mm: don't access vm_flags as 'int'
[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 static void __activate_page(struct page *page, void *arg)
276 {
277         struct zone *zone = page_zone(page);
278
279         if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
280                 int file = page_is_file_cache(page);
281                 int lru = page_lru_base_type(page);
282                 del_page_from_lru_list(zone, page, lru);
283
284                 SetPageActive(page);
285                 lru += LRU_ACTIVE;
286                 add_page_to_lru_list(zone, page, lru);
287                 __count_vm_event(PGACTIVATE);
288
289                 update_page_reclaim_stat(zone, page, file, 1);
290         }
291 }
292
293 #ifdef CONFIG_SMP
294 static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
295
296 static void activate_page_drain(int cpu)
297 {
298         struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
299
300         if (pagevec_count(pvec))
301                 pagevec_lru_move_fn(pvec, __activate_page, NULL);
302 }
303
304 void activate_page(struct page *page)
305 {
306         if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
307                 struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
308
309                 page_cache_get(page);
310                 if (!pagevec_add(pvec, page))
311                         pagevec_lru_move_fn(pvec, __activate_page, NULL);
312                 put_cpu_var(activate_page_pvecs);
313         }
314 }
315
316 #else
317 static inline void activate_page_drain(int cpu)
318 {
319 }
320
321 void activate_page(struct page *page)
322 {
323         struct zone *zone = page_zone(page);
324
325         spin_lock_irq(&zone->lru_lock);
326         __activate_page(page, NULL);
327         spin_unlock_irq(&zone->lru_lock);
328 }
329 #endif
330
331 /*
332  * Mark a page as having seen activity.
333  *
334  * inactive,unreferenced        ->      inactive,referenced
335  * inactive,referenced          ->      active,unreferenced
336  * active,unreferenced          ->      active,referenced
337  */
338 void mark_page_accessed(struct page *page)
339 {
340         if (!PageActive(page) && !PageUnevictable(page) &&
341                         PageReferenced(page) && PageLRU(page)) {
342                 activate_page(page);
343                 ClearPageReferenced(page);
344         } else if (!PageReferenced(page)) {
345                 SetPageReferenced(page);
346         }
347 }
348
349 EXPORT_SYMBOL(mark_page_accessed);
350
351 void __lru_cache_add(struct page *page, enum lru_list lru)
352 {
353         struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];
354
355         page_cache_get(page);
356         if (!pagevec_add(pvec, page))
357                 ____pagevec_lru_add(pvec, lru);
358         put_cpu_var(lru_add_pvecs);
359 }
360 EXPORT_SYMBOL(__lru_cache_add);
361
362 /**
363  * lru_cache_add_lru - add a page to a page list
364  * @page: the page to be added to the LRU.
365  * @lru: the LRU list to which the page is added.
366  */
367 void lru_cache_add_lru(struct page *page, enum lru_list lru)
368 {
369         if (PageActive(page)) {
370                 VM_BUG_ON(PageUnevictable(page));
371                 ClearPageActive(page);
372         } else if (PageUnevictable(page)) {
373                 VM_BUG_ON(PageActive(page));
374                 ClearPageUnevictable(page);
375         }
376
377         VM_BUG_ON(PageLRU(page) || PageActive(page) || PageUnevictable(page));
378         __lru_cache_add(page, lru);
379 }
380
381 /**
382  * add_page_to_unevictable_list - add a page to the unevictable list
383  * @page:  the page to be added to the unevictable list
384  *
385  * Add page directly to its zone's unevictable list.  To avoid races with
386  * tasks that might be making the page evictable, through eg. munlock,
387  * munmap or exit, while it's not on the lru, we want to add the page
388  * while it's locked or otherwise "invisible" to other tasks.  This is
389  * difficult to do when using the pagevec cache, so bypass that.
390  */
391 void add_page_to_unevictable_list(struct page *page)
392 {
393         struct zone *zone = page_zone(page);
394
395         spin_lock_irq(&zone->lru_lock);
396         SetPageUnevictable(page);
397         SetPageLRU(page);
398         add_page_to_lru_list(zone, page, LRU_UNEVICTABLE);
399         spin_unlock_irq(&zone->lru_lock);
400 }
401
402 /*
403  * If the page can not be invalidated, it is moved to the
404  * inactive list to speed up its reclaim.  It is moved to the
405  * head of the list, rather than the tail, to give the flusher
406  * threads some time to write it out, as this is much more
407  * effective than the single-page writeout from reclaim.
408  *
409  * If the page isn't page_mapped and dirty/writeback, the page
410  * could reclaim asap using PG_reclaim.
411  *
412  * 1. active, mapped page -> none
413  * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
414  * 3. inactive, mapped page -> none
415  * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
416  * 5. inactive, clean -> inactive, tail
417  * 6. Others -> none
418  *
419  * In 4, why it moves inactive's head, the VM expects the page would
420  * be write it out by flusher threads as this is much more effective
421  * than the single-page writeout from reclaim.
422  */
423 static void lru_deactivate_fn(struct page *page, void *arg)
424 {
425         int lru, file;
426         bool active;
427         struct zone *zone = page_zone(page);
428
429         if (!PageLRU(page))
430                 return;
431
432         if (PageUnevictable(page))
433                 return;
434
435         /* Some processes are using the page */
436         if (page_mapped(page))
437                 return;
438
439         active = PageActive(page);
440
441         file = page_is_file_cache(page);
442         lru = page_lru_base_type(page);
443         del_page_from_lru_list(zone, page, lru + active);
444         ClearPageActive(page);
445         ClearPageReferenced(page);
446         add_page_to_lru_list(zone, page, lru);
447
448         if (PageWriteback(page) || PageDirty(page)) {
449                 /*
450                  * PG_reclaim could be raced with end_page_writeback
451                  * It can make readahead confusing.  But race window
452                  * is _really_ small and  it's non-critical problem.
453                  */
454                 SetPageReclaim(page);
455         } else {
456                 /*
457                  * The page's writeback ends up during pagevec
458                  * We moves tha page into tail of inactive.
459                  */
460                 list_move_tail(&page->lru, &zone->lru[lru].list);
461                 mem_cgroup_rotate_reclaimable_page(page);
462                 __count_vm_event(PGROTATED);
463         }
464
465         if (active)
466                 __count_vm_event(PGDEACTIVATE);
467         update_page_reclaim_stat(zone, page, file, 0);
468 }
469
470 /*
471  * Drain pages out of the cpu's pagevecs.
472  * Either "cpu" is the current CPU, and preemption has already been
473  * disabled; or "cpu" is being hot-unplugged, and is already dead.
474  */
475 static void drain_cpu_pagevecs(int cpu)
476 {
477         struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
478         struct pagevec *pvec;
479         int lru;
480
481         for_each_lru(lru) {
482                 pvec = &pvecs[lru - LRU_BASE];
483                 if (pagevec_count(pvec))
484                         ____pagevec_lru_add(pvec, lru);
485         }
486
487         pvec = &per_cpu(lru_rotate_pvecs, cpu);
488         if (pagevec_count(pvec)) {
489                 unsigned long flags;
490
491                 /* No harm done if a racing interrupt already did this */
492                 local_irq_save(flags);
493                 pagevec_move_tail(pvec);
494                 local_irq_restore(flags);
495         }
496
497         pvec = &per_cpu(lru_deactivate_pvecs, cpu);
498         if (pagevec_count(pvec))
499                 pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
500
501         activate_page_drain(cpu);
502 }
503
504 /**
505  * deactivate_page - forcefully deactivate a page
506  * @page: page to deactivate
507  *
508  * This function hints the VM that @page is a good reclaim candidate,
509  * for example if its invalidation fails due to the page being dirty
510  * or under writeback.
511  */
512 void deactivate_page(struct page *page)
513 {
514         /*
515          * In a workload with many unevictable page such as mprotect, unevictable
516          * page deactivation for accelerating reclaim is pointless.
517          */
518         if (PageUnevictable(page))
519                 return;
520
521         if (likely(get_page_unless_zero(page))) {
522                 struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
523
524                 if (!pagevec_add(pvec, page))
525                         pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
526                 put_cpu_var(lru_deactivate_pvecs);
527         }
528 }
529
530 void lru_add_drain(void)
531 {
532         drain_cpu_pagevecs(get_cpu());
533         put_cpu();
534 }
535
536 static void lru_add_drain_per_cpu(struct work_struct *dummy)
537 {
538         lru_add_drain();
539 }
540
541 /*
542  * Returns 0 for success
543  */
544 int lru_add_drain_all(void)
545 {
546         return schedule_on_each_cpu(lru_add_drain_per_cpu);
547 }
548
549 /*
550  * Batched page_cache_release().  Decrement the reference count on all the
551  * passed pages.  If it fell to zero then remove the page from the LRU and
552  * free it.
553  *
554  * Avoid taking zone->lru_lock if possible, but if it is taken, retain it
555  * for the remainder of the operation.
556  *
557  * The locking in this function is against shrink_inactive_list(): we recheck
558  * the page count inside the lock to see whether shrink_inactive_list()
559  * grabbed the page via the LRU.  If it did, give up: shrink_inactive_list()
560  * will free it.
561  */
562 void release_pages(struct page **pages, int nr, int cold)
563 {
564         int i;
565         struct pagevec pages_to_free;
566         struct zone *zone = NULL;
567         unsigned long uninitialized_var(flags);
568
569         pagevec_init(&pages_to_free, cold);
570         for (i = 0; i < nr; i++) {
571                 struct page *page = pages[i];
572
573                 if (unlikely(PageCompound(page))) {
574                         if (zone) {
575                                 spin_unlock_irqrestore(&zone->lru_lock, flags);
576                                 zone = NULL;
577                         }
578                         put_compound_page(page);
579                         continue;
580                 }
581
582                 if (!put_page_testzero(page))
583                         continue;
584
585                 if (PageLRU(page)) {
586                         struct zone *pagezone = page_zone(page);
587
588                         if (pagezone != zone) {
589                                 if (zone)
590                                         spin_unlock_irqrestore(&zone->lru_lock,
591                                                                         flags);
592                                 zone = pagezone;
593                                 spin_lock_irqsave(&zone->lru_lock, flags);
594                         }
595                         VM_BUG_ON(!PageLRU(page));
596                         __ClearPageLRU(page);
597                         del_page_from_lru(zone, page);
598                 }
599
600                 if (!pagevec_add(&pages_to_free, page)) {
601                         if (zone) {
602                                 spin_unlock_irqrestore(&zone->lru_lock, flags);
603                                 zone = NULL;
604                         }
605                         __pagevec_free(&pages_to_free);
606                         pagevec_reinit(&pages_to_free);
607                 }
608         }
609         if (zone)
610                 spin_unlock_irqrestore(&zone->lru_lock, flags);
611
612         pagevec_free(&pages_to_free);
613 }
614 EXPORT_SYMBOL(release_pages);
615
616 /*
617  * The pages which we're about to release may be in the deferred lru-addition
618  * queues.  That would prevent them from really being freed right now.  That's
619  * OK from a correctness point of view but is inefficient - those pages may be
620  * cache-warm and we want to give them back to the page allocator ASAP.
621  *
622  * So __pagevec_release() will drain those queues here.  __pagevec_lru_add()
623  * and __pagevec_lru_add_active() call release_pages() directly to avoid
624  * mutual recursion.
625  */
626 void __pagevec_release(struct pagevec *pvec)
627 {
628         lru_add_drain();
629         release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
630         pagevec_reinit(pvec);
631 }
632
633 EXPORT_SYMBOL(__pagevec_release);
634
635 /* used by __split_huge_page_refcount() */
636 void lru_add_page_tail(struct zone* zone,
637                        struct page *page, struct page *page_tail)
638 {
639         int active;
640         enum lru_list lru;
641         const int file = 0;
642         struct list_head *head;
643
644         VM_BUG_ON(!PageHead(page));
645         VM_BUG_ON(PageCompound(page_tail));
646         VM_BUG_ON(PageLRU(page_tail));
647         VM_BUG_ON(!spin_is_locked(&zone->lru_lock));
648
649         SetPageLRU(page_tail);
650
651         if (page_evictable(page_tail, NULL)) {
652                 if (PageActive(page)) {
653                         SetPageActive(page_tail);
654                         active = 1;
655                         lru = LRU_ACTIVE_ANON;
656                 } else {
657                         active = 0;
658                         lru = LRU_INACTIVE_ANON;
659                 }
660                 update_page_reclaim_stat(zone, page_tail, file, active);
661                 if (likely(PageLRU(page)))
662                         head = page->lru.prev;
663                 else
664                         head = &zone->lru[lru].list;
665                 __add_page_to_lru_list(zone, page_tail, lru, head);
666         } else {
667                 SetPageUnevictable(page_tail);
668                 add_page_to_lru_list(zone, page_tail, LRU_UNEVICTABLE);
669         }
670 }
671
672 static void ____pagevec_lru_add_fn(struct page *page, void *arg)
673 {
674         enum lru_list lru = (enum lru_list)arg;
675         struct zone *zone = page_zone(page);
676         int file = is_file_lru(lru);
677         int active = is_active_lru(lru);
678
679         VM_BUG_ON(PageActive(page));
680         VM_BUG_ON(PageUnevictable(page));
681         VM_BUG_ON(PageLRU(page));
682
683         SetPageLRU(page);
684         if (active)
685                 SetPageActive(page);
686         update_page_reclaim_stat(zone, page, file, active);
687         add_page_to_lru_list(zone, page, lru);
688 }
689
690 /*
691  * Add the passed pages to the LRU, then drop the caller's refcount
692  * on them.  Reinitialises the caller's pagevec.
693  */
694 void ____pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
695 {
696         VM_BUG_ON(is_unevictable_lru(lru));
697
698         pagevec_lru_move_fn(pvec, ____pagevec_lru_add_fn, (void *)lru);
699 }
700
701 EXPORT_SYMBOL(____pagevec_lru_add);
702
703 /*
704  * Try to drop buffers from the pages in a pagevec
705  */
706 void pagevec_strip(struct pagevec *pvec)
707 {
708         int i;
709
710         for (i = 0; i < pagevec_count(pvec); i++) {
711                 struct page *page = pvec->pages[i];
712
713                 if (page_has_private(page) && trylock_page(page)) {
714                         if (page_has_private(page))
715                                 try_to_release_page(page, 0);
716                         unlock_page(page);
717                 }
718         }
719 }
720
721 /**
722  * pagevec_lookup - gang pagecache lookup
723  * @pvec:       Where the resulting pages are placed
724  * @mapping:    The address_space to search
725  * @start:      The starting page index
726  * @nr_pages:   The maximum number of pages
727  *
728  * pagevec_lookup() will search for and return a group of up to @nr_pages pages
729  * in the mapping.  The pages are placed in @pvec.  pagevec_lookup() takes a
730  * reference against the pages in @pvec.
731  *
732  * The search returns a group of mapping-contiguous pages with ascending
733  * indexes.  There may be holes in the indices due to not-present pages.
734  *
735  * pagevec_lookup() returns the number of pages which were found.
736  */
737 unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
738                 pgoff_t start, unsigned nr_pages)
739 {
740         pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
741         return pagevec_count(pvec);
742 }
743
744 EXPORT_SYMBOL(pagevec_lookup);
745
746 unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
747                 pgoff_t *index, int tag, unsigned nr_pages)
748 {
749         pvec->nr = find_get_pages_tag(mapping, index, tag,
750                                         nr_pages, pvec->pages);
751         return pagevec_count(pvec);
752 }
753
754 EXPORT_SYMBOL(pagevec_lookup_tag);
755
756 /*
757  * Perform any setup for the swap system
758  */
759 void __init swap_setup(void)
760 {
761         unsigned long megs = totalram_pages >> (20 - PAGE_SHIFT);
762
763 #ifdef CONFIG_SWAP
764         bdi_init(swapper_space.backing_dev_info);
765 #endif
766
767         /* Use a smaller cluster for small-memory machines */
768         if (megs < 16)
769                 page_cluster = 2;
770         else
771                 page_cluster = 3;
772         /*
773          * Right now other parts of the system means that we
774          * _really_ don't want to cluster much more
775          */
776 }