becomes infinitely more attractive than
2230 * anon pages. Try to detect this based on file LRU size.
2231 */
2232 if (global_reclaim(sc)) {
2233 unsigned long pgdatfile;
2234 unsigned long pgdatfree;
2235 int z;
2236 unsigned long total_high_wmark = 0;
2237
2238 pgdatfree = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
2239 pgdatfile = node_page_state(pgdat, NR_ACTIVE_FILE) +
2240 node_page_state(pgdat, NR_INACTIVE_FILE);
2241
2242 for (z = 0; z < MAX_NR_ZONES; z++) {
2243 struct zone *zone = &pgdat->node_zones[z];
2244 if (!managed_zone(zone))
2245 continue;
2246
2247 total_high_wmark += high_wmark_pages(zone);
2248 }
2249
2250 if (unlikely(pgdatfile + pgdatfree <= total_high_wmark)) {
2251 /*
2252 * Force SCAN_ANON if there are enough inactive
2253 * anonymous pages on the LRU in eligible zones.
2254 * Otherwise, the small LRU gets thrashed.
2255 */
2256 if (!inactive_list_is_low(lruvec, false, memcg, sc, false) &&
2257 lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, sc->reclaim_idx)
2258 >> sc->priority) {
2259 scan_balance = SCAN_ANON;
2260 goto out;
2261 }
2262 }
2263 }
2264
2265 /*
2266 * If there is enough inactive page cache, i.e. if the size of the
2267 * inactive list is greater than that of the active list *and* the
2268 * inactive list actually has some pages to scan on this priority, we
2269 * do not reclaim anything from the anonymous working set right now.
2270 * Without the second condition we could end up never scanning an
2271 * lruvec even if it has plenty of old anonymous pages unless the
2272 * system is under heavy pressure.
2273 */
2274 if (!inactive_list_is_low(lruvec, true, memcg, sc, false) &&
2275 lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, sc->reclaim_idx) >> sc->priority) {
2276 scan_balance = SCAN_FILE;
2277 goto out;
2278 }
2279
2280 scan_balance = SCAN_FRACT;
2281
2282 /*
2283 * With swappiness at 100, anonymous and file have the same priority.
2284 * This scanning priority is essentially the inverse of IO cost.
2285 */
2286 anon_prio = swappiness;
2287 file_prio = 200 - anon_prio;
2288
2289 /*
2290 * OK, so we have swap space and a fair amount of page cache
2291 * pages. We use the recently rotated / recently scanned
2292 * ratios to determine how valuable each cache is.
2293 *
2294 * Because workloads change over time (and to avoid overflow)
2295 * we keep these statistics as a floating average, which ends
2296 * up weighing recent references more than old ones.
2297 *
2298 * anon in [0], file in [1]
2299 */
2300
2301 anon = lruvec_lru_size(lruvec, LRU_ACTIVE_ANON, MAX_NR_ZONES) +
2302 lruvec_lru_size(lruvec, LRU_INACTIVE_ANON, MAX_NR_ZONES);
2303 file = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE, MAX_NR_ZONES) +
2304 lruvec_lru_size(lruvec, LRU_INACTIVE_FILE, MAX_NR_ZONES);
2305
2306 spin_lock_irq(&pgdat->lru_lock);
2307 if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
2308 reclaim_stat->recent_scanned[0] /= 2;
2309 reclaim_stat->recent_rotated[0] /= 2;
2310 }
2311
2312 if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
2313 reclaim_stat->recent_scanned[1] /= 2;
2314 reclaim_stat->recent_rotated[1] /= 2;
2315 }
2316
2317 /*
2318 * The amount of pressure on anon vs file pages is inversely
2319 * proportional to the fraction of recently scanned pages on
2320 * each list that were recently referenced and in active use.
2321 */
2322 ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
2323 ap /= reclaim_stat->recent_rotated[0] + 1;
2324
2325 fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
2326 fp /= reclaim_stat->recent_rotated[1] + 1;
2327 spin_unlock_irq(&pgdat->lru_lock);
2328
2329 fraction[0] = ap;
2330 fraction[1] = fp;
2331 denominator = ap + fp + 1;
2332 out:
2333 *lru_pages = 0;
2334 for_each_evictable_lru(lru) {
2335 int file = is_file_lru(lru);
2336 unsigned long size;
2337 unsigned long scan;
2338
2339 size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
2340 scan = size >> sc->priority;
2341 /*
2342 * If the cgroup's already been deleted, make sure to
2343 * scrape out the remaining cache.
2344 */
2345 if (!scan && !mem_cgroup_online(memcg))
2346 scan = min(size, SWAP_CLUSTER_MAX);
2347
2348 switch (scan_balance) {
2349 case SCAN_EQUAL:
2350 /* Scan lists relative to size */
2351 break;
2352 case SCAN_FRACT:
2353 /*
2354 * Scan types proportional to swappiness and
2355 * their relative recent reclaim efficiency.
2356 */
2357 scan = div64_u64(scan * fraction[file],
2358 denominator);
2359 break;
2360 case SCAN_FILE:
2361 case SCAN_ANON:
2362 /* Scan one type exclusively */
2363 if ((scan_balance == SCAN_FILE) != file) {
2364 size = 0;
2365 scan = 0;
2366 }
2367 break;
2368 default:
2369 /* Look ma, no brain */
2370 BUG();
2371 }
2372
2373 *lru_pages += size;
2374 nr[lru] = scan;
2375 }
2376 }
2377
2378 /*
2379 * This is a basic per-node page freer. Used by both kswapd and direct reclaim.
2380 */
2381 static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memcg,
2382 struct scan_control *sc, unsigned long *lru_pages)
2383 {
2384 struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
2385 unsigned long nr[NR_LRU_LISTS];
2386 unsigned long targets[NR_LRU_LISTS];
2387 unsigned long nr_to_scan;
2388 enum lru_list lru;
2389 unsigned long nr_reclaimed = 0;
2390 unsigned long nr_to_reclaim = sc->nr_to_reclaim;
2391 struct blk_plug plug;
2392 bool scan_adjusted;
2393
2394 get_scan_count(lruvec, memcg, sc, nr, lru_pages);
2395
2396 /* Record the original scan target for proportional adjustments later */
2397 memcpy(targets, nr, sizeof(nr));
2398
2399 /*
2400 * Global reclaiming within direct reclaim at DEF_PRIORITY is a normal
2401 * event that can occur when there is little memory pressure e.g.
2402 * multiple streaming readers/writers. Hence, we do not abort scanning
2403 * when the requested number of pages are reclaimed when scanning at
2404 * DEF_PRIORITY on the assumption that the fact we are direct
2405 * reclaiming implies that kswapd is not keeping up and it is best to
2406 * do a batch of work at once. For memcg reclaim one check is made to
2407 * abort proportional reclaim if either the file or anon lru has already
2408 * dropped to zero at the first pass.
2409 */
2410 scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() &&
2411 sc->priority == DEF_PRIORITY);
2412
2413 blk_start_plug(&plug);
2414 while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
2415 nr[LRU_INACTIVE_FILE]) {
2416 unsigned long nr_anon, nr_file, percentage;
2417 unsigned long nr_scanned;
2418
2419 for_each_evictable_lru(lru) {
2420 if (nr[lru]) {
2421 nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
2422 nr[lru] -= nr_to_scan;
2423
2424 nr_reclaimed += shrink_list(lru, nr_to_scan,
2425 lruvec, memcg, sc);
2426 }
2427 }
2428
2429 cond_resched();
2430
2431 if (nr_reclaimed < nr_to_reclaim || scan_adjusted)
2432 continue;
2433
2434 /*
2435 * For kswapd and memcg, reclaim at least the number of pages
2436 * requested. Ensure that the anon and file LRUs are scanned
2437 * proportionally what was requested by get_scan_count(). We
2438 * stop reclaiming one LRU and reduce the amount scanning
2439 * proportional to the original scan target.
2440 */
2441 nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
2442 nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
2443
2444 /*
2445 * It's just vindictive to attack the larger once the smaller
2446 * has gone to zero. And given the way we stop scanning the
2447 * smaller below, this makes sure that we only make one nudge
2448 * towards proportionality once we've got nr_to_reclaim.
2449 */
2450 if (!nr_file || !nr_anon)
2451 break;
2452
2453 if (nr_file > nr_anon) {
2454 unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
2455 targets[LRU_ACTIVE_ANON] + 1;
2456 lru = LRU_BASE;
2457 percentage = nr_anon * 100 / scan_target;
2458 } else {
2459 unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
2460 targets[LRU_ACTIVE_FILE] + 1;
2461 lru = LRU_FILE;
2462 percentage = nr_file * 100 / scan_target;
2463 }
2464
2465 /* Stop scanning the smaller of the LRU */
2466 nr[lru] = 0;
2467 nr[lru + LRU_ACTIVE] = 0;
2468
2469 /*
2470 * Recalculate the other LRU scan count based on its original
2471 * scan target and the percentage scanning already complete
2472 */
2473 lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
2474 nr_scanned = targets[lru] - nr[lru];
2475 nr[lru] = targets[lru] * (100 - percentage) / 100;
2476 nr[lru] -= min(nr[lru], nr_scanned);
2477
2478 lru += LRU_ACTIVE;
2479 nr_scanned = targets[lru] - nr[lru];
2480 nr[lru] = targets[lru] * (100 - percentage) / 100;
2481 nr[lru] -= min(nr[lru], nr_scanned);
2482
2483 scan_adjusted = true;
2484 }
2485 blk_finish_plug(&plug);
2486 sc->nr_reclaimed += nr_reclaimed;
2487
2488 /*
2489 * Even if we did not try to evict anon pages at all, we want to
2490 * rebalance the anon lru active/inactive ratio.
2491 */
2492 if (inactive_list_is_low(lruvec, false, memcg, sc, true))
2493 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2494 sc, LRU_ACTIVE_ANON);
2495 }
2496
2497 /* Use reclaim/compaction for costly allocs or under memory pressure */
2498 static bool in_reclaim_compaction(struct scan_control *sc)
2499 {
2500 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2501 (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
2502 sc->priority < DEF_PRIORITY - 2))
2503 return true;
2504
2505 return false;
2506 }
2507
2508 /*
2509 * Reclaim/compaction is used for high-order allocation requests. It reclaims
2510 * order-0 pages before compacting the zone. should_continue_reclaim() returns
2511 * true if more pages should be reclaimed such that when the page allocator
2512 * calls try_to_compact_zone() that it will have enough free pages to succeed.
2513 * It will give up earlier than that if there is difficulty reclaiming pages.
2514 */
2515 static inline bool should_continue_reclaim(struct pglist_data *pgdat,
2516 unsigned long nr_reclaimed,
2517 unsigned long nr_scanned,
2518 struct scan_control *sc)
2519 {
2520 unsigned long pages_for_compaction;
2521 unsigned long inactive_lru_pages;
2522 int z;
2523
2524 /* If not in reclaim/compaction mode, stop */
2525 if (!in_reclaim_compaction(sc))
2526 return false;
2527
2528 /* Consider stopping depending on scan and reclaim activity */
2529 if (sc->gfp_mask & __GFP_RETRY_MAYFAIL) {
2530 /*
2531 * For __GFP_RETRY_MAYFAIL allocations, stop reclaiming if the
2532 * full LRU list has been scanned and we are still failing
2533 * to reclaim pages. This full LRU scan is potentially
2534 * expensive but a __GFP_RETRY_MAYFAIL caller really wants to succeed
2535 */
2536 if (!nr_reclaimed && !nr_scanned)
2537 return false;
2538 } else {
2539 /*
2540 * For non-__GFP_RETRY_MAYFAIL allocations which can presumably
2541 * fail without consequence, stop if we failed to reclaim
2542 * any pages from the last SWAP_CLUSTER_MAX number of
2543 * pages that were scanned. This will return to the
2544 * caller faster at the risk reclaim/compaction and
2545 * the resulting allocation attempt fails
2546 */
2547 if (!nr_reclaimed)
2548 return false;
2549 }
2550
2551 /*
2552 * If we have not reclaimed enough pages for compaction and the
2553 * inactive lists are large enough, continue reclaiming
2554 */
2555 pages_for_compaction = compact_gap(sc->order);
2556 inactive_lru_pages = node_page_state(pgdat, NR_INACTIVE_FILE);
2557 if (get_nr_swap_pages() > 0)
2558 inactive_lru_pages += node_page_state(pgdat, NR_INACTIVE_ANON);
2559 if (sc->nr_reclaimed < pages_for_compaction &&
2560 inactive_lru_pages > pages_for_compaction)
2561 return true;
2562
2563 /* If compaction would go ahead or the allocation would succeed, stop */
2564 for (z = 0; z <= sc->reclaim_idx; z++) {
2565 struct zone *zone = &pgdat->node_zones[z];
2566 if (!managed_zone(zone))
2567 continue;
2568
2569 switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) {
2570 case COMPACT_SUCCESS:
2571 case COMPACT_CONTINUE:
2572 return false;
2573 default:
2574 /* check next zone */
2575 ;
2576 }
2577 }
2578 return true;
2579 }
2580
2581 static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
2582 {
2583 struct reclaim_state *reclaim_state = current->reclaim_state;
2584 unsigned long nr_reclaimed, nr_scanned;
2585 bool reclaimable = false;
2586
2587 do {
2588 struct mem_cgroup *root = sc->target_mem_cgroup;
2589 struct mem_cgroup_reclaim_cookie reclaim = {
2590 .pgdat = pgdat,
2591 .priority = sc->priority,
2592 };
2593 unsigned long node_lru_pages = 0;
2594 struct mem_cgroup *memcg;
2595
2596 nr_reclaimed = sc->nr_reclaimed;
2597 nr_scanned = sc->nr_scanned;
2598
2599 memcg = mem_cgroup_iter(root, NULL, &reclaim);
2600 do {
2601 unsigned long lru_pages;
2602 unsigned long reclaimed;
2603 unsigned long scanned;
2604
2605 if (mem_cgroup_low(root, memcg)) {
2606 if (!sc->memcg_low_reclaim) {
2607 sc->memcg_low_skipped = 1;
2608 continue;
2609 }
2610 mem_cgroup_event(memcg, MEMCG_LOW);
2611 }
2612
2613 reclaimed = sc->nr_reclaimed;
2614 scanned = sc->nr_scanned;
2615
2616 shrink_node_memcg(pgdat, memcg, sc, &lru_pages);
2617 node_lru_pages += lru_pages;
2618
2619 if (memcg)
2620 shrink_slab(sc->gfp_mask, pgdat->node_id,
2621 memcg, sc->nr_scanned - scanned,
2622 lru_pages);
2623
2624 /* Record the group's reclaim efficiency */
2625 vmpressure(sc->gfp_mask, memcg, false,
2626 sc->nr_scanned - scanned,
2627 sc->nr_reclaimed - reclaimed);
2628
2629 /*
2630 * Direct reclaim and kswapd have to scan all memory
2631 * cgroups to fulfill the overall scan target for the
2632 * node.
2633 *
2634 * Limit reclaim, on the other hand, only cares about
2635 * nr_to_reclaim pages to be reclaimed and it will
2636 * retry with decreasing priority if one round over the
2637 * whole hierarchy is not sufficient.
2638 */
2639 if (!global_reclaim(sc) &&
2640 sc->nr_reclaimed >= sc->nr_to_reclaim) {
2641 mem_cgroup_iter_break(root, memcg);
2642 break;
2643 }
2644 } while ((memcg = mem_cgroup_iter(root, memcg, &reclaim)));
2645
2646 /*
2647 * Shrink the slab caches in the same proportion that
2648 * the eligible LRU pages were scanned.
2649 */
2650 if (global_reclaim(sc))
2651 shrink_slab(sc->gfp_mask, pgdat->node_id, NULL,
2652 sc->nr_scanned - nr_scanned,
2653 node_lru_pages);
2654
2655 if (reclaim_state) {
2656 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2657 reclaim_state->reclaimed_slab = 0;
2658 }
2659
2660 /* Record the subtree's reclaim efficiency */
2661 vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
2662 sc->nr_scanned - nr_scanned,
2663 sc->nr_reclaimed - nr_reclaimed);
2664
2665 if (sc->nr_reclaimed - nr_reclaimed)
2666 reclaimable = true;
2667
2668 } while (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
2669 sc->nr_scanned - nr_scanned, sc));
2670
2671 /*
2672 * Kswapd gives up on balancing particular nodes after too
2673 * many failures to reclaim anything from them and goes to
2674 * sleep. On reclaim progress, reset the failure counter. A
2675 * successful direct reclaim run will revive a dormant kswapd.
2676 */
2677 if (reclaimable)
2678 pgdat->kswapd_failures = 0;
2679
2680 return reclaimable;
2681 }
2682
2683 /*
2684 * Returns true if compaction should go ahead for a costly-order request, or
2685 * the allocation would already succeed without compaction. Return false if we
2686 * should reclaim first.
2687 */
2688 static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
2689 {
2690 unsigned long watermark;
2691 enum compact_result suitable;
2692
2693 suitable = compaction_suitable(zone, sc->order, 0, sc->reclaim_idx);
2694 if (suitable == COMPACT_SUCCESS)
2695 /* Allocation should succeed already. Don't reclaim. */
2696 return true;
2697 if (suitable == COMPACT_SKIPPED)
2698 /* Compaction cannot yet proceed. Do reclaim. */
2699 return false;
2700
2701 /*
2702 * Compaction is already possible, but it takes time to run and there
2703 * are potentially other callers using the pages just freed. So proceed
2704 * with reclaim to make a buffer of free pages available to give
2705 * compaction a reasonable chance of completing and allocating the page.
2706 * Note that we won't actually reclaim the whole buffer in one attempt
2707 * as the target watermark in should_continue_reclaim() is lower. But if
2708 * we are already above the high+gap watermark, don't reclaim at all.
2709 */
2710 watermark = high_wmark_pages(zone) + compact_gap(sc->order);
2711
2712 return zone_watermark_ok_safe(zone, 0, watermark, sc->reclaim_idx);
2713 }
2714
2715 /*
2716 * This is the direct reclaim path, for page-allocating processes. We only
2717 * try to reclaim pages from zones which will satisfy the caller's allocation
2718 * request.
2719 *
2720 * If a zone is deemed to be full of pinned pages then just give it a light
2721 * scan then give up on it.
2722 */
2723 static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
2724 {
2725 struct zoneref *z;
2726 struct zone *zone;
2727 unsigned long nr_soft_reclaimed;
2728 unsigned long nr_soft_scanned;
2729 gfp_t orig_mask;
2730 pg_data_t *last_pgdat = NULL;
2731
2732 /*
2733 * If the number of buffer_heads in the machine exceeds the maximum
2734 * allowed level, force direct reclaim to scan the highmem zone as
2735 * highmem pages could be pinning lowmem pages storing buffer_heads
2736 */
2737 orig_mask = sc->gfp_mask;
2738 if (buffer_heads_over_limit) {
2739 sc->gfp_mask |= __GFP_HIGHMEM;
2740 sc->reclaim_idx = gfp_zone(sc->gfp_mask);
2741 }
2742
2743 for_each_zone_zonelist_nodemask(zone, z, zonelist,
2744 sc->reclaim_idx, sc->nodemask) {
2745 /*
2746 * Take care memory controller reclaiming has small influence
2747 * to global LRU.
2748 */
2749 if (global_reclaim(sc)) {
2750 if (!cpuset_zone_allowed(zone,
2751 GFP_KERNEL | __GFP_HARDWALL))
2752 continue;
2753
2754 /*
2755 * If we already have plenty of memory free for
2756 * compaction in this zone, don't free any more.
2757 * Even though compaction is invoked for any
2758 * non-zero order, only frequent costly order
2759 * reclamation is disruptive enough to become a
2760 * noticeable problem, like transparent huge
2761 * page allocations.
2762 */
2763 if (IS_ENABLED(CONFIG_COMPACTION) &&
2764 sc->order > PAGE_ALLOC_COSTLY_ORDER &&
2765 compaction_ready(zone, sc)) {
2766 sc->compaction_ready = true;
2767 continue;
2768 }
2769
2770 /*
2771 * Shrink each node in the zonelist once. If the
2772 * zonelist is ordered by zone (not the default) then a
2773 * node may be shrunk multiple times but in that case
2774 * the user prefers lower zones being preserved.
2775 */
2776 if (zone->zone_pgdat == last_pgdat)
2777 continue;
2778
2779 /*
2780 * This steals pages from memory cgroups over softlimit
2781 * and returns the number of reclaimed pages and
2782 * scanned pages. This works for global memory pressure
2783 * and balancing, not for a memcg's limit.
2784 */
2785 nr_soft_scanned = 0;
2786 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone->zone_pgdat,
2787 sc->order, sc->gfp_mask,
2788 &nr_soft_scanned);
2789 sc->nr_reclaimed += nr_soft_reclaimed;
2790 sc->nr_scanned += nr_soft_scanned;
2791 /* need some check for avoid more shrink_zone() */
2792 }
2793
2794 /* See comment about same check for global reclaim above */
2795 if (zone->zone_pgdat == last_pgdat)
2796 continue;
2797 last_pgdat = zone->zone_pgdat;
2798 shrink_node(zone->zone_pgdat, sc);
2799 }
2800
2801 /*
2802 * Restore to original mask to avoid the impact on the caller if we
2803 * promoted it to __GFP_HIGHMEM.
2804 */
2805 sc->gfp_mask = orig_mask;
2806 }
2807
2808 static void snapshot_refaults(struct mem_cgroup *root_memcg, pg_data_t *pgdat)
2809 {
2810 struct mem_cgroup *memcg;
2811
2812 memcg = mem_cgroup_iter(root_memcg, NULL, NULL);
2813 do {
2814 unsigned long refaults;
2815 struct lruvec *lruvec;
2816
2817 if (memcg)
2818 refaults = memcg_page_state(memcg, WORKINGSET_ACTIVATE);
2819 else
2820 refaults = node_page_state(pgdat, WORKINGSET_ACTIVATE);
2821
2822 lruvec = mem_cgroup_lruvec(pgdat, memcg);
2823 lruvec->refaults = refaults;
2824 } while ((memcg = mem_cgroup_iter(root_memcg, memcg, NULL)));
2825 }
2826
2827 /*
2828 * This is the main entry point to direct page reclaim.
2829 *
2830 * If a full scan of the inactive list fails to free enough memory then we
2831 * are "out of memory" and something needs to be killed.
2832 *
2833 * If the caller is !__GFP_FS then the probability of a failure is reasonably
2834 * high - the zone may be full of dirty or under-writeback pages, which this
2835 * caller can't do much about. We kick the writeback threads and take explicit
2836 * naps in the hope that some of these pages can be written. But if the
2837 * allocating task holds filesystem locks which prevent writeout this might not
2838 * work, and the allocation attempt will fail.
2839 *
2840 * returns: 0, if no pages reclaimed
2841 * else, the number of pages reclaimed
2842 */
2843 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2844 struct scan_control *sc)
2845 {
2846 int initial_priority = sc->priority;
2847 pg_data_t *last_pgdat;
2848 struct zoneref *z;
2849 struct zone *zone;
2850 retry:
2851 delayacct_freepages_start();
2852
2853 if (global_reclaim(sc))
2854 __count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);
2855
2856 do {
2857 vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
2858 sc->priority);
2859 sc->nr_scanned = 0;
2860 shrink_zones(zonelist, sc);
2861
2862 if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2863 break;
2864
2865 if (sc->compaction_ready)
2866 break;
2867
2868 /*
2869 * If we're getting trouble reclaiming, start doing
2870 * writepage even in laptop mode.
2871 */
2872 if (sc->priority < DEF_PRIORITY - 2)
2873 sc->may_writepage = 1;
2874 } while (--sc->priority >= 0);
2875
2876 last_pgdat = NULL;
2877 for_each_zone_zonelist_nodemask(zone, z, zonelist, sc->reclaim_idx,
2878 sc->nodemask) {
2879 if (zone->zone_pgdat == last_pgdat)
2880 continue;
2881 last_pgdat = zone->zone_pgdat;
2882 snapshot_refaults(sc->target_mem_cgroup, zone->zone_pgdat);
2883 }
2884
2885 delayacct_freepages_end();
2886
2887 if (sc->nr_reclaimed)
2888 return sc->nr_reclaimed;
2889
2890 /* Aborted reclaim to try compaction? don't OOM, then */
2891 if (sc->compaction_ready)
2892 return 1;
2893
2894 /* Untapped cgroup reserves? Don't OOM, retry. */
2895 if (sc->memcg_low_skipped) {
2896 sc->priority = initial_priority;
2897 sc->memcg_low_reclaim = 1;
2898 sc->memcg_low_skipped = 0;
2899 goto retry;
2900 }
2901
2902 return 0;
2903 }
2904
2905 static bool allow_direct_reclaim(pg_data_t *pgdat)
2906 {
2907 struct zone *zone;
2908 unsigned long pfmemalloc_reserve = 0;
2909 unsigned long free_pages = 0;
2910 int i;
2911 bool wmark_ok;
2912
2913 if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
2914 return true;
2915
2916 for (i = 0; i <= ZONE_NORMAL; i++) {
2917 zone = &pgdat->node_zones[i];
2918 if (!managed_zone(zone))
2919 continue;
2920
2921 if (!zone_reclaimable_pages(zone))
2922 continue;
2923
2924 pfmemalloc_reserve += min_wmark_pages(zone);
2925 free_pages += zone_page_state(zone, NR_FREE_PAGES);
2926 }
2927
2928 /* If there are no reserves (unexpected config) then do not throttle */
2929 if (!pfmemalloc_reserve)
2930 return true;
2931
2932 wmark_ok = free_pages > pfmemalloc_reserve / 2;
2933
2934 /* kswapd must be awake if processes are being throttled */
2935 if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2936 pgdat->kswapd_classzone_idx = min(pgdat->kswapd_classzone_idx,
2937 (enum zone_type)ZONE_NORMAL);
2938 wake_up_interruptible(&pgdat->kswapd_wait);
2939 }
2940
2941 return wmark_ok;
2942 }
2943
2944 /*
2945 * Throttle direct reclaimers if backing storage is backed by the network
2946 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
2947 * depleted. kswapd will continue to make progress and wake the processes
2948 * when the low watermark is reached.
2949 *
2950 * Returns true if a fatal signal was delivered during throttling. If this
2951 * happens, the page allocator should not consider triggering the OOM killer.
2952 */
2953 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2954 nodemask_t *nodemask)
2955 {
2956 struct zoneref *z;
2957 struct zone *zone;
2958 pg_data_t *pgdat = NULL;
2959
2960 /*
2961 * Kernel threads should not be throttled as they may be indirectly
2962 * responsible for cleaning pages necessary for reclaim to make forward
2963 * progress. kjournald for example may enter direct reclaim while
2964 * committing a transaction where throttling it could forcing other
2965 * processes to block on log_wait_commit().
2966 */
2967 if (current->flags & PF_KTHREAD)
2968 goto out;
2969
2970 /*
2971 * If a fatal signal is pending, this process should not throttle.
2972 * It should return quickly so it can exit and free its memory
2973 */
2974 if (fatal_signal_pending(current))
2975 goto out;
2976
2977 /*
2978 * Check if the pfmemalloc reserves are ok by finding the first node
2979 * with a usable ZONE_NORMAL or lower zone. The expectation is that
2980 * GFP_KERNEL will be required for allocating network buffers when
2981 * swapping over the network so ZONE_HIGHMEM is unusable.
2982 *
2983 * Throttling is based on the first usable node and throttled processes
2984 * wait on a queue until kswapd makes progress and wakes them. There
2985 * is an affinity then between processes waking up and where reclaim
2986 * progress has been made assuming the process wakes on the same node.
2987 * More importantly, processes running on remote nodes will not compete
2988 * for remote pfmemalloc reserves and processes on different nodes
2989 * should make reasonable progress.
2990 */
2991 for_each_zone_zonelist_nodemask(zone, z, zonelist,
2992 gfp_zone(gfp_mask), nodemask) {
2993 if (zone_idx(zone) > ZONE_NORMAL)
2994 continue;
2995
2996 /* Throttle based on the first usable node */
2997 pgdat = zone->zone_pgdat;
2998 if (allow_direct_reclaim(pgdat))
2999 goto out;
3000 break;
3001 }
3002
3003 /* If no zone was usable by the allocation flags then do not throttle */
3004 if (!pgdat)
3005 goto out;
3006
3007 /* Account for the throttling */
3008 count_vm_event(PGSCAN_DIRECT_THROTTLE);
3009
3010 /*
3011 * If the caller cannot enter the filesystem, it's possible that it
3012 * is due to the caller holding an FS lock or performing a journal
3013 * transaction in the case of a filesystem like ext[3|4]. In this case,
3014 * it is not safe to block on pfmemalloc_wait as kswapd could be
3015 * blocked waiting on the same lock. Instead, throttle for up to a
3016 * second before continuing.
3017 */
3018 if (!(gfp_mask & __GFP_FS)) {
3019 wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
3020 allow_direct_reclaim(pgdat), HZ);
3021
3022 goto check_pending;
3023 }
3024
3025 /* Throttle until kswapd wakes the process */
3026 wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
3027 allow_direct_reclaim(pgdat));
3028
3029 check_pending:
3030 if (fatal_signal_pending(current))
3031 return true;
3032
3033 out:
3034 return false;
3035 }
3036
3037 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
3038 gfp_t gfp_mask, nodemask_t *nodemask)
3039 {
3040 unsigned long nr_reclaimed;
3041 struct scan_control sc = {
3042 .nr_to_reclaim = SWAP_CLUSTER_MAX,
3043 .gfp_mask = current_gfp_context(gfp_mask),
3044 .reclaim_idx = gfp_zone(gfp_mask),
3045 .order = order,
3046 .nodemask = nodemask,
3047 .priority = DEF_PRIORITY,
3048 .may_writepage = !laptop_mode,
3049 .may_unmap = 1,
3050 .may_swap = 1,
3051 };
3052
3053 /*
3054 * Do not enter reclaim if fatal signal was delivered while throttled.
3055 * 1 is returned so that the page allocator does not OOM kill at this
3056 * point.
3057 */
3058 if (throttle_direct_reclaim(sc.gfp_mask, zonelist, nodemask))
3059 return 1;
3060
3061 trace_mm_vmscan_direct_reclaim_begin(order,
3062 sc.may_writepage,
3063 sc.gfp_mask,
3064 sc.reclaim_idx);
3065
3066 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3067
3068 trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
3069
3070 return nr_reclaimed;
3071 }
3072
3073 #ifdef CONFIG_MEMCG
3074
3075 unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
3076 gfp_t gfp_mask, bool noswap,
3077 pg_data_t *pgdat,
3078 unsigned long *nr_scanned)
3079 {
3080 struct scan_control sc = {
3081 .nr_to_reclaim = SWAP_CLUSTER_MAX,
3082 .target_mem_cgroup = memcg,
3083 .may_writepage = !laptop_mode,
3084 .may_unmap = 1,
3085 .reclaim_idx = MAX_NR_ZONES - 1,
3086 .may_swap = !noswap,
3087 };
3088 unsigned long lru_pages;
3089
3090 sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
3091 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
3092
3093 trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
3094 sc.may_writepage,
3095 sc.gfp_mask,
3096 sc.reclaim_idx);
3097
3098 /*
3099 * NOTE: Although we can get the priority field, using it
3100 * here is not a good idea, since it limits the pages we can scan.
3101 * if we don't reclaim here, the shrink_node from balance_pgdat
3102 * will pick up pages from other mem cgroup's as well. We hack
3103 * the priority and make it zero.
3104 */
3105 shrink_node_memcg(pgdat, memcg, &sc, &lru_pages);
3106
3107 trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
3108
3109 *nr_scanned = sc.nr_scanned;
3110 return sc.nr_reclaimed;
3111 }
3112
3113 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
3114 unsigned long nr_pages,
3115 gfp_t gfp_mask,
3116 bool may_swap)
3117 {
3118 struct zonelist *zonelist;
3119 unsigned long nr_reclaimed;
3120 int nid;
3121 unsigned int noreclaim_flag;
3122 struct scan_control sc = {
3123 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3124 .gfp_mask = (current_gfp_context(gfp_mask) & GFP_RECLAIM_MASK) |
3125 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
3126 .reclaim_idx = MAX_NR_ZONES - 1,
3127 .target_mem_cgroup = memcg,
3128 .priority = DEF_PRIORITY,
3129 .may_writepage = !laptop_mode,
3130 .may_unmap = 1,
3131 .may_swap = may_swap,
3132 };
3133
3134 /*
3135 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
3136 * take care of from where we get pages. So the node where we start the
3137 * scan does not need to be the current node.
3138 */
3139 nid = mem_cgroup_select_victim_node(memcg);
3140
3141 zonelist = &NODE_DATA(nid)->node_zonelists[ZONELIST_FALLBACK];
3142
3143 trace_mm_vmscan_memcg_reclaim_begin(0,
3144 sc.may_writepage,
3145 sc.gfp_mask,
3146 sc.reclaim_idx);
3147
3148 noreclaim_flag = memalloc_noreclaim_save();
3149 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3150 memalloc_noreclaim_restore(noreclaim_flag);
3151
3152 trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
3153
3154 return nr_reclaimed;
3155 }
3156 #endif
3157
3158 static void age_active_anon(struct pglist_data *pgdat,
3159 struct scan_control *sc)
3160 {
3161 struct mem_cgroup *memcg;
3162
3163 if (!total_swap_pages)
3164 return;
3165
3166 memcg = mem_cgroup_iter(NULL, NULL, NULL);
3167 do {
3168 struct lruvec *lruvec = mem_cgroup_lruvec(pgdat, memcg);
3169
3170 if (inactive_list_is_low(lruvec, false, memcg, sc, true))
3171 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
3172 sc, LRU_ACTIVE_ANON);
3173
3174 memcg = mem_cgroup_iter(NULL, memcg, NULL);
3175 } while (memcg);
3176 }
3177
3178 /*
3179 * Returns true if there is an eligible zone balanced for the request order
3180 * and classzone_idx
3181 */
3182 static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
3183 {
3184 int i;
3185 unsigned long mark = -1;
3186 struct zone *zone;
3187
3188 for (i = 0; i <= classzone_idx; i++) {
3189 zone = pgdat->node_zones + i;
3190
3191 if (!managed_zone(zone))
3192 continue;
3193
3194 mark = high_wmark_pages(zone);
3195 if (zone_watermark_ok_safe(zone, order, mark, classzone_idx))
3196 return true;
3197 }
3198
3199 /*
3200 * If a node has no populated zone within classzone_idx, it does not
3201 * need balancing by definition. This can happen if a zone-restricted
3202 * allocation tries to wake a remote kswapd.
3203 */
3204 if (mark == -1)
3205 return true;
3206
3207 return false;
3208 }
3209
3210 /* Clear pgdat state for congested, dirty or under writeback. */
3211 static void clear_pgdat_congested(pg_data_t *pgdat)
3212 {
3213 clear_bit(PGDAT_CONGESTED, &pgdat->flags);
3214 clear_bit(PGDAT_DIRTY, &pgdat->flags);
3215 clear_bit(PGDAT_WRITEBACK, &pgdat->flags);
3216 }
3217
3218 /*
3219 * Prepare kswapd for sleeping. This verifies that there are no processes
3220 * waiting in throttle_direct_reclaim() and that watermarks have been met.
3221 *
3222 * Returns true if kswapd is ready to sleep
3223 */
3224 static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, int classzone_idx)
3225 {
3226 /*
3227 * The throttled processes are normally woken up in balance_pgdat() as
3228 * soon as allow_direct_reclaim() is true. But there is a potential
3229 * race between when kswapd checks the watermarks and a process gets
3230 * throttled. There is also a potential race if processes get
3231 * throttled, kswapd wakes, a large process exits thereby balancing the
3232 * zones, which causes kswapd to exit balance_pgdat() before reaching
3233 * the wake up checks. If kswapd is going to sleep, no process should
3234 * be sleeping on pfmemalloc_wait, so wake them now if necessary. If
3235 * the wake up is premature, processes will wake kswapd and get
3236 * throttled again. The difference from wake ups in balance_pgdat() is
3237 * that here we are under prepare_to_wait().
3238 */
3239 if (waitqueue_active(&pgdat->pfmemalloc_wait))
3240 wake_up_all(&pgdat->pfmemalloc_wait);
3241
3242 /* Hopeless node, leave it to direct reclaim */
3243 if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
3244 return true;
3245
3246 if (pgdat_balanced(pgdat, order, classzone_idx)) {
3247 clear_pgdat_congested(pgdat);
3248 return true;
3249 }
3250
3251 return false;
3252 }
3253
3254 /*
3255 * kswapd shrinks a node of pages that are at or below the highest usable
3256 * zone that is currently unbalanced.
3257 *
3258 * Returns true if kswapd scanned at least the requested number of pages to
3259 * reclaim or if the lack of progress was due to pages under writeback.
3260 * This is used to determine if the scanning priority needs to be raised.
3261 */
3262 static bool kswapd_shrink_node(pg_data_t *pgdat,
3263 struct scan_control *sc)
3264 {
3265 struct zone *zone;
3266 int z;
3267
3268 /* Reclaim a number of pages proportional to the number of zones */
3269 sc->nr_to_reclaim = 0;
3270 for (z = 0; z <= sc->reclaim_idx; z++) {
3271 zone = pgdat->node_zones + z;
3272 if (!managed_zone(zone))
3273 continue;
3274
3275 sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX);
3276 }
3277
3278 /*
3279 * Historically care was taken to put equal pressure on all zones but
3280 * now pressure is applied based on node LRU order.
3281 */
3282 shrink_node(pgdat, sc);
3283
3284 /*
3285 * Fragmentation may mean that the system cannot be rebalanced for
3286 * high-order allocations. If twice the allocation size has been
3287 * reclaimed then recheck watermarks only at order-0 to prevent
3288 * excessive reclaim. Assume that a process requested a high-order
3289 * can direct reclaim/compact.
3290 */
3291 if (sc->order && sc->nr_reclaimed >= compact_gap(sc->order))
3292 sc->order = 0;
3293
3294 return sc->nr_scanned >= sc->nr_to_reclaim;
3295 }
3296
3297 /*
3298 * For kswapd, balance_pgdat() will reclaim pages across a node from zones
3299 * that are eligible for use by the caller until at least one zone is
3300 * balanced.
3301 *
3302 * Returns the order kswapd finished reclaiming at.
3303 *
3304 * kswapd scans the zones in the highmem->normal->dma direction. It skips
3305 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
3306 * found to have free_pages <= high_wmark_pages(zone), any page is that zone
3307 * or lower is eligible for reclaim until at least one usable zone is
3308 * balanced.
3309 */
3310 static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
3311 {
3312 int i;
3313 unsigned long nr_soft_reclaimed;
3314 unsigned long nr_soft_scanned;
3315 struct zone *zone;
3316 struct scan_control sc = {
3317 .gfp_mask = GFP_KERNEL,
3318 .order = order,
3319 .priority = DEF_PRIORITY,
3320 .may_writepage = !laptop_mode,
3321 .may_unmap = 1,
3322 .may_swap = 1,
3323 };
3324 count_vm_event(PAGEOUTRUN);
3325
3326 do {
3327 unsigned long nr_reclaimed = sc.nr_reclaimed;
3328 bool raise_priority = true;
3329
3330 sc.reclaim_idx = classzone_idx;
3331
3332 /*
3333 * If the number of buffer_heads exceeds the maximum allowed
3334 * then consider reclaiming from all zones. This has a dual
3335 * purpose -- on 64-bit systems it is expected that
3336 * buffer_heads are stripped during active rotation. On 32-bit
3337 * systems, highmem pages can pin lowmem memory and shrinking
3338 * buffers can relieve lowmem pressure. Reclaim may still not
3339 * go ahead if all eligible zones for the original allocation
3340 * request are balanced to avoid excessive reclaim from kswapd.
3341 */
3342 if (buffer_heads_over_limit) {
3343 for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
3344 zone = pgdat->node_zones + i;
3345 if (!managed_zone(zone))
3346 continue;
3347
3348 sc.reclaim_idx = i;
3349 break;
3350 }
3351 }
3352
3353 /*
3354 * Only reclaim if there are no eligible zones. Note that
3355 * sc.reclaim_idx is not used as buffer_heads_over_limit may
3356 * have adjusted it.
3357 */
3358 if (pgdat_balanced(pgdat, sc.order, classzone_idx))
3359 goto out;
3360
3361 /*
3362 * Do some background aging of the anon list, to give
3363 * pages a chance to be referenced before reclaiming. All
3364 * pages are rotated regardless of classzone as this is
3365 * about consistent aging.
3366 */
3367 age_active_anon(pgdat, &sc);
3368
3369 /*
3370 * If we're getting trouble reclaiming, start doing writepage
3371 * even in laptop mode.
3372 */
3373 if (sc.priority < DEF_PRIORITY - 2)
3374 sc.may_writepage = 1;
3375
3376 /* Call soft limit reclaim before calling shrink_node. */
3377 sc.nr_scanned = 0;
3378 nr_soft_scanned = 0;
3379 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(pgdat, sc.order,
3380 sc.gfp_mask, &nr_soft_scanned);
3381 sc.nr_reclaimed += nr_soft_reclaimed;
3382
3383 /*
3384 * There should be no need to raise the scanning priority if
3385 * enough pages are already being scanned that that high
3386 * watermark would be met at 100% efficiency.
3387 */
3388 if (kswapd_shrink_node(pgdat, &sc))
3389 raise_priority = false;
3390
3391 /*
3392 * If the low watermark is met there is no need for processes
3393 * to be throttled on pfmemalloc_wait as they should not be
3394 * able to safely make forward progress. Wake them
3395 */
3396 if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
3397 allow_direct_reclaim(pgdat))
3398 wake_up_all(&pgdat->pfmemalloc_wait);
3399
3400 /* Check if kswapd should be suspending */
3401 if (try_to_freeze() || kthread_should_stop())
3402 break;
3403
3404 /*
3405 * Raise priority if scanning rate is too low or there was no
3406 * progress in reclaiming pages
3407 */
3408 nr_reclaimed = sc.nr_reclaimed - nr_reclaimed;
3409 if (raise_priority || !nr_reclaimed)
3410 sc.priority--;
3411 } while (sc.priority >= 1);
3412
3413 if (!sc.nr_reclaimed)
3414 pgdat->kswapd_failures++;
3415
3416 out:
3417 snapshot_refaults(NULL, pgdat);
3418 /*
3419 * Return the order kswapd stopped reclaiming at as
3420 * prepare_kswapd_sleep() takes it into account. If another caller
3421 * entered the allocator slow path while kswapd was awake, order will
3422 * remain at the higher level.
3423 */
3424 return sc.order;
3425 }
3426
3427 /*
3428 * pgdat->kswapd_classzone_idx is the highest zone index that a recent
3429 * allocation request woke kswapd for. When kswapd has not woken recently,
3430 * the value is MAX_NR_ZONES which is not a valid index. This compares a
3431 * given classzone and returns it or the highest classzone index kswapd
3432 * was recently woke for.
3433 */
3434 static enum zone_type kswapd_classzone_idx(pg_data_t *pgdat,
3435 enum zone_type classzone_idx)
3436 {
3437 if (pgdat->kswapd_classzone_idx == MAX_NR_ZONES)
3438 return classzone_idx;
3439
3440 return max(pgdat->kswapd_classzone_idx, classzone_idx);
3441 }
3442
3443 static void kswapd_try_to_sleep(pg_data_t *pgdat, int alloc_order, int reclaim_order,
3444 unsigned int classzone_idx)
3445 {
3446 long remaining = 0;
3447 DEFINE_WAIT(wait);
3448
3449 if (freezing(current) || kthread_should_stop())
3450 return;
3451
3452 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3453
3454 /*
3455 * Try to sleep for a short interval. Note that kcompactd will only be
3456 * woken if it is possible to sleep for a short interval. This is
3457 * deliberate on the assumption that if reclaim cannot keep an
3458 * eligible zone balanced that it's also unlikely that compaction will
3459 * succeed.
3460 */
3461 if (prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3462 /*
3463 * Compaction records what page blocks it recently failed to
3464 * isolate pages from and skips them in the future scanning.
3465 * When kswapd is going to sleep, it is reasonable to assume
3466 * that pages and compaction may succeed so reset the cache.
3467 */
3468 reset_isolation_suitable(pgdat);
3469
3470 /*
3471 * We have freed the memory, now we should compact it to make
3472 * allocation of the requested order possible.
3473 */
3474 wakeup_kcompactd(pgdat, alloc_order, classzone_idx);
3475
3476 remaining = schedule_timeout(HZ/10);
3477
3478 /*
3479 * If woken prematurely then reset kswapd_classzone_idx and
3480 * order. The values will either be from a wakeup request or
3481 * the previous request that slept prematurely.
3482 */
3483 if (remaining) {
3484 pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
3485 pgdat->kswapd_order = max(pgdat->kswapd_order, reclaim_order);
3486 }
3487
3488 finish_wait(&pgdat->kswapd_wait, &wait);
3489 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3490 }
3491
3492 /*
3493 * After a short sleep, check if it was a premature sleep. If not, then
3494 * go fully to sleep until explicitly woken up.
3495 */
3496 if (!remaining &&
3497 prepare_kswapd_sleep(pgdat, reclaim_order, classzone_idx)) {
3498 trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
3499
3500 /*
3501 * vmstat counters are not perfectly accurate and the estimated
3502 * value for counters such as NR_FREE_PAGES can deviate from the
3503 * true value by nr_online_cpus * threshold. To avoid the zone
3504 * watermarks being breached while under pressure, we reduce the
3505 * per-cpu vmstat threshold while kswapd is awake and restore
3506 * them before going back to sleep.
3507 */
3508 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
3509
3510 if (!kthread_should_stop())
3511 schedule();
3512
3513 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
3514 } else {
3515 if (remaining)
3516 count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
3517 else
3518 count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
3519 }
3520 finish_wait(&pgdat->kswapd_wait, &wait);
3521 }
3522
3523 /*
3524 * The background pageout daemon, started as a kernel thread
3525 * from the init process.
3526 *
3527 * This basically trickles out pages so that we have _some_
3528 * free memory available even if there is no other activity
3529 * that frees anything up. This is needed for things like routing
3530 * etc, where we otherwise might have all activity going on in
3531 * asynchronous contexts that cannot page things out.
3532 *
3533 * If there are applications that are active memory-allocators
3534 * (most normal use), this basically shouldn't matter.
3535 */
3536 static int kswapd(void *p)
3537 {
3538 unsigned int alloc_order, reclaim_order;
3539 unsigned int classzone_idx = MAX_NR_ZONES - 1;
3540 pg_data_t *pgdat = (pg_data_t*)p;
3541 struct task_struct *tsk = current;
3542
3543 struct reclaim_state reclaim_state = {
3544 .reclaimed_slab = 0,
3545 };
3546 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
3547
3548 if (!cpumask_empty(cpumask))
3549 set_cpus_allowed_ptr(tsk, cpumask);
3550 current->reclaim_state = &reclaim_state;
3551
3552 /*
3553 * Tell the memory management that we're a "memory allocator",
3554 * and that if we need more memory we should get access to it
3555 * regardless (see "__alloc_pages()"). "kswapd" should
3556 * never get caught in the normal page freeing logic.
3557 *
3558 * (Kswapd normally doesn't need memory anyway, but sometimes
3559 * you need a small amount of memory in order to be able to
3560 * page out something else, and this flag essentially protects
3561 * us from recursively trying to free more memory as we're
3562 * trying to free the first piece of memory in the first place).
3563 */
3564 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
3565 set_freezable();
3566
3567 pgdat->kswapd_order = 0;
3568 pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
3569 for ( ; ; ) {
3570 bool ret;
3571
3572 alloc_order = reclaim_order = pgdat->kswapd_order;
3573 classzone_idx = kswapd_classzone_idx(pgdat, classzone_idx);
3574
3575 kswapd_try_sleep:
3576 kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
3577 classzone_idx);
3578
3579 /* Read the new order and classzone_idx */
3580 alloc_order = reclaim_order = pgdat->kswapd_order;
3581 classzone_idx = kswapd_classzone_idx(pgdat, 0);
3582 pgdat->kswapd_order = 0;
3583 pgdat->kswapd_classzone_idx = MAX_NR_ZONES;
3584
3585 ret = try_to_freeze();
3586 if (kthread_should_stop())
3587 break;
3588
3589 /*
3590 * We can speed up thawing tasks if we don't call balance_pgdat
3591 * after returning from the refrigerator
3592 */
3593 if (ret)
3594 continue;
3595
3596 /*
3597 * Reclaim begins at the requested order but if a high-order
3598 * reclaim fails then kswapd falls back to reclaiming for
3599 * order-0. If that happens, kswapd will consider sleeping
3600 * for the order it finished reclaiming at (reclaim_order)
3601 * but kcompactd is woken to compact for the original
3602 * request (alloc_order).
3603 */
3604 trace_mm_vmscan_kswapd_wake(pgdat->node_id, classzone_idx,
3605 alloc_order);
3606 fs_reclaim_acquire(GFP_KERNEL);
3607 reclaim_order = balance_pgdat(pgdat, alloc_order, classzone_idx);
3608 fs_reclaim_release(GFP_KERNEL);
3609 if (reclaim_order < alloc_order)
3610 goto kswapd_try_sleep;
3611 }
3612
3613 tsk->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD);
3614 current->reclaim_state = NULL;
3615
3616 return 0;
3617 }
3618
3619 /*
3620 * A zone is low on free memory, so wake its kswapd task to service it.
3621 */
3622 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
3623 {
3624 pg_data_t *pgdat;
3625
3626 if (!managed_zone(zone))
3627 return;
3628
3629 if (!cpuset_zone_allowed(zone, GFP_KERNEL | __GFP_HARDWALL))
3630 return;
3631 pgdat = zone->zone_pgdat;
3632 pgdat->kswapd_classzone_idx = kswapd_classzone_idx(pgdat,
3633 classzone_idx);
3634 pgdat->kswapd_order = max(pgdat->kswapd_order, order);
3635 if (!waitqueue_active(&pgdat->kswapd_wait))
3636 return;
3637
3638 /* Hopeless node, leave it to direct reclaim */
3639 if (pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES)
3640 return;
3641
3642 if (pgdat_balanced(pgdat, order, classzone_idx))
3643 return;
3644
3645 trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, classzone_idx, order);
3646 wake_up_interruptible(&pgdat->kswapd_wait);
3647 }
3648
3649 #ifdef CONFIG_HIBERNATION
3650 /*
3651 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3652 * freed pages.
3653 *
3654 * Rather than trying to age LRUs the aim is to preserve the overall
3655 * LRU order by reclaiming preferentially
3656 * inactive > active > active referenced > active mapped
3657 */
3658 unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3659 {
3660 struct reclaim_state reclaim_state;
3661 struct scan_control sc = {
3662 .nr_to_reclaim = nr_to_reclaim,
3663 .gfp_mask = GFP_HIGHUSER_MOVABLE,
3664 .reclaim_idx = MAX_NR_ZONES - 1,
3665 .priority = DEF_PRIORITY,
3666 .may_writepage = 1,
3667 .may_unmap = 1,
3668 .may_swap = 1,
3669 .hibernation_mode = 1,
3670 };
3671 struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3672 struct task_struct *p = current;
3673 unsigned long nr_reclaimed;
3674 unsigned int noreclaim_flag;
3675
3676 noreclaim_flag = memalloc_noreclaim_save();
3677 fs_reclaim_acquire(sc.gfp_mask);
3678 reclaim_state.reclaimed_slab = 0;
3679 p->reclaim_state = &reclaim_state;
3680
3681 nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
3682
3683 p->reclaim_state = NULL;
3684 fs_reclaim_release(sc.gfp_mask);
3685 memalloc_noreclaim_restore(noreclaim_flag);
3686
3687 return nr_reclaimed;
3688 }
3689 #endif /* CONFIG_HIBERNATION */
3690
3691 /* It's optimal to keep kswapds on the same CPUs as their memory, but
3692 not required for correctness. So if the last cpu in a node goes
3693 away, we get changed to run anywhere: as the first one comes back,
3694 restore their cpu bindings. */
3695 static int kswapd_cpu_online(unsigned int cpu)
3696 {
3697 int nid;
3698
3699 for_each_node_state(nid, N_MEMORY) {
3700 pg_data_t *pgdat = NODE_DATA(nid);
3701 const struct cpumask *mask;
3702
3703 mask = cpumask_of_node(pgdat->node_id);
3704
3705 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3706 /* One of our CPUs online: restore mask */
3707 set_cpus_allowed_ptr(pgdat->kswapd, mask);
3708 }
3709 return 0;
3710 }
3711
3712 /*
3713 * This kswapd start function will be called by init and node-hot-add.
3714 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3715 */
3716 int kswapd_run(int nid)
3717 {
3718 pg_data_t *pgdat = NODE_DATA(nid);
3719 int ret = 0;
3720
3721 if (pgdat->kswapd)
3722 return 0;
3723
3724 pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3725 if (IS_ERR(pgdat->kswapd)) {
3726 /* failure at boot is fatal */
3727 BUG_ON(system_state < SYSTEM_RUNNING);
3728 pr_err("Failed to start kswapd on node %d\n", nid);
3729 ret = PTR_ERR(pgdat->kswapd);
3730 pgdat->kswapd = NULL;
3731 }
3732 return ret;
3733 }
3734
3735 /*
3736 * Called by memory hotplug when all memory in a node is offlined. Caller must
3737 * hold mem_hotplug_begin/end().
3738 */
3739 void kswapd_stop(int nid)
3740 {
3741 struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3742
3743 if (kswapd) {
3744 kthread_stop(kswapd);
3745 NODE_DATA(nid)->kswapd = NULL;
3746 }
3747 }
3748
3749 static int __init kswapd_init(void)
3750 {
3751 int nid, ret;
3752
3753 swap_setup();
3754 for_each_node_state(nid, N_MEMORY)
3755 kswapd_run(nid);
3756 ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
3757 "mm/vmscan:online", kswapd_cpu_online,
3758 NULL);
3759 WARN_ON(ret < 0);
3760 return 0;
3761 }
3762
3763 module_init(kswapd_init)
3764
3765 #ifdef CONFIG_NUMA
3766 /*
3767 * Node reclaim mode
3768 *
3769 * If non-zero call node_reclaim when the number of free pages falls below
3770 * the watermarks.
3771 */
3772 int node_reclaim_mode __read_mostly;
3773
3774 #define RECLAIM_OFF 0
3775 #define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
3776 #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
3777 #define RECLAIM_UNMAP (1<<2) /* Unmap pages during reclaim */
3778
3779 /*
3780 * Priority for NODE_RECLAIM. This determines the fraction of pages
3781 * of a node considered for each zone_reclaim. 4 scans 1/16th of
3782 * a zone.
3783 */
3784 #define NODE_RECLAIM_PRIORITY 4
3785
3786 /*
3787 * Percentage of pages in a zone that must be unmapped for node_reclaim to
3788 * occur.
3789 */
3790 int sysctl_min_unmapped_ratio = 1;
3791
3792 /*
3793 * If the number of slab pages in a zone grows beyond this percentage then
3794 * slab reclaim needs to occur.
3795 */
3796 int sysctl_min_slab_ratio = 5;
3797
3798 static inline unsigned long node_unmapped_file_pages(struct pglist_data *pgdat)
3799 {
3800 unsigned long file_mapped = node_page_state(pgdat, NR_FILE_MAPPED);
3801 unsigned long file_lru = node_page_state(pgdat, NR_INACTIVE_FILE) +
3802 node_page_state(pgdat, NR_ACTIVE_FILE);
3803
3804 /*
3805 * It's possible for there to be more file mapped pages than
3806 * accounted for by the pages on the file LRU lists because
3807 * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3808 */
3809 return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3810 }
3811
3812 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
3813 static unsigned long node_pagecache_reclaimable(struct pglist_data *pgdat)
3814 {
3815 unsigned long nr_pagecache_reclaimable;
3816 unsigned long delta = 0;
3817
3818 /*
3819 * If RECLAIM_UNMAP is set, then all file pages are considered
3820 * potentially reclaimable. Otherwise, we have to worry about
3821 * pages like swapcache and node_unmapped_file_pages() provides
3822 * a better estimate
3823 */
3824 if (node_reclaim_mode & RECLAIM_UNMAP)
3825 nr_pagecache_reclaimable = node_page_state(pgdat, NR_FILE_PAGES);
3826 else
3827 nr_pagecache_reclaimable = node_unmapped_file_pages(pgdat);
3828
3829 /* If we can't clean pages, remove dirty pages from consideration */
3830 if (!(node_reclaim_mode & RECLAIM_WRITE))
3831 delta += node_page_state(pgdat, NR_FILE_DIRTY);
3832
3833 /* Watch for any possible underflows due to delta */
3834 if (unlikely(delta > nr_pagecache_reclaimable))
3835 delta = nr_pagecache_reclaimable;
3836
3837 return nr_pagecache_reclaimable - delta;
3838 }
3839
3840 /*
3841 * Try to free up some pages from this node through reclaim.
3842 */
3843 static int __node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
3844 {
3845 /* Minimum pages needed in order to stay on node */
3846 const unsigned long nr_pages = 1 << order;
3847 struct task_struct *p = current;
3848 struct reclaim_state reclaim_state;
3849 unsigned int noreclaim_flag;
3850 struct scan_control sc = {
3851 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3852 .gfp_mask = current_gfp_context(gfp_mask),
3853 .order = order,
3854 .priority = NODE_RECLAIM_PRIORITY,
3855 .may_writepage = !!(node_reclaim_mode & RECLAIM_WRITE),
3856 .may_unmap = !!(node_reclaim_mode & RECLAIM_UNMAP),
3857 .may_swap = 1,
3858 .reclaim_idx = gfp_zone(gfp_mask),
3859 };
3860
3861 cond_resched();
3862 /*
3863 * We need to be able to allocate from the reserves for RECLAIM_UNMAP
3864 * and we also need to be able to write out pages for RECLAIM_WRITE
3865 * and RECLAIM_UNMAP.
3866 */
3867 noreclaim_flag = memalloc_noreclaim_save();
3868 p->flags |= PF_SWAPWRITE;
3869 fs_reclaim_acquire(sc.gfp_mask);
3870 reclaim_state.reclaimed_slab = 0;
3871 p->reclaim_state = &reclaim_state;
3872
3873 if (node_pagecache_reclaimable(pgdat) > pgdat->min_unmapped_pages) {
3874 /*
3875 * Free memory by calling shrink zone with increasing
3876 * priorities until we have enough memory freed.
3877 */
3878 do {
3879 shrink_node(pgdat, &sc);
3880 } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3881 }
3882
3883 p->reclaim_state = NULL;
3884 fs_reclaim_release(gfp_mask);
3885 current->flags &= ~PF_SWAPWRITE;
3886 memalloc_noreclaim_restore(noreclaim_flag);
3887 return sc.nr_reclaimed >= nr_pages;
3888 }
3889
3890 int node_reclaim(struct pglist_data *pgdat, gfp_t gfp_mask, unsigned int order)
3891 {
3892 int ret;
3893
3894 /*
3895 * Node reclaim reclaims unmapped file backed pages and
3896 * slab pages if we are over the defined limits.
3897 *
3898 * A small portion of unmapped file backed pages is needed for
3899 * file I/O otherwise pages read by file I/O will be immediately
3900 * thrown out if the node is overallocated. So we do not reclaim
3901 * if less than a specified percentage of the node is used by
3902 * unmapped file backed pages.
3903 */
3904 if (node_pagecache_reclaimable(pgdat) <= pgdat->min_unmapped_pages &&
3905 node_page_state(pgdat, NR_SLAB_RECLAIMABLE) <= pgdat->min_slab_pages)
3906 return NODE_RECLAIM_FULL;
3907
3908 /*
3909 * Do not scan if the allocation should not be delayed.
3910 */
3911 if (!gfpflags_allow_blocking(gfp_mask) || (current->flags & PF_MEMALLOC))
3912 return NODE_RECLAIM_NOSCAN;
3913
3914 /*
3915 * Only run node reclaim on the local node or on nodes that do not
3916 * have associated processors. This will favor the local processor
3917 * over remote processors and spread off node memory allocations
3918 * as wide as possible.
3919 */
3920 if (node_state(pgdat->node_id, N_CPU) && pgdat->node_id != numa_node_id())
3921 return NODE_RECLAIM_NOSCAN;
3922
3923 if (test_and_set_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags))
3924 return NODE_RECLAIM_NOSCAN;
3925
3926 ret = __node_reclaim(pgdat, gfp_mask, order);
3927 clear_bit(PGDAT_RECLAIM_LOCKED, &pgdat->flags);
3928
3929 if (!ret)
3930 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3931
3932 return ret;
3933 }
3934 #endif
3935
3936 /*
3937 * page_evictable - test whether a page is evictable
3938 * @page: the page to test
3939 *
3940 * Test whether page is evictable--i.e., should be placed on active/inactive
3941 * lists vs unevictable list.
3942 *
3943 * Reasons page might not be evictable:
3944 * (1) page's mapping marked unevictable
3945 * (2) page is part of an mlocked VMA
3946 *
3947 */
3948 int page_evictable(struct page *page)
3949 {
3950 return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
3951 }
3952
3953 #ifdef CONFIG_SHMEM
3954 /**
3955 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3956 * @pages: array of pages to check
3957 * @nr_pages: number of pages to check
3958 *
3959 * Checks pages for evictability and moves them to the appropriate lru list.
3960 *
3961 * This function is only used for SysV IPC SHM_UNLOCK.
3962 */
3963 void check_move_unevictable_pages(struct page **pages, int nr_pages)
3964 {
3965 struct lruvec *lruvec;
3966 struct pglist_data *pgdat = NULL;
3967 int pgscanned = 0;
3968 int pgrescued = 0;
3969 int i;
3970
3971 for (i = 0; i < nr_pages; i++) {
3972 struct page *page = pages[i];
3973 struct pglist_data *pagepgdat = page_pgdat(page);
3974
3975 pgscanned++;
3976 if (pagepgdat != pgdat) {
3977 if (pgdat)
3978 spin_unlock_irq(&pgdat->lru_lock);
3979 pgdat = pagepgdat;
3980 spin_lock_irq(&pgdat->lru_lock);
3981 }
3982 lruvec = mem_cgroup_page_lruvec(page, pgdat);
3983
3984 if (!PageLRU(page) || !PageUnevictable(page))
3985 continue;
3986
3987 if (page_evictable(page)) {
3988 enum lru_list lru = page_lru_base_type(page);
3989
3990 VM_BUG_ON_PAGE(PageActive(page), page);
3991 ClearPageUnevictable(page);
3992 del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3993 add_page_to_lru_list(page, lruvec, lru);
3994 pgrescued++;
3995 }
3996 }
3997
3998 if (pgdat) {
3999 __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
4000 __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
4001 spin_unlock_irq(&pgdat->lru_lock);
4002 }
4003 }
4004 #endif /* CONFIG_SHMEM */