5432c230c4cb0d68357e2bbaa18bb21ec48d5831
[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/slab.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 struct scan_control {
52         /* Incremented by the number of inactive pages that were scanned */
53         unsigned long nr_scanned;
54
55         /* Number of pages freed so far during a call to shrink_zones() */
56         unsigned long nr_reclaimed;
57
58         /* This context's GFP mask */
59         gfp_t gfp_mask;
60
61         int may_writepage;
62
63         /* Can mapped pages be reclaimed? */
64         int may_unmap;
65
66         /* Can pages be swapped as part of reclaim? */
67         int may_swap;
68
69         /* This context's SWAP_CLUSTER_MAX. If freeing memory for
70          * suspend, we effectively ignore SWAP_CLUSTER_MAX.
71          * In this context, it doesn't matter that we scan the
72          * whole list at once. */
73         int swap_cluster_max;
74
75         int swappiness;
76
77         int all_unreclaimable;
78
79         int order;
80
81         /* Which cgroup do we reclaim from */
82         struct mem_cgroup *mem_cgroup;
83
84         /*
85          * Nodemask of nodes allowed by the caller. If NULL, all nodes
86          * are scanned.
87          */
88         nodemask_t      *nodemask;
89
90         /* Pluggable isolate pages callback */
91         unsigned long (*isolate_pages)(unsigned long nr, struct list_head *dst,
92                         unsigned long *scanned, int order, int mode,
93                         struct zone *z, struct mem_cgroup *mem_cont,
94                         int active, int file);
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 = (*shrinker->shrink)(0, gfp_mask);
220
221                 delta = (4 * scanned) / shrinker->seeks;
222                 delta *= max_pass;
223                 do_div(delta, lru_pages + 1);
224                 shrinker->nr += delta;
225                 if (shrinker->nr < 0) {
226                         printk(KERN_ERR "shrink_slab: %pF negative objects to "
227                                "delete nr=%ld\n",
228                                shrinker->shrink, shrinker->nr);
229                         shrinker->nr = max_pass;
230                 }
231
232                 /*
233                  * Avoid risking looping forever due to too large nr value:
234                  * never try to free more than twice the estimate number of
235                  * freeable entries.
236                  */
237                 if (shrinker->nr > max_pass * 2)
238                         shrinker->nr = max_pass * 2;
239
240                 total_scan = shrinker->nr;
241                 shrinker->nr = 0;
242
243                 while (total_scan >= SHRINK_BATCH) {
244                         long this_scan = SHRINK_BATCH;
245                         int shrink_ret;
246                         int nr_before;
247
248                         nr_before = (*shrinker->shrink)(0, gfp_mask);
249                         shrink_ret = (*shrinker->shrink)(this_scan, gfp_mask);
250                         if (shrink_ret == -1)
251                                 break;
252                         if (shrink_ret < nr_before)
253                                 ret += nr_before - shrink_ret;
254                         count_vm_events(SLABS_SCANNED, this_scan);
255                         total_scan -= this_scan;
256
257                         cond_resched();
258                 }
259
260                 shrinker->nr += total_scan;
261         }
262         up_read(&shrinker_rwsem);
263         return ret;
264 }
265
266 /* Called without lock on whether page is mapped, so answer is unstable */
267 static inline int page_mapping_inuse(struct page *page)
268 {
269         struct address_space *mapping;
270
271         /* Page is in somebody's page tables. */
272         if (page_mapped(page))
273                 return 1;
274
275         /* Be more reluctant to reclaim swapcache than pagecache */
276         if (PageSwapCache(page))
277                 return 1;
278
279         mapping = page_mapping(page);
280         if (!mapping)
281                 return 0;
282
283         /* File is mmap'd by somebody? */
284         return mapping_mapped(mapping);
285 }
286
287 static inline int is_page_cache_freeable(struct page *page)
288 {
289         /*
290          * A freeable page cache page is referenced only by the caller
291          * that isolated the page, the page cache radix tree and
292          * optional buffer heads at page->private.
293          */
294         return page_count(page) - page_has_private(page) == 2;
295 }
296
297 static int may_write_to_queue(struct backing_dev_info *bdi)
298 {
299         if (current->flags & PF_SWAPWRITE)
300                 return 1;
301         if (!bdi_write_congested(bdi))
302                 return 1;
303         if (bdi == current->backing_dev_info)
304                 return 1;
305         return 0;
306 }
307
308 /*
309  * We detected a synchronous write error writing a page out.  Probably
310  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
311  * fsync(), msync() or close().
312  *
313  * The tricky part is that after writepage we cannot touch the mapping: nothing
314  * prevents it from being freed up.  But we have a ref on the page and once
315  * that page is locked, the mapping is pinned.
316  *
317  * We're allowed to run sleeping lock_page() here because we know the caller has
318  * __GFP_FS.
319  */
320 static void handle_write_error(struct address_space *mapping,
321                                 struct page *page, int error)
322 {
323         lock_page(page);
324         if (page_mapping(page) == mapping)
325                 mapping_set_error(mapping, error);
326         unlock_page(page);
327 }
328
329 /* Request for sync pageout. */
330 enum pageout_io {
331         PAGEOUT_IO_ASYNC,
332         PAGEOUT_IO_SYNC,
333 };
334
335 /* possible outcome of pageout() */
336 typedef enum {
337         /* failed to write page out, page is locked */
338         PAGE_KEEP,
339         /* move page to the active list, page is locked */
340         PAGE_ACTIVATE,
341         /* page has been sent to the disk successfully, page is unlocked */
342         PAGE_SUCCESS,
343         /* page is clean and locked */
344         PAGE_CLEAN,
345 } pageout_t;
346
347 /*
348  * pageout is called by shrink_page_list() for each dirty page.
349  * Calls ->writepage().
350  */
351 static pageout_t pageout(struct page *page, struct address_space *mapping,
352                                                 enum pageout_io sync_writeback)
353 {
354         /*
355          * If the page is dirty, only perform writeback if that write
356          * will be non-blocking.  To prevent this allocation from being
357          * stalled by pagecache activity.  But note that there may be
358          * stalls if we need to run get_block().  We could test
359          * PagePrivate for that.
360          *
361          * If this process is currently in generic_file_write() against
362          * this page's queue, we can perform writeback even if that
363          * will block.
364          *
365          * If the page is swapcache, write it back even if that would
366          * block, for some throttling. This happens by accident, because
367          * swap_backing_dev_info is bust: it doesn't reflect the
368          * congestion state of the swapdevs.  Easy to fix, if needed.
369          * See swapfile.c:page_queue_congested().
370          */
371         if (!is_page_cache_freeable(page))
372                 return PAGE_KEEP;
373         if (!mapping) {
374                 /*
375                  * Some data journaling orphaned pages can have
376                  * page->mapping == NULL while being dirty with clean buffers.
377                  */
378                 if (page_has_private(page)) {
379                         if (try_to_free_buffers(page)) {
380                                 ClearPageDirty(page);
381                                 printk("%s: orphaned page\n", __func__);
382                                 return PAGE_CLEAN;
383                         }
384                 }
385                 return PAGE_KEEP;
386         }
387         if (mapping->a_ops->writepage == NULL)
388                 return PAGE_ACTIVATE;
389         if (!may_write_to_queue(mapping->backing_dev_info))
390                 return PAGE_KEEP;
391
392         if (clear_page_dirty_for_io(page)) {
393                 int res;
394                 struct writeback_control wbc = {
395                         .sync_mode = WB_SYNC_NONE,
396                         .nr_to_write = SWAP_CLUSTER_MAX,
397                         .range_start = 0,
398                         .range_end = LLONG_MAX,
399                         .nonblocking = 1,
400                         .for_reclaim = 1,
401                 };
402
403                 SetPageReclaim(page);
404                 res = mapping->a_ops->writepage(page, &wbc);
405                 if (res < 0)
406                         handle_write_error(mapping, page, res);
407                 if (res == AOP_WRITEPAGE_ACTIVATE) {
408                         ClearPageReclaim(page);
409                         return PAGE_ACTIVATE;
410                 }
411
412                 /*
413                  * Wait on writeback if requested to. This happens when
414                  * direct reclaiming a large contiguous area and the
415                  * first attempt to free a range of pages fails.
416                  */
417                 if (PageWriteback(page) && sync_writeback == PAGEOUT_IO_SYNC)
418                         wait_on_page_writeback(page);
419
420                 if (!PageWriteback(page)) {
421                         /* synchronous write or broken a_ops? */
422                         ClearPageReclaim(page);
423                 }
424                 inc_zone_page_state(page, NR_VMSCAN_WRITE);
425                 return PAGE_SUCCESS;
426         }
427
428         return PAGE_CLEAN;
429 }
430
431 /*
432  * Same as remove_mapping, but if the page is removed from the mapping, it
433  * gets returned with a refcount of 0.
434  */
435 static int __remove_mapping(struct address_space *mapping, struct page *page)
436 {
437         BUG_ON(!PageLocked(page));
438         BUG_ON(mapping != page_mapping(page));
439
440         spin_lock_irq(&mapping->tree_lock);
441         /*
442          * The non racy check for a busy page.
443          *
444          * Must be careful with the order of the tests. When someone has
445          * a ref to the page, it may be possible that they dirty it then
446          * drop the reference. So if PageDirty is tested before page_count
447          * here, then the following race may occur:
448          *
449          * get_user_pages(&page);
450          * [user mapping goes away]
451          * write_to(page);
452          *                              !PageDirty(page)    [good]
453          * SetPageDirty(page);
454          * put_page(page);
455          *                              !page_count(page)   [good, discard it]
456          *
457          * [oops, our write_to data is lost]
458          *
459          * Reversing the order of the tests ensures such a situation cannot
460          * escape unnoticed. The smp_rmb is needed to ensure the page->flags
461          * load is not satisfied before that of page->_count.
462          *
463          * Note that if SetPageDirty is always performed via set_page_dirty,
464          * and thus under tree_lock, then this ordering is not required.
465          */
466         if (!page_freeze_refs(page, 2))
467                 goto cannot_free;
468         /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
469         if (unlikely(PageDirty(page))) {
470                 page_unfreeze_refs(page, 2);
471                 goto cannot_free;
472         }
473
474         if (PageSwapCache(page)) {
475                 swp_entry_t swap = { .val = page_private(page) };
476                 __delete_from_swap_cache(page);
477                 spin_unlock_irq(&mapping->tree_lock);
478                 swapcache_free(swap, page);
479         } else {
480                 __remove_from_page_cache(page);
481                 spin_unlock_irq(&mapping->tree_lock);
482                 mem_cgroup_uncharge_cache_page(page);
483         }
484
485         return 1;
486
487 cannot_free:
488         spin_unlock_irq(&mapping->tree_lock);
489         return 0;
490 }
491
492 /*
493  * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
494  * someone else has a ref on the page, abort and return 0.  If it was
495  * successfully detached, return 1.  Assumes the caller has a single ref on
496  * this page.
497  */
498 int remove_mapping(struct address_space *mapping, struct page *page)
499 {
500         if (__remove_mapping(mapping, page)) {
501                 /*
502                  * Unfreezing the refcount with 1 rather than 2 effectively
503                  * drops the pagecache ref for us without requiring another
504                  * atomic operation.
505                  */
506                 page_unfreeze_refs(page, 1);
507                 return 1;
508         }
509         return 0;
510 }
511
512 /**
513  * putback_lru_page - put previously isolated page onto appropriate LRU list
514  * @page: page to be put back to appropriate lru list
515  *
516  * Add previously isolated @page to appropriate LRU list.
517  * Page may still be unevictable for other reasons.
518  *
519  * lru_lock must not be held, interrupts must be enabled.
520  */
521 void putback_lru_page(struct page *page)
522 {
523         int lru;
524         int active = !!TestClearPageActive(page);
525         int was_unevictable = PageUnevictable(page);
526
527         VM_BUG_ON(PageLRU(page));
528
529 redo:
530         ClearPageUnevictable(page);
531
532         if (page_evictable(page, NULL)) {
533                 /*
534                  * For evictable pages, we can use the cache.
535                  * In event of a race, worst case is we end up with an
536                  * unevictable page on [in]active list.
537                  * We know how to handle that.
538                  */
539                 lru = active + page_lru_base_type(page);
540                 lru_cache_add_lru(page, lru);
541         } else {
542                 /*
543                  * Put unevictable pages directly on zone's unevictable
544                  * list.
545                  */
546                 lru = LRU_UNEVICTABLE;
547                 add_page_to_unevictable_list(page);
548         }
549
550         /*
551          * page's status can change while we move it among lru. If an evictable
552          * page is on unevictable list, it never be freed. To avoid that,
553          * check after we added it to the list, again.
554          */
555         if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) {
556                 if (!isolate_lru_page(page)) {
557                         put_page(page);
558                         goto redo;
559                 }
560                 /* This means someone else dropped this page from LRU
561                  * So, it will be freed or putback to LRU again. There is
562                  * nothing to do here.
563                  */
564         }
565
566         if (was_unevictable && lru != LRU_UNEVICTABLE)
567                 count_vm_event(UNEVICTABLE_PGRESCUED);
568         else if (!was_unevictable && lru == LRU_UNEVICTABLE)
569                 count_vm_event(UNEVICTABLE_PGCULLED);
570
571         put_page(page);         /* drop ref from isolate */
572 }
573
574 /*
575  * shrink_page_list() returns the number of reclaimed pages
576  */
577 static unsigned long shrink_page_list(struct list_head *page_list,
578                                         struct scan_control *sc,
579                                         enum pageout_io sync_writeback)
580 {
581         LIST_HEAD(ret_pages);
582         struct pagevec freed_pvec;
583         int pgactivate = 0;
584         unsigned long nr_reclaimed = 0;
585         unsigned long vm_flags;
586
587         cond_resched();
588
589         pagevec_init(&freed_pvec, 1);
590         while (!list_empty(page_list)) {
591                 struct address_space *mapping;
592                 struct page *page;
593                 int may_enter_fs;
594                 int referenced;
595
596                 cond_resched();
597
598                 page = lru_to_page(page_list);
599                 list_del(&page->lru);
600
601                 if (!trylock_page(page))
602                         goto keep;
603
604                 VM_BUG_ON(PageActive(page));
605
606                 sc->nr_scanned++;
607
608                 if (unlikely(!page_evictable(page, NULL)))
609                         goto cull_mlocked;
610
611                 if (!sc->may_unmap && page_mapped(page))
612                         goto keep_locked;
613
614                 /* Double the slab pressure for mapped and swapcache pages */
615                 if (page_mapped(page) || PageSwapCache(page))
616                         sc->nr_scanned++;
617
618                 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
619                         (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
620
621                 if (PageWriteback(page)) {
622                         /*
623                          * Synchronous reclaim is performed in two passes,
624                          * first an asynchronous pass over the list to
625                          * start parallel writeback, and a second synchronous
626                          * pass to wait for the IO to complete.  Wait here
627                          * for any page for which writeback has already
628                          * started.
629                          */
630                         if (sync_writeback == PAGEOUT_IO_SYNC && may_enter_fs)
631                                 wait_on_page_writeback(page);
632                         else
633                                 goto keep_locked;
634                 }
635
636                 referenced = page_referenced(page, 1,
637                                                 sc->mem_cgroup, &vm_flags);
638                 /*
639                  * In active use or really unfreeable?  Activate it.
640                  * If page which have PG_mlocked lost isoltation race,
641                  * try_to_unmap moves it to unevictable list
642                  */
643                 if (sc->order <= PAGE_ALLOC_COSTLY_ORDER &&
644                                         referenced && page_mapping_inuse(page)
645                                         && !(vm_flags & VM_LOCKED))
646                         goto activate_locked;
647
648                 /*
649                  * Anonymous process memory has backing store?
650                  * Try to allocate it some swap space here.
651                  */
652                 if (PageAnon(page) && !PageSwapCache(page)) {
653                         if (!(sc->gfp_mask & __GFP_IO))
654                                 goto keep_locked;
655                         if (!add_to_swap(page))
656                                 goto activate_locked;
657                         may_enter_fs = 1;
658                 }
659
660                 mapping = page_mapping(page);
661
662                 /*
663                  * The page is mapped into the page tables of one or more
664                  * processes. Try to unmap it here.
665                  */
666                 if (page_mapped(page) && mapping) {
667                         switch (try_to_unmap(page, 0)) {
668                         case SWAP_FAIL:
669                                 goto activate_locked;
670                         case SWAP_AGAIN:
671                                 goto keep_locked;
672                         case SWAP_MLOCK:
673                                 goto cull_mlocked;
674                         case SWAP_SUCCESS:
675                                 ; /* try to free the page below */
676                         }
677                 }
678
679                 if (PageDirty(page)) {
680                         if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced)
681                                 goto keep_locked;
682                         if (!may_enter_fs)
683                                 goto keep_locked;
684                         if (!sc->may_writepage)
685                                 goto keep_locked;
686
687                         /* Page is dirty, try to write it out here */
688                         switch (pageout(page, mapping, sync_writeback)) {
689                         case PAGE_KEEP:
690                                 goto keep_locked;
691                         case PAGE_ACTIVATE:
692                                 goto activate_locked;
693                         case PAGE_SUCCESS:
694                                 if (PageWriteback(page) || PageDirty(page))
695                                         goto keep;
696                                 /*
697                                  * A synchronous write - probably a ramdisk.  Go
698                                  * ahead and try to reclaim the page.
699                                  */
700                                 if (!trylock_page(page))
701                                         goto keep;
702                                 if (PageDirty(page) || PageWriteback(page))
703                                         goto keep_locked;
704                                 mapping = page_mapping(page);
705                         case PAGE_CLEAN:
706                                 ; /* try to free the page below */
707                         }
708                 }
709
710                 /*
711                  * If the page has buffers, try to free the buffer mappings
712                  * associated with this page. If we succeed we try to free
713                  * the page as well.
714                  *
715                  * We do this even if the page is PageDirty().
716                  * try_to_release_page() does not perform I/O, but it is
717                  * possible for a page to have PageDirty set, but it is actually
718                  * clean (all its buffers are clean).  This happens if the
719                  * buffers were written out directly, with submit_bh(). ext3
720                  * will do this, as well as the blockdev mapping.
721                  * try_to_release_page() will discover that cleanness and will
722                  * drop the buffers and mark the page clean - it can be freed.
723                  *
724                  * Rarely, pages can have buffers and no ->mapping.  These are
725                  * the pages which were not successfully invalidated in
726                  * truncate_complete_page().  We try to drop those buffers here
727                  * and if that worked, and the page is no longer mapped into
728                  * process address space (page_count == 1) it can be freed.
729                  * Otherwise, leave the page on the LRU so it is swappable.
730                  */
731                 if (page_has_private(page)) {
732                         if (!try_to_release_page(page, sc->gfp_mask))
733                                 goto activate_locked;
734                         if (!mapping && page_count(page) == 1) {
735                                 unlock_page(page);
736                                 if (put_page_testzero(page))
737                                         goto free_it;
738                                 else {
739                                         /*
740                                          * rare race with speculative reference.
741                                          * the speculative reference will free
742                                          * this page shortly, so we may
743                                          * increment nr_reclaimed here (and
744                                          * leave it off the LRU).
745                                          */
746                                         nr_reclaimed++;
747                                         continue;
748                                 }
749                         }
750                 }
751
752                 if (!mapping || !__remove_mapping(mapping, page))
753                         goto keep_locked;
754
755                 /*
756                  * At this point, we have no other references and there is
757                  * no way to pick any more up (removed from LRU, removed
758                  * from pagecache). Can use non-atomic bitops now (and
759                  * we obviously don't have to worry about waking up a process
760                  * waiting on the page lock, because there are no references.
761                  */
762                 __clear_page_locked(page);
763 free_it:
764                 nr_reclaimed++;
765                 if (!pagevec_add(&freed_pvec, page)) {
766                         __pagevec_free(&freed_pvec);
767                         pagevec_reinit(&freed_pvec);
768                 }
769                 continue;
770
771 cull_mlocked:
772                 if (PageSwapCache(page))
773                         try_to_free_swap(page);
774                 unlock_page(page);
775                 putback_lru_page(page);
776                 continue;
777
778 activate_locked:
779                 /* Not a candidate for swapping, so reclaim swap space. */
780                 if (PageSwapCache(page) && vm_swap_full())
781                         try_to_free_swap(page);
782                 VM_BUG_ON(PageActive(page));
783                 SetPageActive(page);
784                 pgactivate++;
785 keep_locked:
786                 unlock_page(page);
787 keep:
788                 list_add(&page->lru, &ret_pages);
789                 VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
790         }
791         list_splice(&ret_pages, page_list);
792         if (pagevec_count(&freed_pvec))
793                 __pagevec_free(&freed_pvec);
794         count_vm_events(PGACTIVATE, pgactivate);
795         return nr_reclaimed;
796 }
797
798 /* LRU Isolation modes. */
799 #define ISOLATE_INACTIVE 0      /* Isolate inactive pages. */
800 #define ISOLATE_ACTIVE 1        /* Isolate active pages. */
801 #define ISOLATE_BOTH 2          /* Isolate both active and inactive pages. */
802
803 /*
804  * Attempt to remove the specified page from its LRU.  Only take this page
805  * if it is of the appropriate PageActive status.  Pages which are being
806  * freed elsewhere are also ignored.
807  *
808  * page:        page to consider
809  * mode:        one of the LRU isolation modes defined above
810  *
811  * returns 0 on success, -ve errno on failure.
812  */
813 int __isolate_lru_page(struct page *page, int mode, int file)
814 {
815         int ret = -EINVAL;
816
817         /* Only take pages on the LRU. */
818         if (!PageLRU(page))
819                 return ret;
820
821         /*
822          * When checking the active state, we need to be sure we are
823          * dealing with comparible boolean values.  Take the logical not
824          * of each.
825          */
826         if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode))
827                 return ret;
828
829         if (mode != ISOLATE_BOTH && page_is_file_cache(page) != file)
830                 return ret;
831
832         /*
833          * When this function is being called for lumpy reclaim, we
834          * initially look into all LRU pages, active, inactive and
835          * unevictable; only give shrink_page_list evictable pages.
836          */
837         if (PageUnevictable(page))
838                 return ret;
839
840         ret = -EBUSY;
841
842         if (likely(get_page_unless_zero(page))) {
843                 /*
844                  * Be careful not to clear PageLRU until after we're
845                  * sure the page is not being freed elsewhere -- the
846                  * page release code relies on it.
847                  */
848                 ClearPageLRU(page);
849                 ret = 0;
850         }
851
852         return ret;
853 }
854
855 /*
856  * zone->lru_lock is heavily contended.  Some of the functions that
857  * shrink the lists perform better by taking out a batch of pages
858  * and working on them outside the LRU lock.
859  *
860  * For pagecache intensive workloads, this function is the hottest
861  * spot in the kernel (apart from copy_*_user functions).
862  *
863  * Appropriate locks must be held before calling this function.
864  *
865  * @nr_to_scan: The number of pages to look through on the list.
866  * @src:        The LRU list to pull pages off.
867  * @dst:        The temp list to put pages on to.
868  * @scanned:    The number of pages that were scanned.
869  * @order:      The caller's attempted allocation order
870  * @mode:       One of the LRU isolation modes
871  * @file:       True [1] if isolating file [!anon] pages
872  *
873  * returns how many pages were moved onto *@dst.
874  */
875 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
876                 struct list_head *src, struct list_head *dst,
877                 unsigned long *scanned, int order, int mode, int file)
878 {
879         unsigned long nr_taken = 0;
880         unsigned long scan;
881
882         for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
883                 struct page *page;
884                 unsigned long pfn;
885                 unsigned long end_pfn;
886                 unsigned long page_pfn;
887                 int zone_id;
888
889                 page = lru_to_page(src);
890                 prefetchw_prev_lru_page(page, src, flags);
891
892                 VM_BUG_ON(!PageLRU(page));
893
894                 switch (__isolate_lru_page(page, mode, file)) {
895                 case 0:
896                         list_move(&page->lru, dst);
897                         mem_cgroup_del_lru(page);
898                         nr_taken++;
899                         break;
900
901                 case -EBUSY:
902                         /* else it is being freed elsewhere */
903                         list_move(&page->lru, src);
904                         mem_cgroup_rotate_lru_list(page, page_lru(page));
905                         continue;
906
907                 default:
908                         BUG();
909                 }
910
911                 if (!order)
912                         continue;
913
914                 /*
915                  * Attempt to take all pages in the order aligned region
916                  * surrounding the tag page.  Only take those pages of
917                  * the same active state as that tag page.  We may safely
918                  * round the target page pfn down to the requested order
919                  * as the mem_map is guarenteed valid out to MAX_ORDER,
920                  * where that page is in a different zone we will detect
921                  * it from its zone id and abort this block scan.
922                  */
923                 zone_id = page_zone_id(page);
924                 page_pfn = page_to_pfn(page);
925                 pfn = page_pfn & ~((1 << order) - 1);
926                 end_pfn = pfn + (1 << order);
927                 for (; pfn < end_pfn; pfn++) {
928                         struct page *cursor_page;
929
930                         /* The target page is in the block, ignore it. */
931                         if (unlikely(pfn == page_pfn))
932                                 continue;
933
934                         /* Avoid holes within the zone. */
935                         if (unlikely(!pfn_valid_within(pfn)))
936                                 break;
937
938                         cursor_page = pfn_to_page(pfn);
939
940                         /* Check that we have not crossed a zone boundary. */
941                         if (unlikely(page_zone_id(cursor_page) != zone_id))
942                                 continue;
943
944                         /*
945                          * If we don't have enough swap space, reclaiming of
946                          * anon page which don't already have a swap slot is
947                          * pointless.
948                          */
949                         if (nr_swap_pages <= 0 && PageAnon(cursor_page) &&
950                                         !PageSwapCache(cursor_page))
951                                 continue;
952
953                         if (__isolate_lru_page(cursor_page, mode, file) == 0) {
954                                 list_move(&cursor_page->lru, dst);
955                                 mem_cgroup_del_lru(cursor_page);
956                                 nr_taken++;
957                                 scan++;
958                         }
959                 }
960         }
961
962         *scanned = scan;
963         return nr_taken;
964 }
965
966 static unsigned long isolate_pages_global(unsigned long nr,
967                                         struct list_head *dst,
968                                         unsigned long *scanned, int order,
969                                         int mode, struct zone *z,
970                                         struct mem_cgroup *mem_cont,
971                                         int active, int file)
972 {
973         int lru = LRU_BASE;
974         if (active)
975                 lru += LRU_ACTIVE;
976         if (file)
977                 lru += LRU_FILE;
978         return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order,
979                                                                 mode, file);
980 }
981
982 /*
983  * clear_active_flags() is a helper for shrink_active_list(), clearing
984  * any active bits from the pages in the list.
985  */
986 static unsigned long clear_active_flags(struct list_head *page_list,
987                                         unsigned int *count)
988 {
989         int nr_active = 0;
990         int lru;
991         struct page *page;
992
993         list_for_each_entry(page, page_list, lru) {
994                 lru = page_lru_base_type(page);
995                 if (PageActive(page)) {
996                         lru += LRU_ACTIVE;
997                         ClearPageActive(page);
998                         nr_active++;
999                 }
1000                 count[lru]++;
1001         }
1002
1003         return nr_active;
1004 }
1005
1006 /**
1007  * isolate_lru_page - tries to isolate a page from its LRU list
1008  * @page: page to isolate from its LRU list
1009  *
1010  * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1011  * vmstat statistic corresponding to whatever LRU list the page was on.
1012  *
1013  * Returns 0 if the page was removed from an LRU list.
1014  * Returns -EBUSY if the page was not on an LRU list.
1015  *
1016  * The returned page will have PageLRU() cleared.  If it was found on
1017  * the active list, it will have PageActive set.  If it was found on
1018  * the unevictable list, it will have the PageUnevictable bit set. That flag
1019  * may need to be cleared by the caller before letting the page go.
1020  *
1021  * The vmstat statistic corresponding to the list on which the page was
1022  * found will be decremented.
1023  *
1024  * Restrictions:
1025  * (1) Must be called with an elevated refcount on the page. This is a
1026  *     fundamentnal difference from isolate_lru_pages (which is called
1027  *     without a stable reference).
1028  * (2) the lru_lock must not be held.
1029  * (3) interrupts must be enabled.
1030  */
1031 int isolate_lru_page(struct page *page)
1032 {
1033         int ret = -EBUSY;
1034
1035         if (PageLRU(page)) {
1036                 struct zone *zone = page_zone(page);
1037
1038                 spin_lock_irq(&zone->lru_lock);
1039                 if (PageLRU(page) && get_page_unless_zero(page)) {
1040                         int lru = page_lru(page);
1041                         ret = 0;
1042                         ClearPageLRU(page);
1043
1044                         del_page_from_lru_list(zone, page, lru);
1045                 }
1046                 spin_unlock_irq(&zone->lru_lock);
1047         }
1048         return ret;
1049 }
1050
1051 /*
1052  * Are there way too many processes in the direct reclaim path already?
1053  */
1054 static int too_many_isolated(struct zone *zone, int file,
1055                 struct scan_control *sc)
1056 {
1057         unsigned long inactive, isolated;
1058
1059         if (current_is_kswapd())
1060                 return 0;
1061
1062         if (!scanning_global_lru(sc))
1063                 return 0;
1064
1065         if (file) {
1066                 inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1067                 isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1068         } else {
1069                 inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1070                 isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1071         }
1072
1073         return isolated > inactive;
1074 }
1075
1076 /*
1077  * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
1078  * of reclaimed pages
1079  */
1080 static unsigned long shrink_inactive_list(unsigned long max_scan,
1081                         struct zone *zone, struct scan_control *sc,
1082                         int priority, int file)
1083 {
1084         LIST_HEAD(page_list);
1085         struct pagevec pvec;
1086         unsigned long nr_scanned = 0;
1087         unsigned long nr_reclaimed = 0;
1088         struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1089         int lumpy_reclaim = 0;
1090
1091         while (unlikely(too_many_isolated(zone, file, sc))) {
1092                 congestion_wait(WRITE, HZ/10);
1093
1094                 /* We are about to die and free our memory. Return now. */
1095                 if (fatal_signal_pending(current))
1096                         return SWAP_CLUSTER_MAX;
1097         }
1098
1099         /*
1100          * If we need a large contiguous chunk of memory, or have
1101          * trouble getting a small set of contiguous pages, we
1102          * will reclaim both active and inactive pages.
1103          *
1104          * We use the same threshold as pageout congestion_wait below.
1105          */
1106         if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
1107                 lumpy_reclaim = 1;
1108         else if (sc->order && priority < DEF_PRIORITY - 2)
1109                 lumpy_reclaim = 1;
1110
1111         pagevec_init(&pvec, 1);
1112
1113         lru_add_drain();
1114         spin_lock_irq(&zone->lru_lock);
1115         do {
1116                 struct page *page;
1117                 unsigned long nr_taken;
1118                 unsigned long nr_scan;
1119                 unsigned long nr_freed;
1120                 unsigned long nr_active;
1121                 unsigned int count[NR_LRU_LISTS] = { 0, };
1122                 int mode = lumpy_reclaim ? ISOLATE_BOTH : ISOLATE_INACTIVE;
1123                 unsigned long nr_anon;
1124                 unsigned long nr_file;
1125
1126                 nr_taken = sc->isolate_pages(sc->swap_cluster_max,
1127                              &page_list, &nr_scan, sc->order, mode,
1128                                 zone, sc->mem_cgroup, 0, file);
1129
1130                 if (scanning_global_lru(sc)) {
1131                         zone->pages_scanned += nr_scan;
1132                         if (current_is_kswapd())
1133                                 __count_zone_vm_events(PGSCAN_KSWAPD, zone,
1134                                                        nr_scan);
1135                         else
1136                                 __count_zone_vm_events(PGSCAN_DIRECT, zone,
1137                                                        nr_scan);
1138                 }
1139
1140                 if (nr_taken == 0)
1141                         goto done;
1142
1143                 nr_active = clear_active_flags(&page_list, count);
1144                 __count_vm_events(PGDEACTIVATE, nr_active);
1145
1146                 __mod_zone_page_state(zone, NR_ACTIVE_FILE,
1147                                                 -count[LRU_ACTIVE_FILE]);
1148                 __mod_zone_page_state(zone, NR_INACTIVE_FILE,
1149                                                 -count[LRU_INACTIVE_FILE]);
1150                 __mod_zone_page_state(zone, NR_ACTIVE_ANON,
1151                                                 -count[LRU_ACTIVE_ANON]);
1152                 __mod_zone_page_state(zone, NR_INACTIVE_ANON,
1153                                                 -count[LRU_INACTIVE_ANON]);
1154
1155                 nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
1156                 nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
1157                 __mod_zone_page_state(zone, NR_ISOLATED_ANON, nr_anon);
1158                 __mod_zone_page_state(zone, NR_ISOLATED_FILE, nr_file);
1159
1160                 reclaim_stat->recent_scanned[0] += count[LRU_INACTIVE_ANON];
1161                 reclaim_stat->recent_scanned[0] += count[LRU_ACTIVE_ANON];
1162                 reclaim_stat->recent_scanned[1] += count[LRU_INACTIVE_FILE];
1163                 reclaim_stat->recent_scanned[1] += count[LRU_ACTIVE_FILE];
1164
1165                 spin_unlock_irq(&zone->lru_lock);
1166
1167                 nr_scanned += nr_scan;
1168                 nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
1169
1170                 /*
1171                  * If we are direct reclaiming for contiguous pages and we do
1172                  * not reclaim everything in the list, try again and wait
1173                  * for IO to complete. This will stall high-order allocations
1174                  * but that should be acceptable to the caller
1175                  */
1176                 if (nr_freed < nr_taken && !current_is_kswapd() &&
1177                     lumpy_reclaim) {
1178                         congestion_wait(BLK_RW_ASYNC, HZ/10);
1179
1180                         /*
1181                          * The attempt at page out may have made some
1182                          * of the pages active, mark them inactive again.
1183                          */
1184                         nr_active = clear_active_flags(&page_list, count);
1185                         count_vm_events(PGDEACTIVATE, nr_active);
1186
1187                         nr_freed += shrink_page_list(&page_list, sc,
1188                                                         PAGEOUT_IO_SYNC);
1189                 }
1190
1191                 nr_reclaimed += nr_freed;
1192
1193                 local_irq_disable();
1194                 if (current_is_kswapd())
1195                         __count_vm_events(KSWAPD_STEAL, nr_freed);
1196                 __count_zone_vm_events(PGSTEAL, zone, nr_freed);
1197
1198                 spin_lock(&zone->lru_lock);
1199                 /*
1200                  * Put back any unfreeable pages.
1201                  */
1202                 while (!list_empty(&page_list)) {
1203                         int lru;
1204                         page = lru_to_page(&page_list);
1205                         VM_BUG_ON(PageLRU(page));
1206                         list_del(&page->lru);
1207                         if (unlikely(!page_evictable(page, NULL))) {
1208                                 spin_unlock_irq(&zone->lru_lock);
1209                                 putback_lru_page(page);
1210                                 spin_lock_irq(&zone->lru_lock);
1211                                 continue;
1212                         }
1213                         SetPageLRU(page);
1214                         lru = page_lru(page);
1215                         add_page_to_lru_list(zone, page, lru);
1216                         if (is_active_lru(lru)) {
1217                                 int file = is_file_lru(lru);
1218                                 reclaim_stat->recent_rotated[file]++;
1219                         }
1220                         if (!pagevec_add(&pvec, page)) {
1221                                 spin_unlock_irq(&zone->lru_lock);
1222                                 __pagevec_release(&pvec);
1223                                 spin_lock_irq(&zone->lru_lock);
1224                         }
1225                 }
1226                 __mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon);
1227                 __mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file);
1228
1229         } while (nr_scanned < max_scan);
1230
1231 done:
1232         spin_unlock_irq(&zone->lru_lock);
1233         pagevec_release(&pvec);
1234         return nr_reclaimed;
1235 }
1236
1237 /*
1238  * We are about to scan this zone at a certain priority level.  If that priority
1239  * level is smaller (ie: more urgent) than the previous priority, then note
1240  * that priority level within the zone.  This is done so that when the next
1241  * process comes in to scan this zone, it will immediately start out at this
1242  * priority level rather than having to build up its own scanning priority.
1243  * Here, this priority affects only the reclaim-mapped threshold.
1244  */
1245 static inline void note_zone_scanning_priority(struct zone *zone, int priority)
1246 {
1247         if (priority < zone->prev_priority)
1248                 zone->prev_priority = priority;
1249 }
1250
1251 /*
1252  * This moves pages from the active list to the inactive list.
1253  *
1254  * We move them the other way if the page is referenced by one or more
1255  * processes, from rmap.
1256  *
1257  * If the pages are mostly unmapped, the processing is fast and it is
1258  * appropriate to hold zone->lru_lock across the whole operation.  But if
1259  * the pages are mapped, the processing is slow (page_referenced()) so we
1260  * should drop zone->lru_lock around each page.  It's impossible to balance
1261  * this, so instead we remove the pages from the LRU while processing them.
1262  * It is safe to rely on PG_active against the non-LRU pages in here because
1263  * nobody will play with that bit on a non-LRU page.
1264  *
1265  * The downside is that we have to touch page->_count against each page.
1266  * But we had to alter page->flags anyway.
1267  */
1268
1269 static void move_active_pages_to_lru(struct zone *zone,
1270                                      struct list_head *list,
1271                                      enum lru_list lru)
1272 {
1273         unsigned long pgmoved = 0;
1274         struct pagevec pvec;
1275         struct page *page;
1276
1277         pagevec_init(&pvec, 1);
1278
1279         while (!list_empty(list)) {
1280                 page = lru_to_page(list);
1281
1282                 VM_BUG_ON(PageLRU(page));
1283                 SetPageLRU(page);
1284
1285                 list_move(&page->lru, &zone->lru[lru].list);
1286                 mem_cgroup_add_lru_list(page, lru);
1287                 pgmoved++;
1288
1289                 if (!pagevec_add(&pvec, page) || list_empty(list)) {
1290                         spin_unlock_irq(&zone->lru_lock);
1291                         if (buffer_heads_over_limit)
1292                                 pagevec_strip(&pvec);
1293                         __pagevec_release(&pvec);
1294                         spin_lock_irq(&zone->lru_lock);
1295                 }
1296         }
1297         __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1298         if (!is_active_lru(lru))
1299                 __count_vm_events(PGDEACTIVATE, pgmoved);
1300 }
1301
1302 static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
1303                         struct scan_control *sc, int priority, int file)
1304 {
1305         unsigned long nr_taken;
1306         unsigned long pgscanned;
1307         unsigned long vm_flags;
1308         LIST_HEAD(l_hold);      /* The pages which were snipped off */
1309         LIST_HEAD(l_active);
1310         LIST_HEAD(l_inactive);
1311         struct page *page;
1312         struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1313         unsigned long nr_rotated = 0;
1314
1315         lru_add_drain();
1316         spin_lock_irq(&zone->lru_lock);
1317         nr_taken = sc->isolate_pages(nr_pages, &l_hold, &pgscanned, sc->order,
1318                                         ISOLATE_ACTIVE, zone,
1319                                         sc->mem_cgroup, 1, file);
1320         /*
1321          * zone->pages_scanned is used for detect zone's oom
1322          * mem_cgroup remembers nr_scan by itself.
1323          */
1324         if (scanning_global_lru(sc)) {
1325                 zone->pages_scanned += pgscanned;
1326         }
1327         reclaim_stat->recent_scanned[file] += nr_taken;
1328
1329         __count_zone_vm_events(PGREFILL, zone, pgscanned);
1330         if (file)
1331                 __mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken);
1332         else
1333                 __mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken);
1334         __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1335         spin_unlock_irq(&zone->lru_lock);
1336
1337         while (!list_empty(&l_hold)) {
1338                 cond_resched();
1339                 page = lru_to_page(&l_hold);
1340                 list_del(&page->lru);
1341
1342                 if (unlikely(!page_evictable(page, NULL))) {
1343                         putback_lru_page(page);
1344                         continue;
1345                 }
1346
1347                 /* page_referenced clears PageReferenced */
1348                 if (page_mapping_inuse(page) &&
1349                     page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
1350                         nr_rotated++;
1351                         /*
1352                          * Identify referenced, file-backed active pages and
1353                          * give them one more trip around the active list. So
1354                          * that executable code get better chances to stay in
1355                          * memory under moderate memory pressure.  Anon pages
1356                          * are not likely to be evicted by use-once streaming
1357                          * IO, plus JVM can create lots of anon VM_EXEC pages,
1358                          * so we ignore them here.
1359                          */
1360                         if ((vm_flags & VM_EXEC) && !PageAnon(page)) {
1361                                 list_add(&page->lru, &l_active);
1362                                 continue;
1363                         }
1364                 }
1365
1366                 ClearPageActive(page);  /* we are de-activating */
1367                 list_add(&page->lru, &l_inactive);
1368         }
1369
1370         /*
1371          * Move pages back to the lru list.
1372          */
1373         spin_lock_irq(&zone->lru_lock);
1374         /*
1375          * Count referenced pages from currently used mappings as rotated,
1376          * even though only some of them are actually re-activated.  This
1377          * helps balance scan pressure between file and anonymous pages in
1378          * get_scan_ratio.
1379          */
1380         reclaim_stat->recent_rotated[file] += nr_rotated;
1381
1382         move_active_pages_to_lru(zone, &l_active,
1383                                                 LRU_ACTIVE + file * LRU_FILE);
1384         move_active_pages_to_lru(zone, &l_inactive,
1385                                                 LRU_BASE   + file * LRU_FILE);
1386         __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1387         spin_unlock_irq(&zone->lru_lock);
1388 }
1389
1390 static int inactive_anon_is_low_global(struct zone *zone)
1391 {
1392         unsigned long active, inactive;
1393
1394         active = zone_page_state(zone, NR_ACTIVE_ANON);
1395         inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1396
1397         if (inactive * zone->inactive_ratio < active)
1398                 return 1;
1399
1400         return 0;
1401 }
1402
1403 /**
1404  * inactive_anon_is_low - check if anonymous pages need to be deactivated
1405  * @zone: zone to check
1406  * @sc:   scan control of this context
1407  *
1408  * Returns true if the zone does not have enough inactive anon pages,
1409  * meaning some active anon pages need to be deactivated.
1410  */
1411 static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc)
1412 {
1413         int low;
1414
1415         if (scanning_global_lru(sc))
1416                 low = inactive_anon_is_low_global(zone);
1417         else
1418                 low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup);
1419         return low;
1420 }
1421
1422 static int inactive_file_is_low_global(struct zone *zone)
1423 {
1424         unsigned long active, inactive;
1425
1426         active = zone_page_state(zone, NR_ACTIVE_FILE);
1427         inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1428
1429         return (active > inactive);
1430 }
1431
1432 /**
1433  * inactive_file_is_low - check if file pages need to be deactivated
1434  * @zone: zone to check
1435  * @sc:   scan control of this context
1436  *
1437  * When the system is doing streaming IO, memory pressure here
1438  * ensures that active file pages get deactivated, until more
1439  * than half of the file pages are on the inactive list.
1440  *
1441  * Once we get to that situation, protect the system's working
1442  * set from being evicted by disabling active file page aging.
1443  *
1444  * This uses a different ratio than the anonymous pages, because
1445  * the page cache uses a use-once replacement algorithm.
1446  */
1447 static int inactive_file_is_low(struct zone *zone, struct scan_control *sc)
1448 {
1449         int low;
1450
1451         if (scanning_global_lru(sc))
1452                 low = inactive_file_is_low_global(zone);
1453         else
1454                 low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup);
1455         return low;
1456 }
1457
1458 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1459         struct zone *zone, struct scan_control *sc, int priority)
1460 {
1461         int file = is_file_lru(lru);
1462
1463         if (lru == LRU_ACTIVE_FILE && inactive_file_is_low(zone, sc)) {
1464                 shrink_active_list(nr_to_scan, zone, sc, priority, file);
1465                 return 0;
1466         }
1467
1468         if (lru == LRU_ACTIVE_ANON && inactive_anon_is_low(zone, sc)) {
1469                 shrink_active_list(nr_to_scan, zone, sc, priority, file);
1470                 return 0;
1471         }
1472         return shrink_inactive_list(nr_to_scan, zone, sc, priority, file);
1473 }
1474
1475 /*
1476  * Determine how aggressively the anon and file LRU lists should be
1477  * scanned.  The relative value of each set of LRU lists is determined
1478  * by looking at the fraction of the pages scanned we did rotate back
1479  * onto the active list instead of evict.
1480  *
1481  * percent[0] specifies how much pressure to put on ram/swap backed
1482  * memory, while percent[1] determines pressure on the file LRUs.
1483  */
1484 static void get_scan_ratio(struct zone *zone, struct scan_control *sc,
1485                                         unsigned long *percent)
1486 {
1487         unsigned long anon, file, free;
1488         unsigned long anon_prio, file_prio;
1489         unsigned long ap, fp;
1490         struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1491
1492         anon  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
1493                 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
1494         file  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
1495                 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
1496
1497         if (scanning_global_lru(sc)) {
1498                 free  = zone_page_state(zone, NR_FREE_PAGES);
1499                 /* If we have very few page cache pages,
1500                    force-scan anon pages. */
1501                 if (unlikely(file + free <= high_wmark_pages(zone))) {
1502                         percent[0] = 100;
1503                         percent[1] = 0;
1504                         return;
1505                 }
1506         }
1507
1508         /*
1509          * OK, so we have swap space and a fair amount of page cache
1510          * pages.  We use the recently rotated / recently scanned
1511          * ratios to determine how valuable each cache is.
1512          *
1513          * Because workloads change over time (and to avoid overflow)
1514          * we keep these statistics as a floating average, which ends
1515          * up weighing recent references more than old ones.
1516          *
1517          * anon in [0], file in [1]
1518          */
1519         if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1520                 spin_lock_irq(&zone->lru_lock);
1521                 reclaim_stat->recent_scanned[0] /= 2;
1522                 reclaim_stat->recent_rotated[0] /= 2;
1523                 spin_unlock_irq(&zone->lru_lock);
1524         }
1525
1526         if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1527                 spin_lock_irq(&zone->lru_lock);
1528                 reclaim_stat->recent_scanned[1] /= 2;
1529                 reclaim_stat->recent_rotated[1] /= 2;
1530                 spin_unlock_irq(&zone->lru_lock);
1531         }
1532
1533         /*
1534          * With swappiness at 100, anonymous and file have the same priority.
1535          * This scanning priority is essentially the inverse of IO cost.
1536          */
1537         anon_prio = sc->swappiness;
1538         file_prio = 200 - sc->swappiness;
1539
1540         /*
1541          * The amount of pressure on anon vs file pages is inversely
1542          * proportional to the fraction of recently scanned pages on
1543          * each list that were recently referenced and in active use.
1544          */
1545         ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1);
1546         ap /= reclaim_stat->recent_rotated[0] + 1;
1547
1548         fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
1549         fp /= reclaim_stat->recent_rotated[1] + 1;
1550
1551         /* Normalize to percentages */
1552         percent[0] = 100 * ap / (ap + fp + 1);
1553         percent[1] = 100 - percent[0];
1554 }
1555
1556 /*
1557  * Smallish @nr_to_scan's are deposited in @nr_saved_scan,
1558  * until we collected @swap_cluster_max pages to scan.
1559  */
1560 static unsigned long nr_scan_try_batch(unsigned long nr_to_scan,
1561                                        unsigned long *nr_saved_scan,
1562                                        unsigned long swap_cluster_max)
1563 {
1564         unsigned long nr;
1565
1566         *nr_saved_scan += nr_to_scan;
1567         nr = *nr_saved_scan;
1568
1569         if (nr >= swap_cluster_max)
1570                 *nr_saved_scan = 0;
1571         else
1572                 nr = 0;
1573
1574         return nr;
1575 }
1576
1577 /*
1578  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1579  */
1580 static void shrink_zone(int priority, struct zone *zone,
1581                                 struct scan_control *sc)
1582 {
1583         unsigned long nr[NR_LRU_LISTS];
1584         unsigned long nr_to_scan;
1585         unsigned long percent[2];       /* anon @ 0; file @ 1 */
1586         enum lru_list l;
1587         unsigned long nr_reclaimed = sc->nr_reclaimed;
1588         unsigned long swap_cluster_max = sc->swap_cluster_max;
1589         int noswap = 0;
1590
1591         /* If we have no swap space, do not bother scanning anon pages. */
1592         if (!sc->may_swap || (nr_swap_pages <= 0)) {
1593                 noswap = 1;
1594                 percent[0] = 0;
1595                 percent[1] = 100;
1596         } else
1597                 get_scan_ratio(zone, sc, percent);
1598
1599         for_each_evictable_lru(l) {
1600                 int file = is_file_lru(l);
1601                 unsigned long scan;
1602
1603                 scan = zone_nr_lru_pages(zone, sc, l);
1604                 if (priority || noswap) {
1605                         scan >>= priority;
1606                         scan = (scan * percent[file]) / 100;
1607                 }
1608                 if (scanning_global_lru(sc))
1609                         nr[l] = nr_scan_try_batch(scan,
1610                                                   &zone->lru[l].nr_saved_scan,
1611                                                   swap_cluster_max);
1612                 else
1613                         nr[l] = scan;
1614         }
1615
1616         while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1617                                         nr[LRU_INACTIVE_FILE]) {
1618                 for_each_evictable_lru(l) {
1619                         if (nr[l]) {
1620                                 nr_to_scan = min(nr[l], swap_cluster_max);
1621                                 nr[l] -= nr_to_scan;
1622
1623                                 nr_reclaimed += shrink_list(l, nr_to_scan,
1624                                                             zone, sc, priority);
1625                         }
1626                 }
1627                 /*
1628                  * On large memory systems, scan >> priority can become
1629                  * really large. This is fine for the starting priority;
1630                  * we want to put equal scanning pressure on each zone.
1631                  * However, if the VM has a harder time of freeing pages,
1632                  * with multiple processes reclaiming pages, the total
1633                  * freeing target can get unreasonably large.
1634                  */
1635                 if (nr_reclaimed > swap_cluster_max &&
1636                         priority < DEF_PRIORITY && !current_is_kswapd())
1637                         break;
1638         }
1639
1640         sc->nr_reclaimed = nr_reclaimed;
1641
1642         /*
1643          * Even if we did not try to evict anon pages at all, we want to
1644          * rebalance the anon lru active/inactive ratio.
1645          */
1646         if (inactive_anon_is_low(zone, sc) && nr_swap_pages > 0)
1647                 shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);
1648
1649         throttle_vm_writeout(sc->gfp_mask);
1650 }
1651
1652 /*
1653  * This is the direct reclaim path, for page-allocating processes.  We only
1654  * try to reclaim pages from zones which will satisfy the caller's allocation
1655  * request.
1656  *
1657  * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
1658  * Because:
1659  * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1660  *    allocation or
1661  * b) The target zone may be at high_wmark_pages(zone) but the lower zones
1662  *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
1663  *    zone defense algorithm.
1664  *
1665  * If a zone is deemed to be full of pinned pages then just give it a light
1666  * scan then give up on it.
1667  */
1668 static void shrink_zones(int priority, struct zonelist *zonelist,
1669                                         struct scan_control *sc)
1670 {
1671         enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);
1672         struct zoneref *z;
1673         struct zone *zone;
1674
1675         sc->all_unreclaimable = 1;
1676         for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
1677                                         sc->nodemask) {
1678                 if (!populated_zone(zone))
1679                         continue;
1680                 /*
1681                  * Take care memory controller reclaiming has small influence
1682                  * to global LRU.
1683                  */
1684                 if (scanning_global_lru(sc)) {
1685                         if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1686                                 continue;
1687                         note_zone_scanning_priority(zone, priority);
1688
1689                         if (zone_is_all_unreclaimable(zone) &&
1690                                                 priority != DEF_PRIORITY)
1691                                 continue;       /* Let kswapd poll it */
1692                         sc->all_unreclaimable = 0;
1693                 } else {
1694                         /*
1695                          * Ignore cpuset limitation here. We just want to reduce
1696                          * # of used pages by us regardless of memory shortage.
1697                          */
1698                         sc->all_unreclaimable = 0;
1699                         mem_cgroup_note_reclaim_priority(sc->mem_cgroup,
1700                                                         priority);
1701                 }
1702
1703                 shrink_zone(priority, zone, sc);
1704         }
1705 }
1706
1707 /*
1708  * This is the main entry point to direct page reclaim.
1709  *
1710  * If a full scan of the inactive list fails to free enough memory then we
1711  * are "out of memory" and something needs to be killed.
1712  *
1713  * If the caller is !__GFP_FS then the probability of a failure is reasonably
1714  * high - the zone may be full of dirty or under-writeback pages, which this
1715  * caller can't do much about.  We kick pdflush and take explicit naps in the
1716  * hope that some of these pages can be written.  But if the allocating task
1717  * holds filesystem locks which prevent writeout this might not work, and the
1718  * allocation attempt will fail.
1719  *
1720  * returns:     0, if no pages reclaimed
1721  *              else, the number of pages reclaimed
1722  */
1723 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
1724                                         struct scan_control *sc)
1725 {
1726         int priority;
1727         unsigned long ret = 0;
1728         unsigned long total_scanned = 0;
1729         struct reclaim_state *reclaim_state = current->reclaim_state;
1730         unsigned long lru_pages = 0;
1731         struct zoneref *z;
1732         struct zone *zone;
1733         enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);
1734
1735         delayacct_freepages_start();
1736
1737         if (scanning_global_lru(sc))
1738                 count_vm_event(ALLOCSTALL);
1739         /*
1740          * mem_cgroup will not do shrink_slab.
1741          */
1742         if (scanning_global_lru(sc)) {
1743                 for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
1744
1745                         if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1746                                 continue;
1747
1748                         lru_pages += zone_reclaimable_pages(zone);
1749                 }
1750         }
1751
1752         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1753                 sc->nr_scanned = 0;
1754                 if (!priority)
1755                         disable_swap_token();
1756                 shrink_zones(priority, zonelist, sc);
1757                 /*
1758                  * Don't shrink slabs when reclaiming memory from
1759                  * over limit cgroups
1760                  */
1761                 if (scanning_global_lru(sc)) {
1762                         shrink_slab(sc->nr_scanned, sc->gfp_mask, lru_pages);
1763                         if (reclaim_state) {
1764                                 sc->nr_reclaimed += reclaim_state->reclaimed_slab;
1765                                 reclaim_state->reclaimed_slab = 0;
1766                         }
1767                 }
1768                 total_scanned += sc->nr_scanned;
1769                 if (sc->nr_reclaimed >= sc->swap_cluster_max) {
1770                         ret = sc->nr_reclaimed;
1771                         goto out;
1772                 }
1773
1774                 /*
1775                  * Try to write back as many pages as we just scanned.  This
1776                  * tends to cause slow streaming writers to write data to the
1777                  * disk smoothly, at the dirtying rate, which is nice.   But
1778                  * that's undesirable in laptop mode, where we *want* lumpy
1779                  * writeout.  So in laptop mode, write out the whole world.
1780                  */
1781                 if (total_scanned > sc->swap_cluster_max +
1782                                         sc->swap_cluster_max / 2) {
1783                         wakeup_flusher_threads(laptop_mode ? 0 : total_scanned);
1784                         sc->may_writepage = 1;
1785                 }
1786
1787                 /* Take a nap, wait for some writeback to complete */
1788                 if (sc->nr_scanned && priority < DEF_PRIORITY - 2)
1789                         congestion_wait(BLK_RW_ASYNC, HZ/10);
1790         }
1791         /* top priority shrink_zones still had more to do? don't OOM, then */
1792         if (!sc->all_unreclaimable && scanning_global_lru(sc))
1793                 ret = sc->nr_reclaimed;
1794 out:
1795         /*
1796          * Now that we've scanned all the zones at this priority level, note
1797          * that level within the zone so that the next thread which performs
1798          * scanning of this zone will immediately start out at this priority
1799          * level.  This affects only the decision whether or not to bring
1800          * mapped pages onto the inactive list.
1801          */
1802         if (priority < 0)
1803                 priority = 0;
1804
1805         if (scanning_global_lru(sc)) {
1806                 for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
1807
1808                         if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1809                                 continue;
1810
1811                         zone->prev_priority = priority;
1812                 }
1813         } else
1814                 mem_cgroup_record_reclaim_priority(sc->mem_cgroup, priority);
1815
1816         delayacct_freepages_end();
1817
1818         return ret;
1819 }
1820
1821 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
1822                                 gfp_t gfp_mask, nodemask_t *nodemask)
1823 {
1824         struct scan_control sc = {
1825                 .gfp_mask = gfp_mask,
1826                 .may_writepage = !laptop_mode,
1827                 .swap_cluster_max = SWAP_CLUSTER_MAX,
1828                 .may_unmap = 1,
1829                 .may_swap = 1,
1830                 .swappiness = vm_swappiness,
1831                 .order = order,
1832                 .mem_cgroup = NULL,
1833                 .isolate_pages = isolate_pages_global,
1834                 .nodemask = nodemask,
1835         };
1836
1837         return do_try_to_free_pages(zonelist, &sc);
1838 }
1839
1840 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
1841
1842 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
1843                                            gfp_t gfp_mask,
1844                                            bool noswap,
1845                                            unsigned int swappiness)
1846 {
1847         struct scan_control sc = {
1848                 .may_writepage = !laptop_mode,
1849                 .may_unmap = 1,
1850                 .may_swap = !noswap,
1851                 .swap_cluster_max = SWAP_CLUSTER_MAX,
1852                 .swappiness = swappiness,
1853                 .order = 0,
1854                 .mem_cgroup = mem_cont,
1855                 .isolate_pages = mem_cgroup_isolate_pages,
1856                 .nodemask = NULL, /* we don't care the placement */
1857         };
1858         struct zonelist *zonelist;
1859
1860         sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
1861                         (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
1862         zonelist = NODE_DATA(numa_node_id())->node_zonelists;
1863         return do_try_to_free_pages(zonelist, &sc);
1864 }
1865 #endif
1866
1867 /*
1868  * For kswapd, balance_pgdat() will work across all this node's zones until
1869  * they are all at high_wmark_pages(zone).
1870  *
1871  * Returns the number of pages which were actually freed.
1872  *
1873  * There is special handling here for zones which are full of pinned pages.
1874  * This can happen if the pages are all mlocked, or if they are all used by
1875  * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
1876  * What we do is to detect the case where all pages in the zone have been
1877  * scanned twice and there has been zero successful reclaim.  Mark the zone as
1878  * dead and from now on, only perform a short scan.  Basically we're polling
1879  * the zone for when the problem goes away.
1880  *
1881  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
1882  * zones which have free_pages > high_wmark_pages(zone), but once a zone is
1883  * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
1884  * lower zones regardless of the number of free pages in the lower zones. This
1885  * interoperates with the page allocator fallback scheme to ensure that aging
1886  * of pages is balanced across the zones.
1887  */
1888 static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
1889 {
1890         int all_zones_ok;
1891         int priority;
1892         int i;
1893         unsigned long total_scanned;
1894         struct reclaim_state *reclaim_state = current->reclaim_state;
1895         struct scan_control sc = {
1896                 .gfp_mask = GFP_KERNEL,
1897                 .may_unmap = 1,
1898                 .may_swap = 1,
1899                 .swap_cluster_max = SWAP_CLUSTER_MAX,
1900                 .swappiness = vm_swappiness,
1901                 .order = order,
1902                 .mem_cgroup = NULL,
1903                 .isolate_pages = isolate_pages_global,
1904         };
1905         /*
1906          * temp_priority is used to remember the scanning priority at which
1907          * this zone was successfully refilled to
1908          * free_pages == high_wmark_pages(zone).
1909          */
1910         int temp_priority[MAX_NR_ZONES];
1911
1912 loop_again:
1913         total_scanned = 0;
1914         sc.nr_reclaimed = 0;
1915         sc.may_writepage = !laptop_mode;
1916         count_vm_event(PAGEOUTRUN);
1917
1918         for (i = 0; i < pgdat->nr_zones; i++)
1919                 temp_priority[i] = DEF_PRIORITY;
1920
1921         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1922                 int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
1923                 unsigned long lru_pages = 0;
1924
1925                 /* The swap token gets in the way of swapout... */
1926                 if (!priority)
1927                         disable_swap_token();
1928
1929                 all_zones_ok = 1;
1930
1931                 /*
1932                  * Scan in the highmem->dma direction for the highest
1933                  * zone which needs scanning
1934                  */
1935                 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1936                         struct zone *zone = pgdat->node_zones + i;
1937
1938                         if (!populated_zone(zone))
1939                                 continue;
1940
1941                         if (zone_is_all_unreclaimable(zone) &&
1942                             priority != DEF_PRIORITY)
1943                                 continue;
1944
1945                         /*
1946                          * Do some background aging of the anon list, to give
1947                          * pages a chance to be referenced before reclaiming.
1948                          */
1949                         if (inactive_anon_is_low(zone, &sc))
1950                                 shrink_active_list(SWAP_CLUSTER_MAX, zone,
1951                                                         &sc, priority, 0);
1952
1953                         if (!zone_watermark_ok(zone, order,
1954                                         high_wmark_pages(zone), 0, 0)) {
1955                                 end_zone = i;
1956                                 break;
1957                         }
1958                 }
1959                 if (i < 0)
1960                         goto out;
1961
1962                 for (i = 0; i <= end_zone; i++) {
1963                         struct zone *zone = pgdat->node_zones + i;
1964
1965                         lru_pages += zone_reclaimable_pages(zone);
1966                 }
1967
1968                 /*
1969                  * Now scan the zone in the dma->highmem direction, stopping
1970                  * at the last zone which needs scanning.
1971                  *
1972                  * We do this because the page allocator works in the opposite
1973                  * direction.  This prevents the page allocator from allocating
1974                  * pages behind kswapd's direction of progress, which would
1975                  * cause too much scanning of the lower zones.
1976                  */
1977                 for (i = 0; i <= end_zone; i++) {
1978                         struct zone *zone = pgdat->node_zones + i;
1979                         int nr_slab;
1980
1981                         if (!populated_zone(zone))
1982                                 continue;
1983
1984                         if (zone_is_all_unreclaimable(zone) &&
1985                                         priority != DEF_PRIORITY)
1986                                 continue;
1987
1988                         if (!zone_watermark_ok(zone, order,
1989                                         high_wmark_pages(zone), end_zone, 0))
1990                                 all_zones_ok = 0;
1991                         temp_priority[i] = priority;
1992                         sc.nr_scanned = 0;
1993                         note_zone_scanning_priority(zone, priority);
1994                         /*
1995                          * We put equal pressure on every zone, unless one
1996                          * zone has way too many pages free already.
1997                          */
1998                         if (!zone_watermark_ok(zone, order,
1999                                         8*high_wmark_pages(zone), end_zone, 0))
2000                                 shrink_zone(priority, zone, &sc);
2001                         reclaim_state->reclaimed_slab = 0;
2002                         nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
2003                                                 lru_pages);
2004                         sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2005                         total_scanned += sc.nr_scanned;
2006                         if (zone_is_all_unreclaimable(zone))
2007                                 continue;
2008                         if (nr_slab == 0 && zone->pages_scanned >=
2009                                         (zone_reclaimable_pages(zone) * 6))
2010                                         zone_set_flag(zone,
2011                                                       ZONE_ALL_UNRECLAIMABLE);
2012                         /*
2013                          * If we've done a decent amount of scanning and
2014                          * the reclaim ratio is low, start doing writepage
2015                          * even in laptop mode
2016                          */
2017                         if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2018                             total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
2019                                 sc.may_writepage = 1;
2020                 }
2021                 if (all_zones_ok)
2022                         break;          /* kswapd: all done */
2023                 /*
2024                  * OK, kswapd is getting into trouble.  Take a nap, then take
2025                  * another pass across the zones.
2026                  */
2027                 if (total_scanned && priority < DEF_PRIORITY - 2)
2028                         congestion_wait(BLK_RW_ASYNC, HZ/10);
2029
2030                 /*
2031                  * We do this so kswapd doesn't build up large priorities for
2032                  * example when it is freeing in parallel with allocators. It
2033                  * matches the direct reclaim path behaviour in terms of impact
2034                  * on zone->*_priority.
2035                  */
2036                 if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2037                         break;
2038         }
2039 out:
2040         /*
2041          * Note within each zone the priority level at which this zone was
2042          * brought into a happy state.  So that the next thread which scans this
2043          * zone will start out at that priority level.
2044          */
2045         for (i = 0; i < pgdat->nr_zones; i++) {
2046                 struct zone *zone = pgdat->node_zones + i;
2047
2048                 zone->prev_priority = temp_priority[i];
2049         }
2050         if (!all_zones_ok) {
2051                 cond_resched();
2052
2053                 try_to_freeze();
2054
2055                 /*
2056                  * Fragmentation may mean that the system cannot be
2057                  * rebalanced for high-order allocations in all zones.
2058                  * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2059                  * it means the zones have been fully scanned and are still
2060                  * not balanced. For high-order allocations, there is
2061                  * little point trying all over again as kswapd may
2062                  * infinite loop.
2063                  *
2064                  * Instead, recheck all watermarks at order-0 as they
2065                  * are the most important. If watermarks are ok, kswapd will go
2066                  * back to sleep. High-order users can still perform direct
2067                  * reclaim if they wish.
2068                  */
2069                 if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2070                         order = sc.order = 0;
2071
2072                 goto loop_again;
2073         }
2074
2075         return sc.nr_reclaimed;
2076 }
2077
2078 /*
2079  * The background pageout daemon, started as a kernel thread
2080  * from the init process.
2081  *
2082  * This basically trickles out pages so that we have _some_
2083  * free memory available even if there is no other activity
2084  * that frees anything up. This is needed for things like routing
2085  * etc, where we otherwise might have all activity going on in
2086  * asynchronous contexts that cannot page things out.
2087  *
2088  * If there are applications that are active memory-allocators
2089  * (most normal use), this basically shouldn't matter.
2090  */
2091 static int kswapd(void *p)
2092 {
2093         unsigned long order;
2094         pg_data_t *pgdat = (pg_data_t*)p;
2095         struct task_struct *tsk = current;
2096         DEFINE_WAIT(wait);
2097         struct reclaim_state reclaim_state = {
2098                 .reclaimed_slab = 0,
2099         };
2100         const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2101
2102         lockdep_set_current_reclaim_state(GFP_KERNEL);
2103
2104         if (!cpumask_empty(cpumask))
2105                 set_cpus_allowed_ptr(tsk, cpumask);
2106         current->reclaim_state = &reclaim_state;
2107
2108         /*
2109          * Tell the memory management that we're a "memory allocator",
2110          * and that if we need more memory we should get access to it
2111          * regardless (see "__alloc_pages()"). "kswapd" should
2112          * never get caught in the normal page freeing logic.
2113          *
2114          * (Kswapd normally doesn't need memory anyway, but sometimes
2115          * you need a small amount of memory in order to be able to
2116          * page out something else, and this flag essentially protects
2117          * us from recursively trying to free more memory as we're
2118          * trying to free the first piece of memory in the first place).
2119          */
2120         tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2121         set_freezable();
2122
2123         order = 0;
2124         for ( ; ; ) {
2125                 unsigned long new_order;
2126
2127                 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2128                 new_order = pgdat->kswapd_max_order;
2129                 pgdat->kswapd_max_order = 0;
2130                 if (order < new_order) {
2131                         /*
2132                          * Don't sleep if someone wants a larger 'order'
2133                          * allocation
2134                          */
2135                         order = new_order;
2136                 } else {
2137                         if (!freezing(current))
2138                                 schedule();
2139
2140                         order = pgdat->kswapd_max_order;
2141                 }
2142                 finish_wait(&pgdat->kswapd_wait, &wait);
2143
2144                 if (!try_to_freeze()) {
2145                         /* We can speed up thawing tasks if we don't call
2146                          * balance_pgdat after returning from the refrigerator
2147                          */
2148                         balance_pgdat(pgdat, order);
2149                 }
2150         }
2151         return 0;
2152 }
2153
2154 /*
2155  * A zone is low on free memory, so wake its kswapd task to service it.
2156  */
2157 void wakeup_kswapd(struct zone *zone, int order)
2158 {
2159         pg_data_t *pgdat;
2160
2161         if (!populated_zone(zone))
2162                 return;
2163
2164         pgdat = zone->zone_pgdat;
2165         if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
2166                 return;
2167         if (pgdat->kswapd_max_order < order)
2168                 pgdat->kswapd_max_order = order;
2169         if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2170                 return;
2171         if (!waitqueue_active(&pgdat->kswapd_wait))
2172                 return;
2173         wake_up_interruptible(&pgdat->kswapd_wait);
2174 }
2175
2176 /*
2177  * The reclaimable count would be mostly accurate.
2178  * The less reclaimable pages may be
2179  * - mlocked pages, which will be moved to unevictable list when encountered
2180  * - mapped pages, which may require several travels to be reclaimed
2181  * - dirty pages, which is not "instantly" reclaimable
2182  */
2183 unsigned long global_reclaimable_pages(void)
2184 {
2185         int nr;
2186
2187         nr = global_page_state(NR_ACTIVE_FILE) +
2188              global_page_state(NR_INACTIVE_FILE);
2189
2190         if (nr_swap_pages > 0)
2191                 nr += global_page_state(NR_ACTIVE_ANON) +
2192                       global_page_state(NR_INACTIVE_ANON);
2193
2194         return nr;
2195 }
2196
2197 unsigned long zone_reclaimable_pages(struct zone *zone)
2198 {
2199         int nr;
2200
2201         nr = zone_page_state(zone, NR_ACTIVE_FILE) +
2202              zone_page_state(zone, NR_INACTIVE_FILE);
2203
2204         if (nr_swap_pages > 0)
2205                 nr += zone_page_state(zone, NR_ACTIVE_ANON) +
2206                       zone_page_state(zone, NR_INACTIVE_ANON);
2207
2208         return nr;
2209 }
2210
2211 #ifdef CONFIG_HIBERNATION
2212 /*
2213  * Helper function for shrink_all_memory().  Tries to reclaim 'nr_pages' pages
2214  * from LRU lists system-wide, for given pass and priority.
2215  *
2216  * For pass > 3 we also try to shrink the LRU lists that contain a few pages
2217  */
2218 static void shrink_all_zones(unsigned long nr_pages, int prio,
2219                                       int pass, struct scan_control *sc)
2220 {
2221         struct zone *zone;
2222         unsigned long nr_reclaimed = 0;
2223
2224         for_each_populated_zone(zone) {
2225                 enum lru_list l;
2226
2227                 if (zone_is_all_unreclaimable(zone) && prio != DEF_PRIORITY)
2228                         continue;
2229
2230                 for_each_evictable_lru(l) {
2231                         enum zone_stat_item ls = NR_LRU_BASE + l;
2232                         unsigned long lru_pages = zone_page_state(zone, ls);
2233
2234                         /* For pass = 0, we don't shrink the active list */
2235                         if (pass == 0 && (l == LRU_ACTIVE_ANON ||
2236                                                 l == LRU_ACTIVE_FILE))
2237                                 continue;
2238
2239                         zone->lru[l].nr_saved_scan += (lru_pages >> prio) + 1;
2240                         if (zone->lru[l].nr_saved_scan >= nr_pages || pass > 3) {
2241                                 unsigned long nr_to_scan;
2242
2243                                 zone->lru[l].nr_saved_scan = 0;
2244                                 nr_to_scan = min(nr_pages, lru_pages);
2245                                 nr_reclaimed += shrink_list(l, nr_to_scan, zone,
2246                                                                 sc, prio);
2247                                 if (nr_reclaimed >= nr_pages) {
2248                                         sc->nr_reclaimed += nr_reclaimed;
2249                                         return;
2250                                 }
2251                         }
2252                 }
2253         }
2254         sc->nr_reclaimed += nr_reclaimed;
2255 }
2256
2257 /*
2258  * Try to free `nr_pages' of memory, system-wide, and return the number of
2259  * freed pages.
2260  *
2261  * Rather than trying to age LRUs the aim is to preserve the overall
2262  * LRU order by reclaiming preferentially
2263  * inactive > active > active referenced > active mapped
2264  */
2265 unsigned long shrink_all_memory(unsigned long nr_pages)
2266 {
2267         unsigned long lru_pages, nr_slab;
2268         int pass;
2269         struct reclaim_state reclaim_state;
2270         struct scan_control sc = {
2271                 .gfp_mask = GFP_KERNEL,
2272                 .may_unmap = 0,
2273                 .may_writepage = 1,
2274                 .isolate_pages = isolate_pages_global,
2275                 .nr_reclaimed = 0,
2276         };
2277
2278         current->reclaim_state = &reclaim_state;
2279
2280         lru_pages = global_reclaimable_pages();
2281         nr_slab = global_page_state(NR_SLAB_RECLAIMABLE);
2282         /* If slab caches are huge, it's better to hit them first */
2283         while (nr_slab >= lru_pages) {
2284                 reclaim_state.reclaimed_slab = 0;
2285                 shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
2286                 if (!reclaim_state.reclaimed_slab)
2287                         break;
2288
2289                 sc.nr_reclaimed += reclaim_state.reclaimed_slab;
2290                 if (sc.nr_reclaimed >= nr_pages)
2291                         goto out;
2292
2293                 nr_slab -= reclaim_state.reclaimed_slab;
2294         }
2295
2296         /*
2297          * We try to shrink LRUs in 5 passes:
2298          * 0 = Reclaim from inactive_list only
2299          * 1 = Reclaim from active list but don't reclaim mapped
2300          * 2 = 2nd pass of type 1
2301          * 3 = Reclaim mapped (normal reclaim)
2302          * 4 = 2nd pass of type 3
2303          */
2304         for (pass = 0; pass < 5; pass++) {
2305                 int prio;
2306
2307                 /* Force reclaiming mapped pages in the passes #3 and #4 */
2308                 if (pass > 2)
2309                         sc.may_unmap = 1;
2310
2311                 for (prio = DEF_PRIORITY; prio >= 0; prio--) {
2312                         unsigned long nr_to_scan = nr_pages - sc.nr_reclaimed;
2313
2314                         sc.nr_scanned = 0;
2315                         sc.swap_cluster_max = nr_to_scan;
2316                         shrink_all_zones(nr_to_scan, prio, pass, &sc);
2317                         if (sc.nr_reclaimed >= nr_pages)
2318                                 goto out;
2319
2320                         reclaim_state.reclaimed_slab = 0;
2321                         shrink_slab(sc.nr_scanned, sc.gfp_mask,
2322                                     global_reclaimable_pages());
2323                         sc.nr_reclaimed += reclaim_state.reclaimed_slab;
2324                         if (sc.nr_reclaimed >= nr_pages)
2325                                 goto out;
2326
2327                         if (sc.nr_scanned && prio < DEF_PRIORITY - 2)
2328                                 congestion_wait(BLK_RW_ASYNC, HZ / 10);
2329                 }
2330         }
2331
2332         /*
2333          * If sc.nr_reclaimed = 0, we could not shrink LRUs, but there may be
2334          * something in slab caches
2335          */
2336         if (!sc.nr_reclaimed) {
2337                 do {
2338                         reclaim_state.reclaimed_slab = 0;
2339                         shrink_slab(nr_pages, sc.gfp_mask,
2340                                     global_reclaimable_pages());
2341                         sc.nr_reclaimed += reclaim_state.reclaimed_slab;
2342                 } while (sc.nr_reclaimed < nr_pages &&
2343                                 reclaim_state.reclaimed_slab > 0);
2344         }
2345
2346
2347 out:
2348         current->reclaim_state = NULL;
2349
2350         return sc.nr_reclaimed;
2351 }
2352 #endif /* CONFIG_HIBERNATION */
2353
2354 /* It's optimal to keep kswapds on the same CPUs as their memory, but
2355    not required for correctness.  So if the last cpu in a node goes
2356    away, we get changed to run anywhere: as the first one comes back,
2357    restore their cpu bindings. */
2358 static int __devinit cpu_callback(struct notifier_block *nfb,
2359                                   unsigned long action, void *hcpu)
2360 {
2361         int nid;
2362
2363         if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
2364                 for_each_node_state(nid, N_HIGH_MEMORY) {
2365                         pg_data_t *pgdat = NODE_DATA(nid);
2366                         const struct cpumask *mask;
2367
2368                         mask = cpumask_of_node(pgdat->node_id);
2369
2370                         if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2371                                 /* One of our CPUs online: restore mask */
2372                                 set_cpus_allowed_ptr(pgdat->kswapd, mask);
2373                 }
2374         }
2375         return NOTIFY_OK;
2376 }
2377
2378 /*
2379  * This kswapd start function will be called by init and node-hot-add.
2380  * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
2381  */
2382 int kswapd_run(int nid)
2383 {
2384         pg_data_t *pgdat = NODE_DATA(nid);
2385         int ret = 0;
2386
2387         if (pgdat->kswapd)
2388                 return 0;
2389
2390         pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
2391         if (IS_ERR(pgdat->kswapd)) {
2392                 /* failure at boot is fatal */
2393                 BUG_ON(system_state == SYSTEM_BOOTING);
2394                 printk("Failed to start kswapd on node %d\n",nid);
2395                 ret = -1;
2396         }
2397         return ret;
2398 }
2399
2400 static int __init kswapd_init(void)
2401 {
2402         int nid;
2403
2404         swap_setup();
2405         for_each_node_state(nid, N_HIGH_MEMORY)
2406                 kswapd_run(nid);
2407         hotcpu_notifier(cpu_callback, 0);
2408         return 0;
2409 }
2410
2411 module_init(kswapd_init)
2412
2413 #ifdef CONFIG_NUMA
2414 /*
2415  * Zone reclaim mode
2416  *
2417  * If non-zero call zone_reclaim when the number of free pages falls below
2418  * the watermarks.
2419  */
2420 int zone_reclaim_mode __read_mostly;
2421
2422 #define RECLAIM_OFF 0
2423 #define RECLAIM_ZONE (1<<0)     /* Run shrink_inactive_list on the zone */
2424 #define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
2425 #define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
2426
2427 /*
2428  * Priority for ZONE_RECLAIM. This determines the fraction of pages
2429  * of a node considered for each zone_reclaim. 4 scans 1/16th of
2430  * a zone.
2431  */
2432 #define ZONE_RECLAIM_PRIORITY 4
2433
2434 /*
2435  * Percentage of pages in a zone that must be unmapped for zone_reclaim to
2436  * occur.
2437  */
2438 int sysctl_min_unmapped_ratio = 1;
2439
2440 /*
2441  * If the number of slab pages in a zone grows beyond this percentage then
2442  * slab reclaim needs to occur.
2443  */
2444 int sysctl_min_slab_ratio = 5;
2445
2446 static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
2447 {
2448         unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
2449         unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
2450                 zone_page_state(zone, NR_ACTIVE_FILE);
2451
2452         /*
2453          * It's possible for there to be more file mapped pages than
2454          * accounted for by the pages on the file LRU lists because
2455          * tmpfs pages accounted for as ANON can also be FILE_MAPPED
2456          */
2457         return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
2458 }
2459
2460 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
2461 static long zone_pagecache_reclaimable(struct zone *zone)
2462 {
2463         long nr_pagecache_reclaimable;
2464         long delta = 0;
2465
2466         /*
2467          * If RECLAIM_SWAP is set, then all file pages are considered
2468          * potentially reclaimable. Otherwise, we have to worry about
2469          * pages like swapcache and zone_unmapped_file_pages() provides
2470          * a better estimate
2471          */
2472         if (zone_reclaim_mode & RECLAIM_SWAP)
2473                 nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
2474         else
2475                 nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
2476
2477         /* If we can't clean pages, remove dirty pages from consideration */
2478         if (!(zone_reclaim_mode & RECLAIM_WRITE))
2479                 delta += zone_page_state(zone, NR_FILE_DIRTY);
2480
2481         /* Watch for any possible underflows due to delta */
2482         if (unlikely(delta > nr_pagecache_reclaimable))
2483                 delta = nr_pagecache_reclaimable;
2484
2485         return nr_pagecache_reclaimable - delta;
2486 }
2487
2488 /*
2489  * Try to free up some pages from this zone through reclaim.
2490  */
2491 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
2492 {
2493         /* Minimum pages needed in order to stay on node */
2494         const unsigned long nr_pages = 1 << order;
2495         struct task_struct *p = current;
2496         struct reclaim_state reclaim_state;
2497         int priority;
2498         struct scan_control sc = {
2499                 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
2500                 .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
2501                 .may_swap = 1,
2502                 .swap_cluster_max = max_t(unsigned long, nr_pages,
2503                                         SWAP_CLUSTER_MAX),
2504                 .gfp_mask = gfp_mask,
2505                 .swappiness = vm_swappiness,
2506                 .order = order,
2507                 .isolate_pages = isolate_pages_global,
2508         };
2509         unsigned long slab_reclaimable;
2510
2511         disable_swap_token();
2512         cond_resched();
2513         /*
2514          * We need to be able to allocate from the reserves for RECLAIM_SWAP
2515          * and we also need to be able to write out pages for RECLAIM_WRITE
2516          * and RECLAIM_SWAP.
2517          */
2518         p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
2519         reclaim_state.reclaimed_slab = 0;
2520         p->reclaim_state = &reclaim_state;
2521
2522         if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
2523                 /*
2524                  * Free memory by calling shrink zone with increasing
2525                  * priorities until we have enough memory freed.
2526                  */
2527                 priority = ZONE_RECLAIM_PRIORITY;
2528                 do {
2529                         note_zone_scanning_priority(zone, priority);
2530                         shrink_zone(priority, zone, &sc);
2531                         priority--;
2532                 } while (priority >= 0 && sc.nr_reclaimed < nr_pages);
2533         }
2534
2535         slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
2536         if (slab_reclaimable > zone->min_slab_pages) {
2537                 /*
2538                  * shrink_slab() does not currently allow us to determine how
2539                  * many pages were freed in this zone. So we take the current
2540                  * number of slab pages and shake the slab until it is reduced
2541                  * by the same nr_pages that we used for reclaiming unmapped
2542                  * pages.
2543                  *
2544                  * Note that shrink_slab will free memory on all zones and may
2545                  * take a long time.
2546                  */
2547                 while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
2548                         zone_page_state(zone, NR_SLAB_RECLAIMABLE) >
2549                                 slab_reclaimable - nr_pages)
2550                         ;
2551
2552                 /*
2553                  * Update nr_reclaimed by the number of slab pages we
2554                  * reclaimed from this zone.
2555                  */
2556                 sc.nr_reclaimed += slab_reclaimable -
2557                         zone_page_state(zone, NR_SLAB_RECLAIMABLE);
2558         }
2559
2560         p->reclaim_state = NULL;
2561         current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
2562         return sc.nr_reclaimed >= nr_pages;
2563 }
2564
2565 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
2566 {
2567         int node_id;
2568         int ret;
2569
2570         /*
2571          * Zone reclaim reclaims unmapped file backed pages and
2572          * slab pages if we are over the defined limits.
2573          *
2574          * A small portion of unmapped file backed pages is needed for
2575          * file I/O otherwise pages read by file I/O will be immediately
2576          * thrown out if the zone is overallocated. So we do not reclaim
2577          * if less than a specified percentage of the zone is used by
2578          * unmapped file backed pages.
2579          */
2580         if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
2581             zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
2582                 return ZONE_RECLAIM_FULL;
2583
2584         if (zone_is_all_unreclaimable(zone))
2585                 return ZONE_RECLAIM_FULL;
2586
2587         /*
2588          * Do not scan if the allocation should not be delayed.
2589          */
2590         if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
2591                 return ZONE_RECLAIM_NOSCAN;
2592
2593         /*
2594          * Only run zone reclaim on the local zone or on zones that do not
2595          * have associated processors. This will favor the local processor
2596          * over remote processors and spread off node memory allocations
2597          * as wide as possible.
2598          */
2599         node_id = zone_to_nid(zone);
2600         if (node_state(node_id, N_CPU) && node_id != numa_node_id())
2601                 return ZONE_RECLAIM_NOSCAN;
2602
2603         if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
2604                 return ZONE_RECLAIM_NOSCAN;
2605
2606         ret = __zone_reclaim(zone, gfp_mask, order);
2607         zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
2608
2609         if (!ret)
2610                 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
2611
2612         return ret;
2613 }
2614 #endif
2615
2616 /*
2617  * page_evictable - test whether a page is evictable
2618  * @page: the page to test
2619  * @vma: the VMA in which the page is or will be mapped, may be NULL
2620  *
2621  * Test whether page is evictable--i.e., should be placed on active/inactive
2622  * lists vs unevictable list.  The vma argument is !NULL when called from the
2623  * fault path to determine how to instantate a new page.
2624  *
2625  * Reasons page might not be evictable:
2626  * (1) page's mapping marked unevictable
2627  * (2) page is part of an mlocked VMA
2628  *
2629  */
2630 int page_evictable(struct page *page, struct vm_area_struct *vma)
2631 {
2632
2633         if (mapping_unevictable(page_mapping(page)))
2634                 return 0;
2635
2636         if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
2637                 return 0;
2638
2639         return 1;
2640 }
2641
2642 /**
2643  * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list
2644  * @page: page to check evictability and move to appropriate lru list
2645  * @zone: zone page is in
2646  *
2647  * Checks a page for evictability and moves the page to the appropriate
2648  * zone lru list.
2649  *
2650  * Restrictions: zone->lru_lock must be held, page must be on LRU and must
2651  * have PageUnevictable set.
2652  */
2653 static void check_move_unevictable_page(struct page *page, struct zone *zone)
2654 {
2655         VM_BUG_ON(PageActive(page));
2656
2657 retry:
2658         ClearPageUnevictable(page);
2659         if (page_evictable(page, NULL)) {
2660                 enum lru_list l = page_lru_base_type(page);
2661
2662                 __dec_zone_state(zone, NR_UNEVICTABLE);
2663                 list_move(&page->lru, &zone->lru[l].list);
2664                 mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l);
2665                 __inc_zone_state(zone, NR_INACTIVE_ANON + l);
2666                 __count_vm_event(UNEVICTABLE_PGRESCUED);
2667         } else {
2668                 /*
2669                  * rotate unevictable list
2670                  */
2671                 SetPageUnevictable(page);
2672                 list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list);
2673                 mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE);
2674                 if (page_evictable(page, NULL))
2675                         goto retry;
2676         }
2677 }
2678
2679 /**
2680  * scan_mapping_unevictable_pages - scan an address space for evictable pages
2681  * @mapping: struct address_space to scan for evictable pages
2682  *
2683  * Scan all pages in mapping.  Check unevictable pages for
2684  * evictability and move them to the appropriate zone lru list.
2685  */
2686 void scan_mapping_unevictable_pages(struct address_space *mapping)
2687 {
2688         pgoff_t next = 0;
2689         pgoff_t end   = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >>
2690                          PAGE_CACHE_SHIFT;
2691         struct zone *zone;
2692         struct pagevec pvec;
2693
2694         if (mapping->nrpages == 0)
2695                 return;
2696
2697         pagevec_init(&pvec, 0);
2698         while (next < end &&
2699                 pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
2700                 int i;
2701                 int pg_scanned = 0;
2702
2703                 zone = NULL;
2704
2705                 for (i = 0; i < pagevec_count(&pvec); i++) {
2706                         struct page *page = pvec.pages[i];
2707                         pgoff_t page_index = page->index;
2708                         struct zone *pagezone = page_zone(page);
2709
2710                         pg_scanned++;
2711                         if (page_index > next)
2712                                 next = page_index;
2713                         next++;
2714
2715                         if (pagezone != zone) {
2716                                 if (zone)
2717                                         spin_unlock_irq(&zone->lru_lock);
2718                                 zone = pagezone;
2719                                 spin_lock_irq(&zone->lru_lock);
2720                         }
2721
2722                         if (PageLRU(page) && PageUnevictable(page))
2723                                 check_move_unevictable_page(page, zone);
2724                 }
2725                 if (zone)
2726                         spin_unlock_irq(&zone->lru_lock);
2727                 pagevec_release(&pvec);
2728
2729                 count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
2730         }
2731
2732 }
2733
2734 /**
2735  * scan_zone_unevictable_pages - check unevictable list for evictable pages
2736  * @zone - zone of which to scan the unevictable list
2737  *
2738  * Scan @zone's unevictable LRU lists to check for pages that have become
2739  * evictable.  Move those that have to @zone's inactive list where they
2740  * become candidates for reclaim, unless shrink_inactive_zone() decides
2741  * to reactivate them.  Pages that are still unevictable are rotated
2742  * back onto @zone's unevictable list.
2743  */
2744 #define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */
2745 static void scan_zone_unevictable_pages(struct zone *zone)
2746 {
2747         struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list;
2748         unsigned long scan;
2749         unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE);
2750
2751         while (nr_to_scan > 0) {
2752                 unsigned long batch_size = min(nr_to_scan,
2753                                                 SCAN_UNEVICTABLE_BATCH_SIZE);
2754
2755                 spin_lock_irq(&zone->lru_lock);
2756                 for (scan = 0;  scan < batch_size; scan++) {
2757                         struct page *page = lru_to_page(l_unevictable);
2758
2759                         if (!trylock_page(page))
2760                                 continue;
2761
2762                         prefetchw_prev_lru_page(page, l_unevictable, flags);
2763
2764                         if (likely(PageLRU(page) && PageUnevictable(page)))
2765                                 check_move_unevictable_page(page, zone);
2766
2767                         unlock_page(page);
2768                 }
2769                 spin_unlock_irq(&zone->lru_lock);
2770
2771                 nr_to_scan -= batch_size;
2772         }
2773 }
2774
2775
2776 /**
2777  * scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages
2778  *
2779  * A really big hammer:  scan all zones' unevictable LRU lists to check for
2780  * pages that have become evictable.  Move those back to the zones'
2781  * inactive list where they become candidates for reclaim.
2782  * This occurs when, e.g., we have unswappable pages on the unevictable lists,
2783  * and we add swap to the system.  As such, it runs in the context of a task
2784  * that has possibly/probably made some previously unevictable pages
2785  * evictable.
2786  */
2787 static void scan_all_zones_unevictable_pages(void)
2788 {
2789         struct zone *zone;
2790
2791         for_each_zone(zone) {
2792                 scan_zone_unevictable_pages(zone);
2793         }
2794 }
2795
2796 /*
2797  * scan_unevictable_pages [vm] sysctl handler.  On demand re-scan of
2798  * all nodes' unevictable lists for evictable pages
2799  */
2800 unsigned long scan_unevictable_pages;
2801
2802 int scan_unevictable_handler(struct ctl_table *table, int write,
2803                            struct file *file, void __user *buffer,
2804                            size_t *length, loff_t *ppos)
2805 {
2806         proc_doulongvec_minmax(table, write, file, buffer, length, ppos);
2807
2808         if (write && *(unsigned long *)table->data)
2809                 scan_all_zones_unevictable_pages();
2810
2811         scan_unevictable_pages = 0;
2812         return 0;
2813 }
2814
2815 /*
2816  * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
2817  * a specified node's per zone unevictable lists for evictable pages.
2818  */
2819
2820 static ssize_t read_scan_unevictable_node(struct sys_device *dev,
2821                                           struct sysdev_attribute *attr,
2822                                           char *buf)
2823 {
2824         return sprintf(buf, "0\n");     /* always zero; should fit... */
2825 }
2826
2827 static ssize_t write_scan_unevictable_node(struct sys_device *dev,
2828                                            struct sysdev_attribute *attr,
2829                                         const char *buf, size_t count)
2830 {
2831         struct zone *node_zones = NODE_DATA(dev->id)->node_zones;
2832         struct zone *zone;
2833         unsigned long res;
2834         unsigned long req = strict_strtoul(buf, 10, &res);
2835
2836         if (!req)
2837                 return 1;       /* zero is no-op */
2838
2839         for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
2840                 if (!populated_zone(zone))
2841                         continue;
2842                 scan_zone_unevictable_pages(zone);
2843         }
2844         return 1;
2845 }
2846
2847
2848 static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
2849                         read_scan_unevictable_node,
2850                         write_scan_unevictable_node);
2851
2852 int scan_unevictable_register_node(struct node *node)
2853 {
2854         return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages);
2855 }
2856
2857 void scan_unevictable_unregister_node(struct node *node)
2858 {
2859         sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages);
2860 }
2861