xref: /linux/mm/swap.c (revision 0d456bad36d42d16022be045c8a53ddbb59ee478)
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/export.h>
25 #include <linux/mm_inline.h>
26 #include <linux/percpu_counter.h>
27 #include <linux/percpu.h>
28 #include <linux/cpu.h>
29 #include <linux/notifier.h>
30 #include <linux/backing-dev.h>
31 #include <linux/memcontrol.h>
32 #include <linux/gfp.h>
33 
34 #include "internal.h"
35 
36 /* How many pages do we try to swap or page in/out together? */
37 int page_cluster;
38 
39 static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
40 static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
41 static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);
42 
43 /*
44  * This path almost never happens for VM activity - pages are normally
45  * freed via pagevecs.  But it gets used by networking.
46  */
47 static void __page_cache_release(struct page *page)
48 {
49 	if (PageLRU(page)) {
50 		struct zone *zone = page_zone(page);
51 		struct lruvec *lruvec;
52 		unsigned long flags;
53 
54 		spin_lock_irqsave(&zone->lru_lock, flags);
55 		lruvec = mem_cgroup_page_lruvec(page, zone);
56 		VM_BUG_ON(!PageLRU(page));
57 		__ClearPageLRU(page);
58 		del_page_from_lru_list(page, lruvec, page_off_lru(page));
59 		spin_unlock_irqrestore(&zone->lru_lock, flags);
60 	}
61 }
62 
63 static void __put_single_page(struct page *page)
64 {
65 	__page_cache_release(page);
66 	free_hot_cold_page(page, 0);
67 }
68 
69 static void __put_compound_page(struct page *page)
70 {
71 	compound_page_dtor *dtor;
72 
73 	__page_cache_release(page);
74 	dtor = get_compound_page_dtor(page);
75 	(*dtor)(page);
76 }
77 
78 static void put_compound_page(struct page *page)
79 {
80 	if (unlikely(PageTail(page))) {
81 		/* __split_huge_page_refcount can run under us */
82 		struct page *page_head = compound_trans_head(page);
83 
84 		if (likely(page != page_head &&
85 			   get_page_unless_zero(page_head))) {
86 			unsigned long flags;
87 
88 			/*
89 			 * THP can not break up slab pages so avoid taking
90 			 * compound_lock().  Slab performs non-atomic bit ops
91 			 * on page->flags for better performance.  In particular
92 			 * slab_unlock() in slub used to be a hot path.  It is
93 			 * still hot on arches that do not support
94 			 * this_cpu_cmpxchg_double().
95 			 */
96 			if (PageSlab(page_head)) {
97 				if (PageTail(page)) {
98 					if (put_page_testzero(page_head))
99 						VM_BUG_ON(1);
100 
101 					atomic_dec(&page->_mapcount);
102 					goto skip_lock_tail;
103 				} else
104 					goto skip_lock;
105 			}
106 			/*
107 			 * page_head wasn't a dangling pointer but it
108 			 * may not be a head page anymore by the time
109 			 * we obtain the lock. That is ok as long as it
110 			 * can't be freed from under us.
111 			 */
112 			flags = compound_lock_irqsave(page_head);
113 			if (unlikely(!PageTail(page))) {
114 				/* __split_huge_page_refcount run before us */
115 				compound_unlock_irqrestore(page_head, flags);
116 skip_lock:
117 				if (put_page_testzero(page_head))
118 					__put_single_page(page_head);
119 out_put_single:
120 				if (put_page_testzero(page))
121 					__put_single_page(page);
122 				return;
123 			}
124 			VM_BUG_ON(page_head != page->first_page);
125 			/*
126 			 * We can release the refcount taken by
127 			 * get_page_unless_zero() now that
128 			 * __split_huge_page_refcount() is blocked on
129 			 * the compound_lock.
130 			 */
131 			if (put_page_testzero(page_head))
132 				VM_BUG_ON(1);
133 			/* __split_huge_page_refcount will wait now */
134 			VM_BUG_ON(page_mapcount(page) <= 0);
135 			atomic_dec(&page->_mapcount);
136 			VM_BUG_ON(atomic_read(&page_head->_count) <= 0);
137 			VM_BUG_ON(atomic_read(&page->_count) != 0);
138 			compound_unlock_irqrestore(page_head, flags);
139 
140 skip_lock_tail:
141 			if (put_page_testzero(page_head)) {
142 				if (PageHead(page_head))
143 					__put_compound_page(page_head);
144 				else
145 					__put_single_page(page_head);
146 			}
147 		} else {
148 			/* page_head is a dangling pointer */
149 			VM_BUG_ON(PageTail(page));
150 			goto out_put_single;
151 		}
152 	} else if (put_page_testzero(page)) {
153 		if (PageHead(page))
154 			__put_compound_page(page);
155 		else
156 			__put_single_page(page);
157 	}
158 }
159 
160 void put_page(struct page *page)
161 {
162 	if (unlikely(PageCompound(page)))
163 		put_compound_page(page);
164 	else if (put_page_testzero(page))
165 		__put_single_page(page);
166 }
167 EXPORT_SYMBOL(put_page);
168 
169 /*
170  * This function is exported but must not be called by anything other
171  * than get_page(). It implements the slow path of get_page().
172  */
173 bool __get_page_tail(struct page *page)
174 {
175 	/*
176 	 * This takes care of get_page() if run on a tail page
177 	 * returned by one of the get_user_pages/follow_page variants.
178 	 * get_user_pages/follow_page itself doesn't need the compound
179 	 * lock because it runs __get_page_tail_foll() under the
180 	 * proper PT lock that already serializes against
181 	 * split_huge_page().
182 	 */
183 	unsigned long flags;
184 	bool got = false;
185 	struct page *page_head = compound_trans_head(page);
186 
187 	if (likely(page != page_head && get_page_unless_zero(page_head))) {
188 
189 		/* Ref to put_compound_page() comment. */
190 		if (PageSlab(page_head)) {
191 			if (likely(PageTail(page))) {
192 				__get_page_tail_foll(page, false);
193 				return true;
194 			} else {
195 				put_page(page_head);
196 				return false;
197 			}
198 		}
199 
200 		/*
201 		 * page_head wasn't a dangling pointer but it
202 		 * may not be a head page anymore by the time
203 		 * we obtain the lock. That is ok as long as it
204 		 * can't be freed from under us.
205 		 */
206 		flags = compound_lock_irqsave(page_head);
207 		/* here __split_huge_page_refcount won't run anymore */
208 		if (likely(PageTail(page))) {
209 			__get_page_tail_foll(page, false);
210 			got = true;
211 		}
212 		compound_unlock_irqrestore(page_head, flags);
213 		if (unlikely(!got))
214 			put_page(page_head);
215 	}
216 	return got;
217 }
218 EXPORT_SYMBOL(__get_page_tail);
219 
220 /**
221  * put_pages_list() - release a list of pages
222  * @pages: list of pages threaded on page->lru
223  *
224  * Release a list of pages which are strung together on page.lru.  Currently
225  * used by read_cache_pages() and related error recovery code.
226  */
227 void put_pages_list(struct list_head *pages)
228 {
229 	while (!list_empty(pages)) {
230 		struct page *victim;
231 
232 		victim = list_entry(pages->prev, struct page, lru);
233 		list_del(&victim->lru);
234 		page_cache_release(victim);
235 	}
236 }
237 EXPORT_SYMBOL(put_pages_list);
238 
239 /*
240  * get_kernel_pages() - pin kernel pages in memory
241  * @kiov:	An array of struct kvec structures
242  * @nr_segs:	number of segments to pin
243  * @write:	pinning for read/write, currently ignored
244  * @pages:	array that receives pointers to the pages pinned.
245  *		Should be at least nr_segs long.
246  *
247  * Returns number of pages pinned. This may be fewer than the number
248  * requested. If nr_pages is 0 or negative, returns 0. If no pages
249  * were pinned, returns -errno. Each page returned must be released
250  * with a put_page() call when it is finished with.
251  */
252 int get_kernel_pages(const struct kvec *kiov, int nr_segs, int write,
253 		struct page **pages)
254 {
255 	int seg;
256 
257 	for (seg = 0; seg < nr_segs; seg++) {
258 		if (WARN_ON(kiov[seg].iov_len != PAGE_SIZE))
259 			return seg;
260 
261 		pages[seg] = kmap_to_page(kiov[seg].iov_base);
262 		page_cache_get(pages[seg]);
263 	}
264 
265 	return seg;
266 }
267 EXPORT_SYMBOL_GPL(get_kernel_pages);
268 
269 /*
270  * get_kernel_page() - pin a kernel page in memory
271  * @start:	starting kernel address
272  * @write:	pinning for read/write, currently ignored
273  * @pages:	array that receives pointer to the page pinned.
274  *		Must be at least nr_segs long.
275  *
276  * Returns 1 if page is pinned. If the page was not pinned, returns
277  * -errno. The page returned must be released with a put_page() call
278  * when it is finished with.
279  */
280 int get_kernel_page(unsigned long start, int write, struct page **pages)
281 {
282 	const struct kvec kiov = {
283 		.iov_base = (void *)start,
284 		.iov_len = PAGE_SIZE
285 	};
286 
287 	return get_kernel_pages(&kiov, 1, write, pages);
288 }
289 EXPORT_SYMBOL_GPL(get_kernel_page);
290 
291 static void pagevec_lru_move_fn(struct pagevec *pvec,
292 	void (*move_fn)(struct page *page, struct lruvec *lruvec, void *arg),
293 	void *arg)
294 {
295 	int i;
296 	struct zone *zone = NULL;
297 	struct lruvec *lruvec;
298 	unsigned long flags = 0;
299 
300 	for (i = 0; i < pagevec_count(pvec); i++) {
301 		struct page *page = pvec->pages[i];
302 		struct zone *pagezone = page_zone(page);
303 
304 		if (pagezone != zone) {
305 			if (zone)
306 				spin_unlock_irqrestore(&zone->lru_lock, flags);
307 			zone = pagezone;
308 			spin_lock_irqsave(&zone->lru_lock, flags);
309 		}
310 
311 		lruvec = mem_cgroup_page_lruvec(page, zone);
312 		(*move_fn)(page, lruvec, arg);
313 	}
314 	if (zone)
315 		spin_unlock_irqrestore(&zone->lru_lock, flags);
316 	release_pages(pvec->pages, pvec->nr, pvec->cold);
317 	pagevec_reinit(pvec);
318 }
319 
320 static void pagevec_move_tail_fn(struct page *page, struct lruvec *lruvec,
321 				 void *arg)
322 {
323 	int *pgmoved = arg;
324 
325 	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
326 		enum lru_list lru = page_lru_base_type(page);
327 		list_move_tail(&page->lru, &lruvec->lists[lru]);
328 		(*pgmoved)++;
329 	}
330 }
331 
332 /*
333  * pagevec_move_tail() must be called with IRQ disabled.
334  * Otherwise this may cause nasty races.
335  */
336 static void pagevec_move_tail(struct pagevec *pvec)
337 {
338 	int pgmoved = 0;
339 
340 	pagevec_lru_move_fn(pvec, pagevec_move_tail_fn, &pgmoved);
341 	__count_vm_events(PGROTATED, pgmoved);
342 }
343 
344 /*
345  * Writeback is about to end against a page which has been marked for immediate
346  * reclaim.  If it still appears to be reclaimable, move it to the tail of the
347  * inactive list.
348  */
349 void rotate_reclaimable_page(struct page *page)
350 {
351 	if (!PageLocked(page) && !PageDirty(page) && !PageActive(page) &&
352 	    !PageUnevictable(page) && PageLRU(page)) {
353 		struct pagevec *pvec;
354 		unsigned long flags;
355 
356 		page_cache_get(page);
357 		local_irq_save(flags);
358 		pvec = &__get_cpu_var(lru_rotate_pvecs);
359 		if (!pagevec_add(pvec, page))
360 			pagevec_move_tail(pvec);
361 		local_irq_restore(flags);
362 	}
363 }
364 
365 static void update_page_reclaim_stat(struct lruvec *lruvec,
366 				     int file, int rotated)
367 {
368 	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
369 
370 	reclaim_stat->recent_scanned[file]++;
371 	if (rotated)
372 		reclaim_stat->recent_rotated[file]++;
373 }
374 
375 static void __activate_page(struct page *page, struct lruvec *lruvec,
376 			    void *arg)
377 {
378 	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
379 		int file = page_is_file_cache(page);
380 		int lru = page_lru_base_type(page);
381 
382 		del_page_from_lru_list(page, lruvec, lru);
383 		SetPageActive(page);
384 		lru += LRU_ACTIVE;
385 		add_page_to_lru_list(page, lruvec, lru);
386 
387 		__count_vm_event(PGACTIVATE);
388 		update_page_reclaim_stat(lruvec, file, 1);
389 	}
390 }
391 
392 #ifdef CONFIG_SMP
393 static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs);
394 
395 static void activate_page_drain(int cpu)
396 {
397 	struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu);
398 
399 	if (pagevec_count(pvec))
400 		pagevec_lru_move_fn(pvec, __activate_page, NULL);
401 }
402 
403 void activate_page(struct page *page)
404 {
405 	if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
406 		struct pagevec *pvec = &get_cpu_var(activate_page_pvecs);
407 
408 		page_cache_get(page);
409 		if (!pagevec_add(pvec, page))
410 			pagevec_lru_move_fn(pvec, __activate_page, NULL);
411 		put_cpu_var(activate_page_pvecs);
412 	}
413 }
414 
415 #else
416 static inline void activate_page_drain(int cpu)
417 {
418 }
419 
420 void activate_page(struct page *page)
421 {
422 	struct zone *zone = page_zone(page);
423 
424 	spin_lock_irq(&zone->lru_lock);
425 	__activate_page(page, mem_cgroup_page_lruvec(page, zone), NULL);
426 	spin_unlock_irq(&zone->lru_lock);
427 }
428 #endif
429 
430 /*
431  * Mark a page as having seen activity.
432  *
433  * inactive,unreferenced	->	inactive,referenced
434  * inactive,referenced		->	active,unreferenced
435  * active,unreferenced		->	active,referenced
436  */
437 void mark_page_accessed(struct page *page)
438 {
439 	if (!PageActive(page) && !PageUnevictable(page) &&
440 			PageReferenced(page) && PageLRU(page)) {
441 		activate_page(page);
442 		ClearPageReferenced(page);
443 	} else if (!PageReferenced(page)) {
444 		SetPageReferenced(page);
445 	}
446 }
447 EXPORT_SYMBOL(mark_page_accessed);
448 
449 /*
450  * Order of operations is important: flush the pagevec when it's already
451  * full, not when adding the last page, to make sure that last page is
452  * not added to the LRU directly when passed to this function. Because
453  * mark_page_accessed() (called after this when writing) only activates
454  * pages that are on the LRU, linear writes in subpage chunks would see
455  * every PAGEVEC_SIZE page activated, which is unexpected.
456  */
457 void __lru_cache_add(struct page *page, enum lru_list lru)
458 {
459 	struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru];
460 
461 	page_cache_get(page);
462 	if (!pagevec_space(pvec))
463 		__pagevec_lru_add(pvec, lru);
464 	pagevec_add(pvec, page);
465 	put_cpu_var(lru_add_pvecs);
466 }
467 EXPORT_SYMBOL(__lru_cache_add);
468 
469 /**
470  * lru_cache_add_lru - add a page to a page list
471  * @page: the page to be added to the LRU.
472  * @lru: the LRU list to which the page is added.
473  */
474 void lru_cache_add_lru(struct page *page, enum lru_list lru)
475 {
476 	if (PageActive(page)) {
477 		VM_BUG_ON(PageUnevictable(page));
478 		ClearPageActive(page);
479 	} else if (PageUnevictable(page)) {
480 		VM_BUG_ON(PageActive(page));
481 		ClearPageUnevictable(page);
482 	}
483 
484 	VM_BUG_ON(PageLRU(page) || PageActive(page) || PageUnevictable(page));
485 	__lru_cache_add(page, lru);
486 }
487 
488 /**
489  * add_page_to_unevictable_list - add a page to the unevictable list
490  * @page:  the page to be added to the unevictable list
491  *
492  * Add page directly to its zone's unevictable list.  To avoid races with
493  * tasks that might be making the page evictable, through eg. munlock,
494  * munmap or exit, while it's not on the lru, we want to add the page
495  * while it's locked or otherwise "invisible" to other tasks.  This is
496  * difficult to do when using the pagevec cache, so bypass that.
497  */
498 void add_page_to_unevictable_list(struct page *page)
499 {
500 	struct zone *zone = page_zone(page);
501 	struct lruvec *lruvec;
502 
503 	spin_lock_irq(&zone->lru_lock);
504 	lruvec = mem_cgroup_page_lruvec(page, zone);
505 	SetPageUnevictable(page);
506 	SetPageLRU(page);
507 	add_page_to_lru_list(page, lruvec, LRU_UNEVICTABLE);
508 	spin_unlock_irq(&zone->lru_lock);
509 }
510 
511 /*
512  * If the page can not be invalidated, it is moved to the
513  * inactive list to speed up its reclaim.  It is moved to the
514  * head of the list, rather than the tail, to give the flusher
515  * threads some time to write it out, as this is much more
516  * effective than the single-page writeout from reclaim.
517  *
518  * If the page isn't page_mapped and dirty/writeback, the page
519  * could reclaim asap using PG_reclaim.
520  *
521  * 1. active, mapped page -> none
522  * 2. active, dirty/writeback page -> inactive, head, PG_reclaim
523  * 3. inactive, mapped page -> none
524  * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim
525  * 5. inactive, clean -> inactive, tail
526  * 6. Others -> none
527  *
528  * In 4, why it moves inactive's head, the VM expects the page would
529  * be write it out by flusher threads as this is much more effective
530  * than the single-page writeout from reclaim.
531  */
532 static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec,
533 			      void *arg)
534 {
535 	int lru, file;
536 	bool active;
537 
538 	if (!PageLRU(page))
539 		return;
540 
541 	if (PageUnevictable(page))
542 		return;
543 
544 	/* Some processes are using the page */
545 	if (page_mapped(page))
546 		return;
547 
548 	active = PageActive(page);
549 	file = page_is_file_cache(page);
550 	lru = page_lru_base_type(page);
551 
552 	del_page_from_lru_list(page, lruvec, lru + active);
553 	ClearPageActive(page);
554 	ClearPageReferenced(page);
555 	add_page_to_lru_list(page, lruvec, lru);
556 
557 	if (PageWriteback(page) || PageDirty(page)) {
558 		/*
559 		 * PG_reclaim could be raced with end_page_writeback
560 		 * It can make readahead confusing.  But race window
561 		 * is _really_ small and  it's non-critical problem.
562 		 */
563 		SetPageReclaim(page);
564 	} else {
565 		/*
566 		 * The page's writeback ends up during pagevec
567 		 * We moves tha page into tail of inactive.
568 		 */
569 		list_move_tail(&page->lru, &lruvec->lists[lru]);
570 		__count_vm_event(PGROTATED);
571 	}
572 
573 	if (active)
574 		__count_vm_event(PGDEACTIVATE);
575 	update_page_reclaim_stat(lruvec, file, 0);
576 }
577 
578 /*
579  * Drain pages out of the cpu's pagevecs.
580  * Either "cpu" is the current CPU, and preemption has already been
581  * disabled; or "cpu" is being hot-unplugged, and is already dead.
582  */
583 void lru_add_drain_cpu(int cpu)
584 {
585 	struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
586 	struct pagevec *pvec;
587 	int lru;
588 
589 	for_each_lru(lru) {
590 		pvec = &pvecs[lru - LRU_BASE];
591 		if (pagevec_count(pvec))
592 			__pagevec_lru_add(pvec, lru);
593 	}
594 
595 	pvec = &per_cpu(lru_rotate_pvecs, cpu);
596 	if (pagevec_count(pvec)) {
597 		unsigned long flags;
598 
599 		/* No harm done if a racing interrupt already did this */
600 		local_irq_save(flags);
601 		pagevec_move_tail(pvec);
602 		local_irq_restore(flags);
603 	}
604 
605 	pvec = &per_cpu(lru_deactivate_pvecs, cpu);
606 	if (pagevec_count(pvec))
607 		pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
608 
609 	activate_page_drain(cpu);
610 }
611 
612 /**
613  * deactivate_page - forcefully deactivate a page
614  * @page: page to deactivate
615  *
616  * This function hints the VM that @page is a good reclaim candidate,
617  * for example if its invalidation fails due to the page being dirty
618  * or under writeback.
619  */
620 void deactivate_page(struct page *page)
621 {
622 	/*
623 	 * In a workload with many unevictable page such as mprotect, unevictable
624 	 * page deactivation for accelerating reclaim is pointless.
625 	 */
626 	if (PageUnevictable(page))
627 		return;
628 
629 	if (likely(get_page_unless_zero(page))) {
630 		struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs);
631 
632 		if (!pagevec_add(pvec, page))
633 			pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL);
634 		put_cpu_var(lru_deactivate_pvecs);
635 	}
636 }
637 
638 void lru_add_drain(void)
639 {
640 	lru_add_drain_cpu(get_cpu());
641 	put_cpu();
642 }
643 
644 static void lru_add_drain_per_cpu(struct work_struct *dummy)
645 {
646 	lru_add_drain();
647 }
648 
649 /*
650  * Returns 0 for success
651  */
652 int lru_add_drain_all(void)
653 {
654 	return schedule_on_each_cpu(lru_add_drain_per_cpu);
655 }
656 
657 /*
658  * Batched page_cache_release().  Decrement the reference count on all the
659  * passed pages.  If it fell to zero then remove the page from the LRU and
660  * free it.
661  *
662  * Avoid taking zone->lru_lock if possible, but if it is taken, retain it
663  * for the remainder of the operation.
664  *
665  * The locking in this function is against shrink_inactive_list(): we recheck
666  * the page count inside the lock to see whether shrink_inactive_list()
667  * grabbed the page via the LRU.  If it did, give up: shrink_inactive_list()
668  * will free it.
669  */
670 void release_pages(struct page **pages, int nr, int cold)
671 {
672 	int i;
673 	LIST_HEAD(pages_to_free);
674 	struct zone *zone = NULL;
675 	struct lruvec *lruvec;
676 	unsigned long uninitialized_var(flags);
677 
678 	for (i = 0; i < nr; i++) {
679 		struct page *page = pages[i];
680 
681 		if (unlikely(PageCompound(page))) {
682 			if (zone) {
683 				spin_unlock_irqrestore(&zone->lru_lock, flags);
684 				zone = NULL;
685 			}
686 			put_compound_page(page);
687 			continue;
688 		}
689 
690 		if (!put_page_testzero(page))
691 			continue;
692 
693 		if (PageLRU(page)) {
694 			struct zone *pagezone = page_zone(page);
695 
696 			if (pagezone != zone) {
697 				if (zone)
698 					spin_unlock_irqrestore(&zone->lru_lock,
699 									flags);
700 				zone = pagezone;
701 				spin_lock_irqsave(&zone->lru_lock, flags);
702 			}
703 
704 			lruvec = mem_cgroup_page_lruvec(page, zone);
705 			VM_BUG_ON(!PageLRU(page));
706 			__ClearPageLRU(page);
707 			del_page_from_lru_list(page, lruvec, page_off_lru(page));
708 		}
709 
710 		list_add(&page->lru, &pages_to_free);
711 	}
712 	if (zone)
713 		spin_unlock_irqrestore(&zone->lru_lock, flags);
714 
715 	free_hot_cold_page_list(&pages_to_free, cold);
716 }
717 EXPORT_SYMBOL(release_pages);
718 
719 /*
720  * The pages which we're about to release may be in the deferred lru-addition
721  * queues.  That would prevent them from really being freed right now.  That's
722  * OK from a correctness point of view but is inefficient - those pages may be
723  * cache-warm and we want to give them back to the page allocator ASAP.
724  *
725  * So __pagevec_release() will drain those queues here.  __pagevec_lru_add()
726  * and __pagevec_lru_add_active() call release_pages() directly to avoid
727  * mutual recursion.
728  */
729 void __pagevec_release(struct pagevec *pvec)
730 {
731 	lru_add_drain();
732 	release_pages(pvec->pages, pagevec_count(pvec), pvec->cold);
733 	pagevec_reinit(pvec);
734 }
735 EXPORT_SYMBOL(__pagevec_release);
736 
737 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
738 /* used by __split_huge_page_refcount() */
739 void lru_add_page_tail(struct page *page, struct page *page_tail,
740 		       struct lruvec *lruvec)
741 {
742 	int uninitialized_var(active);
743 	enum lru_list lru;
744 	const int file = 0;
745 
746 	VM_BUG_ON(!PageHead(page));
747 	VM_BUG_ON(PageCompound(page_tail));
748 	VM_BUG_ON(PageLRU(page_tail));
749 	VM_BUG_ON(NR_CPUS != 1 &&
750 		  !spin_is_locked(&lruvec_zone(lruvec)->lru_lock));
751 
752 	SetPageLRU(page_tail);
753 
754 	if (page_evictable(page_tail)) {
755 		if (PageActive(page)) {
756 			SetPageActive(page_tail);
757 			active = 1;
758 			lru = LRU_ACTIVE_ANON;
759 		} else {
760 			active = 0;
761 			lru = LRU_INACTIVE_ANON;
762 		}
763 	} else {
764 		SetPageUnevictable(page_tail);
765 		lru = LRU_UNEVICTABLE;
766 	}
767 
768 	if (likely(PageLRU(page)))
769 		list_add_tail(&page_tail->lru, &page->lru);
770 	else {
771 		struct list_head *list_head;
772 		/*
773 		 * Head page has not yet been counted, as an hpage,
774 		 * so we must account for each subpage individually.
775 		 *
776 		 * Use the standard add function to put page_tail on the list,
777 		 * but then correct its position so they all end up in order.
778 		 */
779 		add_page_to_lru_list(page_tail, lruvec, lru);
780 		list_head = page_tail->lru.prev;
781 		list_move_tail(&page_tail->lru, list_head);
782 	}
783 
784 	if (!PageUnevictable(page))
785 		update_page_reclaim_stat(lruvec, file, active);
786 }
787 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
788 
789 static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
790 				 void *arg)
791 {
792 	enum lru_list lru = (enum lru_list)arg;
793 	int file = is_file_lru(lru);
794 	int active = is_active_lru(lru);
795 
796 	VM_BUG_ON(PageActive(page));
797 	VM_BUG_ON(PageUnevictable(page));
798 	VM_BUG_ON(PageLRU(page));
799 
800 	SetPageLRU(page);
801 	if (active)
802 		SetPageActive(page);
803 	add_page_to_lru_list(page, lruvec, lru);
804 	update_page_reclaim_stat(lruvec, file, active);
805 }
806 
807 /*
808  * Add the passed pages to the LRU, then drop the caller's refcount
809  * on them.  Reinitialises the caller's pagevec.
810  */
811 void __pagevec_lru_add(struct pagevec *pvec, enum lru_list lru)
812 {
813 	VM_BUG_ON(is_unevictable_lru(lru));
814 
815 	pagevec_lru_move_fn(pvec, __pagevec_lru_add_fn, (void *)lru);
816 }
817 EXPORT_SYMBOL(__pagevec_lru_add);
818 
819 /**
820  * pagevec_lookup - gang pagecache lookup
821  * @pvec:	Where the resulting pages are placed
822  * @mapping:	The address_space to search
823  * @start:	The starting page index
824  * @nr_pages:	The maximum number of pages
825  *
826  * pagevec_lookup() will search for and return a group of up to @nr_pages pages
827  * in the mapping.  The pages are placed in @pvec.  pagevec_lookup() takes a
828  * reference against the pages in @pvec.
829  *
830  * The search returns a group of mapping-contiguous pages with ascending
831  * indexes.  There may be holes in the indices due to not-present pages.
832  *
833  * pagevec_lookup() returns the number of pages which were found.
834  */
835 unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping,
836 		pgoff_t start, unsigned nr_pages)
837 {
838 	pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages);
839 	return pagevec_count(pvec);
840 }
841 EXPORT_SYMBOL(pagevec_lookup);
842 
843 unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping,
844 		pgoff_t *index, int tag, unsigned nr_pages)
845 {
846 	pvec->nr = find_get_pages_tag(mapping, index, tag,
847 					nr_pages, pvec->pages);
848 	return pagevec_count(pvec);
849 }
850 EXPORT_SYMBOL(pagevec_lookup_tag);
851 
852 /*
853  * Perform any setup for the swap system
854  */
855 void __init swap_setup(void)
856 {
857 	unsigned long megs = totalram_pages >> (20 - PAGE_SHIFT);
858 
859 #ifdef CONFIG_SWAP
860 	bdi_init(swapper_space.backing_dev_info);
861 #endif
862 
863 	/* Use a smaller cluster for small-memory machines */
864 	if (megs < 16)
865 		page_cluster = 2;
866 	else
867 		page_cluster = 3;
868 	/*
869 	 * Right now other parts of the system means that we
870 	 * _really_ don't want to cluster much more
871 	 */
872 }
873