xref: /openbmc/linux/mm/vmscan.c (revision 9d56dd3b083a3bec56e9da35ce07baca81030b03)
1 /*
2  *  linux/mm/vmscan.c
3  *
4  *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
5  *
6  *  Swap reorganised 29.12.95, Stephen Tweedie.
7  *  kswapd added: 7.1.96  sct
8  *  Removed kswapd_ctl limits, and swap out as many pages as needed
9  *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
10  *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
11  *  Multiqueue VM started 5.8.00, Rik van Riel.
12  */
13 
14 #include <linux/mm.h>
15 #include <linux/module.h>
16 #include <linux/slab.h>
17 #include <linux/kernel_stat.h>
18 #include <linux/swap.h>
19 #include <linux/pagemap.h>
20 #include <linux/init.h>
21 #include <linux/highmem.h>
22 #include <linux/vmstat.h>
23 #include <linux/file.h>
24 #include <linux/writeback.h>
25 #include <linux/blkdev.h>
26 #include <linux/buffer_head.h>	/* for try_to_release_page(),
27 					buffer_heads_over_limit */
28 #include <linux/mm_inline.h>
29 #include <linux/pagevec.h>
30 #include <linux/backing-dev.h>
31 #include <linux/rmap.h>
32 #include <linux/topology.h>
33 #include <linux/cpu.h>
34 #include <linux/cpuset.h>
35 #include <linux/notifier.h>
36 #include <linux/rwsem.h>
37 #include <linux/delay.h>
38 #include <linux/kthread.h>
39 #include <linux/freezer.h>
40 #include <linux/memcontrol.h>
41 #include <linux/delayacct.h>
42 #include <linux/sysctl.h>
43 
44 #include <asm/tlbflush.h>
45 #include <asm/div64.h>
46 
47 #include <linux/swapops.h>
48 
49 #include "internal.h"
50 
51 struct scan_control {
52 	/* Incremented by the number of inactive pages that were scanned */
53 	unsigned long nr_scanned;
54 
55 	/* Number of pages freed so far during a call to shrink_zones() */
56 	unsigned long nr_reclaimed;
57 
58 	/* How many pages shrink_list() should reclaim */
59 	unsigned long nr_to_reclaim;
60 
61 	unsigned long hibernation_mode;
62 
63 	/* This context's GFP mask */
64 	gfp_t gfp_mask;
65 
66 	int may_writepage;
67 
68 	/* Can mapped pages be reclaimed? */
69 	int may_unmap;
70 
71 	/* Can pages be swapped as part of reclaim? */
72 	int may_swap;
73 
74 	int swappiness;
75 
76 	int all_unreclaimable;
77 
78 	int order;
79 
80 	/* Which cgroup do we reclaim from */
81 	struct mem_cgroup *mem_cgroup;
82 
83 	/*
84 	 * Nodemask of nodes allowed by the caller. If NULL, all nodes
85 	 * are scanned.
86 	 */
87 	nodemask_t	*nodemask;
88 
89 	/* Pluggable isolate pages callback */
90 	unsigned long (*isolate_pages)(unsigned long nr, struct list_head *dst,
91 			unsigned long *scanned, int order, int mode,
92 			struct zone *z, struct mem_cgroup *mem_cont,
93 			int active, int file);
94 };
95 
96 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
97 
98 #ifdef ARCH_HAS_PREFETCH
99 #define prefetch_prev_lru_page(_page, _base, _field)			\
100 	do {								\
101 		if ((_page)->lru.prev != _base) {			\
102 			struct page *prev;				\
103 									\
104 			prev = lru_to_page(&(_page->lru));		\
105 			prefetch(&prev->_field);			\
106 		}							\
107 	} while (0)
108 #else
109 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
110 #endif
111 
112 #ifdef ARCH_HAS_PREFETCHW
113 #define prefetchw_prev_lru_page(_page, _base, _field)			\
114 	do {								\
115 		if ((_page)->lru.prev != _base) {			\
116 			struct page *prev;				\
117 									\
118 			prev = lru_to_page(&(_page->lru));		\
119 			prefetchw(&prev->_field);			\
120 		}							\
121 	} while (0)
122 #else
123 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
124 #endif
125 
126 /*
127  * From 0 .. 100.  Higher means more swappy.
128  */
129 int vm_swappiness = 60;
130 long vm_total_pages;	/* The total number of pages which the VM controls */
131 
132 static LIST_HEAD(shrinker_list);
133 static DECLARE_RWSEM(shrinker_rwsem);
134 
135 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
136 #define scanning_global_lru(sc)	(!(sc)->mem_cgroup)
137 #else
138 #define scanning_global_lru(sc)	(1)
139 #endif
140 
141 static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
142 						  struct scan_control *sc)
143 {
144 	if (!scanning_global_lru(sc))
145 		return mem_cgroup_get_reclaim_stat(sc->mem_cgroup, zone);
146 
147 	return &zone->reclaim_stat;
148 }
149 
150 static unsigned long zone_nr_lru_pages(struct zone *zone,
151 				struct scan_control *sc, enum lru_list lru)
152 {
153 	if (!scanning_global_lru(sc))
154 		return mem_cgroup_zone_nr_pages(sc->mem_cgroup, zone, lru);
155 
156 	return zone_page_state(zone, NR_LRU_BASE + lru);
157 }
158 
159 
160 /*
161  * Add a shrinker callback to be called from the vm
162  */
163 void register_shrinker(struct shrinker *shrinker)
164 {
165 	shrinker->nr = 0;
166 	down_write(&shrinker_rwsem);
167 	list_add_tail(&shrinker->list, &shrinker_list);
168 	up_write(&shrinker_rwsem);
169 }
170 EXPORT_SYMBOL(register_shrinker);
171 
172 /*
173  * Remove one
174  */
175 void unregister_shrinker(struct shrinker *shrinker)
176 {
177 	down_write(&shrinker_rwsem);
178 	list_del(&shrinker->list);
179 	up_write(&shrinker_rwsem);
180 }
181 EXPORT_SYMBOL(unregister_shrinker);
182 
183 #define SHRINK_BATCH 128
184 /*
185  * Call the shrink functions to age shrinkable caches
186  *
187  * Here we assume it costs one seek to replace a lru page and that it also
188  * takes a seek to recreate a cache object.  With this in mind we age equal
189  * percentages of the lru and ageable caches.  This should balance the seeks
190  * generated by these structures.
191  *
192  * If the vm encountered mapped pages on the LRU it increase the pressure on
193  * slab to avoid swapping.
194  *
195  * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
196  *
197  * `lru_pages' represents the number of on-LRU pages in all the zones which
198  * are eligible for the caller's allocation attempt.  It is used for balancing
199  * slab reclaim versus page reclaim.
200  *
201  * Returns the number of slab objects which we shrunk.
202  */
203 unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
204 			unsigned long lru_pages)
205 {
206 	struct shrinker *shrinker;
207 	unsigned long ret = 0;
208 
209 	if (scanned == 0)
210 		scanned = SWAP_CLUSTER_MAX;
211 
212 	if (!down_read_trylock(&shrinker_rwsem))
213 		return 1;	/* Assume we'll be able to shrink next time */
214 
215 	list_for_each_entry(shrinker, &shrinker_list, list) {
216 		unsigned long long delta;
217 		unsigned long total_scan;
218 		unsigned long max_pass = (*shrinker->shrink)(0, gfp_mask);
219 
220 		delta = (4 * scanned) / shrinker->seeks;
221 		delta *= max_pass;
222 		do_div(delta, lru_pages + 1);
223 		shrinker->nr += delta;
224 		if (shrinker->nr < 0) {
225 			printk(KERN_ERR "shrink_slab: %pF negative objects to "
226 			       "delete nr=%ld\n",
227 			       shrinker->shrink, shrinker->nr);
228 			shrinker->nr = max_pass;
229 		}
230 
231 		/*
232 		 * Avoid risking looping forever due to too large nr value:
233 		 * never try to free more than twice the estimate number of
234 		 * freeable entries.
235 		 */
236 		if (shrinker->nr > max_pass * 2)
237 			shrinker->nr = max_pass * 2;
238 
239 		total_scan = shrinker->nr;
240 		shrinker->nr = 0;
241 
242 		while (total_scan >= SHRINK_BATCH) {
243 			long this_scan = SHRINK_BATCH;
244 			int shrink_ret;
245 			int nr_before;
246 
247 			nr_before = (*shrinker->shrink)(0, gfp_mask);
248 			shrink_ret = (*shrinker->shrink)(this_scan, gfp_mask);
249 			if (shrink_ret == -1)
250 				break;
251 			if (shrink_ret < nr_before)
252 				ret += nr_before - shrink_ret;
253 			count_vm_events(SLABS_SCANNED, this_scan);
254 			total_scan -= this_scan;
255 
256 			cond_resched();
257 		}
258 
259 		shrinker->nr += total_scan;
260 	}
261 	up_read(&shrinker_rwsem);
262 	return ret;
263 }
264 
265 /* Called without lock on whether page is mapped, so answer is unstable */
266 static inline int page_mapping_inuse(struct page *page)
267 {
268 	struct address_space *mapping;
269 
270 	/* Page is in somebody's page tables. */
271 	if (page_mapped(page))
272 		return 1;
273 
274 	/* Be more reluctant to reclaim swapcache than pagecache */
275 	if (PageSwapCache(page))
276 		return 1;
277 
278 	mapping = page_mapping(page);
279 	if (!mapping)
280 		return 0;
281 
282 	/* File is mmap'd by somebody? */
283 	return mapping_mapped(mapping);
284 }
285 
286 static inline int is_page_cache_freeable(struct page *page)
287 {
288 	/*
289 	 * A freeable page cache page is referenced only by the caller
290 	 * that isolated the page, the page cache radix tree and
291 	 * optional buffer heads at page->private.
292 	 */
293 	return page_count(page) - page_has_private(page) == 2;
294 }
295 
296 static int may_write_to_queue(struct backing_dev_info *bdi)
297 {
298 	if (current->flags & PF_SWAPWRITE)
299 		return 1;
300 	if (!bdi_write_congested(bdi))
301 		return 1;
302 	if (bdi == current->backing_dev_info)
303 		return 1;
304 	return 0;
305 }
306 
307 /*
308  * We detected a synchronous write error writing a page out.  Probably
309  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
310  * fsync(), msync() or close().
311  *
312  * The tricky part is that after writepage we cannot touch the mapping: nothing
313  * prevents it from being freed up.  But we have a ref on the page and once
314  * that page is locked, the mapping is pinned.
315  *
316  * We're allowed to run sleeping lock_page() here because we know the caller has
317  * __GFP_FS.
318  */
319 static void handle_write_error(struct address_space *mapping,
320 				struct page *page, int error)
321 {
322 	lock_page(page);
323 	if (page_mapping(page) == mapping)
324 		mapping_set_error(mapping, error);
325 	unlock_page(page);
326 }
327 
328 /* Request for sync pageout. */
329 enum pageout_io {
330 	PAGEOUT_IO_ASYNC,
331 	PAGEOUT_IO_SYNC,
332 };
333 
334 /* possible outcome of pageout() */
335 typedef enum {
336 	/* failed to write page out, page is locked */
337 	PAGE_KEEP,
338 	/* move page to the active list, page is locked */
339 	PAGE_ACTIVATE,
340 	/* page has been sent to the disk successfully, page is unlocked */
341 	PAGE_SUCCESS,
342 	/* page is clean and locked */
343 	PAGE_CLEAN,
344 } pageout_t;
345 
346 /*
347  * pageout is called by shrink_page_list() for each dirty page.
348  * Calls ->writepage().
349  */
350 static pageout_t pageout(struct page *page, struct address_space *mapping,
351 						enum pageout_io sync_writeback)
352 {
353 	/*
354 	 * If the page is dirty, only perform writeback if that write
355 	 * will be non-blocking.  To prevent this allocation from being
356 	 * stalled by pagecache activity.  But note that there may be
357 	 * stalls if we need to run get_block().  We could test
358 	 * PagePrivate for that.
359 	 *
360 	 * If this process is currently in __generic_file_aio_write() against
361 	 * this page's queue, we can perform writeback even if that
362 	 * will block.
363 	 *
364 	 * If the page is swapcache, write it back even if that would
365 	 * block, for some throttling. This happens by accident, because
366 	 * swap_backing_dev_info is bust: it doesn't reflect the
367 	 * congestion state of the swapdevs.  Easy to fix, if needed.
368 	 */
369 	if (!is_page_cache_freeable(page))
370 		return PAGE_KEEP;
371 	if (!mapping) {
372 		/*
373 		 * Some data journaling orphaned pages can have
374 		 * page->mapping == NULL while being dirty with clean buffers.
375 		 */
376 		if (page_has_private(page)) {
377 			if (try_to_free_buffers(page)) {
378 				ClearPageDirty(page);
379 				printk("%s: orphaned page\n", __func__);
380 				return PAGE_CLEAN;
381 			}
382 		}
383 		return PAGE_KEEP;
384 	}
385 	if (mapping->a_ops->writepage == NULL)
386 		return PAGE_ACTIVATE;
387 	if (!may_write_to_queue(mapping->backing_dev_info))
388 		return PAGE_KEEP;
389 
390 	if (clear_page_dirty_for_io(page)) {
391 		int res;
392 		struct writeback_control wbc = {
393 			.sync_mode = WB_SYNC_NONE,
394 			.nr_to_write = SWAP_CLUSTER_MAX,
395 			.range_start = 0,
396 			.range_end = LLONG_MAX,
397 			.nonblocking = 1,
398 			.for_reclaim = 1,
399 		};
400 
401 		SetPageReclaim(page);
402 		res = mapping->a_ops->writepage(page, &wbc);
403 		if (res < 0)
404 			handle_write_error(mapping, page, res);
405 		if (res == AOP_WRITEPAGE_ACTIVATE) {
406 			ClearPageReclaim(page);
407 			return PAGE_ACTIVATE;
408 		}
409 
410 		/*
411 		 * Wait on writeback if requested to. This happens when
412 		 * direct reclaiming a large contiguous area and the
413 		 * first attempt to free a range of pages fails.
414 		 */
415 		if (PageWriteback(page) && sync_writeback == PAGEOUT_IO_SYNC)
416 			wait_on_page_writeback(page);
417 
418 		if (!PageWriteback(page)) {
419 			/* synchronous write or broken a_ops? */
420 			ClearPageReclaim(page);
421 		}
422 		inc_zone_page_state(page, NR_VMSCAN_WRITE);
423 		return PAGE_SUCCESS;
424 	}
425 
426 	return PAGE_CLEAN;
427 }
428 
429 /*
430  * Same as remove_mapping, but if the page is removed from the mapping, it
431  * gets returned with a refcount of 0.
432  */
433 static int __remove_mapping(struct address_space *mapping, struct page *page)
434 {
435 	BUG_ON(!PageLocked(page));
436 	BUG_ON(mapping != page_mapping(page));
437 
438 	spin_lock_irq(&mapping->tree_lock);
439 	/*
440 	 * The non racy check for a busy page.
441 	 *
442 	 * Must be careful with the order of the tests. When someone has
443 	 * a ref to the page, it may be possible that they dirty it then
444 	 * drop the reference. So if PageDirty is tested before page_count
445 	 * here, then the following race may occur:
446 	 *
447 	 * get_user_pages(&page);
448 	 * [user mapping goes away]
449 	 * write_to(page);
450 	 *				!PageDirty(page)    [good]
451 	 * SetPageDirty(page);
452 	 * put_page(page);
453 	 *				!page_count(page)   [good, discard it]
454 	 *
455 	 * [oops, our write_to data is lost]
456 	 *
457 	 * Reversing the order of the tests ensures such a situation cannot
458 	 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
459 	 * load is not satisfied before that of page->_count.
460 	 *
461 	 * Note that if SetPageDirty is always performed via set_page_dirty,
462 	 * and thus under tree_lock, then this ordering is not required.
463 	 */
464 	if (!page_freeze_refs(page, 2))
465 		goto cannot_free;
466 	/* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
467 	if (unlikely(PageDirty(page))) {
468 		page_unfreeze_refs(page, 2);
469 		goto cannot_free;
470 	}
471 
472 	if (PageSwapCache(page)) {
473 		swp_entry_t swap = { .val = page_private(page) };
474 		__delete_from_swap_cache(page);
475 		spin_unlock_irq(&mapping->tree_lock);
476 		swapcache_free(swap, page);
477 	} else {
478 		__remove_from_page_cache(page);
479 		spin_unlock_irq(&mapping->tree_lock);
480 		mem_cgroup_uncharge_cache_page(page);
481 	}
482 
483 	return 1;
484 
485 cannot_free:
486 	spin_unlock_irq(&mapping->tree_lock);
487 	return 0;
488 }
489 
490 /*
491  * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
492  * someone else has a ref on the page, abort and return 0.  If it was
493  * successfully detached, return 1.  Assumes the caller has a single ref on
494  * this page.
495  */
496 int remove_mapping(struct address_space *mapping, struct page *page)
497 {
498 	if (__remove_mapping(mapping, page)) {
499 		/*
500 		 * Unfreezing the refcount with 1 rather than 2 effectively
501 		 * drops the pagecache ref for us without requiring another
502 		 * atomic operation.
503 		 */
504 		page_unfreeze_refs(page, 1);
505 		return 1;
506 	}
507 	return 0;
508 }
509 
510 /**
511  * putback_lru_page - put previously isolated page onto appropriate LRU list
512  * @page: page to be put back to appropriate lru list
513  *
514  * Add previously isolated @page to appropriate LRU list.
515  * Page may still be unevictable for other reasons.
516  *
517  * lru_lock must not be held, interrupts must be enabled.
518  */
519 void putback_lru_page(struct page *page)
520 {
521 	int lru;
522 	int active = !!TestClearPageActive(page);
523 	int was_unevictable = PageUnevictable(page);
524 
525 	VM_BUG_ON(PageLRU(page));
526 
527 redo:
528 	ClearPageUnevictable(page);
529 
530 	if (page_evictable(page, NULL)) {
531 		/*
532 		 * For evictable pages, we can use the cache.
533 		 * In event of a race, worst case is we end up with an
534 		 * unevictable page on [in]active list.
535 		 * We know how to handle that.
536 		 */
537 		lru = active + page_lru_base_type(page);
538 		lru_cache_add_lru(page, lru);
539 	} else {
540 		/*
541 		 * Put unevictable pages directly on zone's unevictable
542 		 * list.
543 		 */
544 		lru = LRU_UNEVICTABLE;
545 		add_page_to_unevictable_list(page);
546 		/*
547 		 * When racing with an mlock clearing (page is
548 		 * unlocked), make sure that if the other thread does
549 		 * not observe our setting of PG_lru and fails
550 		 * isolation, we see PG_mlocked cleared below and move
551 		 * the page back to the evictable list.
552 		 *
553 		 * The other side is TestClearPageMlocked().
554 		 */
555 		smp_mb();
556 	}
557 
558 	/*
559 	 * page's status can change while we move it among lru. If an evictable
560 	 * page is on unevictable list, it never be freed. To avoid that,
561 	 * check after we added it to the list, again.
562 	 */
563 	if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) {
564 		if (!isolate_lru_page(page)) {
565 			put_page(page);
566 			goto redo;
567 		}
568 		/* This means someone else dropped this page from LRU
569 		 * So, it will be freed or putback to LRU again. There is
570 		 * nothing to do here.
571 		 */
572 	}
573 
574 	if (was_unevictable && lru != LRU_UNEVICTABLE)
575 		count_vm_event(UNEVICTABLE_PGRESCUED);
576 	else if (!was_unevictable && lru == LRU_UNEVICTABLE)
577 		count_vm_event(UNEVICTABLE_PGCULLED);
578 
579 	put_page(page);		/* drop ref from isolate */
580 }
581 
582 /*
583  * shrink_page_list() returns the number of reclaimed pages
584  */
585 static unsigned long shrink_page_list(struct list_head *page_list,
586 					struct scan_control *sc,
587 					enum pageout_io sync_writeback)
588 {
589 	LIST_HEAD(ret_pages);
590 	struct pagevec freed_pvec;
591 	int pgactivate = 0;
592 	unsigned long nr_reclaimed = 0;
593 	unsigned long vm_flags;
594 
595 	cond_resched();
596 
597 	pagevec_init(&freed_pvec, 1);
598 	while (!list_empty(page_list)) {
599 		struct address_space *mapping;
600 		struct page *page;
601 		int may_enter_fs;
602 		int referenced;
603 
604 		cond_resched();
605 
606 		page = lru_to_page(page_list);
607 		list_del(&page->lru);
608 
609 		if (!trylock_page(page))
610 			goto keep;
611 
612 		VM_BUG_ON(PageActive(page));
613 
614 		sc->nr_scanned++;
615 
616 		if (unlikely(!page_evictable(page, NULL)))
617 			goto cull_mlocked;
618 
619 		if (!sc->may_unmap && page_mapped(page))
620 			goto keep_locked;
621 
622 		/* Double the slab pressure for mapped and swapcache pages */
623 		if (page_mapped(page) || PageSwapCache(page))
624 			sc->nr_scanned++;
625 
626 		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
627 			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
628 
629 		if (PageWriteback(page)) {
630 			/*
631 			 * Synchronous reclaim is performed in two passes,
632 			 * first an asynchronous pass over the list to
633 			 * start parallel writeback, and a second synchronous
634 			 * pass to wait for the IO to complete.  Wait here
635 			 * for any page for which writeback has already
636 			 * started.
637 			 */
638 			if (sync_writeback == PAGEOUT_IO_SYNC && may_enter_fs)
639 				wait_on_page_writeback(page);
640 			else
641 				goto keep_locked;
642 		}
643 
644 		referenced = page_referenced(page, 1,
645 						sc->mem_cgroup, &vm_flags);
646 		/*
647 		 * In active use or really unfreeable?  Activate it.
648 		 * If page which have PG_mlocked lost isoltation race,
649 		 * try_to_unmap moves it to unevictable list
650 		 */
651 		if (sc->order <= PAGE_ALLOC_COSTLY_ORDER &&
652 					referenced && page_mapping_inuse(page)
653 					&& !(vm_flags & VM_LOCKED))
654 			goto activate_locked;
655 
656 		/*
657 		 * Anonymous process memory has backing store?
658 		 * Try to allocate it some swap space here.
659 		 */
660 		if (PageAnon(page) && !PageSwapCache(page)) {
661 			if (!(sc->gfp_mask & __GFP_IO))
662 				goto keep_locked;
663 			if (!add_to_swap(page))
664 				goto activate_locked;
665 			may_enter_fs = 1;
666 		}
667 
668 		mapping = page_mapping(page);
669 
670 		/*
671 		 * The page is mapped into the page tables of one or more
672 		 * processes. Try to unmap it here.
673 		 */
674 		if (page_mapped(page) && mapping) {
675 			switch (try_to_unmap(page, TTU_UNMAP)) {
676 			case SWAP_FAIL:
677 				goto activate_locked;
678 			case SWAP_AGAIN:
679 				goto keep_locked;
680 			case SWAP_MLOCK:
681 				goto cull_mlocked;
682 			case SWAP_SUCCESS:
683 				; /* try to free the page below */
684 			}
685 		}
686 
687 		if (PageDirty(page)) {
688 			if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced)
689 				goto keep_locked;
690 			if (!may_enter_fs)
691 				goto keep_locked;
692 			if (!sc->may_writepage)
693 				goto keep_locked;
694 
695 			/* Page is dirty, try to write it out here */
696 			switch (pageout(page, mapping, sync_writeback)) {
697 			case PAGE_KEEP:
698 				goto keep_locked;
699 			case PAGE_ACTIVATE:
700 				goto activate_locked;
701 			case PAGE_SUCCESS:
702 				if (PageWriteback(page) || PageDirty(page))
703 					goto keep;
704 				/*
705 				 * A synchronous write - probably a ramdisk.  Go
706 				 * ahead and try to reclaim the page.
707 				 */
708 				if (!trylock_page(page))
709 					goto keep;
710 				if (PageDirty(page) || PageWriteback(page))
711 					goto keep_locked;
712 				mapping = page_mapping(page);
713 			case PAGE_CLEAN:
714 				; /* try to free the page below */
715 			}
716 		}
717 
718 		/*
719 		 * If the page has buffers, try to free the buffer mappings
720 		 * associated with this page. If we succeed we try to free
721 		 * the page as well.
722 		 *
723 		 * We do this even if the page is PageDirty().
724 		 * try_to_release_page() does not perform I/O, but it is
725 		 * possible for a page to have PageDirty set, but it is actually
726 		 * clean (all its buffers are clean).  This happens if the
727 		 * buffers were written out directly, with submit_bh(). ext3
728 		 * will do this, as well as the blockdev mapping.
729 		 * try_to_release_page() will discover that cleanness and will
730 		 * drop the buffers and mark the page clean - it can be freed.
731 		 *
732 		 * Rarely, pages can have buffers and no ->mapping.  These are
733 		 * the pages which were not successfully invalidated in
734 		 * truncate_complete_page().  We try to drop those buffers here
735 		 * and if that worked, and the page is no longer mapped into
736 		 * process address space (page_count == 1) it can be freed.
737 		 * Otherwise, leave the page on the LRU so it is swappable.
738 		 */
739 		if (page_has_private(page)) {
740 			if (!try_to_release_page(page, sc->gfp_mask))
741 				goto activate_locked;
742 			if (!mapping && page_count(page) == 1) {
743 				unlock_page(page);
744 				if (put_page_testzero(page))
745 					goto free_it;
746 				else {
747 					/*
748 					 * rare race with speculative reference.
749 					 * the speculative reference will free
750 					 * this page shortly, so we may
751 					 * increment nr_reclaimed here (and
752 					 * leave it off the LRU).
753 					 */
754 					nr_reclaimed++;
755 					continue;
756 				}
757 			}
758 		}
759 
760 		if (!mapping || !__remove_mapping(mapping, page))
761 			goto keep_locked;
762 
763 		/*
764 		 * At this point, we have no other references and there is
765 		 * no way to pick any more up (removed from LRU, removed
766 		 * from pagecache). Can use non-atomic bitops now (and
767 		 * we obviously don't have to worry about waking up a process
768 		 * waiting on the page lock, because there are no references.
769 		 */
770 		__clear_page_locked(page);
771 free_it:
772 		nr_reclaimed++;
773 		if (!pagevec_add(&freed_pvec, page)) {
774 			__pagevec_free(&freed_pvec);
775 			pagevec_reinit(&freed_pvec);
776 		}
777 		continue;
778 
779 cull_mlocked:
780 		if (PageSwapCache(page))
781 			try_to_free_swap(page);
782 		unlock_page(page);
783 		putback_lru_page(page);
784 		continue;
785 
786 activate_locked:
787 		/* Not a candidate for swapping, so reclaim swap space. */
788 		if (PageSwapCache(page) && vm_swap_full())
789 			try_to_free_swap(page);
790 		VM_BUG_ON(PageActive(page));
791 		SetPageActive(page);
792 		pgactivate++;
793 keep_locked:
794 		unlock_page(page);
795 keep:
796 		list_add(&page->lru, &ret_pages);
797 		VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
798 	}
799 	list_splice(&ret_pages, page_list);
800 	if (pagevec_count(&freed_pvec))
801 		__pagevec_free(&freed_pvec);
802 	count_vm_events(PGACTIVATE, pgactivate);
803 	return nr_reclaimed;
804 }
805 
806 /* LRU Isolation modes. */
807 #define ISOLATE_INACTIVE 0	/* Isolate inactive pages. */
808 #define ISOLATE_ACTIVE 1	/* Isolate active pages. */
809 #define ISOLATE_BOTH 2		/* Isolate both active and inactive pages. */
810 
811 /*
812  * Attempt to remove the specified page from its LRU.  Only take this page
813  * if it is of the appropriate PageActive status.  Pages which are being
814  * freed elsewhere are also ignored.
815  *
816  * page:	page to consider
817  * mode:	one of the LRU isolation modes defined above
818  *
819  * returns 0 on success, -ve errno on failure.
820  */
821 int __isolate_lru_page(struct page *page, int mode, int file)
822 {
823 	int ret = -EINVAL;
824 
825 	/* Only take pages on the LRU. */
826 	if (!PageLRU(page))
827 		return ret;
828 
829 	/*
830 	 * When checking the active state, we need to be sure we are
831 	 * dealing with comparible boolean values.  Take the logical not
832 	 * of each.
833 	 */
834 	if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode))
835 		return ret;
836 
837 	if (mode != ISOLATE_BOTH && page_is_file_cache(page) != file)
838 		return ret;
839 
840 	/*
841 	 * When this function is being called for lumpy reclaim, we
842 	 * initially look into all LRU pages, active, inactive and
843 	 * unevictable; only give shrink_page_list evictable pages.
844 	 */
845 	if (PageUnevictable(page))
846 		return ret;
847 
848 	ret = -EBUSY;
849 
850 	if (likely(get_page_unless_zero(page))) {
851 		/*
852 		 * Be careful not to clear PageLRU until after we're
853 		 * sure the page is not being freed elsewhere -- the
854 		 * page release code relies on it.
855 		 */
856 		ClearPageLRU(page);
857 		ret = 0;
858 	}
859 
860 	return ret;
861 }
862 
863 /*
864  * zone->lru_lock is heavily contended.  Some of the functions that
865  * shrink the lists perform better by taking out a batch of pages
866  * and working on them outside the LRU lock.
867  *
868  * For pagecache intensive workloads, this function is the hottest
869  * spot in the kernel (apart from copy_*_user functions).
870  *
871  * Appropriate locks must be held before calling this function.
872  *
873  * @nr_to_scan:	The number of pages to look through on the list.
874  * @src:	The LRU list to pull pages off.
875  * @dst:	The temp list to put pages on to.
876  * @scanned:	The number of pages that were scanned.
877  * @order:	The caller's attempted allocation order
878  * @mode:	One of the LRU isolation modes
879  * @file:	True [1] if isolating file [!anon] pages
880  *
881  * returns how many pages were moved onto *@dst.
882  */
883 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
884 		struct list_head *src, struct list_head *dst,
885 		unsigned long *scanned, int order, int mode, int file)
886 {
887 	unsigned long nr_taken = 0;
888 	unsigned long scan;
889 
890 	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
891 		struct page *page;
892 		unsigned long pfn;
893 		unsigned long end_pfn;
894 		unsigned long page_pfn;
895 		int zone_id;
896 
897 		page = lru_to_page(src);
898 		prefetchw_prev_lru_page(page, src, flags);
899 
900 		VM_BUG_ON(!PageLRU(page));
901 
902 		switch (__isolate_lru_page(page, mode, file)) {
903 		case 0:
904 			list_move(&page->lru, dst);
905 			mem_cgroup_del_lru(page);
906 			nr_taken++;
907 			break;
908 
909 		case -EBUSY:
910 			/* else it is being freed elsewhere */
911 			list_move(&page->lru, src);
912 			mem_cgroup_rotate_lru_list(page, page_lru(page));
913 			continue;
914 
915 		default:
916 			BUG();
917 		}
918 
919 		if (!order)
920 			continue;
921 
922 		/*
923 		 * Attempt to take all pages in the order aligned region
924 		 * surrounding the tag page.  Only take those pages of
925 		 * the same active state as that tag page.  We may safely
926 		 * round the target page pfn down to the requested order
927 		 * as the mem_map is guarenteed valid out to MAX_ORDER,
928 		 * where that page is in a different zone we will detect
929 		 * it from its zone id and abort this block scan.
930 		 */
931 		zone_id = page_zone_id(page);
932 		page_pfn = page_to_pfn(page);
933 		pfn = page_pfn & ~((1 << order) - 1);
934 		end_pfn = pfn + (1 << order);
935 		for (; pfn < end_pfn; pfn++) {
936 			struct page *cursor_page;
937 
938 			/* The target page is in the block, ignore it. */
939 			if (unlikely(pfn == page_pfn))
940 				continue;
941 
942 			/* Avoid holes within the zone. */
943 			if (unlikely(!pfn_valid_within(pfn)))
944 				break;
945 
946 			cursor_page = pfn_to_page(pfn);
947 
948 			/* Check that we have not crossed a zone boundary. */
949 			if (unlikely(page_zone_id(cursor_page) != zone_id))
950 				continue;
951 
952 			/*
953 			 * If we don't have enough swap space, reclaiming of
954 			 * anon page which don't already have a swap slot is
955 			 * pointless.
956 			 */
957 			if (nr_swap_pages <= 0 && PageAnon(cursor_page) &&
958 					!PageSwapCache(cursor_page))
959 				continue;
960 
961 			if (__isolate_lru_page(cursor_page, mode, file) == 0) {
962 				list_move(&cursor_page->lru, dst);
963 				mem_cgroup_del_lru(cursor_page);
964 				nr_taken++;
965 				scan++;
966 			}
967 		}
968 	}
969 
970 	*scanned = scan;
971 	return nr_taken;
972 }
973 
974 static unsigned long isolate_pages_global(unsigned long nr,
975 					struct list_head *dst,
976 					unsigned long *scanned, int order,
977 					int mode, struct zone *z,
978 					struct mem_cgroup *mem_cont,
979 					int active, int file)
980 {
981 	int lru = LRU_BASE;
982 	if (active)
983 		lru += LRU_ACTIVE;
984 	if (file)
985 		lru += LRU_FILE;
986 	return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order,
987 								mode, file);
988 }
989 
990 /*
991  * clear_active_flags() is a helper for shrink_active_list(), clearing
992  * any active bits from the pages in the list.
993  */
994 static unsigned long clear_active_flags(struct list_head *page_list,
995 					unsigned int *count)
996 {
997 	int nr_active = 0;
998 	int lru;
999 	struct page *page;
1000 
1001 	list_for_each_entry(page, page_list, lru) {
1002 		lru = page_lru_base_type(page);
1003 		if (PageActive(page)) {
1004 			lru += LRU_ACTIVE;
1005 			ClearPageActive(page);
1006 			nr_active++;
1007 		}
1008 		count[lru]++;
1009 	}
1010 
1011 	return nr_active;
1012 }
1013 
1014 /**
1015  * isolate_lru_page - tries to isolate a page from its LRU list
1016  * @page: page to isolate from its LRU list
1017  *
1018  * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1019  * vmstat statistic corresponding to whatever LRU list the page was on.
1020  *
1021  * Returns 0 if the page was removed from an LRU list.
1022  * Returns -EBUSY if the page was not on an LRU list.
1023  *
1024  * The returned page will have PageLRU() cleared.  If it was found on
1025  * the active list, it will have PageActive set.  If it was found on
1026  * the unevictable list, it will have the PageUnevictable bit set. That flag
1027  * may need to be cleared by the caller before letting the page go.
1028  *
1029  * The vmstat statistic corresponding to the list on which the page was
1030  * found will be decremented.
1031  *
1032  * Restrictions:
1033  * (1) Must be called with an elevated refcount on the page. This is a
1034  *     fundamentnal difference from isolate_lru_pages (which is called
1035  *     without a stable reference).
1036  * (2) the lru_lock must not be held.
1037  * (3) interrupts must be enabled.
1038  */
1039 int isolate_lru_page(struct page *page)
1040 {
1041 	int ret = -EBUSY;
1042 
1043 	if (PageLRU(page)) {
1044 		struct zone *zone = page_zone(page);
1045 
1046 		spin_lock_irq(&zone->lru_lock);
1047 		if (PageLRU(page) && get_page_unless_zero(page)) {
1048 			int lru = page_lru(page);
1049 			ret = 0;
1050 			ClearPageLRU(page);
1051 
1052 			del_page_from_lru_list(zone, page, lru);
1053 		}
1054 		spin_unlock_irq(&zone->lru_lock);
1055 	}
1056 	return ret;
1057 }
1058 
1059 /*
1060  * Are there way too many processes in the direct reclaim path already?
1061  */
1062 static int too_many_isolated(struct zone *zone, int file,
1063 		struct scan_control *sc)
1064 {
1065 	unsigned long inactive, isolated;
1066 
1067 	if (current_is_kswapd())
1068 		return 0;
1069 
1070 	if (!scanning_global_lru(sc))
1071 		return 0;
1072 
1073 	if (file) {
1074 		inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1075 		isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1076 	} else {
1077 		inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1078 		isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1079 	}
1080 
1081 	return isolated > inactive;
1082 }
1083 
1084 /*
1085  * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
1086  * of reclaimed pages
1087  */
1088 static unsigned long shrink_inactive_list(unsigned long max_scan,
1089 			struct zone *zone, struct scan_control *sc,
1090 			int priority, int file)
1091 {
1092 	LIST_HEAD(page_list);
1093 	struct pagevec pvec;
1094 	unsigned long nr_scanned = 0;
1095 	unsigned long nr_reclaimed = 0;
1096 	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1097 	int lumpy_reclaim = 0;
1098 
1099 	while (unlikely(too_many_isolated(zone, file, sc))) {
1100 		congestion_wait(BLK_RW_ASYNC, HZ/10);
1101 
1102 		/* We are about to die and free our memory. Return now. */
1103 		if (fatal_signal_pending(current))
1104 			return SWAP_CLUSTER_MAX;
1105 	}
1106 
1107 	/*
1108 	 * If we need a large contiguous chunk of memory, or have
1109 	 * trouble getting a small set of contiguous pages, we
1110 	 * will reclaim both active and inactive pages.
1111 	 *
1112 	 * We use the same threshold as pageout congestion_wait below.
1113 	 */
1114 	if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
1115 		lumpy_reclaim = 1;
1116 	else if (sc->order && priority < DEF_PRIORITY - 2)
1117 		lumpy_reclaim = 1;
1118 
1119 	pagevec_init(&pvec, 1);
1120 
1121 	lru_add_drain();
1122 	spin_lock_irq(&zone->lru_lock);
1123 	do {
1124 		struct page *page;
1125 		unsigned long nr_taken;
1126 		unsigned long nr_scan;
1127 		unsigned long nr_freed;
1128 		unsigned long nr_active;
1129 		unsigned int count[NR_LRU_LISTS] = { 0, };
1130 		int mode = lumpy_reclaim ? ISOLATE_BOTH : ISOLATE_INACTIVE;
1131 		unsigned long nr_anon;
1132 		unsigned long nr_file;
1133 
1134 		nr_taken = sc->isolate_pages(SWAP_CLUSTER_MAX,
1135 			     &page_list, &nr_scan, sc->order, mode,
1136 				zone, sc->mem_cgroup, 0, file);
1137 
1138 		if (scanning_global_lru(sc)) {
1139 			zone->pages_scanned += nr_scan;
1140 			if (current_is_kswapd())
1141 				__count_zone_vm_events(PGSCAN_KSWAPD, zone,
1142 						       nr_scan);
1143 			else
1144 				__count_zone_vm_events(PGSCAN_DIRECT, zone,
1145 						       nr_scan);
1146 		}
1147 
1148 		if (nr_taken == 0)
1149 			goto done;
1150 
1151 		nr_active = clear_active_flags(&page_list, count);
1152 		__count_vm_events(PGDEACTIVATE, nr_active);
1153 
1154 		__mod_zone_page_state(zone, NR_ACTIVE_FILE,
1155 						-count[LRU_ACTIVE_FILE]);
1156 		__mod_zone_page_state(zone, NR_INACTIVE_FILE,
1157 						-count[LRU_INACTIVE_FILE]);
1158 		__mod_zone_page_state(zone, NR_ACTIVE_ANON,
1159 						-count[LRU_ACTIVE_ANON]);
1160 		__mod_zone_page_state(zone, NR_INACTIVE_ANON,
1161 						-count[LRU_INACTIVE_ANON]);
1162 
1163 		nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
1164 		nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
1165 		__mod_zone_page_state(zone, NR_ISOLATED_ANON, nr_anon);
1166 		__mod_zone_page_state(zone, NR_ISOLATED_FILE, nr_file);
1167 
1168 		reclaim_stat->recent_scanned[0] += nr_anon;
1169 		reclaim_stat->recent_scanned[1] += nr_file;
1170 
1171 		spin_unlock_irq(&zone->lru_lock);
1172 
1173 		nr_scanned += nr_scan;
1174 		nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
1175 
1176 		/*
1177 		 * If we are direct reclaiming for contiguous pages and we do
1178 		 * not reclaim everything in the list, try again and wait
1179 		 * for IO to complete. This will stall high-order allocations
1180 		 * but that should be acceptable to the caller
1181 		 */
1182 		if (nr_freed < nr_taken && !current_is_kswapd() &&
1183 		    lumpy_reclaim) {
1184 			congestion_wait(BLK_RW_ASYNC, HZ/10);
1185 
1186 			/*
1187 			 * The attempt at page out may have made some
1188 			 * of the pages active, mark them inactive again.
1189 			 */
1190 			nr_active = clear_active_flags(&page_list, count);
1191 			count_vm_events(PGDEACTIVATE, nr_active);
1192 
1193 			nr_freed += shrink_page_list(&page_list, sc,
1194 							PAGEOUT_IO_SYNC);
1195 		}
1196 
1197 		nr_reclaimed += nr_freed;
1198 
1199 		local_irq_disable();
1200 		if (current_is_kswapd())
1201 			__count_vm_events(KSWAPD_STEAL, nr_freed);
1202 		__count_zone_vm_events(PGSTEAL, zone, nr_freed);
1203 
1204 		spin_lock(&zone->lru_lock);
1205 		/*
1206 		 * Put back any unfreeable pages.
1207 		 */
1208 		while (!list_empty(&page_list)) {
1209 			int lru;
1210 			page = lru_to_page(&page_list);
1211 			VM_BUG_ON(PageLRU(page));
1212 			list_del(&page->lru);
1213 			if (unlikely(!page_evictable(page, NULL))) {
1214 				spin_unlock_irq(&zone->lru_lock);
1215 				putback_lru_page(page);
1216 				spin_lock_irq(&zone->lru_lock);
1217 				continue;
1218 			}
1219 			SetPageLRU(page);
1220 			lru = page_lru(page);
1221 			add_page_to_lru_list(zone, page, lru);
1222 			if (is_active_lru(lru)) {
1223 				int file = is_file_lru(lru);
1224 				reclaim_stat->recent_rotated[file]++;
1225 			}
1226 			if (!pagevec_add(&pvec, page)) {
1227 				spin_unlock_irq(&zone->lru_lock);
1228 				__pagevec_release(&pvec);
1229 				spin_lock_irq(&zone->lru_lock);
1230 			}
1231 		}
1232 		__mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon);
1233 		__mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file);
1234 
1235   	} while (nr_scanned < max_scan);
1236 
1237 done:
1238 	spin_unlock_irq(&zone->lru_lock);
1239 	pagevec_release(&pvec);
1240 	return nr_reclaimed;
1241 }
1242 
1243 /*
1244  * We are about to scan this zone at a certain priority level.  If that priority
1245  * level is smaller (ie: more urgent) than the previous priority, then note
1246  * that priority level within the zone.  This is done so that when the next
1247  * process comes in to scan this zone, it will immediately start out at this
1248  * priority level rather than having to build up its own scanning priority.
1249  * Here, this priority affects only the reclaim-mapped threshold.
1250  */
1251 static inline void note_zone_scanning_priority(struct zone *zone, int priority)
1252 {
1253 	if (priority < zone->prev_priority)
1254 		zone->prev_priority = priority;
1255 }
1256 
1257 /*
1258  * This moves pages from the active list to the inactive list.
1259  *
1260  * We move them the other way if the page is referenced by one or more
1261  * processes, from rmap.
1262  *
1263  * If the pages are mostly unmapped, the processing is fast and it is
1264  * appropriate to hold zone->lru_lock across the whole operation.  But if
1265  * the pages are mapped, the processing is slow (page_referenced()) so we
1266  * should drop zone->lru_lock around each page.  It's impossible to balance
1267  * this, so instead we remove the pages from the LRU while processing them.
1268  * It is safe to rely on PG_active against the non-LRU pages in here because
1269  * nobody will play with that bit on a non-LRU page.
1270  *
1271  * The downside is that we have to touch page->_count against each page.
1272  * But we had to alter page->flags anyway.
1273  */
1274 
1275 static void move_active_pages_to_lru(struct zone *zone,
1276 				     struct list_head *list,
1277 				     enum lru_list lru)
1278 {
1279 	unsigned long pgmoved = 0;
1280 	struct pagevec pvec;
1281 	struct page *page;
1282 
1283 	pagevec_init(&pvec, 1);
1284 
1285 	while (!list_empty(list)) {
1286 		page = lru_to_page(list);
1287 
1288 		VM_BUG_ON(PageLRU(page));
1289 		SetPageLRU(page);
1290 
1291 		list_move(&page->lru, &zone->lru[lru].list);
1292 		mem_cgroup_add_lru_list(page, lru);
1293 		pgmoved++;
1294 
1295 		if (!pagevec_add(&pvec, page) || list_empty(list)) {
1296 			spin_unlock_irq(&zone->lru_lock);
1297 			if (buffer_heads_over_limit)
1298 				pagevec_strip(&pvec);
1299 			__pagevec_release(&pvec);
1300 			spin_lock_irq(&zone->lru_lock);
1301 		}
1302 	}
1303 	__mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1304 	if (!is_active_lru(lru))
1305 		__count_vm_events(PGDEACTIVATE, pgmoved);
1306 }
1307 
1308 static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
1309 			struct scan_control *sc, int priority, int file)
1310 {
1311 	unsigned long nr_taken;
1312 	unsigned long pgscanned;
1313 	unsigned long vm_flags;
1314 	LIST_HEAD(l_hold);	/* The pages which were snipped off */
1315 	LIST_HEAD(l_active);
1316 	LIST_HEAD(l_inactive);
1317 	struct page *page;
1318 	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1319 	unsigned long nr_rotated = 0;
1320 
1321 	lru_add_drain();
1322 	spin_lock_irq(&zone->lru_lock);
1323 	nr_taken = sc->isolate_pages(nr_pages, &l_hold, &pgscanned, sc->order,
1324 					ISOLATE_ACTIVE, zone,
1325 					sc->mem_cgroup, 1, file);
1326 	/*
1327 	 * zone->pages_scanned is used for detect zone's oom
1328 	 * mem_cgroup remembers nr_scan by itself.
1329 	 */
1330 	if (scanning_global_lru(sc)) {
1331 		zone->pages_scanned += pgscanned;
1332 	}
1333 	reclaim_stat->recent_scanned[file] += nr_taken;
1334 
1335 	__count_zone_vm_events(PGREFILL, zone, pgscanned);
1336 	if (file)
1337 		__mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken);
1338 	else
1339 		__mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken);
1340 	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1341 	spin_unlock_irq(&zone->lru_lock);
1342 
1343 	while (!list_empty(&l_hold)) {
1344 		cond_resched();
1345 		page = lru_to_page(&l_hold);
1346 		list_del(&page->lru);
1347 
1348 		if (unlikely(!page_evictable(page, NULL))) {
1349 			putback_lru_page(page);
1350 			continue;
1351 		}
1352 
1353 		/* page_referenced clears PageReferenced */
1354 		if (page_mapping_inuse(page) &&
1355 		    page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
1356 			nr_rotated++;
1357 			/*
1358 			 * Identify referenced, file-backed active pages and
1359 			 * give them one more trip around the active list. So
1360 			 * that executable code get better chances to stay in
1361 			 * memory under moderate memory pressure.  Anon pages
1362 			 * are not likely to be evicted by use-once streaming
1363 			 * IO, plus JVM can create lots of anon VM_EXEC pages,
1364 			 * so we ignore them here.
1365 			 */
1366 			if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1367 				list_add(&page->lru, &l_active);
1368 				continue;
1369 			}
1370 		}
1371 
1372 		ClearPageActive(page);	/* we are de-activating */
1373 		list_add(&page->lru, &l_inactive);
1374 	}
1375 
1376 	/*
1377 	 * Move pages back to the lru list.
1378 	 */
1379 	spin_lock_irq(&zone->lru_lock);
1380 	/*
1381 	 * Count referenced pages from currently used mappings as rotated,
1382 	 * even though only some of them are actually re-activated.  This
1383 	 * helps balance scan pressure between file and anonymous pages in
1384 	 * get_scan_ratio.
1385 	 */
1386 	reclaim_stat->recent_rotated[file] += nr_rotated;
1387 
1388 	move_active_pages_to_lru(zone, &l_active,
1389 						LRU_ACTIVE + file * LRU_FILE);
1390 	move_active_pages_to_lru(zone, &l_inactive,
1391 						LRU_BASE   + file * LRU_FILE);
1392 	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1393 	spin_unlock_irq(&zone->lru_lock);
1394 }
1395 
1396 static int inactive_anon_is_low_global(struct zone *zone)
1397 {
1398 	unsigned long active, inactive;
1399 
1400 	active = zone_page_state(zone, NR_ACTIVE_ANON);
1401 	inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1402 
1403 	if (inactive * zone->inactive_ratio < active)
1404 		return 1;
1405 
1406 	return 0;
1407 }
1408 
1409 /**
1410  * inactive_anon_is_low - check if anonymous pages need to be deactivated
1411  * @zone: zone to check
1412  * @sc:   scan control of this context
1413  *
1414  * Returns true if the zone does not have enough inactive anon pages,
1415  * meaning some active anon pages need to be deactivated.
1416  */
1417 static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc)
1418 {
1419 	int low;
1420 
1421 	if (scanning_global_lru(sc))
1422 		low = inactive_anon_is_low_global(zone);
1423 	else
1424 		low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup);
1425 	return low;
1426 }
1427 
1428 static int inactive_file_is_low_global(struct zone *zone)
1429 {
1430 	unsigned long active, inactive;
1431 
1432 	active = zone_page_state(zone, NR_ACTIVE_FILE);
1433 	inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1434 
1435 	return (active > inactive);
1436 }
1437 
1438 /**
1439  * inactive_file_is_low - check if file pages need to be deactivated
1440  * @zone: zone to check
1441  * @sc:   scan control of this context
1442  *
1443  * When the system is doing streaming IO, memory pressure here
1444  * ensures that active file pages get deactivated, until more
1445  * than half of the file pages are on the inactive list.
1446  *
1447  * Once we get to that situation, protect the system's working
1448  * set from being evicted by disabling active file page aging.
1449  *
1450  * This uses a different ratio than the anonymous pages, because
1451  * the page cache uses a use-once replacement algorithm.
1452  */
1453 static int inactive_file_is_low(struct zone *zone, struct scan_control *sc)
1454 {
1455 	int low;
1456 
1457 	if (scanning_global_lru(sc))
1458 		low = inactive_file_is_low_global(zone);
1459 	else
1460 		low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup);
1461 	return low;
1462 }
1463 
1464 static int inactive_list_is_low(struct zone *zone, struct scan_control *sc,
1465 				int file)
1466 {
1467 	if (file)
1468 		return inactive_file_is_low(zone, sc);
1469 	else
1470 		return inactive_anon_is_low(zone, sc);
1471 }
1472 
1473 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1474 	struct zone *zone, struct scan_control *sc, int priority)
1475 {
1476 	int file = is_file_lru(lru);
1477 
1478 	if (is_active_lru(lru)) {
1479 		if (inactive_list_is_low(zone, sc, file))
1480 		    shrink_active_list(nr_to_scan, zone, sc, priority, file);
1481 		return 0;
1482 	}
1483 
1484 	return shrink_inactive_list(nr_to_scan, zone, sc, priority, file);
1485 }
1486 
1487 /*
1488  * Determine how aggressively the anon and file LRU lists should be
1489  * scanned.  The relative value of each set of LRU lists is determined
1490  * by looking at the fraction of the pages scanned we did rotate back
1491  * onto the active list instead of evict.
1492  *
1493  * percent[0] specifies how much pressure to put on ram/swap backed
1494  * memory, while percent[1] determines pressure on the file LRUs.
1495  */
1496 static void get_scan_ratio(struct zone *zone, struct scan_control *sc,
1497 					unsigned long *percent)
1498 {
1499 	unsigned long anon, file, free;
1500 	unsigned long anon_prio, file_prio;
1501 	unsigned long ap, fp;
1502 	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1503 
1504 	anon  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
1505 		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
1506 	file  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
1507 		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
1508 
1509 	if (scanning_global_lru(sc)) {
1510 		free  = zone_page_state(zone, NR_FREE_PAGES);
1511 		/* If we have very few page cache pages,
1512 		   force-scan anon pages. */
1513 		if (unlikely(file + free <= high_wmark_pages(zone))) {
1514 			percent[0] = 100;
1515 			percent[1] = 0;
1516 			return;
1517 		}
1518 	}
1519 
1520 	/*
1521 	 * OK, so we have swap space and a fair amount of page cache
1522 	 * pages.  We use the recently rotated / recently scanned
1523 	 * ratios to determine how valuable each cache is.
1524 	 *
1525 	 * Because workloads change over time (and to avoid overflow)
1526 	 * we keep these statistics as a floating average, which ends
1527 	 * up weighing recent references more than old ones.
1528 	 *
1529 	 * anon in [0], file in [1]
1530 	 */
1531 	if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1532 		spin_lock_irq(&zone->lru_lock);
1533 		reclaim_stat->recent_scanned[0] /= 2;
1534 		reclaim_stat->recent_rotated[0] /= 2;
1535 		spin_unlock_irq(&zone->lru_lock);
1536 	}
1537 
1538 	if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1539 		spin_lock_irq(&zone->lru_lock);
1540 		reclaim_stat->recent_scanned[1] /= 2;
1541 		reclaim_stat->recent_rotated[1] /= 2;
1542 		spin_unlock_irq(&zone->lru_lock);
1543 	}
1544 
1545 	/*
1546 	 * With swappiness at 100, anonymous and file have the same priority.
1547 	 * This scanning priority is essentially the inverse of IO cost.
1548 	 */
1549 	anon_prio = sc->swappiness;
1550 	file_prio = 200 - sc->swappiness;
1551 
1552 	/*
1553 	 * The amount of pressure on anon vs file pages is inversely
1554 	 * proportional to the fraction of recently scanned pages on
1555 	 * each list that were recently referenced and in active use.
1556 	 */
1557 	ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1);
1558 	ap /= reclaim_stat->recent_rotated[0] + 1;
1559 
1560 	fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
1561 	fp /= reclaim_stat->recent_rotated[1] + 1;
1562 
1563 	/* Normalize to percentages */
1564 	percent[0] = 100 * ap / (ap + fp + 1);
1565 	percent[1] = 100 - percent[0];
1566 }
1567 
1568 /*
1569  * Smallish @nr_to_scan's are deposited in @nr_saved_scan,
1570  * until we collected @swap_cluster_max pages to scan.
1571  */
1572 static unsigned long nr_scan_try_batch(unsigned long nr_to_scan,
1573 				       unsigned long *nr_saved_scan)
1574 {
1575 	unsigned long nr;
1576 
1577 	*nr_saved_scan += nr_to_scan;
1578 	nr = *nr_saved_scan;
1579 
1580 	if (nr >= SWAP_CLUSTER_MAX)
1581 		*nr_saved_scan = 0;
1582 	else
1583 		nr = 0;
1584 
1585 	return nr;
1586 }
1587 
1588 /*
1589  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1590  */
1591 static void shrink_zone(int priority, struct zone *zone,
1592 				struct scan_control *sc)
1593 {
1594 	unsigned long nr[NR_LRU_LISTS];
1595 	unsigned long nr_to_scan;
1596 	unsigned long percent[2];	/* anon @ 0; file @ 1 */
1597 	enum lru_list l;
1598 	unsigned long nr_reclaimed = sc->nr_reclaimed;
1599 	unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1600 	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1601 	int noswap = 0;
1602 
1603 	/* If we have no swap space, do not bother scanning anon pages. */
1604 	if (!sc->may_swap || (nr_swap_pages <= 0)) {
1605 		noswap = 1;
1606 		percent[0] = 0;
1607 		percent[1] = 100;
1608 	} else
1609 		get_scan_ratio(zone, sc, percent);
1610 
1611 	for_each_evictable_lru(l) {
1612 		int file = is_file_lru(l);
1613 		unsigned long scan;
1614 
1615 		scan = zone_nr_lru_pages(zone, sc, l);
1616 		if (priority || noswap) {
1617 			scan >>= priority;
1618 			scan = (scan * percent[file]) / 100;
1619 		}
1620 		nr[l] = nr_scan_try_batch(scan,
1621 					  &reclaim_stat->nr_saved_scan[l]);
1622 	}
1623 
1624 	while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1625 					nr[LRU_INACTIVE_FILE]) {
1626 		for_each_evictable_lru(l) {
1627 			if (nr[l]) {
1628 				nr_to_scan = min_t(unsigned long,
1629 						   nr[l], SWAP_CLUSTER_MAX);
1630 				nr[l] -= nr_to_scan;
1631 
1632 				nr_reclaimed += shrink_list(l, nr_to_scan,
1633 							    zone, sc, priority);
1634 			}
1635 		}
1636 		/*
1637 		 * On large memory systems, scan >> priority can become
1638 		 * really large. This is fine for the starting priority;
1639 		 * we want to put equal scanning pressure on each zone.
1640 		 * However, if the VM has a harder time of freeing pages,
1641 		 * with multiple processes reclaiming pages, the total
1642 		 * freeing target can get unreasonably large.
1643 		 */
1644 		if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)
1645 			break;
1646 	}
1647 
1648 	sc->nr_reclaimed = nr_reclaimed;
1649 
1650 	/*
1651 	 * Even if we did not try to evict anon pages at all, we want to
1652 	 * rebalance the anon lru active/inactive ratio.
1653 	 */
1654 	if (inactive_anon_is_low(zone, sc) && nr_swap_pages > 0)
1655 		shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);
1656 
1657 	throttle_vm_writeout(sc->gfp_mask);
1658 }
1659 
1660 /*
1661  * This is the direct reclaim path, for page-allocating processes.  We only
1662  * try to reclaim pages from zones which will satisfy the caller's allocation
1663  * request.
1664  *
1665  * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
1666  * Because:
1667  * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1668  *    allocation or
1669  * b) The target zone may be at high_wmark_pages(zone) but the lower zones
1670  *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
1671  *    zone defense algorithm.
1672  *
1673  * If a zone is deemed to be full of pinned pages then just give it a light
1674  * scan then give up on it.
1675  */
1676 static void shrink_zones(int priority, struct zonelist *zonelist,
1677 					struct scan_control *sc)
1678 {
1679 	enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);
1680 	struct zoneref *z;
1681 	struct zone *zone;
1682 
1683 	sc->all_unreclaimable = 1;
1684 	for_each_zone_zonelist_nodemask(zone, z, zonelist, high_zoneidx,
1685 					sc->nodemask) {
1686 		if (!populated_zone(zone))
1687 			continue;
1688 		/*
1689 		 * Take care memory controller reclaiming has small influence
1690 		 * to global LRU.
1691 		 */
1692 		if (scanning_global_lru(sc)) {
1693 			if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1694 				continue;
1695 			note_zone_scanning_priority(zone, priority);
1696 
1697 			if (zone_is_all_unreclaimable(zone) &&
1698 						priority != DEF_PRIORITY)
1699 				continue;	/* Let kswapd poll it */
1700 			sc->all_unreclaimable = 0;
1701 		} else {
1702 			/*
1703 			 * Ignore cpuset limitation here. We just want to reduce
1704 			 * # of used pages by us regardless of memory shortage.
1705 			 */
1706 			sc->all_unreclaimable = 0;
1707 			mem_cgroup_note_reclaim_priority(sc->mem_cgroup,
1708 							priority);
1709 		}
1710 
1711 		shrink_zone(priority, zone, sc);
1712 	}
1713 }
1714 
1715 /*
1716  * This is the main entry point to direct page reclaim.
1717  *
1718  * If a full scan of the inactive list fails to free enough memory then we
1719  * are "out of memory" and something needs to be killed.
1720  *
1721  * If the caller is !__GFP_FS then the probability of a failure is reasonably
1722  * high - the zone may be full of dirty or under-writeback pages, which this
1723  * caller can't do much about.  We kick the writeback threads and take explicit
1724  * naps in the hope that some of these pages can be written.  But if the
1725  * allocating task holds filesystem locks which prevent writeout this might not
1726  * work, and the allocation attempt will fail.
1727  *
1728  * returns:	0, if no pages reclaimed
1729  * 		else, the number of pages reclaimed
1730  */
1731 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
1732 					struct scan_control *sc)
1733 {
1734 	int priority;
1735 	unsigned long ret = 0;
1736 	unsigned long total_scanned = 0;
1737 	struct reclaim_state *reclaim_state = current->reclaim_state;
1738 	unsigned long lru_pages = 0;
1739 	struct zoneref *z;
1740 	struct zone *zone;
1741 	enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);
1742 	unsigned long writeback_threshold;
1743 
1744 	delayacct_freepages_start();
1745 
1746 	if (scanning_global_lru(sc))
1747 		count_vm_event(ALLOCSTALL);
1748 	/*
1749 	 * mem_cgroup will not do shrink_slab.
1750 	 */
1751 	if (scanning_global_lru(sc)) {
1752 		for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
1753 
1754 			if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1755 				continue;
1756 
1757 			lru_pages += zone_reclaimable_pages(zone);
1758 		}
1759 	}
1760 
1761 	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1762 		sc->nr_scanned = 0;
1763 		if (!priority)
1764 			disable_swap_token();
1765 		shrink_zones(priority, zonelist, sc);
1766 		/*
1767 		 * Don't shrink slabs when reclaiming memory from
1768 		 * over limit cgroups
1769 		 */
1770 		if (scanning_global_lru(sc)) {
1771 			shrink_slab(sc->nr_scanned, sc->gfp_mask, lru_pages);
1772 			if (reclaim_state) {
1773 				sc->nr_reclaimed += reclaim_state->reclaimed_slab;
1774 				reclaim_state->reclaimed_slab = 0;
1775 			}
1776 		}
1777 		total_scanned += sc->nr_scanned;
1778 		if (sc->nr_reclaimed >= sc->nr_to_reclaim) {
1779 			ret = sc->nr_reclaimed;
1780 			goto out;
1781 		}
1782 
1783 		/*
1784 		 * Try to write back as many pages as we just scanned.  This
1785 		 * tends to cause slow streaming writers to write data to the
1786 		 * disk smoothly, at the dirtying rate, which is nice.   But
1787 		 * that's undesirable in laptop mode, where we *want* lumpy
1788 		 * writeout.  So in laptop mode, write out the whole world.
1789 		 */
1790 		writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
1791 		if (total_scanned > writeback_threshold) {
1792 			wakeup_flusher_threads(laptop_mode ? 0 : total_scanned);
1793 			sc->may_writepage = 1;
1794 		}
1795 
1796 		/* Take a nap, wait for some writeback to complete */
1797 		if (!sc->hibernation_mode && sc->nr_scanned &&
1798 		    priority < DEF_PRIORITY - 2)
1799 			congestion_wait(BLK_RW_ASYNC, HZ/10);
1800 	}
1801 	/* top priority shrink_zones still had more to do? don't OOM, then */
1802 	if (!sc->all_unreclaimable && scanning_global_lru(sc))
1803 		ret = sc->nr_reclaimed;
1804 out:
1805 	/*
1806 	 * Now that we've scanned all the zones at this priority level, note
1807 	 * that level within the zone so that the next thread which performs
1808 	 * scanning of this zone will immediately start out at this priority
1809 	 * level.  This affects only the decision whether or not to bring
1810 	 * mapped pages onto the inactive list.
1811 	 */
1812 	if (priority < 0)
1813 		priority = 0;
1814 
1815 	if (scanning_global_lru(sc)) {
1816 		for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
1817 
1818 			if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1819 				continue;
1820 
1821 			zone->prev_priority = priority;
1822 		}
1823 	} else
1824 		mem_cgroup_record_reclaim_priority(sc->mem_cgroup, priority);
1825 
1826 	delayacct_freepages_end();
1827 
1828 	return ret;
1829 }
1830 
1831 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
1832 				gfp_t gfp_mask, nodemask_t *nodemask)
1833 {
1834 	struct scan_control sc = {
1835 		.gfp_mask = gfp_mask,
1836 		.may_writepage = !laptop_mode,
1837 		.nr_to_reclaim = SWAP_CLUSTER_MAX,
1838 		.may_unmap = 1,
1839 		.may_swap = 1,
1840 		.swappiness = vm_swappiness,
1841 		.order = order,
1842 		.mem_cgroup = NULL,
1843 		.isolate_pages = isolate_pages_global,
1844 		.nodemask = nodemask,
1845 	};
1846 
1847 	return do_try_to_free_pages(zonelist, &sc);
1848 }
1849 
1850 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
1851 
1852 unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
1853 						gfp_t gfp_mask, bool noswap,
1854 						unsigned int swappiness,
1855 						struct zone *zone, int nid)
1856 {
1857 	struct scan_control sc = {
1858 		.may_writepage = !laptop_mode,
1859 		.may_unmap = 1,
1860 		.may_swap = !noswap,
1861 		.swappiness = swappiness,
1862 		.order = 0,
1863 		.mem_cgroup = mem,
1864 		.isolate_pages = mem_cgroup_isolate_pages,
1865 	};
1866 	nodemask_t nm  = nodemask_of_node(nid);
1867 
1868 	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
1869 			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
1870 	sc.nodemask = &nm;
1871 	sc.nr_reclaimed = 0;
1872 	sc.nr_scanned = 0;
1873 	/*
1874 	 * NOTE: Although we can get the priority field, using it
1875 	 * here is not a good idea, since it limits the pages we can scan.
1876 	 * if we don't reclaim here, the shrink_zone from balance_pgdat
1877 	 * will pick up pages from other mem cgroup's as well. We hack
1878 	 * the priority and make it zero.
1879 	 */
1880 	shrink_zone(0, zone, &sc);
1881 	return sc.nr_reclaimed;
1882 }
1883 
1884 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
1885 					   gfp_t gfp_mask,
1886 					   bool noswap,
1887 					   unsigned int swappiness)
1888 {
1889 	struct zonelist *zonelist;
1890 	struct scan_control sc = {
1891 		.may_writepage = !laptop_mode,
1892 		.may_unmap = 1,
1893 		.may_swap = !noswap,
1894 		.nr_to_reclaim = SWAP_CLUSTER_MAX,
1895 		.swappiness = swappiness,
1896 		.order = 0,
1897 		.mem_cgroup = mem_cont,
1898 		.isolate_pages = mem_cgroup_isolate_pages,
1899 		.nodemask = NULL, /* we don't care the placement */
1900 	};
1901 
1902 	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
1903 			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
1904 	zonelist = NODE_DATA(numa_node_id())->node_zonelists;
1905 	return do_try_to_free_pages(zonelist, &sc);
1906 }
1907 #endif
1908 
1909 /* is kswapd sleeping prematurely? */
1910 static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
1911 {
1912 	int i;
1913 
1914 	/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
1915 	if (remaining)
1916 		return 1;
1917 
1918 	/* If after HZ/10, a zone is below the high mark, it's premature */
1919 	for (i = 0; i < pgdat->nr_zones; i++) {
1920 		struct zone *zone = pgdat->node_zones + i;
1921 
1922 		if (!populated_zone(zone))
1923 			continue;
1924 
1925 		if (zone_is_all_unreclaimable(zone))
1926 			continue;
1927 
1928 		if (!zone_watermark_ok(zone, order, high_wmark_pages(zone),
1929 								0, 0))
1930 			return 1;
1931 	}
1932 
1933 	return 0;
1934 }
1935 
1936 /*
1937  * For kswapd, balance_pgdat() will work across all this node's zones until
1938  * they are all at high_wmark_pages(zone).
1939  *
1940  * Returns the number of pages which were actually freed.
1941  *
1942  * There is special handling here for zones which are full of pinned pages.
1943  * This can happen if the pages are all mlocked, or if they are all used by
1944  * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
1945  * What we do is to detect the case where all pages in the zone have been
1946  * scanned twice and there has been zero successful reclaim.  Mark the zone as
1947  * dead and from now on, only perform a short scan.  Basically we're polling
1948  * the zone for when the problem goes away.
1949  *
1950  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
1951  * zones which have free_pages > high_wmark_pages(zone), but once a zone is
1952  * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
1953  * lower zones regardless of the number of free pages in the lower zones. This
1954  * interoperates with the page allocator fallback scheme to ensure that aging
1955  * of pages is balanced across the zones.
1956  */
1957 static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
1958 {
1959 	int all_zones_ok;
1960 	int priority;
1961 	int i;
1962 	unsigned long total_scanned;
1963 	struct reclaim_state *reclaim_state = current->reclaim_state;
1964 	struct scan_control sc = {
1965 		.gfp_mask = GFP_KERNEL,
1966 		.may_unmap = 1,
1967 		.may_swap = 1,
1968 		/*
1969 		 * kswapd doesn't want to be bailed out while reclaim. because
1970 		 * we want to put equal scanning pressure on each zone.
1971 		 */
1972 		.nr_to_reclaim = ULONG_MAX,
1973 		.swappiness = vm_swappiness,
1974 		.order = order,
1975 		.mem_cgroup = NULL,
1976 		.isolate_pages = isolate_pages_global,
1977 	};
1978 	/*
1979 	 * temp_priority is used to remember the scanning priority at which
1980 	 * this zone was successfully refilled to
1981 	 * free_pages == high_wmark_pages(zone).
1982 	 */
1983 	int temp_priority[MAX_NR_ZONES];
1984 
1985 loop_again:
1986 	total_scanned = 0;
1987 	sc.nr_reclaimed = 0;
1988 	sc.may_writepage = !laptop_mode;
1989 	count_vm_event(PAGEOUTRUN);
1990 
1991 	for (i = 0; i < pgdat->nr_zones; i++)
1992 		temp_priority[i] = DEF_PRIORITY;
1993 
1994 	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1995 		int end_zone = 0;	/* Inclusive.  0 = ZONE_DMA */
1996 		unsigned long lru_pages = 0;
1997 		int has_under_min_watermark_zone = 0;
1998 
1999 		/* The swap token gets in the way of swapout... */
2000 		if (!priority)
2001 			disable_swap_token();
2002 
2003 		all_zones_ok = 1;
2004 
2005 		/*
2006 		 * Scan in the highmem->dma direction for the highest
2007 		 * zone which needs scanning
2008 		 */
2009 		for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2010 			struct zone *zone = pgdat->node_zones + i;
2011 
2012 			if (!populated_zone(zone))
2013 				continue;
2014 
2015 			if (zone_is_all_unreclaimable(zone) &&
2016 			    priority != DEF_PRIORITY)
2017 				continue;
2018 
2019 			/*
2020 			 * Do some background aging of the anon list, to give
2021 			 * pages a chance to be referenced before reclaiming.
2022 			 */
2023 			if (inactive_anon_is_low(zone, &sc))
2024 				shrink_active_list(SWAP_CLUSTER_MAX, zone,
2025 							&sc, priority, 0);
2026 
2027 			if (!zone_watermark_ok(zone, order,
2028 					high_wmark_pages(zone), 0, 0)) {
2029 				end_zone = i;
2030 				break;
2031 			}
2032 		}
2033 		if (i < 0)
2034 			goto out;
2035 
2036 		for (i = 0; i <= end_zone; i++) {
2037 			struct zone *zone = pgdat->node_zones + i;
2038 
2039 			lru_pages += zone_reclaimable_pages(zone);
2040 		}
2041 
2042 		/*
2043 		 * Now scan the zone in the dma->highmem direction, stopping
2044 		 * at the last zone which needs scanning.
2045 		 *
2046 		 * We do this because the page allocator works in the opposite
2047 		 * direction.  This prevents the page allocator from allocating
2048 		 * pages behind kswapd's direction of progress, which would
2049 		 * cause too much scanning of the lower zones.
2050 		 */
2051 		for (i = 0; i <= end_zone; i++) {
2052 			struct zone *zone = pgdat->node_zones + i;
2053 			int nr_slab;
2054 			int nid, zid;
2055 
2056 			if (!populated_zone(zone))
2057 				continue;
2058 
2059 			if (zone_is_all_unreclaimable(zone) &&
2060 					priority != DEF_PRIORITY)
2061 				continue;
2062 
2063 			if (!zone_watermark_ok(zone, order,
2064 					high_wmark_pages(zone), end_zone, 0))
2065 				all_zones_ok = 0;
2066 			temp_priority[i] = priority;
2067 			sc.nr_scanned = 0;
2068 			note_zone_scanning_priority(zone, priority);
2069 
2070 			nid = pgdat->node_id;
2071 			zid = zone_idx(zone);
2072 			/*
2073 			 * Call soft limit reclaim before calling shrink_zone.
2074 			 * For now we ignore the return value
2075 			 */
2076 			mem_cgroup_soft_limit_reclaim(zone, order, sc.gfp_mask,
2077 							nid, zid);
2078 			/*
2079 			 * We put equal pressure on every zone, unless one
2080 			 * zone has way too many pages free already.
2081 			 */
2082 			if (!zone_watermark_ok(zone, order,
2083 					8*high_wmark_pages(zone), end_zone, 0))
2084 				shrink_zone(priority, zone, &sc);
2085 			reclaim_state->reclaimed_slab = 0;
2086 			nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
2087 						lru_pages);
2088 			sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2089 			total_scanned += sc.nr_scanned;
2090 			if (zone_is_all_unreclaimable(zone))
2091 				continue;
2092 			if (nr_slab == 0 && zone->pages_scanned >=
2093 					(zone_reclaimable_pages(zone) * 6))
2094 					zone_set_flag(zone,
2095 						      ZONE_ALL_UNRECLAIMABLE);
2096 			/*
2097 			 * If we've done a decent amount of scanning and
2098 			 * the reclaim ratio is low, start doing writepage
2099 			 * even in laptop mode
2100 			 */
2101 			if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2102 			    total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
2103 				sc.may_writepage = 1;
2104 
2105 			/*
2106 			 * We are still under min water mark. it mean we have
2107 			 * GFP_ATOMIC allocation failure risk. Hurry up!
2108 			 */
2109 			if (!zone_watermark_ok(zone, order, min_wmark_pages(zone),
2110 					      end_zone, 0))
2111 				has_under_min_watermark_zone = 1;
2112 
2113 		}
2114 		if (all_zones_ok)
2115 			break;		/* kswapd: all done */
2116 		/*
2117 		 * OK, kswapd is getting into trouble.  Take a nap, then take
2118 		 * another pass across the zones.
2119 		 */
2120 		if (total_scanned && (priority < DEF_PRIORITY - 2)) {
2121 			if (has_under_min_watermark_zone)
2122 				count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
2123 			else
2124 				congestion_wait(BLK_RW_ASYNC, HZ/10);
2125 		}
2126 
2127 		/*
2128 		 * We do this so kswapd doesn't build up large priorities for
2129 		 * example when it is freeing in parallel with allocators. It
2130 		 * matches the direct reclaim path behaviour in terms of impact
2131 		 * on zone->*_priority.
2132 		 */
2133 		if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2134 			break;
2135 	}
2136 out:
2137 	/*
2138 	 * Note within each zone the priority level at which this zone was
2139 	 * brought into a happy state.  So that the next thread which scans this
2140 	 * zone will start out at that priority level.
2141 	 */
2142 	for (i = 0; i < pgdat->nr_zones; i++) {
2143 		struct zone *zone = pgdat->node_zones + i;
2144 
2145 		zone->prev_priority = temp_priority[i];
2146 	}
2147 	if (!all_zones_ok) {
2148 		cond_resched();
2149 
2150 		try_to_freeze();
2151 
2152 		/*
2153 		 * Fragmentation may mean that the system cannot be
2154 		 * rebalanced for high-order allocations in all zones.
2155 		 * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2156 		 * it means the zones have been fully scanned and are still
2157 		 * not balanced. For high-order allocations, there is
2158 		 * little point trying all over again as kswapd may
2159 		 * infinite loop.
2160 		 *
2161 		 * Instead, recheck all watermarks at order-0 as they
2162 		 * are the most important. If watermarks are ok, kswapd will go
2163 		 * back to sleep. High-order users can still perform direct
2164 		 * reclaim if they wish.
2165 		 */
2166 		if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2167 			order = sc.order = 0;
2168 
2169 		goto loop_again;
2170 	}
2171 
2172 	return sc.nr_reclaimed;
2173 }
2174 
2175 /*
2176  * The background pageout daemon, started as a kernel thread
2177  * from the init process.
2178  *
2179  * This basically trickles out pages so that we have _some_
2180  * free memory available even if there is no other activity
2181  * that frees anything up. This is needed for things like routing
2182  * etc, where we otherwise might have all activity going on in
2183  * asynchronous contexts that cannot page things out.
2184  *
2185  * If there are applications that are active memory-allocators
2186  * (most normal use), this basically shouldn't matter.
2187  */
2188 static int kswapd(void *p)
2189 {
2190 	unsigned long order;
2191 	pg_data_t *pgdat = (pg_data_t*)p;
2192 	struct task_struct *tsk = current;
2193 	DEFINE_WAIT(wait);
2194 	struct reclaim_state reclaim_state = {
2195 		.reclaimed_slab = 0,
2196 	};
2197 	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2198 
2199 	lockdep_set_current_reclaim_state(GFP_KERNEL);
2200 
2201 	if (!cpumask_empty(cpumask))
2202 		set_cpus_allowed_ptr(tsk, cpumask);
2203 	current->reclaim_state = &reclaim_state;
2204 
2205 	/*
2206 	 * Tell the memory management that we're a "memory allocator",
2207 	 * and that if we need more memory we should get access to it
2208 	 * regardless (see "__alloc_pages()"). "kswapd" should
2209 	 * never get caught in the normal page freeing logic.
2210 	 *
2211 	 * (Kswapd normally doesn't need memory anyway, but sometimes
2212 	 * you need a small amount of memory in order to be able to
2213 	 * page out something else, and this flag essentially protects
2214 	 * us from recursively trying to free more memory as we're
2215 	 * trying to free the first piece of memory in the first place).
2216 	 */
2217 	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2218 	set_freezable();
2219 
2220 	order = 0;
2221 	for ( ; ; ) {
2222 		unsigned long new_order;
2223 		int ret;
2224 
2225 		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2226 		new_order = pgdat->kswapd_max_order;
2227 		pgdat->kswapd_max_order = 0;
2228 		if (order < new_order) {
2229 			/*
2230 			 * Don't sleep if someone wants a larger 'order'
2231 			 * allocation
2232 			 */
2233 			order = new_order;
2234 		} else {
2235 			if (!freezing(current) && !kthread_should_stop()) {
2236 				long remaining = 0;
2237 
2238 				/* Try to sleep for a short interval */
2239 				if (!sleeping_prematurely(pgdat, order, remaining)) {
2240 					remaining = schedule_timeout(HZ/10);
2241 					finish_wait(&pgdat->kswapd_wait, &wait);
2242 					prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2243 				}
2244 
2245 				/*
2246 				 * After a short sleep, check if it was a
2247 				 * premature sleep. If not, then go fully
2248 				 * to sleep until explicitly woken up
2249 				 */
2250 				if (!sleeping_prematurely(pgdat, order, remaining))
2251 					schedule();
2252 				else {
2253 					if (remaining)
2254 						count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2255 					else
2256 						count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2257 				}
2258 			}
2259 
2260 			order = pgdat->kswapd_max_order;
2261 		}
2262 		finish_wait(&pgdat->kswapd_wait, &wait);
2263 
2264 		ret = try_to_freeze();
2265 		if (kthread_should_stop())
2266 			break;
2267 
2268 		/*
2269 		 * We can speed up thawing tasks if we don't call balance_pgdat
2270 		 * after returning from the refrigerator
2271 		 */
2272 		if (!ret)
2273 			balance_pgdat(pgdat, order);
2274 	}
2275 	return 0;
2276 }
2277 
2278 /*
2279  * A zone is low on free memory, so wake its kswapd task to service it.
2280  */
2281 void wakeup_kswapd(struct zone *zone, int order)
2282 {
2283 	pg_data_t *pgdat;
2284 
2285 	if (!populated_zone(zone))
2286 		return;
2287 
2288 	pgdat = zone->zone_pgdat;
2289 	if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
2290 		return;
2291 	if (pgdat->kswapd_max_order < order)
2292 		pgdat->kswapd_max_order = order;
2293 	if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2294 		return;
2295 	if (!waitqueue_active(&pgdat->kswapd_wait))
2296 		return;
2297 	wake_up_interruptible(&pgdat->kswapd_wait);
2298 }
2299 
2300 /*
2301  * The reclaimable count would be mostly accurate.
2302  * The less reclaimable pages may be
2303  * - mlocked pages, which will be moved to unevictable list when encountered
2304  * - mapped pages, which may require several travels to be reclaimed
2305  * - dirty pages, which is not "instantly" reclaimable
2306  */
2307 unsigned long global_reclaimable_pages(void)
2308 {
2309 	int nr;
2310 
2311 	nr = global_page_state(NR_ACTIVE_FILE) +
2312 	     global_page_state(NR_INACTIVE_FILE);
2313 
2314 	if (nr_swap_pages > 0)
2315 		nr += global_page_state(NR_ACTIVE_ANON) +
2316 		      global_page_state(NR_INACTIVE_ANON);
2317 
2318 	return nr;
2319 }
2320 
2321 unsigned long zone_reclaimable_pages(struct zone *zone)
2322 {
2323 	int nr;
2324 
2325 	nr = zone_page_state(zone, NR_ACTIVE_FILE) +
2326 	     zone_page_state(zone, NR_INACTIVE_FILE);
2327 
2328 	if (nr_swap_pages > 0)
2329 		nr += zone_page_state(zone, NR_ACTIVE_ANON) +
2330 		      zone_page_state(zone, NR_INACTIVE_ANON);
2331 
2332 	return nr;
2333 }
2334 
2335 #ifdef CONFIG_HIBERNATION
2336 /*
2337  * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
2338  * freed pages.
2339  *
2340  * Rather than trying to age LRUs the aim is to preserve the overall
2341  * LRU order by reclaiming preferentially
2342  * inactive > active > active referenced > active mapped
2343  */
2344 unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
2345 {
2346 	struct reclaim_state reclaim_state;
2347 	struct scan_control sc = {
2348 		.gfp_mask = GFP_HIGHUSER_MOVABLE,
2349 		.may_swap = 1,
2350 		.may_unmap = 1,
2351 		.may_writepage = 1,
2352 		.nr_to_reclaim = nr_to_reclaim,
2353 		.hibernation_mode = 1,
2354 		.swappiness = vm_swappiness,
2355 		.order = 0,
2356 		.isolate_pages = isolate_pages_global,
2357 	};
2358 	struct zonelist * zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
2359 	struct task_struct *p = current;
2360 	unsigned long nr_reclaimed;
2361 
2362 	p->flags |= PF_MEMALLOC;
2363 	lockdep_set_current_reclaim_state(sc.gfp_mask);
2364 	reclaim_state.reclaimed_slab = 0;
2365 	p->reclaim_state = &reclaim_state;
2366 
2367 	nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
2368 
2369 	p->reclaim_state = NULL;
2370 	lockdep_clear_current_reclaim_state();
2371 	p->flags &= ~PF_MEMALLOC;
2372 
2373 	return nr_reclaimed;
2374 }
2375 #endif /* CONFIG_HIBERNATION */
2376 
2377 /* It's optimal to keep kswapds on the same CPUs as their memory, but
2378    not required for correctness.  So if the last cpu in a node goes
2379    away, we get changed to run anywhere: as the first one comes back,
2380    restore their cpu bindings. */
2381 static int __devinit cpu_callback(struct notifier_block *nfb,
2382 				  unsigned long action, void *hcpu)
2383 {
2384 	int nid;
2385 
2386 	if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
2387 		for_each_node_state(nid, N_HIGH_MEMORY) {
2388 			pg_data_t *pgdat = NODE_DATA(nid);
2389 			const struct cpumask *mask;
2390 
2391 			mask = cpumask_of_node(pgdat->node_id);
2392 
2393 			if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2394 				/* One of our CPUs online: restore mask */
2395 				set_cpus_allowed_ptr(pgdat->kswapd, mask);
2396 		}
2397 	}
2398 	return NOTIFY_OK;
2399 }
2400 
2401 /*
2402  * This kswapd start function will be called by init and node-hot-add.
2403  * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
2404  */
2405 int kswapd_run(int nid)
2406 {
2407 	pg_data_t *pgdat = NODE_DATA(nid);
2408 	int ret = 0;
2409 
2410 	if (pgdat->kswapd)
2411 		return 0;
2412 
2413 	pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
2414 	if (IS_ERR(pgdat->kswapd)) {
2415 		/* failure at boot is fatal */
2416 		BUG_ON(system_state == SYSTEM_BOOTING);
2417 		printk("Failed to start kswapd on node %d\n",nid);
2418 		ret = -1;
2419 	}
2420 	return ret;
2421 }
2422 
2423 /*
2424  * Called by memory hotplug when all memory in a node is offlined.
2425  */
2426 void kswapd_stop(int nid)
2427 {
2428 	struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
2429 
2430 	if (kswapd)
2431 		kthread_stop(kswapd);
2432 }
2433 
2434 static int __init kswapd_init(void)
2435 {
2436 	int nid;
2437 
2438 	swap_setup();
2439 	for_each_node_state(nid, N_HIGH_MEMORY)
2440  		kswapd_run(nid);
2441 	hotcpu_notifier(cpu_callback, 0);
2442 	return 0;
2443 }
2444 
2445 module_init(kswapd_init)
2446 
2447 #ifdef CONFIG_NUMA
2448 /*
2449  * Zone reclaim mode
2450  *
2451  * If non-zero call zone_reclaim when the number of free pages falls below
2452  * the watermarks.
2453  */
2454 int zone_reclaim_mode __read_mostly;
2455 
2456 #define RECLAIM_OFF 0
2457 #define RECLAIM_ZONE (1<<0)	/* Run shrink_inactive_list on the zone */
2458 #define RECLAIM_WRITE (1<<1)	/* Writeout pages during reclaim */
2459 #define RECLAIM_SWAP (1<<2)	/* Swap pages out during reclaim */
2460 
2461 /*
2462  * Priority for ZONE_RECLAIM. This determines the fraction of pages
2463  * of a node considered for each zone_reclaim. 4 scans 1/16th of
2464  * a zone.
2465  */
2466 #define ZONE_RECLAIM_PRIORITY 4
2467 
2468 /*
2469  * Percentage of pages in a zone that must be unmapped for zone_reclaim to
2470  * occur.
2471  */
2472 int sysctl_min_unmapped_ratio = 1;
2473 
2474 /*
2475  * If the number of slab pages in a zone grows beyond this percentage then
2476  * slab reclaim needs to occur.
2477  */
2478 int sysctl_min_slab_ratio = 5;
2479 
2480 static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
2481 {
2482 	unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
2483 	unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
2484 		zone_page_state(zone, NR_ACTIVE_FILE);
2485 
2486 	/*
2487 	 * It's possible for there to be more file mapped pages than
2488 	 * accounted for by the pages on the file LRU lists because
2489 	 * tmpfs pages accounted for as ANON can also be FILE_MAPPED
2490 	 */
2491 	return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
2492 }
2493 
2494 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
2495 static long zone_pagecache_reclaimable(struct zone *zone)
2496 {
2497 	long nr_pagecache_reclaimable;
2498 	long delta = 0;
2499 
2500 	/*
2501 	 * If RECLAIM_SWAP is set, then all file pages are considered
2502 	 * potentially reclaimable. Otherwise, we have to worry about
2503 	 * pages like swapcache and zone_unmapped_file_pages() provides
2504 	 * a better estimate
2505 	 */
2506 	if (zone_reclaim_mode & RECLAIM_SWAP)
2507 		nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
2508 	else
2509 		nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
2510 
2511 	/* If we can't clean pages, remove dirty pages from consideration */
2512 	if (!(zone_reclaim_mode & RECLAIM_WRITE))
2513 		delta += zone_page_state(zone, NR_FILE_DIRTY);
2514 
2515 	/* Watch for any possible underflows due to delta */
2516 	if (unlikely(delta > nr_pagecache_reclaimable))
2517 		delta = nr_pagecache_reclaimable;
2518 
2519 	return nr_pagecache_reclaimable - delta;
2520 }
2521 
2522 /*
2523  * Try to free up some pages from this zone through reclaim.
2524  */
2525 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
2526 {
2527 	/* Minimum pages needed in order to stay on node */
2528 	const unsigned long nr_pages = 1 << order;
2529 	struct task_struct *p = current;
2530 	struct reclaim_state reclaim_state;
2531 	int priority;
2532 	struct scan_control sc = {
2533 		.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
2534 		.may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
2535 		.may_swap = 1,
2536 		.nr_to_reclaim = max_t(unsigned long, nr_pages,
2537 				       SWAP_CLUSTER_MAX),
2538 		.gfp_mask = gfp_mask,
2539 		.swappiness = vm_swappiness,
2540 		.order = order,
2541 		.isolate_pages = isolate_pages_global,
2542 	};
2543 	unsigned long slab_reclaimable;
2544 
2545 	disable_swap_token();
2546 	cond_resched();
2547 	/*
2548 	 * We need to be able to allocate from the reserves for RECLAIM_SWAP
2549 	 * and we also need to be able to write out pages for RECLAIM_WRITE
2550 	 * and RECLAIM_SWAP.
2551 	 */
2552 	p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
2553 	reclaim_state.reclaimed_slab = 0;
2554 	p->reclaim_state = &reclaim_state;
2555 
2556 	if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
2557 		/*
2558 		 * Free memory by calling shrink zone with increasing
2559 		 * priorities until we have enough memory freed.
2560 		 */
2561 		priority = ZONE_RECLAIM_PRIORITY;
2562 		do {
2563 			note_zone_scanning_priority(zone, priority);
2564 			shrink_zone(priority, zone, &sc);
2565 			priority--;
2566 		} while (priority >= 0 && sc.nr_reclaimed < nr_pages);
2567 	}
2568 
2569 	slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
2570 	if (slab_reclaimable > zone->min_slab_pages) {
2571 		/*
2572 		 * shrink_slab() does not currently allow us to determine how
2573 		 * many pages were freed in this zone. So we take the current
2574 		 * number of slab pages and shake the slab until it is reduced
2575 		 * by the same nr_pages that we used for reclaiming unmapped
2576 		 * pages.
2577 		 *
2578 		 * Note that shrink_slab will free memory on all zones and may
2579 		 * take a long time.
2580 		 */
2581 		while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
2582 			zone_page_state(zone, NR_SLAB_RECLAIMABLE) >
2583 				slab_reclaimable - nr_pages)
2584 			;
2585 
2586 		/*
2587 		 * Update nr_reclaimed by the number of slab pages we
2588 		 * reclaimed from this zone.
2589 		 */
2590 		sc.nr_reclaimed += slab_reclaimable -
2591 			zone_page_state(zone, NR_SLAB_RECLAIMABLE);
2592 	}
2593 
2594 	p->reclaim_state = NULL;
2595 	current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
2596 	return sc.nr_reclaimed >= nr_pages;
2597 }
2598 
2599 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
2600 {
2601 	int node_id;
2602 	int ret;
2603 
2604 	/*
2605 	 * Zone reclaim reclaims unmapped file backed pages and
2606 	 * slab pages if we are over the defined limits.
2607 	 *
2608 	 * A small portion of unmapped file backed pages is needed for
2609 	 * file I/O otherwise pages read by file I/O will be immediately
2610 	 * thrown out if the zone is overallocated. So we do not reclaim
2611 	 * if less than a specified percentage of the zone is used by
2612 	 * unmapped file backed pages.
2613 	 */
2614 	if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
2615 	    zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
2616 		return ZONE_RECLAIM_FULL;
2617 
2618 	if (zone_is_all_unreclaimable(zone))
2619 		return ZONE_RECLAIM_FULL;
2620 
2621 	/*
2622 	 * Do not scan if the allocation should not be delayed.
2623 	 */
2624 	if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
2625 		return ZONE_RECLAIM_NOSCAN;
2626 
2627 	/*
2628 	 * Only run zone reclaim on the local zone or on zones that do not
2629 	 * have associated processors. This will favor the local processor
2630 	 * over remote processors and spread off node memory allocations
2631 	 * as wide as possible.
2632 	 */
2633 	node_id = zone_to_nid(zone);
2634 	if (node_state(node_id, N_CPU) && node_id != numa_node_id())
2635 		return ZONE_RECLAIM_NOSCAN;
2636 
2637 	if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
2638 		return ZONE_RECLAIM_NOSCAN;
2639 
2640 	ret = __zone_reclaim(zone, gfp_mask, order);
2641 	zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
2642 
2643 	if (!ret)
2644 		count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
2645 
2646 	return ret;
2647 }
2648 #endif
2649 
2650 /*
2651  * page_evictable - test whether a page is evictable
2652  * @page: the page to test
2653  * @vma: the VMA in which the page is or will be mapped, may be NULL
2654  *
2655  * Test whether page is evictable--i.e., should be placed on active/inactive
2656  * lists vs unevictable list.  The vma argument is !NULL when called from the
2657  * fault path to determine how to instantate a new page.
2658  *
2659  * Reasons page might not be evictable:
2660  * (1) page's mapping marked unevictable
2661  * (2) page is part of an mlocked VMA
2662  *
2663  */
2664 int page_evictable(struct page *page, struct vm_area_struct *vma)
2665 {
2666 
2667 	if (mapping_unevictable(page_mapping(page)))
2668 		return 0;
2669 
2670 	if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
2671 		return 0;
2672 
2673 	return 1;
2674 }
2675 
2676 /**
2677  * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list
2678  * @page: page to check evictability and move to appropriate lru list
2679  * @zone: zone page is in
2680  *
2681  * Checks a page for evictability and moves the page to the appropriate
2682  * zone lru list.
2683  *
2684  * Restrictions: zone->lru_lock must be held, page must be on LRU and must
2685  * have PageUnevictable set.
2686  */
2687 static void check_move_unevictable_page(struct page *page, struct zone *zone)
2688 {
2689 	VM_BUG_ON(PageActive(page));
2690 
2691 retry:
2692 	ClearPageUnevictable(page);
2693 	if (page_evictable(page, NULL)) {
2694 		enum lru_list l = page_lru_base_type(page);
2695 
2696 		__dec_zone_state(zone, NR_UNEVICTABLE);
2697 		list_move(&page->lru, &zone->lru[l].list);
2698 		mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l);
2699 		__inc_zone_state(zone, NR_INACTIVE_ANON + l);
2700 		__count_vm_event(UNEVICTABLE_PGRESCUED);
2701 	} else {
2702 		/*
2703 		 * rotate unevictable list
2704 		 */
2705 		SetPageUnevictable(page);
2706 		list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list);
2707 		mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE);
2708 		if (page_evictable(page, NULL))
2709 			goto retry;
2710 	}
2711 }
2712 
2713 /**
2714  * scan_mapping_unevictable_pages - scan an address space for evictable pages
2715  * @mapping: struct address_space to scan for evictable pages
2716  *
2717  * Scan all pages in mapping.  Check unevictable pages for
2718  * evictability and move them to the appropriate zone lru list.
2719  */
2720 void scan_mapping_unevictable_pages(struct address_space *mapping)
2721 {
2722 	pgoff_t next = 0;
2723 	pgoff_t end   = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >>
2724 			 PAGE_CACHE_SHIFT;
2725 	struct zone *zone;
2726 	struct pagevec pvec;
2727 
2728 	if (mapping->nrpages == 0)
2729 		return;
2730 
2731 	pagevec_init(&pvec, 0);
2732 	while (next < end &&
2733 		pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
2734 		int i;
2735 		int pg_scanned = 0;
2736 
2737 		zone = NULL;
2738 
2739 		for (i = 0; i < pagevec_count(&pvec); i++) {
2740 			struct page *page = pvec.pages[i];
2741 			pgoff_t page_index = page->index;
2742 			struct zone *pagezone = page_zone(page);
2743 
2744 			pg_scanned++;
2745 			if (page_index > next)
2746 				next = page_index;
2747 			next++;
2748 
2749 			if (pagezone != zone) {
2750 				if (zone)
2751 					spin_unlock_irq(&zone->lru_lock);
2752 				zone = pagezone;
2753 				spin_lock_irq(&zone->lru_lock);
2754 			}
2755 
2756 			if (PageLRU(page) && PageUnevictable(page))
2757 				check_move_unevictable_page(page, zone);
2758 		}
2759 		if (zone)
2760 			spin_unlock_irq(&zone->lru_lock);
2761 		pagevec_release(&pvec);
2762 
2763 		count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
2764 	}
2765 
2766 }
2767 
2768 /**
2769  * scan_zone_unevictable_pages - check unevictable list for evictable pages
2770  * @zone - zone of which to scan the unevictable list
2771  *
2772  * Scan @zone's unevictable LRU lists to check for pages that have become
2773  * evictable.  Move those that have to @zone's inactive list where they
2774  * become candidates for reclaim, unless shrink_inactive_zone() decides
2775  * to reactivate them.  Pages that are still unevictable are rotated
2776  * back onto @zone's unevictable list.
2777  */
2778 #define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */
2779 static void scan_zone_unevictable_pages(struct zone *zone)
2780 {
2781 	struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list;
2782 	unsigned long scan;
2783 	unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE);
2784 
2785 	while (nr_to_scan > 0) {
2786 		unsigned long batch_size = min(nr_to_scan,
2787 						SCAN_UNEVICTABLE_BATCH_SIZE);
2788 
2789 		spin_lock_irq(&zone->lru_lock);
2790 		for (scan = 0;  scan < batch_size; scan++) {
2791 			struct page *page = lru_to_page(l_unevictable);
2792 
2793 			if (!trylock_page(page))
2794 				continue;
2795 
2796 			prefetchw_prev_lru_page(page, l_unevictable, flags);
2797 
2798 			if (likely(PageLRU(page) && PageUnevictable(page)))
2799 				check_move_unevictable_page(page, zone);
2800 
2801 			unlock_page(page);
2802 		}
2803 		spin_unlock_irq(&zone->lru_lock);
2804 
2805 		nr_to_scan -= batch_size;
2806 	}
2807 }
2808 
2809 
2810 /**
2811  * scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages
2812  *
2813  * A really big hammer:  scan all zones' unevictable LRU lists to check for
2814  * pages that have become evictable.  Move those back to the zones'
2815  * inactive list where they become candidates for reclaim.
2816  * This occurs when, e.g., we have unswappable pages on the unevictable lists,
2817  * and we add swap to the system.  As such, it runs in the context of a task
2818  * that has possibly/probably made some previously unevictable pages
2819  * evictable.
2820  */
2821 static void scan_all_zones_unevictable_pages(void)
2822 {
2823 	struct zone *zone;
2824 
2825 	for_each_zone(zone) {
2826 		scan_zone_unevictable_pages(zone);
2827 	}
2828 }
2829 
2830 /*
2831  * scan_unevictable_pages [vm] sysctl handler.  On demand re-scan of
2832  * all nodes' unevictable lists for evictable pages
2833  */
2834 unsigned long scan_unevictable_pages;
2835 
2836 int scan_unevictable_handler(struct ctl_table *table, int write,
2837 			   void __user *buffer,
2838 			   size_t *length, loff_t *ppos)
2839 {
2840 	proc_doulongvec_minmax(table, write, buffer, length, ppos);
2841 
2842 	if (write && *(unsigned long *)table->data)
2843 		scan_all_zones_unevictable_pages();
2844 
2845 	scan_unevictable_pages = 0;
2846 	return 0;
2847 }
2848 
2849 /*
2850  * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
2851  * a specified node's per zone unevictable lists for evictable pages.
2852  */
2853 
2854 static ssize_t read_scan_unevictable_node(struct sys_device *dev,
2855 					  struct sysdev_attribute *attr,
2856 					  char *buf)
2857 {
2858 	return sprintf(buf, "0\n");	/* always zero; should fit... */
2859 }
2860 
2861 static ssize_t write_scan_unevictable_node(struct sys_device *dev,
2862 					   struct sysdev_attribute *attr,
2863 					const char *buf, size_t count)
2864 {
2865 	struct zone *node_zones = NODE_DATA(dev->id)->node_zones;
2866 	struct zone *zone;
2867 	unsigned long res;
2868 	unsigned long req = strict_strtoul(buf, 10, &res);
2869 
2870 	if (!req)
2871 		return 1;	/* zero is no-op */
2872 
2873 	for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
2874 		if (!populated_zone(zone))
2875 			continue;
2876 		scan_zone_unevictable_pages(zone);
2877 	}
2878 	return 1;
2879 }
2880 
2881 
2882 static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
2883 			read_scan_unevictable_node,
2884 			write_scan_unevictable_node);
2885 
2886 int scan_unevictable_register_node(struct node *node)
2887 {
2888 	return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages);
2889 }
2890 
2891 void scan_unevictable_unregister_node(struct node *node)
2892 {
2893 	sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages);
2894 }
2895 
2896