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