mm: check PageUnevictable in lru_deactivate_fn()
[linux-2.6.git] / mm / swap.c
1 /*
2  *  linux/mm/swap.c
3  *
4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
5  */
6
7 /*
8  * This file contains the default values for the operation of the
9  * Linux VM subsystem. Fine-tuning documentation can be found in
10  * Documentation/sysctl/vm.txt.
11  * Started 18.12.91
12  * Swap aging added 23.2.95, Stephen Tweedie.
13  * Buffermem limits added 12.3.98, Rik van Riel.
14  */
15
16 #include <linux/mm.h>
17 #include <linux/sched.h>
18 #include <linux/kernel_stat.h>
19 #include <linux/swap.h>
20 #include <linux/mman.h>
21 #include <linux/pagemap.h>
22 #include <linux/pagevec.h>
23 #include <linux/init.h>
24 #include <linux/module.h>
25 #include <linux/mm_inline.h>
26 #include <linux/buffer_head.h>  /* for try_to_release_page() */
27 #include <linux/percpu_counter.h>
28 #include <linux/percpu.h>
29 #include <linux/cpu.h>
30 #include <linux/notifier.h>
31 #include <linux/backing-dev.h>
32 #include <linux/memcontrol.h>
33 #include <linux/gfp.h>
34
35 #include "internal.h"
36
37 /* How many pages do we try to swap or page in/out together? */
38 int page_cluster;
39
40 static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
41 static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
42 static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);
43
44 /*
45  * This path almost never happens for VM activity - pages are normally
46  * freed via pagevecs.  But it gets used by networking.
47  */
48 static void __page_cache_release(struct page *page)
49 {
50         if (PageLRU(page)) {
51                 unsigned long flags;
52                 struct zone *zone = page_zone(page);
53
54                 spin_lock_irqsave(&zone->lru_lock, flags);
55                 VM_BUG_ON(!PageLRU(page));
56                 __ClearPageLRU(page);
57                 del_page_from_lru(zone, page);
58                 spin_unlock_irqrestore(&zone->lru_lock, flags);
59         }
60 }
61
62 static void __put_single_page(struct page *page)
63 {
64         __page_cache_release(page);
65         free_hot_cold_page(page, 0);
66 }
67
68 static void __put_compound_page(struct page *page)
69 {
70         compound_page_dtor *dtor;
71
72         __page_cache_release(page);
73         dtor = get_compound_page_dtor(page);
74         (*dtor)(page);
75 }
76
77 static void put_compound_page(struct page *page)
78 {
79         if (unlikely(PageTail(page))) {
80                 /* __split_huge_page_refcount can run under us */
81                 struct page *page_head = page->first_page;
82                 smp_rmb();
83                 /*
84                  * If PageTail is still set after smp_rmb() we can be sure
85                  * that the page->first_page we read wasn't a dangling pointer.
86                  * See __split_huge_page_refcount() smp_wmb().
87                  */
88                 if (likely(PageTail(page) && get_page_unless_zero(page_head))) {
89                         unsigned long flags;
90                         /*
91                          * Verify that our page_head wasn't converted
92                          * to a a regular page before we got a
93                          * reference on it.
94                          */
95                         if (unlikely(!PageHead(page_head))) {
96                                 /* PageHead is cleared after PageTail */
97                                 smp_rmb();
98                                 VM_BUG_ON(PageTail(page));
99                                 goto out_put_head;
100                         }
101                         /*
102                          * Only run compound_lock on a valid PageHead,
103                          * after having it pinned with
104                          * get_page_unless_zero() above.
105                          */
106                         smp_mb();
107                         /* page_head wasn't a dangling pointer */
108                         flags = compound_lock_irqsave(page_head);
109                         if (unlikely(!PageTail(page))) {
110                                 /* __split_huge_page_refcount run before us */
111                                 compound_unlock_irqrestore(page_head, flags);
112                                 VM_BUG_ON(PageHead(page_head));
113                         out_put_head:
114                                 if (put_page_testzero(page_head))
115                                         __put_single_page(page_head);
116                         out_put_single:
117                                 if (put_page_testzero(page))
118                                         __put_single_page(page);
119                                 return;
120                         }
121                         VM_BUG_ON(page_head != page->first_page);
122                         /*
123                          * We can release the refcount taken by
124                          * get_page_unless_zero now that
125                          * split_huge_page_refcount is blocked on the
126                          * compound_lock.
127                          */
128                         if (put_page_testzero(page_head))
129                                 VM_BUG_ON(1);
130                         /* __split_huge_page_refcount will wait now */
131                         VM_BUG_ON(atomic_read(&page->_count) <= 0);
132                         atomic_dec(&page->_count);
133                         VM_BUG_ON(atomic_read(&page_head->_count) <= 0);
134                         compound_unlock_irqrestore(page_head, flags);
135                         if (put_page_testzero(page_head)) {
136                                 if (PageHead(page_head))
137                                         __put_compound_page(page_head);
138                                 else
139                                         __put_single_page(page_head);
140                         }
141                 } else {
142                         /* page_head is a dangling pointer */
143                         VM_BUG_ON(PageTail(page));
144                         goto out_put_single;
145                 }
146         } else if (put_page_testzero(page)) {
147                 if (PageHead(page))
148                         __put_compound_page(page);
149                 else
150                         __put_single_page(page);
151         }
152 }
153
154 void put_page(struct page *page)
155 {
156         if (unlikely(PageCompound(page)))
157                 put_compound_page(page);
158         else if (put_page_testzero(page))
159                 __put_single_page(page);
160 }
161 EXPORT_SYMBOL(put_page);
162
163 /**
164  * put_pages_list() - release a list of pages
165  * @pages: list of pages threaded on page->lru
166  *
167  * Release a list of pages which are strung together on page.lru.  Currently
168  * used by read_cache_pages() and related error recovery code.
169  */
170 void put_pages_list(struct list_head *pages)
171 {
172         while (!list_empty(pages)) {
173                 struct page *victim;
174
175                 victim = list_entry(pages->prev, struct page, lru);
176                 list_del(&victim->lru);
177                 page_cache_release(victim);
178         }
179 }
180 EXPORT_SYMBOL(put_pages_list);
181
182 static void pagevec_lru_move_fn(struct pagevec *pvec,
183                                 void (*move_fn)(struct page *page, void *arg),
184                                 void *arg)
185 {
186         int i;
187         struct zone *zone = NULL;
188         unsigned long flags = 0;
189
190         for (i = 0; i < pagevec_count(pvec); i++) {
191                 struct page *page = pvec->pages[i];
192                 struct zone *pagezone = page_zone(page);
193
194                 if (pagezone != zone) {
195                         if (zone)
196                                 spin_unlock_irqrestore(&zone->lru_lock, flags);
197                         zone = pagezone;
198                         spin_lock_irqsave(&zone->lru_lock, flags);
199                 }
200
201                 (*move_fn)(page, arg);
202         }
203         if (zone)
204                 spin_unlock_irqrestore(&zone->lru_lock, flags);
205         release_pages(pvec->pages, pvec->nr, pvec->cold);
206         pagevec_reinit(pvec);
207 }
208
209 static void pagevec_move_tail_fn(struct page *page, void *arg)
210 {
211         int *pgmoved = arg;
212         struct zone *zone = page_zone(page);
213
214         if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
215                 enum lru_list lru = page_lru_base_type(page);
216                 list_move_tail(&page->lru, &zone->lru[lru].list);
217                 mem_cgroup_rotate_reclaimable_page(page);
218                 (*pgmoved)++;
219         }
220 }
221
222 /*
223  * pagevec_move_tail() must be called with IRQ disabled.
224  * Otherwise this may cause nasty races.
225  */
226 static void pagevec_move_tail(struct pagevec *pvec)
227 {
228         int pgmoved = 0;
229
230         pagevec_lru_move_fn(pvec, pagevec_move_tail_fn, &pgmoved);
231         __count_vm_events(PGROTATED, pgmoved);
232 }
233
234 /*
235  * Writeback is about to end against a page which has been marked for immediate
236  * reclaim.  If it still appears to be reclaimable, move it to the tail of the
237  * inactive list.
238  */
239 void rotate_reclaimable_page(struct page *page)
240 {
241         if (!PageLocked(page) && !PageDirty(page) && !PageActive(page) &&
242             !PageUnevictable(page) && PageLRU(page)) {
243                 struct pagevec *pvec;
244                 unsigned long flags;
245
246                 page_cache_get(page);
247                 local_irq_save(flags);
248                 pvec = &__get_cpu_var(lru_rotate_pvecs);
249                 if (!pagevec_add(pvec, page))
250                         pagevec_move_tail(pvec);
251                 local_irq_restore(flags);
252         }
253 }
254
255 static void update_page_reclaim_stat(struct zone *zone, struct page *page,
256                                      int file, int rotated)
257 {
258         struct zone_reclaim_stat *reclaim_stat = &zone->reclaim_stat;
259         struct zone_reclaim_stat *memcg_reclaim_stat;
260
261         memcg_reclaim_stat = mem_cgroup_get_reclaim_stat_from_page(page);
262
263         reclaim_stat->recent_scanned[file]++;
264         if (rotated)
265                 reclaim_stat->recent_rotated[file]++;
266
267         if (!memcg_reclaim_stat)
268                 return;
269
270         memcg_reclaim_stat->recent_scanned[file]++;
271         if (rotated)
272                 memcg_reclaim_stat->recent_rotated[file]++;
273 }
274
275 /*
276  * FIXME: speed this up?
277  */
278 void activate_page(struct page *page)
279 {
280         struct zone *zone = page_zone(page);
281
282         spin_lock_irq(&zone->lru_lock);
283         if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
284                 int file = page_is_file_cache(page);
285                 int lru = page_lru_base_type(page);
286                 del_page_from_lru_list(zone, page, lru);
287
288                 SetPageActive(page);
289                 lru += LRU_ACTIVE;
290                 add_page_to_lru_list(zone, page, lru);
291                 __count_vm_event(PGACTIVATE);
292
293                 update_page_reclaim_stat(zone, page, file, 1);
294         }
295         spin_unlock_irq(&zone->lru_lock);
296 }
297
298 /*
299  * Mark a page as having seen activity.
300  *
301  * inactive,unreferenced        ->      inactive,referenced
302  * inactive,referenced          ->      active,unreferenced
303  * active,unreferenced          ->      active,referenced
304  */
305 void mark_page_accessed(struct page *page)
306 {
307         if (!PageActive(page) && !PageUnevictable(page) &&
308                         PageReferenced(page) && PageLRU(page)) {
309                 activate_page(page);
310                 ClearPageReferenced(page);
311         } else if (!PageReferenced(page)) {
312                 SetPageReferenced(page);
313         }
314 }
315
316 EXPORT_SYMBOL(mark_page_accessed);
317
318 void __lru_cache_add(struct page *page, enum lru_list lru)
319 {
320         struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];
321
322         page_cache_get(page);
323         if (!pagevec_add(pvec, page))
324                 ____pagevec_lru_add(pvec, lru);
325         put_cpu_var(lru_add_pvecs);
326 }
327 EXPORT_SYMBOL(__lru_cache_add);
328
329 /**
330  * lru_cache_add_lru - add a page to a page list
331  * @page: the page to be added to the LRU.
332  * @lru: the LRU list to which the page is added.
333  */
334 void lru_cache_add_lru(struct page *page, enum lru_list lru)
335 {
336         if (PageActive(page)) {
337                 VM_BUG_ON(PageUnevictable(page));
338                 ClearPageActive(page);
339         } else if (PageUnevictable(page)) {
340                 VM_BUG_ON(PageActive(page));
341                 ClearPageUnevictable(page);
342         }
343
344         VM_BUG_ON(PageLRU(page) || PageActive(page) || PageUnevictable(page));
345         __lru_cache_add(page, lru);
346 }
347
348 /**
349  * add_page_to_unevictable_list - add a page to the unevictable list
350  * @page:  the page to be added to the unevictable list
351  *
352  * Add page directly to its zone's unevictable list.  To avoid races with
353  * tasks that might be making the page evictable, through eg. munlock,
354  * munmap or exit, while it's not on the lru, we want to add the page
355  * while it's locked or otherwise "invisible" to other tasks.  This is
356  * difficult to do when using the pagevec cache, so bypass that.
357  */
358 void add_page_to_unevictable_list(struct page *page)
359 {
360         struct zone *zone = page_zone(page);
361
362         spin_lock_irq(&zone->lru_lock);
363         SetPageUnevictable(page);
364         SetPageLRU(page);
365         add_page_to_lru_list(zone, page, LRU_UNEVICTABLE);
366         spin_unlock_irq(&zone->lru_lock);
367 }
368
369 /*
370  * If the page can not be invalidated, it is moved to the
371  * inactive list to speed up its reclaim.  It is moved to the
372  * head of the list, rather than the tail, to give the flusher
373  * threads some time to write it out, as this is much more
374  * effective than the single-page writeout from reclaim.
375  *
376  * If the page isn't page_mapped and dirty/writeback, the page
377  * could reclaim asap using PG_reclaim.
378  *
379  * 1. active, mapped page -> none
380  * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
381  * 3. inactive, mapped page -> none
382  * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
383  * 5. inactive, clean -> inactive, tail
384  * 6. Others -> none
385  *
386  * In 4, why it moves inactive's head, the VM expects the page would
387  * be write it out by flusher threads as this is much more effective
388  * than the single-page writeout from reclaim.
389  */
390 static void lru_deactivate_fn(struct page *page, void *arg)
391 {
392         int lru, file;
393         bool active;
394         struct zone *zone = page_zone(page);
395
396         if (!PageLRU(page))
397                 return;
398
399         if (PageUnevictable(page))
400                 return;
401
402         /* Some processes are using the page */
403         if (page_mapped(page))
404                 return;
405
406         active = PageActive(page);
407
408         file = page_is_file_cache(page);
409         lru = page_lru_base_type(page);
410         del_page_from_lru_list(zone, page, lru + active);
411         ClearPageActive(page);
412         ClearPageReferenced(page);
413         add_page_to_lru_list(zone, page, lru);
414
415         if (PageWriteback(page) || PageDirty(page)) {
416                 /*
417                  * PG_reclaim could be raced with end_page_writeback
418                  * It can make readahead confusing.  But race window
419                  * is _really_ small and  it's non-critical problem.
420                  */
421                 SetPageReclaim(page);
422         } else {
423                 /*
424                  * The page's writeback ends up during pagevec
425                  * We moves tha page into tail of inactive.
426                  */
427                 list_move_tail(&page->lru, &zone->lru[lru].list);
428                 mem_cgroup_rotate_reclaimable_page(page);
429                 __count_vm_event(PGROTATED);
430         }
431
432         if (active)
433                 __count_vm_event(PGDEACTIVATE);
434         update_page_reclaim_stat(zone, page, file, 0);
435 }
436
437 /*
438  * Drain pages out of the cpu's pagevecs.
439  * Either "cpu" is the current CPU, and preemption has already been
440  * disabled; or "cpu" is being hot-unplugged, and is already dead.
441  */
442 static void drain_cpu_pagevecs(int cpu)
443 {
444         struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
445         struct pagevec *pvec;
446         int lru;
447
448         for_each_lru(lru) {
449                 pvec = &pvecs[lru - LRU_BASE];
450                 if (pagevec_count(pvec))
451                         ____pagevec_lru_add(pvec, lru);
452         }
453
454         pvec = &per_cpu(lru_rotate_pvecs, cpu);
455         if (pagevec_count(pvec)) {
456                 unsigned long flags;
457
458                 /* No harm done if a racing interrupt already did this */
459                 local_irq_save(flags);
460                 pagevec_move_tail(pvec);
461                 local_irq_restore(flags);
462         }
463
464         pvec = &per_cpu(lru_deactivate_pvecs, cpu);
465         if (pagevec_count(pvec))
466                 pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
467 }
468
469 /**
470  * deactivate_page - forcefully deactivate a page
471  * @page: page to deactivate
472  *
473  * This function hints the VM that @page is a good reclaim candidate,
474  * for example if its invalidation fails due to the page being dirty
475  * or under writeback.
476  */
477 void deactivate_page(struct page *page)
478 {
479         if (likely(get_page_unless_zero(page))) {
480                 struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
481
482                 if (!pagevec_add(pvec, page))
483                         pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
484                 put_cpu_var(lru_deactivate_pvecs);
485         }
486 }
487
488 void lru_add_drain(void)
489 {
490         drain_cpu_pagevecs(get_cpu());
491         put_cpu();
492 }
493
494 static void lru_add_drain_per_cpu(struct work_struct *dummy)
495 {
496         lru_add_drain();
497 }
498
499 /*
500  * Returns 0 for success
501  */
502 int lru_add_drain_all(void)
503 {
504         return schedule_on_each_cpu(lru_add_drain_per_cpu);
505 }
506
507 /*
508  * Batched page_cache_release().  Decrement the reference count on all the
509  * passed pages.  If it fell to zero then remove the page from the LRU and
510  * free it.
511  *
512  * Avoid taking zone->lru_lock if possible, but if it is taken, retain it
513  * for the remainder of the operation.
514  *
515  * The locking in this function is against shrink_inactive_list(): we recheck
516  * the page count inside the lock to see whether shrink_inactive_list()
517  * grabbed the page via the LRU.  If it did, give up: shrink_inactive_list()
518  * will free it.
519  */
520 void release_pages(struct page **pages, int nr, int cold)
521 {
522         int i;
523         struct pagevec pages_to_free;
524         struct zone *zone = NULL;
525         unsigned long uninitialized_var(flags);
526
527         pagevec_init(&pages_to_free, cold);
528         for (i = 0; i < nr; i++) {
529                 struct page *page = pages[i];
530
531                 if (unlikely(PageCompound(page))) {
532                         if (zone) {
533                                 spin_unlock_irqrestore(&zone->lru_lock, flags);
534                                 zone = NULL;
535                         }
536                         put_compound_page(page);
537                         continue;
538                 }
539
540                 if (!put_page_testzero(page))
541                         continue;
542
543                 if (PageLRU(page)) {
544                         struct zone *pagezone = page_zone(page);
545
546                         if (pagezone != zone) {
547                                 if (zone)
548                                         spin_unlock_irqrestore(&zone->lru_lock,
549                                                                         flags);
550                                 zone = pagezone;
551                                 spin_lock_irqsave(&zone->lru_lock, flags);
552                         }
553                         VM_BUG_ON(!PageLRU(page));
554                         __ClearPageLRU(page);
555                         del_page_from_lru(zone, page);
556                 }
557
558                 if (!pagevec_add(&pages_to_free, page)) {
559                         if (zone) {
560                                 spin_unlock_irqrestore(&zone->lru_lock, flags);
561                                 zone = NULL;
562                         }
563                         __pagevec_free(&pages_to_free);
564                         pagevec_reinit(&pages_to_free);
565                 }
566         }
567         if (zone)
568                 spin_unlock_irqrestore(&zone->lru_lock, flags);
569
570         pagevec_free(&pages_to_free);
571 }
572 EXPORT_SYMBOL(release_pages);
573
574 /*
575  * The pages which we're about to release may be in the deferred lru-addition
576  * queues.  That would prevent them from really being freed right now.  That's
577  * OK from a correctness point of view but is inefficient - those pages may be
578  * cache-warm and we want to give them back to the page allocator ASAP.
579  *
580  * So __pagevec_release() will drain those queues here.  __pagevec_lru_add()
581  * and __pagevec_lru_add_active() call release_pages() directly to avoid
582  * mutual recursion.
583  */
584 void __pagevec_release(struct pagevec *pvec)
585 {
586         lru_add_drain();
587         release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
588         pagevec_reinit(pvec);
589 }
590
591 EXPORT_SYMBOL(__pagevec_release);
592
593 /* used by __split_huge_page_refcount() */
594 void lru_add_page_tail(struct zone* zone,
595                        struct page *page, struct page *page_tail)
596 {
597         int active;
598         enum lru_list lru;
599         const int file = 0;
600         struct list_head *head;
601
602         VM_BUG_ON(!PageHead(page));
603         VM_BUG_ON(PageCompound(page_tail));
604         VM_BUG_ON(PageLRU(page_tail));
605         VM_BUG_ON(!spin_is_locked(&zone->lru_lock));
606
607         SetPageLRU(page_tail);
608
609         if (page_evictable(page_tail, NULL)) {
610                 if (PageActive(page)) {
611                         SetPageActive(page_tail);
612                         active = 1;
613                         lru = LRU_ACTIVE_ANON;
614                 } else {
615                         active = 0;
616                         lru = LRU_INACTIVE_ANON;
617                 }
618                 update_page_reclaim_stat(zone, page_tail, file, active);
619                 if (likely(PageLRU(page)))
620                         head = page->lru.prev;
621                 else
622                         head = &zone->lru[lru].list;
623                 __add_page_to_lru_list(zone, page_tail, lru, head);
624         } else {
625                 SetPageUnevictable(page_tail);
626                 add_page_to_lru_list(zone, page_tail, LRU_UNEVICTABLE);
627         }
628 }
629
630 static void ____pagevec_lru_add_fn(struct page *page, void *arg)
631 {
632         enum lru_list lru = (enum lru_list)arg;
633         struct zone *zone = page_zone(page);
634         int file = is_file_lru(lru);
635         int active = is_active_lru(lru);
636
637         VM_BUG_ON(PageActive(page));
638         VM_BUG_ON(PageUnevictable(page));
639         VM_BUG_ON(PageLRU(page));
640
641         SetPageLRU(page);
642         if (active)
643                 SetPageActive(page);
644         update_page_reclaim_stat(zone, page, file, active);
645         add_page_to_lru_list(zone, page, lru);
646 }
647
648 /*
649  * Add the passed pages to the LRU, then drop the caller's refcount
650  * on them.  Reinitialises the caller's pagevec.
651  */
652 void ____pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
653 {
654         VM_BUG_ON(is_unevictable_lru(lru));
655
656         pagevec_lru_move_fn(pvec, ____pagevec_lru_add_fn, (void *)lru);
657 }
658
659 EXPORT_SYMBOL(____pagevec_lru_add);
660
661 /*
662  * Try to drop buffers from the pages in a pagevec
663  */
664 void pagevec_strip(struct pagevec *pvec)
665 {
666         int i;
667
668         for (i = 0; i < pagevec_count(pvec); i++) {
669                 struct page *page = pvec->pages[i];
670
671                 if (page_has_private(page) && trylock_page(page)) {
672                         if (page_has_private(page))
673                                 try_to_release_page(page, 0);
674                         unlock_page(page);
675                 }
676         }
677 }
678
679 /**
680  * pagevec_lookup - gang pagecache lookup
681  * @pvec:       Where the resulting pages are placed
682  * @mapping:    The address_space to search
683  * @start:      The starting page index
684  * @nr_pages:   The maximum number of pages
685  *
686  * pagevec_lookup() will search for and return a group of up to @nr_pages pages
687  * in the mapping.  The pages are placed in @pvec.  pagevec_lookup() takes a
688  * reference against the pages in @pvec.
689  *
690  * The search returns a group of mapping-contiguous pages with ascending
691  * indexes.  There may be holes in the indices due to not-present pages.
692  *
693  * pagevec_lookup() returns the number of pages which were found.
694  */
695 unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
696                 pgoff_t start, unsigned nr_pages)
697 {
698         pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
699         return pagevec_count(pvec);
700 }
701
702 EXPORT_SYMBOL(pagevec_lookup);
703
704 unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
705                 pgoff_t *index, int tag, unsigned nr_pages)
706 {
707         pvec->nr = find_get_pages_tag(mapping, index, tag,
708                                         nr_pages, pvec->pages);
709         return pagevec_count(pvec);
710 }
711
712 EXPORT_SYMBOL(pagevec_lookup_tag);
713
714 /*
715  * Perform any setup for the swap system
716  */
717 void __init swap_setup(void)
718 {
719         unsigned long megs = totalram_pages >> (20 - PAGE_SHIFT);
720
721 #ifdef CONFIG_SWAP
722         bdi_init(swapper_space.backing_dev_info);
723 #endif
724
725         /* Use a smaller cluster for small-memory machines */
726         if (megs < 16)
727                 page_cluster = 2;
728         else
729                 page_cluster = 3;
730         /*
731          * Right now other parts of the system means that we
732          * _really_ don't want to cluster much more
733          */
734 }