mm: compaction: ensure that the compaction free scanner does not move to the next...
[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 #include <linux/oom.h>
45 #include <linux/prefetch.h>
46
47 #include <asm/tlbflush.h>
48 #include <asm/div64.h>
49
50 #include <linux/swapops.h>
51
52 #include "internal.h"
53
54 #define CREATE_TRACE_POINTS
55 #include <trace/events/vmscan.h>
56
57 /*
58  * reclaim_mode determines how the inactive list is shrunk
59  * RECLAIM_MODE_SINGLE: Reclaim only order-0 pages
60  * RECLAIM_MODE_ASYNC:  Do not block
61  * RECLAIM_MODE_SYNC:   Allow blocking e.g. call wait_on_page_writeback
62  * RECLAIM_MODE_LUMPYRECLAIM: For high-order allocations, take a reference
63  *                      page from the LRU and reclaim all pages within a
64  *                      naturally aligned range
65  * RECLAIM_MODE_COMPACTION: For high-order allocations, reclaim a number of
66  *                      order-0 pages and then compact the zone
67  */
68 typedef unsigned __bitwise__ reclaim_mode_t;
69 #define RECLAIM_MODE_SINGLE             ((__force reclaim_mode_t)0x01u)
70 #define RECLAIM_MODE_ASYNC              ((__force reclaim_mode_t)0x02u)
71 #define RECLAIM_MODE_SYNC               ((__force reclaim_mode_t)0x04u)
72 #define RECLAIM_MODE_LUMPYRECLAIM       ((__force reclaim_mode_t)0x08u)
73 #define RECLAIM_MODE_COMPACTION         ((__force reclaim_mode_t)0x10u)
74
75 struct scan_control {
76         /* Incremented by the number of inactive pages that were scanned */
77         unsigned long nr_scanned;
78
79         /* Number of pages freed so far during a call to shrink_zones() */
80         unsigned long nr_reclaimed;
81
82         /* How many pages shrink_list() should reclaim */
83         unsigned long nr_to_reclaim;
84
85         unsigned long hibernation_mode;
86
87         /* This context's GFP mask */
88         gfp_t gfp_mask;
89
90         int may_writepage;
91
92         /* Can mapped pages be reclaimed? */
93         int may_unmap;
94
95         /* Can pages be swapped as part of reclaim? */
96         int may_swap;
97
98         int swappiness;
99
100         int order;
101
102         /*
103          * Intend to reclaim enough continuous memory rather than reclaim
104          * enough amount of memory. i.e, mode for high order allocation.
105          */
106         reclaim_mode_t reclaim_mode;
107
108         /* Which cgroup do we reclaim from */
109         struct mem_cgroup *mem_cgroup;
110
111         /*
112          * Nodemask of nodes allowed by the caller. If NULL, all nodes
113          * are scanned.
114          */
115         nodemask_t      *nodemask;
116 };
117
118 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
119
120 #ifdef ARCH_HAS_PREFETCH
121 #define prefetch_prev_lru_page(_page, _base, _field)                    \
122         do {                                                            \
123                 if ((_page)->lru.prev != _base) {                       \
124                         struct page *prev;                              \
125                                                                         \
126                         prev = lru_to_page(&(_page->lru));              \
127                         prefetch(&prev->_field);                        \
128                 }                                                       \
129         } while (0)
130 #else
131 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
132 #endif
133
134 #ifdef ARCH_HAS_PREFETCHW
135 #define prefetchw_prev_lru_page(_page, _base, _field)                   \
136         do {                                                            \
137                 if ((_page)->lru.prev != _base) {                       \
138                         struct page *prev;                              \
139                                                                         \
140                         prev = lru_to_page(&(_page->lru));              \
141                         prefetchw(&prev->_field);                       \
142                 }                                                       \
143         } while (0)
144 #else
145 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
146 #endif
147
148 /*
149  * From 0 .. 100.  Higher means more swappy.
150  */
151 int vm_swappiness = 60;
152 long vm_total_pages;    /* The total number of pages which the VM controls */
153
154 static LIST_HEAD(shrinker_list);
155 static DECLARE_RWSEM(shrinker_rwsem);
156
157 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
158 #define scanning_global_lru(sc) (!(sc)->mem_cgroup)
159 #else
160 #define scanning_global_lru(sc) (1)
161 #endif
162
163 static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
164                                                   struct scan_control *sc)
165 {
166         if (!scanning_global_lru(sc))
167                 return mem_cgroup_get_reclaim_stat(sc->mem_cgroup, zone);
168
169         return &zone->reclaim_stat;
170 }
171
172 static unsigned long zone_nr_lru_pages(struct zone *zone,
173                                 struct scan_control *sc, enum lru_list lru)
174 {
175         if (!scanning_global_lru(sc))
176                 return mem_cgroup_zone_nr_lru_pages(sc->mem_cgroup, zone, lru);
177
178         return zone_page_state(zone, NR_LRU_BASE + lru);
179 }
180
181
182 /*
183  * Add a shrinker callback to be called from the vm
184  */
185 void register_shrinker(struct shrinker *shrinker)
186 {
187         shrinker->nr = 0;
188         down_write(&shrinker_rwsem);
189         list_add_tail(&shrinker->list, &shrinker_list);
190         up_write(&shrinker_rwsem);
191 }
192 EXPORT_SYMBOL(register_shrinker);
193
194 /*
195  * Remove one
196  */
197 void unregister_shrinker(struct shrinker *shrinker)
198 {
199         down_write(&shrinker_rwsem);
200         list_del(&shrinker->list);
201         up_write(&shrinker_rwsem);
202 }
203 EXPORT_SYMBOL(unregister_shrinker);
204
205 static inline int do_shrinker_shrink(struct shrinker *shrinker,
206                                      struct shrink_control *sc,
207                                      unsigned long nr_to_scan)
208 {
209         sc->nr_to_scan = nr_to_scan;
210         return (*shrinker->shrink)(shrinker, sc);
211 }
212
213 #define SHRINK_BATCH 128
214 /*
215  * Call the shrink functions to age shrinkable caches
216  *
217  * Here we assume it costs one seek to replace a lru page and that it also
218  * takes a seek to recreate a cache object.  With this in mind we age equal
219  * percentages of the lru and ageable caches.  This should balance the seeks
220  * generated by these structures.
221  *
222  * If the vm encountered mapped pages on the LRU it increase the pressure on
223  * slab to avoid swapping.
224  *
225  * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
226  *
227  * `lru_pages' represents the number of on-LRU pages in all the zones which
228  * are eligible for the caller's allocation attempt.  It is used for balancing
229  * slab reclaim versus page reclaim.
230  *
231  * Returns the number of slab objects which we shrunk.
232  */
233 unsigned long shrink_slab(struct shrink_control *shrink,
234                           unsigned long nr_pages_scanned,
235                           unsigned long lru_pages)
236 {
237         struct shrinker *shrinker;
238         unsigned long ret = 0;
239
240         if (nr_pages_scanned == 0)
241                 nr_pages_scanned = SWAP_CLUSTER_MAX;
242
243         if (!down_read_trylock(&shrinker_rwsem)) {
244                 /* Assume we'll be able to shrink next time */
245                 ret = 1;
246                 goto out;
247         }
248
249         list_for_each_entry(shrinker, &shrinker_list, list) {
250                 unsigned long long delta;
251                 unsigned long total_scan;
252                 unsigned long max_pass;
253
254                 max_pass = do_shrinker_shrink(shrinker, shrink, 0);
255                 delta = (4 * nr_pages_scanned) / shrinker->seeks;
256                 delta *= max_pass;
257                 do_div(delta, lru_pages + 1);
258                 shrinker->nr += delta;
259                 if (shrinker->nr < 0) {
260                         printk(KERN_ERR "shrink_slab: %pF negative objects to "
261                                "delete nr=%ld\n",
262                                shrinker->shrink, shrinker->nr);
263                         shrinker->nr = max_pass;
264                 }
265
266                 /*
267                  * Avoid risking looping forever due to too large nr value:
268                  * never try to free more than twice the estimate number of
269                  * freeable entries.
270                  */
271                 if (shrinker->nr > max_pass * 2)
272                         shrinker->nr = max_pass * 2;
273
274                 total_scan = shrinker->nr;
275                 shrinker->nr = 0;
276
277                 while (total_scan >= SHRINK_BATCH) {
278                         long this_scan = SHRINK_BATCH;
279                         int shrink_ret;
280                         int nr_before;
281
282                         nr_before = do_shrinker_shrink(shrinker, shrink, 0);
283                         shrink_ret = do_shrinker_shrink(shrinker, shrink,
284                                                         this_scan);
285                         if (shrink_ret == -1)
286                                 break;
287                         if (shrink_ret < nr_before)
288                                 ret += nr_before - shrink_ret;
289                         count_vm_events(SLABS_SCANNED, this_scan);
290                         total_scan -= this_scan;
291
292                         cond_resched();
293                 }
294
295                 shrinker->nr += total_scan;
296         }
297         up_read(&shrinker_rwsem);
298 out:
299         cond_resched();
300         return ret;
301 }
302
303 static void set_reclaim_mode(int priority, struct scan_control *sc,
304                                    bool sync)
305 {
306         reclaim_mode_t syncmode = sync ? RECLAIM_MODE_SYNC : RECLAIM_MODE_ASYNC;
307
308         /*
309          * Initially assume we are entering either lumpy reclaim or
310          * reclaim/compaction.Depending on the order, we will either set the
311          * sync mode or just reclaim order-0 pages later.
312          */
313         if (COMPACTION_BUILD)
314                 sc->reclaim_mode = RECLAIM_MODE_COMPACTION;
315         else
316                 sc->reclaim_mode = RECLAIM_MODE_LUMPYRECLAIM;
317
318         /*
319          * Avoid using lumpy reclaim or reclaim/compaction if possible by
320          * restricting when its set to either costly allocations or when
321          * under memory pressure
322          */
323         if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
324                 sc->reclaim_mode |= syncmode;
325         else if (sc->order && priority < DEF_PRIORITY - 2)
326                 sc->reclaim_mode |= syncmode;
327         else
328                 sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
329 }
330
331 static void reset_reclaim_mode(struct scan_control *sc)
332 {
333         sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
334 }
335
336 static inline int is_page_cache_freeable(struct page *page)
337 {
338         /*
339          * A freeable page cache page is referenced only by the caller
340          * that isolated the page, the page cache radix tree and
341          * optional buffer heads at page->private.
342          */
343         return page_count(page) - page_has_private(page) == 2;
344 }
345
346 static int may_write_to_queue(struct backing_dev_info *bdi,
347                               struct scan_control *sc)
348 {
349         if (current->flags & PF_SWAPWRITE)
350                 return 1;
351         if (!bdi_write_congested(bdi))
352                 return 1;
353         if (bdi == current->backing_dev_info)
354                 return 1;
355
356         /* lumpy reclaim for hugepage often need a lot of write */
357         if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
358                 return 1;
359         return 0;
360 }
361
362 /*
363  * We detected a synchronous write error writing a page out.  Probably
364  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
365  * fsync(), msync() or close().
366  *
367  * The tricky part is that after writepage we cannot touch the mapping: nothing
368  * prevents it from being freed up.  But we have a ref on the page and once
369  * that page is locked, the mapping is pinned.
370  *
371  * We're allowed to run sleeping lock_page() here because we know the caller has
372  * __GFP_FS.
373  */
374 static void handle_write_error(struct address_space *mapping,
375                                 struct page *page, int error)
376 {
377         lock_page(page);
378         if (page_mapping(page) == mapping)
379                 mapping_set_error(mapping, error);
380         unlock_page(page);
381 }
382
383 /* possible outcome of pageout() */
384 typedef enum {
385         /* failed to write page out, page is locked */
386         PAGE_KEEP,
387         /* move page to the active list, page is locked */
388         PAGE_ACTIVATE,
389         /* page has been sent to the disk successfully, page is unlocked */
390         PAGE_SUCCESS,
391         /* page is clean and locked */
392         PAGE_CLEAN,
393 } pageout_t;
394
395 /*
396  * pageout is called by shrink_page_list() for each dirty page.
397  * Calls ->writepage().
398  */
399 static pageout_t pageout(struct page *page, struct address_space *mapping,
400                          struct scan_control *sc)
401 {
402         /*
403          * If the page is dirty, only perform writeback if that write
404          * will be non-blocking.  To prevent this allocation from being
405          * stalled by pagecache activity.  But note that there may be
406          * stalls if we need to run get_block().  We could test
407          * PagePrivate for that.
408          *
409          * If this process is currently in __generic_file_aio_write() against
410          * this page's queue, we can perform writeback even if that
411          * will block.
412          *
413          * If the page is swapcache, write it back even if that would
414          * block, for some throttling. This happens by accident, because
415          * swap_backing_dev_info is bust: it doesn't reflect the
416          * congestion state of the swapdevs.  Easy to fix, if needed.
417          */
418         if (!is_page_cache_freeable(page))
419                 return PAGE_KEEP;
420         if (!mapping) {
421                 /*
422                  * Some data journaling orphaned pages can have
423                  * page->mapping == NULL while being dirty with clean buffers.
424                  */
425                 if (page_has_private(page)) {
426                         if (try_to_free_buffers(page)) {
427                                 ClearPageDirty(page);
428                                 printk("%s: orphaned page\n", __func__);
429                                 return PAGE_CLEAN;
430                         }
431                 }
432                 return PAGE_KEEP;
433         }
434         if (mapping->a_ops->writepage == NULL)
435                 return PAGE_ACTIVATE;
436         if (!may_write_to_queue(mapping->backing_dev_info, sc))
437                 return PAGE_KEEP;
438
439         if (clear_page_dirty_for_io(page)) {
440                 int res;
441                 struct writeback_control wbc = {
442                         .sync_mode = WB_SYNC_NONE,
443                         .nr_to_write = SWAP_CLUSTER_MAX,
444                         .range_start = 0,
445                         .range_end = LLONG_MAX,
446                         .for_reclaim = 1,
447                 };
448
449                 SetPageReclaim(page);
450                 res = mapping->a_ops->writepage(page, &wbc);
451                 if (res < 0)
452                         handle_write_error(mapping, page, res);
453                 if (res == AOP_WRITEPAGE_ACTIVATE) {
454                         ClearPageReclaim(page);
455                         return PAGE_ACTIVATE;
456                 }
457
458                 /*
459                  * Wait on writeback if requested to. This happens when
460                  * direct reclaiming a large contiguous area and the
461                  * first attempt to free a range of pages fails.
462                  */
463                 if (PageWriteback(page) &&
464                     (sc->reclaim_mode & RECLAIM_MODE_SYNC))
465                         wait_on_page_writeback(page);
466
467                 if (!PageWriteback(page)) {
468                         /* synchronous write or broken a_ops? */
469                         ClearPageReclaim(page);
470                 }
471                 trace_mm_vmscan_writepage(page,
472                         trace_reclaim_flags(page, sc->reclaim_mode));
473                 inc_zone_page_state(page, NR_VMSCAN_WRITE);
474                 return PAGE_SUCCESS;
475         }
476
477         return PAGE_CLEAN;
478 }
479
480 /*
481  * Same as remove_mapping, but if the page is removed from the mapping, it
482  * gets returned with a refcount of 0.
483  */
484 static int __remove_mapping(struct address_space *mapping, struct page *page)
485 {
486         BUG_ON(!PageLocked(page));
487         BUG_ON(mapping != page_mapping(page));
488
489         spin_lock_irq(&mapping->tree_lock);
490         /*
491          * The non racy check for a busy page.
492          *
493          * Must be careful with the order of the tests. When someone has
494          * a ref to the page, it may be possible that they dirty it then
495          * drop the reference. So if PageDirty is tested before page_count
496          * here, then the following race may occur:
497          *
498          * get_user_pages(&page);
499          * [user mapping goes away]
500          * write_to(page);
501          *                              !PageDirty(page)    [good]
502          * SetPageDirty(page);
503          * put_page(page);
504          *                              !page_count(page)   [good, discard it]
505          *
506          * [oops, our write_to data is lost]
507          *
508          * Reversing the order of the tests ensures such a situation cannot
509          * escape unnoticed. The smp_rmb is needed to ensure the page->flags
510          * load is not satisfied before that of page->_count.
511          *
512          * Note that if SetPageDirty is always performed via set_page_dirty,
513          * and thus under tree_lock, then this ordering is not required.
514          */
515         if (!page_freeze_refs(page, 2))
516                 goto cannot_free;
517         /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
518         if (unlikely(PageDirty(page))) {
519                 page_unfreeze_refs(page, 2);
520                 goto cannot_free;
521         }
522
523         if (PageSwapCache(page)) {
524                 swp_entry_t swap = { .val = page_private(page) };
525                 __delete_from_swap_cache(page);
526                 spin_unlock_irq(&mapping->tree_lock);
527                 swapcache_free(swap, page);
528         } else {
529                 void (*freepage)(struct page *);
530
531                 freepage = mapping->a_ops->freepage;
532
533                 __delete_from_page_cache(page);
534                 spin_unlock_irq(&mapping->tree_lock);
535                 mem_cgroup_uncharge_cache_page(page);
536
537                 if (freepage != NULL)
538                         freepage(page);
539         }
540
541         return 1;
542
543 cannot_free:
544         spin_unlock_irq(&mapping->tree_lock);
545         return 0;
546 }
547
548 /*
549  * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
550  * someone else has a ref on the page, abort and return 0.  If it was
551  * successfully detached, return 1.  Assumes the caller has a single ref on
552  * this page.
553  */
554 int remove_mapping(struct address_space *mapping, struct page *page)
555 {
556         if (__remove_mapping(mapping, page)) {
557                 /*
558                  * Unfreezing the refcount with 1 rather than 2 effectively
559                  * drops the pagecache ref for us without requiring another
560                  * atomic operation.
561                  */
562                 page_unfreeze_refs(page, 1);
563                 return 1;
564         }
565         return 0;
566 }
567
568 /**
569  * putback_lru_page - put previously isolated page onto appropriate LRU list
570  * @page: page to be put back to appropriate lru list
571  *
572  * Add previously isolated @page to appropriate LRU list.
573  * Page may still be unevictable for other reasons.
574  *
575  * lru_lock must not be held, interrupts must be enabled.
576  */
577 void putback_lru_page(struct page *page)
578 {
579         int lru;
580         int active = !!TestClearPageActive(page);
581         int was_unevictable = PageUnevictable(page);
582
583         VM_BUG_ON(PageLRU(page));
584
585 redo:
586         ClearPageUnevictable(page);
587
588         if (page_evictable(page, NULL)) {
589                 /*
590                  * For evictable pages, we can use the cache.
591                  * In event of a race, worst case is we end up with an
592                  * unevictable page on [in]active list.
593                  * We know how to handle that.
594                  */
595                 lru = active + page_lru_base_type(page);
596                 lru_cache_add_lru(page, lru);
597         } else {
598                 /*
599                  * Put unevictable pages directly on zone's unevictable
600                  * list.
601                  */
602                 lru = LRU_UNEVICTABLE;
603                 add_page_to_unevictable_list(page);
604                 /*
605                  * When racing with an mlock clearing (page is
606                  * unlocked), make sure that if the other thread does
607                  * not observe our setting of PG_lru and fails
608                  * isolation, we see PG_mlocked cleared below and move
609                  * the page back to the evictable list.
610                  *
611                  * The other side is TestClearPageMlocked().
612                  */
613                 smp_mb();
614         }
615
616         /*
617          * page's status can change while we move it among lru. If an evictable
618          * page is on unevictable list, it never be freed. To avoid that,
619          * check after we added it to the list, again.
620          */
621         if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) {
622                 if (!isolate_lru_page(page)) {
623                         put_page(page);
624                         goto redo;
625                 }
626                 /* This means someone else dropped this page from LRU
627                  * So, it will be freed or putback to LRU again. There is
628                  * nothing to do here.
629                  */
630         }
631
632         if (was_unevictable && lru != LRU_UNEVICTABLE)
633                 count_vm_event(UNEVICTABLE_PGRESCUED);
634         else if (!was_unevictable && lru == LRU_UNEVICTABLE)
635                 count_vm_event(UNEVICTABLE_PGCULLED);
636
637         put_page(page);         /* drop ref from isolate */
638 }
639
640 enum page_references {
641         PAGEREF_RECLAIM,
642         PAGEREF_RECLAIM_CLEAN,
643         PAGEREF_KEEP,
644         PAGEREF_ACTIVATE,
645 };
646
647 static enum page_references page_check_references(struct page *page,
648                                                   struct scan_control *sc)
649 {
650         int referenced_ptes, referenced_page;
651         unsigned long vm_flags;
652
653         referenced_ptes = page_referenced(page, 1, sc->mem_cgroup, &vm_flags);
654         referenced_page = TestClearPageReferenced(page);
655
656         /* Lumpy reclaim - ignore references */
657         if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM)
658                 return PAGEREF_RECLAIM;
659
660         /*
661          * Mlock lost the isolation race with us.  Let try_to_unmap()
662          * move the page to the unevictable list.
663          */
664         if (vm_flags & VM_LOCKED)
665                 return PAGEREF_RECLAIM;
666
667         if (referenced_ptes) {
668                 if (PageAnon(page))
669                         return PAGEREF_ACTIVATE;
670                 /*
671                  * All mapped pages start out with page table
672                  * references from the instantiating fault, so we need
673                  * to look twice if a mapped file page is used more
674                  * than once.
675                  *
676                  * Mark it and spare it for another trip around the
677                  * inactive list.  Another page table reference will
678                  * lead to its activation.
679                  *
680                  * Note: the mark is set for activated pages as well
681                  * so that recently deactivated but used pages are
682                  * quickly recovered.
683                  */
684                 SetPageReferenced(page);
685
686                 if (referenced_page)
687                         return PAGEREF_ACTIVATE;
688
689                 return PAGEREF_KEEP;
690         }
691
692         /* Reclaim if clean, defer dirty pages to writeback */
693         if (referenced_page && !PageSwapBacked(page))
694                 return PAGEREF_RECLAIM_CLEAN;
695
696         return PAGEREF_RECLAIM;
697 }
698
699 static noinline_for_stack void free_page_list(struct list_head *free_pages)
700 {
701         struct pagevec freed_pvec;
702         struct page *page, *tmp;
703
704         pagevec_init(&freed_pvec, 1);
705
706         list_for_each_entry_safe(page, tmp, free_pages, lru) {
707                 list_del(&page->lru);
708                 if (!pagevec_add(&freed_pvec, page)) {
709                         __pagevec_free(&freed_pvec);
710                         pagevec_reinit(&freed_pvec);
711                 }
712         }
713
714         pagevec_free(&freed_pvec);
715 }
716
717 /*
718  * shrink_page_list() returns the number of reclaimed pages
719  */
720 static unsigned long shrink_page_list(struct list_head *page_list,
721                                       struct zone *zone,
722                                       struct scan_control *sc)
723 {
724         LIST_HEAD(ret_pages);
725         LIST_HEAD(free_pages);
726         int pgactivate = 0;
727         unsigned long nr_dirty = 0;
728         unsigned long nr_congested = 0;
729         unsigned long nr_reclaimed = 0;
730
731         cond_resched();
732
733         while (!list_empty(page_list)) {
734                 enum page_references references;
735                 struct address_space *mapping;
736                 struct page *page;
737                 int may_enter_fs;
738
739                 cond_resched();
740
741                 page = lru_to_page(page_list);
742                 list_del(&page->lru);
743
744                 if (!trylock_page(page))
745                         goto keep;
746
747                 VM_BUG_ON(PageActive(page));
748                 VM_BUG_ON(page_zone(page) != zone);
749
750                 sc->nr_scanned++;
751
752                 if (unlikely(!page_evictable(page, NULL)))
753                         goto cull_mlocked;
754
755                 if (!sc->may_unmap && page_mapped(page))
756                         goto keep_locked;
757
758                 /* Double the slab pressure for mapped and swapcache pages */
759                 if (page_mapped(page) || PageSwapCache(page))
760                         sc->nr_scanned++;
761
762                 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
763                         (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
764
765                 if (PageWriteback(page)) {
766                         /*
767                          * Synchronous reclaim is performed in two passes,
768                          * first an asynchronous pass over the list to
769                          * start parallel writeback, and a second synchronous
770                          * pass to wait for the IO to complete.  Wait here
771                          * for any page for which writeback has already
772                          * started.
773                          */
774                         if ((sc->reclaim_mode & RECLAIM_MODE_SYNC) &&
775                             may_enter_fs)
776                                 wait_on_page_writeback(page);
777                         else {
778                                 unlock_page(page);
779                                 goto keep_lumpy;
780                         }
781                 }
782
783                 references = page_check_references(page, sc);
784                 switch (references) {
785                 case PAGEREF_ACTIVATE:
786                         goto activate_locked;
787                 case PAGEREF_KEEP:
788                         goto keep_locked;
789                 case PAGEREF_RECLAIM:
790                 case PAGEREF_RECLAIM_CLEAN:
791                         ; /* try to reclaim the page below */
792                 }
793
794                 /*
795                  * Anonymous process memory has backing store?
796                  * Try to allocate it some swap space here.
797                  */
798                 if (PageAnon(page) && !PageSwapCache(page)) {
799                         if (!(sc->gfp_mask & __GFP_IO))
800                                 goto keep_locked;
801                         if (!add_to_swap(page))
802                                 goto activate_locked;
803                         may_enter_fs = 1;
804                 }
805
806                 mapping = page_mapping(page);
807
808                 /*
809                  * The page is mapped into the page tables of one or more
810                  * processes. Try to unmap it here.
811                  */
812                 if (page_mapped(page) && mapping) {
813                         switch (try_to_unmap(page, TTU_UNMAP)) {
814                         case SWAP_FAIL:
815                                 goto activate_locked;
816                         case SWAP_AGAIN:
817                                 goto keep_locked;
818                         case SWAP_MLOCK:
819                                 goto cull_mlocked;
820                         case SWAP_SUCCESS:
821                                 ; /* try to free the page below */
822                         }
823                 }
824
825                 if (PageDirty(page)) {
826                         nr_dirty++;
827
828                         if (references == PAGEREF_RECLAIM_CLEAN)
829                                 goto keep_locked;
830                         if (!may_enter_fs)
831                                 goto keep_locked;
832                         if (!sc->may_writepage)
833                                 goto keep_locked;
834
835                         /* Page is dirty, try to write it out here */
836                         switch (pageout(page, mapping, sc)) {
837                         case PAGE_KEEP:
838                                 nr_congested++;
839                                 goto keep_locked;
840                         case PAGE_ACTIVATE:
841                                 goto activate_locked;
842                         case PAGE_SUCCESS:
843                                 if (PageWriteback(page))
844                                         goto keep_lumpy;
845                                 if (PageDirty(page))
846                                         goto keep;
847
848                                 /*
849                                  * A synchronous write - probably a ramdisk.  Go
850                                  * ahead and try to reclaim the page.
851                                  */
852                                 if (!trylock_page(page))
853                                         goto keep;
854                                 if (PageDirty(page) || PageWriteback(page))
855                                         goto keep_locked;
856                                 mapping = page_mapping(page);
857                         case PAGE_CLEAN:
858                                 ; /* try to free the page below */
859                         }
860                 }
861
862                 /*
863                  * If the page has buffers, try to free the buffer mappings
864                  * associated with this page. If we succeed we try to free
865                  * the page as well.
866                  *
867                  * We do this even if the page is PageDirty().
868                  * try_to_release_page() does not perform I/O, but it is
869                  * possible for a page to have PageDirty set, but it is actually
870                  * clean (all its buffers are clean).  This happens if the
871                  * buffers were written out directly, with submit_bh(). ext3
872                  * will do this, as well as the blockdev mapping.
873                  * try_to_release_page() will discover that cleanness and will
874                  * drop the buffers and mark the page clean - it can be freed.
875                  *
876                  * Rarely, pages can have buffers and no ->mapping.  These are
877                  * the pages which were not successfully invalidated in
878                  * truncate_complete_page().  We try to drop those buffers here
879                  * and if that worked, and the page is no longer mapped into
880                  * process address space (page_count == 1) it can be freed.
881                  * Otherwise, leave the page on the LRU so it is swappable.
882                  */
883                 if (page_has_private(page)) {
884                         if (!try_to_release_page(page, sc->gfp_mask))
885                                 goto activate_locked;
886                         if (!mapping && page_count(page) == 1) {
887                                 unlock_page(page);
888                                 if (put_page_testzero(page))
889                                         goto free_it;
890                                 else {
891                                         /*
892                                          * rare race with speculative reference.
893                                          * the speculative reference will free
894                                          * this page shortly, so we may
895                                          * increment nr_reclaimed here (and
896                                          * leave it off the LRU).
897                                          */
898                                         nr_reclaimed++;
899                                         continue;
900                                 }
901                         }
902                 }
903
904                 if (!mapping || !__remove_mapping(mapping, page))
905                         goto keep_locked;
906
907                 /*
908                  * At this point, we have no other references and there is
909                  * no way to pick any more up (removed from LRU, removed
910                  * from pagecache). Can use non-atomic bitops now (and
911                  * we obviously don't have to worry about waking up a process
912                  * waiting on the page lock, because there are no references.
913                  */
914                 __clear_page_locked(page);
915 free_it:
916                 nr_reclaimed++;
917
918                 /*
919                  * Is there need to periodically free_page_list? It would
920                  * appear not as the counts should be low
921                  */
922                 list_add(&page->lru, &free_pages);
923                 continue;
924
925 cull_mlocked:
926                 if (PageSwapCache(page))
927                         try_to_free_swap(page);
928                 unlock_page(page);
929                 putback_lru_page(page);
930                 reset_reclaim_mode(sc);
931                 continue;
932
933 activate_locked:
934                 /* Not a candidate for swapping, so reclaim swap space. */
935                 if (PageSwapCache(page) && vm_swap_full())
936                         try_to_free_swap(page);
937                 VM_BUG_ON(PageActive(page));
938                 SetPageActive(page);
939                 pgactivate++;
940 keep_locked:
941                 unlock_page(page);
942 keep:
943                 reset_reclaim_mode(sc);
944 keep_lumpy:
945                 list_add(&page->lru, &ret_pages);
946                 VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
947         }
948
949         /*
950          * Tag a zone as congested if all the dirty pages encountered were
951          * backed by a congested BDI. In this case, reclaimers should just
952          * back off and wait for congestion to clear because further reclaim
953          * will encounter the same problem
954          */
955         if (nr_dirty && nr_dirty == nr_congested && scanning_global_lru(sc))
956                 zone_set_flag(zone, ZONE_CONGESTED);
957
958         free_page_list(&free_pages);
959
960         list_splice(&ret_pages, page_list);
961         count_vm_events(PGACTIVATE, pgactivate);
962         return nr_reclaimed;
963 }
964
965 /*
966  * Attempt to remove the specified page from its LRU.  Only take this page
967  * if it is of the appropriate PageActive status.  Pages which are being
968  * freed elsewhere are also ignored.
969  *
970  * page:        page to consider
971  * mode:        one of the LRU isolation modes defined above
972  *
973  * returns 0 on success, -ve errno on failure.
974  */
975 int __isolate_lru_page(struct page *page, int mode, int file)
976 {
977         int ret = -EINVAL;
978
979         /* Only take pages on the LRU. */
980         if (!PageLRU(page))
981                 return ret;
982
983         /*
984          * When checking the active state, we need to be sure we are
985          * dealing with comparible boolean values.  Take the logical not
986          * of each.
987          */
988         if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode))
989                 return ret;
990
991         if (mode != ISOLATE_BOTH && page_is_file_cache(page) != file)
992                 return ret;
993
994         /*
995          * When this function is being called for lumpy reclaim, we
996          * initially look into all LRU pages, active, inactive and
997          * unevictable; only give shrink_page_list evictable pages.
998          */
999         if (PageUnevictable(page))
1000                 return ret;
1001
1002         ret = -EBUSY;
1003
1004         if (likely(get_page_unless_zero(page))) {
1005                 /*
1006                  * Be careful not to clear PageLRU until after we're
1007                  * sure the page is not being freed elsewhere -- the
1008                  * page release code relies on it.
1009                  */
1010                 ClearPageLRU(page);
1011                 ret = 0;
1012         }
1013
1014         return ret;
1015 }
1016
1017 /*
1018  * zone->lru_lock is heavily contended.  Some of the functions that
1019  * shrink the lists perform better by taking out a batch of pages
1020  * and working on them outside the LRU lock.
1021  *
1022  * For pagecache intensive workloads, this function is the hottest
1023  * spot in the kernel (apart from copy_*_user functions).
1024  *
1025  * Appropriate locks must be held before calling this function.
1026  *
1027  * @nr_to_scan: The number of pages to look through on the list.
1028  * @src:        The LRU list to pull pages off.
1029  * @dst:        The temp list to put pages on to.
1030  * @scanned:    The number of pages that were scanned.
1031  * @order:      The caller's attempted allocation order
1032  * @mode:       One of the LRU isolation modes
1033  * @file:       True [1] if isolating file [!anon] pages
1034  *
1035  * returns how many pages were moved onto *@dst.
1036  */
1037 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1038                 struct list_head *src, struct list_head *dst,
1039                 unsigned long *scanned, int order, int mode, int file)
1040 {
1041         unsigned long nr_taken = 0;
1042         unsigned long nr_lumpy_taken = 0;
1043         unsigned long nr_lumpy_dirty = 0;
1044         unsigned long nr_lumpy_failed = 0;
1045         unsigned long scan;
1046
1047         for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1048                 struct page *page;
1049                 unsigned long pfn;
1050                 unsigned long end_pfn;
1051                 unsigned long page_pfn;
1052                 int zone_id;
1053
1054                 page = lru_to_page(src);
1055                 prefetchw_prev_lru_page(page, src, flags);
1056
1057                 VM_BUG_ON(!PageLRU(page));
1058
1059                 switch (__isolate_lru_page(page, mode, file)) {
1060                 case 0:
1061                         list_move(&page->lru, dst);
1062                         mem_cgroup_del_lru(page);
1063                         nr_taken += hpage_nr_pages(page);
1064                         break;
1065
1066                 case -EBUSY:
1067                         /* else it is being freed elsewhere */
1068                         list_move(&page->lru, src);
1069                         mem_cgroup_rotate_lru_list(page, page_lru(page));
1070                         continue;
1071
1072                 default:
1073                         BUG();
1074                 }
1075
1076                 if (!order)
1077                         continue;
1078
1079                 /*
1080                  * Attempt to take all pages in the order aligned region
1081                  * surrounding the tag page.  Only take those pages of
1082                  * the same active state as that tag page.  We may safely
1083                  * round the target page pfn down to the requested order
1084                  * as the mem_map is guaranteed valid out to MAX_ORDER,
1085                  * where that page is in a different zone we will detect
1086                  * it from its zone id and abort this block scan.
1087                  */
1088                 zone_id = page_zone_id(page);
1089                 page_pfn = page_to_pfn(page);
1090                 pfn = page_pfn & ~((1 << order) - 1);
1091                 end_pfn = pfn + (1 << order);
1092                 for (; pfn < end_pfn; pfn++) {
1093                         struct page *cursor_page;
1094
1095                         /* The target page is in the block, ignore it. */
1096                         if (unlikely(pfn == page_pfn))
1097                                 continue;
1098
1099                         /* Avoid holes within the zone. */
1100                         if (unlikely(!pfn_valid_within(pfn)))
1101                                 break;
1102
1103                         cursor_page = pfn_to_page(pfn);
1104
1105                         /* Check that we have not crossed a zone boundary. */
1106                         if (unlikely(page_zone_id(cursor_page) != zone_id))
1107                                 break;
1108
1109                         /*
1110                          * If we don't have enough swap space, reclaiming of
1111                          * anon page which don't already have a swap slot is
1112                          * pointless.
1113                          */
1114                         if (nr_swap_pages <= 0 && PageAnon(cursor_page) &&
1115                             !PageSwapCache(cursor_page))
1116                                 break;
1117
1118                         if (__isolate_lru_page(cursor_page, mode, file) == 0) {
1119                                 list_move(&cursor_page->lru, dst);
1120                                 mem_cgroup_del_lru(cursor_page);
1121                                 nr_taken += hpage_nr_pages(page);
1122                                 nr_lumpy_taken++;
1123                                 if (PageDirty(cursor_page))
1124                                         nr_lumpy_dirty++;
1125                                 scan++;
1126                         } else {
1127                                 /* the page is freed already. */
1128                                 if (!page_count(cursor_page))
1129                                         continue;
1130                                 break;
1131                         }
1132                 }
1133
1134                 /* If we break out of the loop above, lumpy reclaim failed */
1135                 if (pfn < end_pfn)
1136                         nr_lumpy_failed++;
1137         }
1138
1139         *scanned = scan;
1140
1141         trace_mm_vmscan_lru_isolate(order,
1142                         nr_to_scan, scan,
1143                         nr_taken,
1144                         nr_lumpy_taken, nr_lumpy_dirty, nr_lumpy_failed,
1145                         mode);
1146         return nr_taken;
1147 }
1148
1149 static unsigned long isolate_pages_global(unsigned long nr,
1150                                         struct list_head *dst,
1151                                         unsigned long *scanned, int order,
1152                                         int mode, struct zone *z,
1153                                         int active, int file)
1154 {
1155         int lru = LRU_BASE;
1156         if (active)
1157                 lru += LRU_ACTIVE;
1158         if (file)
1159                 lru += LRU_FILE;
1160         return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order,
1161                                                                 mode, file);
1162 }
1163
1164 /*
1165  * clear_active_flags() is a helper for shrink_active_list(), clearing
1166  * any active bits from the pages in the list.
1167  */
1168 static unsigned long clear_active_flags(struct list_head *page_list,
1169                                         unsigned int *count)
1170 {
1171         int nr_active = 0;
1172         int lru;
1173         struct page *page;
1174
1175         list_for_each_entry(page, page_list, lru) {
1176                 int numpages = hpage_nr_pages(page);
1177                 lru = page_lru_base_type(page);
1178                 if (PageActive(page)) {
1179                         lru += LRU_ACTIVE;
1180                         ClearPageActive(page);
1181                         nr_active += numpages;
1182                 }
1183                 if (count)
1184                         count[lru] += numpages;
1185         }
1186
1187         return nr_active;
1188 }
1189
1190 /**
1191  * isolate_lru_page - tries to isolate a page from its LRU list
1192  * @page: page to isolate from its LRU list
1193  *
1194  * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1195  * vmstat statistic corresponding to whatever LRU list the page was on.
1196  *
1197  * Returns 0 if the page was removed from an LRU list.
1198  * Returns -EBUSY if the page was not on an LRU list.
1199  *
1200  * The returned page will have PageLRU() cleared.  If it was found on
1201  * the active list, it will have PageActive set.  If it was found on
1202  * the unevictable list, it will have the PageUnevictable bit set. That flag
1203  * may need to be cleared by the caller before letting the page go.
1204  *
1205  * The vmstat statistic corresponding to the list on which the page was
1206  * found will be decremented.
1207  *
1208  * Restrictions:
1209  * (1) Must be called with an elevated refcount on the page. This is a
1210  *     fundamentnal difference from isolate_lru_pages (which is called
1211  *     without a stable reference).
1212  * (2) the lru_lock must not be held.
1213  * (3) interrupts must be enabled.
1214  */
1215 int isolate_lru_page(struct page *page)
1216 {
1217         int ret = -EBUSY;
1218
1219         VM_BUG_ON(!page_count(page));
1220
1221         if (PageLRU(page)) {
1222                 struct zone *zone = page_zone(page);
1223
1224                 spin_lock_irq(&zone->lru_lock);
1225                 if (PageLRU(page)) {
1226                         int lru = page_lru(page);
1227                         ret = 0;
1228                         get_page(page);
1229                         ClearPageLRU(page);
1230
1231                         del_page_from_lru_list(zone, page, lru);
1232                 }
1233                 spin_unlock_irq(&zone->lru_lock);
1234         }
1235         return ret;
1236 }
1237
1238 /*
1239  * Are there way too many processes in the direct reclaim path already?
1240  */
1241 static int too_many_isolated(struct zone *zone, int file,
1242                 struct scan_control *sc)
1243 {
1244         unsigned long inactive, isolated;
1245
1246         if (current_is_kswapd())
1247                 return 0;
1248
1249         if (!scanning_global_lru(sc))
1250                 return 0;
1251
1252         if (file) {
1253                 inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1254                 isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1255         } else {
1256                 inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1257                 isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1258         }
1259
1260         return isolated > inactive;
1261 }
1262
1263 /*
1264  * TODO: Try merging with migrations version of putback_lru_pages
1265  */
1266 static noinline_for_stack void
1267 putback_lru_pages(struct zone *zone, struct scan_control *sc,
1268                                 unsigned long nr_anon, unsigned long nr_file,
1269                                 struct list_head *page_list)
1270 {
1271         struct page *page;
1272         struct pagevec pvec;
1273         struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1274
1275         pagevec_init(&pvec, 1);
1276
1277         /*
1278          * Put back any unfreeable pages.
1279          */
1280         spin_lock(&zone->lru_lock);
1281         while (!list_empty(page_list)) {
1282                 int lru;
1283                 page = lru_to_page(page_list);
1284                 VM_BUG_ON(PageLRU(page));
1285                 list_del(&page->lru);
1286                 if (unlikely(!page_evictable(page, NULL))) {
1287                         spin_unlock_irq(&zone->lru_lock);
1288                         putback_lru_page(page);
1289                         spin_lock_irq(&zone->lru_lock);
1290                         continue;
1291                 }
1292                 SetPageLRU(page);
1293                 lru = page_lru(page);
1294                 add_page_to_lru_list(zone, page, lru);
1295                 if (is_active_lru(lru)) {
1296                         int file = is_file_lru(lru);
1297                         int numpages = hpage_nr_pages(page);
1298                         reclaim_stat->recent_rotated[file] += numpages;
1299                 }
1300                 if (!pagevec_add(&pvec, page)) {
1301                         spin_unlock_irq(&zone->lru_lock);
1302                         __pagevec_release(&pvec);
1303                         spin_lock_irq(&zone->lru_lock);
1304                 }
1305         }
1306         __mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon);
1307         __mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file);
1308
1309         spin_unlock_irq(&zone->lru_lock);
1310         pagevec_release(&pvec);
1311 }
1312
1313 static noinline_for_stack void update_isolated_counts(struct zone *zone,
1314                                         struct scan_control *sc,
1315                                         unsigned long *nr_anon,
1316                                         unsigned long *nr_file,
1317                                         struct list_head *isolated_list)
1318 {
1319         unsigned long nr_active;
1320         unsigned int count[NR_LRU_LISTS] = { 0, };
1321         struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1322
1323         nr_active = clear_active_flags(isolated_list, count);
1324         __count_vm_events(PGDEACTIVATE, nr_active);
1325
1326         __mod_zone_page_state(zone, NR_ACTIVE_FILE,
1327                               -count[LRU_ACTIVE_FILE]);
1328         __mod_zone_page_state(zone, NR_INACTIVE_FILE,
1329                               -count[LRU_INACTIVE_FILE]);
1330         __mod_zone_page_state(zone, NR_ACTIVE_ANON,
1331                               -count[LRU_ACTIVE_ANON]);
1332         __mod_zone_page_state(zone, NR_INACTIVE_ANON,
1333                               -count[LRU_INACTIVE_ANON]);
1334
1335         *nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
1336         *nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
1337         __mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon);
1338         __mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file);
1339
1340         reclaim_stat->recent_scanned[0] += *nr_anon;
1341         reclaim_stat->recent_scanned[1] += *nr_file;
1342 }
1343
1344 /*
1345  * Returns true if the caller should wait to clean dirty/writeback pages.
1346  *
1347  * If we are direct reclaiming for contiguous pages and we do not reclaim
1348  * everything in the list, try again and wait for writeback IO to complete.
1349  * This will stall high-order allocations noticeably. Only do that when really
1350  * need to free the pages under high memory pressure.
1351  */
1352 static inline bool should_reclaim_stall(unsigned long nr_taken,
1353                                         unsigned long nr_freed,
1354                                         int priority,
1355                                         struct scan_control *sc)
1356 {
1357         int lumpy_stall_priority;
1358
1359         /* kswapd should not stall on sync IO */
1360         if (current_is_kswapd())
1361                 return false;
1362
1363         /* Only stall on lumpy reclaim */
1364         if (sc->reclaim_mode & RECLAIM_MODE_SINGLE)
1365                 return false;
1366
1367         /* If we have relaimed everything on the isolated list, no stall */
1368         if (nr_freed == nr_taken)
1369                 return false;
1370
1371         /*
1372          * For high-order allocations, there are two stall thresholds.
1373          * High-cost allocations stall immediately where as lower
1374          * order allocations such as stacks require the scanning
1375          * priority to be much higher before stalling.
1376          */
1377         if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
1378                 lumpy_stall_priority = DEF_PRIORITY;
1379         else
1380                 lumpy_stall_priority = DEF_PRIORITY / 3;
1381
1382         return priority <= lumpy_stall_priority;
1383 }
1384
1385 /*
1386  * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
1387  * of reclaimed pages
1388  */
1389 static noinline_for_stack unsigned long
1390 shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
1391                         struct scan_control *sc, int priority, int file)
1392 {
1393         LIST_HEAD(page_list);
1394         unsigned long nr_scanned;
1395         unsigned long nr_reclaimed = 0;
1396         unsigned long nr_taken;
1397         unsigned long nr_anon;
1398         unsigned long nr_file;
1399
1400         while (unlikely(too_many_isolated(zone, file, sc))) {
1401                 congestion_wait(BLK_RW_ASYNC, HZ/10);
1402
1403                 /* We are about to die and free our memory. Return now. */
1404                 if (fatal_signal_pending(current))
1405                         return SWAP_CLUSTER_MAX;
1406         }
1407
1408         set_reclaim_mode(priority, sc, false);
1409         lru_add_drain();
1410         spin_lock_irq(&zone->lru_lock);
1411
1412         if (scanning_global_lru(sc)) {
1413                 nr_taken = isolate_pages_global(nr_to_scan,
1414                         &page_list, &nr_scanned, sc->order,
1415                         sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ?
1416                                         ISOLATE_BOTH : ISOLATE_INACTIVE,
1417                         zone, 0, file);
1418                 zone->pages_scanned += nr_scanned;
1419                 if (current_is_kswapd())
1420                         __count_zone_vm_events(PGSCAN_KSWAPD, zone,
1421                                                nr_scanned);
1422                 else
1423                         __count_zone_vm_events(PGSCAN_DIRECT, zone,
1424                                                nr_scanned);
1425         } else {
1426                 nr_taken = mem_cgroup_isolate_pages(nr_to_scan,
1427                         &page_list, &nr_scanned, sc->order,
1428                         sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ?
1429                                         ISOLATE_BOTH : ISOLATE_INACTIVE,
1430                         zone, sc->mem_cgroup,
1431                         0, file);
1432                 /*
1433                  * mem_cgroup_isolate_pages() keeps track of
1434                  * scanned pages on its own.
1435                  */
1436         }
1437
1438         if (nr_taken == 0) {
1439                 spin_unlock_irq(&zone->lru_lock);
1440                 return 0;
1441         }
1442
1443         update_isolated_counts(zone, sc, &nr_anon, &nr_file, &page_list);
1444
1445         spin_unlock_irq(&zone->lru_lock);
1446
1447         nr_reclaimed = shrink_page_list(&page_list, zone, sc);
1448
1449         /* Check if we should syncronously wait for writeback */
1450         if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) {
1451                 set_reclaim_mode(priority, sc, true);
1452                 nr_reclaimed += shrink_page_list(&page_list, zone, sc);
1453         }
1454
1455         local_irq_disable();
1456         if (current_is_kswapd())
1457                 __count_vm_events(KSWAPD_STEAL, nr_reclaimed);
1458         __count_zone_vm_events(PGSTEAL, zone, nr_reclaimed);
1459
1460         putback_lru_pages(zone, sc, nr_anon, nr_file, &page_list);
1461
1462         trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1463                 zone_idx(zone),
1464                 nr_scanned, nr_reclaimed,
1465                 priority,
1466                 trace_shrink_flags(file, sc->reclaim_mode));
1467         return nr_reclaimed;
1468 }
1469
1470 /*
1471  * This moves pages from the active list to the inactive list.
1472  *
1473  * We move them the other way if the page is referenced by one or more
1474  * processes, from rmap.
1475  *
1476  * If the pages are mostly unmapped, the processing is fast and it is
1477  * appropriate to hold zone->lru_lock across the whole operation.  But if
1478  * the pages are mapped, the processing is slow (page_referenced()) so we
1479  * should drop zone->lru_lock around each page.  It's impossible to balance
1480  * this, so instead we remove the pages from the LRU while processing them.
1481  * It is safe to rely on PG_active against the non-LRU pages in here because
1482  * nobody will play with that bit on a non-LRU page.
1483  *
1484  * The downside is that we have to touch page->_count against each page.
1485  * But we had to alter page->flags anyway.
1486  */
1487
1488 static void move_active_pages_to_lru(struct zone *zone,
1489                                      struct list_head *list,
1490                                      enum lru_list lru)
1491 {
1492         unsigned long pgmoved = 0;
1493         struct pagevec pvec;
1494         struct page *page;
1495
1496         pagevec_init(&pvec, 1);
1497
1498         while (!list_empty(list)) {
1499                 page = lru_to_page(list);
1500
1501                 VM_BUG_ON(PageLRU(page));
1502                 SetPageLRU(page);
1503
1504                 list_move(&page->lru, &zone->lru[lru].list);
1505                 mem_cgroup_add_lru_list(page, lru);
1506                 pgmoved += hpage_nr_pages(page);
1507
1508                 if (!pagevec_add(&pvec, page) || list_empty(list)) {
1509                         spin_unlock_irq(&zone->lru_lock);
1510                         if (buffer_heads_over_limit)
1511                                 pagevec_strip(&pvec);
1512                         __pagevec_release(&pvec);
1513                         spin_lock_irq(&zone->lru_lock);
1514                 }
1515         }
1516         __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1517         if (!is_active_lru(lru))
1518                 __count_vm_events(PGDEACTIVATE, pgmoved);
1519 }
1520
1521 static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
1522                         struct scan_control *sc, int priority, int file)
1523 {
1524         unsigned long nr_taken;
1525         unsigned long pgscanned;
1526         unsigned long vm_flags;
1527         LIST_HEAD(l_hold);      /* The pages which were snipped off */
1528         LIST_HEAD(l_active);
1529         LIST_HEAD(l_inactive);
1530         struct page *page;
1531         struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1532         unsigned long nr_rotated = 0;
1533
1534         lru_add_drain();
1535         spin_lock_irq(&zone->lru_lock);
1536         if (scanning_global_lru(sc)) {
1537                 nr_taken = isolate_pages_global(nr_pages, &l_hold,
1538                                                 &pgscanned, sc->order,
1539                                                 ISOLATE_ACTIVE, zone,
1540                                                 1, file);
1541                 zone->pages_scanned += pgscanned;
1542         } else {
1543                 nr_taken = mem_cgroup_isolate_pages(nr_pages, &l_hold,
1544                                                 &pgscanned, sc->order,
1545                                                 ISOLATE_ACTIVE, zone,
1546                                                 sc->mem_cgroup, 1, file);
1547                 /*
1548                  * mem_cgroup_isolate_pages() keeps track of
1549                  * scanned pages on its own.
1550                  */
1551         }
1552
1553         reclaim_stat->recent_scanned[file] += nr_taken;
1554
1555         __count_zone_vm_events(PGREFILL, zone, pgscanned);
1556         if (file)
1557                 __mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken);
1558         else
1559                 __mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken);
1560         __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1561         spin_unlock_irq(&zone->lru_lock);
1562
1563         while (!list_empty(&l_hold)) {
1564                 cond_resched();
1565                 page = lru_to_page(&l_hold);
1566                 list_del(&page->lru);
1567
1568                 if (unlikely(!page_evictable(page, NULL))) {
1569                         putback_lru_page(page);
1570                         continue;
1571                 }
1572
1573                 if (page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
1574                         nr_rotated += hpage_nr_pages(page);
1575                         /*
1576                          * Identify referenced, file-backed active pages and
1577                          * give them one more trip around the active list. So
1578                          * that executable code get better chances to stay in
1579                          * memory under moderate memory pressure.  Anon pages
1580                          * are not likely to be evicted by use-once streaming
1581                          * IO, plus JVM can create lots of anon VM_EXEC pages,
1582                          * so we ignore them here.
1583                          */
1584                         if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1585                                 list_add(&page->lru, &l_active);
1586                                 continue;
1587                         }
1588                 }
1589
1590                 ClearPageActive(page);  /* we are de-activating */
1591                 list_add(&page->lru, &l_inactive);
1592         }
1593
1594         /*
1595          * Move pages back to the lru list.
1596          */
1597         spin_lock_irq(&zone->lru_lock);
1598         /*
1599          * Count referenced pages from currently used mappings as rotated,
1600          * even though only some of them are actually re-activated.  This
1601          * helps balance scan pressure between file and anonymous pages in
1602          * get_scan_ratio.
1603          */
1604         reclaim_stat->recent_rotated[file] += nr_rotated;
1605
1606         move_active_pages_to_lru(zone, &l_active,
1607                                                 LRU_ACTIVE + file * LRU_FILE);
1608         move_active_pages_to_lru(zone, &l_inactive,
1609                                                 LRU_BASE   + file * LRU_FILE);
1610         __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1611         spin_unlock_irq(&zone->lru_lock);
1612 }
1613
1614 #ifdef CONFIG_SWAP
1615 static int inactive_anon_is_low_global(struct zone *zone)
1616 {
1617         unsigned long active, inactive;
1618
1619         active = zone_page_state(zone, NR_ACTIVE_ANON);
1620         inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1621
1622         if (inactive * zone->inactive_ratio < active)
1623                 return 1;
1624
1625         return 0;
1626 }
1627
1628 /**
1629  * inactive_anon_is_low - check if anonymous pages need to be deactivated
1630  * @zone: zone to check
1631  * @sc:   scan control of this context
1632  *
1633  * Returns true if the zone does not have enough inactive anon pages,
1634  * meaning some active anon pages need to be deactivated.
1635  */
1636 static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc)
1637 {
1638         int low;
1639
1640         /*
1641          * If we don't have swap space, anonymous page deactivation
1642          * is pointless.
1643          */
1644         if (!total_swap_pages)
1645                 return 0;
1646
1647         if (scanning_global_lru(sc))
1648                 low = inactive_anon_is_low_global(zone);
1649         else
1650                 low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup);
1651         return low;
1652 }
1653 #else
1654 static inline int inactive_anon_is_low(struct zone *zone,
1655                                         struct scan_control *sc)
1656 {
1657         return 0;
1658 }
1659 #endif
1660
1661 static int inactive_file_is_low_global(struct zone *zone)
1662 {
1663         unsigned long active, inactive;
1664
1665         active = zone_page_state(zone, NR_ACTIVE_FILE);
1666         inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1667
1668         return (active > inactive);
1669 }
1670
1671 /**
1672  * inactive_file_is_low - check if file pages need to be deactivated
1673  * @zone: zone to check
1674  * @sc:   scan control of this context
1675  *
1676  * When the system is doing streaming IO, memory pressure here
1677  * ensures that active file pages get deactivated, until more
1678  * than half of the file pages are on the inactive list.
1679  *
1680  * Once we get to that situation, protect the system's working
1681  * set from being evicted by disabling active file page aging.
1682  *
1683  * This uses a different ratio than the anonymous pages, because
1684  * the page cache uses a use-once replacement algorithm.
1685  */
1686 static int inactive_file_is_low(struct zone *zone, struct scan_control *sc)
1687 {
1688         int low;
1689
1690         if (scanning_global_lru(sc))
1691                 low = inactive_file_is_low_global(zone);
1692         else
1693                 low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup);
1694         return low;
1695 }
1696
1697 static int inactive_list_is_low(struct zone *zone, struct scan_control *sc,
1698                                 int file)
1699 {
1700         if (file)
1701                 return inactive_file_is_low(zone, sc);
1702         else
1703                 return inactive_anon_is_low(zone, sc);
1704 }
1705
1706 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1707         struct zone *zone, struct scan_control *sc, int priority)
1708 {
1709         int file = is_file_lru(lru);
1710
1711         if (is_active_lru(lru)) {
1712                 if (inactive_list_is_low(zone, sc, file))
1713                     shrink_active_list(nr_to_scan, zone, sc, priority, file);
1714                 return 0;
1715         }
1716
1717         return shrink_inactive_list(nr_to_scan, zone, sc, priority, file);
1718 }
1719
1720 /*
1721  * Determine how aggressively the anon and file LRU lists should be
1722  * scanned.  The relative value of each set of LRU lists is determined
1723  * by looking at the fraction of the pages scanned we did rotate back
1724  * onto the active list instead of evict.
1725  *
1726  * nr[0] = anon pages to scan; nr[1] = file pages to scan
1727  */
1728 static void get_scan_count(struct zone *zone, struct scan_control *sc,
1729                                         unsigned long *nr, int priority)
1730 {
1731         unsigned long anon, file, free;
1732         unsigned long anon_prio, file_prio;
1733         unsigned long ap, fp;
1734         struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1735         u64 fraction[2], denominator;
1736         enum lru_list l;
1737         int noswap = 0;
1738         int force_scan = 0;
1739
1740
1741         anon  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
1742                 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
1743         file  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
1744                 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
1745
1746         if (((anon + file) >> priority) < SWAP_CLUSTER_MAX) {
1747                 /* kswapd does zone balancing and need to scan this zone */
1748                 if (scanning_global_lru(sc) && current_is_kswapd())
1749                         force_scan = 1;
1750                 /* memcg may have small limit and need to avoid priority drop */
1751                 if (!scanning_global_lru(sc))
1752                         force_scan = 1;
1753         }
1754
1755         /* If we have no swap space, do not bother scanning anon pages. */
1756         if (!sc->may_swap || (nr_swap_pages <= 0)) {
1757                 noswap = 1;
1758                 fraction[0] = 0;
1759                 fraction[1] = 1;
1760                 denominator = 1;
1761                 goto out;
1762         }
1763
1764         if (scanning_global_lru(sc)) {
1765                 free  = zone_page_state(zone, NR_FREE_PAGES);
1766                 /* If we have very few page cache pages,
1767                    force-scan anon pages. */
1768                 if (unlikely(file + free <= high_wmark_pages(zone))) {
1769                         fraction[0] = 1;
1770                         fraction[1] = 0;
1771                         denominator = 1;
1772                         goto out;
1773                 }
1774         }
1775
1776         /*
1777          * With swappiness at 100, anonymous and file have the same priority.
1778          * This scanning priority is essentially the inverse of IO cost.
1779          */
1780         anon_prio = sc->swappiness;
1781         file_prio = 200 - sc->swappiness;
1782
1783         /*
1784          * OK, so we have swap space and a fair amount of page cache
1785          * pages.  We use the recently rotated / recently scanned
1786          * ratios to determine how valuable each cache is.
1787          *
1788          * Because workloads change over time (and to avoid overflow)
1789          * we keep these statistics as a floating average, which ends
1790          * up weighing recent references more than old ones.
1791          *
1792          * anon in [0], file in [1]
1793          */
1794         spin_lock_irq(&zone->lru_lock);
1795         if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1796                 reclaim_stat->recent_scanned[0] /= 2;
1797                 reclaim_stat->recent_rotated[0] /= 2;
1798         }
1799
1800         if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1801                 reclaim_stat->recent_scanned[1] /= 2;
1802                 reclaim_stat->recent_rotated[1] /= 2;
1803         }
1804
1805         /*
1806          * The amount of pressure on anon vs file pages is inversely
1807          * proportional to the fraction of recently scanned pages on
1808          * each list that were recently referenced and in active use.
1809          */
1810         ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1);
1811         ap /= reclaim_stat->recent_rotated[0] + 1;
1812
1813         fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
1814         fp /= reclaim_stat->recent_rotated[1] + 1;
1815         spin_unlock_irq(&zone->lru_lock);
1816
1817         fraction[0] = ap;
1818         fraction[1] = fp;
1819         denominator = ap + fp + 1;
1820 out:
1821         for_each_evictable_lru(l) {
1822                 int file = is_file_lru(l);
1823                 unsigned long scan;
1824
1825                 scan = zone_nr_lru_pages(zone, sc, l);
1826                 if (priority || noswap) {
1827                         scan >>= priority;
1828                         scan = div64_u64(scan * fraction[file], denominator);
1829                 }
1830
1831                 /*
1832                  * If zone is small or memcg is small, nr[l] can be 0.
1833                  * This results no-scan on this priority and priority drop down.
1834                  * For global direct reclaim, it can visit next zone and tend
1835                  * not to have problems. For global kswapd, it's for zone
1836                  * balancing and it need to scan a small amounts. When using
1837                  * memcg, priority drop can cause big latency. So, it's better
1838                  * to scan small amount. See may_noscan above.
1839                  */
1840                 if (!scan && force_scan) {
1841                         if (file)
1842                                 scan = SWAP_CLUSTER_MAX;
1843                         else if (!noswap)
1844                                 scan = SWAP_CLUSTER_MAX;
1845                 }
1846                 nr[l] = scan;
1847         }
1848 }
1849
1850 /*
1851  * Reclaim/compaction depends on a number of pages being freed. To avoid
1852  * disruption to the system, a small number of order-0 pages continue to be
1853  * rotated and reclaimed in the normal fashion. However, by the time we get
1854  * back to the allocator and call try_to_compact_zone(), we ensure that
1855  * there are enough free pages for it to be likely successful
1856  */
1857 static inline bool should_continue_reclaim(struct zone *zone,
1858                                         unsigned long nr_reclaimed,
1859                                         unsigned long nr_scanned,
1860                                         struct scan_control *sc)
1861 {
1862         unsigned long pages_for_compaction;
1863         unsigned long inactive_lru_pages;
1864
1865         /* If not in reclaim/compaction mode, stop */
1866         if (!(sc->reclaim_mode & RECLAIM_MODE_COMPACTION))
1867                 return false;
1868
1869         /* Consider stopping depending on scan and reclaim activity */
1870         if (sc->gfp_mask & __GFP_REPEAT) {
1871                 /*
1872                  * For __GFP_REPEAT allocations, stop reclaiming if the
1873                  * full LRU list has been scanned and we are still failing
1874                  * to reclaim pages. This full LRU scan is potentially
1875                  * expensive but a __GFP_REPEAT caller really wants to succeed
1876                  */
1877                 if (!nr_reclaimed && !nr_scanned)
1878                         return false;
1879         } else {
1880                 /*
1881                  * For non-__GFP_REPEAT allocations which can presumably
1882                  * fail without consequence, stop if we failed to reclaim
1883                  * any pages from the last SWAP_CLUSTER_MAX number of
1884                  * pages that were scanned. This will return to the
1885                  * caller faster at the risk reclaim/compaction and
1886                  * the resulting allocation attempt fails
1887                  */
1888                 if (!nr_reclaimed)
1889                         return false;
1890         }
1891
1892         /*
1893          * If we have not reclaimed enough pages for compaction and the
1894          * inactive lists are large enough, continue reclaiming
1895          */
1896         pages_for_compaction = (2UL << sc->order);
1897         inactive_lru_pages = zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON) +
1898                                 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
1899         if (sc->nr_reclaimed < pages_for_compaction &&
1900                         inactive_lru_pages > pages_for_compaction)
1901                 return true;
1902
1903         /* If compaction would go ahead or the allocation would succeed, stop */
1904         switch (compaction_suitable(zone, sc->order)) {
1905         case COMPACT_PARTIAL:
1906         case COMPACT_CONTINUE:
1907                 return false;
1908         default:
1909                 return true;
1910         }
1911 }
1912
1913 /*
1914  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1915  */
1916 static void shrink_zone(int priority, struct zone *zone,
1917                                 struct scan_control *sc)
1918 {
1919         unsigned long nr[NR_LRU_LISTS];
1920         unsigned long nr_to_scan;
1921         enum lru_list l;
1922         unsigned long nr_reclaimed, nr_scanned;
1923         unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1924
1925 restart:
1926         nr_reclaimed = 0;
1927         nr_scanned = sc->nr_scanned;
1928         get_scan_count(zone, sc, nr, priority);
1929
1930         while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1931                                         nr[LRU_INACTIVE_FILE]) {
1932                 for_each_evictable_lru(l) {
1933                         if (nr[l]) {
1934                                 nr_to_scan = min_t(unsigned long,
1935                                                    nr[l], SWAP_CLUSTER_MAX);
1936                                 nr[l] -= nr_to_scan;
1937
1938                                 nr_reclaimed += shrink_list(l, nr_to_scan,
1939                                                             zone, sc, priority);
1940                         }
1941                 }
1942                 /*
1943                  * On large memory systems, scan >> priority can become
1944                  * really large. This is fine for the starting priority;
1945                  * we want to put equal scanning pressure on each zone.
1946                  * However, if the VM has a harder time of freeing pages,
1947                  * with multiple processes reclaiming pages, the total
1948                  * freeing target can get unreasonably large.
1949                  */
1950                 if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)
1951                         break;
1952         }
1953         sc->nr_reclaimed += nr_reclaimed;
1954
1955         /*
1956          * Even if we did not try to evict anon pages at all, we want to
1957          * rebalance the anon lru active/inactive ratio.
1958          */
1959         if (inactive_anon_is_low(zone, sc))
1960                 shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);
1961
1962         /* reclaim/compaction might need reclaim to continue */
1963         if (should_continue_reclaim(zone, nr_reclaimed,
1964                                         sc->nr_scanned - nr_scanned, sc))
1965                 goto restart;
1966
1967         throttle_vm_writeout(sc->gfp_mask);
1968 }
1969
1970 /*
1971  * This is the direct reclaim path, for page-allocating processes.  We only
1972  * try to reclaim pages from zones which will satisfy the caller's allocation
1973  * request.
1974  *
1975  * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
1976  * Because:
1977  * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1978  *    allocation or
1979  * b) The target zone may be at high_wmark_pages(zone) but the lower zones
1980  *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
1981  *    zone defense algorithm.
1982  *
1983  * If a zone is deemed to be full of pinned pages then just give it a light
1984  * scan then give up on it.
1985  */
1986 static unsigned long shrink_zones(int priority, struct zonelist *zonelist,
1987                                         struct scan_control *sc)
1988 {
1989         struct zoneref *z;
1990         struct zone *zone;
1991         unsigned long nr_soft_reclaimed;
1992         unsigned long nr_soft_scanned;
1993         unsigned long total_scanned = 0;
1994
1995         for_each_zone_zonelist_nodemask(zone, z, zonelist,
1996                                         gfp_zone(sc->gfp_mask), sc->nodemask) {
1997                 if (!populated_zone(zone))
1998                         continue;
1999                 /*
2000                  * Take care memory controller reclaiming has small influence
2001                  * to global LRU.
2002                  */
2003                 if (scanning_global_lru(sc)) {
2004                         if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2005                                 continue;
2006                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2007                                 continue;       /* Let kswapd poll it */
2008                 }
2009
2010                 nr_soft_scanned = 0;
2011                 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2012                                                         sc->order, sc->gfp_mask,
2013                                                         &nr_soft_scanned);
2014                 sc->nr_reclaimed += nr_soft_reclaimed;
2015                 total_scanned += nr_soft_scanned;
2016
2017                 shrink_zone(priority, zone, sc);
2018         }
2019
2020         return total_scanned;
2021 }
2022
2023 static bool zone_reclaimable(struct zone *zone)
2024 {
2025         return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
2026 }
2027
2028 /* All zones in zonelist are unreclaimable? */
2029 static bool all_unreclaimable(struct zonelist *zonelist,
2030                 struct scan_control *sc)
2031 {
2032         struct zoneref *z;
2033         struct zone *zone;
2034
2035         for_each_zone_zonelist_nodemask(zone, z, zonelist,
2036                         gfp_zone(sc->gfp_mask), sc->nodemask) {
2037                 if (!populated_zone(zone))
2038                         continue;
2039                 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2040                         continue;
2041                 if (!zone->all_unreclaimable)
2042                         return false;
2043         }
2044
2045         return true;
2046 }
2047
2048 /*
2049  * This is the main entry point to direct page reclaim.
2050  *
2051  * If a full scan of the inactive list fails to free enough memory then we
2052  * are "out of memory" and something needs to be killed.
2053  *
2054  * If the caller is !__GFP_FS then the probability of a failure is reasonably
2055  * high - the zone may be full of dirty or under-writeback pages, which this
2056  * caller can't do much about.  We kick the writeback threads and take explicit
2057  * naps in the hope that some of these pages can be written.  But if the
2058  * allocating task holds filesystem locks which prevent writeout this might not
2059  * work, and the allocation attempt will fail.
2060  *
2061  * returns:     0, if no pages reclaimed
2062  *              else, the number of pages reclaimed
2063  */
2064 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2065                                         struct scan_control *sc,
2066                                         struct shrink_control *shrink)
2067 {
2068         int priority;
2069         unsigned long total_scanned = 0;
2070         struct reclaim_state *reclaim_state = current->reclaim_state;
2071         struct zoneref *z;
2072         struct zone *zone;
2073         unsigned long writeback_threshold;
2074
2075         get_mems_allowed();
2076         delayacct_freepages_start();
2077
2078         if (scanning_global_lru(sc))
2079                 count_vm_event(ALLOCSTALL);
2080
2081         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
2082                 sc->nr_scanned = 0;
2083                 if (!priority)
2084                         disable_swap_token(sc->mem_cgroup);
2085                 total_scanned += shrink_zones(priority, zonelist, sc);
2086                 /*
2087                  * Don't shrink slabs when reclaiming memory from
2088                  * over limit cgroups
2089                  */
2090                 if (scanning_global_lru(sc)) {
2091                         unsigned long lru_pages = 0;
2092                         for_each_zone_zonelist(zone, z, zonelist,
2093                                         gfp_zone(sc->gfp_mask)) {
2094                                 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2095                                         continue;
2096
2097                                 lru_pages += zone_reclaimable_pages(zone);
2098                         }
2099
2100                         shrink_slab(shrink, sc->nr_scanned, lru_pages);
2101                         if (reclaim_state) {
2102                                 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2103                                 reclaim_state->reclaimed_slab = 0;
2104                         }
2105                 }
2106                 total_scanned += sc->nr_scanned;
2107                 if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2108                         goto out;
2109
2110                 /*
2111                  * Try to write back as many pages as we just scanned.  This
2112                  * tends to cause slow streaming writers to write data to the
2113                  * disk smoothly, at the dirtying rate, which is nice.   But
2114                  * that's undesirable in laptop mode, where we *want* lumpy
2115                  * writeout.  So in laptop mode, write out the whole world.
2116                  */
2117                 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2118                 if (total_scanned > writeback_threshold) {
2119                         wakeup_flusher_threads(laptop_mode ? 0 : total_scanned);
2120                         sc->may_writepage = 1;
2121                 }
2122
2123                 /* Take a nap, wait for some writeback to complete */
2124                 if (!sc->hibernation_mode && sc->nr_scanned &&
2125                     priority < DEF_PRIORITY - 2) {
2126                         struct zone *preferred_zone;
2127
2128                         first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
2129                                                 &cpuset_current_mems_allowed,
2130                                                 &preferred_zone);
2131                         wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
2132                 }
2133         }
2134
2135 out:
2136         delayacct_freepages_end();
2137         put_mems_allowed();
2138
2139         if (sc->nr_reclaimed)
2140                 return sc->nr_reclaimed;
2141
2142         /*
2143          * As hibernation is going on, kswapd is freezed so that it can't mark
2144          * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2145          * check.
2146          */
2147         if (oom_killer_disabled)
2148                 return 0;
2149
2150         /* top priority shrink_zones still had more to do? don't OOM, then */
2151         if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc))
2152                 return 1;
2153
2154         return 0;
2155 }
2156
2157 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2158                                 gfp_t gfp_mask, nodemask_t *nodemask)
2159 {
2160         unsigned long nr_reclaimed;
2161         struct scan_control sc = {
2162                 .gfp_mask = gfp_mask,
2163                 .may_writepage = !laptop_mode,
2164                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2165                 .may_unmap = 1,
2166                 .may_swap = 1,
2167                 .swappiness = vm_swappiness,
2168                 .order = order,
2169                 .mem_cgroup = NULL,
2170                 .nodemask = nodemask,
2171         };
2172         struct shrink_control shrink = {
2173                 .gfp_mask = sc.gfp_mask,
2174         };
2175
2176         trace_mm_vmscan_direct_reclaim_begin(order,
2177                                 sc.may_writepage,
2178                                 gfp_mask);
2179
2180         nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2181
2182         trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2183
2184         return nr_reclaimed;
2185 }
2186
2187 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
2188
2189 unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
2190                                                 gfp_t gfp_mask, bool noswap,
2191                                                 unsigned int swappiness,
2192                                                 struct zone *zone,
2193                                                 unsigned long *nr_scanned)
2194 {
2195         struct scan_control sc = {
2196                 .nr_scanned = 0,
2197                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2198                 .may_writepage = !laptop_mode,
2199                 .may_unmap = 1,
2200                 .may_swap = !noswap,
2201                 .swappiness = swappiness,
2202                 .order = 0,
2203                 .mem_cgroup = mem,
2204         };
2205
2206         sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2207                         (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2208
2209         trace_mm_vmscan_memcg_softlimit_reclaim_begin(0,
2210                                                       sc.may_writepage,
2211                                                       sc.gfp_mask);
2212
2213         /*
2214          * NOTE: Although we can get the priority field, using it
2215          * here is not a good idea, since it limits the pages we can scan.
2216          * if we don't reclaim here, the shrink_zone from balance_pgdat
2217          * will pick up pages from other mem cgroup's as well. We hack
2218          * the priority and make it zero.
2219          */
2220         shrink_zone(0, zone, &sc);
2221
2222         trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2223
2224         *nr_scanned = sc.nr_scanned;
2225         return sc.nr_reclaimed;
2226 }
2227
2228 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
2229                                            gfp_t gfp_mask,
2230                                            bool noswap,
2231                                            unsigned int swappiness)
2232 {
2233         struct zonelist *zonelist;
2234         unsigned long nr_reclaimed;
2235         int nid;
2236         struct scan_control sc = {
2237                 .may_writepage = !laptop_mode,
2238                 .may_unmap = 1,
2239                 .may_swap = !noswap,
2240                 .nr_to_reclaim = SWAP_CLUSTER_MAX,
2241                 .swappiness = swappiness,
2242                 .order = 0,
2243                 .mem_cgroup = mem_cont,
2244                 .nodemask = NULL, /* we don't care the placement */
2245                 .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2246                                 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2247         };
2248         struct shrink_control shrink = {
2249                 .gfp_mask = sc.gfp_mask,
2250         };
2251
2252         /*
2253          * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2254          * take care of from where we get pages. So the node where we start the
2255          * scan does not need to be the current node.
2256          */
2257         nid = mem_cgroup_select_victim_node(mem_cont);
2258
2259         zonelist = NODE_DATA(nid)->node_zonelists;
2260
2261         trace_mm_vmscan_memcg_reclaim_begin(0,
2262                                             sc.may_writepage,
2263                                             sc.gfp_mask);
2264
2265         nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2266
2267         trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2268
2269         return nr_reclaimed;
2270 }
2271 #endif
2272
2273 /*
2274  * pgdat_balanced is used when checking if a node is balanced for high-order
2275  * allocations. Only zones that meet watermarks and are in a zone allowed
2276  * by the callers classzone_idx are added to balanced_pages. The total of
2277  * balanced pages must be at least 25% of the zones allowed by classzone_idx
2278  * for the node to be considered balanced. Forcing all zones to be balanced
2279  * for high orders can cause excessive reclaim when there are imbalanced zones.
2280  * The choice of 25% is due to
2281  *   o a 16M DMA zone that is balanced will not balance a zone on any
2282  *     reasonable sized machine
2283  *   o On all other machines, the top zone must be at least a reasonable
2284  *     percentage of the middle zones. For example, on 32-bit x86, highmem
2285  *     would need to be at least 256M for it to be balance a whole node.
2286  *     Similarly, on x86-64 the Normal zone would need to be at least 1G
2287  *     to balance a node on its own. These seemed like reasonable ratios.
2288  */
2289 static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
2290                                                 int classzone_idx)
2291 {
2292         unsigned long present_pages = 0;
2293         int i;
2294
2295         for (i = 0; i <= classzone_idx; i++)
2296                 present_pages += pgdat->node_zones[i].present_pages;
2297
2298         return balanced_pages > (present_pages >> 2);
2299 }
2300
2301 /* is kswapd sleeping prematurely? */
2302 static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
2303                                         int classzone_idx)
2304 {
2305         int i;
2306         unsigned long balanced = 0;
2307         bool all_zones_ok = true;
2308
2309         /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2310         if (remaining)
2311                 return true;
2312
2313         /* Check the watermark levels */
2314         for (i = 0; i < pgdat->nr_zones; i++) {
2315                 struct zone *zone = pgdat->node_zones + i;
2316
2317                 if (!populated_zone(zone))
2318                         continue;
2319
2320                 /*
2321                  * balance_pgdat() skips over all_unreclaimable after
2322                  * DEF_PRIORITY. Effectively, it considers them balanced so
2323                  * they must be considered balanced here as well if kswapd
2324                  * is to sleep
2325                  */
2326                 if (zone->all_unreclaimable) {
2327                         balanced += zone->present_pages;
2328                         continue;
2329                 }
2330
2331                 if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
2332                                                         classzone_idx, 0))
2333                         all_zones_ok = false;
2334                 else
2335                         balanced += zone->present_pages;
2336         }
2337
2338         /*
2339          * For high-order requests, the balanced zones must contain at least
2340          * 25% of the nodes pages for kswapd to sleep. For order-0, all zones
2341          * must be balanced
2342          */
2343         if (order)
2344                 return !pgdat_balanced(pgdat, balanced, classzone_idx);
2345         else
2346                 return !all_zones_ok;
2347 }
2348
2349 /*
2350  * For kswapd, balance_pgdat() will work across all this node's zones until
2351  * they are all at high_wmark_pages(zone).
2352  *
2353  * Returns the final order kswapd was reclaiming at
2354  *
2355  * There is special handling here for zones which are full of pinned pages.
2356  * This can happen if the pages are all mlocked, or if they are all used by
2357  * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
2358  * What we do is to detect the case where all pages in the zone have been
2359  * scanned twice and there has been zero successful reclaim.  Mark the zone as
2360  * dead and from now on, only perform a short scan.  Basically we're polling
2361  * the zone for when the problem goes away.
2362  *
2363  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
2364  * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2365  * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2366  * lower zones regardless of the number of free pages in the lower zones. This
2367  * interoperates with the page allocator fallback scheme to ensure that aging
2368  * of pages is balanced across the zones.
2369  */
2370 static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2371                                                         int *classzone_idx)
2372 {
2373         int all_zones_ok;
2374         unsigned long balanced;
2375         int priority;
2376         int i;
2377         int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
2378         unsigned long total_scanned;
2379         struct reclaim_state *reclaim_state = current->reclaim_state;
2380         unsigned long nr_soft_reclaimed;
2381         unsigned long nr_soft_scanned;
2382         struct scan_control sc = {
2383                 .gfp_mask = GFP_KERNEL,
2384                 .may_unmap = 1,
2385                 .may_swap = 1,
2386                 /*
2387                  * kswapd doesn't want to be bailed out while reclaim. because
2388                  * we want to put equal scanning pressure on each zone.
2389                  */
2390                 .nr_to_reclaim = ULONG_MAX,
2391                 .swappiness = vm_swappiness,
2392                 .order = order,
2393                 .mem_cgroup = NULL,
2394         };
2395         struct shrink_control shrink = {
2396                 .gfp_mask = sc.gfp_mask,
2397         };
2398 loop_again:
2399         total_scanned = 0;
2400         sc.nr_reclaimed = 0;
2401         sc.may_writepage = !laptop_mode;
2402         count_vm_event(PAGEOUTRUN);
2403
2404         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
2405                 unsigned long lru_pages = 0;
2406                 int has_under_min_watermark_zone = 0;
2407
2408                 /* The swap token gets in the way of swapout... */
2409                 if (!priority)
2410                         disable_swap_token(NULL);
2411
2412                 all_zones_ok = 1;
2413                 balanced = 0;
2414
2415                 /*
2416                  * Scan in the highmem->dma direction for the highest
2417                  * zone which needs scanning
2418                  */
2419                 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2420                         struct zone *zone = pgdat->node_zones + i;
2421
2422                         if (!populated_zone(zone))
2423                                 continue;
2424
2425                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2426                                 continue;
2427
2428                         /*
2429                          * Do some background aging of the anon list, to give
2430                          * pages a chance to be referenced before reclaiming.
2431                          */
2432                         if (inactive_anon_is_low(zone, &sc))
2433                                 shrink_active_list(SWAP_CLUSTER_MAX, zone,
2434                                                         &sc, priority, 0);
2435
2436                         if (!zone_watermark_ok_safe(zone, order,
2437                                         high_wmark_pages(zone), 0, 0)) {
2438                                 end_zone = i;
2439                                 *classzone_idx = i;
2440                                 break;
2441                         }
2442                 }
2443                 if (i < 0)
2444                         goto out;
2445
2446                 for (i = 0; i <= end_zone; i++) {
2447                         struct zone *zone = pgdat->node_zones + i;
2448
2449                         lru_pages += zone_reclaimable_pages(zone);
2450                 }
2451
2452                 /*
2453                  * Now scan the zone in the dma->highmem direction, stopping
2454                  * at the last zone which needs scanning.
2455                  *
2456                  * We do this because the page allocator works in the opposite
2457                  * direction.  This prevents the page allocator from allocating
2458                  * pages behind kswapd's direction of progress, which would
2459                  * cause too much scanning of the lower zones.
2460                  */
2461                 for (i = 0; i <= end_zone; i++) {
2462                         struct zone *zone = pgdat->node_zones + i;
2463                         int nr_slab;
2464                         unsigned long balance_gap;
2465
2466                         if (!populated_zone(zone))
2467                                 continue;
2468
2469                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2470                                 continue;
2471
2472                         sc.nr_scanned = 0;
2473
2474                         nr_soft_scanned = 0;
2475                         /*
2476                          * Call soft limit reclaim before calling shrink_zone.
2477                          */
2478                         nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2479                                                         order, sc.gfp_mask,
2480                                                         &nr_soft_scanned);
2481                         sc.nr_reclaimed += nr_soft_reclaimed;
2482                         total_scanned += nr_soft_scanned;
2483
2484                         /*
2485                          * We put equal pressure on every zone, unless
2486                          * one zone has way too many pages free
2487                          * already. The "too many pages" is defined
2488                          * as the high wmark plus a "gap" where the
2489                          * gap is either the low watermark or 1%
2490                          * of the zone, whichever is smaller.
2491                          */
2492                         balance_gap = min(low_wmark_pages(zone),
2493                                 (zone->present_pages +
2494                                         KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2495                                 KSWAPD_ZONE_BALANCE_GAP_RATIO);
2496                         if (!zone_watermark_ok_safe(zone, order,
2497                                         high_wmark_pages(zone) + balance_gap,
2498                                         end_zone, 0))
2499                                 shrink_zone(priority, zone, &sc);
2500                         reclaim_state->reclaimed_slab = 0;
2501                         nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages);
2502                         sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2503                         total_scanned += sc.nr_scanned;
2504
2505                         if (zone->all_unreclaimable)
2506                                 continue;
2507                         if (nr_slab == 0 &&
2508                             !zone_reclaimable(zone))
2509                                 zone->all_unreclaimable = 1;
2510                         /*
2511                          * If we've done a decent amount of scanning and
2512                          * the reclaim ratio is low, start doing writepage
2513                          * even in laptop mode
2514                          */
2515                         if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2516                             total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
2517                                 sc.may_writepage = 1;
2518
2519                         if (!zone_watermark_ok_safe(zone, order,
2520                                         high_wmark_pages(zone), end_zone, 0)) {
2521                                 all_zones_ok = 0;
2522                                 /*
2523                                  * We are still under min water mark.  This
2524                                  * means that we have a GFP_ATOMIC allocation
2525                                  * failure risk. Hurry up!
2526                                  */
2527                                 if (!zone_watermark_ok_safe(zone, order,
2528                                             min_wmark_pages(zone), end_zone, 0))
2529                                         has_under_min_watermark_zone = 1;
2530                         } else {
2531                                 /*
2532                                  * If a zone reaches its high watermark,
2533                                  * consider it to be no longer congested. It's
2534                                  * possible there are dirty pages backed by
2535                                  * congested BDIs but as pressure is relieved,
2536                                  * spectulatively avoid congestion waits
2537                                  */
2538                                 zone_clear_flag(zone, ZONE_CONGESTED);
2539                                 if (i <= *classzone_idx)
2540                                         balanced += zone->present_pages;
2541                         }
2542
2543                 }
2544                 if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
2545                         break;          /* kswapd: all done */
2546                 /*
2547                  * OK, kswapd is getting into trouble.  Take a nap, then take
2548                  * another pass across the zones.
2549                  */
2550                 if (total_scanned && (priority < DEF_PRIORITY - 2)) {
2551                         if (has_under_min_watermark_zone)
2552                                 count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
2553                         else
2554                                 congestion_wait(BLK_RW_ASYNC, HZ/10);
2555                 }
2556
2557                 /*
2558                  * We do this so kswapd doesn't build up large priorities for
2559                  * example when it is freeing in parallel with allocators. It
2560                  * matches the direct reclaim path behaviour in terms of impact
2561                  * on zone->*_priority.
2562                  */
2563                 if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2564                         break;
2565         }
2566 out:
2567
2568         /*
2569          * order-0: All zones must meet high watermark for a balanced node
2570          * high-order: Balanced zones must make up at least 25% of the node
2571          *             for the node to be balanced
2572          */
2573         if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) {
2574                 cond_resched();
2575
2576                 try_to_freeze();
2577
2578                 /*
2579                  * Fragmentation may mean that the system cannot be
2580                  * rebalanced for high-order allocations in all zones.
2581                  * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2582                  * it means the zones have been fully scanned and are still
2583                  * not balanced. For high-order allocations, there is
2584                  * little point trying all over again as kswapd may
2585                  * infinite loop.
2586                  *
2587                  * Instead, recheck all watermarks at order-0 as they
2588                  * are the most important. If watermarks are ok, kswapd will go
2589                  * back to sleep. High-order users can still perform direct
2590                  * reclaim if they wish.
2591                  */
2592                 if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2593                         order = sc.order = 0;
2594
2595                 goto loop_again;
2596         }
2597
2598         /*
2599          * If kswapd was reclaiming at a higher order, it has the option of
2600          * sleeping without all zones being balanced. Before it does, it must
2601          * ensure that the watermarks for order-0 on *all* zones are met and
2602          * that the congestion flags are cleared. The congestion flag must
2603          * be cleared as kswapd is the only mechanism that clears the flag
2604          * and it is potentially going to sleep here.
2605          */
2606         if (order) {
2607                 for (i = 0; i <= end_zone; i++) {
2608                         struct zone *zone = pgdat->node_zones + i;
2609
2610                         if (!populated_zone(zone))
2611                                 continue;
2612
2613                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2614                                 continue;
2615
2616                         /* Confirm the zone is balanced for order-0 */
2617                         if (!zone_watermark_ok(zone, 0,
2618                                         high_wmark_pages(zone), 0, 0)) {
2619                                 order = sc.order = 0;
2620                                 goto loop_again;
2621                         }
2622
2623                         /* If balanced, clear the congested flag */
2624                         zone_clear_flag(zone, ZONE_CONGESTED);
2625                 }
2626         }
2627
2628         /*
2629          * Return the order we were reclaiming at so sleeping_prematurely()
2630          * makes a decision on the order we were last reclaiming at. However,
2631          * if another caller entered the allocator slow path while kswapd
2632          * was awake, order will remain at the higher level
2633          */
2634         *classzone_idx = end_zone;
2635         return order;
2636 }
2637
2638 static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
2639 {
2640         long remaining = 0;
2641         DEFINE_WAIT(wait);
2642
2643         if (freezing(current) || kthread_should_stop())
2644                 return;
2645
2646         prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2647
2648         /* Try to sleep for a short interval */
2649         if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
2650                 remaining = schedule_timeout(HZ/10);
2651                 finish_wait(&pgdat->kswapd_wait, &wait);
2652                 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2653         }
2654
2655         /*
2656          * After a short sleep, check if it was a premature sleep. If not, then
2657          * go fully to sleep until explicitly woken up.
2658          */
2659         if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
2660                 trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
2661
2662                 /*
2663                  * vmstat counters are not perfectly accurate and the estimated
2664                  * value for counters such as NR_FREE_PAGES can deviate from the
2665                  * true value by nr_online_cpus * threshold. To avoid the zone
2666                  * watermarks being breached while under pressure, we reduce the
2667                  * per-cpu vmstat threshold while kswapd is awake and restore
2668                  * them before going back to sleep.
2669                  */
2670                 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
2671                 schedule();
2672                 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
2673         } else {
2674                 if (remaining)
2675                         count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2676                 else
2677                         count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2678         }
2679         finish_wait(&pgdat->kswapd_wait, &wait);
2680 }
2681
2682 /*
2683  * The background pageout daemon, started as a kernel thread
2684  * from the init process.
2685  *
2686  * This basically trickles out pages so that we have _some_
2687  * free memory available even if there is no other activity
2688  * that frees anything up. This is needed for things like routing
2689  * etc, where we otherwise might have all activity going on in
2690  * asynchronous contexts that cannot page things out.
2691  *
2692  * If there are applications that are active memory-allocators
2693  * (most normal use), this basically shouldn't matter.
2694  */
2695 static int kswapd(void *p)
2696 {
2697         unsigned long order;
2698         int classzone_idx;
2699         pg_data_t *pgdat = (pg_data_t*)p;
2700         struct task_struct *tsk = current;
2701
2702         struct reclaim_state reclaim_state = {
2703                 .reclaimed_slab = 0,
2704         };
2705         const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2706
2707         lockdep_set_current_reclaim_state(GFP_KERNEL);
2708
2709         if (!cpumask_empty(cpumask))
2710                 set_cpus_allowed_ptr(tsk, cpumask);
2711         current->reclaim_state = &reclaim_state;
2712
2713         /*
2714          * Tell the memory management that we're a "memory allocator",
2715          * and that if we need more memory we should get access to it
2716          * regardless (see "__alloc_pages()"). "kswapd" should
2717          * never get caught in the normal page freeing logic.
2718          *
2719          * (Kswapd normally doesn't need memory anyway, but sometimes
2720          * you need a small amount of memory in order to be able to
2721          * page out something else, and this flag essentially protects
2722          * us from recursively trying to free more memory as we're
2723          * trying to free the first piece of memory in the first place).
2724          */
2725         tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2726         set_freezable();
2727
2728         order = 0;
2729         classzone_idx = MAX_NR_ZONES - 1;
2730         for ( ; ; ) {
2731                 unsigned long new_order;
2732                 int new_classzone_idx;
2733                 int ret;
2734
2735                 new_order = pgdat->kswapd_max_order;
2736                 new_classzone_idx = pgdat->classzone_idx;
2737                 pgdat->kswapd_max_order = 0;
2738                 pgdat->classzone_idx = MAX_NR_ZONES - 1;
2739                 if (order < new_order || classzone_idx > new_classzone_idx) {
2740                         /*
2741                          * Don't sleep if someone wants a larger 'order'
2742                          * allocation or has tigher zone constraints
2743                          */
2744                         order = new_order;
2745                         classzone_idx = new_classzone_idx;
2746                 } else {
2747                         kswapd_try_to_sleep(pgdat, order, classzone_idx);
2748                         order = pgdat->kswapd_max_order;
2749                         classzone_idx = pgdat->classzone_idx;
2750                         pgdat->kswapd_max_order = 0;
2751                         pgdat->classzone_idx = MAX_NR_ZONES - 1;
2752                 }
2753
2754                 ret = try_to_freeze();
2755                 if (kthread_should_stop())
2756                         break;
2757
2758                 /*
2759                  * We can speed up thawing tasks if we don't call balance_pgdat
2760                  * after returning from the refrigerator
2761                  */
2762                 if (!ret) {
2763                         trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
2764                         order = balance_pgdat(pgdat, order, &classzone_idx);
2765                 }
2766         }
2767         return 0;
2768 }
2769
2770 /*
2771  * A zone is low on free memory, so wake its kswapd task to service it.
2772  */
2773 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
2774 {
2775         pg_data_t *pgdat;
2776
2777         if (!populated_zone(zone))
2778                 return;
2779
2780         if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2781                 return;
2782         pgdat = zone->zone_pgdat;
2783         if (pgdat->kswapd_max_order < order) {
2784                 pgdat->kswapd_max_order = order;
2785                 pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
2786         }
2787         if (!waitqueue_active(&pgdat->kswapd_wait))
2788                 return;
2789         if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
2790                 return;
2791
2792         trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
2793         wake_up_interruptible(&pgdat->kswapd_wait);
2794 }
2795
2796 /*
2797  * The reclaimable count would be mostly accurate.
2798  * The less reclaimable pages may be
2799  * - mlocked pages, which will be moved to unevictable list when encountered
2800  * - mapped pages, which may require several travels to be reclaimed
2801  * - dirty pages, which is not "instantly" reclaimable
2802  */
2803 unsigned long global_reclaimable_pages(void)
2804 {
2805         int nr;
2806
2807         nr = global_page_state(NR_ACTIVE_FILE) +
2808              global_page_state(NR_INACTIVE_FILE);
2809
2810         if (nr_swap_pages > 0)
2811                 nr += global_page_state(NR_ACTIVE_ANON) +
2812                       global_page_state(NR_INACTIVE_ANON);
2813
2814         return nr;
2815 }
2816
2817 unsigned long zone_reclaimable_pages(struct zone *zone)
2818 {
2819         int nr;
2820
2821         nr = zone_page_state(zone, NR_ACTIVE_FILE) +
2822              zone_page_state(zone, NR_INACTIVE_FILE);
2823
2824         if (nr_swap_pages > 0)
2825                 nr += zone_page_state(zone, NR_ACTIVE_ANON) +
2826                       zone_page_state(zone, NR_INACTIVE_ANON);
2827
2828         return nr;
2829 }
2830
2831 #ifdef CONFIG_HIBERNATION
2832 /*
2833  * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
2834  * freed pages.
2835  *
2836  * Rather than trying to age LRUs the aim is to preserve the overall
2837  * LRU order by reclaiming preferentially
2838  * inactive > active > active referenced > active mapped
2839  */
2840 unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
2841 {
2842         struct reclaim_state reclaim_state;
2843         struct scan_control sc = {
2844                 .gfp_mask = GFP_HIGHUSER_MOVABLE,
2845                 .may_swap = 1,
2846                 .may_unmap = 1,
2847                 .may_writepage = 1,
2848                 .nr_to_reclaim = nr_to_reclaim,
2849                 .hibernation_mode = 1,
2850                 .swappiness = vm_swappiness,
2851                 .order = 0,
2852         };
2853         struct shrink_control shrink = {
2854                 .gfp_mask = sc.gfp_mask,
2855         };
2856         struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
2857         struct task_struct *p = current;
2858         unsigned long nr_reclaimed;
2859
2860         p->flags |= PF_MEMALLOC;
2861         lockdep_set_current_reclaim_state(sc.gfp_mask);
2862         reclaim_state.reclaimed_slab = 0;
2863         p->reclaim_state = &reclaim_state;
2864
2865         nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2866
2867         p->reclaim_state = NULL;
2868         lockdep_clear_current_reclaim_state();
2869         p->flags &= ~PF_MEMALLOC;
2870
2871         return nr_reclaimed;
2872 }
2873 #endif /* CONFIG_HIBERNATION */
2874
2875 /* It's optimal to keep kswapds on the same CPUs as their memory, but
2876    not required for correctness.  So if the last cpu in a node goes
2877    away, we get changed to run anywhere: as the first one comes back,
2878    restore their cpu bindings. */
2879 static int __devinit cpu_callback(struct notifier_block *nfb,
2880                                   unsigned long action, void *hcpu)
2881 {
2882         int nid;
2883
2884         if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
2885                 for_each_node_state(nid, N_HIGH_MEMORY) {
2886                         pg_data_t *pgdat = NODE_DATA(nid);
2887                         const struct cpumask *mask;
2888
2889                         mask = cpumask_of_node(pgdat->node_id);
2890
2891                         if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2892                                 /* One of our CPUs online: restore mask */
2893                                 set_cpus_allowed_ptr(pgdat->kswapd, mask);
2894                 }
2895         }
2896         return NOTIFY_OK;
2897 }
2898
2899 /*
2900  * This kswapd start function will be called by init and node-hot-add.
2901  * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
2902  */
2903 int kswapd_run(int nid)
2904 {
2905         pg_data_t *pgdat = NODE_DATA(nid);
2906         int ret = 0;
2907
2908         if (pgdat->kswapd)
2909                 return 0;
2910
2911         pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
2912         if (IS_ERR(pgdat->kswapd)) {
2913                 /* failure at boot is fatal */
2914                 BUG_ON(system_state == SYSTEM_BOOTING);
2915                 printk("Failed to start kswapd on node %d\n",nid);
2916                 ret = -1;
2917         }
2918         return ret;
2919 }
2920
2921 /*
2922  * Called by memory hotplug when all memory in a node is offlined.
2923  */
2924 void kswapd_stop(int nid)
2925 {
2926         struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
2927
2928         if (kswapd)
2929                 kthread_stop(kswapd);
2930 }
2931
2932 static int __init kswapd_init(void)
2933 {
2934         int nid;
2935
2936         swap_setup();
2937         for_each_node_state(nid, N_HIGH_MEMORY)
2938                 kswapd_run(nid);
2939         hotcpu_notifier(cpu_callback, 0);
2940         return 0;
2941 }
2942
2943 module_init(kswapd_init)
2944
2945 #ifdef CONFIG_NUMA
2946 /*
2947  * Zone reclaim mode
2948  *
2949  * If non-zero call zone_reclaim when the number of free pages falls below
2950  * the watermarks.
2951  */
2952 int zone_reclaim_mode __read_mostly;
2953
2954 #define RECLAIM_OFF 0
2955 #define RECLAIM_ZONE (1<<0)     /* Run shrink_inactive_list on the zone */
2956 #define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
2957 #define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
2958
2959 /*
2960  * Priority for ZONE_RECLAIM. This determines the fraction of pages
2961  * of a node considered for each zone_reclaim. 4 scans 1/16th of
2962  * a zone.
2963  */
2964 #define ZONE_RECLAIM_PRIORITY 4
2965
2966 /*
2967  * Percentage of pages in a zone that must be unmapped for zone_reclaim to
2968  * occur.
2969  */
2970 int sysctl_min_unmapped_ratio = 1;
2971
2972 /*
2973  * If the number of slab pages in a zone grows beyond this percentage then
2974  * slab reclaim needs to occur.
2975  */
2976 int sysctl_min_slab_ratio = 5;
2977
2978 static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
2979 {
2980         unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
2981         unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
2982                 zone_page_state(zone, NR_ACTIVE_FILE);
2983
2984         /*
2985          * It's possible for there to be more file mapped pages than
2986          * accounted for by the pages on the file LRU lists because
2987          * tmpfs pages accounted for as ANON can also be FILE_MAPPED
2988          */
2989         return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
2990 }
2991
2992 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
2993 static long zone_pagecache_reclaimable(struct zone *zone)
2994 {
2995         long nr_pagecache_reclaimable;
2996         long delta = 0;
2997
2998         /*
2999          * If RECLAIM_SWAP is set, then all file pages are considered
3000          * potentially reclaimable. Otherwise, we have to worry about
3001          * pages like swapcache and zone_unmapped_file_pages() provides
3002          * a better estimate
3003          */
3004         if (zone_reclaim_mode & RECLAIM_SWAP)
3005                 nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3006         else
3007                 nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3008
3009         /* If we can't clean pages, remove dirty pages from consideration */
3010         if (!(zone_reclaim_mode & RECLAIM_WRITE))
3011                 delta += zone_page_state(zone, NR_FILE_DIRTY);
3012
3013         /* Watch for any possible underflows due to delta */
3014         if (unlikely(delta > nr_pagecache_reclaimable))
3015                 delta = nr_pagecache_reclaimable;
3016
3017         return nr_pagecache_reclaimable - delta;
3018 }
3019
3020 /*
3021  * Try to free up some pages from this zone through reclaim.
3022  */
3023 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3024 {
3025         /* Minimum pages needed in order to stay on node */
3026         const unsigned long nr_pages = 1 << order;
3027         struct task_struct *p = current;
3028         struct reclaim_state reclaim_state;
3029         int priority;
3030         struct scan_control sc = {
3031                 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3032                 .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3033                 .may_swap = 1,
3034                 .nr_to_reclaim = max_t(unsigned long, nr_pages,
3035                                        SWAP_CLUSTER_MAX),
3036                 .gfp_mask = gfp_mask,
3037                 .swappiness = vm_swappiness,
3038                 .order = order,
3039         };
3040         struct shrink_control shrink = {
3041                 .gfp_mask = sc.gfp_mask,
3042         };
3043         unsigned long nr_slab_pages0, nr_slab_pages1;
3044
3045         cond_resched();
3046         /*
3047          * We need to be able to allocate from the reserves for RECLAIM_SWAP
3048          * and we also need to be able to write out pages for RECLAIM_WRITE
3049          * and RECLAIM_SWAP.
3050          */
3051         p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3052         lockdep_set_current_reclaim_state(gfp_mask);
3053         reclaim_state.reclaimed_slab = 0;
3054         p->reclaim_state = &reclaim_state;
3055
3056         if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3057                 /*
3058                  * Free memory by calling shrink zone with increasing
3059                  * priorities until we have enough memory freed.
3060                  */
3061                 priority = ZONE_RECLAIM_PRIORITY;
3062                 do {
3063                         shrink_zone(priority, zone, &sc);
3064                         priority--;
3065                 } while (priority >= 0 && sc.nr_reclaimed < nr_pages);
3066         }
3067
3068         nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3069         if (nr_slab_pages0 > zone->min_slab_pages) {
3070                 /*
3071                  * shrink_slab() does not currently allow us to determine how
3072                  * many pages were freed in this zone. So we take the current
3073                  * number of slab pages and shake the slab until it is reduced
3074                  * by the same nr_pages that we used for reclaiming unmapped
3075                  * pages.
3076                  *
3077                  * Note that shrink_slab will free memory on all zones and may
3078                  * take a long time.
3079                  */
3080                 for (;;) {
3081                         unsigned long lru_pages = zone_reclaimable_pages(zone);
3082
3083                         /* No reclaimable slab or very low memory pressure */
3084                         if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3085                                 break;
3086
3087                         /* Freed enough memory */
3088                         nr_slab_pages1 = zone_page_state(zone,
3089                                                         NR_SLAB_RECLAIMABLE);
3090                         if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3091                                 break;
3092                 }
3093
3094                 /*
3095                  * Update nr_reclaimed by the number of slab pages we
3096                  * reclaimed from this zone.
3097                  */
3098                 nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3099                 if (nr_slab_pages1 < nr_slab_pages0)
3100                         sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3101         }
3102
3103         p->reclaim_state = NULL;
3104         current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3105         lockdep_clear_current_reclaim_state();
3106         return sc.nr_reclaimed >= nr_pages;
3107 }
3108
3109 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3110 {
3111         int node_id;
3112         int ret;
3113
3114         /*
3115          * Zone reclaim reclaims unmapped file backed pages and
3116          * slab pages if we are over the defined limits.
3117          *
3118          * A small portion of unmapped file backed pages is needed for
3119          * file I/O otherwise pages read by file I/O will be immediately
3120          * thrown out if the zone is overallocated. So we do not reclaim
3121          * if less than a specified percentage of the zone is used by
3122          * unmapped file backed pages.
3123          */
3124         if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3125             zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3126                 return ZONE_RECLAIM_FULL;
3127
3128         if (zone->all_unreclaimable)
3129                 return ZONE_RECLAIM_FULL;
3130
3131         /*
3132          * Do not scan if the allocation should not be delayed.
3133          */
3134         if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3135                 return ZONE_RECLAIM_NOSCAN;
3136
3137         /*
3138          * Only run zone reclaim on the local zone or on zones that do not
3139          * have associated processors. This will favor the local processor
3140          * over remote processors and spread off node memory allocations
3141          * as wide as possible.
3142          */
3143         node_id = zone_to_nid(zone);
3144         if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3145                 return ZONE_RECLAIM_NOSCAN;
3146
3147         if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3148                 return ZONE_RECLAIM_NOSCAN;
3149
3150         ret = __zone_reclaim(zone, gfp_mask, order);
3151         zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3152
3153         if (!ret)
3154                 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3155
3156         return ret;
3157 }
3158 #endif
3159
3160 /*
3161  * page_evictable - test whether a page is evictable
3162  * @page: the page to test
3163  * @vma: the VMA in which the page is or will be mapped, may be NULL
3164  *
3165  * Test whether page is evictable--i.e., should be placed on active/inactive
3166  * lists vs unevictable list.  The vma argument is !NULL when called from the
3167  * fault path to determine how to instantate a new page.
3168  *
3169  * Reasons page might not be evictable:
3170  * (1) page's mapping marked unevictable
3171  * (2) page is part of an mlocked VMA
3172  *
3173  */
3174 int page_evictable(struct page *page, struct vm_area_struct *vma)
3175 {
3176
3177         if (mapping_unevictable(page_mapping(page)))
3178                 return 0;
3179
3180         if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
3181                 return 0;
3182
3183         return 1;
3184 }
3185
3186 /**
3187  * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list
3188  * @page: page to check evictability and move to appropriate lru list
3189  * @zone: zone page is in
3190  *
3191  * Checks a page for evictability and moves the page to the appropriate
3192  * zone lru list.
3193  *
3194  * Restrictions: zone->lru_lock must be held, page must be on LRU and must
3195  * have PageUnevictable set.
3196  */
3197 static void check_move_unevictable_page(struct page *page, struct zone *zone)
3198 {
3199         VM_BUG_ON(PageActive(page));
3200
3201 retry:
3202         ClearPageUnevictable(page);
3203         if (page_evictable(page, NULL)) {
3204                 enum lru_list l = page_lru_base_type(page);
3205
3206                 __dec_zone_state(zone, NR_UNEVICTABLE);
3207                 list_move(&page->lru, &zone->lru[l].list);
3208                 mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l);
3209                 __inc_zone_state(zone, NR_INACTIVE_ANON + l);
3210                 __count_vm_event(UNEVICTABLE_PGRESCUED);
3211         } else {
3212                 /*
3213                  * rotate unevictable list
3214                  */
3215                 SetPageUnevictable(page);
3216                 list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list);
3217                 mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE);
3218                 if (page_evictable(page, NULL))
3219                         goto retry;
3220         }
3221 }
3222
3223 /**
3224  * scan_mapping_unevictable_pages - scan an address space for evictable pages
3225  * @mapping: struct address_space to scan for evictable pages
3226  *
3227  * Scan all pages in mapping.  Check unevictable pages for
3228  * evictability and move them to the appropriate zone lru list.
3229  */
3230 void scan_mapping_unevictable_pages(struct address_space *mapping)
3231 {
3232         pgoff_t next = 0;
3233         pgoff_t end   = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >>
3234                          PAGE_CACHE_SHIFT;
3235         struct zone *zone;
3236         struct pagevec pvec;
3237
3238         if (mapping->nrpages == 0)
3239                 return;
3240
3241         pagevec_init(&pvec, 0);
3242         while (next < end &&
3243                 pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
3244                 int i;
3245                 int pg_scanned = 0;
3246
3247                 zone = NULL;
3248
3249                 for (i = 0; i < pagevec_count(&pvec); i++) {
3250                         struct page *page = pvec.pages[i];
3251                         pgoff_t page_index = page->index;
3252                         struct zone *pagezone = page_zone(page);
3253
3254                         pg_scanned++;
3255                         if (page_index > next)
3256                                 next = page_index;
3257                         next++;
3258
3259                         if (pagezone != zone) {
3260                                 if (zone)
3261                                         spin_unlock_irq(&zone->lru_lock);
3262                                 zone = pagezone;
3263                                 spin_lock_irq(&zone->lru_lock);
3264                         }
3265
3266                         if (PageLRU(page) && PageUnevictable(page))
3267                                 check_move_unevictable_page(page, zone);
3268                 }
3269                 if (zone)
3270                         spin_unlock_irq(&zone->lru_lock);
3271                 pagevec_release(&pvec);
3272
3273                 count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
3274         }
3275
3276 }
3277
3278 /**
3279  * scan_zone_unevictable_pages - check unevictable list for evictable pages
3280  * @zone - zone of which to scan the unevictable list
3281  *
3282  * Scan @zone's unevictable LRU lists to check for pages that have become
3283  * evictable.  Move those that have to @zone's inactive list where they
3284  * become candidates for reclaim, unless shrink_inactive_zone() decides
3285  * to reactivate them.  Pages that are still unevictable are rotated
3286  * back onto @zone's unevictable list.
3287  */
3288 #define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */
3289 static void scan_zone_unevictable_pages(struct zone *zone)
3290 {
3291         struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list;
3292         unsigned long scan;
3293         unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE);
3294
3295         while (nr_to_scan > 0) {
3296                 unsigned long batch_size = min(nr_to_scan,
3297                                                 SCAN_UNEVICTABLE_BATCH_SIZE);
3298
3299                 spin_lock_irq(&zone->lru_lock);
3300                 for (scan = 0;  scan < batch_size; scan++) {
3301                         struct page *page = lru_to_page(l_unevictable);
3302
3303                         if (!trylock_page(page))
3304                                 continue;
3305
3306                         prefetchw_prev_lru_page(page, l_unevictable, flags);
3307
3308                         if (likely(PageLRU(page) && PageUnevictable(page)))
3309                                 check_move_unevictable_page(page, zone);
3310
3311                         unlock_page(page);
3312                 }
3313                 spin_unlock_irq(&zone->lru_lock);
3314
3315                 nr_to_scan -= batch_size;
3316         }
3317 }
3318
3319
3320 /**
3321  * scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages
3322  *
3323  * A really big hammer:  scan all zones' unevictable LRU lists to check for
3324  * pages that have become evictable.  Move those back to the zones'
3325  * inactive list where they become candidates for reclaim.
3326  * This occurs when, e.g., we have unswappable pages on the unevictable lists,
3327  * and we add swap to the system.  As such, it runs in the context of a task
3328  * that has possibly/probably made some previously unevictable pages
3329  * evictable.
3330  */
3331 static void scan_all_zones_unevictable_pages(void)
3332 {
3333         struct zone *zone;
3334
3335         for_each_zone(zone) {
3336                 scan_zone_unevictable_pages(zone);
3337         }
3338 }
3339
3340 /*
3341  * scan_unevictable_pages [vm] sysctl handler.  On demand re-scan of
3342  * all nodes' unevictable lists for evictable pages
3343  */
3344 unsigned long scan_unevictable_pages;
3345
3346 int scan_unevictable_handler(struct ctl_table *table, int write,
3347                            void __user *buffer,
3348                            size_t *length, loff_t *ppos)
3349 {
3350         proc_doulongvec_minmax(table, write, buffer, length, ppos);
3351
3352         if (write && *(unsigned long *)table->data)
3353                 scan_all_zones_unevictable_pages();
3354
3355         scan_unevictable_pages = 0;
3356         return 0;
3357 }
3358
3359 #ifdef CONFIG_NUMA
3360 /*
3361  * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
3362  * a specified node's per zone unevictable lists for evictable pages.
3363  */
3364
3365 static ssize_t read_scan_unevictable_node(struct sys_device *dev,
3366                                           struct sysdev_attribute *attr,
3367                                           char *buf)
3368 {
3369         return sprintf(buf, "0\n");     /* always zero; should fit... */
3370 }
3371
3372 static ssize_t write_scan_unevictable_node(struct sys_device *dev,
3373                                            struct sysdev_attribute *attr,
3374                                         const char *buf, size_t count)
3375 {
3376         struct zone *node_zones = NODE_DATA(dev->id)->node_zones;
3377         struct zone *zone;
3378         unsigned long res;
3379         unsigned long req = strict_strtoul(buf, 10, &res);
3380
3381         if (!req)
3382                 return 1;       /* zero is no-op */
3383
3384         for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
3385                 if (!populated_zone(zone))
3386                         continue;
3387                 scan_zone_unevictable_pages(zone);
3388         }
3389         return 1;
3390 }
3391
3392
3393 static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3394                         read_scan_unevictable_node,
3395                         write_scan_unevictable_node);
3396
3397 int scan_unevictable_register_node(struct node *node)
3398 {
3399         return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages);
3400 }
3401
3402 void scan_unevictable_unregister_node(struct node *node)
3403 {
3404         sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages);
3405 }
3406 #endif