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