f6616e81fac75d4b703d8c238549e0dc51115062
[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
41 #include <asm/tlbflush.h>
42 #include <asm/div64.h>
43
44 #include <linux/swapops.h>
45
46 #include "internal.h"
47
48 struct scan_control {
49         /* Incremented by the number of inactive pages that were scanned */
50         unsigned long nr_scanned;
51
52         /* This context's GFP mask */
53         gfp_t gfp_mask;
54
55         int may_writepage;
56
57         /* Can pages be swapped as part of reclaim? */
58         int may_swap;
59
60         /* This context's SWAP_CLUSTER_MAX. If freeing memory for
61          * suspend, we effectively ignore SWAP_CLUSTER_MAX.
62          * In this context, it doesn't matter that we scan the
63          * whole list at once. */
64         int swap_cluster_max;
65
66         int swappiness;
67
68         int all_unreclaimable;
69 };
70
71 /*
72  * The list of shrinker callbacks used by to apply pressure to
73  * ageable caches.
74  */
75 struct shrinker {
76         shrinker_t              shrinker;
77         struct list_head        list;
78         int                     seeks;  /* seeks to recreate an obj */
79         long                    nr;     /* objs pending delete */
80 };
81
82 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
83
84 #ifdef ARCH_HAS_PREFETCH
85 #define prefetch_prev_lru_page(_page, _base, _field)                    \
86         do {                                                            \
87                 if ((_page)->lru.prev != _base) {                       \
88                         struct page *prev;                              \
89                                                                         \
90                         prev = lru_to_page(&(_page->lru));              \
91                         prefetch(&prev->_field);                        \
92                 }                                                       \
93         } while (0)
94 #else
95 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
96 #endif
97
98 #ifdef ARCH_HAS_PREFETCHW
99 #define prefetchw_prev_lru_page(_page, _base, _field)                   \
100         do {                                                            \
101                 if ((_page)->lru.prev != _base) {                       \
102                         struct page *prev;                              \
103                                                                         \
104                         prev = lru_to_page(&(_page->lru));              \
105                         prefetchw(&prev->_field);                       \
106                 }                                                       \
107         } while (0)
108 #else
109 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
110 #endif
111
112 /*
113  * From 0 .. 100.  Higher means more swappy.
114  */
115 int vm_swappiness = 60;
116 long vm_total_pages;    /* The total number of pages which the VM controls */
117
118 static LIST_HEAD(shrinker_list);
119 static DECLARE_RWSEM(shrinker_rwsem);
120
121 /*
122  * Add a shrinker callback to be called from the vm
123  */
124 struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
125 {
126         struct shrinker *shrinker;
127
128         shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
129         if (shrinker) {
130                 shrinker->shrinker = theshrinker;
131                 shrinker->seeks = seeks;
132                 shrinker->nr = 0;
133                 down_write(&shrinker_rwsem);
134                 list_add_tail(&shrinker->list, &shrinker_list);
135                 up_write(&shrinker_rwsem);
136         }
137         return shrinker;
138 }
139 EXPORT_SYMBOL(set_shrinker);
140
141 /*
142  * Remove one
143  */
144 void remove_shrinker(struct shrinker *shrinker)
145 {
146         down_write(&shrinker_rwsem);
147         list_del(&shrinker->list);
148         up_write(&shrinker_rwsem);
149         kfree(shrinker);
150 }
151 EXPORT_SYMBOL(remove_shrinker);
152
153 #define SHRINK_BATCH 128
154 /*
155  * Call the shrink functions to age shrinkable caches
156  *
157  * Here we assume it costs one seek to replace a lru page and that it also
158  * takes a seek to recreate a cache object.  With this in mind we age equal
159  * percentages of the lru and ageable caches.  This should balance the seeks
160  * generated by these structures.
161  *
162  * If the vm encounted mapped pages on the LRU it increase the pressure on
163  * slab to avoid swapping.
164  *
165  * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
166  *
167  * `lru_pages' represents the number of on-LRU pages in all the zones which
168  * are eligible for the caller's allocation attempt.  It is used for balancing
169  * slab reclaim versus page reclaim.
170  *
171  * Returns the number of slab objects which we shrunk.
172  */
173 unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
174                         unsigned long lru_pages)
175 {
176         struct shrinker *shrinker;
177         unsigned long ret = 0;
178
179         if (scanned == 0)
180                 scanned = SWAP_CLUSTER_MAX;
181
182         if (!down_read_trylock(&shrinker_rwsem))
183                 return 1;       /* Assume we'll be able to shrink next time */
184
185         list_for_each_entry(shrinker, &shrinker_list, list) {
186                 unsigned long long delta;
187                 unsigned long total_scan;
188                 unsigned long max_pass = (*shrinker->shrinker)(0, gfp_mask);
189
190                 delta = (4 * scanned) / shrinker->seeks;
191                 delta *= max_pass;
192                 do_div(delta, lru_pages + 1);
193                 shrinker->nr += delta;
194                 if (shrinker->nr < 0) {
195                         printk(KERN_ERR "%s: nr=%ld\n",
196                                         __FUNCTION__, shrinker->nr);
197                         shrinker->nr = max_pass;
198                 }
199
200                 /*
201                  * Avoid risking looping forever due to too large nr value:
202                  * never try to free more than twice the estimate number of
203                  * freeable entries.
204                  */
205                 if (shrinker->nr > max_pass * 2)
206                         shrinker->nr = max_pass * 2;
207
208                 total_scan = shrinker->nr;
209                 shrinker->nr = 0;
210
211                 while (total_scan >= SHRINK_BATCH) {
212                         long this_scan = SHRINK_BATCH;
213                         int shrink_ret;
214                         int nr_before;
215
216                         nr_before = (*shrinker->shrinker)(0, gfp_mask);
217                         shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
218                         if (shrink_ret == -1)
219                                 break;
220                         if (shrink_ret < nr_before)
221                                 ret += nr_before - shrink_ret;
222                         count_vm_events(SLABS_SCANNED, this_scan);
223                         total_scan -= this_scan;
224
225                         cond_resched();
226                 }
227
228                 shrinker->nr += total_scan;
229         }
230         up_read(&shrinker_rwsem);
231         return ret;
232 }
233
234 /* Called without lock on whether page is mapped, so answer is unstable */
235 static inline int page_mapping_inuse(struct page *page)
236 {
237         struct address_space *mapping;
238
239         /* Page is in somebody's page tables. */
240         if (page_mapped(page))
241                 return 1;
242
243         /* Be more reluctant to reclaim swapcache than pagecache */
244         if (PageSwapCache(page))
245                 return 1;
246
247         mapping = page_mapping(page);
248         if (!mapping)
249                 return 0;
250
251         /* File is mmap'd by somebody? */
252         return mapping_mapped(mapping);
253 }
254
255 static inline int is_page_cache_freeable(struct page *page)
256 {
257         return page_count(page) - !!PagePrivate(page) == 2;
258 }
259
260 static int may_write_to_queue(struct backing_dev_info *bdi)
261 {
262         if (current->flags & PF_SWAPWRITE)
263                 return 1;
264         if (!bdi_write_congested(bdi))
265                 return 1;
266         if (bdi == current->backing_dev_info)
267                 return 1;
268         return 0;
269 }
270
271 /*
272  * We detected a synchronous write error writing a page out.  Probably
273  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
274  * fsync(), msync() or close().
275  *
276  * The tricky part is that after writepage we cannot touch the mapping: nothing
277  * prevents it from being freed up.  But we have a ref on the page and once
278  * that page is locked, the mapping is pinned.
279  *
280  * We're allowed to run sleeping lock_page() here because we know the caller has
281  * __GFP_FS.
282  */
283 static void handle_write_error(struct address_space *mapping,
284                                 struct page *page, int error)
285 {
286         lock_page(page);
287         if (page_mapping(page) == mapping) {
288                 if (error == -ENOSPC)
289                         set_bit(AS_ENOSPC, &mapping->flags);
290                 else
291                         set_bit(AS_EIO, &mapping->flags);
292         }
293         unlock_page(page);
294 }
295
296 /* possible outcome of pageout() */
297 typedef enum {
298         /* failed to write page out, page is locked */
299         PAGE_KEEP,
300         /* move page to the active list, page is locked */
301         PAGE_ACTIVATE,
302         /* page has been sent to the disk successfully, page is unlocked */
303         PAGE_SUCCESS,
304         /* page is clean and locked */
305         PAGE_CLEAN,
306 } pageout_t;
307
308 /*
309  * pageout is called by shrink_page_list() for each dirty page.
310  * Calls ->writepage().
311  */
312 static pageout_t pageout(struct page *page, struct address_space *mapping)
313 {
314         /*
315          * If the page is dirty, only perform writeback if that write
316          * will be non-blocking.  To prevent this allocation from being
317          * stalled by pagecache activity.  But note that there may be
318          * stalls if we need to run get_block().  We could test
319          * PagePrivate for that.
320          *
321          * If this process is currently in generic_file_write() against
322          * this page's queue, we can perform writeback even if that
323          * will block.
324          *
325          * If the page is swapcache, write it back even if that would
326          * block, for some throttling. This happens by accident, because
327          * swap_backing_dev_info is bust: it doesn't reflect the
328          * congestion state of the swapdevs.  Easy to fix, if needed.
329          * See swapfile.c:page_queue_congested().
330          */
331         if (!is_page_cache_freeable(page))
332                 return PAGE_KEEP;
333         if (!mapping) {
334                 /*
335                  * Some data journaling orphaned pages can have
336                  * page->mapping == NULL while being dirty with clean buffers.
337                  */
338                 if (PagePrivate(page)) {
339                         if (try_to_free_buffers(page)) {
340                                 ClearPageDirty(page);
341                                 printk("%s: orphaned page\n", __FUNCTION__);
342                                 return PAGE_CLEAN;
343                         }
344                 }
345                 return PAGE_KEEP;
346         }
347         if (mapping->a_ops->writepage == NULL)
348                 return PAGE_ACTIVATE;
349         if (!may_write_to_queue(mapping->backing_dev_info))
350                 return PAGE_KEEP;
351
352         if (clear_page_dirty_for_io(page)) {
353                 int res;
354                 struct writeback_control wbc = {
355                         .sync_mode = WB_SYNC_NONE,
356                         .nr_to_write = SWAP_CLUSTER_MAX,
357                         .range_start = 0,
358                         .range_end = LLONG_MAX,
359                         .nonblocking = 1,
360                         .for_reclaim = 1,
361                 };
362
363                 SetPageReclaim(page);
364                 res = mapping->a_ops->writepage(page, &wbc);
365                 if (res < 0)
366                         handle_write_error(mapping, page, res);
367                 if (res == AOP_WRITEPAGE_ACTIVATE) {
368                         ClearPageReclaim(page);
369                         return PAGE_ACTIVATE;
370                 }
371                 if (!PageWriteback(page)) {
372                         /* synchronous write or broken a_ops? */
373                         ClearPageReclaim(page);
374                 }
375                 inc_zone_page_state(page, NR_VMSCAN_WRITE);
376                 return PAGE_SUCCESS;
377         }
378
379         return PAGE_CLEAN;
380 }
381
382 /*
383  * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
384  * someone else has a ref on the page, abort and return 0.  If it was
385  * successfully detached, return 1.  Assumes the caller has a single ref on
386  * this page.
387  */
388 int remove_mapping(struct address_space *mapping, struct page *page)
389 {
390         BUG_ON(!PageLocked(page));
391         BUG_ON(mapping != page_mapping(page));
392
393         write_lock_irq(&mapping->tree_lock);
394         /*
395          * The non racy check for a busy page.
396          *
397          * Must be careful with the order of the tests. When someone has
398          * a ref to the page, it may be possible that they dirty it then
399          * drop the reference. So if PageDirty is tested before page_count
400          * here, then the following race may occur:
401          *
402          * get_user_pages(&page);
403          * [user mapping goes away]
404          * write_to(page);
405          *                              !PageDirty(page)    [good]
406          * SetPageDirty(page);
407          * put_page(page);
408          *                              !page_count(page)   [good, discard it]
409          *
410          * [oops, our write_to data is lost]
411          *
412          * Reversing the order of the tests ensures such a situation cannot
413          * escape unnoticed. The smp_rmb is needed to ensure the page->flags
414          * load is not satisfied before that of page->_count.
415          *
416          * Note that if SetPageDirty is always performed via set_page_dirty,
417          * and thus under tree_lock, then this ordering is not required.
418          */
419         if (unlikely(page_count(page) != 2))
420                 goto cannot_free;
421         smp_rmb();
422         if (unlikely(PageDirty(page)))
423                 goto cannot_free;
424
425         if (PageSwapCache(page)) {
426                 swp_entry_t swap = { .val = page_private(page) };
427                 __delete_from_swap_cache(page);
428                 write_unlock_irq(&mapping->tree_lock);
429                 swap_free(swap);
430                 __put_page(page);       /* The pagecache ref */
431                 return 1;
432         }
433
434         __remove_from_page_cache(page);
435         write_unlock_irq(&mapping->tree_lock);
436         __put_page(page);
437         return 1;
438
439 cannot_free:
440         write_unlock_irq(&mapping->tree_lock);
441         return 0;
442 }
443
444 /*
445  * shrink_page_list() returns the number of reclaimed pages
446  */
447 static unsigned long shrink_page_list(struct list_head *page_list,
448                                         struct scan_control *sc)
449 {
450         LIST_HEAD(ret_pages);
451         struct pagevec freed_pvec;
452         int pgactivate = 0;
453         unsigned long nr_reclaimed = 0;
454
455         cond_resched();
456
457         pagevec_init(&freed_pvec, 1);
458         while (!list_empty(page_list)) {
459                 struct address_space *mapping;
460                 struct page *page;
461                 int may_enter_fs;
462                 int referenced;
463
464                 cond_resched();
465
466                 page = lru_to_page(page_list);
467                 list_del(&page->lru);
468
469                 if (TestSetPageLocked(page))
470                         goto keep;
471
472                 VM_BUG_ON(PageActive(page));
473
474                 sc->nr_scanned++;
475
476                 if (!sc->may_swap && page_mapped(page))
477                         goto keep_locked;
478
479                 /* Double the slab pressure for mapped and swapcache pages */
480                 if (page_mapped(page) || PageSwapCache(page))
481                         sc->nr_scanned++;
482
483                 if (PageWriteback(page))
484                         goto keep_locked;
485
486                 referenced = page_referenced(page, 1);
487                 /* In active use or really unfreeable?  Activate it. */
488                 if (referenced && page_mapping_inuse(page))
489                         goto activate_locked;
490
491 #ifdef CONFIG_SWAP
492                 /*
493                  * Anonymous process memory has backing store?
494                  * Try to allocate it some swap space here.
495                  */
496                 if (PageAnon(page) && !PageSwapCache(page))
497                         if (!add_to_swap(page, GFP_ATOMIC))
498                                 goto activate_locked;
499 #endif /* CONFIG_SWAP */
500
501                 mapping = page_mapping(page);
502                 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
503                         (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
504
505                 /*
506                  * The page is mapped into the page tables of one or more
507                  * processes. Try to unmap it here.
508                  */
509                 if (page_mapped(page) && mapping) {
510                         switch (try_to_unmap(page, 0)) {
511                         case SWAP_FAIL:
512                                 goto activate_locked;
513                         case SWAP_AGAIN:
514                                 goto keep_locked;
515                         case SWAP_SUCCESS:
516                                 ; /* try to free the page below */
517                         }
518                 }
519
520                 if (PageDirty(page)) {
521                         if (referenced)
522                                 goto keep_locked;
523                         if (!may_enter_fs)
524                                 goto keep_locked;
525                         if (!sc->may_writepage)
526                                 goto keep_locked;
527
528                         /* Page is dirty, try to write it out here */
529                         switch(pageout(page, mapping)) {
530                         case PAGE_KEEP:
531                                 goto keep_locked;
532                         case PAGE_ACTIVATE:
533                                 goto activate_locked;
534                         case PAGE_SUCCESS:
535                                 if (PageWriteback(page) || PageDirty(page))
536                                         goto keep;
537                                 /*
538                                  * A synchronous write - probably a ramdisk.  Go
539                                  * ahead and try to reclaim the page.
540                                  */
541                                 if (TestSetPageLocked(page))
542                                         goto keep;
543                                 if (PageDirty(page) || PageWriteback(page))
544                                         goto keep_locked;
545                                 mapping = page_mapping(page);
546                         case PAGE_CLEAN:
547                                 ; /* try to free the page below */
548                         }
549                 }
550
551                 /*
552                  * If the page has buffers, try to free the buffer mappings
553                  * associated with this page. If we succeed we try to free
554                  * the page as well.
555                  *
556                  * We do this even if the page is PageDirty().
557                  * try_to_release_page() does not perform I/O, but it is
558                  * possible for a page to have PageDirty set, but it is actually
559                  * clean (all its buffers are clean).  This happens if the
560                  * buffers were written out directly, with submit_bh(). ext3
561                  * will do this, as well as the blockdev mapping. 
562                  * try_to_release_page() will discover that cleanness and will
563                  * drop the buffers and mark the page clean - it can be freed.
564                  *
565                  * Rarely, pages can have buffers and no ->mapping.  These are
566                  * the pages which were not successfully invalidated in
567                  * truncate_complete_page().  We try to drop those buffers here
568                  * and if that worked, and the page is no longer mapped into
569                  * process address space (page_count == 1) it can be freed.
570                  * Otherwise, leave the page on the LRU so it is swappable.
571                  */
572                 if (PagePrivate(page)) {
573                         if (!try_to_release_page(page, sc->gfp_mask))
574                                 goto activate_locked;
575                         if (!mapping && page_count(page) == 1)
576                                 goto free_it;
577                 }
578
579                 if (!mapping || !remove_mapping(mapping, page))
580                         goto keep_locked;
581
582 free_it:
583                 unlock_page(page);
584                 nr_reclaimed++;
585                 if (!pagevec_add(&freed_pvec, page))
586                         __pagevec_release_nonlru(&freed_pvec);
587                 continue;
588
589 activate_locked:
590                 SetPageActive(page);
591                 pgactivate++;
592 keep_locked:
593                 unlock_page(page);
594 keep:
595                 list_add(&page->lru, &ret_pages);
596                 VM_BUG_ON(PageLRU(page));
597         }
598         list_splice(&ret_pages, page_list);
599         if (pagevec_count(&freed_pvec))
600                 __pagevec_release_nonlru(&freed_pvec);
601         count_vm_events(PGACTIVATE, pgactivate);
602         return nr_reclaimed;
603 }
604
605 /*
606  * zone->lru_lock is heavily contended.  Some of the functions that
607  * shrink the lists perform better by taking out a batch of pages
608  * and working on them outside the LRU lock.
609  *
610  * For pagecache intensive workloads, this function is the hottest
611  * spot in the kernel (apart from copy_*_user functions).
612  *
613  * Appropriate locks must be held before calling this function.
614  *
615  * @nr_to_scan: The number of pages to look through on the list.
616  * @src:        The LRU list to pull pages off.
617  * @dst:        The temp list to put pages on to.
618  * @scanned:    The number of pages that were scanned.
619  *
620  * returns how many pages were moved onto *@dst.
621  */
622 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
623                 struct list_head *src, struct list_head *dst,
624                 unsigned long *scanned)
625 {
626         unsigned long nr_taken = 0;
627         struct page *page;
628         unsigned long scan;
629
630         for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
631                 struct list_head *target;
632                 page = lru_to_page(src);
633                 prefetchw_prev_lru_page(page, src, flags);
634
635                 VM_BUG_ON(!PageLRU(page));
636
637                 list_del(&page->lru);
638                 target = src;
639                 if (likely(get_page_unless_zero(page))) {
640                         /*
641                          * Be careful not to clear PageLRU until after we're
642                          * sure the page is not being freed elsewhere -- the
643                          * page release code relies on it.
644                          */
645                         ClearPageLRU(page);
646                         target = dst;
647                         nr_taken++;
648                 } /* else it is being freed elsewhere */
649
650                 list_add(&page->lru, target);
651         }
652
653         *scanned = scan;
654         return nr_taken;
655 }
656
657 /*
658  * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
659  * of reclaimed pages
660  */
661 static unsigned long shrink_inactive_list(unsigned long max_scan,
662                                 struct zone *zone, struct scan_control *sc)
663 {
664         LIST_HEAD(page_list);
665         struct pagevec pvec;
666         unsigned long nr_scanned = 0;
667         unsigned long nr_reclaimed = 0;
668
669         pagevec_init(&pvec, 1);
670
671         lru_add_drain();
672         spin_lock_irq(&zone->lru_lock);
673         do {
674                 struct page *page;
675                 unsigned long nr_taken;
676                 unsigned long nr_scan;
677                 unsigned long nr_freed;
678
679                 nr_taken = isolate_lru_pages(sc->swap_cluster_max,
680                                              &zone->inactive_list,
681                                              &page_list, &nr_scan);
682                 zone->nr_inactive -= nr_taken;
683                 zone->pages_scanned += nr_scan;
684                 spin_unlock_irq(&zone->lru_lock);
685
686                 nr_scanned += nr_scan;
687                 nr_freed = shrink_page_list(&page_list, sc);
688                 nr_reclaimed += nr_freed;
689                 local_irq_disable();
690                 if (current_is_kswapd()) {
691                         __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scan);
692                         __count_vm_events(KSWAPD_STEAL, nr_freed);
693                 } else
694                         __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scan);
695                 __count_vm_events(PGACTIVATE, nr_freed);
696
697                 if (nr_taken == 0)
698                         goto done;
699
700                 spin_lock(&zone->lru_lock);
701                 /*
702                  * Put back any unfreeable pages.
703                  */
704                 while (!list_empty(&page_list)) {
705                         page = lru_to_page(&page_list);
706                         VM_BUG_ON(PageLRU(page));
707                         SetPageLRU(page);
708                         list_del(&page->lru);
709                         if (PageActive(page))
710                                 add_page_to_active_list(zone, page);
711                         else
712                                 add_page_to_inactive_list(zone, page);
713                         if (!pagevec_add(&pvec, page)) {
714                                 spin_unlock_irq(&zone->lru_lock);
715                                 __pagevec_release(&pvec);
716                                 spin_lock_irq(&zone->lru_lock);
717                         }
718                 }
719         } while (nr_scanned < max_scan);
720         spin_unlock(&zone->lru_lock);
721 done:
722         local_irq_enable();
723         pagevec_release(&pvec);
724         return nr_reclaimed;
725 }
726
727 /*
728  * We are about to scan this zone at a certain priority level.  If that priority
729  * level is smaller (ie: more urgent) than the previous priority, then note
730  * that priority level within the zone.  This is done so that when the next
731  * process comes in to scan this zone, it will immediately start out at this
732  * priority level rather than having to build up its own scanning priority.
733  * Here, this priority affects only the reclaim-mapped threshold.
734  */
735 static inline void note_zone_scanning_priority(struct zone *zone, int priority)
736 {
737         if (priority < zone->prev_priority)
738                 zone->prev_priority = priority;
739 }
740
741 static inline int zone_is_near_oom(struct zone *zone)
742 {
743         return zone->pages_scanned >= (zone->nr_active + zone->nr_inactive)*3;
744 }
745
746 /*
747  * This moves pages from the active list to the inactive list.
748  *
749  * We move them the other way if the page is referenced by one or more
750  * processes, from rmap.
751  *
752  * If the pages are mostly unmapped, the processing is fast and it is
753  * appropriate to hold zone->lru_lock across the whole operation.  But if
754  * the pages are mapped, the processing is slow (page_referenced()) so we
755  * should drop zone->lru_lock around each page.  It's impossible to balance
756  * this, so instead we remove the pages from the LRU while processing them.
757  * It is safe to rely on PG_active against the non-LRU pages in here because
758  * nobody will play with that bit on a non-LRU page.
759  *
760  * The downside is that we have to touch page->_count against each page.
761  * But we had to alter page->flags anyway.
762  */
763 static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
764                                 struct scan_control *sc, int priority)
765 {
766         unsigned long pgmoved;
767         int pgdeactivate = 0;
768         unsigned long pgscanned;
769         LIST_HEAD(l_hold);      /* The pages which were snipped off */
770         LIST_HEAD(l_inactive);  /* Pages to go onto the inactive_list */
771         LIST_HEAD(l_active);    /* Pages to go onto the active_list */
772         struct page *page;
773         struct pagevec pvec;
774         int reclaim_mapped = 0;
775
776         if (sc->may_swap) {
777                 long mapped_ratio;
778                 long distress;
779                 long swap_tendency;
780
781                 if (zone_is_near_oom(zone))
782                         goto force_reclaim_mapped;
783
784                 /*
785                  * `distress' is a measure of how much trouble we're having
786                  * reclaiming pages.  0 -> no problems.  100 -> great trouble.
787                  */
788                 distress = 100 >> min(zone->prev_priority, priority);
789
790                 /*
791                  * The point of this algorithm is to decide when to start
792                  * reclaiming mapped memory instead of just pagecache.  Work out
793                  * how much memory
794                  * is mapped.
795                  */
796                 mapped_ratio = ((global_page_state(NR_FILE_MAPPED) +
797                                 global_page_state(NR_ANON_PAGES)) * 100) /
798                                         vm_total_pages;
799
800                 /*
801                  * Now decide how much we really want to unmap some pages.  The
802                  * mapped ratio is downgraded - just because there's a lot of
803                  * mapped memory doesn't necessarily mean that page reclaim
804                  * isn't succeeding.
805                  *
806                  * The distress ratio is important - we don't want to start
807                  * going oom.
808                  *
809                  * A 100% value of vm_swappiness overrides this algorithm
810                  * altogether.
811                  */
812                 swap_tendency = mapped_ratio / 2 + distress + sc->swappiness;
813
814                 /*
815                  * Now use this metric to decide whether to start moving mapped
816                  * memory onto the inactive list.
817                  */
818                 if (swap_tendency >= 100)
819 force_reclaim_mapped:
820                         reclaim_mapped = 1;
821         }
822
823         lru_add_drain();
824         spin_lock_irq(&zone->lru_lock);
825         pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
826                                     &l_hold, &pgscanned);
827         zone->pages_scanned += pgscanned;
828         zone->nr_active -= pgmoved;
829         spin_unlock_irq(&zone->lru_lock);
830
831         while (!list_empty(&l_hold)) {
832                 cond_resched();
833                 page = lru_to_page(&l_hold);
834                 list_del(&page->lru);
835                 if (page_mapped(page)) {
836                         if (!reclaim_mapped ||
837                             (total_swap_pages == 0 && PageAnon(page)) ||
838                             page_referenced(page, 0)) {
839                                 list_add(&page->lru, &l_active);
840                                 continue;
841                         }
842                 }
843                 list_add(&page->lru, &l_inactive);
844         }
845
846         pagevec_init(&pvec, 1);
847         pgmoved = 0;
848         spin_lock_irq(&zone->lru_lock);
849         while (!list_empty(&l_inactive)) {
850                 page = lru_to_page(&l_inactive);
851                 prefetchw_prev_lru_page(page, &l_inactive, flags);
852                 VM_BUG_ON(PageLRU(page));
853                 SetPageLRU(page);
854                 VM_BUG_ON(!PageActive(page));
855                 ClearPageActive(page);
856
857                 list_move(&page->lru, &zone->inactive_list);
858                 pgmoved++;
859                 if (!pagevec_add(&pvec, page)) {
860                         zone->nr_inactive += pgmoved;
861                         spin_unlock_irq(&zone->lru_lock);
862                         pgdeactivate += pgmoved;
863                         pgmoved = 0;
864                         if (buffer_heads_over_limit)
865                                 pagevec_strip(&pvec);
866                         __pagevec_release(&pvec);
867                         spin_lock_irq(&zone->lru_lock);
868                 }
869         }
870         zone->nr_inactive += pgmoved;
871         pgdeactivate += pgmoved;
872         if (buffer_heads_over_limit) {
873                 spin_unlock_irq(&zone->lru_lock);
874                 pagevec_strip(&pvec);
875                 spin_lock_irq(&zone->lru_lock);
876         }
877
878         pgmoved = 0;
879         while (!list_empty(&l_active)) {
880                 page = lru_to_page(&l_active);
881                 prefetchw_prev_lru_page(page, &l_active, flags);
882                 VM_BUG_ON(PageLRU(page));
883                 SetPageLRU(page);
884                 VM_BUG_ON(!PageActive(page));
885                 list_move(&page->lru, &zone->active_list);
886                 pgmoved++;
887                 if (!pagevec_add(&pvec, page)) {
888                         zone->nr_active += pgmoved;
889                         pgmoved = 0;
890                         spin_unlock_irq(&zone->lru_lock);
891                         __pagevec_release(&pvec);
892                         spin_lock_irq(&zone->lru_lock);
893                 }
894         }
895         zone->nr_active += pgmoved;
896
897         __count_zone_vm_events(PGREFILL, zone, pgscanned);
898         __count_vm_events(PGDEACTIVATE, pgdeactivate);
899         spin_unlock_irq(&zone->lru_lock);
900
901         pagevec_release(&pvec);
902 }
903
904 /*
905  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
906  */
907 static unsigned long shrink_zone(int priority, struct zone *zone,
908                                 struct scan_control *sc)
909 {
910         unsigned long nr_active;
911         unsigned long nr_inactive;
912         unsigned long nr_to_scan;
913         unsigned long nr_reclaimed = 0;
914
915         atomic_inc(&zone->reclaim_in_progress);
916
917         /*
918          * Add one to `nr_to_scan' just to make sure that the kernel will
919          * slowly sift through the active list.
920          */
921         zone->nr_scan_active += (zone->nr_active >> priority) + 1;
922         nr_active = zone->nr_scan_active;
923         if (nr_active >= sc->swap_cluster_max)
924                 zone->nr_scan_active = 0;
925         else
926                 nr_active = 0;
927
928         zone->nr_scan_inactive += (zone->nr_inactive >> priority) + 1;
929         nr_inactive = zone->nr_scan_inactive;
930         if (nr_inactive >= sc->swap_cluster_max)
931                 zone->nr_scan_inactive = 0;
932         else
933                 nr_inactive = 0;
934
935         while (nr_active || nr_inactive) {
936                 if (nr_active) {
937                         nr_to_scan = min(nr_active,
938                                         (unsigned long)sc->swap_cluster_max);
939                         nr_active -= nr_to_scan;
940                         shrink_active_list(nr_to_scan, zone, sc, priority);
941                 }
942
943                 if (nr_inactive) {
944                         nr_to_scan = min(nr_inactive,
945                                         (unsigned long)sc->swap_cluster_max);
946                         nr_inactive -= nr_to_scan;
947                         nr_reclaimed += shrink_inactive_list(nr_to_scan, zone,
948                                                                 sc);
949                 }
950         }
951
952         throttle_vm_writeout();
953
954         atomic_dec(&zone->reclaim_in_progress);
955         return nr_reclaimed;
956 }
957
958 /*
959  * This is the direct reclaim path, for page-allocating processes.  We only
960  * try to reclaim pages from zones which will satisfy the caller's allocation
961  * request.
962  *
963  * We reclaim from a zone even if that zone is over pages_high.  Because:
964  * a) The caller may be trying to free *extra* pages to satisfy a higher-order
965  *    allocation or
966  * b) The zones may be over pages_high but they must go *over* pages_high to
967  *    satisfy the `incremental min' zone defense algorithm.
968  *
969  * Returns the number of reclaimed pages.
970  *
971  * If a zone is deemed to be full of pinned pages then just give it a light
972  * scan then give up on it.
973  */
974 static unsigned long shrink_zones(int priority, struct zone **zones,
975                                         struct scan_control *sc)
976 {
977         unsigned long nr_reclaimed = 0;
978         int i;
979
980         sc->all_unreclaimable = 1;
981         for (i = 0; zones[i] != NULL; i++) {
982                 struct zone *zone = zones[i];
983
984                 if (!populated_zone(zone))
985                         continue;
986
987                 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
988                         continue;
989
990                 note_zone_scanning_priority(zone, priority);
991
992                 if (zone->all_unreclaimable && priority != DEF_PRIORITY)
993                         continue;       /* Let kswapd poll it */
994
995                 sc->all_unreclaimable = 0;
996
997                 nr_reclaimed += shrink_zone(priority, zone, sc);
998         }
999         return nr_reclaimed;
1000 }
1001  
1002 /*
1003  * This is the main entry point to direct page reclaim.
1004  *
1005  * If a full scan of the inactive list fails to free enough memory then we
1006  * are "out of memory" and something needs to be killed.
1007  *
1008  * If the caller is !__GFP_FS then the probability of a failure is reasonably
1009  * high - the zone may be full of dirty or under-writeback pages, which this
1010  * caller can't do much about.  We kick pdflush and take explicit naps in the
1011  * hope that some of these pages can be written.  But if the allocating task
1012  * holds filesystem locks which prevent writeout this might not work, and the
1013  * allocation attempt will fail.
1014  */
1015 unsigned long try_to_free_pages(struct zone **zones, gfp_t gfp_mask)
1016 {
1017         int priority;
1018         int ret = 0;
1019         unsigned long total_scanned = 0;
1020         unsigned long nr_reclaimed = 0;
1021         struct reclaim_state *reclaim_state = current->reclaim_state;
1022         unsigned long lru_pages = 0;
1023         int i;
1024         struct scan_control sc = {
1025                 .gfp_mask = gfp_mask,
1026                 .may_writepage = !laptop_mode,
1027                 .swap_cluster_max = SWAP_CLUSTER_MAX,
1028                 .may_swap = 1,
1029                 .swappiness = vm_swappiness,
1030         };
1031
1032         count_vm_event(ALLOCSTALL);
1033
1034         for (i = 0; zones[i] != NULL; i++) {
1035                 struct zone *zone = zones[i];
1036
1037                 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1038                         continue;
1039
1040                 lru_pages += zone->nr_active + zone->nr_inactive;
1041         }
1042
1043         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1044                 sc.nr_scanned = 0;
1045                 if (!priority)
1046                         disable_swap_token();
1047                 nr_reclaimed += shrink_zones(priority, zones, &sc);
1048                 shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
1049                 if (reclaim_state) {
1050                         nr_reclaimed += reclaim_state->reclaimed_slab;
1051                         reclaim_state->reclaimed_slab = 0;
1052                 }
1053                 total_scanned += sc.nr_scanned;
1054                 if (nr_reclaimed >= sc.swap_cluster_max) {
1055                         ret = 1;
1056                         goto out;
1057                 }
1058
1059                 /*
1060                  * Try to write back as many pages as we just scanned.  This
1061                  * tends to cause slow streaming writers to write data to the
1062                  * disk smoothly, at the dirtying rate, which is nice.   But
1063                  * that's undesirable in laptop mode, where we *want* lumpy
1064                  * writeout.  So in laptop mode, write out the whole world.
1065                  */
1066                 if (total_scanned > sc.swap_cluster_max +
1067                                         sc.swap_cluster_max / 2) {
1068                         wakeup_pdflush(laptop_mode ? 0 : total_scanned);
1069                         sc.may_writepage = 1;
1070                 }
1071
1072                 /* Take a nap, wait for some writeback to complete */
1073                 if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
1074                         congestion_wait(WRITE, HZ/10);
1075         }
1076         /* top priority shrink_caches still had more to do? don't OOM, then */
1077         if (!sc.all_unreclaimable)
1078                 ret = 1;
1079 out:
1080         /*
1081          * Now that we've scanned all the zones at this priority level, note
1082          * that level within the zone so that the next thread which performs
1083          * scanning of this zone will immediately start out at this priority
1084          * level.  This affects only the decision whether or not to bring
1085          * mapped pages onto the inactive list.
1086          */
1087         if (priority < 0)
1088                 priority = 0;
1089         for (i = 0; zones[i] != 0; i++) {
1090                 struct zone *zone = zones[i];
1091
1092                 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1093                         continue;
1094
1095                 zone->prev_priority = priority;
1096         }
1097         return ret;
1098 }
1099
1100 /*
1101  * For kswapd, balance_pgdat() will work across all this node's zones until
1102  * they are all at pages_high.
1103  *
1104  * Returns the number of pages which were actually freed.
1105  *
1106  * There is special handling here for zones which are full of pinned pages.
1107  * This can happen if the pages are all mlocked, or if they are all used by
1108  * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
1109  * What we do is to detect the case where all pages in the zone have been
1110  * scanned twice and there has been zero successful reclaim.  Mark the zone as
1111  * dead and from now on, only perform a short scan.  Basically we're polling
1112  * the zone for when the problem goes away.
1113  *
1114  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
1115  * zones which have free_pages > pages_high, but once a zone is found to have
1116  * free_pages <= pages_high, we scan that zone and the lower zones regardless
1117  * of the number of free pages in the lower zones.  This interoperates with
1118  * the page allocator fallback scheme to ensure that aging of pages is balanced
1119  * across the zones.
1120  */
1121 static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
1122 {
1123         int all_zones_ok;
1124         int priority;
1125         int i;
1126         unsigned long total_scanned;
1127         unsigned long nr_reclaimed;
1128         struct reclaim_state *reclaim_state = current->reclaim_state;
1129         struct scan_control sc = {
1130                 .gfp_mask = GFP_KERNEL,
1131                 .may_swap = 1,
1132                 .swap_cluster_max = SWAP_CLUSTER_MAX,
1133                 .swappiness = vm_swappiness,
1134         };
1135         /*
1136          * temp_priority is used to remember the scanning priority at which
1137          * this zone was successfully refilled to free_pages == pages_high.
1138          */
1139         int temp_priority[MAX_NR_ZONES];
1140
1141 loop_again:
1142         total_scanned = 0;
1143         nr_reclaimed = 0;
1144         sc.may_writepage = !laptop_mode;
1145         count_vm_event(PAGEOUTRUN);
1146
1147         for (i = 0; i < pgdat->nr_zones; i++)
1148                 temp_priority[i] = DEF_PRIORITY;
1149
1150         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1151                 int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
1152                 unsigned long lru_pages = 0;
1153
1154                 /* The swap token gets in the way of swapout... */
1155                 if (!priority)
1156                         disable_swap_token();
1157
1158                 all_zones_ok = 1;
1159
1160                 /*
1161                  * Scan in the highmem->dma direction for the highest
1162                  * zone which needs scanning
1163                  */
1164                 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1165                         struct zone *zone = pgdat->node_zones + i;
1166
1167                         if (!populated_zone(zone))
1168                                 continue;
1169
1170                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1171                                 continue;
1172
1173                         if (!zone_watermark_ok(zone, order, zone->pages_high,
1174                                                0, 0)) {
1175                                 end_zone = i;
1176                                 break;
1177                         }
1178                 }
1179                 if (i < 0)
1180                         goto out;
1181
1182                 for (i = 0; i <= end_zone; i++) {
1183                         struct zone *zone = pgdat->node_zones + i;
1184
1185                         lru_pages += zone->nr_active + zone->nr_inactive;
1186                 }
1187
1188                 /*
1189                  * Now scan the zone in the dma->highmem direction, stopping
1190                  * at the last zone which needs scanning.
1191                  *
1192                  * We do this because the page allocator works in the opposite
1193                  * direction.  This prevents the page allocator from allocating
1194                  * pages behind kswapd's direction of progress, which would
1195                  * cause too much scanning of the lower zones.
1196                  */
1197                 for (i = 0; i <= end_zone; i++) {
1198                         struct zone *zone = pgdat->node_zones + i;
1199                         int nr_slab;
1200
1201                         if (!populated_zone(zone))
1202                                 continue;
1203
1204                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1205                                 continue;
1206
1207                         if (!zone_watermark_ok(zone, order, zone->pages_high,
1208                                                end_zone, 0))
1209                                 all_zones_ok = 0;
1210                         temp_priority[i] = priority;
1211                         sc.nr_scanned = 0;
1212                         note_zone_scanning_priority(zone, priority);
1213                         nr_reclaimed += shrink_zone(priority, zone, &sc);
1214                         reclaim_state->reclaimed_slab = 0;
1215                         nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
1216                                                 lru_pages);
1217                         nr_reclaimed += reclaim_state->reclaimed_slab;
1218                         total_scanned += sc.nr_scanned;
1219                         if (zone->all_unreclaimable)
1220                                 continue;
1221                         if (nr_slab == 0 && zone->pages_scanned >=
1222                                     (zone->nr_active + zone->nr_inactive) * 6)
1223                                 zone->all_unreclaimable = 1;
1224                         /*
1225                          * If we've done a decent amount of scanning and
1226                          * the reclaim ratio is low, start doing writepage
1227                          * even in laptop mode
1228                          */
1229                         if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1230                             total_scanned > nr_reclaimed + nr_reclaimed / 2)
1231                                 sc.may_writepage = 1;
1232                 }
1233                 if (all_zones_ok)
1234                         break;          /* kswapd: all done */
1235                 /*
1236                  * OK, kswapd is getting into trouble.  Take a nap, then take
1237                  * another pass across the zones.
1238                  */
1239                 if (total_scanned && priority < DEF_PRIORITY - 2)
1240                         congestion_wait(WRITE, HZ/10);
1241
1242                 /*
1243                  * We do this so kswapd doesn't build up large priorities for
1244                  * example when it is freeing in parallel with allocators. It
1245                  * matches the direct reclaim path behaviour in terms of impact
1246                  * on zone->*_priority.
1247                  */
1248                 if (nr_reclaimed >= SWAP_CLUSTER_MAX)
1249                         break;
1250         }
1251 out:
1252         /*
1253          * Note within each zone the priority level at which this zone was
1254          * brought into a happy state.  So that the next thread which scans this
1255          * zone will start out at that priority level.
1256          */
1257         for (i = 0; i < pgdat->nr_zones; i++) {
1258                 struct zone *zone = pgdat->node_zones + i;
1259
1260                 zone->prev_priority = temp_priority[i];
1261         }
1262         if (!all_zones_ok) {
1263                 cond_resched();
1264
1265                 try_to_freeze();
1266
1267                 goto loop_again;
1268         }
1269
1270         return nr_reclaimed;
1271 }
1272
1273 /*
1274  * The background pageout daemon, started as a kernel thread
1275  * from the init process. 
1276  *
1277  * This basically trickles out pages so that we have _some_
1278  * free memory available even if there is no other activity
1279  * that frees anything up. This is needed for things like routing
1280  * etc, where we otherwise might have all activity going on in
1281  * asynchronous contexts that cannot page things out.
1282  *
1283  * If there are applications that are active memory-allocators
1284  * (most normal use), this basically shouldn't matter.
1285  */
1286 static int kswapd(void *p)
1287 {
1288         unsigned long order;
1289         pg_data_t *pgdat = (pg_data_t*)p;
1290         struct task_struct *tsk = current;
1291         DEFINE_WAIT(wait);
1292         struct reclaim_state reclaim_state = {
1293                 .reclaimed_slab = 0,
1294         };
1295         cpumask_t cpumask;
1296
1297         cpumask = node_to_cpumask(pgdat->node_id);
1298         if (!cpus_empty(cpumask))
1299                 set_cpus_allowed(tsk, cpumask);
1300         current->reclaim_state = &reclaim_state;
1301
1302         /*
1303          * Tell the memory management that we're a "memory allocator",
1304          * and that if we need more memory we should get access to it
1305          * regardless (see "__alloc_pages()"). "kswapd" should
1306          * never get caught in the normal page freeing logic.
1307          *
1308          * (Kswapd normally doesn't need memory anyway, but sometimes
1309          * you need a small amount of memory in order to be able to
1310          * page out something else, and this flag essentially protects
1311          * us from recursively trying to free more memory as we're
1312          * trying to free the first piece of memory in the first place).
1313          */
1314         tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
1315
1316         order = 0;
1317         for ( ; ; ) {
1318                 unsigned long new_order;
1319
1320                 try_to_freeze();
1321
1322                 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1323                 new_order = pgdat->kswapd_max_order;
1324                 pgdat->kswapd_max_order = 0;
1325                 if (order < new_order) {
1326                         /*
1327                          * Don't sleep if someone wants a larger 'order'
1328                          * allocation
1329                          */
1330                         order = new_order;
1331                 } else {
1332                         schedule();
1333                         order = pgdat->kswapd_max_order;
1334                 }
1335                 finish_wait(&pgdat->kswapd_wait, &wait);
1336
1337                 balance_pgdat(pgdat, order);
1338         }
1339         return 0;
1340 }
1341
1342 /*
1343  * A zone is low on free memory, so wake its kswapd task to service it.
1344  */
1345 void wakeup_kswapd(struct zone *zone, int order)
1346 {
1347         pg_data_t *pgdat;
1348
1349         if (!populated_zone(zone))
1350                 return;
1351
1352         pgdat = zone->zone_pgdat;
1353         if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0))
1354                 return;
1355         if (pgdat->kswapd_max_order < order)
1356                 pgdat->kswapd_max_order = order;
1357         if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1358                 return;
1359         if (!waitqueue_active(&pgdat->kswapd_wait))
1360                 return;
1361         wake_up_interruptible(&pgdat->kswapd_wait);
1362 }
1363
1364 #ifdef CONFIG_PM
1365 /*
1366  * Helper function for shrink_all_memory().  Tries to reclaim 'nr_pages' pages
1367  * from LRU lists system-wide, for given pass and priority, and returns the
1368  * number of reclaimed pages
1369  *
1370  * For pass > 3 we also try to shrink the LRU lists that contain a few pages
1371  */
1372 static unsigned long shrink_all_zones(unsigned long nr_pages, int pass,
1373                                       int prio, struct scan_control *sc)
1374 {
1375         struct zone *zone;
1376         unsigned long nr_to_scan, ret = 0;
1377
1378         for_each_zone(zone) {
1379
1380                 if (!populated_zone(zone))
1381                         continue;
1382
1383                 if (zone->all_unreclaimable && prio != DEF_PRIORITY)
1384                         continue;
1385
1386                 /* For pass = 0 we don't shrink the active list */
1387                 if (pass > 0) {
1388                         zone->nr_scan_active += (zone->nr_active >> prio) + 1;
1389                         if (zone->nr_scan_active >= nr_pages || pass > 3) {
1390                                 zone->nr_scan_active = 0;
1391                                 nr_to_scan = min(nr_pages, zone->nr_active);
1392                                 shrink_active_list(nr_to_scan, zone, sc, prio);
1393                         }
1394                 }
1395
1396                 zone->nr_scan_inactive += (zone->nr_inactive >> prio) + 1;
1397                 if (zone->nr_scan_inactive >= nr_pages || pass > 3) {
1398                         zone->nr_scan_inactive = 0;
1399                         nr_to_scan = min(nr_pages, zone->nr_inactive);
1400                         ret += shrink_inactive_list(nr_to_scan, zone, sc);
1401                         if (ret >= nr_pages)
1402                                 return ret;
1403                 }
1404         }
1405
1406         return ret;
1407 }
1408
1409 /*
1410  * Try to free `nr_pages' of memory, system-wide, and return the number of
1411  * freed pages.
1412  *
1413  * Rather than trying to age LRUs the aim is to preserve the overall
1414  * LRU order by reclaiming preferentially
1415  * inactive > active > active referenced > active mapped
1416  */
1417 unsigned long shrink_all_memory(unsigned long nr_pages)
1418 {
1419         unsigned long lru_pages, nr_slab;
1420         unsigned long ret = 0;
1421         int pass;
1422         struct reclaim_state reclaim_state;
1423         struct zone *zone;
1424         struct scan_control sc = {
1425                 .gfp_mask = GFP_KERNEL,
1426                 .may_swap = 0,
1427                 .swap_cluster_max = nr_pages,
1428                 .may_writepage = 1,
1429                 .swappiness = vm_swappiness,
1430         };
1431
1432         current->reclaim_state = &reclaim_state;
1433
1434         lru_pages = 0;
1435         for_each_zone(zone)
1436                 lru_pages += zone->nr_active + zone->nr_inactive;
1437
1438         nr_slab = global_page_state(NR_SLAB_RECLAIMABLE);
1439         /* If slab caches are huge, it's better to hit them first */
1440         while (nr_slab >= lru_pages) {
1441                 reclaim_state.reclaimed_slab = 0;
1442                 shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
1443                 if (!reclaim_state.reclaimed_slab)
1444                         break;
1445
1446                 ret += reclaim_state.reclaimed_slab;
1447                 if (ret >= nr_pages)
1448                         goto out;
1449
1450                 nr_slab -= reclaim_state.reclaimed_slab;
1451         }
1452
1453         /*
1454          * We try to shrink LRUs in 5 passes:
1455          * 0 = Reclaim from inactive_list only
1456          * 1 = Reclaim from active list but don't reclaim mapped
1457          * 2 = 2nd pass of type 1
1458          * 3 = Reclaim mapped (normal reclaim)
1459          * 4 = 2nd pass of type 3
1460          */
1461         for (pass = 0; pass < 5; pass++) {
1462                 int prio;
1463
1464                 /* Needed for shrinking slab caches later on */
1465                 if (!lru_pages)
1466                         for_each_zone(zone) {
1467                                 lru_pages += zone->nr_active;
1468                                 lru_pages += zone->nr_inactive;
1469                         }
1470
1471                 /* Force reclaiming mapped pages in the passes #3 and #4 */
1472                 if (pass > 2) {
1473                         sc.may_swap = 1;
1474                         sc.swappiness = 100;
1475                 }
1476
1477                 for (prio = DEF_PRIORITY; prio >= 0; prio--) {
1478                         unsigned long nr_to_scan = nr_pages - ret;
1479
1480                         sc.nr_scanned = 0;
1481                         ret += shrink_all_zones(nr_to_scan, prio, pass, &sc);
1482                         if (ret >= nr_pages)
1483                                 goto out;
1484
1485                         reclaim_state.reclaimed_slab = 0;
1486                         shrink_slab(sc.nr_scanned, sc.gfp_mask, lru_pages);
1487                         ret += reclaim_state.reclaimed_slab;
1488                         if (ret >= nr_pages)
1489                                 goto out;
1490
1491                         if (sc.nr_scanned && prio < DEF_PRIORITY - 2)
1492                                 congestion_wait(WRITE, HZ / 10);
1493                 }
1494
1495                 lru_pages = 0;
1496         }
1497
1498         /*
1499          * If ret = 0, we could not shrink LRUs, but there may be something
1500          * in slab caches
1501          */
1502         if (!ret)
1503                 do {
1504                         reclaim_state.reclaimed_slab = 0;
1505                         shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
1506                         ret += reclaim_state.reclaimed_slab;
1507                 } while (ret < nr_pages && reclaim_state.reclaimed_slab > 0);
1508
1509 out:
1510         current->reclaim_state = NULL;
1511
1512         return ret;
1513 }
1514 #endif
1515
1516 #ifdef CONFIG_HOTPLUG_CPU
1517 /* It's optimal to keep kswapds on the same CPUs as their memory, but
1518    not required for correctness.  So if the last cpu in a node goes
1519    away, we get changed to run anywhere: as the first one comes back,
1520    restore their cpu bindings. */
1521 static int __devinit cpu_callback(struct notifier_block *nfb,
1522                                   unsigned long action, void *hcpu)
1523 {
1524         pg_data_t *pgdat;
1525         cpumask_t mask;
1526
1527         if (action == CPU_ONLINE) {
1528                 for_each_online_pgdat(pgdat) {
1529                         mask = node_to_cpumask(pgdat->node_id);
1530                         if (any_online_cpu(mask) != NR_CPUS)
1531                                 /* One of our CPUs online: restore mask */
1532                                 set_cpus_allowed(pgdat->kswapd, mask);
1533                 }
1534         }
1535         return NOTIFY_OK;
1536 }
1537 #endif /* CONFIG_HOTPLUG_CPU */
1538
1539 /*
1540  * This kswapd start function will be called by init and node-hot-add.
1541  * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
1542  */
1543 int kswapd_run(int nid)
1544 {
1545         pg_data_t *pgdat = NODE_DATA(nid);
1546         int ret = 0;
1547
1548         if (pgdat->kswapd)
1549                 return 0;
1550
1551         pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
1552         if (IS_ERR(pgdat->kswapd)) {
1553                 /* failure at boot is fatal */
1554                 BUG_ON(system_state == SYSTEM_BOOTING);
1555                 printk("Failed to start kswapd on node %d\n",nid);
1556                 ret = -1;
1557         }
1558         return ret;
1559 }
1560
1561 static int __init kswapd_init(void)
1562 {
1563         int nid;
1564
1565         swap_setup();
1566         for_each_online_node(nid)
1567                 kswapd_run(nid);
1568         hotcpu_notifier(cpu_callback, 0);
1569         return 0;
1570 }
1571
1572 module_init(kswapd_init)
1573
1574 #ifdef CONFIG_NUMA
1575 /*
1576  * Zone reclaim mode
1577  *
1578  * If non-zero call zone_reclaim when the number of free pages falls below
1579  * the watermarks.
1580  */
1581 int zone_reclaim_mode __read_mostly;
1582
1583 #define RECLAIM_OFF 0
1584 #define RECLAIM_ZONE (1<<0)     /* Run shrink_cache on the zone */
1585 #define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
1586 #define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
1587
1588 /*
1589  * Priority for ZONE_RECLAIM. This determines the fraction of pages
1590  * of a node considered for each zone_reclaim. 4 scans 1/16th of
1591  * a zone.
1592  */
1593 #define ZONE_RECLAIM_PRIORITY 4
1594
1595 /*
1596  * Percentage of pages in a zone that must be unmapped for zone_reclaim to
1597  * occur.
1598  */
1599 int sysctl_min_unmapped_ratio = 1;
1600
1601 /*
1602  * If the number of slab pages in a zone grows beyond this percentage then
1603  * slab reclaim needs to occur.
1604  */
1605 int sysctl_min_slab_ratio = 5;
1606
1607 /*
1608  * Try to free up some pages from this zone through reclaim.
1609  */
1610 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1611 {
1612         /* Minimum pages needed in order to stay on node */
1613         const unsigned long nr_pages = 1 << order;
1614         struct task_struct *p = current;
1615         struct reclaim_state reclaim_state;
1616         int priority;
1617         unsigned long nr_reclaimed = 0;
1618         struct scan_control sc = {
1619                 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
1620                 .may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP),
1621                 .swap_cluster_max = max_t(unsigned long, nr_pages,
1622                                         SWAP_CLUSTER_MAX),
1623                 .gfp_mask = gfp_mask,
1624                 .swappiness = vm_swappiness,
1625         };
1626         unsigned long slab_reclaimable;
1627
1628         disable_swap_token();
1629         cond_resched();
1630         /*
1631          * We need to be able to allocate from the reserves for RECLAIM_SWAP
1632          * and we also need to be able to write out pages for RECLAIM_WRITE
1633          * and RECLAIM_SWAP.
1634          */
1635         p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
1636         reclaim_state.reclaimed_slab = 0;
1637         p->reclaim_state = &reclaim_state;
1638
1639         if (zone_page_state(zone, NR_FILE_PAGES) -
1640                 zone_page_state(zone, NR_FILE_MAPPED) >
1641                 zone->min_unmapped_pages) {
1642                 /*
1643                  * Free memory by calling shrink zone with increasing
1644                  * priorities until we have enough memory freed.
1645                  */
1646                 priority = ZONE_RECLAIM_PRIORITY;
1647                 do {
1648                         note_zone_scanning_priority(zone, priority);
1649                         nr_reclaimed += shrink_zone(priority, zone, &sc);
1650                         priority--;
1651                 } while (priority >= 0 && nr_reclaimed < nr_pages);
1652         }
1653
1654         slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
1655         if (slab_reclaimable > zone->min_slab_pages) {
1656                 /*
1657                  * shrink_slab() does not currently allow us to determine how
1658                  * many pages were freed in this zone. So we take the current
1659                  * number of slab pages and shake the slab until it is reduced
1660                  * by the same nr_pages that we used for reclaiming unmapped
1661                  * pages.
1662                  *
1663                  * Note that shrink_slab will free memory on all zones and may
1664                  * take a long time.
1665                  */
1666                 while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
1667                         zone_page_state(zone, NR_SLAB_RECLAIMABLE) >
1668                                 slab_reclaimable - nr_pages)
1669                         ;
1670
1671                 /*
1672                  * Update nr_reclaimed by the number of slab pages we
1673                  * reclaimed from this zone.
1674                  */
1675                 nr_reclaimed += slab_reclaimable -
1676                         zone_page_state(zone, NR_SLAB_RECLAIMABLE);
1677         }
1678
1679         p->reclaim_state = NULL;
1680         current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
1681         return nr_reclaimed >= nr_pages;
1682 }
1683
1684 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1685 {
1686         cpumask_t mask;
1687         int node_id;
1688
1689         /*
1690          * Zone reclaim reclaims unmapped file backed pages and
1691          * slab pages if we are over the defined limits.
1692          *
1693          * A small portion of unmapped file backed pages is needed for
1694          * file I/O otherwise pages read by file I/O will be immediately
1695          * thrown out if the zone is overallocated. So we do not reclaim
1696          * if less than a specified percentage of the zone is used by
1697          * unmapped file backed pages.
1698          */
1699         if (zone_page_state(zone, NR_FILE_PAGES) -
1700             zone_page_state(zone, NR_FILE_MAPPED) <= zone->min_unmapped_pages
1701             && zone_page_state(zone, NR_SLAB_RECLAIMABLE)
1702                         <= zone->min_slab_pages)
1703                 return 0;
1704
1705         /*
1706          * Avoid concurrent zone reclaims, do not reclaim in a zone that does
1707          * not have reclaimable pages and if we should not delay the allocation
1708          * then do not scan.
1709          */
1710         if (!(gfp_mask & __GFP_WAIT) ||
1711                 zone->all_unreclaimable ||
1712                 atomic_read(&zone->reclaim_in_progress) > 0 ||
1713                 (current->flags & PF_MEMALLOC))
1714                         return 0;
1715
1716         /*
1717          * Only run zone reclaim on the local zone or on zones that do not
1718          * have associated processors. This will favor the local processor
1719          * over remote processors and spread off node memory allocations
1720          * as wide as possible.
1721          */
1722         node_id = zone_to_nid(zone);
1723         mask = node_to_cpumask(node_id);
1724         if (!cpus_empty(mask) && node_id != numa_node_id())
1725                 return 0;
1726         return __zone_reclaim(zone, gfp_mask, order);
1727 }
1728 #endif