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