[PATCH] memory hotplug prep: break out zone initialization
[linux-2.6] / 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/file.h>
23 #include <linux/writeback.h>
24 #include <linux/blkdev.h>
25 #include <linux/buffer_head.h>  /* for try_to_release_page(),
26                                         buffer_heads_over_limit */
27 #include <linux/mm_inline.h>
28 #include <linux/pagevec.h>
29 #include <linux/backing-dev.h>
30 #include <linux/rmap.h>
31 #include <linux/topology.h>
32 #include <linux/cpu.h>
33 #include <linux/cpuset.h>
34 #include <linux/notifier.h>
35 #include <linux/rwsem.h>
36
37 #include <asm/tlbflush.h>
38 #include <asm/div64.h>
39
40 #include <linux/swapops.h>
41
42 /* possible outcome of pageout() */
43 typedef enum {
44         /* failed to write page out, page is locked */
45         PAGE_KEEP,
46         /* move page to the active list, page is locked */
47         PAGE_ACTIVATE,
48         /* page has been sent to the disk successfully, page is unlocked */
49         PAGE_SUCCESS,
50         /* page is clean and locked */
51         PAGE_CLEAN,
52 } pageout_t;
53
54 struct scan_control {
55         /* Ask refill_inactive_zone, or shrink_cache to scan this many pages */
56         unsigned long nr_to_scan;
57
58         /* Incremented by the number of inactive pages that were scanned */
59         unsigned long nr_scanned;
60
61         /* Incremented by the number of pages reclaimed */
62         unsigned long nr_reclaimed;
63
64         unsigned long nr_mapped;        /* From page_state */
65
66         /* How many pages shrink_cache() should reclaim */
67         int nr_to_reclaim;
68
69         /* Ask shrink_caches, or shrink_zone to scan at this priority */
70         unsigned int priority;
71
72         /* This context's GFP mask */
73         gfp_t gfp_mask;
74
75         int may_writepage;
76
77         /* Can pages be swapped as part of reclaim? */
78         int may_swap;
79
80         /* This context's SWAP_CLUSTER_MAX. If freeing memory for
81          * suspend, we effectively ignore SWAP_CLUSTER_MAX.
82          * In this context, it doesn't matter that we scan the
83          * whole list at once. */
84         int swap_cluster_max;
85 };
86
87 /*
88  * The list of shrinker callbacks used by to apply pressure to
89  * ageable caches.
90  */
91 struct shrinker {
92         shrinker_t              shrinker;
93         struct list_head        list;
94         int                     seeks;  /* seeks to recreate an obj */
95         long                    nr;     /* objs pending delete */
96 };
97
98 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
99
100 #ifdef ARCH_HAS_PREFETCH
101 #define prefetch_prev_lru_page(_page, _base, _field)                    \
102         do {                                                            \
103                 if ((_page)->lru.prev != _base) {                       \
104                         struct page *prev;                              \
105                                                                         \
106                         prev = lru_to_page(&(_page->lru));              \
107                         prefetch(&prev->_field);                        \
108                 }                                                       \
109         } while (0)
110 #else
111 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
112 #endif
113
114 #ifdef ARCH_HAS_PREFETCHW
115 #define prefetchw_prev_lru_page(_page, _base, _field)                   \
116         do {                                                            \
117                 if ((_page)->lru.prev != _base) {                       \
118                         struct page *prev;                              \
119                                                                         \
120                         prev = lru_to_page(&(_page->lru));              \
121                         prefetchw(&prev->_field);                       \
122                 }                                                       \
123         } while (0)
124 #else
125 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
126 #endif
127
128 /*
129  * From 0 .. 100.  Higher means more swappy.
130  */
131 int vm_swappiness = 60;
132 static long total_memory;
133
134 static LIST_HEAD(shrinker_list);
135 static DECLARE_RWSEM(shrinker_rwsem);
136
137 /*
138  * Add a shrinker callback to be called from the vm
139  */
140 struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
141 {
142         struct shrinker *shrinker;
143
144         shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
145         if (shrinker) {
146                 shrinker->shrinker = theshrinker;
147                 shrinker->seeks = seeks;
148                 shrinker->nr = 0;
149                 down_write(&shrinker_rwsem);
150                 list_add_tail(&shrinker->list, &shrinker_list);
151                 up_write(&shrinker_rwsem);
152         }
153         return shrinker;
154 }
155 EXPORT_SYMBOL(set_shrinker);
156
157 /*
158  * Remove one
159  */
160 void remove_shrinker(struct shrinker *shrinker)
161 {
162         down_write(&shrinker_rwsem);
163         list_del(&shrinker->list);
164         up_write(&shrinker_rwsem);
165         kfree(shrinker);
166 }
167 EXPORT_SYMBOL(remove_shrinker);
168
169 #define SHRINK_BATCH 128
170 /*
171  * Call the shrink functions to age shrinkable caches
172  *
173  * Here we assume it costs one seek to replace a lru page and that it also
174  * takes a seek to recreate a cache object.  With this in mind we age equal
175  * percentages of the lru and ageable caches.  This should balance the seeks
176  * generated by these structures.
177  *
178  * If the vm encounted mapped pages on the LRU it increase the pressure on
179  * slab to avoid swapping.
180  *
181  * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
182  *
183  * `lru_pages' represents the number of on-LRU pages in all the zones which
184  * are eligible for the caller's allocation attempt.  It is used for balancing
185  * slab reclaim versus page reclaim.
186  *
187  * Returns the number of slab objects which we shrunk.
188  */
189 static int shrink_slab(unsigned long scanned, gfp_t gfp_mask,
190                         unsigned long lru_pages)
191 {
192         struct shrinker *shrinker;
193         int ret = 0;
194
195         if (scanned == 0)
196                 scanned = SWAP_CLUSTER_MAX;
197
198         if (!down_read_trylock(&shrinker_rwsem))
199                 return 1;       /* Assume we'll be able to shrink next time */
200
201         list_for_each_entry(shrinker, &shrinker_list, list) {
202                 unsigned long long delta;
203                 unsigned long total_scan;
204
205                 delta = (4 * scanned) / shrinker->seeks;
206                 delta *= (*shrinker->shrinker)(0, gfp_mask);
207                 do_div(delta, lru_pages + 1);
208                 shrinker->nr += delta;
209                 if (shrinker->nr < 0)
210                         shrinker->nr = LONG_MAX;        /* It wrapped! */
211
212                 total_scan = shrinker->nr;
213                 shrinker->nr = 0;
214
215                 while (total_scan >= SHRINK_BATCH) {
216                         long this_scan = SHRINK_BATCH;
217                         int shrink_ret;
218                         int nr_before;
219
220                         nr_before = (*shrinker->shrinker)(0, gfp_mask);
221                         shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
222                         if (shrink_ret == -1)
223                                 break;
224                         if (shrink_ret < nr_before)
225                                 ret += nr_before - shrink_ret;
226                         mod_page_state(slabs_scanned, this_scan);
227                         total_scan -= this_scan;
228
229                         cond_resched();
230                 }
231
232                 shrinker->nr += total_scan;
233         }
234         up_read(&shrinker_rwsem);
235         return ret;
236 }
237
238 /* Called without lock on whether page is mapped, so answer is unstable */
239 static inline int page_mapping_inuse(struct page *page)
240 {
241         struct address_space *mapping;
242
243         /* Page is in somebody's page tables. */
244         if (page_mapped(page))
245                 return 1;
246
247         /* Be more reluctant to reclaim swapcache than pagecache */
248         if (PageSwapCache(page))
249                 return 1;
250
251         mapping = page_mapping(page);
252         if (!mapping)
253                 return 0;
254
255         /* File is mmap'd by somebody? */
256         return mapping_mapped(mapping);
257 }
258
259 static inline int is_page_cache_freeable(struct page *page)
260 {
261         return page_count(page) - !!PagePrivate(page) == 2;
262 }
263
264 static int may_write_to_queue(struct backing_dev_info *bdi)
265 {
266         if (current_is_kswapd())
267                 return 1;
268         if (current_is_pdflush())       /* This is unlikely, but why not... */
269                 return 1;
270         if (!bdi_write_congested(bdi))
271                 return 1;
272         if (bdi == current->backing_dev_info)
273                 return 1;
274         return 0;
275 }
276
277 /*
278  * We detected a synchronous write error writing a page out.  Probably
279  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
280  * fsync(), msync() or close().
281  *
282  * The tricky part is that after writepage we cannot touch the mapping: nothing
283  * prevents it from being freed up.  But we have a ref on the page and once
284  * that page is locked, the mapping is pinned.
285  *
286  * We're allowed to run sleeping lock_page() here because we know the caller has
287  * __GFP_FS.
288  */
289 static void handle_write_error(struct address_space *mapping,
290                                 struct page *page, int error)
291 {
292         lock_page(page);
293         if (page_mapping(page) == mapping) {
294                 if (error == -ENOSPC)
295                         set_bit(AS_ENOSPC, &mapping->flags);
296                 else
297                         set_bit(AS_EIO, &mapping->flags);
298         }
299         unlock_page(page);
300 }
301
302 /*
303  * pageout is called by shrink_list() for each dirty page. Calls ->writepage().
304  */
305 static pageout_t pageout(struct page *page, struct address_space *mapping)
306 {
307         /*
308          * If the page is dirty, only perform writeback if that write
309          * will be non-blocking.  To prevent this allocation from being
310          * stalled by pagecache activity.  But note that there may be
311          * stalls if we need to run get_block().  We could test
312          * PagePrivate for that.
313          *
314          * If this process is currently in generic_file_write() against
315          * this page's queue, we can perform writeback even if that
316          * will block.
317          *
318          * If the page is swapcache, write it back even if that would
319          * block, for some throttling. This happens by accident, because
320          * swap_backing_dev_info is bust: it doesn't reflect the
321          * congestion state of the swapdevs.  Easy to fix, if needed.
322          * See swapfile.c:page_queue_congested().
323          */
324         if (!is_page_cache_freeable(page))
325                 return PAGE_KEEP;
326         if (!mapping) {
327                 /*
328                  * Some data journaling orphaned pages can have
329                  * page->mapping == NULL while being dirty with clean buffers.
330                  */
331                 if (PagePrivate(page)) {
332                         if (try_to_free_buffers(page)) {
333                                 ClearPageDirty(page);
334                                 printk("%s: orphaned page\n", __FUNCTION__);
335                                 return PAGE_CLEAN;
336                         }
337                 }
338                 return PAGE_KEEP;
339         }
340         if (mapping->a_ops->writepage == NULL)
341                 return PAGE_ACTIVATE;
342         if (!may_write_to_queue(mapping->backing_dev_info))
343                 return PAGE_KEEP;
344
345         if (clear_page_dirty_for_io(page)) {
346                 int res;
347                 struct writeback_control wbc = {
348                         .sync_mode = WB_SYNC_NONE,
349                         .nr_to_write = SWAP_CLUSTER_MAX,
350                         .nonblocking = 1,
351                         .for_reclaim = 1,
352                 };
353
354                 SetPageReclaim(page);
355                 res = mapping->a_ops->writepage(page, &wbc);
356                 if (res < 0)
357                         handle_write_error(mapping, page, res);
358                 if (res == WRITEPAGE_ACTIVATE) {
359                         ClearPageReclaim(page);
360                         return PAGE_ACTIVATE;
361                 }
362                 if (!PageWriteback(page)) {
363                         /* synchronous write or broken a_ops? */
364                         ClearPageReclaim(page);
365                 }
366
367                 return PAGE_SUCCESS;
368         }
369
370         return PAGE_CLEAN;
371 }
372
373 /*
374  * shrink_list adds the number of reclaimed pages to sc->nr_reclaimed
375  */
376 static int shrink_list(struct list_head *page_list, struct scan_control *sc)
377 {
378         LIST_HEAD(ret_pages);
379         struct pagevec freed_pvec;
380         int pgactivate = 0;
381         int reclaimed = 0;
382
383         cond_resched();
384
385         pagevec_init(&freed_pvec, 1);
386         while (!list_empty(page_list)) {
387                 struct address_space *mapping;
388                 struct page *page;
389                 int may_enter_fs;
390                 int referenced;
391
392                 cond_resched();
393
394                 page = lru_to_page(page_list);
395                 list_del(&page->lru);
396
397                 if (TestSetPageLocked(page))
398                         goto keep;
399
400                 BUG_ON(PageActive(page));
401
402                 sc->nr_scanned++;
403                 /* Double the slab pressure for mapped and swapcache pages */
404                 if (page_mapped(page) || PageSwapCache(page))
405                         sc->nr_scanned++;
406
407                 if (PageWriteback(page))
408                         goto keep_locked;
409
410                 referenced = page_referenced(page, 1, sc->priority <= 0);
411                 /* In active use or really unfreeable?  Activate it. */
412                 if (referenced && page_mapping_inuse(page))
413                         goto activate_locked;
414
415 #ifdef CONFIG_SWAP
416                 /*
417                  * Anonymous process memory has backing store?
418                  * Try to allocate it some swap space here.
419                  */
420                 if (PageAnon(page) && !PageSwapCache(page)) {
421                         if (!sc->may_swap)
422                                 goto keep_locked;
423                         if (!add_to_swap(page))
424                                 goto activate_locked;
425                 }
426 #endif /* CONFIG_SWAP */
427
428                 mapping = page_mapping(page);
429                 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
430                         (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
431
432                 /*
433                  * The page is mapped into the page tables of one or more
434                  * processes. Try to unmap it here.
435                  */
436                 if (page_mapped(page) && mapping) {
437                         switch (try_to_unmap(page)) {
438                         case SWAP_FAIL:
439                                 goto activate_locked;
440                         case SWAP_AGAIN:
441                                 goto keep_locked;
442                         case SWAP_SUCCESS:
443                                 ; /* try to free the page below */
444                         }
445                 }
446
447                 if (PageDirty(page)) {
448                         if (referenced)
449                                 goto keep_locked;
450                         if (!may_enter_fs)
451                                 goto keep_locked;
452                         if (laptop_mode && !sc->may_writepage)
453                                 goto keep_locked;
454
455                         /* Page is dirty, try to write it out here */
456                         switch(pageout(page, mapping)) {
457                         case PAGE_KEEP:
458                                 goto keep_locked;
459                         case PAGE_ACTIVATE:
460                                 goto activate_locked;
461                         case PAGE_SUCCESS:
462                                 if (PageWriteback(page) || PageDirty(page))
463                                         goto keep;
464                                 /*
465                                  * A synchronous write - probably a ramdisk.  Go
466                                  * ahead and try to reclaim the page.
467                                  */
468                                 if (TestSetPageLocked(page))
469                                         goto keep;
470                                 if (PageDirty(page) || PageWriteback(page))
471                                         goto keep_locked;
472                                 mapping = page_mapping(page);
473                         case PAGE_CLEAN:
474                                 ; /* try to free the page below */
475                         }
476                 }
477
478                 /*
479                  * If the page has buffers, try to free the buffer mappings
480                  * associated with this page. If we succeed we try to free
481                  * the page as well.
482                  *
483                  * We do this even if the page is PageDirty().
484                  * try_to_release_page() does not perform I/O, but it is
485                  * possible for a page to have PageDirty set, but it is actually
486                  * clean (all its buffers are clean).  This happens if the
487                  * buffers were written out directly, with submit_bh(). ext3
488                  * will do this, as well as the blockdev mapping. 
489                  * try_to_release_page() will discover that cleanness and will
490                  * drop the buffers and mark the page clean - it can be freed.
491                  *
492                  * Rarely, pages can have buffers and no ->mapping.  These are
493                  * the pages which were not successfully invalidated in
494                  * truncate_complete_page().  We try to drop those buffers here
495                  * and if that worked, and the page is no longer mapped into
496                  * process address space (page_count == 1) it can be freed.
497                  * Otherwise, leave the page on the LRU so it is swappable.
498                  */
499                 if (PagePrivate(page)) {
500                         if (!try_to_release_page(page, sc->gfp_mask))
501                                 goto activate_locked;
502                         if (!mapping && page_count(page) == 1)
503                                 goto free_it;
504                 }
505
506                 if (!mapping)
507                         goto keep_locked;       /* truncate got there first */
508
509                 write_lock_irq(&mapping->tree_lock);
510
511                 /*
512                  * The non-racy check for busy page.  It is critical to check
513                  * PageDirty _after_ making sure that the page is freeable and
514                  * not in use by anybody.       (pagecache + us == 2)
515                  */
516                 if (unlikely(page_count(page) != 2))
517                         goto cannot_free;
518                 smp_rmb();
519                 if (unlikely(PageDirty(page)))
520                         goto cannot_free;
521
522 #ifdef CONFIG_SWAP
523                 if (PageSwapCache(page)) {
524                         swp_entry_t swap = { .val = page_private(page) };
525                         __delete_from_swap_cache(page);
526                         write_unlock_irq(&mapping->tree_lock);
527                         swap_free(swap);
528                         __put_page(page);       /* The pagecache ref */
529                         goto free_it;
530                 }
531 #endif /* CONFIG_SWAP */
532
533                 __remove_from_page_cache(page);
534                 write_unlock_irq(&mapping->tree_lock);
535                 __put_page(page);
536
537 free_it:
538                 unlock_page(page);
539                 reclaimed++;
540                 if (!pagevec_add(&freed_pvec, page))
541                         __pagevec_release_nonlru(&freed_pvec);
542                 continue;
543
544 cannot_free:
545                 write_unlock_irq(&mapping->tree_lock);
546                 goto keep_locked;
547
548 activate_locked:
549                 SetPageActive(page);
550                 pgactivate++;
551 keep_locked:
552                 unlock_page(page);
553 keep:
554                 list_add(&page->lru, &ret_pages);
555                 BUG_ON(PageLRU(page));
556         }
557         list_splice(&ret_pages, page_list);
558         if (pagevec_count(&freed_pvec))
559                 __pagevec_release_nonlru(&freed_pvec);
560         mod_page_state(pgactivate, pgactivate);
561         sc->nr_reclaimed += reclaimed;
562         return reclaimed;
563 }
564
565 /*
566  * zone->lru_lock is heavily contended.  Some of the functions that
567  * shrink the lists perform better by taking out a batch of pages
568  * and working on them outside the LRU lock.
569  *
570  * For pagecache intensive workloads, this function is the hottest
571  * spot in the kernel (apart from copy_*_user functions).
572  *
573  * Appropriate locks must be held before calling this function.
574  *
575  * @nr_to_scan: The number of pages to look through on the list.
576  * @src:        The LRU list to pull pages off.
577  * @dst:        The temp list to put pages on to.
578  * @scanned:    The number of pages that were scanned.
579  *
580  * returns how many pages were moved onto *@dst.
581  */
582 static int isolate_lru_pages(int nr_to_scan, struct list_head *src,
583                              struct list_head *dst, int *scanned)
584 {
585         int nr_taken = 0;
586         struct page *page;
587         int scan = 0;
588
589         while (scan++ < nr_to_scan && !list_empty(src)) {
590                 page = lru_to_page(src);
591                 prefetchw_prev_lru_page(page, src, flags);
592
593                 if (!TestClearPageLRU(page))
594                         BUG();
595                 list_del(&page->lru);
596                 if (get_page_testone(page)) {
597                         /*
598                          * It is being freed elsewhere
599                          */
600                         __put_page(page);
601                         SetPageLRU(page);
602                         list_add(&page->lru, src);
603                         continue;
604                 } else {
605                         list_add(&page->lru, dst);
606                         nr_taken++;
607                 }
608         }
609
610         *scanned = scan;
611         return nr_taken;
612 }
613
614 /*
615  * shrink_cache() adds the number of pages reclaimed to sc->nr_reclaimed
616  */
617 static void shrink_cache(struct zone *zone, struct scan_control *sc)
618 {
619         LIST_HEAD(page_list);
620         struct pagevec pvec;
621         int max_scan = sc->nr_to_scan;
622
623         pagevec_init(&pvec, 1);
624
625         lru_add_drain();
626         spin_lock_irq(&zone->lru_lock);
627         while (max_scan > 0) {
628                 struct page *page;
629                 int nr_taken;
630                 int nr_scan;
631                 int nr_freed;
632
633                 nr_taken = isolate_lru_pages(sc->swap_cluster_max,
634                                              &zone->inactive_list,
635                                              &page_list, &nr_scan);
636                 zone->nr_inactive -= nr_taken;
637                 zone->pages_scanned += nr_scan;
638                 spin_unlock_irq(&zone->lru_lock);
639
640                 if (nr_taken == 0)
641                         goto done;
642
643                 max_scan -= nr_scan;
644                 if (current_is_kswapd())
645                         mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
646                 else
647                         mod_page_state_zone(zone, pgscan_direct, nr_scan);
648                 nr_freed = shrink_list(&page_list, sc);
649                 if (current_is_kswapd())
650                         mod_page_state(kswapd_steal, nr_freed);
651                 mod_page_state_zone(zone, pgsteal, nr_freed);
652                 sc->nr_to_reclaim -= nr_freed;
653
654                 spin_lock_irq(&zone->lru_lock);
655                 /*
656                  * Put back any unfreeable pages.
657                  */
658                 while (!list_empty(&page_list)) {
659                         page = lru_to_page(&page_list);
660                         if (TestSetPageLRU(page))
661                                 BUG();
662                         list_del(&page->lru);
663                         if (PageActive(page))
664                                 add_page_to_active_list(zone, page);
665                         else
666                                 add_page_to_inactive_list(zone, page);
667                         if (!pagevec_add(&pvec, page)) {
668                                 spin_unlock_irq(&zone->lru_lock);
669                                 __pagevec_release(&pvec);
670                                 spin_lock_irq(&zone->lru_lock);
671                         }
672                 }
673         }
674         spin_unlock_irq(&zone->lru_lock);
675 done:
676         pagevec_release(&pvec);
677 }
678
679 /*
680  * This moves pages from the active list to the inactive list.
681  *
682  * We move them the other way if the page is referenced by one or more
683  * processes, from rmap.
684  *
685  * If the pages are mostly unmapped, the processing is fast and it is
686  * appropriate to hold zone->lru_lock across the whole operation.  But if
687  * the pages are mapped, the processing is slow (page_referenced()) so we
688  * should drop zone->lru_lock around each page.  It's impossible to balance
689  * this, so instead we remove the pages from the LRU while processing them.
690  * It is safe to rely on PG_active against the non-LRU pages in here because
691  * nobody will play with that bit on a non-LRU page.
692  *
693  * The downside is that we have to touch page->_count against each page.
694  * But we had to alter page->flags anyway.
695  */
696 static void
697 refill_inactive_zone(struct zone *zone, struct scan_control *sc)
698 {
699         int pgmoved;
700         int pgdeactivate = 0;
701         int pgscanned;
702         int nr_pages = sc->nr_to_scan;
703         LIST_HEAD(l_hold);      /* The pages which were snipped off */
704         LIST_HEAD(l_inactive);  /* Pages to go onto the inactive_list */
705         LIST_HEAD(l_active);    /* Pages to go onto the active_list */
706         struct page *page;
707         struct pagevec pvec;
708         int reclaim_mapped = 0;
709         long mapped_ratio;
710         long distress;
711         long swap_tendency;
712
713         lru_add_drain();
714         spin_lock_irq(&zone->lru_lock);
715         pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
716                                     &l_hold, &pgscanned);
717         zone->pages_scanned += pgscanned;
718         zone->nr_active -= pgmoved;
719         spin_unlock_irq(&zone->lru_lock);
720
721         /*
722          * `distress' is a measure of how much trouble we're having reclaiming
723          * pages.  0 -> no problems.  100 -> great trouble.
724          */
725         distress = 100 >> zone->prev_priority;
726
727         /*
728          * The point of this algorithm is to decide when to start reclaiming
729          * mapped memory instead of just pagecache.  Work out how much memory
730          * is mapped.
731          */
732         mapped_ratio = (sc->nr_mapped * 100) / total_memory;
733
734         /*
735          * Now decide how much we really want to unmap some pages.  The mapped
736          * ratio is downgraded - just because there's a lot of mapped memory
737          * doesn't necessarily mean that page reclaim isn't succeeding.
738          *
739          * The distress ratio is important - we don't want to start going oom.
740          *
741          * A 100% value of vm_swappiness overrides this algorithm altogether.
742          */
743         swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
744
745         /*
746          * Now use this metric to decide whether to start moving mapped memory
747          * onto the inactive list.
748          */
749         if (swap_tendency >= 100)
750                 reclaim_mapped = 1;
751
752         while (!list_empty(&l_hold)) {
753                 cond_resched();
754                 page = lru_to_page(&l_hold);
755                 list_del(&page->lru);
756                 if (page_mapped(page)) {
757                         if (!reclaim_mapped ||
758                             (total_swap_pages == 0 && PageAnon(page)) ||
759                             page_referenced(page, 0, sc->priority <= 0)) {
760                                 list_add(&page->lru, &l_active);
761                                 continue;
762                         }
763                 }
764                 list_add(&page->lru, &l_inactive);
765         }
766
767         pagevec_init(&pvec, 1);
768         pgmoved = 0;
769         spin_lock_irq(&zone->lru_lock);
770         while (!list_empty(&l_inactive)) {
771                 page = lru_to_page(&l_inactive);
772                 prefetchw_prev_lru_page(page, &l_inactive, flags);
773                 if (TestSetPageLRU(page))
774                         BUG();
775                 if (!TestClearPageActive(page))
776                         BUG();
777                 list_move(&page->lru, &zone->inactive_list);
778                 pgmoved++;
779                 if (!pagevec_add(&pvec, page)) {
780                         zone->nr_inactive += pgmoved;
781                         spin_unlock_irq(&zone->lru_lock);
782                         pgdeactivate += pgmoved;
783                         pgmoved = 0;
784                         if (buffer_heads_over_limit)
785                                 pagevec_strip(&pvec);
786                         __pagevec_release(&pvec);
787                         spin_lock_irq(&zone->lru_lock);
788                 }
789         }
790         zone->nr_inactive += pgmoved;
791         pgdeactivate += pgmoved;
792         if (buffer_heads_over_limit) {
793                 spin_unlock_irq(&zone->lru_lock);
794                 pagevec_strip(&pvec);
795                 spin_lock_irq(&zone->lru_lock);
796         }
797
798         pgmoved = 0;
799         while (!list_empty(&l_active)) {
800                 page = lru_to_page(&l_active);
801                 prefetchw_prev_lru_page(page, &l_active, flags);
802                 if (TestSetPageLRU(page))
803                         BUG();
804                 BUG_ON(!PageActive(page));
805                 list_move(&page->lru, &zone->active_list);
806                 pgmoved++;
807                 if (!pagevec_add(&pvec, page)) {
808                         zone->nr_active += pgmoved;
809                         pgmoved = 0;
810                         spin_unlock_irq(&zone->lru_lock);
811                         __pagevec_release(&pvec);
812                         spin_lock_irq(&zone->lru_lock);
813                 }
814         }
815         zone->nr_active += pgmoved;
816         spin_unlock_irq(&zone->lru_lock);
817         pagevec_release(&pvec);
818
819         mod_page_state_zone(zone, pgrefill, pgscanned);
820         mod_page_state(pgdeactivate, pgdeactivate);
821 }
822
823 /*
824  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
825  */
826 static void
827 shrink_zone(struct zone *zone, struct scan_control *sc)
828 {
829         unsigned long nr_active;
830         unsigned long nr_inactive;
831
832         atomic_inc(&zone->reclaim_in_progress);
833
834         /*
835          * Add one to `nr_to_scan' just to make sure that the kernel will
836          * slowly sift through the active list.
837          */
838         zone->nr_scan_active += (zone->nr_active >> sc->priority) + 1;
839         nr_active = zone->nr_scan_active;
840         if (nr_active >= sc->swap_cluster_max)
841                 zone->nr_scan_active = 0;
842         else
843                 nr_active = 0;
844
845         zone->nr_scan_inactive += (zone->nr_inactive >> sc->priority) + 1;
846         nr_inactive = zone->nr_scan_inactive;
847         if (nr_inactive >= sc->swap_cluster_max)
848                 zone->nr_scan_inactive = 0;
849         else
850                 nr_inactive = 0;
851
852         sc->nr_to_reclaim = sc->swap_cluster_max;
853
854         while (nr_active || nr_inactive) {
855                 if (nr_active) {
856                         sc->nr_to_scan = min(nr_active,
857                                         (unsigned long)sc->swap_cluster_max);
858                         nr_active -= sc->nr_to_scan;
859                         refill_inactive_zone(zone, sc);
860                 }
861
862                 if (nr_inactive) {
863                         sc->nr_to_scan = min(nr_inactive,
864                                         (unsigned long)sc->swap_cluster_max);
865                         nr_inactive -= sc->nr_to_scan;
866                         shrink_cache(zone, sc);
867                         if (sc->nr_to_reclaim <= 0)
868                                 break;
869                 }
870         }
871
872         throttle_vm_writeout();
873
874         atomic_dec(&zone->reclaim_in_progress);
875 }
876
877 /*
878  * This is the direct reclaim path, for page-allocating processes.  We only
879  * try to reclaim pages from zones which will satisfy the caller's allocation
880  * request.
881  *
882  * We reclaim from a zone even if that zone is over pages_high.  Because:
883  * a) The caller may be trying to free *extra* pages to satisfy a higher-order
884  *    allocation or
885  * b) The zones may be over pages_high but they must go *over* pages_high to
886  *    satisfy the `incremental min' zone defense algorithm.
887  *
888  * Returns the number of reclaimed pages.
889  *
890  * If a zone is deemed to be full of pinned pages then just give it a light
891  * scan then give up on it.
892  */
893 static void
894 shrink_caches(struct zone **zones, struct scan_control *sc)
895 {
896         int i;
897
898         for (i = 0; zones[i] != NULL; i++) {
899                 struct zone *zone = zones[i];
900
901                 if (zone->present_pages == 0)
902                         continue;
903
904                 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
905                         continue;
906
907                 zone->temp_priority = sc->priority;
908                 if (zone->prev_priority > sc->priority)
909                         zone->prev_priority = sc->priority;
910
911                 if (zone->all_unreclaimable && sc->priority != DEF_PRIORITY)
912                         continue;       /* Let kswapd poll it */
913
914                 shrink_zone(zone, sc);
915         }
916 }
917  
918 /*
919  * This is the main entry point to direct page reclaim.
920  *
921  * If a full scan of the inactive list fails to free enough memory then we
922  * are "out of memory" and something needs to be killed.
923  *
924  * If the caller is !__GFP_FS then the probability of a failure is reasonably
925  * high - the zone may be full of dirty or under-writeback pages, which this
926  * caller can't do much about.  We kick pdflush and take explicit naps in the
927  * hope that some of these pages can be written.  But if the allocating task
928  * holds filesystem locks which prevent writeout this might not work, and the
929  * allocation attempt will fail.
930  */
931 int try_to_free_pages(struct zone **zones, gfp_t gfp_mask)
932 {
933         int priority;
934         int ret = 0;
935         int total_scanned = 0, total_reclaimed = 0;
936         struct reclaim_state *reclaim_state = current->reclaim_state;
937         struct scan_control sc;
938         unsigned long lru_pages = 0;
939         int i;
940
941         sc.gfp_mask = gfp_mask;
942         sc.may_writepage = 0;
943         sc.may_swap = 1;
944
945         inc_page_state(allocstall);
946
947         for (i = 0; zones[i] != NULL; i++) {
948                 struct zone *zone = zones[i];
949
950                 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
951                         continue;
952
953                 zone->temp_priority = DEF_PRIORITY;
954                 lru_pages += zone->nr_active + zone->nr_inactive;
955         }
956
957         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
958                 sc.nr_mapped = read_page_state(nr_mapped);
959                 sc.nr_scanned = 0;
960                 sc.nr_reclaimed = 0;
961                 sc.priority = priority;
962                 sc.swap_cluster_max = SWAP_CLUSTER_MAX;
963                 shrink_caches(zones, &sc);
964                 shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
965                 if (reclaim_state) {
966                         sc.nr_reclaimed += reclaim_state->reclaimed_slab;
967                         reclaim_state->reclaimed_slab = 0;
968                 }
969                 total_scanned += sc.nr_scanned;
970                 total_reclaimed += sc.nr_reclaimed;
971                 if (total_reclaimed >= sc.swap_cluster_max) {
972                         ret = 1;
973                         goto out;
974                 }
975
976                 /*
977                  * Try to write back as many pages as we just scanned.  This
978                  * tends to cause slow streaming writers to write data to the
979                  * disk smoothly, at the dirtying rate, which is nice.   But
980                  * that's undesirable in laptop mode, where we *want* lumpy
981                  * writeout.  So in laptop mode, write out the whole world.
982                  */
983                 if (total_scanned > sc.swap_cluster_max + sc.swap_cluster_max/2) {
984                         wakeup_pdflush(laptop_mode ? 0 : total_scanned);
985                         sc.may_writepage = 1;
986                 }
987
988                 /* Take a nap, wait for some writeback to complete */
989                 if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
990                         blk_congestion_wait(WRITE, HZ/10);
991         }
992 out:
993         for (i = 0; zones[i] != 0; i++) {
994                 struct zone *zone = zones[i];
995
996                 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
997                         continue;
998
999                 zone->prev_priority = zone->temp_priority;
1000         }
1001         return ret;
1002 }
1003
1004 /*
1005  * For kswapd, balance_pgdat() will work across all this node's zones until
1006  * they are all at pages_high.
1007  *
1008  * If `nr_pages' is non-zero then it is the number of pages which are to be
1009  * reclaimed, regardless of the zone occupancies.  This is a software suspend
1010  * special.
1011  *
1012  * Returns the number of pages which were actually freed.
1013  *
1014  * There is special handling here for zones which are full of pinned pages.
1015  * This can happen if the pages are all mlocked, or if they are all used by
1016  * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
1017  * What we do is to detect the case where all pages in the zone have been
1018  * scanned twice and there has been zero successful reclaim.  Mark the zone as
1019  * dead and from now on, only perform a short scan.  Basically we're polling
1020  * the zone for when the problem goes away.
1021  *
1022  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
1023  * zones which have free_pages > pages_high, but once a zone is found to have
1024  * free_pages <= pages_high, we scan that zone and the lower zones regardless
1025  * of the number of free pages in the lower zones.  This interoperates with
1026  * the page allocator fallback scheme to ensure that aging of pages is balanced
1027  * across the zones.
1028  */
1029 static int balance_pgdat(pg_data_t *pgdat, int nr_pages, int order)
1030 {
1031         int to_free = nr_pages;
1032         int all_zones_ok;
1033         int priority;
1034         int i;
1035         int total_scanned, total_reclaimed;
1036         struct reclaim_state *reclaim_state = current->reclaim_state;
1037         struct scan_control sc;
1038
1039 loop_again:
1040         total_scanned = 0;
1041         total_reclaimed = 0;
1042         sc.gfp_mask = GFP_KERNEL;
1043         sc.may_writepage = 0;
1044         sc.may_swap = 1;
1045         sc.nr_mapped = read_page_state(nr_mapped);
1046
1047         inc_page_state(pageoutrun);
1048
1049         for (i = 0; i < pgdat->nr_zones; i++) {
1050                 struct zone *zone = pgdat->node_zones + i;
1051
1052                 zone->temp_priority = DEF_PRIORITY;
1053         }
1054
1055         for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1056                 int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
1057                 unsigned long lru_pages = 0;
1058
1059                 all_zones_ok = 1;
1060
1061                 if (nr_pages == 0) {
1062                         /*
1063                          * Scan in the highmem->dma direction for the highest
1064                          * zone which needs scanning
1065                          */
1066                         for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1067                                 struct zone *zone = pgdat->node_zones + i;
1068
1069                                 if (zone->present_pages == 0)
1070                                         continue;
1071
1072                                 if (zone->all_unreclaimable &&
1073                                                 priority != DEF_PRIORITY)
1074                                         continue;
1075
1076                                 if (!zone_watermark_ok(zone, order,
1077                                                 zone->pages_high, 0, 0, 0)) {
1078                                         end_zone = i;
1079                                         goto scan;
1080                                 }
1081                         }
1082                         goto out;
1083                 } else {
1084                         end_zone = pgdat->nr_zones - 1;
1085                 }
1086 scan:
1087                 for (i = 0; i <= end_zone; i++) {
1088                         struct zone *zone = pgdat->node_zones + i;
1089
1090                         lru_pages += zone->nr_active + zone->nr_inactive;
1091                 }
1092
1093                 /*
1094                  * Now scan the zone in the dma->highmem direction, stopping
1095                  * at the last zone which needs scanning.
1096                  *
1097                  * We do this because the page allocator works in the opposite
1098                  * direction.  This prevents the page allocator from allocating
1099                  * pages behind kswapd's direction of progress, which would
1100                  * cause too much scanning of the lower zones.
1101                  */
1102                 for (i = 0; i <= end_zone; i++) {
1103                         struct zone *zone = pgdat->node_zones + i;
1104                         int nr_slab;
1105
1106                         if (zone->present_pages == 0)
1107                                 continue;
1108
1109                         if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1110                                 continue;
1111
1112                         if (nr_pages == 0) {    /* Not software suspend */
1113                                 if (!zone_watermark_ok(zone, order,
1114                                                 zone->pages_high, end_zone, 0, 0))
1115                                         all_zones_ok = 0;
1116                         }
1117                         zone->temp_priority = priority;
1118                         if (zone->prev_priority > priority)
1119                                 zone->prev_priority = priority;
1120                         sc.nr_scanned = 0;
1121                         sc.nr_reclaimed = 0;
1122                         sc.priority = priority;
1123                         sc.swap_cluster_max = nr_pages? nr_pages : SWAP_CLUSTER_MAX;
1124                         atomic_inc(&zone->reclaim_in_progress);
1125                         shrink_zone(zone, &sc);
1126                         atomic_dec(&zone->reclaim_in_progress);
1127                         reclaim_state->reclaimed_slab = 0;
1128                         nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
1129                                                 lru_pages);
1130                         sc.nr_reclaimed += reclaim_state->reclaimed_slab;
1131                         total_reclaimed += sc.nr_reclaimed;
1132                         total_scanned += sc.nr_scanned;
1133                         if (zone->all_unreclaimable)
1134                                 continue;
1135                         if (nr_slab == 0 && zone->pages_scanned >=
1136                                     (zone->nr_active + zone->nr_inactive) * 4)
1137                                 zone->all_unreclaimable = 1;
1138                         /*
1139                          * If we've done a decent amount of scanning and
1140                          * the reclaim ratio is low, start doing writepage
1141                          * even in laptop mode
1142                          */
1143                         if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1144                             total_scanned > total_reclaimed+total_reclaimed/2)
1145                                 sc.may_writepage = 1;
1146                 }
1147                 if (nr_pages && to_free > total_reclaimed)
1148                         continue;       /* swsusp: need to do more work */
1149                 if (all_zones_ok)
1150                         break;          /* kswapd: all done */
1151                 /*
1152                  * OK, kswapd is getting into trouble.  Take a nap, then take
1153                  * another pass across the zones.
1154                  */
1155                 if (total_scanned && priority < DEF_PRIORITY - 2)
1156                         blk_congestion_wait(WRITE, HZ/10);
1157
1158                 /*
1159                  * We do this so kswapd doesn't build up large priorities for
1160                  * example when it is freeing in parallel with allocators. It
1161                  * matches the direct reclaim path behaviour in terms of impact
1162                  * on zone->*_priority.
1163                  */
1164                 if ((total_reclaimed >= SWAP_CLUSTER_MAX) && (!nr_pages))
1165                         break;
1166         }
1167 out:
1168         for (i = 0; i < pgdat->nr_zones; i++) {
1169                 struct zone *zone = pgdat->node_zones + i;
1170
1171                 zone->prev_priority = zone->temp_priority;
1172         }
1173         if (!all_zones_ok) {
1174                 cond_resched();
1175                 goto loop_again;
1176         }
1177
1178         return total_reclaimed;
1179 }
1180
1181 /*
1182  * The background pageout daemon, started as a kernel thread
1183  * from the init process. 
1184  *
1185  * This basically trickles out pages so that we have _some_
1186  * free memory available even if there is no other activity
1187  * that frees anything up. This is needed for things like routing
1188  * etc, where we otherwise might have all activity going on in
1189  * asynchronous contexts that cannot page things out.
1190  *
1191  * If there are applications that are active memory-allocators
1192  * (most normal use), this basically shouldn't matter.
1193  */
1194 static int kswapd(void *p)
1195 {
1196         unsigned long order;
1197         pg_data_t *pgdat = (pg_data_t*)p;
1198         struct task_struct *tsk = current;
1199         DEFINE_WAIT(wait);
1200         struct reclaim_state reclaim_state = {
1201                 .reclaimed_slab = 0,
1202         };
1203         cpumask_t cpumask;
1204
1205         daemonize("kswapd%d", pgdat->node_id);
1206         cpumask = node_to_cpumask(pgdat->node_id);
1207         if (!cpus_empty(cpumask))
1208                 set_cpus_allowed(tsk, cpumask);
1209         current->reclaim_state = &reclaim_state;
1210
1211         /*
1212          * Tell the memory management that we're a "memory allocator",
1213          * and that if we need more memory we should get access to it
1214          * regardless (see "__alloc_pages()"). "kswapd" should
1215          * never get caught in the normal page freeing logic.
1216          *
1217          * (Kswapd normally doesn't need memory anyway, but sometimes
1218          * you need a small amount of memory in order to be able to
1219          * page out something else, and this flag essentially protects
1220          * us from recursively trying to free more memory as we're
1221          * trying to free the first piece of memory in the first place).
1222          */
1223         tsk->flags |= PF_MEMALLOC|PF_KSWAPD;
1224
1225         order = 0;
1226         for ( ; ; ) {
1227                 unsigned long new_order;
1228
1229                 try_to_freeze();
1230
1231                 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1232                 new_order = pgdat->kswapd_max_order;
1233                 pgdat->kswapd_max_order = 0;
1234                 if (order < new_order) {
1235                         /*
1236                          * Don't sleep if someone wants a larger 'order'
1237                          * allocation
1238                          */
1239                         order = new_order;
1240                 } else {
1241                         schedule();
1242                         order = pgdat->kswapd_max_order;
1243                 }
1244                 finish_wait(&pgdat->kswapd_wait, &wait);
1245
1246                 balance_pgdat(pgdat, 0, order);
1247         }
1248         return 0;
1249 }
1250
1251 /*
1252  * A zone is low on free memory, so wake its kswapd task to service it.
1253  */
1254 void wakeup_kswapd(struct zone *zone, int order)
1255 {
1256         pg_data_t *pgdat;
1257
1258         if (zone->present_pages == 0)
1259                 return;
1260
1261         pgdat = zone->zone_pgdat;
1262         if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0, 0))
1263                 return;
1264         if (pgdat->kswapd_max_order < order)
1265                 pgdat->kswapd_max_order = order;
1266         if (!cpuset_zone_allowed(zone, __GFP_HARDWALL))
1267                 return;
1268         if (!waitqueue_active(&pgdat->kswapd_wait))
1269                 return;
1270         wake_up_interruptible(&pgdat->kswapd_wait);
1271 }
1272
1273 #ifdef CONFIG_PM
1274 /*
1275  * Try to free `nr_pages' of memory, system-wide.  Returns the number of freed
1276  * pages.
1277  */
1278 int shrink_all_memory(int nr_pages)
1279 {
1280         pg_data_t *pgdat;
1281         int nr_to_free = nr_pages;
1282         int ret = 0;
1283         struct reclaim_state reclaim_state = {
1284                 .reclaimed_slab = 0,
1285         };
1286
1287         current->reclaim_state = &reclaim_state;
1288         for_each_pgdat(pgdat) {
1289                 int freed;
1290                 freed = balance_pgdat(pgdat, nr_to_free, 0);
1291                 ret += freed;
1292                 nr_to_free -= freed;
1293                 if (nr_to_free <= 0)
1294                         break;
1295         }
1296         current->reclaim_state = NULL;
1297         return ret;
1298 }
1299 #endif
1300
1301 #ifdef CONFIG_HOTPLUG_CPU
1302 /* It's optimal to keep kswapds on the same CPUs as their memory, but
1303    not required for correctness.  So if the last cpu in a node goes
1304    away, we get changed to run anywhere: as the first one comes back,
1305    restore their cpu bindings. */
1306 static int __devinit cpu_callback(struct notifier_block *nfb,
1307                                   unsigned long action,
1308                                   void *hcpu)
1309 {
1310         pg_data_t *pgdat;
1311         cpumask_t mask;
1312
1313         if (action == CPU_ONLINE) {
1314                 for_each_pgdat(pgdat) {
1315                         mask = node_to_cpumask(pgdat->node_id);
1316                         if (any_online_cpu(mask) != NR_CPUS)
1317                                 /* One of our CPUs online: restore mask */
1318                                 set_cpus_allowed(pgdat->kswapd, mask);
1319                 }
1320         }
1321         return NOTIFY_OK;
1322 }
1323 #endif /* CONFIG_HOTPLUG_CPU */
1324
1325 static int __init kswapd_init(void)
1326 {
1327         pg_data_t *pgdat;
1328         swap_setup();
1329         for_each_pgdat(pgdat)
1330                 pgdat->kswapd
1331                 = find_task_by_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL));
1332         total_memory = nr_free_pagecache_pages();
1333         hotcpu_notifier(cpu_callback, 0);
1334         return 0;
1335 }
1336
1337 module_init(kswapd_init)
1338
1339
1340 /*
1341  * Try to free up some pages from this zone through reclaim.
1342  */
1343 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1344 {
1345         struct scan_control sc;
1346         int nr_pages = 1 << order;
1347         int total_reclaimed = 0;
1348
1349         /* The reclaim may sleep, so don't do it if sleep isn't allowed */
1350         if (!(gfp_mask & __GFP_WAIT))
1351                 return 0;
1352         if (zone->all_unreclaimable)
1353                 return 0;
1354
1355         sc.gfp_mask = gfp_mask;
1356         sc.may_writepage = 0;
1357         sc.may_swap = 0;
1358         sc.nr_mapped = read_page_state(nr_mapped);
1359         sc.nr_scanned = 0;
1360         sc.nr_reclaimed = 0;
1361         /* scan at the highest priority */
1362         sc.priority = 0;
1363
1364         if (nr_pages > SWAP_CLUSTER_MAX)
1365                 sc.swap_cluster_max = nr_pages;
1366         else
1367                 sc.swap_cluster_max = SWAP_CLUSTER_MAX;
1368
1369         /* Don't reclaim the zone if there are other reclaimers active */
1370         if (atomic_read(&zone->reclaim_in_progress) > 0)
1371                 goto out;
1372
1373         shrink_zone(zone, &sc);
1374         total_reclaimed = sc.nr_reclaimed;
1375
1376  out:
1377         return total_reclaimed;
1378 }
1379
1380 asmlinkage long sys_set_zone_reclaim(unsigned int node, unsigned int zone,
1381                                      unsigned int state)
1382 {
1383         struct zone *z;
1384         int i;
1385
1386         if (!capable(CAP_SYS_ADMIN))
1387                 return -EACCES;
1388
1389         if (node >= MAX_NUMNODES || !node_online(node))
1390                 return -EINVAL;
1391
1392         /* This will break if we ever add more zones */
1393         if (!(zone & (1<<ZONE_DMA|1<<ZONE_NORMAL|1<<ZONE_HIGHMEM)))
1394                 return -EINVAL;
1395
1396         for (i = 0; i < MAX_NR_ZONES; i++) {
1397                 if (!(zone & 1<<i))
1398                         continue;
1399
1400                 z = &NODE_DATA(node)->node_zones[i];
1401
1402                 if (state)
1403                         z->reclaim_pages = 1;
1404                 else
1405                         z->reclaim_pages = 0;
1406         }
1407
1408         return 0;
1409 }