thp: madvise(MADV_HUGEPAGE)
[linux-2.6.git] / mm / vmscan.c
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/pagevec.h>
30 #include <linux/backing-dev.h>
31 #include <linux/rmap.h>
32 #include <linux/topology.h>
33 #include <linux/cpu.h>
34 #include <linux/cpuset.h>
35 #include <linux/compaction.h>
36 #include <linux/notifier.h>
37 #include <linux/rwsem.h>
38 #include <linux/delay.h>
39 #include <linux/kthread.h>
40 #include <linux/freezer.h>
41 #include <linux/memcontrol.h>
42 #include <linux/delayacct.h>
43 #include <linux/sysctl.h>
44
45 #include <asm/tlbflush.h>
46 #include <asm/div64.h>
47
48 #include <linux/swapops.h>
49
50 #include "internal.h"
51
52 #define CREATE_TRACE_POINTS
53 #include <trace/events/vmscan.h>
54
55 /*
56  * reclaim_mode determines how the inactive list is shrunk
57  * RECLAIM_MODE_SINGLE: Reclaim only order-0 pages
58  * RECLAIM_MODE_ASYNC:  Do not block
59  * RECLAIM_MODE_SYNC:   Allow blocking e.g. call wait_on_page_writeback
60  * RECLAIM_MODE_LUMPYRECLAIM: For high-order allocations, take a reference
61  *                      page from the LRU and reclaim all pages within a
62  *                      naturally aligned range
63  * RECLAIM_MODE_COMPACTION: For high-order allocations, reclaim a number of
64  *                      order-0 pages and then compact the zone
65  */
66 typedef unsigned __bitwise__ reclaim_mode_t;
67 #define RECLAIM_MODE_SINGLE             ((__force reclaim_mode_t)0x01u)
68 #define RECLAIM_MODE_ASYNC              ((__force reclaim_mode_t)0x02u)
69 #define RECLAIM_MODE_SYNC               ((__force reclaim_mode_t)0x04u)
70 #define RECLAIM_MODE_LUMPYRECLAIM       ((__force reclaim_mode_t)0x08u)
71 #define RECLAIM_MODE_COMPACTION         ((__force reclaim_mode_t)0x10u)
72
73 struct scan_control {
74         /* Incremented by the number of inactive pages that were scanned */
75         unsigned long nr_scanned;
76
77         /* Number of pages freed so far during a call to shrink_zones() */
78         unsigned long nr_reclaimed;
79
80         /* How many pages shrink_list() should reclaim */
81         unsigned long nr_to_reclaim;
82
83         unsigned long hibernation_mode;
84
85         /* This context's GFP mask */
86         gfp_t gfp_mask;
87
88         int may_writepage;
89
90         /* Can mapped pages be reclaimed? */
91         int may_unmap;
92
93         /* Can pages be swapped as part of reclaim? */
94         int may_swap;
95
96         int swappiness;
97
98         int order;
99
100         /*
101          * Intend to reclaim enough continuous memory rather than reclaim
102          * enough amount of memory. i.e, mode for high order allocation.
103          */
104         reclaim_mode_t reclaim_mode;
105
106         /* Which cgroup do we reclaim from */
107         struct mem_cgroup *mem_cgroup;
108
109         /*
110          * Nodemask of nodes allowed by the caller. If NULL, all nodes
111          * are scanned.
112          */
113         nodemask_t      *nodemask;
114 };
115
116 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
117
118 #ifdef ARCH_HAS_PREFETCH
119 #define prefetch_prev_lru_page(_page, _base, _field)                    \
120         do {                                                            \
121                 if ((_page)->lru.prev != _base) {                       \
122                         struct page *prev;                              \
123                                                                         \
124                         prev = lru_to_page(&(_page->lru));              \
125                         prefetch(&prev->_field);                        \
126                 }                                                       \
127         } while (0)
128 #else
129 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
130 #endif
131
132 #ifdef ARCH_HAS_PREFETCHW
133 #define prefetchw_prev_lru_page(_page, _base, _field)                   \
134         do {                                                            \
135                 if ((_page)->lru.prev != _base) {                       \
136                         struct page *prev;                              \
137                                                                         \
138                         prev = lru_to_page(&(_page->lru));              \
139                         prefetchw(&prev->_field);                       \
140                 }                                                       \
141         } while (0)
142 #else
143 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
144 #endif
145
146 /*
147  * From 0 .. 100.  Higher means more swappy.
148  */
149 int vm_swappiness = 60;
150 long vm_total_pages;    /* The total number of pages which the VM controls */
151
152 static LIST_HEAD(shrinker_list);
153 static DECLARE_RWSEM(shrinker_rwsem);
154
155 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
156 #define scanning_global_lru(sc) (!(sc)->mem_cgroup)
157 #else
158 #define scanning_global_lru(sc) (1)
159 #endif
160
161 static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
162                                                   struct scan_control *sc)
163 {
164         if (!scanning_global_lru(sc))
165                 return mem_cgroup_get_reclaim_stat(sc->mem_cgroup, zone);
166
167         return &zone->reclaim_stat;
168 }
169
170 static unsigned long zone_nr_lru_pages(struct zone *zone,
171                                 struct scan_control *sc, enum lru_list lru)
172 {
173         if (!scanning_global_lru(sc))
174                 return mem_cgroup_zone_nr_pages(sc->mem_cgroup, zone, lru);
175
176         return zone_page_state(zone, NR_LRU_BASE + lru);
177 }
178
179
180 /*
181  * Add a shrinker callback to be called from the vm
182  */
183 void register_shrinker(struct shrinker *shrinker)
184 {
185         shrinker->nr = 0;
186         down_write(&shrinker_rwsem);
187         list_add_tail(&shrinker->list, &shrinker_list);
188         up_write(&shrinker_rwsem);
189 }
190 EXPORT_SYMBOL(register_shrinker);
191
192 /*
193  * Remove one
194  */
195 void unregister_shrinker(struct shrinker *shrinker)
196 {
197         down_write(&shrinker_rwsem);
198         list_del(&shrinker->list);
199         up_write(&shrinker_rwsem);
200 }
201 EXPORT_SYMBOL(unregister_shrinker);
202
203 #define SHRINK_BATCH 128
204 /*
205  * Call the shrink functions to age shrinkable caches
206  *
207  * Here we assume it costs one seek to replace a lru page and that it also
208  * takes a seek to recreate a cache object.  With this in mind we age equal
209  * percentages of the lru and ageable caches.  This should balance the seeks
210  * generated by these structures.
211  *
212  * If the vm encountered mapped pages on the LRU it increase the pressure on
213  * slab to avoid swapping.
214  *
215  * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
216  *
217  * `lru_pages' represents the number of on-LRU pages in all the zones which
218  * are eligible for the caller's allocation attempt.  It is used for balancing
219  * slab reclaim versus page reclaim.
220  *
221  * Returns the number of slab objects which we shrunk.
222  */
223 unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
224                         unsigned long lru_pages)
225 {
226         struct shrinker *shrinker;
227         unsigned long ret = 0;
228
229         if (scanned == 0)
230                 scanned = SWAP_CLUSTER_MAX;
231
232         if (!down_read_trylock(&shrinker_rwsem))
233                 return 1;       /* Assume we'll be able to shrink next time */
234
235         list_for_each_entry(shrinker, &shrinker_list, list) {
236                 unsigned long long delta;
237                 unsigned long total_scan;
238                 unsigned long max_pass;
239
240                 max_pass = (*shrinker->shrink)(shrinker, 0, gfp_mask);
241                 delta = (4 * scanned) / shrinker->seeks;
242                 delta *= max_pass;
243                 do_div(delta, lru_pages + 1);
244                 shrinker->nr += delta;
245                 if (shrinker->nr < 0) {
246                         printk(KERN_ERR "shrink_slab: %pF negative objects to "
247                                "delete nr=%ld\n",
248                                shrinker->shrink, shrinker->nr);
249                         shrinker->nr = max_pass;
250                 }
251
252                 /*
253                  * Avoid risking looping forever due to too large nr value:
254                  * never try to free more than twice the estimate number of
255                  * freeable entries.
256                  */
257                 if (shrinker->nr > max_pass * 2)
258                         shrinker->nr = max_pass * 2;
259
260                 total_scan = shrinker->nr;
261                 shrinker->nr = 0;
262
263                 while (total_scan >= SHRINK_BATCH) {
264                         long this_scan = SHRINK_BATCH;
265                         int shrink_ret;
266                         int nr_before;
267
268                         nr_before = (*shrinker->shrink)(shrinker, 0, gfp_mask);
269                         shrink_ret = (*shrinker->shrink)(shrinker, this_scan,
270                                                                 gfp_mask);
271                         if (shrink_ret == -1)
272                                 break;
273                         if (shrink_ret < nr_before)
274                                 ret += nr_before - shrink_ret;
275                         count_vm_events(SLABS_SCANNED, this_scan);
276                         total_scan -= this_scan;
277
278                         cond_resched();
279                 }
280
281                 shrinker->nr += total_scan;
282         }
283         up_read(&shrinker_rwsem);
284         return ret;
285 }
286
287 static void set_reclaim_mode(int priority, struct scan_control *sc,
288                                    bool sync)
289 {
290         reclaim_mode_t syncmode = sync ? RECLAIM_MODE_SYNC : RECLAIM_MODE_ASYNC;
291
292         /*
293          * Initially assume we are entering either lumpy reclaim or
294          * reclaim/compaction.Depending on the order, we will either set the
295          * sync mode or just reclaim order-0 pages later.
296          */
297         if (COMPACTION_BUILD)
298                 sc->reclaim_mode = RECLAIM_MODE_COMPACTION;
299         else
300                 sc->reclaim_mode = RECLAIM_MODE_LUMPYRECLAIM;
301
302         /*
303          * Avoid using lumpy reclaim or reclaim/compaction if possible by
304          * restricting when its set to either costly allocations or when
305          * under memory pressure
306          */
307         if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
308                 sc->reclaim_mode |= syncmode;
309         else if (sc->order && priority < DEF_PRIORITY - 2)
310                 sc->reclaim_mode |= syncmode;
311         else
312                 sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
313 }
314
315 static void reset_reclaim_mode(struct scan_control *sc)
316 {
317         sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
318 }
319
320 static inline int is_page_cache_freeable(struct page *page)
321 {
322         /*
323          * A freeable page cache page is referenced only by the caller
324          * that isolated the page, the page cache radix tree and
325          * optional buffer heads at page->private.
326          */
327         return page_count(page) - page_has_private(page) == 2;
328 }
329
330 static int may_write_to_queue(struct backing_dev_info *bdi,
331                               struct scan_control *sc)
332 {
333         if (current->flags & PF_SWAPWRITE)
334                 return 1;
335         if (!bdi_write_congested(bdi))
336                 return 1;
337         if (bdi == current->backing_dev_info)
338                 return 1;
339
340         /* lumpy reclaim for hugepage often need a lot of write */
341         if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
342                 return 1;
343         return 0;
344 }
345
346 /*
347  * We detected a synchronous write error writing a page out.  Probably
348  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
349  * fsync(), msync() or close().
350  *
351  * The tricky part is that after writepage we cannot touch the mapping: nothing
352  * prevents it from being freed up.  But we have a ref on the page and once
353  * that page is locked, the mapping is pinned.
354  *
355  * We're allowed to run sleeping lock_page() here because we know the caller has
356  * __GFP_FS.
357  */
358 static void handle_write_error(struct address_space *mapping,
359                                 struct page *page, int error)
360 {
361         lock_page_nosync(page);
362         if (page_mapping(page) == mapping)
363                 mapping_set_error(mapping, error);
364         unlock_page(page);
365 }
366
367 /* possible outcome of pageout() */
368 typedef enum {
369         /* failed to write page out, page is locked */
370         PAGE_KEEP,
371         /* move page to the active list, page is locked */
372         PAGE_ACTIVATE,
373         /* page has been sent to the disk successfully, page is unlocked */
374         PAGE_SUCCESS,
375         /* page is clean and locked */
376         PAGE_CLEAN,
377 } pageout_t;
378
379 /*
380  * pageout is called by shrink_page_list() for each dirty page.
381  * Calls ->writepage().
382  */
383 static pageout_t pageout(struct page *page, struct address_space *mapping,
384                          struct scan_control *sc)
385 {
386         /*
387          * If the page is dirty, only perform writeback if that write
388          * will be non-blocking.  To prevent this allocation from being
389          * stalled by pagecache activity.  But note that there may be
390          * stalls if we need to run get_block().  We could test
391          * PagePrivate for that.
392          *
393          * If this process is currently in __generic_file_aio_write() against
394          * this page's queue, we can perform writeback even if that
395          * will block.
396          *
397          * If the page is swapcache, write it back even if that would
398          * block, for some throttling. This happens by accident, because
399          * swap_backing_dev_info is bust: it doesn't reflect the
400          * congestion state of the swapdevs.  Easy to fix, if needed.
401          */
402         if (!is_page_cache_freeable(page))
403                 return PAGE_KEEP;
404         if (!mapping) {
405                 /*
406                  * Some data journaling orphaned pages can have
407                  * page->mapping == NULL while being dirty with clean buffers.
408                  */
409                 if (page_has_private(page)) {
410                         if (try_to_free_buffers(page)) {
411                                 ClearPageDirty(page);
412                                 printk("%s: orphaned page\n", __func__);
413                                 return PAGE_CLEAN;
414                         }
415                 }
416                 return PAGE_KEEP;
417         }
418         if (mapping->a_ops->writepage == NULL)
419                 return PAGE_ACTIVATE;
420         if (!may_write_to_queue(mapping->backing_dev_info, sc))
421                 return PAGE_KEEP;
422
423         if (clear_page_dirty_for_io(page)) {
424                 int res;
425                 struct writeback_control wbc = {
426                         .sync_mode = WB_SYNC_NONE,
427                         .nr_to_write = SWAP_CLUSTER_MAX,
428                         .range_start = 0,
429                         .range_end = LLONG_MAX,
430                         .for_reclaim = 1,
431                 };
432
433                 SetPageReclaim(page);
434                 res = mapping->a_ops->writepage(page, &wbc);
435                 if (res < 0)
436                         handle_write_error(mapping, page, res);
437                 if (res == AOP_WRITEPAGE_ACTIVATE) {
438                         ClearPageReclaim(page);
439                         return PAGE_ACTIVATE;
440                 }
441
442                 /*
443                  * Wait on writeback if requested to. This happens when
444                  * direct reclaiming a large contiguous area and the
445                  * first attempt to free a range of pages fails.
446                  */
447                 if (PageWriteback(page) &&
448                     (sc->reclaim_mode & RECLAIM_MODE_SYNC))
449                         wait_on_page_writeback(page);
450
451                 if (!PageWriteback(page)) {
452                         /* synchronous write or broken a_ops? */
453                         ClearPageReclaim(page);
454                 }
455                 trace_mm_vmscan_writepage(page,
456                         trace_reclaim_flags(page, sc->reclaim_mode));
457                 inc_zone_page_state(page, NR_VMSCAN_WRITE);
458                 return PAGE_SUCCESS;
459         }
460
461         return PAGE_CLEAN;
462 }
463
464 /*
465  * Same as remove_mapping, but if the page is removed from the mapping, it
466  * gets returned with a refcount of 0.
467  */
468 static int __remove_mapping(struct address_space *mapping, struct page *page)
469 {
470         BUG_ON(!PageLocked(page));
471         BUG_ON(mapping != page_mapping(page));
472
473         spin_lock_irq(&mapping->tree_lock);
474         /*
475          * The non racy check for a busy page.
476          *
477          * Must be careful with the order of the tests. When someone has
478          * a ref to the page, it may be possible that they dirty it then
479          * drop the reference. So if PageDirty is tested before page_count
480          * here, then the following race may occur:
481          *
482          * get_user_pages(&page);
483          * [user mapping goes away]
484          * write_to(page);
485          *                              !PageDirty(page)    [good]
486          * SetPageDirty(page);
487          * put_page(page);
488          *                              !page_count(page)   [good, discard it]
489          *
490          * [oops, our write_to data is lost]
491          *
492          * Reversing the order of the tests ensures such a situation cannot
493          * escape unnoticed. The smp_rmb is needed to ensure the page->flags
494          * load is not satisfied before that of page->_count.
495          *
496          * Note that if SetPageDirty is always performed via set_page_dirty,
497          * and thus under tree_lock, then this ordering is not required.
498          */
499         if (!page_freeze_refs(page, 2))
500                 goto cannot_free;
501         /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
502         if (unlikely(PageDirty(page))) {
503                 page_unfreeze_refs(page, 2);
504                 goto cannot_free;
505         }
506
507         if (PageSwapCache(page)) {
508                 swp_entry_t swap = { .val = page_private(page) };
509                 __delete_from_swap_cache(page);
510                 spin_unlock_irq(&mapping->tree_lock);
511                 swapcache_free(swap, page);
512         } else {
513                 void (*freepage)(struct page *);
514
515                 freepage = mapping->a_ops->freepage;
516
517                 __remove_from_page_cache(page);
518                 spin_unlock_irq(&mapping->tree_lock);
519                 mem_cgroup_uncharge_cache_page(page);
520
521                 if (freepage != NULL)
522                         freepage(page);
523         }
524
525         return 1;
526
527 cannot_free:
528         spin_unlock_irq(&mapping->tree_lock);
529         return 0;
530 }
531
532 /*
533  * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
534  * someone else has a ref on the page, abort and return 0.  If it was
535  * successfully detached, return 1.  Assumes the caller has a single ref on
536  * this page.
537  */
538 int remove_mapping(struct address_space *mapping, struct page *page)
539 {
540         if (__remove_mapping(mapping, page)) {
541                 /*
542                  * Unfreezing the refcount with 1 rather than 2 effectively
543                  * drops the pagecache ref for us without requiring another
544                  * atomic operation.
545                  */
546                 page_unfreeze_refs(page, 1);
547                 return 1;
548         }
549         return 0;
550 }
551
552 /**
553  * putback_lru_page - put previously isolated page onto appropriate LRU list
554  * @page: page to be put back to appropriate lru list
555  *
556  * Add previously isolated @page to appropriate LRU list.
557  * Page may still be unevictable for other reasons.
558  *
559  * lru_lock must not be held, interrupts must be enabled.
560  */
561 void putback_lru_page(struct page *page)
562 {
563         int lru;
564         int active = !!TestClearPageActive(page);
565         int was_unevictable = PageUnevictable(page);
566
567         VM_BUG_ON(PageLRU(page));
568
569 redo:
570         ClearPageUnevictable(page);
571
572         if (page_evictable(page, NULL)) {
573                 /*
574                  * For evictable pages, we can use the cache.
575                  * In event of a race, worst case is we end up with an
576                  * unevictable page on [in]active list.
577                  * We know how to handle that.
578                  */
579                 lru = active + page_lru_base_type(page);
580                 lru_cache_add_lru(page, lru);
581         } else {
582                 /*
583                  * Put unevictable pages directly on zone's unevictable
584                  * list.
585                  */
586                 lru = LRU_UNEVICTABLE;
587                 add_page_to_unevictable_list(page);
588                 /*
589                  * When racing with an mlock clearing (page is
590                  * unlocked), make sure that if the other thread does
591                  * not observe our setting of PG_lru and fails
592                  * isolation, we see PG_mlocked cleared below and move
593                  * the page back to the evictable list.
594                  *
595                  * The other side is TestClearPageMlocked().
596                  */
597                 smp_mb();
598         }
599
600         /*
601          * page's status can change while we move it among lru. If an evictable
602          * page is on unevictable list, it never be freed. To avoid that,
603          * check after we added it to the list, again.
604          */
605         if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) {
606                 if (!isolate_lru_page(page)) {
607                         put_page(page);
608                         goto redo;
609                 }
610                 /* This means someone else dropped this page from LRU
611                  * So, it will be freed or putback to LRU again. There is
612                  * nothing to do here.
613                  */
614         }
615
616         if (was_unevictable && lru != LRU_UNEVICTABLE)
617                 count_vm_event(UNEVICTABLE_PGRESCUED);
618         else if (!was_unevictable && lru == LRU_UNEVICTABLE)
619                 count_vm_event(UNEVICTABLE_PGCULLED);
620
621         put_page(page);         /* drop ref from isolate */
622 }
623
624 enum page_references {
625         PAGEREF_RECLAIM,
626         PAGEREF_RECLAIM_CLEAN,
627         PAGEREF_KEEP,
628         PAGEREF_ACTIVATE,
629 };
630
631 static enum page_references page_check_references(struct page *page,
632                                                   struct scan_control *sc)
633 {
634         int referenced_ptes, referenced_page;
635         unsigned long vm_flags;
636
637         referenced_ptes = page_referenced(page, 1, sc->mem_cgroup, &vm_flags);
638         referenced_page = TestClearPageReferenced(page);
639
640         /* Lumpy reclaim - ignore references */
641         if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM)
642                 return PAGEREF_RECLAIM;
643
644         /*
645          * Mlock lost the isolation race with us.  Let try_to_unmap()
646          * move the page to the unevictable list.
647          */
648         if (vm_flags & VM_LOCKED)
649                 return PAGEREF_RECLAIM;
650
651         if (referenced_ptes) {
652                 if (PageAnon(page))
653                         return PAGEREF_ACTIVATE;
654                 /*
655                  * All mapped pages start out with page table
656                  * references from the instantiating fault, so we need
657                  * to look twice if a mapped file page is used more
658                  * than once.
659                  *
660                  * Mark it and spare it for another trip around the
661                  * inactive list.  Another page table reference will
662                  * lead to its activation.
663                  *
664                  * Note: the mark is set for activated pages as well
665                  * so that recently deactivated but used pages are
666                  * quickly recovered.
667                  */
668                 SetPageReferenced(page);
669
670                 if (referenced_page)
671                         return PAGEREF_ACTIVATE;
672
673                 return PAGEREF_KEEP;
674         }
675
676         /* Reclaim if clean, defer dirty pages to writeback */
677         if (referenced_page && !PageSwapBacked(page))
678                 return PAGEREF_RECLAIM_CLEAN;
679
680         return PAGEREF_RECLAIM;
681 }
682
683 static noinline_for_stack void free_page_list(struct list_head *free_pages)
684 {
685         struct pagevec freed_pvec;
686         struct page *page, *tmp;
687
688         pagevec_init(&freed_pvec, 1);
689
690         list_for_each_entry_safe(page, tmp, free_pages, lru) {
691                 list_del(&page->lru);
692                 if (!pagevec_add(&freed_pvec, page)) {
693                         __pagevec_free(&freed_pvec);
694                         pagevec_reinit(&freed_pvec);
695                 }
696         }
697
698         pagevec_free(&freed_pvec);
699 }
700
701 /*
702  * shrink_page_list() returns the number of reclaimed pages
703  */
704 static unsigned long shrink_page_list(struct list_head *page_list,
705                                       struct zone *zone,
706                                       struct scan_control *sc)
707 {
708         LIST_HEAD(ret_pages);
709         LIST_HEAD(free_pages);
710         int pgactivate = 0;
711         unsigned long nr_dirty = 0;
712         unsigned long nr_congested = 0;
713         unsigned long nr_reclaimed = 0;
714
715         cond_resched();
716
717         while (!list_empty(page_list)) {
718                 enum page_references references;
719                 struct address_space *mapping;
720                 struct page *page;
721                 int may_enter_fs;
722
723                 cond_resched();
724
725                 page = lru_to_page(page_list);
726                 list_del(&page->lru);
727
728                 if (!trylock_page(page))
729                         goto keep;
730
731                 VM_BUG_ON(PageActive(page));
732                 VM_BUG_ON(page_zone(page) != zone);
733
734                 sc->nr_scanned++;
735
736                 if (unlikely(!page_evictable(page, NULL)))
737                         goto cull_mlocked;
738
739                 if (!sc->may_unmap && page_mapped(page))
740                         goto keep_locked;
741
742                 /* Double the slab pressure for mapped and swapcache pages */
743                 if (page_mapped(page) || PageSwapCache(page))
744                         sc->nr_scanned++;
745
746                 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
747                         (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
748
749                 if (PageWriteback(page)) {
750                         /*
751                          * Synchronous reclaim is performed in two passes,
752                          * first an asynchronous pass over the list to
753                          * start parallel writeback, and a second synchronous
754                          * pass to wait for the IO to complete.  Wait here
755                          * for any page for which writeback has already
756                          * started.
757                          */
758                         if ((sc->reclaim_mode & RECLAIM_MODE_SYNC) &&
759                             may_enter_fs)
760                                 wait_on_page_writeback(page);
761                         else {
762                                 unlock_page(page);
763                                 goto keep_lumpy;
764                         }
765                 }
766
767                 references = page_check_references(page, sc);
768                 switch (references) {
769                 case PAGEREF_ACTIVATE:
770                         goto activate_locked;
771                 case PAGEREF_KEEP:
772                         goto keep_locked;
773                 case PAGEREF_RECLAIM:
774                 case PAGEREF_RECLAIM_CLEAN:
775                         ; /* try to reclaim the page below */
776                 }
777
778                 /*
779                  * Anonymous process memory has backing store?
780                  * Try to allocate it some swap space here.
781                  */
782                 if (PageAnon(page) && !PageSwapCache(page)) {
783                         if (!(sc->gfp_mask & __GFP_IO))
784                                 goto keep_locked;
785                         if (!add_to_swap(page))
786                                 goto activate_locked;
787                         may_enter_fs = 1;
788                 }
789
790                 mapping = page_mapping(page);
791
792                 /*
793                  * The page is mapped into the page tables of one or more
794                  * processes. Try to unmap it here.
795                  */
796                 if (page_mapped(page) && mapping) {
797                         switch (try_to_unmap(page, TTU_UNMAP)) {
798                         case SWAP_FAIL:
799                                 goto activate_locked;
800                         case SWAP_AGAIN:
801                                 goto keep_locked;
802                         case SWAP_MLOCK:
803                                 goto cull_mlocked;
804                         case SWAP_SUCCESS:
805                                 ; /* try to free the page below */
806                         }
807                 }
808
809                 if (PageDirty(page)) {
810                         nr_dirty++;
811
812                         if (references == PAGEREF_RECLAIM_CLEAN)
813                                 goto keep_locked;
814                         if (!may_enter_fs)
815                                 goto keep_locked;
816                         if (!sc->may_writepage)
817                                 goto keep_locked;
818
819                         /* Page is dirty, try to write it out here */
820                         switch (pageout(page, mapping, sc)) {
821                         case PAGE_KEEP:
822                                 nr_congested++;
823                                 goto keep_locked;
824                         case PAGE_ACTIVATE:
825                                 goto activate_locked;
826                         case PAGE_SUCCESS:
827                                 if (PageWriteback(page))
828                                         goto keep_lumpy;
829                                 if (PageDirty(page))
830                                         goto keep;
831
832                                 /*
833                                  * A synchronous write - probably a ramdisk.  Go
834                                  * ahead and try to reclaim the page.
835                                  */
836                                 if (!trylock_page(page))
837                                         goto keep;
838                                 if (PageDirty(page) || PageWriteback(page))
839                                         goto keep_locked;
840                                 mapping = page_mapping(page);
841                         case PAGE_CLEAN:
842                                 ; /* try to free the page below */
843                         }
844                 }
845
846                 /*
847                  * If the page has buffers, try to free the buffer mappings
848                  * associated with this page. If we succeed we try to free
849                  * the page as well.
850                  *
851                  * We do this even if the page is PageDirty().
852                  * try_to_release_page() does not perform I/O, but it is
853                  * possible for a page to have PageDirty set, but it is actually
854                  * clean (all its buffers are clean).  This happens if the
855                  * buffers were written out directly, with submit_bh(). ext3
856                  * will do this, as well as the blockdev mapping.
857                  * try_to_release_page() will discover that cleanness and will
858                  * drop the buffers and mark the page clean - it can be freed.
859                  *
860                  * Rarely, pages can have buffers and no ->mapping.  These are
861                  * the pages which were not successfully invalidated in
862                  * truncate_complete_page().  We try to drop those buffers here
863                  * and if that worked, and the page is no longer mapped into
864                  * process address space (page_count == 1) it can be freed.
865                  * Otherwise, leave the page on the LRU so it is swappable.
866                  */
867                 if (page_has_private(page)) {
868                         if (!try_to_release_page(page, sc->gfp_mask))
869                                 goto activate_locked;
870                         if (!mapping && page_count(page) == 1) {
871                                 unlock_page(page);
872                                 if (put_page_testzero(page))
873                                         goto free_it;
874                                 else {
875                                         /*
876                                          * rare race with speculative reference.
877                                          * the speculative reference will free
878                                          * this page shortly, so we may
879                                          * increment nr_reclaimed here (and
880                                          * leave it off the LRU).
881                                          */
882                                         nr_reclaimed++;
883                                         continue;
884                                 }
885                         }
886                 }
887
888                 if (!mapping || !__remove_mapping(mapping, page))
889                         goto keep_locked;
890
891                 /*
892                  * At this point, we have no other references and there is
893                  * no way to pick any more up (removed from LRU, removed
894                  * from pagecache). Can use non-atomic bitops now (and
895                  * we obviously don't have to worry about waking up a process
896                  * waiting on the page lock, because there are no references.
897                  */
898                 __clear_page_locked(page);
899 free_it:
900                 nr_reclaimed++;
901
902                 /*
903                  * Is there need to periodically free_page_list? It would
904                  * appear not as the counts should be low
905                  */
906                 list_add(&page->lru, &free_pages);
907                 continue;
908
909 cull_mlocked:
910                 if (PageSwapCache(page))
911                         try_to_free_swap(page);
912                 unlock_page(page);
913                 putback_lru_page(page);
914                 reset_reclaim_mode(sc);
915                 continue;
916
917 activate_locked:
918                 /* Not a candidate for swapping, so reclaim swap space. */
919                 if (PageSwapCache(page) && vm_swap_full())
920                         try_to_free_swap(page);
921                 VM_BUG_ON(PageActive(page));
922                 SetPageActive(page);
923                 pgactivate++;
924 keep_locked:
925                 unlock_page(page);
926 keep:
927                 reset_reclaim_mode(sc);
928 keep_lumpy:
929                 list_add(&page->lru, &ret_pages);
930                 VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
931         }
932
933         /*
934          * Tag a zone as congested if all the dirty pages encountered were
935          * backed by a congested BDI. In this case, reclaimers should just
936          * back off and wait for congestion to clear because further reclaim
937          * will encounter the same problem
938          */
939         if (nr_dirty == nr_congested && nr_dirty != 0)
940                 zone_set_flag(zone, ZONE_CONGESTED);
941
942         free_page_list(&free_pages);
943
944         list_splice(&ret_pages, page_list);
945         count_vm_events(PGACTIVATE, pgactivate);
946         return nr_reclaimed;
947 }
948
949 /*
950  * Attempt to remove the specified page from its LRU.  Only take this page
951  * if it is of the appropriate PageActive status.  Pages which are being
952  * freed elsewhere are also ignored.
953  *
954  * page:        page to consider
955  * mode:        one of the LRU isolation modes defined above
956  *
957  * returns 0 on success, -ve errno on failure.
958  */
959 int __isolate_lru_page(struct page *page, int mode, int file)
960 {
961         int ret = -EINVAL;
962
963         /* Only take pages on the LRU. */
964         if (!PageLRU(page))
965                 return ret;
966
967         /*
968          * When checking the active state, we need to be sure we are
969          * dealing with comparible boolean values.  Take the logical not
970          * of each.
971          */
972         if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode))
973                 return ret;
974
975         if (mode != ISOLATE_BOTH && page_is_file_cache(page) != file)
976                 return ret;
977
978         /*
979          * When this function is being called for lumpy reclaim, we
980          * initially look into all LRU pages, active, inactive and
981          * unevictable; only give shrink_page_list evictable pages.
982          */
983         if (PageUnevictable(page))
984                 return ret;
985
986         ret = -EBUSY;
987
988         if (likely(get_page_unless_zero(page))) {
989                 /*
990                  * Be careful not to clear PageLRU until after we're
991                  * sure the page is not being freed elsewhere -- the
992                  * page release code relies on it.
993                  */
994                 ClearPageLRU(page);
995                 ret = 0;
996         }
997
998         return ret;
999 }
1000
1001 /*
1002  * zone->lru_lock is heavily contended.  Some of the functions that
1003  * shrink the lists perform better by taking out a batch of pages
1004  * and working on them outside the LRU lock.
1005  *
1006  * For pagecache intensive workloads, this function is the hottest
1007  * spot in the kernel (apart from copy_*_user functions).
1008  *
1009  * Appropriate locks must be held before calling this function.
1010  *
1011  * @nr_to_scan: The number of pages to look through on the list.
1012  * @src:        The LRU list to pull pages off.
1013  * @dst:        The temp list to put pages on to.
1014  * @scanned:    The number of pages that were scanned.
1015  * @order:      The caller's attempted allocation order
1016  * @mode:       One of the LRU isolation modes
1017  * @file:       True [1] if isolating file [!anon] pages
1018  *
1019  * returns how many pages were moved onto *@dst.
1020  */
1021 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1022                 struct list_head *src, struct list_head *dst,
1023                 unsigned long *scanned, int order, int mode, int file)
1024 {
1025         unsigned long nr_taken = 0;
1026         unsigned long nr_lumpy_taken = 0;
1027         unsigned long nr_lumpy_dirty = 0;
1028         unsigned long nr_lumpy_failed = 0;
1029         unsigned long scan;
1030
1031         for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1032                 struct page *page;
1033                 unsigned long pfn;
1034                 unsigned long end_pfn;
1035                 unsigned long page_pfn;
1036                 int zone_id;
1037
1038                 page = lru_to_page(src);
1039                 prefetchw_prev_lru_page(page, src, flags);
1040
1041                 VM_BUG_ON(!PageLRU(page));
1042
1043                 switch (__isolate_lru_page(page, mode, file)) {
1044                 case 0:
1045                         list_move(&page->lru, dst);
1046                         mem_cgroup_del_lru(page);
1047                         nr_taken++;
1048                         break;
1049
1050                 case -EBUSY:
1051                         /* else it is being freed elsewhere */
1052                         list_move(&page->lru, src);
1053                         mem_cgroup_rotate_lru_list(page, page_lru(page));
1054                         continue;
1055
1056                 default:
1057                         BUG();
1058                 }
1059
1060                 if (!order)
1061                         continue;
1062
1063                 /*
1064                  * Attempt to take all pages in the order aligned region
1065                  * surrounding the tag page.  Only take those pages of
1066                  * the same active state as that tag page.  We may safely
1067                  * round the target page pfn down to the requested order
1068                  * as the mem_map is guarenteed valid out to MAX_ORDER,
1069                  * where that page is in a different zone we will detect
1070                  * it from its zone id and abort this block scan.
1071                  */
1072                 zone_id = page_zone_id(page);
1073                 page_pfn = page_to_pfn(page);
1074                 pfn = page_pfn & ~((1 << order) - 1);
1075                 end_pfn = pfn + (1 << order);
1076                 for (; pfn < end_pfn; pfn++) {
1077                         struct page *cursor_page;
1078
1079                         /* The target page is in the block, ignore it. */
1080                         if (unlikely(pfn == page_pfn))
1081                                 continue;
1082
1083                         /* Avoid holes within the zone. */
1084                         if (unlikely(!pfn_valid_within(pfn)))
1085                                 break;
1086
1087                         cursor_page = pfn_to_page(pfn);
1088
1089                         /* Check that we have not crossed a zone boundary. */
1090                         if (unlikely(page_zone_id(cursor_page) != zone_id))
1091                                 break;
1092
1093                         /*
1094                          * If we don't have enough swap space, reclaiming of
1095                          * anon page which don't already have a swap slot is
1096                          * pointless.
1097                          */
1098                         if (nr_swap_pages <= 0 && PageAnon(cursor_page) &&
1099                             !PageSwapCache(cursor_page))
1100                                 break;
1101
1102                         if (__isolate_lru_page(cursor_page, mode, file) == 0) {
1103                                 list_move(&cursor_page->lru, dst);
1104                                 mem_cgroup_del_lru(cursor_page);
1105                                 nr_taken++;
1106                                 nr_lumpy_taken++;
1107                                 if (PageDirty(cursor_page))
1108                                         nr_lumpy_dirty++;
1109                                 scan++;
1110                         } else {
1111                                 /* the page is freed already. */
1112                                 if (!page_count(cursor_page))
1113                                         continue;
1114                                 break;
1115                         }
1116                 }
1117
1118                 /* If we break out of the loop above, lumpy reclaim failed */
1119                 if (pfn < end_pfn)
1120                         nr_lumpy_failed++;
1121         }
1122
1123         *scanned = scan;
1124
1125         trace_mm_vmscan_lru_isolate(order,
1126                         nr_to_scan, scan,
1127                         nr_taken,
1128                         nr_lumpy_taken, nr_lumpy_dirty, nr_lumpy_failed,
1129                         mode);
1130         return nr_taken;
1131 }
1132
1133 static unsigned long isolate_pages_global(unsigned long nr,
1134                                         struct list_head *dst,
1135                                         unsigned long *scanned, int order,
1136                                         int mode, struct zone *z,
1137                                         int active, int file)
1138 {
1139         int lru = LRU_BASE;
1140         if (active)
1141                 lru += LRU_ACTIVE;
1142         if (file)
1143                 lru += LRU_FILE;
1144         return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order,
1145                                                                 mode, file);
1146 }
1147
1148 /*
1149  * clear_active_flags() is a helper for shrink_active_list(), clearing
1150  * any active bits from the pages in the list.
1151  */
1152 static unsigned long clear_active_flags(struct list_head *page_list,
1153                                         unsigned int *count)
1154 {
1155         int nr_active = 0;
1156         int lru;
1157         struct page *page;
1158
1159         list_for_each_entry(page, page_list, lru) {
1160                 lru = page_lru_base_type(page);
1161                 if (PageActive(page)) {
1162                         lru += LRU_ACTIVE;
1163                         ClearPageActive(page);
1164                         nr_active++;
1165                 }
1166                 if (count)
1167                         count[lru]++;
1168         }
1169
1170         return nr_active;
1171 }
1172
1173 /**
1174  * isolate_lru_page - tries to isolate a page from its LRU list
1175  * @page: page to isolate from its LRU list
1176  *
1177  * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1178  * vmstat statistic corresponding to whatever LRU list the page was on.
1179  *
1180  * Returns 0 if the page was removed from an LRU list.
1181  * Returns -EBUSY if the page was not on an LRU list.
1182  *
1183  * The returned page will have PageLRU() cleared.  If it was found on
1184  * the active list, it will have PageActive set.  If it was found on
1185  * the unevictable list, it will have the PageUnevictable bit set. That flag
1186  * may need to be cleared by the caller before letting the page go.
1187  *
1188  * The vmstat statistic corresponding to the list on which the page was
1189  * found will be decremented.
1190  *
1191  * Restrictions:
1192  * (1) Must be called with an elevated refcount on the page. This is a
1193  *     fundamentnal difference from isolate_lru_pages (which is called
1194  *     without a stable reference).
1195  * (2) the lru_lock must not be held.
1196  * (3) interrupts must be enabled.
1197  */
1198 int isolate_lru_page(struct page *page)
1199 {
1200         int ret = -EBUSY;
1201
1202         if (PageLRU(page)) {
1203                 struct zone *zone = page_zone(page);
1204
1205                 spin_lock_irq(&zone->lru_lock);
1206                 if (PageLRU(page) && get_page_unless_zero(page)) {
1207                         int lru = page_lru(page);
1208                         ret = 0;
1209                         ClearPageLRU(page);
1210
1211                         del_page_from_lru_list(zone, page, lru);
1212                 }
1213                 spin_unlock_irq(&zone->lru_lock);
1214         }
1215         return ret;
1216 }
1217
1218 /*
1219  * Are there way too many processes in the direct reclaim path already?
1220  */
1221 static int too_many_isolated(struct zone *zone, int file,
1222                 struct scan_control *sc)
1223 {
1224         unsigned long inactive, isolated;
1225
1226         if (current_is_kswapd())
1227                 return 0;
1228
1229         if (!scanning_global_lru(sc))
1230                 return 0;
1231
1232         if (file) {
1233                 inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1234                 isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1235         } else {
1236                 inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1237                 isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1238         }
1239
1240         return isolated > inactive;
1241 }
1242
1243 /*
1244  * TODO: Try merging with migrations version of putback_lru_pages
1245  */
1246 static noinline_for_stack void
1247 putback_lru_pages(struct zone *zone, struct scan_control *sc,
1248                                 unsigned long nr_anon, unsigned long nr_file,
1249                                 struct list_head *page_list)
1250 {
1251         struct page *page;
1252         struct pagevec pvec;
1253         struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1254
1255         pagevec_init(&pvec, 1);
1256
1257         /*
1258          * Put back any unfreeable pages.
1259          */
1260         spin_lock(&zone->lru_lock);
1261         while (!list_empty(page_list)) {
1262                 int lru;
1263                 page = lru_to_page(page_list);
1264                 VM_BUG_ON(PageLRU(page));
1265                 list_del(&page->lru);
1266                 if (unlikely(!page_evictable(page, NULL))) {
1267                         spin_unlock_irq(&zone->lru_lock);
1268                         putback_lru_page(page);
1269                         spin_lock_irq(&zone->lru_lock);
1270                         continue;
1271                 }
1272                 SetPageLRU(page);
1273                 lru = page_lru(page);
1274                 add_page_to_lru_list(zone, page, lru);
1275                 if (is_active_lru(lru)) {
1276                         int file = is_file_lru(lru);
1277                         reclaim_stat->recent_rotated[file]++;
1278                 }
1279                 if (!pagevec_add(&pvec, page)) {
1280                         spin_unlock_irq(&zone->lru_lock);
1281                         __pagevec_release(&pvec);
1282                         spin_lock_irq(&zone->lru_lock);
1283                 }
1284         }
1285         __mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon);
1286         __mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file);
1287
1288         spin_unlock_irq(&zone->lru_lock);
1289         pagevec_release(&pvec);
1290 }
1291
1292 static noinline_for_stack void update_isolated_counts(struct zone *zone,
1293                                         struct scan_control *sc,
1294                                         unsigned long *nr_anon,
1295                                         unsigned long *nr_file,
1296                                         struct list_head *isolated_list)
1297 {
1298         unsigned long nr_active;
1299         unsigned int count[NR_LRU_LISTS] = { 0, };
1300         struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1301
1302         nr_active = clear_active_flags(isolated_list, count);
1303         __count_vm_events(PGDEACTIVATE, nr_active);
1304
1305         __mod_zone_page_state(zone, NR_ACTIVE_FILE,
1306                               -count[LRU_ACTIVE_FILE]);
1307         __mod_zone_page_state(zone, NR_INACTIVE_FILE,
1308                               -count[LRU_INACTIVE_FILE]);
1309         __mod_zone_page_state(zone, NR_ACTIVE_ANON,
1310                               -count[LRU_ACTIVE_ANON]);
1311         __mod_zone_page_state(zone, NR_INACTIVE_ANON,
1312                               -count[LRU_INACTIVE_ANON]);
1313
1314         *nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
1315         *nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
1316         __mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon);
1317         __mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file);
1318
1319         reclaim_stat->recent_scanned[0] += *nr_anon;
1320         reclaim_stat->recent_scanned[1] += *nr_file;
1321 }
1322
1323 /*
1324  * Returns true if the caller should wait to clean dirty/writeback pages.
1325  *
1326  * If we are direct reclaiming for contiguous pages and we do not reclaim
1327  * everything in the list, try again and wait for writeback IO to complete.
1328  * This will stall high-order allocations noticeably. Only do that when really
1329  * need to free the pages under high memory pressure.
1330  */
1331 static inline bool should_reclaim_stall(unsigned long nr_taken,
1332                                         unsigned long nr_freed,
1333                                         int priority,
1334                                         struct scan_control *sc)
1335 {
1336         int lumpy_stall_priority;
1337
1338         /* kswapd should not stall on sync IO */
1339         if (current_is_kswapd())
1340                 return false;
1341
1342         /* Only stall on lumpy reclaim */
1343         if (sc->reclaim_mode & RECLAIM_MODE_SINGLE)
1344                 return false;
1345
1346         /* If we have relaimed everything on the isolated list, no stall */
1347         if (nr_freed == nr_taken)
1348                 return false;
1349
1350         /*
1351          * For high-order allocations, there are two stall thresholds.
1352          * High-cost allocations stall immediately where as lower
1353          * order allocations such as stacks require the scanning
1354          * priority to be much higher before stalling.
1355          */
1356         if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
1357                 lumpy_stall_priority = DEF_PRIORITY;
1358         else
1359                 lumpy_stall_priority = DEF_PRIORITY / 3;
1360
1361         return priority <= lumpy_stall_priority;
1362 }
1363
1364 /*
1365  * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
1366  * of reclaimed pages
1367  */
1368 static noinline_for_stack unsigned long
1369 shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
1370                         struct scan_control *sc, int priority, int file)
1371 {
1372         LIST_HEAD(page_list);
1373         unsigned long nr_scanned;
1374         unsigned long nr_reclaimed = 0;
1375         unsigned long nr_taken;
1376         unsigned long nr_anon;
1377         unsigned long nr_file;
1378
1379         while (unlikely(too_many_isolated(zone, file, sc))) {
1380                 congestion_wait(BLK_RW_ASYNC, HZ/10);
1381
1382                 /* We are about to die and free our memory. Return now. */
1383                 if (fatal_signal_pending(current))
1384                         return SWAP_CLUSTER_MAX;
1385         }
1386
1387         set_reclaim_mode(priority, sc, false);
1388         lru_add_drain();
1389         spin_lock_irq(&zone->lru_lock);
1390
1391         if (scanning_global_lru(sc)) {
1392                 nr_taken = isolate_pages_global(nr_to_scan,
1393                         &page_list, &nr_scanned, sc->order,
1394                         sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ?
1395                                         ISOLATE_BOTH : ISOLATE_INACTIVE,
1396                         zone, 0, file);
1397                 zone->pages_scanned += nr_scanned;
1398                 if (current_is_kswapd())
1399                         __count_zone_vm_events(PGSCAN_KSWAPD, zone,
1400                                                nr_scanned);
1401                 else
1402                         __count_zone_vm_events(PGSCAN_DIRECT, zone,
1403                                                nr_scanned);
1404         } else {
1405                 nr_taken = mem_cgroup_isolate_pages(nr_to_scan,
1406                         &page_list, &nr_scanned, sc->order,
1407                         sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ?
1408                                         ISOLATE_BOTH : ISOLATE_INACTIVE,
1409                         zone, sc->mem_cgroup,
1410                         0, file);
1411                 /*
1412                  * mem_cgroup_isolate_pages() keeps track of
1413                  * scanned pages on its own.
1414                  */
1415         }
1416
1417         if (nr_taken == 0) {
1418                 spin_unlock_irq(&zone->lru_lock);
1419                 return 0;
1420         }
1421
1422         update_isolated_counts(zone, sc, &nr_anon, &nr_file, &page_list);
1423
1424         spin_unlock_irq(&zone->lru_lock);
1425
1426         nr_reclaimed = shrink_page_list(&page_list, zone, sc);
1427
1428         /* Check if we should syncronously wait for writeback */
1429         if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) {
1430                 set_reclaim_mode(priority, sc, true);
1431                 nr_reclaimed += shrink_page_list(&page_list, zone, sc);
1432         }
1433
1434         local_irq_disable();
1435         if (current_is_kswapd())
1436                 __count_vm_events(KSWAPD_STEAL, nr_reclaimed);
1437         __count_zone_vm_events(PGSTEAL, zone, nr_reclaimed);
1438
1439         putback_lru_pages(zone, sc, nr_anon, nr_file, &page_list);
1440
1441         trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1442                 zone_idx(zone),
1443                 nr_scanned, nr_reclaimed,
1444                 priority,
1445                 trace_shrink_flags(file, sc->reclaim_mode));
1446         return nr_reclaimed;
1447 }
1448
1449 /*
1450  * This moves pages from the active list to the inactive list.
1451  *
1452  * We move them the other way if the page is referenced by one or more
1453  * processes, from rmap.
1454  *
1455  * If the pages are mostly unmapped, the processing is fast and it is
1456  * appropriate to hold zone->lru_lock across the whole operation.  But if
1457  * the pages are mapped, the processing is slow (page_referenced()) so we
1458  * should drop zone->lru_lock around each page.  It's impossible to balance
1459  * this, so instead we remove the pages from the LRU while processing them.
1460  * It is safe to rely on PG_active against the non-LRU pages in here because
1461  * nobody will play with that bit on a non-LRU page.
1462  *
1463  * The downside is that we have to touch page->_count against each page.
1464  * But we had to alter page->flags anyway.
1465  */
1466
1467 static void move_active_pages_to_lru(struct zone *zone,
1468                                      struct list_head *list,
1469                                      enum lru_list lru)
1470 {
1471         unsigned long pgmoved = 0;
1472         struct pagevec pvec;
1473         struct page *page;
1474
1475         pagevec_init(&pvec, 1);
1476
1477         while (!list_empty(list)) {
1478                 page = lru_to_page(list);
1479
1480                 VM_BUG_ON(PageLRU(page));
1481                 SetPageLRU(page);
1482
1483                 list_move(&page->lru, &zone->lru[lru].list);
1484                 mem_cgroup_add_lru_list(page, lru);
1485                 pgmoved++;
1486
1487                 if (!pagevec_add(&pvec, page) || list_empty(list)) {
1488                         spin_unlock_irq(&zone->lru_lock);
1489                         if (buffer_heads_over_limit)
1490                                 pagevec_strip(&pvec);
1491                         __pagevec_release(&pvec);
1492                         spin_lock_irq(&zone->lru_lock);
1493                 }
1494         }
1495         __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1496         if (!is_active_lru(lru))
1497                 __count_vm_events(PGDEACTIVATE, pgmoved);
1498 }
1499
1500 static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
1501                         struct scan_control *sc, int priority, int file)
1502 {
1503         unsigned long nr_taken;
1504         unsigned long pgscanned;
1505         unsigned long vm_flags;
1506         LIST_HEAD(l_hold);      /* The pages which were snipped off */
1507         LIST_HEAD(l_active);
1508         LIST_HEAD(l_inactive);
1509         struct page *page;
1510         struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1511         unsigned long nr_rotated = 0;
1512
1513         lru_add_drain();
1514         spin_lock_irq(&zone->lru_lock);
1515         if (scanning_global_lru(sc)) {
1516                 nr_taken = isolate_pages_global(nr_pages, &l_hold,
1517                                                 &pgscanned, sc->order,
1518                                                 ISOLATE_ACTIVE, zone,
1519                                                 1, file);
1520                 zone->pages_scanned += pgscanned;
1521         } else {
1522                 nr_taken = mem_cgroup_isolate_pages(nr_pages, &l_hold,
1523                                                 &pgscanned, sc->order,
1524                                                 ISOLATE_ACTIVE, zone,
1525                                                 sc->mem_cgroup, 1, file);
1526                 /*
1527                  * mem_cgroup_isolate_pages() keeps track of
1528                  * scanned pages on its own.
1529                  */
1530         }
1531
1532         reclaim_stat->recent_scanned[file] += nr_taken;
1533
1534         __count_zone_vm_events(PGREFILL, zone, pgscanned);
1535         if (file)
1536                 __mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken);
1537         else
1538                 __mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken);
1539         __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1540         spin_unlock_irq(&zone->lru_lock);
1541
1542         while (!list_empty(&l_hold)) {
1543                 cond_resched();
1544                 page = lru_to_page(&l_hold);
1545                 list_del(&page->lru);
1546
1547                 if (unlikely(!page_evictable(page, NULL))) {
1548                         putback_lru_page(page);
1549                         continue;
1550                 }
1551
1552                 if (page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
1553                         nr_rotated++;
1554                         /*
1555                          * Identify referenced, file-backed active pages and
1556                          * give them one more trip around the active list. So
1557                          * that executable code get better chances to stay in
1558                          * memory under moderate memory pressure.  Anon pages
1559                          * are not likely to be evicted by use-once streaming
1560                          * IO, plus JVM can create lots of anon VM_EXEC pages,
1561                          * so we ignore them here.
1562                          */
1563                         if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1564                                 list_add(&page->lru, &l_active);
1565                                 continue;
1566                         }
1567                 }
1568
1569                 ClearPageActive(page);  /* we are de-activating */
1570                 list_add(&page->lru, &l_inactive);
1571         }
1572
1573         /*
1574          * Move pages back to the lru list.
1575          */
1576         spin_lock_irq(&zone->lru_lock);
1577         /*
1578          * Count referenced pages from currently used mappings as rotated,
1579          * even though only some of them are actually re-activated.  This
1580          * helps balance scan pressure between file and anonymous pages in
1581          * get_scan_ratio.
1582          */
1583         reclaim_stat->recent_rotated[file] += nr_rotated;
1584
1585         move_active_pages_to_lru(zone, &l_active,
1586                                                 LRU_ACTIVE + file * LRU_FILE);
1587         move_active_pages_to_lru(zone, &l_inactive,
1588                                                 LRU_BASE   + file * LRU_FILE);
1589         __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1590         spin_unlock_irq(&zone->lru_lock);
1591 }
1592
1593 #ifdef CONFIG_SWAP
1594 static int inactive_anon_is_low_global(struct zone *zone)
1595 {
1596         unsigned long active, inactive;
1597
1598         active = zone_page_state(zone, NR_ACTIVE_ANON);
1599         inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1600
1601         if (inactive * zone->inactive_ratio < active)
1602                 return 1;
1603
1604         return 0;
1605 }
1606
1607 /**
1608  * inactive_anon_is_low - check if anonymous pages need to be deactivated
1609  * @zone: zone to check
1610  * @sc:   scan control of this context
1611  *
1612  * Returns true if the zone does not have enough inactive anon pages,
1613  * meaning some active anon pages need to be deactivated.
1614  */
1615 static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc)
1616 {
1617         int low;
1618
1619         /*
1620          * If we don't have swap space, anonymous page deactivation
1621          * is pointless.
1622          */
1623         if (!total_swap_pages)
1624                 return 0;
1625
1626         if (scanning_global_lru(sc))
1627                 low = inactive_anon_is_low_global(zone);
1628         else
1629                 low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup);
1630         return low;
1631 }
1632 #else
1633 static inline int inactive_anon_is_low(struct zone *zone,
1634                                         struct scan_control *sc)
1635 {
1636         return 0;
1637 }
1638 #endif
1639
1640 static int inactive_file_is_low_global(struct zone *zone)
1641 {
1642         unsigned long active, inactive;
1643
1644         active = zone_page_state(zone, NR_ACTIVE_FILE);
1645         inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1646
1647         return (active > inactive);
1648 }
1649
1650 /**
1651  * inactive_file_is_low - check if file pages need to be deactivated
1652  * @zone: zone to check
1653  * @sc:   scan control of this context
1654  *
1655  * When the system is doing streaming IO, memory pressure here
1656  * ensures that active file pages get deactivated, until more
1657  * than half of the file pages are on the inactive list.
1658  *
1659  * Once we get to that situation, protect the system's working
1660  * set from being evicted by disabling active file page aging.
1661  *
1662  * This uses a different ratio than the anonymous pages, because
1663  * the page cache uses a use-once replacement algorithm.
1664  */
1665 static int inactive_file_is_low(struct zone *zone, struct scan_control *sc)
1666 {
1667         int low;
1668
1669         if (scanning_global_lru(sc))
1670                 low = inactive_file_is_low_global(zone);
1671         else
1672                 low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup);
1673         return low;
1674 }
1675
1676 static int inactive_list_is_low(struct zone *zone, struct scan_control *sc,
1677                                 int file)
1678 {
1679         if (file)
1680                 return inactive_file_is_low(zone, sc);
1681         else
1682                 return inactive_anon_is_low(zone, sc);
1683 }
1684
1685 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1686         struct zone *zone, struct scan_control *sc, int priority)
1687 {
1688         int file = is_file_lru(lru);
1689
1690         if (is_active_lru(lru)) {
1691                 if (inactive_list_is_low(zone, sc, file))
1692                     shrink_active_list(nr_to_scan, zone, sc, priority, file);
1693                 return 0;
1694         }
1695
1696         return shrink_inactive_list(nr_to_scan, zone, sc, priority, file);
1697 }
1698
1699 /*
1700  * Smallish @nr_to_scan's are deposited in @nr_saved_scan,
1701  * until we collected @swap_cluster_max pages to scan.
1702  */
1703 static unsigned long nr_scan_try_batch(unsigned long nr_to_scan,
1704                                        unsigned long *nr_saved_scan)
1705 {
1706         unsigned long nr;
1707
1708         *nr_saved_scan += nr_to_scan;
1709         nr = *nr_saved_scan;
1710
1711         if (nr >= SWAP_CLUSTER_MAX)
1712                 *nr_saved_scan = 0;
1713         else
1714                 nr = 0;
1715
1716         return nr;
1717 }
1718
1719 /*
1720  * Determine how aggressively the anon and file LRU lists should be
1721  * scanned.  The relative value of each set of LRU lists is determined
1722  * by looking at the fraction of the pages scanned we did rotate back
1723  * onto the active list instead of evict.
1724  *
1725  * nr[0] = anon pages to scan; nr[1] = file pages to scan
1726  */
1727 static void get_scan_count(struct zone *zone, struct scan_control *sc,
1728                                         unsigned long *nr, int priority)
1729 {
1730         unsigned long anon, file, free;
1731         unsigned long anon_prio, file_prio;
1732         unsigned long ap, fp;
1733         struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1734         u64 fraction[2], denominator;
1735         enum lru_list l;
1736         int noswap = 0;
1737
1738         /* If we have no swap space, do not bother scanning anon pages. */
1739         if (!sc->may_swap || (nr_swap_pages <= 0)) {
1740                 noswap = 1;
1741                 fraction[0] = 0;
1742                 fraction[1] = 1;
1743                 denominator = 1;
1744                 goto out;
1745         }
1746
1747         anon  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
1748                 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
1749         file  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
1750                 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
1751
1752         if (scanning_global_lru(sc)) {
1753                 free  = zone_page_state(zone, NR_FREE_PAGES);
1754                 /* If we have very few page cache pages,
1755                    force-scan anon pages. */
1756                 if (unlikely(file + free <= high_wmark_pages(zone))) {
1757                         fraction[0] = 1;
1758                         fraction[1] = 0;
1759                         denominator = 1;
1760                         goto out;
1761                 }
1762         }
1763
1764         /*
1765          * With swappiness at 100, anonymous and file have the same priority.
1766          * This scanning priority is essentially the inverse of IO cost.
1767          */
1768         anon_prio = sc->swappiness;
1769         file_prio = 200 - sc->swappiness;
1770
1771         /*
1772          * OK, so we have swap space and a fair amount of page cache
1773          * pages.  We use the recently rotated / recently scanned
1774          * ratios to determine how valuable each cache is.
1775          *
1776          * Because workloads change over time (and to avoid overflow)
1777          * we keep these statistics as a floating average, which ends
1778          * up weighing recent references more than old ones.
1779          *
1780          * anon in [0], file in [1]
1781          */
1782         spin_lock_irq(&zone->lru_lock);
1783         if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1784                 reclaim_stat->recent_scanned[0] /= 2;
1785                 reclaim_stat->recent_rotated[0] /= 2;
1786         }
1787
1788         if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1789                 reclaim_stat->recent_scanned[1] /= 2;
1790                 reclaim_stat->recent_rotated[1] /= 2;
1791         }
1792
1793         /*
1794          * The amount of pressure on anon vs file pages is inversely
1795          * proportional to the fraction of recently scanned pages on
1796          * each list that were recently referenced and in active use.
1797          */
1798         ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1);
1799         ap /= reclaim_stat->recent_rotated[0] + 1;
1800
1801         fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
1802         fp /= reclaim_stat->recent_rotated[1] + 1;
1803         spin_unlock_irq(&zone->lru_lock);
1804
1805         fraction[0] = ap;
1806         fraction[1] = fp;
1807         denominator = ap + fp + 1;
1808 out:
1809         for_each_evictable_lru(l) {
1810                 int file = is_file_lru(l);
1811                 unsigned long scan;
1812
1813                 scan = zone_nr_lru_pages(zone, sc, l);
1814                 if (priority || noswap) {
1815                         scan >>= priority;
1816                         scan = div64_u64(scan * fraction[file], denominator);
1817                 }
1818                 nr[l] = nr_scan_try_batch(scan,
1819                                           &reclaim_stat->nr_saved_scan[l]);
1820         }
1821 }
1822
1823 /*
1824  * Reclaim/compaction depends on a number of pages being freed. To avoid
1825  * disruption to the system, a small number of order-0 pages continue to be
1826  * rotated and reclaimed in the normal fashion. However, by the time we get
1827  * back to the allocator and call try_to_compact_zone(), we ensure that
1828  * there are enough free pages for it to be likely successful
1829  */
1830 static inline bool should_continue_reclaim(struct zone *zone,
1831                                         unsigned long nr_reclaimed,
1832                                         unsigned long nr_scanned,
1833                                         struct scan_control *sc)
1834 {
1835         unsigned long pages_for_compaction;
1836         unsigned long inactive_lru_pages;
1837
1838         /* If not in reclaim/compaction mode, stop */
1839         if (!(sc->reclaim_mode & RECLAIM_MODE_COMPACTION))
1840                 return false;
1841
1842         /*
1843          * If we failed to reclaim and have scanned the full list, stop.
1844          * NOTE: Checking just nr_reclaimed would exit reclaim/compaction far
1845          *       faster but obviously would be less likely to succeed
1846          *       allocation. If this is desirable, use GFP_REPEAT to decide
1847          *       if both reclaimed and scanned should be checked or just
1848          *       reclaimed
1849          */
1850         if (!nr_reclaimed && !nr_scanned)
1851                 return false;
1852
1853         /*
1854          * If we have not reclaimed enough pages for compaction and the
1855          * inactive lists are large enough, continue reclaiming
1856          */
1857         pages_for_compaction = (2UL << sc->order);
1858         inactive_lru_pages = zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON) +
1859                                 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
1860         if (sc->nr_reclaimed < pages_for_compaction &&
1861                         inactive_lru_pages > pages_for_compaction)
1862                 return true;
1863
1864         /* If compaction would go ahead or the allocation would succeed, stop */
1865         switch (compaction_suitable(zone, sc->order)) {
1866         case COMPACT_PARTIAL:
1867         case COMPACT_CONTINUE:
1868                 return false;
1869         default:
1870                 return true;
1871         }
1872 }
1873
1874 /*
1875  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1876  */
1877 static void shrink_zone(int priority, struct zone *zone,
1878                                 struct scan_control *sc)
1879 {
1880         unsigned long nr[NR_LRU_LISTS];
1881         unsigned long nr_to_scan;
1882         enum lru_list l;
1883         unsigned long nr_reclaimed;
1884         unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1885         unsigned long nr_scanned = sc->nr_scanned;
1886
1887 restart:
1888         nr_reclaimed = 0;
1889         get_scan_count(zone, sc, nr, priority);
1890
1891         while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1892                                         nr[LRU_INACTIVE_FILE]) {
1893                 for_each_evictable_lru(l) {
1894                         if (nr[l]) {
1895                                 nr_to_scan = min_t(unsigned long,
1896                                                    nr[l], SWAP_CLUSTER_MAX);
1897                                 nr[l] -= nr_to_scan;
1898
1899                                 nr_reclaimed += shrink_list(l, nr_to_scan,
1900                                                             zone, sc, priority);
1901                         }
1902                 }
1903                 /*
1904                  * On large memory systems, scan >> priority can become
1905                  * really large. This is fine for the starting priority;
1906                  * we want to put equal scanning pressure on each zone.
1907                  * However, if the VM has a harder time of freeing pages,
1908                  * with multiple processes reclaiming pages, the total
1909                  * freeing target can get unreasonably large.
1910                  */
1911                 if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)
1912                         break;
1913         }
1914         sc->nr_reclaimed += nr_reclaimed;
1915
1916         /*
1917          * Even if we did not try to evict anon pages at all, we want to
1918          * rebalance the anon lru active/inactive ratio.
1919          */
1920         if (inactive_anon_is_low(zone, sc))
1921                 shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);
1922
1923         /* reclaim/compaction might need reclaim to continue */
1924         if (should_continue_reclaim(zone, nr_reclaimed,
1925                                         sc->nr_scanned - nr_scanned, sc))
1926                 goto restart;
1927
1928         throttle_vm_writeout(sc->gfp_mask);
1929 }
1930
1931 /*
1932  * This is the direct reclaim path, for page-allocating processes.  We only
1933  * try to reclaim pages from zones which will satisfy the caller's allocation
1934  * request.
1935  *
1936  * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
1937  * Because:
1938  * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1939  *    allocation or
1940  * b) The target zone may be at high_wmark_pages(zone) but the lower zones
1941  *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
1942  *    zone defense algorithm.
1943  *
1944  * If a zone is deemed to be full of pinned pages then just give it a light
1945  * scan then give up on it.
1946  */
1947 static void shrink_zones(int priority, struct zonelist *zonelist,
1948                                         struct scan_control *sc)
1949 {
1950         struct zoneref *z;
1951         struct zone *zone;
1952
1953         for_each_zone_zonelist_nodemask(zone, z, zonelist,
1954                                         gfp_zone(sc->gfp_mask), sc->nodemask) {
1955                 if (!populated_zone(zone))
1956                         continue;
1957                 /*
1958                  * Take care memory controller reclaiming has small influence
1959                  * to global LRU.
1960                  */
1961                 if (scanning_global_lru(sc)) {
1962                         if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1963                                 continue;
1964                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1965                                 continue;       /* Let kswapd poll it */
1966                 }
1967
1968                 shrink_zone(priority, zone, sc);
1969         }
1970 }
1971
1972 static bool zone_reclaimable(struct zone *zone)
1973 {
1974         return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
1975 }
1976
1977 /*
1978  * As hibernation is going on, kswapd is freezed so that it can't mark
1979  * the zone into all_unreclaimable. It can't handle OOM during hibernation.
1980  * So let's check zone's unreclaimable in direct reclaim as well as kswapd.
1981  */
1982 static bool all_unreclaimable(struct zonelist *zonelist,
1983                 struct scan_control *sc)
1984 {
1985         struct zoneref *z;
1986         struct zone *zone;
1987         bool all_unreclaimable = true;
1988
1989         for_each_zone_zonelist_nodemask(zone, z, zonelist,
1990                         gfp_zone(sc->gfp_mask), sc->nodemask) {
1991                 if (!populated_zone(zone))
1992                         continue;
1993                 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1994                         continue;
1995                 if (zone_reclaimable(zone)) {
1996                         all_unreclaimable = false;
1997                         break;
1998                 }
1999         }
2000
2001         return all_unreclaimable;
2002 }
2003
2004 /*
2005  * This is the main entry point to direct page reclaim.
2006  *
2007  * If a full scan of the inactive list fails to free enough memory then we
2008  * are "out of memory" and something needs to be killed.
2009  *
2010  * If the caller is !__GFP_FS then the probability of a failure is reasonably
2011  * high - the zone may be full of dirty or under-writeback pages, which this
2012  * caller can't do much about.  We kick the writeback threads and take explicit
2013  * naps in the hope that some of these pages can be written.  But if the
2014  * allocating task holds filesystem locks which prevent writeout this might not
2015  * work, and the allocation attempt will fail.
2016  *
2017  * returns:     0, if no pages reclaimed
2018  *              else, the number of pages reclaimed
2019  */
2020 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2021                                         struct scan_control *sc)
2022 {
2023         int priority;
2024         unsigned long total_scanned = 0;
2025         struct reclaim_state *reclaim_state = current->reclaim_state;
2026         struct zoneref *z;
2027         struct zone *zone;
2028         unsigned long writeback_threshold;
2029
2030         get_mems_allowed();
2031         delayacct_freepages_start();
2032
2033         if (scanning_global_lru(sc))
2034                 count_vm_event(ALLOCSTALL);
2035
2036         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
2037                 sc->nr_scanned = 0;
2038                 if (!priority)
2039                         disable_swap_token();
2040                 shrink_zones(priority, zonelist, sc);
2041                 /*
2042                  * Don't shrink slabs when reclaiming memory from
2043                  * over limit cgroups
2044                  */
2045                 if (scanning_global_lru(sc)) {
2046                         unsigned long lru_pages = 0;
2047                         for_each_zone_zonelist(zone, z, zonelist,
2048                                         gfp_zone(sc->gfp_mask)) {
2049                                 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2050                                         continue;
2051
2052                                 lru_pages += zone_reclaimable_pages(zone);
2053                         }
2054
2055                         shrink_slab(sc->nr_scanned, sc->gfp_mask, lru_pages);
2056                         if (reclaim_state) {
2057                                 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2058                                 reclaim_state->reclaimed_slab = 0;
2059                         }
2060                 }
2061                 total_scanned += sc->nr_scanned;
2062                 if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2063                         goto out;
2064
2065                 /*
2066                  * Try to write back as many pages as we just scanned.  This
2067                  * tends to cause slow streaming writers to write data to the
2068                  * disk smoothly, at the dirtying rate, which is nice.   But
2069                  * that's undesirable in laptop mode, where we *want* lumpy
2070                  * writeout.  So in laptop mode, write out the whole world.
2071                  */
2072                 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2073                 if (total_scanned > writeback_threshold) {
2074                         wakeup_flusher_threads(laptop_mode ? 0 : total_scanned);
2075                         sc->may_writepage = 1;
2076                 }
2077
2078                 /* Take a nap, wait for some writeback to complete */
2079                 if (!sc->hibernation_mode && sc->nr_scanned &&
2080                     priority < DEF_PRIORITY - 2) {
2081                         struct zone *preferred_zone;
2082
2083                         first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
2084                                                         NULL, &preferred_zone);
2085                         wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
2086                 }
2087         }
2088
2089 out:
2090         delayacct_freepages_end();
2091         put_mems_allowed();
2092
2093         if (sc->nr_reclaimed)
2094                 return sc->nr_reclaimed;
2095
2096         /* top priority shrink_zones still had more to do? don't OOM, then */
2097         if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc))
2098                 return 1;
2099
2100         return 0;
2101 }
2102
2103 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2104                                 gfp_t gfp_mask, nodemask_t *nodemask)
2105 {
2106         unsigned long nr_reclaimed;
2107         struct scan_control sc = {
2108                 .gfp_mask = gfp_mask,
2109                 .may_writepage = !laptop_mode,
2110                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2111                 .may_unmap = 1,
2112                 .may_swap = 1,
2113                 .swappiness = vm_swappiness,
2114                 .order = order,
2115                 .mem_cgroup = NULL,
2116                 .nodemask = nodemask,
2117         };
2118
2119         trace_mm_vmscan_direct_reclaim_begin(order,
2120                                 sc.may_writepage,
2121                                 gfp_mask);
2122
2123         nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2124
2125         trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2126
2127         return nr_reclaimed;
2128 }
2129
2130 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
2131
2132 unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
2133                                                 gfp_t gfp_mask, bool noswap,
2134                                                 unsigned int swappiness,
2135                                                 struct zone *zone)
2136 {
2137         struct scan_control sc = {
2138                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2139                 .may_writepage = !laptop_mode,
2140                 .may_unmap = 1,
2141                 .may_swap = !noswap,
2142                 .swappiness = swappiness,
2143                 .order = 0,
2144                 .mem_cgroup = mem,
2145         };
2146         sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2147                         (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2148
2149         trace_mm_vmscan_memcg_softlimit_reclaim_begin(0,
2150                                                       sc.may_writepage,
2151                                                       sc.gfp_mask);
2152
2153         /*
2154          * NOTE: Although we can get the priority field, using it
2155          * here is not a good idea, since it limits the pages we can scan.
2156          * if we don't reclaim here, the shrink_zone from balance_pgdat
2157          * will pick up pages from other mem cgroup's as well. We hack
2158          * the priority and make it zero.
2159          */
2160         shrink_zone(0, zone, &sc);
2161
2162         trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2163
2164         return sc.nr_reclaimed;
2165 }
2166
2167 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
2168                                            gfp_t gfp_mask,
2169                                            bool noswap,
2170                                            unsigned int swappiness)
2171 {
2172         struct zonelist *zonelist;
2173         unsigned long nr_reclaimed;
2174         struct scan_control sc = {
2175                 .may_writepage = !laptop_mode,
2176                 .may_unmap = 1,
2177                 .may_swap = !noswap,
2178                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2179                 .swappiness = swappiness,
2180                 .order = 0,
2181                 .mem_cgroup = mem_cont,
2182                 .nodemask = NULL, /* we don't care the placement */
2183         };
2184
2185         sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2186                         (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2187         zonelist = NODE_DATA(numa_node_id())->node_zonelists;
2188
2189         trace_mm_vmscan_memcg_reclaim_begin(0,
2190                                             sc.may_writepage,
2191                                             sc.gfp_mask);
2192
2193         nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2194
2195         trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2196
2197         return nr_reclaimed;
2198 }
2199 #endif
2200
2201 /*
2202  * pgdat_balanced is used when checking if a node is balanced for high-order
2203  * allocations. Only zones that meet watermarks and are in a zone allowed
2204  * by the callers classzone_idx are added to balanced_pages. The total of
2205  * balanced pages must be at least 25% of the zones allowed by classzone_idx
2206  * for the node to be considered balanced. Forcing all zones to be balanced
2207  * for high orders can cause excessive reclaim when there are imbalanced zones.
2208  * The choice of 25% is due to
2209  *   o a 16M DMA zone that is balanced will not balance a zone on any
2210  *     reasonable sized machine
2211  *   o On all other machines, the top zone must be at least a reasonable
2212  *     precentage of the middle zones. For example, on 32-bit x86, highmem
2213  *     would need to be at least 256M for it to be balance a whole node.
2214  *     Similarly, on x86-64 the Normal zone would need to be at least 1G
2215  *     to balance a node on its own. These seemed like reasonable ratios.
2216  */
2217 static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
2218                                                 int classzone_idx)
2219 {
2220         unsigned long present_pages = 0;
2221         int i;
2222
2223         for (i = 0; i <= classzone_idx; i++)
2224                 present_pages += pgdat->node_zones[i].present_pages;
2225
2226         return balanced_pages > (present_pages >> 2);
2227 }
2228
2229 /* is kswapd sleeping prematurely? */
2230 static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
2231                                         int classzone_idx)
2232 {
2233         int i;
2234         unsigned long balanced = 0;
2235         bool all_zones_ok = true;
2236
2237         /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2238         if (remaining)
2239                 return true;
2240
2241         /* Check the watermark levels */
2242         for (i = 0; i < pgdat->nr_zones; i++) {
2243                 struct zone *zone = pgdat->node_zones + i;
2244
2245                 if (!populated_zone(zone))
2246                         continue;
2247
2248                 /*
2249                  * balance_pgdat() skips over all_unreclaimable after
2250                  * DEF_PRIORITY. Effectively, it considers them balanced so
2251                  * they must be considered balanced here as well if kswapd
2252                  * is to sleep
2253                  */
2254                 if (zone->all_unreclaimable) {
2255                         balanced += zone->present_pages;
2256                         continue;
2257                 }
2258
2259                 if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
2260                                                         classzone_idx, 0))
2261                         all_zones_ok = false;
2262                 else
2263                         balanced += zone->present_pages;
2264         }
2265
2266         /*
2267          * For high-order requests, the balanced zones must contain at least
2268          * 25% of the nodes pages for kswapd to sleep. For order-0, all zones
2269          * must be balanced
2270          */
2271         if (order)
2272                 return pgdat_balanced(pgdat, balanced, classzone_idx);
2273         else
2274                 return !all_zones_ok;
2275 }
2276
2277 /*
2278  * For kswapd, balance_pgdat() will work across all this node's zones until
2279  * they are all at high_wmark_pages(zone).
2280  *
2281  * Returns the final order kswapd was reclaiming at
2282  *
2283  * There is special handling here for zones which are full of pinned pages.
2284  * This can happen if the pages are all mlocked, or if they are all used by
2285  * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
2286  * What we do is to detect the case where all pages in the zone have been
2287  * scanned twice and there has been zero successful reclaim.  Mark the zone as
2288  * dead and from now on, only perform a short scan.  Basically we're polling
2289  * the zone for when the problem goes away.
2290  *
2291  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
2292  * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2293  * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2294  * lower zones regardless of the number of free pages in the lower zones. This
2295  * interoperates with the page allocator fallback scheme to ensure that aging
2296  * of pages is balanced across the zones.
2297  */
2298 static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2299                                                         int *classzone_idx)
2300 {
2301         int all_zones_ok;
2302         unsigned long balanced;
2303         int priority;
2304         int i;
2305         int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
2306         unsigned long total_scanned;
2307         struct reclaim_state *reclaim_state = current->reclaim_state;
2308         struct scan_control sc = {
2309                 .gfp_mask = GFP_KERNEL,
2310                 .may_unmap = 1,
2311                 .may_swap = 1,
2312                 /*
2313                  * kswapd doesn't want to be bailed out while reclaim. because
2314                  * we want to put equal scanning pressure on each zone.
2315                  */
2316                 .nr_to_reclaim = ULONG_MAX,
2317                 .swappiness = vm_swappiness,
2318                 .order = order,
2319                 .mem_cgroup = NULL,
2320         };
2321 loop_again:
2322         total_scanned = 0;
2323         sc.nr_reclaimed = 0;
2324         sc.may_writepage = !laptop_mode;
2325         count_vm_event(PAGEOUTRUN);
2326
2327         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
2328                 unsigned long lru_pages = 0;
2329                 int has_under_min_watermark_zone = 0;
2330
2331                 /* The swap token gets in the way of swapout... */
2332                 if (!priority)
2333                         disable_swap_token();
2334
2335                 all_zones_ok = 1;
2336                 balanced = 0;
2337
2338                 /*
2339                  * Scan in the highmem->dma direction for the highest
2340                  * zone which needs scanning
2341                  */
2342                 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2343                         struct zone *zone = pgdat->node_zones + i;
2344
2345                         if (!populated_zone(zone))
2346                                 continue;
2347
2348                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2349                                 continue;
2350
2351                         /*
2352                          * Do some background aging of the anon list, to give
2353                          * pages a chance to be referenced before reclaiming.
2354                          */
2355                         if (inactive_anon_is_low(zone, &sc))
2356                                 shrink_active_list(SWAP_CLUSTER_MAX, zone,
2357                                                         &sc, priority, 0);
2358
2359                         if (!zone_watermark_ok_safe(zone, order,
2360                                         high_wmark_pages(zone), 0, 0)) {
2361                                 end_zone = i;
2362                                 *classzone_idx = i;
2363                                 break;
2364                         }
2365                 }
2366                 if (i < 0)
2367                         goto out;
2368
2369                 for (i = 0; i <= end_zone; i++) {
2370                         struct zone *zone = pgdat->node_zones + i;
2371
2372                         lru_pages += zone_reclaimable_pages(zone);
2373                 }
2374
2375                 /*
2376                  * Now scan the zone in the dma->highmem direction, stopping
2377                  * at the last zone which needs scanning.
2378                  *
2379                  * We do this because the page allocator works in the opposite
2380                  * direction.  This prevents the page allocator from allocating
2381                  * pages behind kswapd's direction of progress, which would
2382                  * cause too much scanning of the lower zones.
2383                  */
2384                 for (i = 0; i <= end_zone; i++) {
2385                         struct zone *zone = pgdat->node_zones + i;
2386                         int nr_slab;
2387
2388                         if (!populated_zone(zone))
2389                                 continue;
2390
2391                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2392                                 continue;
2393
2394                         sc.nr_scanned = 0;
2395
2396                         /*
2397                          * Call soft limit reclaim before calling shrink_zone.
2398                          * For now we ignore the return value
2399                          */
2400                         mem_cgroup_soft_limit_reclaim(zone, order, sc.gfp_mask);
2401
2402                         /*
2403                          * We put equal pressure on every zone, unless one
2404                          * zone has way too many pages free already.
2405                          */
2406                         if (!zone_watermark_ok_safe(zone, order,
2407                                         8*high_wmark_pages(zone), end_zone, 0))
2408                                 shrink_zone(priority, zone, &sc);
2409                         reclaim_state->reclaimed_slab = 0;
2410                         nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
2411                                                 lru_pages);
2412                         sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2413                         total_scanned += sc.nr_scanned;
2414                         if (zone->all_unreclaimable)
2415                                 continue;
2416                         if (nr_slab == 0 && !zone_reclaimable(zone))
2417                                 zone->all_unreclaimable = 1;
2418                         /*
2419                          * If we've done a decent amount of scanning and
2420                          * the reclaim ratio is low, start doing writepage
2421                          * even in laptop mode
2422                          */
2423                         if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2424                             total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
2425                                 sc.may_writepage = 1;
2426
2427                         /*
2428                          * Compact the zone for higher orders to reduce
2429                          * latencies for higher-order allocations that
2430                          * would ordinarily call try_to_compact_pages()
2431                          */
2432                         if (sc.order > PAGE_ALLOC_COSTLY_ORDER)
2433                                 compact_zone_order(zone, sc.order, sc.gfp_mask,
2434                                                         false);
2435
2436                         if (!zone_watermark_ok_safe(zone, order,
2437                                         high_wmark_pages(zone), end_zone, 0)) {
2438                                 all_zones_ok = 0;
2439                                 /*
2440                                  * We are still under min water mark.  This
2441                                  * means that we have a GFP_ATOMIC allocation
2442                                  * failure risk. Hurry up!
2443                                  */
2444                                 if (!zone_watermark_ok_safe(zone, order,
2445                                             min_wmark_pages(zone), end_zone, 0))
2446                                         has_under_min_watermark_zone = 1;
2447                         } else {
2448                                 /*
2449                                  * If a zone reaches its high watermark,
2450                                  * consider it to be no longer congested. It's
2451                                  * possible there are dirty pages backed by
2452                                  * congested BDIs but as pressure is relieved,
2453                                  * spectulatively avoid congestion waits
2454                                  */
2455                                 zone_clear_flag(zone, ZONE_CONGESTED);
2456                                 if (i <= *classzone_idx)
2457                                         balanced += zone->present_pages;
2458                         }
2459
2460                 }
2461                 if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
2462                         break;          /* kswapd: all done */
2463                 /*
2464                  * OK, kswapd is getting into trouble.  Take a nap, then take
2465                  * another pass across the zones.
2466                  */
2467                 if (total_scanned && (priority < DEF_PRIORITY - 2)) {
2468                         if (has_under_min_watermark_zone)
2469                                 count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
2470                         else
2471                                 congestion_wait(BLK_RW_ASYNC, HZ/10);
2472                 }
2473
2474                 /*
2475                  * We do this so kswapd doesn't build up large priorities for
2476                  * example when it is freeing in parallel with allocators. It
2477                  * matches the direct reclaim path behaviour in terms of impact
2478                  * on zone->*_priority.
2479                  */
2480                 if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2481                         break;
2482         }
2483 out:
2484
2485         /*
2486          * order-0: All zones must meet high watermark for a balanced node
2487          * high-order: Balanced zones must make up at least 25% of the node
2488          *             for the node to be balanced
2489          */
2490         if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) {
2491                 cond_resched();
2492
2493                 try_to_freeze();
2494
2495                 /*
2496                  * Fragmentation may mean that the system cannot be
2497                  * rebalanced for high-order allocations in all zones.
2498                  * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2499                  * it means the zones have been fully scanned and are still
2500                  * not balanced. For high-order allocations, there is
2501                  * little point trying all over again as kswapd may
2502                  * infinite loop.
2503                  *
2504                  * Instead, recheck all watermarks at order-0 as they
2505                  * are the most important. If watermarks are ok, kswapd will go
2506                  * back to sleep. High-order users can still perform direct
2507                  * reclaim if they wish.
2508                  */
2509                 if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2510                         order = sc.order = 0;
2511
2512                 goto loop_again;
2513         }
2514
2515         /*
2516          * If kswapd was reclaiming at a higher order, it has the option of
2517          * sleeping without all zones being balanced. Before it does, it must
2518          * ensure that the watermarks for order-0 on *all* zones are met and
2519          * that the congestion flags are cleared. The congestion flag must
2520          * be cleared as kswapd is the only mechanism that clears the flag
2521          * and it is potentially going to sleep here.
2522          */
2523         if (order) {
2524                 for (i = 0; i <= end_zone; i++) {
2525                         struct zone *zone = pgdat->node_zones + i;
2526
2527                         if (!populated_zone(zone))
2528                                 continue;
2529
2530                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2531                                 continue;
2532
2533                         /* Confirm the zone is balanced for order-0 */
2534                         if (!zone_watermark_ok(zone, 0,
2535                                         high_wmark_pages(zone), 0, 0)) {
2536                                 order = sc.order = 0;
2537                                 goto loop_again;
2538                         }
2539
2540                         /* If balanced, clear the congested flag */
2541                         zone_clear_flag(zone, ZONE_CONGESTED);
2542                 }
2543         }
2544
2545         /*
2546          * Return the order we were reclaiming at so sleeping_prematurely()
2547          * makes a decision on the order we were last reclaiming at. However,
2548          * if another caller entered the allocator slow path while kswapd
2549          * was awake, order will remain at the higher level
2550          */
2551         *classzone_idx = end_zone;
2552         return order;
2553 }
2554
2555 static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
2556 {
2557         long remaining = 0;
2558         DEFINE_WAIT(wait);
2559
2560         if (freezing(current) || kthread_should_stop())
2561                 return;
2562
2563         prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2564
2565         /* Try to sleep for a short interval */
2566         if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
2567                 remaining = schedule_timeout(HZ/10);
2568                 finish_wait(&pgdat->kswapd_wait, &wait);
2569                 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2570         }
2571
2572         /*
2573          * After a short sleep, check if it was a premature sleep. If not, then
2574          * go fully to sleep until explicitly woken up.
2575          */
2576         if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
2577                 trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
2578
2579                 /*
2580                  * vmstat counters are not perfectly accurate and the estimated
2581                  * value for counters such as NR_FREE_PAGES can deviate from the
2582                  * true value by nr_online_cpus * threshold. To avoid the zone
2583                  * watermarks being breached while under pressure, we reduce the
2584                  * per-cpu vmstat threshold while kswapd is awake and restore
2585                  * them before going back to sleep.
2586                  */
2587                 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
2588                 schedule();
2589                 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
2590         } else {
2591                 if (remaining)
2592                         count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2593                 else
2594                         count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2595         }
2596         finish_wait(&pgdat->kswapd_wait, &wait);
2597 }
2598
2599 /*
2600  * The background pageout daemon, started as a kernel thread
2601  * from the init process.
2602  *
2603  * This basically trickles out pages so that we have _some_
2604  * free memory available even if there is no other activity
2605  * that frees anything up. This is needed for things like routing
2606  * etc, where we otherwise might have all activity going on in
2607  * asynchronous contexts that cannot page things out.
2608  *
2609  * If there are applications that are active memory-allocators
2610  * (most normal use), this basically shouldn't matter.
2611  */
2612 static int kswapd(void *p)
2613 {
2614         unsigned long order;
2615         int classzone_idx;
2616         pg_data_t *pgdat = (pg_data_t*)p;
2617         struct task_struct *tsk = current;
2618
2619         struct reclaim_state reclaim_state = {
2620                 .reclaimed_slab = 0,
2621         };
2622         const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2623
2624         lockdep_set_current_reclaim_state(GFP_KERNEL);
2625
2626         if (!cpumask_empty(cpumask))
2627                 set_cpus_allowed_ptr(tsk, cpumask);
2628         current->reclaim_state = &reclaim_state;
2629
2630         /*
2631          * Tell the memory management that we're a "memory allocator",
2632          * and that if we need more memory we should get access to it
2633          * regardless (see "__alloc_pages()"). "kswapd" should
2634          * never get caught in the normal page freeing logic.
2635          *
2636          * (Kswapd normally doesn't need memory anyway, but sometimes
2637          * you need a small amount of memory in order to be able to
2638          * page out something else, and this flag essentially protects
2639          * us from recursively trying to free more memory as we're
2640          * trying to free the first piece of memory in the first place).
2641          */
2642         tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2643         set_freezable();
2644
2645         order = 0;
2646         classzone_idx = MAX_NR_ZONES - 1;
2647         for ( ; ; ) {
2648                 unsigned long new_order;
2649                 int new_classzone_idx;
2650                 int ret;
2651
2652                 new_order = pgdat->kswapd_max_order;
2653                 new_classzone_idx = pgdat->classzone_idx;
2654                 pgdat->kswapd_max_order = 0;
2655                 pgdat->classzone_idx = MAX_NR_ZONES - 1;
2656                 if (order < new_order || classzone_idx > new_classzone_idx) {
2657                         /*
2658                          * Don't sleep if someone wants a larger 'order'
2659                          * allocation or has tigher zone constraints
2660                          */
2661                         order = new_order;
2662                         classzone_idx = new_classzone_idx;
2663                 } else {
2664                         kswapd_try_to_sleep(pgdat, order, classzone_idx);
2665                         order = pgdat->kswapd_max_order;
2666                         classzone_idx = pgdat->classzone_idx;
2667                         pgdat->kswapd_max_order = 0;
2668                         pgdat->classzone_idx = MAX_NR_ZONES - 1;
2669                 }
2670
2671                 ret = try_to_freeze();
2672                 if (kthread_should_stop())
2673                         break;
2674
2675                 /*
2676                  * We can speed up thawing tasks if we don't call balance_pgdat
2677                  * after returning from the refrigerator
2678                  */
2679                 if (!ret) {
2680                         trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
2681                         order = balance_pgdat(pgdat, order, &classzone_idx);
2682                 }
2683         }
2684         return 0;
2685 }
2686
2687 /*
2688  * A zone is low on free memory, so wake its kswapd task to service it.
2689  */
2690 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
2691 {
2692         pg_data_t *pgdat;
2693
2694         if (!populated_zone(zone))
2695                 return;
2696
2697         if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2698                 return;
2699         pgdat = zone->zone_pgdat;
2700         if (pgdat->kswapd_max_order < order) {
2701                 pgdat->kswapd_max_order = order;
2702                 pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
2703         }
2704         if (!waitqueue_active(&pgdat->kswapd_wait))
2705                 return;
2706         if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
2707                 return;
2708
2709         trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
2710         wake_up_interruptible(&pgdat->kswapd_wait);
2711 }
2712
2713 /*
2714  * The reclaimable count would be mostly accurate.
2715  * The less reclaimable pages may be
2716  * - mlocked pages, which will be moved to unevictable list when encountered
2717  * - mapped pages, which may require several travels to be reclaimed
2718  * - dirty pages, which is not "instantly" reclaimable
2719  */
2720 unsigned long global_reclaimable_pages(void)
2721 {
2722         int nr;
2723
2724         nr = global_page_state(NR_ACTIVE_FILE) +
2725              global_page_state(NR_INACTIVE_FILE);
2726
2727         if (nr_swap_pages > 0)
2728                 nr += global_page_state(NR_ACTIVE_ANON) +
2729                       global_page_state(NR_INACTIVE_ANON);
2730
2731         return nr;
2732 }
2733
2734 unsigned long zone_reclaimable_pages(struct zone *zone)
2735 {
2736         int nr;
2737
2738         nr = zone_page_state(zone, NR_ACTIVE_FILE) +
2739              zone_page_state(zone, NR_INACTIVE_FILE);
2740
2741         if (nr_swap_pages > 0)
2742                 nr += zone_page_state(zone, NR_ACTIVE_ANON) +
2743                       zone_page_state(zone, NR_INACTIVE_ANON);
2744
2745         return nr;
2746 }
2747
2748 #ifdef CONFIG_HIBERNATION
2749 /*
2750  * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
2751  * freed pages.
2752  *
2753  * Rather than trying to age LRUs the aim is to preserve the overall
2754  * LRU order by reclaiming preferentially
2755  * inactive > active > active referenced > active mapped
2756  */
2757 unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
2758 {
2759         struct reclaim_state reclaim_state;
2760         struct scan_control sc = {
2761                 .gfp_mask = GFP_HIGHUSER_MOVABLE,
2762                 .may_swap = 1,
2763                 .may_unmap = 1,
2764                 .may_writepage = 1,
2765                 .nr_to_reclaim = nr_to_reclaim,
2766                 .hibernation_mode = 1,
2767                 .swappiness = vm_swappiness,
2768                 .order = 0,
2769         };
2770         struct zonelist * zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
2771         struct task_struct *p = current;
2772         unsigned long nr_reclaimed;
2773
2774         p->flags |= PF_MEMALLOC;
2775         lockdep_set_current_reclaim_state(sc.gfp_mask);
2776         reclaim_state.reclaimed_slab = 0;
2777         p->reclaim_state = &reclaim_state;
2778
2779         nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2780
2781         p->reclaim_state = NULL;
2782         lockdep_clear_current_reclaim_state();
2783         p->flags &= ~PF_MEMALLOC;
2784
2785         return nr_reclaimed;
2786 }
2787 #endif /* CONFIG_HIBERNATION */
2788
2789 /* It's optimal to keep kswapds on the same CPUs as their memory, but
2790    not required for correctness.  So if the last cpu in a node goes
2791    away, we get changed to run anywhere: as the first one comes back,
2792    restore their cpu bindings. */
2793 static int __devinit cpu_callback(struct notifier_block *nfb,
2794                                   unsigned long action, void *hcpu)
2795 {
2796         int nid;
2797
2798         if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
2799                 for_each_node_state(nid, N_HIGH_MEMORY) {
2800                         pg_data_t *pgdat = NODE_DATA(nid);
2801                         const struct cpumask *mask;
2802
2803                         mask = cpumask_of_node(pgdat->node_id);
2804
2805                         if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2806                                 /* One of our CPUs online: restore mask */
2807                                 set_cpus_allowed_ptr(pgdat->kswapd, mask);
2808                 }
2809         }
2810         return NOTIFY_OK;
2811 }
2812
2813 /*
2814  * This kswapd start function will be called by init and node-hot-add.
2815  * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
2816  */
2817 int kswapd_run(int nid)
2818 {
2819         pg_data_t *pgdat = NODE_DATA(nid);
2820         int ret = 0;
2821
2822         if (pgdat->kswapd)
2823                 return 0;
2824
2825         pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
2826         if (IS_ERR(pgdat->kswapd)) {
2827                 /* failure at boot is fatal */
2828                 BUG_ON(system_state == SYSTEM_BOOTING);
2829                 printk("Failed to start kswapd on node %d\n",nid);
2830                 ret = -1;
2831         }
2832         return ret;
2833 }
2834
2835 /*
2836  * Called by memory hotplug when all memory in a node is offlined.
2837  */
2838 void kswapd_stop(int nid)
2839 {
2840         struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
2841
2842         if (kswapd)
2843                 kthread_stop(kswapd);
2844 }
2845
2846 static int __init kswapd_init(void)
2847 {
2848         int nid;
2849
2850         swap_setup();
2851         for_each_node_state(nid, N_HIGH_MEMORY)
2852                 kswapd_run(nid);
2853         hotcpu_notifier(cpu_callback, 0);
2854         return 0;
2855 }
2856
2857 module_init(kswapd_init)
2858
2859 #ifdef CONFIG_NUMA
2860 /*
2861  * Zone reclaim mode
2862  *
2863  * If non-zero call zone_reclaim when the number of free pages falls below
2864  * the watermarks.
2865  */
2866 int zone_reclaim_mode __read_mostly;
2867
2868 #define RECLAIM_OFF 0
2869 #define RECLAIM_ZONE (1<<0)     /* Run shrink_inactive_list on the zone */
2870 #define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
2871 #define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
2872
2873 /*
2874  * Priority for ZONE_RECLAIM. This determines the fraction of pages
2875  * of a node considered for each zone_reclaim. 4 scans 1/16th of
2876  * a zone.
2877  */
2878 #define ZONE_RECLAIM_PRIORITY 4
2879
2880 /*
2881  * Percentage of pages in a zone that must be unmapped for zone_reclaim to
2882  * occur.
2883  */
2884 int sysctl_min_unmapped_ratio = 1;
2885
2886 /*
2887  * If the number of slab pages in a zone grows beyond this percentage then
2888  * slab reclaim needs to occur.
2889  */
2890 int sysctl_min_slab_ratio = 5;
2891
2892 static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
2893 {
2894         unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
2895         unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
2896                 zone_page_state(zone, NR_ACTIVE_FILE);
2897
2898         /*
2899          * It's possible for there to be more file mapped pages than
2900          * accounted for by the pages on the file LRU lists because
2901          * tmpfs pages accounted for as ANON can also be FILE_MAPPED
2902          */
2903         return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
2904 }
2905
2906 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
2907 static long zone_pagecache_reclaimable(struct zone *zone)
2908 {
2909         long nr_pagecache_reclaimable;
2910         long delta = 0;
2911
2912         /*
2913          * If RECLAIM_SWAP is set, then all file pages are considered
2914          * potentially reclaimable. Otherwise, we have to worry about
2915          * pages like swapcache and zone_unmapped_file_pages() provides
2916          * a better estimate
2917          */
2918         if (zone_reclaim_mode & RECLAIM_SWAP)
2919                 nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
2920         else
2921                 nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
2922
2923         /* If we can't clean pages, remove dirty pages from consideration */
2924         if (!(zone_reclaim_mode & RECLAIM_WRITE))
2925                 delta += zone_page_state(zone, NR_FILE_DIRTY);
2926
2927         /* Watch for any possible underflows due to delta */
2928         if (unlikely(delta > nr_pagecache_reclaimable))
2929                 delta = nr_pagecache_reclaimable;
2930
2931         return nr_pagecache_reclaimable - delta;
2932 }
2933
2934 /*
2935  * Try to free up some pages from this zone through reclaim.
2936  */
2937 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
2938 {
2939         /* Minimum pages needed in order to stay on node */
2940         const unsigned long nr_pages = 1 << order;
2941         struct task_struct *p = current;
2942         struct reclaim_state reclaim_state;
2943         int priority;
2944         struct scan_control sc = {
2945                 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
2946                 .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
2947                 .may_swap = 1,
2948                 .nr_to_reclaim = max_t(unsigned long, nr_pages,
2949                                        SWAP_CLUSTER_MAX),
2950                 .gfp_mask = gfp_mask,
2951                 .swappiness = vm_swappiness,
2952                 .order = order,
2953         };
2954         unsigned long nr_slab_pages0, nr_slab_pages1;
2955
2956         cond_resched();
2957         /*
2958          * We need to be able to allocate from the reserves for RECLAIM_SWAP
2959          * and we also need to be able to write out pages for RECLAIM_WRITE
2960          * and RECLAIM_SWAP.
2961          */
2962         p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
2963         lockdep_set_current_reclaim_state(gfp_mask);
2964         reclaim_state.reclaimed_slab = 0;
2965         p->reclaim_state = &reclaim_state;
2966
2967         if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
2968                 /*
2969                  * Free memory by calling shrink zone with increasing
2970                  * priorities until we have enough memory freed.
2971                  */
2972                 priority = ZONE_RECLAIM_PRIORITY;
2973                 do {
2974                         shrink_zone(priority, zone, &sc);
2975                         priority--;
2976                 } while (priority >= 0 && sc.nr_reclaimed < nr_pages);
2977         }
2978
2979         nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
2980         if (nr_slab_pages0 > zone->min_slab_pages) {
2981                 /*
2982                  * shrink_slab() does not currently allow us to determine how
2983                  * many pages were freed in this zone. So we take the current
2984                  * number of slab pages and shake the slab until it is reduced
2985                  * by the same nr_pages that we used for reclaiming unmapped
2986                  * pages.
2987                  *
2988                  * Note that shrink_slab will free memory on all zones and may
2989                  * take a long time.
2990                  */
2991                 for (;;) {
2992                         unsigned long lru_pages = zone_reclaimable_pages(zone);
2993
2994                         /* No reclaimable slab or very low memory pressure */
2995                         if (!shrink_slab(sc.nr_scanned, gfp_mask, lru_pages))
2996                                 break;
2997
2998                         /* Freed enough memory */
2999                         nr_slab_pages1 = zone_page_state(zone,
3000                                                         NR_SLAB_RECLAIMABLE);
3001                         if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3002                                 break;
3003                 }
3004
3005                 /*
3006                  * Update nr_reclaimed by the number of slab pages we
3007                  * reclaimed from this zone.
3008                  */
3009                 nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3010                 if (nr_slab_pages1 < nr_slab_pages0)
3011                         sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3012         }
3013
3014         p->reclaim_state = NULL;
3015         current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3016         lockdep_clear_current_reclaim_state();
3017         return sc.nr_reclaimed >= nr_pages;
3018 }
3019
3020 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3021 {
3022         int node_id;
3023         int ret;
3024
3025         /*
3026          * Zone reclaim reclaims unmapped file backed pages and
3027          * slab pages if we are over the defined limits.
3028          *
3029          * A small portion of unmapped file backed pages is needed for
3030          * file I/O otherwise pages read by file I/O will be immediately
3031          * thrown out if the zone is overallocated. So we do not reclaim
3032          * if less than a specified percentage of the zone is used by
3033          * unmapped file backed pages.
3034          */
3035         if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3036             zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3037                 return ZONE_RECLAIM_FULL;
3038
3039         if (zone->all_unreclaimable)
3040                 return ZONE_RECLAIM_FULL;
3041
3042         /*
3043          * Do not scan if the allocation should not be delayed.
3044          */
3045         if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3046                 return ZONE_RECLAIM_NOSCAN;
3047
3048         /*
3049          * Only run zone reclaim on the local zone or on zones that do not
3050          * have associated processors. This will favor the local processor
3051          * over remote processors and spread off node memory allocations
3052          * as wide as possible.
3053          */
3054         node_id = zone_to_nid(zone);
3055         if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3056                 return ZONE_RECLAIM_NOSCAN;
3057
3058         if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3059                 return ZONE_RECLAIM_NOSCAN;
3060
3061         ret = __zone_reclaim(zone, gfp_mask, order);
3062         zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3063
3064         if (!ret)
3065                 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3066
3067         return ret;
3068 }
3069 #endif
3070
3071 /*
3072  * page_evictable - test whether a page is evictable
3073  * @page: the page to test
3074  * @vma: the VMA in which the page is or will be mapped, may be NULL
3075  *
3076  * Test whether page is evictable--i.e., should be placed on active/inactive
3077  * lists vs unevictable list.  The vma argument is !NULL when called from the
3078  * fault path to determine how to instantate a new page.
3079  *
3080  * Reasons page might not be evictable:
3081  * (1) page's mapping marked unevictable
3082  * (2) page is part of an mlocked VMA
3083  *
3084  */
3085 int page_evictable(struct page *page, struct vm_area_struct *vma)
3086 {
3087
3088         if (mapping_unevictable(page_mapping(page)))
3089                 return 0;
3090
3091         if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
3092                 return 0;
3093
3094         return 1;
3095 }
3096
3097 /**
3098  * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list
3099  * @page: page to check evictability and move to appropriate lru list
3100  * @zone: zone page is in
3101  *
3102  * Checks a page for evictability and moves the page to the appropriate
3103  * zone lru list.
3104  *
3105  * Restrictions: zone->lru_lock must be held, page must be on LRU and must
3106  * have PageUnevictable set.
3107  */
3108 static void check_move_unevictable_page(struct page *page, struct zone *zone)
3109 {
3110         VM_BUG_ON(PageActive(page));
3111
3112 retry:
3113         ClearPageUnevictable(page);
3114         if (page_evictable(page, NULL)) {
3115                 enum lru_list l = page_lru_base_type(page);
3116
3117                 __dec_zone_state(zone, NR_UNEVICTABLE);
3118                 list_move(&page->lru, &zone->lru[l].list);
3119                 mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l);
3120                 __inc_zone_state(zone, NR_INACTIVE_ANON + l);
3121                 __count_vm_event(UNEVICTABLE_PGRESCUED);
3122         } else {
3123                 /*
3124                  * rotate unevictable list
3125                  */
3126                 SetPageUnevictable(page);
3127                 list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list);
3128                 mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE);
3129                 if (page_evictable(page, NULL))
3130                         goto retry;
3131         }
3132 }
3133
3134 /**
3135  * scan_mapping_unevictable_pages - scan an address space for evictable pages
3136  * @mapping: struct address_space to scan for evictable pages
3137  *
3138  * Scan all pages in mapping.  Check unevictable pages for
3139  * evictability and move them to the appropriate zone lru list.
3140  */
3141 void scan_mapping_unevictable_pages(struct address_space *mapping)
3142 {
3143         pgoff_t next = 0;
3144         pgoff_t end   = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >>
3145                          PAGE_CACHE_SHIFT;
3146         struct zone *zone;
3147         struct pagevec pvec;
3148
3149         if (mapping->nrpages == 0)
3150                 return;
3151
3152         pagevec_init(&pvec, 0);
3153         while (next < end &&
3154                 pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
3155                 int i;
3156                 int pg_scanned = 0;
3157
3158                 zone = NULL;
3159
3160                 for (i = 0; i < pagevec_count(&pvec); i++) {
3161                         struct page *page = pvec.pages[i];
3162                         pgoff_t page_index = page->index;
3163                         struct zone *pagezone = page_zone(page);
3164
3165                         pg_scanned++;
3166                         if (page_index > next)
3167                                 next = page_index;
3168                         next++;
3169
3170                         if (pagezone != zone) {
3171                                 if (zone)
3172                                         spin_unlock_irq(&zone->lru_lock);
3173                                 zone = pagezone;
3174                                 spin_lock_irq(&zone->lru_lock);
3175                         }
3176
3177                         if (PageLRU(page) && PageUnevictable(page))
3178                                 check_move_unevictable_page(page, zone);
3179                 }
3180                 if (zone)
3181                         spin_unlock_irq(&zone->lru_lock);
3182                 pagevec_release(&pvec);
3183
3184                 count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
3185         }
3186
3187 }
3188
3189 /**
3190  * scan_zone_unevictable_pages - check unevictable list for evictable pages
3191  * @zone - zone of which to scan the unevictable list
3192  *
3193  * Scan @zone's unevictable LRU lists to check for pages that have become
3194  * evictable.  Move those that have to @zone's inactive list where they
3195  * become candidates for reclaim, unless shrink_inactive_zone() decides
3196  * to reactivate them.  Pages that are still unevictable are rotated
3197  * back onto @zone's unevictable list.
3198  */
3199 #define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */
3200 static void scan_zone_unevictable_pages(struct zone *zone)
3201 {
3202         struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list;
3203         unsigned long scan;
3204         unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE);
3205
3206         while (nr_to_scan > 0) {
3207                 unsigned long batch_size = min(nr_to_scan,
3208                                                 SCAN_UNEVICTABLE_BATCH_SIZE);
3209
3210                 spin_lock_irq(&zone->lru_lock);
3211                 for (scan = 0;  scan < batch_size; scan++) {
3212                         struct page *page = lru_to_page(l_unevictable);
3213
3214                         if (!trylock_page(page))
3215                                 continue;
3216
3217                         prefetchw_prev_lru_page(page, l_unevictable, flags);
3218
3219                         if (likely(PageLRU(page) && PageUnevictable(page)))
3220                                 check_move_unevictable_page(page, zone);
3221
3222                         unlock_page(page);
3223                 }
3224                 spin_unlock_irq(&zone->lru_lock);
3225
3226                 nr_to_scan -= batch_size;
3227         }
3228 }
3229
3230
3231 /**
3232  * scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages
3233  *
3234  * A really big hammer:  scan all zones' unevictable LRU lists to check for
3235  * pages that have become evictable.  Move those back to the zones'
3236  * inactive list where they become candidates for reclaim.
3237  * This occurs when, e.g., we have unswappable pages on the unevictable lists,
3238  * and we add swap to the system.  As such, it runs in the context of a task
3239  * that has possibly/probably made some previously unevictable pages
3240  * evictable.
3241  */
3242 static void scan_all_zones_unevictable_pages(void)
3243 {
3244         struct zone *zone;
3245
3246         for_each_zone(zone) {
3247                 scan_zone_unevictable_pages(zone);
3248         }
3249 }
3250
3251 /*
3252  * scan_unevictable_pages [vm] sysctl handler.  On demand re-scan of
3253  * all nodes' unevictable lists for evictable pages
3254  */
3255 unsigned long scan_unevictable_pages;
3256
3257 int scan_unevictable_handler(struct ctl_table *table, int write,
3258                            void __user *buffer,
3259                            size_t *length, loff_t *ppos)
3260 {
3261         proc_doulongvec_minmax(table, write, buffer, length, ppos);
3262
3263         if (write && *(unsigned long *)table->data)
3264                 scan_all_zones_unevictable_pages();
3265
3266         scan_unevictable_pages = 0;
3267         return 0;
3268 }
3269
3270 #ifdef CONFIG_NUMA
3271 /*
3272  * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
3273  * a specified node's per zone unevictable lists for evictable pages.
3274  */
3275
3276 static ssize_t read_scan_unevictable_node(struct sys_device *dev,
3277                                           struct sysdev_attribute *attr,
3278                                           char *buf)
3279 {
3280         return sprintf(buf, "0\n");     /* always zero; should fit... */
3281 }
3282
3283 static ssize_t write_scan_unevictable_node(struct sys_device *dev,
3284                                            struct sysdev_attribute *attr,
3285                                         const char *buf, size_t count)
3286 {
3287         struct zone *node_zones = NODE_DATA(dev->id)->node_zones;
3288         struct zone *zone;
3289         unsigned long res;
3290         unsigned long req = strict_strtoul(buf, 10, &res);
3291
3292         if (!req)
3293                 return 1;       /* zero is no-op */
3294
3295         for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
3296                 if (!populated_zone(zone))
3297                         continue;
3298                 scan_zone_unevictable_pages(zone);
3299         }
3300         return 1;
3301 }
3302
3303
3304 static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3305                         read_scan_unevictable_node,
3306                         write_scan_unevictable_node);
3307
3308 int scan_unevictable_register_node(struct node *node)
3309 {
3310         return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages);
3311 }
3312
3313 void scan_unevictable_unregister_node(struct node *node)
3314 {
3315         sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages);
3316 }
3317 #endif