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1 /*
2  *  linux/mm/vmscan.c
3  *
4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
5  *
6  *  Swap reorganised 29.12.95, Stephen Tweedie.
7  *  kswapd added: 7.1.96  sct
8  *  Removed kswapd_ctl limits, and swap out as many pages as needed
9  *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
10  *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
11  *  Multiqueue VM started 5.8.00, Rik van Riel.
12  */
13
14 #include <linux/mm.h>
15 #include <linux/module.h>
16 #include <linux/gfp.h>
17 #include <linux/kernel_stat.h>
18 #include <linux/swap.h>
19 #include <linux/pagemap.h>
20 #include <linux/init.h>
21 #include <linux/highmem.h>
22 #include <linux/vmstat.h>
23 #include <linux/file.h>
24 #include <linux/writeback.h>
25 #include <linux/blkdev.h>
26 #include <linux/buffer_head.h>  /* for try_to_release_page(),
27                                         buffer_heads_over_limit */
28 #include <linux/mm_inline.h>
29 #include <linux/backing-dev.h>
30 #include <linux/rmap.h>
31 #include <linux/topology.h>
32 #include <linux/cpu.h>
33 #include <linux/cpuset.h>
34 #include <linux/compaction.h>
35 #include <linux/notifier.h>
36 #include <linux/rwsem.h>
37 #include <linux/delay.h>
38 #include <linux/kthread.h>
39 #include <linux/freezer.h>
40 #include <linux/memcontrol.h>
41 #include <linux/delayacct.h>
42 #include <linux/sysctl.h>
43 #include <linux/oom.h>
44 #include <linux/prefetch.h>
45
46 #include <asm/tlbflush.h>
47 #include <asm/div64.h>
48
49 #include <linux/swapops.h>
50
51 #include "internal.h"
52
53 #define CREATE_TRACE_POINTS
54 #include <trace/events/vmscan.h>
55
56 struct scan_control {
57         /* Incremented by the number of inactive pages that were scanned */
58         unsigned long nr_scanned;
59
60         /* Number of pages freed so far during a call to shrink_zones() */
61         unsigned long nr_reclaimed;
62
63         /* How many pages shrink_list() should reclaim */
64         unsigned long nr_to_reclaim;
65
66         unsigned long hibernation_mode;
67
68         /* This context's GFP mask */
69         gfp_t gfp_mask;
70
71         int may_writepage;
72
73         /* Can mapped pages be reclaimed? */
74         int may_unmap;
75
76         /* Can pages be swapped as part of reclaim? */
77         int may_swap;
78
79         int order;
80
81         /* Scan (total_size >> priority) pages at once */
82         int priority;
83
84         /*
85          * The memory cgroup that hit its limit and as a result is the
86          * primary target of this reclaim invocation.
87          */
88         struct mem_cgroup *target_mem_cgroup;
89
90         /*
91          * Nodemask of nodes allowed by the caller. If NULL, all nodes
92          * are scanned.
93          */
94         nodemask_t      *nodemask;
95 };
96
97 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
98
99 #ifdef ARCH_HAS_PREFETCH
100 #define prefetch_prev_lru_page(_page, _base, _field)                    \
101         do {                                                            \
102                 if ((_page)->lru.prev != _base) {                       \
103                         struct page *prev;                              \
104                                                                         \
105                         prev = lru_to_page(&(_page->lru));              \
106                         prefetch(&prev->_field);                        \
107                 }                                                       \
108         } while (0)
109 #else
110 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
111 #endif
112
113 #ifdef ARCH_HAS_PREFETCHW
114 #define prefetchw_prev_lru_page(_page, _base, _field)                   \
115         do {                                                            \
116                 if ((_page)->lru.prev != _base) {                       \
117                         struct page *prev;                              \
118                                                                         \
119                         prev = lru_to_page(&(_page->lru));              \
120                         prefetchw(&prev->_field);                       \
121                 }                                                       \
122         } while (0)
123 #else
124 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
125 #endif
126
127 /*
128  * From 0 .. 100.  Higher means more swappy.
129  */
130 int vm_swappiness = 60;
131 long vm_total_pages;    /* The total number of pages which the VM controls */
132
133 static LIST_HEAD(shrinker_list);
134 static DECLARE_RWSEM(shrinker_rwsem);
135
136 #ifdef CONFIG_MEMCG
137 static bool global_reclaim(struct scan_control *sc)
138 {
139         return !sc->target_mem_cgroup;
140 }
141 #else
142 static bool global_reclaim(struct scan_control *sc)
143 {
144         return true;
145 }
146 #endif
147
148 static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
149 {
150         if (!mem_cgroup_disabled())
151                 return mem_cgroup_get_lru_size(lruvec, lru);
152
153         return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);
154 }
155
156 /*
157  * Add a shrinker callback to be called from the vm
158  */
159 void register_shrinker(struct shrinker *shrinker)
160 {
161         atomic_long_set(&shrinker->nr_in_batch, 0);
162         down_write(&shrinker_rwsem);
163         list_add_tail(&shrinker->list, &shrinker_list);
164         up_write(&shrinker_rwsem);
165 }
166 EXPORT_SYMBOL(register_shrinker);
167
168 /*
169  * Remove one
170  */
171 void unregister_shrinker(struct shrinker *shrinker)
172 {
173         down_write(&shrinker_rwsem);
174         list_del(&shrinker->list);
175         up_write(&shrinker_rwsem);
176 }
177 EXPORT_SYMBOL(unregister_shrinker);
178
179 static inline int do_shrinker_shrink(struct shrinker *shrinker,
180                                      struct shrink_control *sc,
181                                      unsigned long nr_to_scan)
182 {
183         sc->nr_to_scan = nr_to_scan;
184         return (*shrinker->shrink)(shrinker, sc);
185 }
186
187 #define SHRINK_BATCH 128
188 /*
189  * Call the shrink functions to age shrinkable caches
190  *
191  * Here we assume it costs one seek to replace a lru page and that it also
192  * takes a seek to recreate a cache object.  With this in mind we age equal
193  * percentages of the lru and ageable caches.  This should balance the seeks
194  * generated by these structures.
195  *
196  * If the vm encountered mapped pages on the LRU it increase the pressure on
197  * slab to avoid swapping.
198  *
199  * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
200  *
201  * `lru_pages' represents the number of on-LRU pages in all the zones which
202  * are eligible for the caller's allocation attempt.  It is used for balancing
203  * slab reclaim versus page reclaim.
204  *
205  * Returns the number of slab objects which we shrunk.
206  */
207 unsigned long shrink_slab(struct shrink_control *shrink,
208                           unsigned long nr_pages_scanned,
209                           unsigned long lru_pages)
210 {
211         struct shrinker *shrinker;
212         unsigned long ret = 0;
213
214         if (nr_pages_scanned == 0)
215                 nr_pages_scanned = SWAP_CLUSTER_MAX;
216
217         if (!down_read_trylock(&shrinker_rwsem)) {
218                 /* Assume we'll be able to shrink next time */
219                 ret = 1;
220                 goto out;
221         }
222
223         list_for_each_entry(shrinker, &shrinker_list, list) {
224                 unsigned long long delta;
225                 long total_scan;
226                 long max_pass;
227                 int shrink_ret = 0;
228                 long nr;
229                 long new_nr;
230                 long batch_size = shrinker->batch ? shrinker->batch
231                                                   : SHRINK_BATCH;
232
233                 max_pass = do_shrinker_shrink(shrinker, shrink, 0);
234                 if (max_pass <= 0)
235                         continue;
236
237                 /*
238                  * copy the current shrinker scan count into a local variable
239                  * and zero it so that other concurrent shrinker invocations
240                  * don't also do this scanning work.
241                  */
242                 nr = atomic_long_xchg(&shrinker->nr_in_batch, 0);
243
244                 total_scan = nr;
245                 delta = (4 * nr_pages_scanned) / shrinker->seeks;
246                 delta *= max_pass;
247                 do_div(delta, lru_pages + 1);
248                 total_scan += delta;
249                 if (total_scan < 0) {
250                         printk(KERN_ERR "shrink_slab: %pF negative objects to "
251                                "delete nr=%ld\n",
252                                shrinker->shrink, total_scan);
253                         total_scan = max_pass;
254                 }
255
256                 /*
257                  * We need to avoid excessive windup on filesystem shrinkers
258                  * due to large numbers of GFP_NOFS allocations causing the
259                  * shrinkers to return -1 all the time. This results in a large
260                  * nr being built up so when a shrink that can do some work
261                  * comes along it empties the entire cache due to nr >>>
262                  * max_pass.  This is bad for sustaining a working set in
263                  * memory.
264                  *
265                  * Hence only allow the shrinker to scan the entire cache when
266                  * a large delta change is calculated directly.
267                  */
268                 if (delta < max_pass / 4)
269                         total_scan = min(total_scan, max_pass / 2);
270
271                 /*
272                  * Avoid risking looping forever due to too large nr value:
273                  * never try to free more than twice the estimate number of
274                  * freeable entries.
275                  */
276                 if (total_scan > max_pass * 2)
277                         total_scan = max_pass * 2;
278
279                 trace_mm_shrink_slab_start(shrinker, shrink, nr,
280                                         nr_pages_scanned, lru_pages,
281                                         max_pass, delta, total_scan);
282
283                 while (total_scan >= batch_size) {
284                         int nr_before;
285
286                         nr_before = do_shrinker_shrink(shrinker, shrink, 0);
287                         shrink_ret = do_shrinker_shrink(shrinker, shrink,
288                                                         batch_size);
289                         if (shrink_ret == -1)
290                                 break;
291                         if (shrink_ret < nr_before)
292                                 ret += nr_before - shrink_ret;
293                         count_vm_events(SLABS_SCANNED, batch_size);
294                         total_scan -= batch_size;
295
296                         cond_resched();
297                 }
298
299                 /*
300                  * move the unused scan count back into the shrinker in a
301                  * manner that handles concurrent updates. If we exhausted the
302                  * scan, there is no need to do an update.
303                  */
304                 if (total_scan > 0)
305                         new_nr = atomic_long_add_return(total_scan,
306                                         &shrinker->nr_in_batch);
307                 else
308                         new_nr = atomic_long_read(&shrinker->nr_in_batch);
309
310                 trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
311         }
312         up_read(&shrinker_rwsem);
313 out:
314         cond_resched();
315         return ret;
316 }
317
318 static inline int is_page_cache_freeable(struct page *page)
319 {
320         /*
321          * A freeable page cache page is referenced only by the caller
322          * that isolated the page, the page cache radix tree and
323          * optional buffer heads at page->private.
324          */
325         return page_count(page) - page_has_private(page) == 2;
326 }
327
328 static int may_write_to_queue(struct backing_dev_info *bdi,
329                               struct scan_control *sc)
330 {
331         if (current->flags & PF_SWAPWRITE)
332                 return 1;
333         if (!bdi_write_congested(bdi))
334                 return 1;
335         if (bdi == current->backing_dev_info)
336                 return 1;
337         return 0;
338 }
339
340 /*
341  * We detected a synchronous write error writing a page out.  Probably
342  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
343  * fsync(), msync() or close().
344  *
345  * The tricky part is that after writepage we cannot touch the mapping: nothing
346  * prevents it from being freed up.  But we have a ref on the page and once
347  * that page is locked, the mapping is pinned.
348  *
349  * We're allowed to run sleeping lock_page() here because we know the caller has
350  * __GFP_FS.
351  */
352 static void handle_write_error(struct address_space *mapping,
353                                 struct page *page, int error)
354 {
355         lock_page(page);
356         if (page_mapping(page) == mapping)
357                 mapping_set_error(mapping, error);
358         unlock_page(page);
359 }
360
361 /* possible outcome of pageout() */
362 typedef enum {
363         /* failed to write page out, page is locked */
364         PAGE_KEEP,
365         /* move page to the active list, page is locked */
366         PAGE_ACTIVATE,
367         /* page has been sent to the disk successfully, page is unlocked */
368         PAGE_SUCCESS,
369         /* page is clean and locked */
370         PAGE_CLEAN,
371 } pageout_t;
372
373 /*
374  * pageout is called by shrink_page_list() for each dirty page.
375  * Calls ->writepage().
376  */
377 static pageout_t pageout(struct page *page, struct address_space *mapping,
378                          struct scan_control *sc)
379 {
380         /*
381          * If the page is dirty, only perform writeback if that write
382          * will be non-blocking.  To prevent this allocation from being
383          * stalled by pagecache activity.  But note that there may be
384          * stalls if we need to run get_block().  We could test
385          * PagePrivate for that.
386          *
387          * If this process is currently in __generic_file_aio_write() against
388          * this page's queue, we can perform writeback even if that
389          * will block.
390          *
391          * If the page is swapcache, write it back even if that would
392          * block, for some throttling. This happens by accident, because
393          * swap_backing_dev_info is bust: it doesn't reflect the
394          * congestion state of the swapdevs.  Easy to fix, if needed.
395          */
396         if (!is_page_cache_freeable(page))
397                 return PAGE_KEEP;
398         if (!mapping) {
399                 /*
400                  * Some data journaling orphaned pages can have
401                  * page->mapping == NULL while being dirty with clean buffers.
402                  */
403                 if (page_has_private(page)) {
404                         if (try_to_free_buffers(page)) {
405                                 ClearPageDirty(page);
406                                 printk("%s: orphaned page\n", __func__);
407                                 return PAGE_CLEAN;
408                         }
409                 }
410                 return PAGE_KEEP;
411         }
412         if (mapping->a_ops->writepage == NULL)
413                 return PAGE_ACTIVATE;
414         if (!may_write_to_queue(mapping->backing_dev_info, sc))
415                 return PAGE_KEEP;
416
417         if (clear_page_dirty_for_io(page)) {
418                 int res;
419                 struct writeback_control wbc = {
420                         .sync_mode = WB_SYNC_NONE,
421                         .nr_to_write = SWAP_CLUSTER_MAX,
422                         .range_start = 0,
423                         .range_end = LLONG_MAX,
424                         .for_reclaim = 1,
425                 };
426
427                 SetPageReclaim(page);
428                 res = mapping->a_ops->writepage(page, &wbc);
429                 if (res < 0)
430                         handle_write_error(mapping, page, res);
431                 if (res == AOP_WRITEPAGE_ACTIVATE) {
432                         ClearPageReclaim(page);
433                         return PAGE_ACTIVATE;
434                 }
435
436                 if (!PageWriteback(page)) {
437                         /* synchronous write or broken a_ops? */
438                         ClearPageReclaim(page);
439                 }
440                 trace_mm_vmscan_writepage(page, trace_reclaim_flags(page));
441                 inc_zone_page_state(page, NR_VMSCAN_WRITE);
442                 return PAGE_SUCCESS;
443         }
444
445         return PAGE_CLEAN;
446 }
447
448 /*
449  * Same as remove_mapping, but if the page is removed from the mapping, it
450  * gets returned with a refcount of 0.
451  */
452 static int __remove_mapping(struct address_space *mapping, struct page *page)
453 {
454         BUG_ON(!PageLocked(page));
455         BUG_ON(mapping != page_mapping(page));
456
457         spin_lock_irq(&mapping->tree_lock);
458         /*
459          * The non racy check for a busy page.
460          *
461          * Must be careful with the order of the tests. When someone has
462          * a ref to the page, it may be possible that they dirty it then
463          * drop the reference. So if PageDirty is tested before page_count
464          * here, then the following race may occur:
465          *
466          * get_user_pages(&page);
467          * [user mapping goes away]
468          * write_to(page);
469          *                              !PageDirty(page)    [good]
470          * SetPageDirty(page);
471          * put_page(page);
472          *                              !page_count(page)   [good, discard it]
473          *
474          * [oops, our write_to data is lost]
475          *
476          * Reversing the order of the tests ensures such a situation cannot
477          * escape unnoticed. The smp_rmb is needed to ensure the page->flags
478          * load is not satisfied before that of page->_count.
479          *
480          * Note that if SetPageDirty is always performed via set_page_dirty,
481          * and thus under tree_lock, then this ordering is not required.
482          */
483         if (!page_freeze_refs(page, 2))
484                 goto cannot_free;
485         /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
486         if (unlikely(PageDirty(page))) {
487                 page_unfreeze_refs(page, 2);
488                 goto cannot_free;
489         }
490
491         if (PageSwapCache(page)) {
492                 swp_entry_t swap = { .val = page_private(page) };
493                 __delete_from_swap_cache(page);
494                 spin_unlock_irq(&mapping->tree_lock);
495                 swapcache_free(swap, page);
496         } else {
497                 void (*freepage)(struct page *);
498
499                 freepage = mapping->a_ops->freepage;
500
501                 __delete_from_page_cache(page);
502                 spin_unlock_irq(&mapping->tree_lock);
503                 mem_cgroup_uncharge_cache_page(page);
504
505                 if (freepage != NULL)
506                         freepage(page);
507         }
508
509         return 1;
510
511 cannot_free:
512         spin_unlock_irq(&mapping->tree_lock);
513         return 0;
514 }
515
516 /*
517  * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
518  * someone else has a ref on the page, abort and return 0.  If it was
519  * successfully detached, return 1.  Assumes the caller has a single ref on
520  * this page.
521  */
522 int remove_mapping(struct address_space *mapping, struct page *page)
523 {
524         if (__remove_mapping(mapping, page)) {
525                 /*
526                  * Unfreezing the refcount with 1 rather than 2 effectively
527                  * drops the pagecache ref for us without requiring another
528                  * atomic operation.
529                  */
530                 page_unfreeze_refs(page, 1);
531                 return 1;
532         }
533         return 0;
534 }
535
536 /**
537  * putback_lru_page - put previously isolated page onto appropriate LRU list
538  * @page: page to be put back to appropriate lru list
539  *
540  * Add previously isolated @page to appropriate LRU list.
541  * Page may still be unevictable for other reasons.
542  *
543  * lru_lock must not be held, interrupts must be enabled.
544  */
545 void putback_lru_page(struct page *page)
546 {
547         int lru;
548         int active = !!TestClearPageActive(page);
549         int was_unevictable = PageUnevictable(page);
550
551         VM_BUG_ON(PageLRU(page));
552
553 redo:
554         ClearPageUnevictable(page);
555
556         if (page_evictable(page)) {
557                 /*
558                  * For evictable pages, we can use the cache.
559                  * In event of a race, worst case is we end up with an
560                  * unevictable page on [in]active list.
561                  * We know how to handle that.
562                  */
563                 lru = active + page_lru_base_type(page);
564                 lru_cache_add_lru(page, lru);
565         } else {
566                 /*
567                  * Put unevictable pages directly on zone's unevictable
568                  * list.
569                  */
570                 lru = LRU_UNEVICTABLE;
571                 add_page_to_unevictable_list(page);
572                 /*
573                  * When racing with an mlock or AS_UNEVICTABLE clearing
574                  * (page is unlocked) make sure that if the other thread
575                  * does not observe our setting of PG_lru and fails
576                  * isolation/check_move_unevictable_pages,
577                  * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
578                  * the page back to the evictable list.
579                  *
580                  * The other side is TestClearPageMlocked() or shmem_lock().
581                  */
582                 smp_mb();
583         }
584
585         /*
586          * page's status can change while we move it among lru. If an evictable
587          * page is on unevictable list, it never be freed. To avoid that,
588          * check after we added it to the list, again.
589          */
590         if (lru == LRU_UNEVICTABLE && page_evictable(page)) {
591                 if (!isolate_lru_page(page)) {
592                         put_page(page);
593                         goto redo;
594                 }
595                 /* This means someone else dropped this page from LRU
596                  * So, it will be freed or putback to LRU again. There is
597                  * nothing to do here.
598                  */
599         }
600
601         if (was_unevictable && lru != LRU_UNEVICTABLE)
602                 count_vm_event(UNEVICTABLE_PGRESCUED);
603         else if (!was_unevictable && lru == LRU_UNEVICTABLE)
604                 count_vm_event(UNEVICTABLE_PGCULLED);
605
606         put_page(page);         /* drop ref from isolate */
607 }
608
609 enum page_references {
610         PAGEREF_RECLAIM,
611         PAGEREF_RECLAIM_CLEAN,
612         PAGEREF_KEEP,
613         PAGEREF_ACTIVATE,
614 };
615
616 static enum page_references page_check_references(struct page *page,
617                                                   struct scan_control *sc)
618 {
619         int referenced_ptes, referenced_page;
620         unsigned long vm_flags;
621
622         referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
623                                           &vm_flags);
624         referenced_page = TestClearPageReferenced(page);
625
626         /*
627          * Mlock lost the isolation race with us.  Let try_to_unmap()
628          * move the page to the unevictable list.
629          */
630         if (vm_flags & VM_LOCKED)
631                 return PAGEREF_RECLAIM;
632
633         if (referenced_ptes) {
634                 if (PageSwapBacked(page))
635                         return PAGEREF_ACTIVATE;
636                 /*
637                  * All mapped pages start out with page table
638                  * references from the instantiating fault, so we need
639                  * to look twice if a mapped file page is used more
640                  * than once.
641                  *
642                  * Mark it and spare it for another trip around the
643                  * inactive list.  Another page table reference will
644                  * lead to its activation.
645                  *
646                  * Note: the mark is set for activated pages as well
647                  * so that recently deactivated but used pages are
648                  * quickly recovered.
649                  */
650                 SetPageReferenced(page);
651
652                 if (referenced_page || referenced_ptes > 1)
653                         return PAGEREF_ACTIVATE;
654
655                 /*
656                  * Activate file-backed executable pages after first usage.
657                  */
658                 if (vm_flags & VM_EXEC)
659                         return PAGEREF_ACTIVATE;
660
661                 return PAGEREF_KEEP;
662         }
663
664         /* Reclaim if clean, defer dirty pages to writeback */
665         if (referenced_page && !PageSwapBacked(page))
666                 return PAGEREF_RECLAIM_CLEAN;
667
668         return PAGEREF_RECLAIM;
669 }
670
671 /*
672  * shrink_page_list() returns the number of reclaimed pages
673  */
674 static unsigned long shrink_page_list(struct list_head *page_list,
675                                       struct zone *zone,
676                                       struct scan_control *sc,
677                                       enum ttu_flags ttu_flags,
678                                       unsigned long *ret_nr_dirty,
679                                       unsigned long *ret_nr_writeback,
680                                       bool force_reclaim)
681 {
682         LIST_HEAD(ret_pages);
683         LIST_HEAD(free_pages);
684         int pgactivate = 0;
685         unsigned long nr_dirty = 0;
686         unsigned long nr_congested = 0;
687         unsigned long nr_reclaimed = 0;
688         unsigned long nr_writeback = 0;
689
690         cond_resched();
691
692         mem_cgroup_uncharge_start();
693         while (!list_empty(page_list)) {
694                 struct address_space *mapping;
695                 struct page *page;
696                 int may_enter_fs;
697                 enum page_references references = PAGEREF_RECLAIM_CLEAN;
698
699                 cond_resched();
700
701                 page = lru_to_page(page_list);
702                 list_del(&page->lru);
703
704                 if (!trylock_page(page))
705                         goto keep;
706
707                 VM_BUG_ON(PageActive(page));
708                 VM_BUG_ON(page_zone(page) != zone);
709
710                 sc->nr_scanned++;
711
712                 if (unlikely(!page_evictable(page)))
713                         goto cull_mlocked;
714
715                 if (!sc->may_unmap && page_mapped(page))
716                         goto keep_locked;
717
718                 /* Double the slab pressure for mapped and swapcache pages */
719                 if (page_mapped(page) || PageSwapCache(page))
720                         sc->nr_scanned++;
721
722                 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
723                         (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
724
725                 if (PageWriteback(page)) {
726                         /*
727                          * memcg doesn't have any dirty pages throttling so we
728                          * could easily OOM just because too many pages are in
729                          * writeback and there is nothing else to reclaim.
730                          *
731                          * Check __GFP_IO, certainly because a loop driver
732                          * thread might enter reclaim, and deadlock if it waits
733                          * on a page for which it is needed to do the write
734                          * (loop masks off __GFP_IO|__GFP_FS for this reason);
735                          * but more thought would probably show more reasons.
736                          *
737                          * Don't require __GFP_FS, since we're not going into
738                          * the FS, just waiting on its writeback completion.
739                          * Worryingly, ext4 gfs2 and xfs allocate pages with
740                          * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so
741                          * testing may_enter_fs here is liable to OOM on them.
742                          */
743                         if (global_reclaim(sc) ||
744                             !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
745                                 /*
746                                  * This is slightly racy - end_page_writeback()
747                                  * might have just cleared PageReclaim, then
748                                  * setting PageReclaim here end up interpreted
749                                  * as PageReadahead - but that does not matter
750                                  * enough to care.  What we do want is for this
751                                  * page to have PageReclaim set next time memcg
752                                  * reclaim reaches the tests above, so it will
753                                  * then wait_on_page_writeback() to avoid OOM;
754                                  * and it's also appropriate in global reclaim.
755                                  */
756                                 SetPageReclaim(page);
757                                 nr_writeback++;
758                                 goto keep_locked;
759                         }
760                         wait_on_page_writeback(page);
761                 }
762
763                 if (!force_reclaim)
764                         references = page_check_references(page, sc);
765
766                 switch (references) {
767                 case PAGEREF_ACTIVATE:
768                         goto activate_locked;
769                 case PAGEREF_KEEP:
770                         goto keep_locked;
771                 case PAGEREF_RECLAIM:
772                 case PAGEREF_RECLAIM_CLEAN:
773                         ; /* try to reclaim the page below */
774                 }
775
776                 /*
777                  * Anonymous process memory has backing store?
778                  * Try to allocate it some swap space here.
779                  */
780                 if (PageAnon(page) && !PageSwapCache(page)) {
781                         if (!(sc->gfp_mask & __GFP_IO))
782                                 goto keep_locked;
783                         if (!add_to_swap(page))
784                                 goto activate_locked;
785                         may_enter_fs = 1;
786                 }
787
788                 mapping = page_mapping(page);
789
790                 /*
791                  * The page is mapped into the page tables of one or more
792                  * processes. Try to unmap it here.
793                  */
794                 if (page_mapped(page) && mapping) {
795                         switch (try_to_unmap(page, ttu_flags)) {
796                         case SWAP_FAIL:
797                                 goto activate_locked;
798                         case SWAP_AGAIN:
799                                 goto keep_locked;
800                         case SWAP_MLOCK:
801                                 goto cull_mlocked;
802                         case SWAP_SUCCESS:
803                                 ; /* try to free the page below */
804                         }
805                 }
806
807                 if (PageDirty(page)) {
808                         nr_dirty++;
809
810                         /*
811                          * Only kswapd can writeback filesystem pages to
812                          * avoid risk of stack overflow but do not writeback
813                          * unless under significant pressure.
814                          */
815                         if (page_is_file_cache(page) &&
816                                         (!current_is_kswapd() ||
817                                          sc->priority >= DEF_PRIORITY - 2)) {
818                                 /*
819                                  * Immediately reclaim when written back.
820                                  * Similar in principal to deactivate_page()
821                                  * except we already have the page isolated
822                                  * and know it's dirty
823                                  */
824                                 inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
825                                 SetPageReclaim(page);
826
827                                 goto keep_locked;
828                         }
829
830                         if (references == PAGEREF_RECLAIM_CLEAN)
831                                 goto keep_locked;
832                         if (!may_enter_fs)
833                                 goto keep_locked;
834                         if (!sc->may_writepage)
835                                 goto keep_locked;
836
837                         /* Page is dirty, try to write it out here */
838                         switch (pageout(page, mapping, sc)) {
839                         case PAGE_KEEP:
840                                 nr_congested++;
841                                 goto keep_locked;
842                         case PAGE_ACTIVATE:
843                                 goto activate_locked;
844                         case PAGE_SUCCESS:
845                                 if (PageWriteback(page))
846                                         goto keep;
847                                 if (PageDirty(page))
848                                         goto keep;
849
850                                 /*
851                                  * A synchronous write - probably a ramdisk.  Go
852                                  * ahead and try to reclaim the page.
853                                  */
854                                 if (!trylock_page(page))
855                                         goto keep;
856                                 if (PageDirty(page) || PageWriteback(page))
857                                         goto keep_locked;
858                                 mapping = page_mapping(page);
859                         case PAGE_CLEAN:
860                                 ; /* try to free the page below */
861                         }
862                 }
863
864                 /*
865                  * If the page has buffers, try to free the buffer mappings
866                  * associated with this page. If we succeed we try to free
867                  * the page as well.
868                  *
869                  * We do this even if the page is PageDirty().
870                  * try_to_release_page() does not perform I/O, but it is
871                  * possible for a page to have PageDirty set, but it is actually
872                  * clean (all its buffers are clean).  This happens if the
873                  * buffers were written out directly, with submit_bh(). ext3
874                  * will do this, as well as the blockdev mapping.
875                  * try_to_release_page() will discover that cleanness and will
876                  * drop the buffers and mark the page clean - it can be freed.
877                  *
878                  * Rarely, pages can have buffers and no ->mapping.  These are
879                  * the pages which were not successfully invalidated in
880                  * truncate_complete_page().  We try to drop those buffers here
881                  * and if that worked, and the page is no longer mapped into
882                  * process address space (page_count == 1) it can be freed.
883                  * Otherwise, leave the page on the LRU so it is swappable.
884                  */
885                 if (page_has_private(page)) {
886                         if (!try_to_release_page(page, sc->gfp_mask))
887                                 goto activate_locked;
888                         if (!mapping && page_count(page) == 1) {
889                                 unlock_page(page);
890                                 if (put_page_testzero(page))
891                                         goto free_it;
892                                 else {
893                                         /*
894                                          * rare race with speculative reference.
895                                          * the speculative reference will free
896                                          * this page shortly, so we may
897                                          * increment nr_reclaimed here (and
898                                          * leave it off the LRU).
899                                          */
900                                         nr_reclaimed++;
901                                         continue;
902                                 }
903                         }
904                 }
905
906                 if (!mapping || !__remove_mapping(mapping, page))
907                         goto keep_locked;
908
909                 /*
910                  * At this point, we have no other references and there is
911                  * no way to pick any more up (removed from LRU, removed
912                  * from pagecache). Can use non-atomic bitops now (and
913                  * we obviously don't have to worry about waking up a process
914                  * waiting on the page lock, because there are no references.
915                  */
916                 __clear_page_locked(page);
917 free_it:
918                 nr_reclaimed++;
919
920                 /*
921                  * Is there need to periodically free_page_list? It would
922                  * appear not as the counts should be low
923                  */
924                 list_add(&page->lru, &free_pages);
925                 continue;
926
927 cull_mlocked:
928                 if (PageSwapCache(page))
929                         try_to_free_swap(page);
930                 unlock_page(page);
931                 putback_lru_page(page);
932                 continue;
933
934 activate_locked:
935                 /* Not a candidate for swapping, so reclaim swap space. */
936                 if (PageSwapCache(page) && vm_swap_full())
937                         try_to_free_swap(page);
938                 VM_BUG_ON(PageActive(page));
939                 SetPageActive(page);
940                 pgactivate++;
941 keep_locked:
942                 unlock_page(page);
943 keep:
944                 list_add(&page->lru, &ret_pages);
945                 VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
946         }
947
948         /*
949          * Tag a zone as congested if all the dirty pages encountered were
950          * backed by a congested BDI. In this case, reclaimers should just
951          * back off and wait for congestion to clear because further reclaim
952          * will encounter the same problem
953          */
954         if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
955                 zone_set_flag(zone, ZONE_CONGESTED);
956
957         free_hot_cold_page_list(&free_pages, 1);
958
959         list_splice(&ret_pages, page_list);
960         count_vm_events(PGACTIVATE, pgactivate);
961         mem_cgroup_uncharge_end();
962         *ret_nr_dirty += nr_dirty;
963         *ret_nr_writeback += nr_writeback;
964         return nr_reclaimed;
965 }
966
967 unsigned long reclaim_clean_pages_from_list(struct zone *zone,
968                                             struct list_head *page_list)
969 {
970         struct scan_control sc = {
971                 .gfp_mask = GFP_KERNEL,
972                 .priority = DEF_PRIORITY,
973                 .may_unmap = 1,
974         };
975         unsigned long ret, dummy1, dummy2;
976         struct page *page, *next;
977         LIST_HEAD(clean_pages);
978
979         list_for_each_entry_safe(page, next, page_list, lru) {
980                 if (page_is_file_cache(page) && !PageDirty(page)) {
981                         ClearPageActive(page);
982                         list_move(&page->lru, &clean_pages);
983                 }
984         }
985
986         ret = shrink_page_list(&clean_pages, zone, &sc,
987                                 TTU_UNMAP|TTU_IGNORE_ACCESS,
988                                 &dummy1, &dummy2, true);
989         list_splice(&clean_pages, page_list);
990         __mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
991         return ret;
992 }
993
994 /*
995  * Attempt to remove the specified page from its LRU.  Only take this page
996  * if it is of the appropriate PageActive status.  Pages which are being
997  * freed elsewhere are also ignored.
998  *
999  * page:        page to consider
1000  * mode:        one of the LRU isolation modes defined above
1001  *
1002  * returns 0 on success, -ve errno on failure.
1003  */
1004 int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1005 {
1006         int ret = -EINVAL;
1007
1008         /* Only take pages on the LRU. */
1009         if (!PageLRU(page))
1010                 return ret;
1011
1012         /* Compaction should not handle unevictable pages but CMA can do so */
1013         if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1014                 return ret;
1015
1016         ret = -EBUSY;
1017
1018         /*
1019          * To minimise LRU disruption, the caller can indicate that it only
1020          * wants to isolate pages it will be able to operate on without
1021          * blocking - clean pages for the most part.
1022          *
1023          * ISOLATE_CLEAN means that only clean pages should be isolated. This
1024          * is used by reclaim when it is cannot write to backing storage
1025          *
1026          * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1027          * that it is possible to migrate without blocking
1028          */
1029         if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
1030                 /* All the caller can do on PageWriteback is block */
1031                 if (PageWriteback(page))
1032                         return ret;
1033
1034                 if (PageDirty(page)) {
1035                         struct address_space *mapping;
1036
1037                         /* ISOLATE_CLEAN means only clean pages */
1038                         if (mode & ISOLATE_CLEAN)
1039                                 return ret;
1040
1041                         /*
1042                          * Only pages without mappings or that have a
1043                          * ->migratepage callback are possible to migrate
1044                          * without blocking
1045                          */
1046                         mapping = page_mapping(page);
1047                         if (mapping && !mapping->a_ops->migratepage)
1048                                 return ret;
1049                 }
1050         }
1051
1052         if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1053                 return ret;
1054
1055         if (likely(get_page_unless_zero(page))) {
1056                 /*
1057                  * Be careful not to clear PageLRU until after we're
1058                  * sure the page is not being freed elsewhere -- the
1059                  * page release code relies on it.
1060                  */
1061                 ClearPageLRU(page);
1062                 ret = 0;
1063         }
1064
1065         return ret;
1066 }
1067
1068 /*
1069  * zone->lru_lock is heavily contended.  Some of the functions that
1070  * shrink the lists perform better by taking out a batch of pages
1071  * and working on them outside the LRU lock.
1072  *
1073  * For pagecache intensive workloads, this function is the hottest
1074  * spot in the kernel (apart from copy_*_user functions).
1075  *
1076  * Appropriate locks must be held before calling this function.
1077  *
1078  * @nr_to_scan: The number of pages to look through on the list.
1079  * @lruvec:     The LRU vector to pull pages from.
1080  * @dst:        The temp list to put pages on to.
1081  * @nr_scanned: The number of pages that were scanned.
1082  * @sc:         The scan_control struct for this reclaim session
1083  * @mode:       One of the LRU isolation modes
1084  * @lru:        LRU list id for isolating
1085  *
1086  * returns how many pages were moved onto *@dst.
1087  */
1088 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1089                 struct lruvec *lruvec, struct list_head *dst,
1090                 unsigned long *nr_scanned, struct scan_control *sc,
1091                 isolate_mode_t mode, enum lru_list lru)
1092 {
1093         struct list_head *src = &lruvec->lists[lru];
1094         unsigned long nr_taken = 0;
1095         unsigned long scan;
1096
1097         for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1098                 struct page *page;
1099                 int nr_pages;
1100
1101                 page = lru_to_page(src);
1102                 prefetchw_prev_lru_page(page, src, flags);
1103
1104                 VM_BUG_ON(!PageLRU(page));
1105
1106                 switch (__isolate_lru_page(page, mode)) {
1107                 case 0:
1108                         nr_pages = hpage_nr_pages(page);
1109                         mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
1110                         list_move(&page->lru, dst);
1111                         nr_taken += nr_pages;
1112                         break;
1113
1114                 case -EBUSY:
1115                         /* else it is being freed elsewhere */
1116                         list_move(&page->lru, src);
1117                         continue;
1118
1119                 default:
1120                         BUG();
1121                 }
1122         }
1123
1124         *nr_scanned = scan;
1125         trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
1126                                     nr_taken, mode, is_file_lru(lru));
1127         return nr_taken;
1128 }
1129
1130 /**
1131  * isolate_lru_page - tries to isolate a page from its LRU list
1132  * @page: page to isolate from its LRU list
1133  *
1134  * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1135  * vmstat statistic corresponding to whatever LRU list the page was on.
1136  *
1137  * Returns 0 if the page was removed from an LRU list.
1138  * Returns -EBUSY if the page was not on an LRU list.
1139  *
1140  * The returned page will have PageLRU() cleared.  If it was found on
1141  * the active list, it will have PageActive set.  If it was found on
1142  * the unevictable list, it will have the PageUnevictable bit set. That flag
1143  * may need to be cleared by the caller before letting the page go.
1144  *
1145  * The vmstat statistic corresponding to the list on which the page was
1146  * found will be decremented.
1147  *
1148  * Restrictions:
1149  * (1) Must be called with an elevated refcount on the page. This is a
1150  *     fundamentnal difference from isolate_lru_pages (which is called
1151  *     without a stable reference).
1152  * (2) the lru_lock must not be held.
1153  * (3) interrupts must be enabled.
1154  */
1155 int isolate_lru_page(struct page *page)
1156 {
1157         int ret = -EBUSY;
1158
1159         VM_BUG_ON(!page_count(page));
1160
1161         if (PageLRU(page)) {
1162                 struct zone *zone = page_zone(page);
1163                 struct lruvec *lruvec;
1164
1165                 spin_lock_irq(&zone->lru_lock);
1166                 lruvec = mem_cgroup_page_lruvec(page, zone);
1167                 if (PageLRU(page)) {
1168                         int lru = page_lru(page);
1169                         get_page(page);
1170                         ClearPageLRU(page);
1171                         del_page_from_lru_list(page, lruvec, lru);
1172                         ret = 0;
1173                 }
1174                 spin_unlock_irq(&zone->lru_lock);
1175         }
1176         return ret;
1177 }
1178
1179 /*
1180  * Are there way too many processes in the direct reclaim path already?
1181  */
1182 static int too_many_isolated(struct zone *zone, int file,
1183                 struct scan_control *sc)
1184 {
1185         unsigned long inactive, isolated;
1186
1187         if (current_is_kswapd())
1188                 return 0;
1189
1190         if (!global_reclaim(sc))
1191                 return 0;
1192
1193         if (file) {
1194                 inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1195                 isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1196         } else {
1197                 inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1198                 isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1199         }
1200
1201         return isolated > inactive;
1202 }
1203
1204 static noinline_for_stack void
1205 putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1206 {
1207         struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1208         struct zone *zone = lruvec_zone(lruvec);
1209         LIST_HEAD(pages_to_free);
1210
1211         /*
1212          * Put back any unfreeable pages.
1213          */
1214         while (!list_empty(page_list)) {
1215                 struct page *page = lru_to_page(page_list);
1216                 int lru;
1217
1218                 VM_BUG_ON(PageLRU(page));
1219                 list_del(&page->lru);
1220                 if (unlikely(!page_evictable(page))) {
1221                         spin_unlock_irq(&zone->lru_lock);
1222                         putback_lru_page(page);
1223                         spin_lock_irq(&zone->lru_lock);
1224                         continue;
1225                 }
1226
1227                 lruvec = mem_cgroup_page_lruvec(page, zone);
1228
1229                 SetPageLRU(page);
1230                 lru = page_lru(page);
1231                 add_page_to_lru_list(page, lruvec, lru);
1232
1233                 if (is_active_lru(lru)) {
1234                         int file = is_file_lru(lru);
1235                         int numpages = hpage_nr_pages(page);
1236                         reclaim_stat->recent_rotated[file] += numpages;
1237                 }
1238                 if (put_page_testzero(page)) {
1239                         __ClearPageLRU(page);
1240                         __ClearPageActive(page);
1241                         del_page_from_lru_list(page, lruvec, lru);
1242
1243                         if (unlikely(PageCompound(page))) {
1244                                 spin_unlock_irq(&zone->lru_lock);
1245                                 (*get_compound_page_dtor(page))(page);
1246                                 spin_lock_irq(&zone->lru_lock);
1247                         } else
1248                                 list_add(&page->lru, &pages_to_free);
1249                 }
1250         }
1251
1252         /*
1253          * To save our caller's stack, now use input list for pages to free.
1254          */
1255         list_splice(&pages_to_free, page_list);
1256 }
1257
1258 /*
1259  * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
1260  * of reclaimed pages
1261  */
1262 static noinline_for_stack unsigned long
1263 shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1264                      struct scan_control *sc, enum lru_list lru)
1265 {
1266         LIST_HEAD(page_list);
1267         unsigned long nr_scanned;
1268         unsigned long nr_reclaimed = 0;
1269         unsigned long nr_taken;
1270         unsigned long nr_dirty = 0;
1271         unsigned long nr_writeback = 0;
1272         isolate_mode_t isolate_mode = 0;
1273         int file = is_file_lru(lru);
1274         struct zone *zone = lruvec_zone(lruvec);
1275         struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1276
1277         while (unlikely(too_many_isolated(zone, file, sc))) {
1278                 congestion_wait(BLK_RW_ASYNC, HZ/10);
1279
1280                 /* We are about to die and free our memory. Return now. */
1281                 if (fatal_signal_pending(current))
1282                         return SWAP_CLUSTER_MAX;
1283         }
1284
1285         lru_add_drain();
1286
1287         if (!sc->may_unmap)
1288                 isolate_mode |= ISOLATE_UNMAPPED;
1289         if (!sc->may_writepage)
1290                 isolate_mode |= ISOLATE_CLEAN;
1291
1292         spin_lock_irq(&zone->lru_lock);
1293
1294         nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1295                                      &nr_scanned, sc, isolate_mode, lru);
1296
1297         __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1298         __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1299
1300         if (global_reclaim(sc)) {
1301                 zone->pages_scanned += nr_scanned;
1302                 if (current_is_kswapd())
1303                         __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1304                 else
1305                         __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1306         }
1307         spin_unlock_irq(&zone->lru_lock);
1308
1309         if (nr_taken == 0)
1310                 return 0;
1311
1312         nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
1313                                         &nr_dirty, &nr_writeback, false);
1314
1315         spin_lock_irq(&zone->lru_lock);
1316
1317         reclaim_stat->recent_scanned[file] += nr_taken;
1318
1319         if (global_reclaim(sc)) {
1320                 if (current_is_kswapd())
1321                         __count_zone_vm_events(PGSTEAL_KSWAPD, zone,
1322                                                nr_reclaimed);
1323                 else
1324                         __count_zone_vm_events(PGSTEAL_DIRECT, zone,
1325                                                nr_reclaimed);
1326         }
1327
1328         putback_inactive_pages(lruvec, &page_list);
1329
1330         __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1331
1332         spin_unlock_irq(&zone->lru_lock);
1333
1334         free_hot_cold_page_list(&page_list, 1);
1335
1336         /*
1337          * If reclaim is isolating dirty pages under writeback, it implies
1338          * that the long-lived page allocation rate is exceeding the page
1339          * laundering rate. Either the global limits are not being effective
1340          * at throttling processes due to the page distribution throughout
1341          * zones or there is heavy usage of a slow backing device. The
1342          * only option is to throttle from reclaim context which is not ideal
1343          * as there is no guarantee the dirtying process is throttled in the
1344          * same way balance_dirty_pages() manages.
1345          *
1346          * This scales the number of dirty pages that must be under writeback
1347          * before throttling depending on priority. It is a simple backoff
1348          * function that has the most effect in the range DEF_PRIORITY to
1349          * DEF_PRIORITY-2 which is the priority reclaim is considered to be
1350          * in trouble and reclaim is considered to be in trouble.
1351          *
1352          * DEF_PRIORITY   100% isolated pages must be PageWriteback to throttle
1353          * DEF_PRIORITY-1  50% must be PageWriteback
1354          * DEF_PRIORITY-2  25% must be PageWriteback, kswapd in trouble
1355          * ...
1356          * DEF_PRIORITY-6 For SWAP_CLUSTER_MAX isolated pages, throttle if any
1357          *                     isolated page is PageWriteback
1358          */
1359         if (nr_writeback && nr_writeback >=
1360                         (nr_taken >> (DEF_PRIORITY - sc->priority)))
1361                 wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
1362
1363         trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1364                 zone_idx(zone),
1365                 nr_scanned, nr_reclaimed,
1366                 sc->priority,
1367                 trace_shrink_flags(file));
1368         return nr_reclaimed;
1369 }
1370
1371 /*
1372  * This moves pages from the active list to the inactive list.
1373  *
1374  * We move them the other way if the page is referenced by one or more
1375  * processes, from rmap.
1376  *
1377  * If the pages are mostly unmapped, the processing is fast and it is
1378  * appropriate to hold zone->lru_lock across the whole operation.  But if
1379  * the pages are mapped, the processing is slow (page_referenced()) so we
1380  * should drop zone->lru_lock around each page.  It's impossible to balance
1381  * this, so instead we remove the pages from the LRU while processing them.
1382  * It is safe to rely on PG_active against the non-LRU pages in here because
1383  * nobody will play with that bit on a non-LRU page.
1384  *
1385  * The downside is that we have to touch page->_count against each page.
1386  * But we had to alter page->flags anyway.
1387  */
1388
1389 static void move_active_pages_to_lru(struct lruvec *lruvec,
1390                                      struct list_head *list,
1391                                      struct list_head *pages_to_free,
1392                                      enum lru_list lru)
1393 {
1394         struct zone *zone = lruvec_zone(lruvec);
1395         unsigned long pgmoved = 0;
1396         struct page *page;
1397         int nr_pages;
1398
1399         while (!list_empty(list)) {
1400                 page = lru_to_page(list);
1401                 lruvec = mem_cgroup_page_lruvec(page, zone);
1402
1403                 VM_BUG_ON(PageLRU(page));
1404                 SetPageLRU(page);
1405
1406                 nr_pages = hpage_nr_pages(page);
1407                 mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1408                 list_move(&page->lru, &lruvec->lists[lru]);
1409                 pgmoved += nr_pages;
1410
1411                 if (put_page_testzero(page)) {
1412                         __ClearPageLRU(page);
1413                         __ClearPageActive(page);
1414                         del_page_from_lru_list(page, lruvec, lru);
1415
1416                         if (unlikely(PageCompound(page))) {
1417                                 spin_unlock_irq(&zone->lru_lock);
1418                                 (*get_compound_page_dtor(page))(page);
1419                                 spin_lock_irq(&zone->lru_lock);
1420                         } else
1421                                 list_add(&page->lru, pages_to_free);
1422                 }
1423         }
1424         __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1425         if (!is_active_lru(lru))
1426                 __count_vm_events(PGDEACTIVATE, pgmoved);
1427 }
1428
1429 static void shrink_active_list(unsigned long nr_to_scan,
1430                                struct lruvec *lruvec,
1431                                struct scan_control *sc,
1432                                enum lru_list lru)
1433 {
1434         unsigned long nr_taken;
1435         unsigned long nr_scanned;
1436         unsigned long vm_flags;
1437         LIST_HEAD(l_hold);      /* The pages which were snipped off */
1438         LIST_HEAD(l_active);
1439         LIST_HEAD(l_inactive);
1440         struct page *page;
1441         struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1442         unsigned long nr_rotated = 0;
1443         isolate_mode_t isolate_mode = 0;
1444         int file = is_file_lru(lru);
1445         struct zone *zone = lruvec_zone(lruvec);
1446
1447         lru_add_drain();
1448
1449         if (!sc->may_unmap)
1450                 isolate_mode |= ISOLATE_UNMAPPED;
1451         if (!sc->may_writepage)
1452                 isolate_mode |= ISOLATE_CLEAN;
1453
1454         spin_lock_irq(&zone->lru_lock);
1455
1456         nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1457                                      &nr_scanned, sc, isolate_mode, lru);
1458         if (global_reclaim(sc))
1459                 zone->pages_scanned += nr_scanned;
1460
1461         reclaim_stat->recent_scanned[file] += nr_taken;
1462
1463         __count_zone_vm_events(PGREFILL, zone, nr_scanned);
1464         __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1465         __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1466         spin_unlock_irq(&zone->lru_lock);
1467
1468         while (!list_empty(&l_hold)) {
1469                 cond_resched();
1470                 page = lru_to_page(&l_hold);
1471                 list_del(&page->lru);
1472
1473                 if (unlikely(!page_evictable(page))) {
1474                         putback_lru_page(page);
1475                         continue;
1476                 }
1477
1478                 if (unlikely(buffer_heads_over_limit)) {
1479                         if (page_has_private(page) && trylock_page(page)) {
1480                                 if (page_has_private(page))
1481                                         try_to_release_page(page, 0);
1482                                 unlock_page(page);
1483                         }
1484                 }
1485
1486                 if (page_referenced(page, 0, sc->target_mem_cgroup,
1487                                     &vm_flags)) {
1488                         nr_rotated += hpage_nr_pages(page);
1489                         /*
1490                          * Identify referenced, file-backed active pages and
1491                          * give them one more trip around the active list. So
1492                          * that executable code get better chances to stay in
1493                          * memory under moderate memory pressure.  Anon pages
1494                          * are not likely to be evicted by use-once streaming
1495                          * IO, plus JVM can create lots of anon VM_EXEC pages,
1496                          * so we ignore them here.
1497                          */
1498                         if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1499                                 list_add(&page->lru, &l_active);
1500                                 continue;
1501                         }
1502                 }
1503
1504                 ClearPageActive(page);  /* we are de-activating */
1505                 list_add(&page->lru, &l_inactive);
1506         }
1507
1508         /*
1509          * Move pages back to the lru list.
1510          */
1511         spin_lock_irq(&zone->lru_lock);
1512         /*
1513          * Count referenced pages from currently used mappings as rotated,
1514          * even though only some of them are actually re-activated.  This
1515          * helps balance scan pressure between file and anonymous pages in
1516          * get_scan_ratio.
1517          */
1518         reclaim_stat->recent_rotated[file] += nr_rotated;
1519
1520         move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1521         move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1522         __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1523         spin_unlock_irq(&zone->lru_lock);
1524
1525         free_hot_cold_page_list(&l_hold, 1);
1526 }
1527
1528 #ifdef CONFIG_SWAP
1529 static int inactive_anon_is_low_global(struct zone *zone)
1530 {
1531         unsigned long active, inactive;
1532
1533         active = zone_page_state(zone, NR_ACTIVE_ANON);
1534         inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1535
1536         if (inactive * zone->inactive_ratio < active)
1537                 return 1;
1538
1539         return 0;
1540 }
1541
1542 /**
1543  * inactive_anon_is_low - check if anonymous pages need to be deactivated
1544  * @lruvec: LRU vector to check
1545  *
1546  * Returns true if the zone does not have enough inactive anon pages,
1547  * meaning some active anon pages need to be deactivated.
1548  */
1549 static int inactive_anon_is_low(struct lruvec *lruvec)
1550 {
1551         /*
1552          * If we don't have swap space, anonymous page deactivation
1553          * is pointless.
1554          */
1555         if (!total_swap_pages)
1556                 return 0;
1557
1558         if (!mem_cgroup_disabled())
1559                 return mem_cgroup_inactive_anon_is_low(lruvec);
1560
1561         return inactive_anon_is_low_global(lruvec_zone(lruvec));
1562 }
1563 #else
1564 static inline int inactive_anon_is_low(struct lruvec *lruvec)
1565 {
1566         return 0;
1567 }
1568 #endif
1569
1570 static int inactive_file_is_low_global(struct zone *zone)
1571 {
1572         unsigned long active, inactive;
1573
1574         active = zone_page_state(zone, NR_ACTIVE_FILE);
1575         inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1576
1577         return (active > inactive);
1578 }
1579
1580 /**
1581  * inactive_file_is_low - check if file pages need to be deactivated
1582  * @lruvec: LRU vector to check
1583  *
1584  * When the system is doing streaming IO, memory pressure here
1585  * ensures that active file pages get deactivated, until more
1586  * than half of the file pages are on the inactive list.
1587  *
1588  * Once we get to that situation, protect the system's working
1589  * set from being evicted by disabling active file page aging.
1590  *
1591  * This uses a different ratio than the anonymous pages, because
1592  * the page cache uses a use-once replacement algorithm.
1593  */
1594 static int inactive_file_is_low(struct lruvec *lruvec)
1595 {
1596         if (!mem_cgroup_disabled())
1597                 return mem_cgroup_inactive_file_is_low(lruvec);
1598
1599         return inactive_file_is_low_global(lruvec_zone(lruvec));
1600 }
1601
1602 static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1603 {
1604         if (is_file_lru(lru))
1605                 return inactive_file_is_low(lruvec);
1606         else
1607                 return inactive_anon_is_low(lruvec);
1608 }
1609
1610 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1611                                  struct lruvec *lruvec, struct scan_control *sc)
1612 {
1613         if (is_active_lru(lru)) {
1614                 if (inactive_list_is_low(lruvec, lru))
1615                         shrink_active_list(nr_to_scan, lruvec, sc, lru);
1616                 return 0;
1617         }
1618
1619         return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1620 }
1621
1622 static int vmscan_swappiness(struct scan_control *sc)
1623 {
1624         if (global_reclaim(sc))
1625                 return vm_swappiness;
1626         return mem_cgroup_swappiness(sc->target_mem_cgroup);
1627 }
1628
1629 /*
1630  * Determine how aggressively the anon and file LRU lists should be
1631  * scanned.  The relative value of each set of LRU lists is determined
1632  * by looking at the fraction of the pages scanned we did rotate back
1633  * onto the active list instead of evict.
1634  *
1635  * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
1636  * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
1637  */
1638 static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
1639                            unsigned long *nr)
1640 {
1641         unsigned long anon, file, free;
1642         unsigned long anon_prio, file_prio;
1643         unsigned long ap, fp;
1644         struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1645         u64 fraction[2], denominator;
1646         enum lru_list lru;
1647         int noswap = 0;
1648         bool force_scan = false;
1649         struct zone *zone = lruvec_zone(lruvec);
1650
1651         /*
1652          * If the zone or memcg is small, nr[l] can be 0.  This
1653          * results in no scanning on this priority and a potential
1654          * priority drop.  Global direct reclaim can go to the next
1655          * zone and tends to have no problems. Global kswapd is for
1656          * zone balancing and it needs to scan a minimum amount. When
1657          * reclaiming for a memcg, a priority drop can cause high
1658          * latencies, so it's better to scan a minimum amount there as
1659          * well.
1660          */
1661         if (current_is_kswapd() && zone->all_unreclaimable)
1662                 force_scan = true;
1663         if (!global_reclaim(sc))
1664                 force_scan = true;
1665
1666         /* If we have no swap space, do not bother scanning anon pages. */
1667         if (!sc->may_swap || (nr_swap_pages <= 0)) {
1668                 noswap = 1;
1669                 fraction[0] = 0;
1670                 fraction[1] = 1;
1671                 denominator = 1;
1672                 goto out;
1673         }
1674
1675         anon  = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
1676                 get_lru_size(lruvec, LRU_INACTIVE_ANON);
1677         file  = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
1678                 get_lru_size(lruvec, LRU_INACTIVE_FILE);
1679
1680         if (global_reclaim(sc)) {
1681                 free  = zone_page_state(zone, NR_FREE_PAGES);
1682                 /* If we have very few page cache pages,
1683                    force-scan anon pages. */
1684                 if (unlikely(file + free <= high_wmark_pages(zone))) {
1685                         fraction[0] = 1;
1686                         fraction[1] = 0;
1687                         denominator = 1;
1688                         goto out;
1689                 }
1690         }
1691
1692         /*
1693          * With swappiness at 100, anonymous and file have the same priority.
1694          * This scanning priority is essentially the inverse of IO cost.
1695          */
1696         anon_prio = vmscan_swappiness(sc);
1697         file_prio = 200 - anon_prio;
1698
1699         /*
1700          * OK, so we have swap space and a fair amount of page cache
1701          * pages.  We use the recently rotated / recently scanned
1702          * ratios to determine how valuable each cache is.
1703          *
1704          * Because workloads change over time (and to avoid overflow)
1705          * we keep these statistics as a floating average, which ends
1706          * up weighing recent references more than old ones.
1707          *
1708          * anon in [0], file in [1]
1709          */
1710         spin_lock_irq(&zone->lru_lock);
1711         if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1712                 reclaim_stat->recent_scanned[0] /= 2;
1713                 reclaim_stat->recent_rotated[0] /= 2;
1714         }
1715
1716         if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1717                 reclaim_stat->recent_scanned[1] /= 2;
1718                 reclaim_stat->recent_rotated[1] /= 2;
1719         }
1720
1721         /*
1722          * The amount of pressure on anon vs file pages is inversely
1723          * proportional to the fraction of recently scanned pages on
1724          * each list that were recently referenced and in active use.
1725          */
1726         ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1727         ap /= reclaim_stat->recent_rotated[0] + 1;
1728
1729         fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
1730         fp /= reclaim_stat->recent_rotated[1] + 1;
1731         spin_unlock_irq(&zone->lru_lock);
1732
1733         fraction[0] = ap;
1734         fraction[1] = fp;
1735         denominator = ap + fp + 1;
1736 out:
1737         for_each_evictable_lru(lru) {
1738                 int file = is_file_lru(lru);
1739                 unsigned long scan;
1740
1741                 scan = get_lru_size(lruvec, lru);
1742                 if (sc->priority || noswap || !vmscan_swappiness(sc)) {
1743                         scan >>= sc->priority;
1744                         if (!scan && force_scan)
1745                                 scan = SWAP_CLUSTER_MAX;
1746                         scan = div64_u64(scan * fraction[file], denominator);
1747                 }
1748                 nr[lru] = scan;
1749         }
1750 }
1751
1752 /* Use reclaim/compaction for costly allocs or under memory pressure */
1753 static bool in_reclaim_compaction(struct scan_control *sc)
1754 {
1755         if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
1756                         (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
1757                          sc->priority < DEF_PRIORITY - 2))
1758                 return true;
1759
1760         return false;
1761 }
1762
1763 /*
1764  * Reclaim/compaction is used for high-order allocation requests. It reclaims
1765  * order-0 pages before compacting the zone. should_continue_reclaim() returns
1766  * true if more pages should be reclaimed such that when the page allocator
1767  * calls try_to_compact_zone() that it will have enough free pages to succeed.
1768  * It will give up earlier than that if there is difficulty reclaiming pages.
1769  */
1770 static inline bool should_continue_reclaim(struct lruvec *lruvec,
1771                                         unsigned long nr_reclaimed,
1772                                         unsigned long nr_scanned,
1773                                         struct scan_control *sc)
1774 {
1775         unsigned long pages_for_compaction;
1776         unsigned long inactive_lru_pages;
1777
1778         /* If not in reclaim/compaction mode, stop */
1779         if (!in_reclaim_compaction(sc))
1780                 return false;
1781
1782         /* Consider stopping depending on scan and reclaim activity */
1783         if (sc->gfp_mask & __GFP_REPEAT) {
1784                 /*
1785                  * For __GFP_REPEAT allocations, stop reclaiming if the
1786                  * full LRU list has been scanned and we are still failing
1787                  * to reclaim pages. This full LRU scan is potentially
1788                  * expensive but a __GFP_REPEAT caller really wants to succeed
1789                  */
1790                 if (!nr_reclaimed && !nr_scanned)
1791                         return false;
1792         } else {
1793                 /*
1794                  * For non-__GFP_REPEAT allocations which can presumably
1795                  * fail without consequence, stop if we failed to reclaim
1796                  * any pages from the last SWAP_CLUSTER_MAX number of
1797                  * pages that were scanned. This will return to the
1798                  * caller faster at the risk reclaim/compaction and
1799                  * the resulting allocation attempt fails
1800                  */
1801                 if (!nr_reclaimed)
1802                         return false;
1803         }
1804
1805         /*
1806          * If we have not reclaimed enough pages for compaction and the
1807          * inactive lists are large enough, continue reclaiming
1808          */
1809         pages_for_compaction = (2UL << sc->order);
1810         inactive_lru_pages = get_lru_size(lruvec, LRU_INACTIVE_FILE);
1811         if (nr_swap_pages > 0)
1812                 inactive_lru_pages += get_lru_size(lruvec, LRU_INACTIVE_ANON);
1813         if (sc->nr_reclaimed < pages_for_compaction &&
1814                         inactive_lru_pages > pages_for_compaction)
1815                 return true;
1816
1817         /* If compaction would go ahead or the allocation would succeed, stop */
1818         switch (compaction_suitable(lruvec_zone(lruvec), sc->order)) {
1819         case COMPACT_PARTIAL:
1820         case COMPACT_CONTINUE:
1821                 return false;
1822         default:
1823                 return true;
1824         }
1825 }
1826
1827 /*
1828  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1829  */
1830 static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
1831 {
1832         unsigned long nr[NR_LRU_LISTS];
1833         unsigned long nr_to_scan;
1834         enum lru_list lru;
1835         unsigned long nr_reclaimed, nr_scanned;
1836         unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1837         struct blk_plug plug;
1838
1839 restart:
1840         nr_reclaimed = 0;
1841         nr_scanned = sc->nr_scanned;
1842         get_scan_count(lruvec, sc, nr);
1843
1844         blk_start_plug(&plug);
1845         while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1846                                         nr[LRU_INACTIVE_FILE]) {
1847                 for_each_evictable_lru(lru) {
1848                         if (nr[lru]) {
1849                                 nr_to_scan = min_t(unsigned long,
1850                                                    nr[lru], SWAP_CLUSTER_MAX);
1851                                 nr[lru] -= nr_to_scan;
1852
1853                                 nr_reclaimed += shrink_list(lru, nr_to_scan,
1854                                                             lruvec, sc);
1855                         }
1856                 }
1857                 /*
1858                  * On large memory systems, scan >> priority can become
1859                  * really large. This is fine for the starting priority;
1860                  * we want to put equal scanning pressure on each zone.
1861                  * However, if the VM has a harder time of freeing pages,
1862                  * with multiple processes reclaiming pages, the total
1863                  * freeing target can get unreasonably large.
1864                  */
1865                 if (nr_reclaimed >= nr_to_reclaim &&
1866                     sc->priority < DEF_PRIORITY)
1867                         break;
1868         }
1869         blk_finish_plug(&plug);
1870         sc->nr_reclaimed += nr_reclaimed;
1871
1872         /*
1873          * Even if we did not try to evict anon pages at all, we want to
1874          * rebalance the anon lru active/inactive ratio.
1875          */
1876         if (inactive_anon_is_low(lruvec))
1877                 shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
1878                                    sc, LRU_ACTIVE_ANON);
1879
1880         /* reclaim/compaction might need reclaim to continue */
1881         if (should_continue_reclaim(lruvec, nr_reclaimed,
1882                                     sc->nr_scanned - nr_scanned, sc))
1883                 goto restart;
1884
1885         throttle_vm_writeout(sc->gfp_mask);
1886 }
1887
1888 static void shrink_zone(struct zone *zone, struct scan_control *sc)
1889 {
1890         struct mem_cgroup *root = sc->target_mem_cgroup;
1891         struct mem_cgroup_reclaim_cookie reclaim = {
1892                 .zone = zone,
1893                 .priority = sc->priority,
1894         };
1895         struct mem_cgroup *memcg;
1896
1897         memcg = mem_cgroup_iter(root, NULL, &reclaim);
1898         do {
1899                 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
1900
1901                 shrink_lruvec(lruvec, sc);
1902
1903                 /*
1904                  * Limit reclaim has historically picked one memcg and
1905                  * scanned it with decreasing priority levels until
1906                  * nr_to_reclaim had been reclaimed.  This priority
1907                  * cycle is thus over after a single memcg.
1908                  *
1909                  * Direct reclaim and kswapd, on the other hand, have
1910                  * to scan all memory cgroups to fulfill the overall
1911                  * scan target for the zone.
1912                  */
1913                 if (!global_reclaim(sc)) {
1914                         mem_cgroup_iter_break(root, memcg);
1915                         break;
1916                 }
1917                 memcg = mem_cgroup_iter(root, memcg, &reclaim);
1918         } while (memcg);
1919 }
1920
1921 /* Returns true if compaction should go ahead for a high-order request */
1922 static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
1923 {
1924         unsigned long balance_gap, watermark;
1925         bool watermark_ok;
1926
1927         /* Do not consider compaction for orders reclaim is meant to satisfy */
1928         if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
1929                 return false;
1930
1931         /*
1932          * Compaction takes time to run and there are potentially other
1933          * callers using the pages just freed. Continue reclaiming until
1934          * there is a buffer of free pages available to give compaction
1935          * a reasonable chance of completing and allocating the page
1936          */
1937         balance_gap = min(low_wmark_pages(zone),
1938                 (zone->present_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
1939                         KSWAPD_ZONE_BALANCE_GAP_RATIO);
1940         watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
1941         watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
1942
1943         /*
1944          * If compaction is deferred, reclaim up to a point where
1945          * compaction will have a chance of success when re-enabled
1946          */
1947         if (compaction_deferred(zone, sc->order))
1948                 return watermark_ok;
1949
1950         /* If compaction is not ready to start, keep reclaiming */
1951         if (!compaction_suitable(zone, sc->order))
1952                 return false;
1953
1954         return watermark_ok;
1955 }
1956
1957 /*
1958  * This is the direct reclaim path, for page-allocating processes.  We only
1959  * try to reclaim pages from zones which will satisfy the caller's allocation
1960  * request.
1961  *
1962  * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
1963  * Because:
1964  * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1965  *    allocation or
1966  * b) The target zone may be at high_wmark_pages(zone) but the lower zones
1967  *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
1968  *    zone defense algorithm.
1969  *
1970  * If a zone is deemed to be full of pinned pages then just give it a light
1971  * scan then give up on it.
1972  *
1973  * This function returns true if a zone is being reclaimed for a costly
1974  * high-order allocation and compaction is ready to begin. This indicates to
1975  * the caller that it should consider retrying the allocation instead of
1976  * further reclaim.
1977  */
1978 static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
1979 {
1980         struct zoneref *z;
1981         struct zone *zone;
1982         unsigned long nr_soft_reclaimed;
1983         unsigned long nr_soft_scanned;
1984         bool aborted_reclaim = false;
1985
1986         /*
1987          * If the number of buffer_heads in the machine exceeds the maximum
1988          * allowed level, force direct reclaim to scan the highmem zone as
1989          * highmem pages could be pinning lowmem pages storing buffer_heads
1990          */
1991         if (buffer_heads_over_limit)
1992                 sc->gfp_mask |= __GFP_HIGHMEM;
1993
1994         for_each_zone_zonelist_nodemask(zone, z, zonelist,
1995                                         gfp_zone(sc->gfp_mask), sc->nodemask) {
1996                 if (!populated_zone(zone))
1997                         continue;
1998                 /*
1999                  * Take care memory controller reclaiming has small influence
2000                  * to global LRU.
2001                  */
2002                 if (global_reclaim(sc)) {
2003                         if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2004                                 continue;
2005                         if (zone->all_unreclaimable &&
2006                                         sc->priority != DEF_PRIORITY)
2007                                 continue;       /* Let kswapd poll it */
2008                         if (IS_ENABLED(CONFIG_COMPACTION)) {
2009                                 /*
2010                                  * If we already have plenty of memory free for
2011                                  * compaction in this zone, don't free any more.
2012                                  * Even though compaction is invoked for any
2013                                  * non-zero order, only frequent costly order
2014                                  * reclamation is disruptive enough to become a
2015                                  * noticeable problem, like transparent huge
2016                                  * page allocations.
2017                                  */
2018                                 if (compaction_ready(zone, sc)) {
2019                                         aborted_reclaim = true;
2020                                         continue;
2021                                 }
2022                         }
2023                         /*
2024                          * This steals pages from memory cgroups over softlimit
2025                          * and returns the number of reclaimed pages and
2026                          * scanned pages. This works for global memory pressure
2027                          * and balancing, not for a memcg's limit.
2028                          */
2029                         nr_soft_scanned = 0;
2030                         nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2031                                                 sc->order, sc->gfp_mask,
2032                                                 &nr_soft_scanned);
2033                         sc->nr_reclaimed += nr_soft_reclaimed;
2034                         sc->nr_scanned += nr_soft_scanned;
2035                         /* need some check for avoid more shrink_zone() */
2036                 }
2037
2038                 shrink_zone(zone, sc);
2039         }
2040
2041         return aborted_reclaim;
2042 }
2043
2044 static bool zone_reclaimable(struct zone *zone)
2045 {
2046         return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
2047 }
2048
2049 /* All zones in zonelist are unreclaimable? */
2050 static bool all_unreclaimable(struct zonelist *zonelist,
2051                 struct scan_control *sc)
2052 {
2053         struct zoneref *z;
2054         struct zone *zone;
2055
2056         for_each_zone_zonelist_nodemask(zone, z, zonelist,
2057                         gfp_zone(sc->gfp_mask), sc->nodemask) {
2058                 if (!populated_zone(zone))
2059                         continue;
2060                 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2061                         continue;
2062                 if (!zone->all_unreclaimable)
2063                         return false;
2064         }
2065
2066         return true;
2067 }
2068
2069 /*
2070  * This is the main entry point to direct page reclaim.
2071  *
2072  * If a full scan of the inactive list fails to free enough memory then we
2073  * are "out of memory" and something needs to be killed.
2074  *
2075  * If the caller is !__GFP_FS then the probability of a failure is reasonably
2076  * high - the zone may be full of dirty or under-writeback pages, which this
2077  * caller can't do much about.  We kick the writeback threads and take explicit
2078  * naps in the hope that some of these pages can be written.  But if the
2079  * allocating task holds filesystem locks which prevent writeout this might not
2080  * work, and the allocation attempt will fail.
2081  *
2082  * returns:     0, if no pages reclaimed
2083  *              else, the number of pages reclaimed
2084  */
2085 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2086                                         struct scan_control *sc,
2087                                         struct shrink_control *shrink)
2088 {
2089         unsigned long total_scanned = 0;
2090         struct reclaim_state *reclaim_state = current->reclaim_state;
2091         struct zoneref *z;
2092         struct zone *zone;
2093         unsigned long writeback_threshold;
2094         bool aborted_reclaim;
2095
2096         delayacct_freepages_start();
2097
2098         if (global_reclaim(sc))
2099                 count_vm_event(ALLOCSTALL);
2100
2101         do {
2102                 sc->nr_scanned = 0;
2103                 aborted_reclaim = shrink_zones(zonelist, sc);
2104
2105                 /*
2106                  * Don't shrink slabs when reclaiming memory from
2107                  * over limit cgroups
2108                  */
2109                 if (global_reclaim(sc)) {
2110                         unsigned long lru_pages = 0;
2111                         for_each_zone_zonelist(zone, z, zonelist,
2112                                         gfp_zone(sc->gfp_mask)) {
2113                                 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2114                                         continue;
2115
2116                                 lru_pages += zone_reclaimable_pages(zone);
2117                         }
2118
2119                         shrink_slab(shrink, sc->nr_scanned, lru_pages);
2120                         if (reclaim_state) {
2121                                 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2122                                 reclaim_state->reclaimed_slab = 0;
2123                         }
2124                 }
2125                 total_scanned += sc->nr_scanned;
2126                 if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2127                         goto out;
2128
2129                 /*
2130                  * Try to write back as many pages as we just scanned.  This
2131                  * tends to cause slow streaming writers to write data to the
2132                  * disk smoothly, at the dirtying rate, which is nice.   But
2133                  * that's undesirable in laptop mode, where we *want* lumpy
2134                  * writeout.  So in laptop mode, write out the whole world.
2135                  */
2136                 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2137                 if (total_scanned > writeback_threshold) {
2138                         wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2139                                                 WB_REASON_TRY_TO_FREE_PAGES);
2140                         sc->may_writepage = 1;
2141                 }
2142
2143                 /* Take a nap, wait for some writeback to complete */
2144                 if (!sc->hibernation_mode && sc->nr_scanned &&
2145                     sc->priority < DEF_PRIORITY - 2) {
2146                         struct zone *preferred_zone;
2147
2148                         first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
2149                                                 &cpuset_current_mems_allowed,
2150                                                 &preferred_zone);
2151                         wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
2152                 }
2153         } while (--sc->priority >= 0);
2154
2155 out:
2156         delayacct_freepages_end();
2157
2158         if (sc->nr_reclaimed)
2159                 return sc->nr_reclaimed;
2160
2161         /*
2162          * As hibernation is going on, kswapd is freezed so that it can't mark
2163          * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2164          * check.
2165          */
2166         if (oom_killer_disabled)
2167                 return 0;
2168
2169         /* Aborted reclaim to try compaction? don't OOM, then */
2170         if (aborted_reclaim)
2171                 return 1;
2172
2173         /* top priority shrink_zones still had more to do? don't OOM, then */
2174         if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2175                 return 1;
2176
2177         return 0;
2178 }
2179
2180 static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2181 {
2182         struct zone *zone;
2183         unsigned long pfmemalloc_reserve = 0;
2184         unsigned long free_pages = 0;
2185         int i;
2186         bool wmark_ok;
2187
2188         for (i = 0; i <= ZONE_NORMAL; i++) {
2189                 zone = &pgdat->node_zones[i];
2190                 pfmemalloc_reserve += min_wmark_pages(zone);
2191                 free_pages += zone_page_state(zone, NR_FREE_PAGES);
2192         }
2193
2194         wmark_ok = free_pages > pfmemalloc_reserve / 2;
2195
2196         /* kswapd must be awake if processes are being throttled */
2197         if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2198                 pgdat->classzone_idx = min(pgdat->classzone_idx,
2199                                                 (enum zone_type)ZONE_NORMAL);
2200                 wake_up_interruptible(&pgdat->kswapd_wait);
2201         }
2202
2203         return wmark_ok;
2204 }
2205
2206 /*
2207  * Throttle direct reclaimers if backing storage is backed by the network
2208  * and the PFMEMALLOC reserve for the preferred node is getting dangerously
2209  * depleted. kswapd will continue to make progress and wake the processes
2210  * when the low watermark is reached.
2211  *
2212  * Returns true if a fatal signal was delivered during throttling. If this
2213  * happens, the page allocator should not consider triggering the OOM killer.
2214  */
2215 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2216                                         nodemask_t *nodemask)
2217 {
2218         struct zone *zone;
2219         int high_zoneidx = gfp_zone(gfp_mask);
2220         pg_data_t *pgdat;
2221
2222         /*
2223          * Kernel threads should not be throttled as they may be indirectly
2224          * responsible for cleaning pages necessary for reclaim to make forward
2225          * progress. kjournald for example may enter direct reclaim while
2226          * committing a transaction where throttling it could forcing other
2227          * processes to block on log_wait_commit().
2228          */
2229         if (current->flags & PF_KTHREAD)
2230                 goto out;
2231
2232         /*
2233          * If a fatal signal is pending, this process should not throttle.
2234          * It should return quickly so it can exit and free its memory
2235          */
2236         if (fatal_signal_pending(current))
2237                 goto out;
2238
2239         /* Check if the pfmemalloc reserves are ok */
2240         first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
2241         pgdat = zone->zone_pgdat;
2242         if (pfmemalloc_watermark_ok(pgdat))
2243                 goto out;
2244
2245         /* Account for the throttling */
2246         count_vm_event(PGSCAN_DIRECT_THROTTLE);
2247
2248         /*
2249          * If the caller cannot enter the filesystem, it's possible that it
2250          * is due to the caller holding an FS lock or performing a journal
2251          * transaction in the case of a filesystem like ext[3|4]. In this case,
2252          * it is not safe to block on pfmemalloc_wait as kswapd could be
2253          * blocked waiting on the same lock. Instead, throttle for up to a
2254          * second before continuing.
2255          */
2256         if (!(gfp_mask & __GFP_FS)) {
2257                 wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2258                         pfmemalloc_watermark_ok(pgdat), HZ);
2259
2260                 goto check_pending;
2261         }
2262
2263         /* Throttle until kswapd wakes the process */
2264         wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2265                 pfmemalloc_watermark_ok(pgdat));
2266
2267 check_pending:
2268         if (fatal_signal_pending(current))
2269                 return true;
2270
2271 out:
2272         return false;
2273 }
2274
2275 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2276                                 gfp_t gfp_mask, nodemask_t *nodemask)
2277 {
2278         unsigned long nr_reclaimed;
2279         struct scan_control sc = {
2280                 .gfp_mask = gfp_mask,
2281                 .may_writepage = !laptop_mode,
2282                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2283                 .may_unmap = 1,
2284                 .may_swap = 1,
2285                 .order = order,
2286                 .priority = DEF_PRIORITY,
2287                 .target_mem_cgroup = NULL,
2288                 .nodemask = nodemask,
2289         };
2290         struct shrink_control shrink = {
2291                 .gfp_mask = sc.gfp_mask,
2292         };
2293
2294         /*
2295          * Do not enter reclaim if fatal signal was delivered while throttled.
2296          * 1 is returned so that the page allocator does not OOM kill at this
2297          * point.
2298          */
2299         if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2300                 return 1;
2301
2302         trace_mm_vmscan_direct_reclaim_begin(order,
2303                                 sc.may_writepage,
2304                                 gfp_mask);
2305
2306         nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2307
2308         trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2309
2310         return nr_reclaimed;
2311 }
2312
2313 #ifdef CONFIG_MEMCG
2314
2315 unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2316                                                 gfp_t gfp_mask, bool noswap,
2317                                                 struct zone *zone,
2318                                                 unsigned long *nr_scanned)
2319 {
2320         struct scan_control sc = {
2321                 .nr_scanned = 0,
2322                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2323                 .may_writepage = !laptop_mode,
2324                 .may_unmap = 1,
2325                 .may_swap = !noswap,
2326                 .order = 0,
2327                 .priority = 0,
2328                 .target_mem_cgroup = memcg,
2329         };
2330         struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2331
2332         sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2333                         (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2334
2335         trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2336                                                       sc.may_writepage,
2337                                                       sc.gfp_mask);
2338
2339         /*
2340          * NOTE: Although we can get the priority field, using it
2341          * here is not a good idea, since it limits the pages we can scan.
2342          * if we don't reclaim here, the shrink_zone from balance_pgdat
2343          * will pick up pages from other mem cgroup's as well. We hack
2344          * the priority and make it zero.
2345          */
2346         shrink_lruvec(lruvec, &sc);
2347
2348         trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2349
2350         *nr_scanned = sc.nr_scanned;
2351         return sc.nr_reclaimed;
2352 }
2353
2354 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
2355                                            gfp_t gfp_mask,
2356                                            bool noswap)
2357 {
2358         struct zonelist *zonelist;
2359         unsigned long nr_reclaimed;
2360         int nid;
2361         struct scan_control sc = {
2362                 .may_writepage = !laptop_mode,
2363                 .may_unmap = 1,
2364                 .may_swap = !noswap,
2365                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2366                 .order = 0,
2367                 .priority = DEF_PRIORITY,
2368                 .target_mem_cgroup = memcg,
2369                 .nodemask = NULL, /* we don't care the placement */
2370                 .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2371                                 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2372         };
2373         struct shrink_control shrink = {
2374                 .gfp_mask = sc.gfp_mask,
2375         };
2376
2377         /*
2378          * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2379          * take care of from where we get pages. So the node where we start the
2380          * scan does not need to be the current node.
2381          */
2382         nid = mem_cgroup_select_victim_node(memcg);
2383
2384         zonelist = NODE_DATA(nid)->node_zonelists;
2385
2386         trace_mm_vmscan_memcg_reclaim_begin(0,
2387                                             sc.may_writepage,
2388                                             sc.gfp_mask);
2389
2390         nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2391
2392         trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2393
2394         return nr_reclaimed;
2395 }
2396 #endif
2397
2398 static void age_active_anon(struct zone *zone, struct scan_control *sc)
2399 {
2400         struct mem_cgroup *memcg;
2401
2402         if (!total_swap_pages)
2403                 return;
2404
2405         memcg = mem_cgroup_iter(NULL, NULL, NULL);
2406         do {
2407                 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2408
2409                 if (inactive_anon_is_low(lruvec))
2410                         shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2411                                            sc, LRU_ACTIVE_ANON);
2412
2413                 memcg = mem_cgroup_iter(NULL, memcg, NULL);
2414         } while (memcg);
2415 }
2416
2417 static bool zone_balanced(struct zone *zone, int order,
2418                           unsigned long balance_gap, int classzone_idx)
2419 {
2420         if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) +
2421                                     balance_gap, classzone_idx, 0))
2422                 return false;
2423
2424         if (IS_ENABLED(CONFIG_COMPACTION) && order &&
2425             !compaction_suitable(zone, order))
2426                 return false;
2427
2428         return true;
2429 }
2430
2431 /*
2432  * pgdat_balanced is used when checking if a node is balanced for high-order
2433  * allocations. Only zones that meet watermarks and are in a zone allowed
2434  * by the callers classzone_idx are added to balanced_pages. The total of
2435  * balanced pages must be at least 25% of the zones allowed by classzone_idx
2436  * for the node to be considered balanced. Forcing all zones to be balanced
2437  * for high orders can cause excessive reclaim when there are imbalanced zones.
2438  * The choice of 25% is due to
2439  *   o a 16M DMA zone that is balanced will not balance a zone on any
2440  *     reasonable sized machine
2441  *   o On all other machines, the top zone must be at least a reasonable
2442  *     percentage of the middle zones. For example, on 32-bit x86, highmem
2443  *     would need to be at least 256M for it to be balance a whole node.
2444  *     Similarly, on x86-64 the Normal zone would need to be at least 1G
2445  *     to balance a node on its own. These seemed like reasonable ratios.
2446  */
2447 static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
2448                                                 int classzone_idx)
2449 {
2450         unsigned long present_pages = 0;
2451         int i;
2452
2453         for (i = 0; i <= classzone_idx; i++)
2454                 present_pages += pgdat->node_zones[i].present_pages;
2455
2456         /* A special case here: if zone has no page, we think it's balanced */
2457         return balanced_pages >= (present_pages >> 2);
2458 }
2459
2460 /*
2461  * Prepare kswapd for sleeping. This verifies that there are no processes
2462  * waiting in throttle_direct_reclaim() and that watermarks have been met.
2463  *
2464  * Returns true if kswapd is ready to sleep
2465  */
2466 static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
2467                                         int classzone_idx)
2468 {
2469         int i;
2470         unsigned long balanced = 0;
2471         bool all_zones_ok = true;
2472
2473         /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2474         if (remaining)
2475                 return false;
2476
2477         /*
2478          * There is a potential race between when kswapd checks its watermarks
2479          * and a process gets throttled. There is also a potential race if
2480          * processes get throttled, kswapd wakes, a large process exits therby
2481          * balancing the zones that causes kswapd to miss a wakeup. If kswapd
2482          * is going to sleep, no process should be sleeping on pfmemalloc_wait
2483          * so wake them now if necessary. If necessary, processes will wake
2484          * kswapd and get throttled again
2485          */
2486         if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
2487                 wake_up(&pgdat->pfmemalloc_wait);
2488                 return false;
2489         }
2490
2491         /* Check the watermark levels */
2492         for (i = 0; i <= classzone_idx; i++) {
2493                 struct zone *zone = pgdat->node_zones + i;
2494
2495                 if (!populated_zone(zone))
2496                         continue;
2497
2498                 /*
2499                  * balance_pgdat() skips over all_unreclaimable after
2500                  * DEF_PRIORITY. Effectively, it considers them balanced so
2501                  * they must be considered balanced here as well if kswapd
2502                  * is to sleep
2503                  */
2504                 if (zone->all_unreclaimable) {
2505                         balanced += zone->present_pages;
2506                         continue;
2507                 }
2508
2509                 if (!zone_balanced(zone, order, 0, i))
2510                         all_zones_ok = false;
2511                 else
2512                         balanced += zone->present_pages;
2513         }
2514
2515         /*
2516          * For high-order requests, the balanced zones must contain at least
2517          * 25% of the nodes pages for kswapd to sleep. For order-0, all zones
2518          * must be balanced
2519          */
2520         if (order)
2521                 return pgdat_balanced(pgdat, balanced, classzone_idx);
2522         else
2523                 return all_zones_ok;
2524 }
2525
2526 /*
2527  * For kswapd, balance_pgdat() will work across all this node's zones until
2528  * they are all at high_wmark_pages(zone).
2529  *
2530  * Returns the final order kswapd was reclaiming at
2531  *
2532  * There is special handling here for zones which are full of pinned pages.
2533  * This can happen if the pages are all mlocked, or if they are all used by
2534  * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
2535  * What we do is to detect the case where all pages in the zone have been
2536  * scanned twice and there has been zero successful reclaim.  Mark the zone as
2537  * dead and from now on, only perform a short scan.  Basically we're polling
2538  * the zone for when the problem goes away.
2539  *
2540  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
2541  * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2542  * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2543  * lower zones regardless of the number of free pages in the lower zones. This
2544  * interoperates with the page allocator fallback scheme to ensure that aging
2545  * of pages is balanced across the zones.
2546  */
2547 static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2548                                                         int *classzone_idx)
2549 {
2550         int all_zones_ok;
2551         unsigned long balanced;
2552         int i;
2553         int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
2554         unsigned long total_scanned;
2555         struct reclaim_state *reclaim_state = current->reclaim_state;
2556         unsigned long nr_soft_reclaimed;
2557         unsigned long nr_soft_scanned;
2558         struct scan_control sc = {
2559                 .gfp_mask = GFP_KERNEL,
2560                 .may_unmap = 1,
2561                 .may_swap = 1,
2562                 /*
2563                  * kswapd doesn't want to be bailed out while reclaim. because
2564                  * we want to put equal scanning pressure on each zone.
2565                  */
2566                 .nr_to_reclaim = ULONG_MAX,
2567                 .order = order,
2568                 .target_mem_cgroup = NULL,
2569         };
2570         struct shrink_control shrink = {
2571                 .gfp_mask = sc.gfp_mask,
2572         };
2573 loop_again:
2574         total_scanned = 0;
2575         sc.priority = DEF_PRIORITY;
2576         sc.nr_reclaimed = 0;
2577         sc.may_writepage = !laptop_mode;
2578         count_vm_event(PAGEOUTRUN);
2579
2580         do {
2581                 unsigned long lru_pages = 0;
2582                 int has_under_min_watermark_zone = 0;
2583
2584                 all_zones_ok = 1;
2585                 balanced = 0;
2586
2587                 /*
2588                  * Scan in the highmem->dma direction for the highest
2589                  * zone which needs scanning
2590                  */
2591                 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2592                         struct zone *zone = pgdat->node_zones + i;
2593
2594                         if (!populated_zone(zone))
2595                                 continue;
2596
2597                         if (zone->all_unreclaimable &&
2598                             sc.priority != DEF_PRIORITY)
2599                                 continue;
2600
2601                         /*
2602                          * Do some background aging of the anon list, to give
2603                          * pages a chance to be referenced before reclaiming.
2604                          */
2605                         age_active_anon(zone, &sc);
2606
2607                         /*
2608                          * If the number of buffer_heads in the machine
2609                          * exceeds the maximum allowed level and this node
2610                          * has a highmem zone, force kswapd to reclaim from
2611                          * it to relieve lowmem pressure.
2612                          */
2613                         if (buffer_heads_over_limit && is_highmem_idx(i)) {
2614                                 end_zone = i;
2615                                 break;
2616                         }
2617
2618                         if (!zone_balanced(zone, order, 0, 0)) {
2619                                 end_zone = i;
2620                                 break;
2621                         } else {
2622                                 /* If balanced, clear the congested flag */
2623                                 zone_clear_flag(zone, ZONE_CONGESTED);
2624                         }
2625                 }
2626                 if (i < 0)
2627                         goto out;
2628
2629                 for (i = 0; i <= end_zone; i++) {
2630                         struct zone *zone = pgdat->node_zones + i;
2631
2632                         lru_pages += zone_reclaimable_pages(zone);
2633                 }
2634
2635                 /*
2636                  * Now scan the zone in the dma->highmem direction, stopping
2637                  * at the last zone which needs scanning.
2638                  *
2639                  * We do this because the page allocator works in the opposite
2640                  * direction.  This prevents the page allocator from allocating
2641                  * pages behind kswapd's direction of progress, which would
2642                  * cause too much scanning of the lower zones.
2643                  */
2644                 for (i = 0; i <= end_zone; i++) {
2645                         struct zone *zone = pgdat->node_zones + i;
2646                         int nr_slab, testorder;
2647                         unsigned long balance_gap;
2648
2649                         if (!populated_zone(zone))
2650                                 continue;
2651
2652                         if (zone->all_unreclaimable &&
2653                             sc.priority != DEF_PRIORITY)
2654                                 continue;
2655
2656                         sc.nr_scanned = 0;
2657
2658                         nr_soft_scanned = 0;
2659                         /*
2660                          * Call soft limit reclaim before calling shrink_zone.
2661                          */
2662                         nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2663                                                         order, sc.gfp_mask,
2664                                                         &nr_soft_scanned);
2665                         sc.nr_reclaimed += nr_soft_reclaimed;
2666                         total_scanned += nr_soft_scanned;
2667
2668                         /*
2669                          * We put equal pressure on every zone, unless
2670                          * one zone has way too many pages free
2671                          * already. The "too many pages" is defined
2672                          * as the high wmark plus a "gap" where the
2673                          * gap is either the low watermark or 1%
2674                          * of the zone, whichever is smaller.
2675                          */
2676                         balance_gap = min(low_wmark_pages(zone),
2677                                 (zone->present_pages +
2678                                         KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2679                                 KSWAPD_ZONE_BALANCE_GAP_RATIO);
2680                         /*
2681                          * Kswapd reclaims only single pages with compaction
2682                          * enabled. Trying too hard to reclaim until contiguous
2683                          * free pages have become available can hurt performance
2684                          * by evicting too much useful data from memory.
2685                          * Do not reclaim more than needed for compaction.
2686                          */
2687                         testorder = order;
2688                         if (IS_ENABLED(CONFIG_COMPACTION) && order &&
2689                                         compaction_suitable(zone, order) !=
2690                                                 COMPACT_SKIPPED)
2691                                 testorder = 0;
2692
2693                         if ((buffer_heads_over_limit && is_highmem_idx(i)) ||
2694                             !zone_balanced(zone, testorder,
2695                                            balance_gap, end_zone)) {
2696                                 shrink_zone(zone, &sc);
2697
2698                                 reclaim_state->reclaimed_slab = 0;
2699                                 nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages);
2700                                 sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2701                                 total_scanned += sc.nr_scanned;
2702
2703                                 if (nr_slab == 0 && !zone_reclaimable(zone))
2704                                         zone->all_unreclaimable = 1;
2705                         }
2706
2707                         /*
2708                          * If we've done a decent amount of scanning and
2709                          * the reclaim ratio is low, start doing writepage
2710                          * even in laptop mode
2711                          */
2712                         if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2713                             total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
2714                                 sc.may_writepage = 1;
2715
2716                         if (zone->all_unreclaimable) {
2717                                 if (end_zone && end_zone == i)
2718                                         end_zone--;
2719                                 continue;
2720                         }
2721
2722                         if (!zone_balanced(zone, testorder, 0, end_zone)) {
2723                                 all_zones_ok = 0;
2724                                 /*
2725                                  * We are still under min water mark.  This
2726                                  * means that we have a GFP_ATOMIC allocation
2727                                  * failure risk. Hurry up!
2728                                  */
2729                                 if (!zone_watermark_ok_safe(zone, order,
2730                                             min_wmark_pages(zone), end_zone, 0))
2731                                         has_under_min_watermark_zone = 1;
2732                         } else {
2733                                 /*
2734                                  * If a zone reaches its high watermark,
2735                                  * consider it to be no longer congested. It's
2736                                  * possible there are dirty pages backed by
2737                                  * congested BDIs but as pressure is relieved,
2738                                  * speculatively avoid congestion waits
2739                                  */
2740                                 zone_clear_flag(zone, ZONE_CONGESTED);
2741                                 if (i <= *classzone_idx)
2742                                         balanced += zone->present_pages;
2743                         }
2744
2745                 }
2746
2747                 /*
2748                  * If the low watermark is met there is no need for processes
2749                  * to be throttled on pfmemalloc_wait as they should not be
2750                  * able to safely make forward progress. Wake them
2751                  */
2752                 if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
2753                                 pfmemalloc_watermark_ok(pgdat))
2754                         wake_up(&pgdat->pfmemalloc_wait);
2755
2756                 if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
2757                         break;          /* kswapd: all done */
2758                 /*
2759                  * OK, kswapd is getting into trouble.  Take a nap, then take
2760                  * another pass across the zones.
2761                  */
2762                 if (total_scanned && (sc.priority < DEF_PRIORITY - 2)) {
2763                         if (has_under_min_watermark_zone)
2764                                 count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
2765                         else
2766                                 congestion_wait(BLK_RW_ASYNC, HZ/10);
2767                 }
2768
2769                 /*
2770                  * We do this so kswapd doesn't build up large priorities for
2771                  * example when it is freeing in parallel with allocators. It
2772                  * matches the direct reclaim path behaviour in terms of impact
2773                  * on zone->*_priority.
2774                  */
2775                 if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2776                         break;
2777         } while (--sc.priority >= 0);
2778 out:
2779
2780         /*
2781          * order-0: All zones must meet high watermark for a balanced node
2782          * high-order: Balanced zones must make up at least 25% of the node
2783          *             for the node to be balanced
2784          */
2785         if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) {
2786                 cond_resched();
2787
2788                 try_to_freeze();
2789
2790                 /*
2791                  * Fragmentation may mean that the system cannot be
2792                  * rebalanced for high-order allocations in all zones.
2793                  * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2794                  * it means the zones have been fully scanned and are still
2795                  * not balanced. For high-order allocations, there is
2796                  * little point trying all over again as kswapd may
2797                  * infinite loop.
2798                  *
2799                  * Instead, recheck all watermarks at order-0 as they
2800                  * are the most important. If watermarks are ok, kswapd will go
2801                  * back to sleep. High-order users can still perform direct
2802                  * reclaim if they wish.
2803                  */
2804                 if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2805                         order = sc.order = 0;
2806
2807                 goto loop_again;
2808         }
2809
2810         /*
2811          * If kswapd was reclaiming at a higher order, it has the option of
2812          * sleeping without all zones being balanced. Before it does, it must
2813          * ensure that the watermarks for order-0 on *all* zones are met and
2814          * that the congestion flags are cleared. The congestion flag must
2815          * be cleared as kswapd is the only mechanism that clears the flag
2816          * and it is potentially going to sleep here.
2817          */
2818         if (order) {
2819                 int zones_need_compaction = 1;
2820
2821                 for (i = 0; i <= end_zone; i++) {
2822                         struct zone *zone = pgdat->node_zones + i;
2823
2824                         if (!populated_zone(zone))
2825                                 continue;
2826
2827                         /* Check if the memory needs to be defragmented. */
2828                         if (zone_watermark_ok(zone, order,
2829                                     low_wmark_pages(zone), *classzone_idx, 0))
2830                                 zones_need_compaction = 0;
2831                 }
2832
2833                 if (zones_need_compaction)
2834                         compact_pgdat(pgdat, order);
2835         }
2836
2837         /*
2838          * Return the order we were reclaiming at so prepare_kswapd_sleep()
2839          * makes a decision on the order we were last reclaiming at. However,
2840          * if another caller entered the allocator slow path while kswapd
2841          * was awake, order will remain at the higher level
2842          */
2843         *classzone_idx = end_zone;
2844         return order;
2845 }
2846
2847 static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
2848 {
2849         long remaining = 0;
2850         DEFINE_WAIT(wait);
2851
2852         if (freezing(current) || kthread_should_stop())
2853                 return;
2854
2855         prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2856
2857         /* Try to sleep for a short interval */
2858         if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2859                 remaining = schedule_timeout(HZ/10);
2860                 finish_wait(&pgdat->kswapd_wait, &wait);
2861                 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2862         }
2863
2864         /*
2865          * After a short sleep, check if it was a premature sleep. If not, then
2866          * go fully to sleep until explicitly woken up.
2867          */
2868         if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2869                 trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
2870
2871                 /*
2872                  * vmstat counters are not perfectly accurate and the estimated
2873                  * value for counters such as NR_FREE_PAGES can deviate from the
2874                  * true value by nr_online_cpus * threshold. To avoid the zone
2875                  * watermarks being breached while under pressure, we reduce the
2876                  * per-cpu vmstat threshold while kswapd is awake and restore
2877                  * them before going back to sleep.
2878                  */
2879                 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
2880
2881                 /*
2882                  * Compaction records what page blocks it recently failed to
2883                  * isolate pages from and skips them in the future scanning.
2884                  * When kswapd is going to sleep, it is reasonable to assume
2885                  * that pages and compaction may succeed so reset the cache.
2886                  */
2887                 reset_isolation_suitable(pgdat);
2888
2889                 if (!kthread_should_stop())
2890                         schedule();
2891
2892                 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
2893         } else {
2894                 if (remaining)
2895                         count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2896                 else
2897                         count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2898         }
2899         finish_wait(&pgdat->kswapd_wait, &wait);
2900 }
2901
2902 /*
2903  * The background pageout daemon, started as a kernel thread
2904  * from the init process.
2905  *
2906  * This basically trickles out pages so that we have _some_
2907  * free memory available even if there is no other activity
2908  * that frees anything up. This is needed for things like routing
2909  * etc, where we otherwise might have all activity going on in
2910  * asynchronous contexts that cannot page things out.
2911  *
2912  * If there are applications that are active memory-allocators
2913  * (most normal use), this basically shouldn't matter.
2914  */
2915 static int kswapd(void *p)
2916 {
2917         unsigned long order, new_order;
2918         unsigned balanced_order;
2919         int classzone_idx, new_classzone_idx;
2920         int balanced_classzone_idx;
2921         pg_data_t *pgdat = (pg_data_t*)p;
2922         struct task_struct *tsk = current;
2923
2924         struct reclaim_state reclaim_state = {
2925                 .reclaimed_slab = 0,
2926         };
2927         const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2928
2929         lockdep_set_current_reclaim_state(GFP_KERNEL);
2930
2931         if (!cpumask_empty(cpumask))
2932                 set_cpus_allowed_ptr(tsk, cpumask);
2933         current->reclaim_state = &reclaim_state;
2934
2935         /*
2936          * Tell the memory management that we're a "memory allocator",
2937          * and that if we need more memory we should get access to it
2938          * regardless (see "__alloc_pages()"). "kswapd" should
2939          * never get caught in the normal page freeing logic.
2940          *
2941          * (Kswapd normally doesn't need memory anyway, but sometimes
2942          * you need a small amount of memory in order to be able to
2943          * page out something else, and this flag essentially protects
2944          * us from recursively trying to free more memory as we're
2945          * trying to free the first piece of memory in the first place).
2946          */
2947         tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2948         set_freezable();
2949
2950         order = new_order = 0;
2951         balanced_order = 0;
2952         classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
2953         balanced_classzone_idx = classzone_idx;
2954         for ( ; ; ) {
2955                 int ret;
2956
2957                 /*
2958                  * If the last balance_pgdat was unsuccessful it's unlikely a
2959                  * new request of a similar or harder type will succeed soon
2960                  * so consider going to sleep on the basis we reclaimed at
2961                  */
2962                 if (balanced_classzone_idx >= new_classzone_idx &&
2963                                         balanced_order == new_order) {
2964                         new_order = pgdat->kswapd_max_order;
2965                         new_classzone_idx = pgdat->classzone_idx;
2966                         pgdat->kswapd_max_order =  0;
2967                         pgdat->classzone_idx = pgdat->nr_zones - 1;
2968                 }
2969
2970                 if (order < new_order || classzone_idx > new_classzone_idx) {
2971                         /*
2972                          * Don't sleep if someone wants a larger 'order'
2973                          * allocation or has tigher zone constraints
2974                          */
2975                         order = new_order;
2976                         classzone_idx = new_classzone_idx;
2977                 } else {
2978                         kswapd_try_to_sleep(pgdat, balanced_order,
2979                                                 balanced_classzone_idx);
2980                         order = pgdat->kswapd_max_order;
2981                         classzone_idx = pgdat->classzone_idx;
2982                         new_order = order;
2983                         new_classzone_idx = classzone_idx;
2984                         pgdat->kswapd_max_order = 0;
2985                         pgdat->classzone_idx = pgdat->nr_zones - 1;
2986                 }
2987
2988                 ret = try_to_freeze();
2989                 if (kthread_should_stop())
2990                         break;
2991
2992                 /*
2993                  * We can speed up thawing tasks if we don't call balance_pgdat
2994                  * after returning from the refrigerator
2995                  */
2996                 if (!ret) {
2997                         trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
2998                         balanced_classzone_idx = classzone_idx;
2999                         balanced_order = balance_pgdat(pgdat, order,
3000                                                 &balanced_classzone_idx);
3001                 }
3002         }
3003
3004         current->reclaim_state = NULL;
3005         return 0;
3006 }
3007
3008 /*
3009  * A zone is low on free memory, so wake its kswapd task to service it.
3010  */
3011 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
3012 {
3013         pg_data_t *pgdat;
3014
3015         if (!populated_zone(zone))
3016                 return;
3017
3018         if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
3019                 return;
3020         pgdat = zone->zone_pgdat;
3021         if (pgdat->kswapd_max_order < order) {
3022                 pgdat->kswapd_max_order = order;
3023                 pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
3024         }
3025         if (!waitqueue_active(&pgdat->kswapd_wait))
3026                 return;
3027         if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
3028                 return;
3029
3030         trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3031         wake_up_interruptible(&pgdat->kswapd_wait);
3032 }
3033
3034 /*
3035  * The reclaimable count would be mostly accurate.
3036  * The less reclaimable pages may be
3037  * - mlocked pages, which will be moved to unevictable list when encountered
3038  * - mapped pages, which may require several travels to be reclaimed
3039  * - dirty pages, which is not "instantly" reclaimable
3040  */
3041 unsigned long global_reclaimable_pages(void)
3042 {
3043         int nr;
3044
3045         nr = global_page_state(NR_ACTIVE_FILE) +
3046              global_page_state(NR_INACTIVE_FILE);
3047
3048         if (nr_swap_pages > 0)
3049                 nr += global_page_state(NR_ACTIVE_ANON) +
3050                       global_page_state(NR_INACTIVE_ANON);
3051
3052         return nr;
3053 }
3054
3055 unsigned long zone_reclaimable_pages(struct zone *zone)
3056 {
3057         int nr;
3058
3059         nr = zone_page_state(zone, NR_ACTIVE_FILE) +
3060              zone_page_state(zone, NR_INACTIVE_FILE);
3061
3062         if (nr_swap_pages > 0)
3063                 nr += zone_page_state(zone, NR_ACTIVE_ANON) +
3064                       zone_page_state(zone, NR_INACTIVE_ANON);
3065
3066         return nr;
3067 }
3068
3069 #ifdef CONFIG_HIBERNATION
3070 /*
3071  * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3072  * freed pages.
3073  *
3074  * Rather than trying to age LRUs the aim is to preserve the overall
3075  * LRU order by reclaiming preferentially
3076  * inactive > active > active referenced > active mapped
3077  */
3078 unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3079 {
3080         struct reclaim_state reclaim_state;
3081         struct scan_control sc = {
3082                 .gfp_mask = GFP_HIGHUSER_MOVABLE,
3083                 .may_swap = 1,
3084                 .may_unmap = 1,
3085                 .may_writepage = 1,
3086                 .nr_to_reclaim = nr_to_reclaim,
3087                 .hibernation_mode = 1,
3088                 .order = 0,
3089                 .priority = DEF_PRIORITY,
3090         };
3091         struct shrink_control shrink = {
3092                 .gfp_mask = sc.gfp_mask,
3093         };
3094         struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3095         struct task_struct *p = current;
3096         unsigned long nr_reclaimed;
3097
3098         p->flags |= PF_MEMALLOC;
3099         lockdep_set_current_reclaim_state(sc.gfp_mask);
3100         reclaim_state.reclaimed_slab = 0;
3101         p->reclaim_state = &reclaim_state;
3102
3103         nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
3104
3105         p->reclaim_state = NULL;
3106         lockdep_clear_current_reclaim_state();
3107         p->flags &= ~PF_MEMALLOC;
3108
3109         return nr_reclaimed;
3110 }
3111 #endif /* CONFIG_HIBERNATION */
3112
3113 /* It's optimal to keep kswapds on the same CPUs as their memory, but
3114    not required for correctness.  So if the last cpu in a node goes
3115    away, we get changed to run anywhere: as the first one comes back,
3116    restore their cpu bindings. */
3117 static int __devinit cpu_callback(struct notifier_block *nfb,
3118                                   unsigned long action, void *hcpu)
3119 {
3120         int nid;
3121
3122         if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
3123                 for_each_node_state(nid, N_HIGH_MEMORY) {
3124                         pg_data_t *pgdat = NODE_DATA(nid);
3125                         const struct cpumask *mask;
3126
3127                         mask = cpumask_of_node(pgdat->node_id);
3128
3129                         if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3130                                 /* One of our CPUs online: restore mask */
3131                                 set_cpus_allowed_ptr(pgdat->kswapd, mask);
3132                 }
3133         }
3134         return NOTIFY_OK;
3135 }
3136
3137 /*
3138  * This kswapd start function will be called by init and node-hot-add.
3139  * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3140  */
3141 int kswapd_run(int nid)
3142 {
3143         pg_data_t *pgdat = NODE_DATA(nid);
3144         int ret = 0;
3145
3146         if (pgdat->kswapd)
3147                 return 0;
3148
3149         pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3150         if (IS_ERR(pgdat->kswapd)) {
3151                 /* failure at boot is fatal */
3152                 BUG_ON(system_state == SYSTEM_BOOTING);
3153                 pgdat->kswapd = NULL;
3154                 pr_err("Failed to start kswapd on node %d\n", nid);
3155                 ret = PTR_ERR(pgdat->kswapd);
3156         }
3157         return ret;
3158 }
3159
3160 /*
3161  * Called by memory hotplug when all memory in a node is offlined.  Caller must
3162  * hold lock_memory_hotplug().
3163  */
3164 void kswapd_stop(int nid)
3165 {
3166         struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3167
3168         if (kswapd) {
3169                 kthread_stop(kswapd);
3170                 NODE_DATA(nid)->kswapd = NULL;
3171         }
3172 }
3173
3174 static int __init kswapd_init(void)
3175 {
3176         int nid;
3177
3178         swap_setup();
3179         for_each_node_state(nid, N_HIGH_MEMORY)
3180                 kswapd_run(nid);
3181         hotcpu_notifier(cpu_callback, 0);
3182         return 0;
3183 }
3184
3185 module_init(kswapd_init)
3186
3187 #ifdef CONFIG_NUMA
3188 /*
3189  * Zone reclaim mode
3190  *
3191  * If non-zero call zone_reclaim when the number of free pages falls below
3192  * the watermarks.
3193  */
3194 int zone_reclaim_mode __read_mostly;
3195
3196 #define RECLAIM_OFF 0
3197 #define RECLAIM_ZONE (1<<0)     /* Run shrink_inactive_list on the zone */
3198 #define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
3199 #define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
3200
3201 /*
3202  * Priority for ZONE_RECLAIM. This determines the fraction of pages
3203  * of a node considered for each zone_reclaim. 4 scans 1/16th of
3204  * a zone.
3205  */
3206 #define ZONE_RECLAIM_PRIORITY 4
3207
3208 /*
3209  * Percentage of pages in a zone that must be unmapped for zone_reclaim to
3210  * occur.
3211  */
3212 int sysctl_min_unmapped_ratio = 1;
3213
3214 /*
3215  * If the number of slab pages in a zone grows beyond this percentage then
3216  * slab reclaim needs to occur.
3217  */
3218 int sysctl_min_slab_ratio = 5;
3219
3220 static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3221 {
3222         unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3223         unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3224                 zone_page_state(zone, NR_ACTIVE_FILE);
3225
3226         /*
3227          * It's possible for there to be more file mapped pages than
3228          * accounted for by the pages on the file LRU lists because
3229          * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3230          */
3231         return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3232 }
3233
3234 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
3235 static long zone_pagecache_reclaimable(struct zone *zone)
3236 {
3237         long nr_pagecache_reclaimable;
3238         long delta = 0;
3239
3240         /*
3241          * If RECLAIM_SWAP is set, then all file pages are considered
3242          * potentially reclaimable. Otherwise, we have to worry about
3243          * pages like swapcache and zone_unmapped_file_pages() provides
3244          * a better estimate
3245          */
3246         if (zone_reclaim_mode & RECLAIM_SWAP)
3247                 nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3248         else
3249                 nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3250
3251         /* If we can't clean pages, remove dirty pages from consideration */
3252         if (!(zone_reclaim_mode & RECLAIM_WRITE))
3253                 delta += zone_page_state(zone, NR_FILE_DIRTY);
3254
3255         /* Watch for any possible underflows due to delta */
3256         if (unlikely(delta > nr_pagecache_reclaimable))
3257                 delta = nr_pagecache_reclaimable;
3258
3259         return nr_pagecache_reclaimable - delta;
3260 }
3261
3262 /*
3263  * Try to free up some pages from this zone through reclaim.
3264  */
3265 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3266 {
3267         /* Minimum pages needed in order to stay on node */
3268         const unsigned long nr_pages = 1 << order;
3269         struct task_struct *p = current;
3270         struct reclaim_state reclaim_state;
3271         struct scan_control sc = {
3272                 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3273                 .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3274                 .may_swap = 1,
3275                 .nr_to_reclaim = max_t(unsigned long, nr_pages,
3276                                        SWAP_CLUSTER_MAX),
3277                 .gfp_mask = gfp_mask,
3278                 .order = order,
3279                 .priority = ZONE_RECLAIM_PRIORITY,
3280         };
3281         struct shrink_control shrink = {
3282                 .gfp_mask = sc.gfp_mask,
3283         };
3284         unsigned long nr_slab_pages0, nr_slab_pages1;
3285
3286         cond_resched();
3287         /*
3288          * We need to be able to allocate from the reserves for RECLAIM_SWAP
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