xref: /openbmc/linux/mm/vmscan.c (revision 81d67439)
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/gfp.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/compaction.h>
36 #include <linux/notifier.h>
37 #include <linux/rwsem.h>
38 #include <linux/delay.h>
39 #include <linux/kthread.h>
40 #include <linux/freezer.h>
41 #include <linux/memcontrol.h>
42 #include <linux/delayacct.h>
43 #include <linux/sysctl.h>
44 #include <linux/oom.h>
45 #include <linux/prefetch.h>
46 
47 #include <asm/tlbflush.h>
48 #include <asm/div64.h>
49 
50 #include <linux/swapops.h>
51 
52 #include "internal.h"
53 
54 #define CREATE_TRACE_POINTS
55 #include <trace/events/vmscan.h>
56 
57 /*
58  * reclaim_mode determines how the inactive list is shrunk
59  * RECLAIM_MODE_SINGLE: Reclaim only order-0 pages
60  * RECLAIM_MODE_ASYNC:  Do not block
61  * RECLAIM_MODE_SYNC:   Allow blocking e.g. call wait_on_page_writeback
62  * RECLAIM_MODE_LUMPYRECLAIM: For high-order allocations, take a reference
63  *			page from the LRU and reclaim all pages within a
64  *			naturally aligned range
65  * RECLAIM_MODE_COMPACTION: For high-order allocations, reclaim a number of
66  *			order-0 pages and then compact the zone
67  */
68 typedef unsigned __bitwise__ reclaim_mode_t;
69 #define RECLAIM_MODE_SINGLE		((__force reclaim_mode_t)0x01u)
70 #define RECLAIM_MODE_ASYNC		((__force reclaim_mode_t)0x02u)
71 #define RECLAIM_MODE_SYNC		((__force reclaim_mode_t)0x04u)
72 #define RECLAIM_MODE_LUMPYRECLAIM	((__force reclaim_mode_t)0x08u)
73 #define RECLAIM_MODE_COMPACTION		((__force reclaim_mode_t)0x10u)
74 
75 struct scan_control {
76 	/* Incremented by the number of inactive pages that were scanned */
77 	unsigned long nr_scanned;
78 
79 	/* Number of pages freed so far during a call to shrink_zones() */
80 	unsigned long nr_reclaimed;
81 
82 	/* How many pages shrink_list() should reclaim */
83 	unsigned long nr_to_reclaim;
84 
85 	unsigned long hibernation_mode;
86 
87 	/* This context's GFP mask */
88 	gfp_t gfp_mask;
89 
90 	int may_writepage;
91 
92 	/* Can mapped pages be reclaimed? */
93 	int may_unmap;
94 
95 	/* Can pages be swapped as part of reclaim? */
96 	int may_swap;
97 
98 	int swappiness;
99 
100 	int order;
101 
102 	/*
103 	 * Intend to reclaim enough continuous memory rather than reclaim
104 	 * enough amount of memory. i.e, mode for high order allocation.
105 	 */
106 	reclaim_mode_t reclaim_mode;
107 
108 	/* Which cgroup do we reclaim from */
109 	struct mem_cgroup *mem_cgroup;
110 
111 	/*
112 	 * Nodemask of nodes allowed by the caller. If NULL, all nodes
113 	 * are scanned.
114 	 */
115 	nodemask_t	*nodemask;
116 };
117 
118 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
119 
120 #ifdef ARCH_HAS_PREFETCH
121 #define prefetch_prev_lru_page(_page, _base, _field)			\
122 	do {								\
123 		if ((_page)->lru.prev != _base) {			\
124 			struct page *prev;				\
125 									\
126 			prev = lru_to_page(&(_page->lru));		\
127 			prefetch(&prev->_field);			\
128 		}							\
129 	} while (0)
130 #else
131 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
132 #endif
133 
134 #ifdef ARCH_HAS_PREFETCHW
135 #define prefetchw_prev_lru_page(_page, _base, _field)			\
136 	do {								\
137 		if ((_page)->lru.prev != _base) {			\
138 			struct page *prev;				\
139 									\
140 			prev = lru_to_page(&(_page->lru));		\
141 			prefetchw(&prev->_field);			\
142 		}							\
143 	} while (0)
144 #else
145 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
146 #endif
147 
148 /*
149  * From 0 .. 100.  Higher means more swappy.
150  */
151 int vm_swappiness = 60;
152 long vm_total_pages;	/* The total number of pages which the VM controls */
153 
154 static LIST_HEAD(shrinker_list);
155 static DECLARE_RWSEM(shrinker_rwsem);
156 
157 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
158 #define scanning_global_lru(sc)	(!(sc)->mem_cgroup)
159 #else
160 #define scanning_global_lru(sc)	(1)
161 #endif
162 
163 static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
164 						  struct scan_control *sc)
165 {
166 	if (!scanning_global_lru(sc))
167 		return mem_cgroup_get_reclaim_stat(sc->mem_cgroup, zone);
168 
169 	return &zone->reclaim_stat;
170 }
171 
172 static unsigned long zone_nr_lru_pages(struct zone *zone,
173 				struct scan_control *sc, enum lru_list lru)
174 {
175 	if (!scanning_global_lru(sc))
176 		return mem_cgroup_zone_nr_lru_pages(sc->mem_cgroup, zone, lru);
177 
178 	return zone_page_state(zone, NR_LRU_BASE + lru);
179 }
180 
181 
182 /*
183  * Add a shrinker callback to be called from the vm
184  */
185 void register_shrinker(struct shrinker *shrinker)
186 {
187 	shrinker->nr = 0;
188 	down_write(&shrinker_rwsem);
189 	list_add_tail(&shrinker->list, &shrinker_list);
190 	up_write(&shrinker_rwsem);
191 }
192 EXPORT_SYMBOL(register_shrinker);
193 
194 /*
195  * Remove one
196  */
197 void unregister_shrinker(struct shrinker *shrinker)
198 {
199 	down_write(&shrinker_rwsem);
200 	list_del(&shrinker->list);
201 	up_write(&shrinker_rwsem);
202 }
203 EXPORT_SYMBOL(unregister_shrinker);
204 
205 static inline int do_shrinker_shrink(struct shrinker *shrinker,
206 				     struct shrink_control *sc,
207 				     unsigned long nr_to_scan)
208 {
209 	sc->nr_to_scan = nr_to_scan;
210 	return (*shrinker->shrink)(shrinker, sc);
211 }
212 
213 #define SHRINK_BATCH 128
214 /*
215  * Call the shrink functions to age shrinkable caches
216  *
217  * Here we assume it costs one seek to replace a lru page and that it also
218  * takes a seek to recreate a cache object.  With this in mind we age equal
219  * percentages of the lru and ageable caches.  This should balance the seeks
220  * generated by these structures.
221  *
222  * If the vm encountered mapped pages on the LRU it increase the pressure on
223  * slab to avoid swapping.
224  *
225  * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
226  *
227  * `lru_pages' represents the number of on-LRU pages in all the zones which
228  * are eligible for the caller's allocation attempt.  It is used for balancing
229  * slab reclaim versus page reclaim.
230  *
231  * Returns the number of slab objects which we shrunk.
232  */
233 unsigned long shrink_slab(struct shrink_control *shrink,
234 			  unsigned long nr_pages_scanned,
235 			  unsigned long lru_pages)
236 {
237 	struct shrinker *shrinker;
238 	unsigned long ret = 0;
239 
240 	if (nr_pages_scanned == 0)
241 		nr_pages_scanned = SWAP_CLUSTER_MAX;
242 
243 	if (!down_read_trylock(&shrinker_rwsem)) {
244 		/* Assume we'll be able to shrink next time */
245 		ret = 1;
246 		goto out;
247 	}
248 
249 	list_for_each_entry(shrinker, &shrinker_list, list) {
250 		unsigned long long delta;
251 		unsigned long total_scan;
252 		unsigned long max_pass;
253 		int shrink_ret = 0;
254 		long nr;
255 		long new_nr;
256 		long batch_size = shrinker->batch ? shrinker->batch
257 						  : SHRINK_BATCH;
258 
259 		/*
260 		 * copy the current shrinker scan count into a local variable
261 		 * and zero it so that other concurrent shrinker invocations
262 		 * don't also do this scanning work.
263 		 */
264 		do {
265 			nr = shrinker->nr;
266 		} while (cmpxchg(&shrinker->nr, nr, 0) != nr);
267 
268 		total_scan = nr;
269 		max_pass = do_shrinker_shrink(shrinker, shrink, 0);
270 		delta = (4 * nr_pages_scanned) / shrinker->seeks;
271 		delta *= max_pass;
272 		do_div(delta, lru_pages + 1);
273 		total_scan += delta;
274 		if (total_scan < 0) {
275 			printk(KERN_ERR "shrink_slab: %pF negative objects to "
276 			       "delete nr=%ld\n",
277 			       shrinker->shrink, total_scan);
278 			total_scan = max_pass;
279 		}
280 
281 		/*
282 		 * We need to avoid excessive windup on filesystem shrinkers
283 		 * due to large numbers of GFP_NOFS allocations causing the
284 		 * shrinkers to return -1 all the time. This results in a large
285 		 * nr being built up so when a shrink that can do some work
286 		 * comes along it empties the entire cache due to nr >>>
287 		 * max_pass.  This is bad for sustaining a working set in
288 		 * memory.
289 		 *
290 		 * Hence only allow the shrinker to scan the entire cache when
291 		 * a large delta change is calculated directly.
292 		 */
293 		if (delta < max_pass / 4)
294 			total_scan = min(total_scan, max_pass / 2);
295 
296 		/*
297 		 * Avoid risking looping forever due to too large nr value:
298 		 * never try to free more than twice the estimate number of
299 		 * freeable entries.
300 		 */
301 		if (total_scan > max_pass * 2)
302 			total_scan = max_pass * 2;
303 
304 		trace_mm_shrink_slab_start(shrinker, shrink, nr,
305 					nr_pages_scanned, lru_pages,
306 					max_pass, delta, total_scan);
307 
308 		while (total_scan >= batch_size) {
309 			int nr_before;
310 
311 			nr_before = do_shrinker_shrink(shrinker, shrink, 0);
312 			shrink_ret = do_shrinker_shrink(shrinker, shrink,
313 							batch_size);
314 			if (shrink_ret == -1)
315 				break;
316 			if (shrink_ret < nr_before)
317 				ret += nr_before - shrink_ret;
318 			count_vm_events(SLABS_SCANNED, batch_size);
319 			total_scan -= batch_size;
320 
321 			cond_resched();
322 		}
323 
324 		/*
325 		 * move the unused scan count back into the shrinker in a
326 		 * manner that handles concurrent updates. If we exhausted the
327 		 * scan, there is no need to do an update.
328 		 */
329 		do {
330 			nr = shrinker->nr;
331 			new_nr = total_scan + nr;
332 			if (total_scan <= 0)
333 				break;
334 		} while (cmpxchg(&shrinker->nr, nr, new_nr) != nr);
335 
336 		trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
337 	}
338 	up_read(&shrinker_rwsem);
339 out:
340 	cond_resched();
341 	return ret;
342 }
343 
344 static void set_reclaim_mode(int priority, struct scan_control *sc,
345 				   bool sync)
346 {
347 	reclaim_mode_t syncmode = sync ? RECLAIM_MODE_SYNC : RECLAIM_MODE_ASYNC;
348 
349 	/*
350 	 * Initially assume we are entering either lumpy reclaim or
351 	 * reclaim/compaction.Depending on the order, we will either set the
352 	 * sync mode or just reclaim order-0 pages later.
353 	 */
354 	if (COMPACTION_BUILD)
355 		sc->reclaim_mode = RECLAIM_MODE_COMPACTION;
356 	else
357 		sc->reclaim_mode = RECLAIM_MODE_LUMPYRECLAIM;
358 
359 	/*
360 	 * Avoid using lumpy reclaim or reclaim/compaction if possible by
361 	 * restricting when its set to either costly allocations or when
362 	 * under memory pressure
363 	 */
364 	if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
365 		sc->reclaim_mode |= syncmode;
366 	else if (sc->order && priority < DEF_PRIORITY - 2)
367 		sc->reclaim_mode |= syncmode;
368 	else
369 		sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
370 }
371 
372 static void reset_reclaim_mode(struct scan_control *sc)
373 {
374 	sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
375 }
376 
377 static inline int is_page_cache_freeable(struct page *page)
378 {
379 	/*
380 	 * A freeable page cache page is referenced only by the caller
381 	 * that isolated the page, the page cache radix tree and
382 	 * optional buffer heads at page->private.
383 	 */
384 	return page_count(page) - page_has_private(page) == 2;
385 }
386 
387 static int may_write_to_queue(struct backing_dev_info *bdi,
388 			      struct scan_control *sc)
389 {
390 	if (current->flags & PF_SWAPWRITE)
391 		return 1;
392 	if (!bdi_write_congested(bdi))
393 		return 1;
394 	if (bdi == current->backing_dev_info)
395 		return 1;
396 
397 	/* lumpy reclaim for hugepage often need a lot of write */
398 	if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
399 		return 1;
400 	return 0;
401 }
402 
403 /*
404  * We detected a synchronous write error writing a page out.  Probably
405  * -ENOSPC.  We need to propagate that into the address_space for a subsequent
406  * fsync(), msync() or close().
407  *
408  * The tricky part is that after writepage we cannot touch the mapping: nothing
409  * prevents it from being freed up.  But we have a ref on the page and once
410  * that page is locked, the mapping is pinned.
411  *
412  * We're allowed to run sleeping lock_page() here because we know the caller has
413  * __GFP_FS.
414  */
415 static void handle_write_error(struct address_space *mapping,
416 				struct page *page, int error)
417 {
418 	lock_page(page);
419 	if (page_mapping(page) == mapping)
420 		mapping_set_error(mapping, error);
421 	unlock_page(page);
422 }
423 
424 /* possible outcome of pageout() */
425 typedef enum {
426 	/* failed to write page out, page is locked */
427 	PAGE_KEEP,
428 	/* move page to the active list, page is locked */
429 	PAGE_ACTIVATE,
430 	/* page has been sent to the disk successfully, page is unlocked */
431 	PAGE_SUCCESS,
432 	/* page is clean and locked */
433 	PAGE_CLEAN,
434 } pageout_t;
435 
436 /*
437  * pageout is called by shrink_page_list() for each dirty page.
438  * Calls ->writepage().
439  */
440 static pageout_t pageout(struct page *page, struct address_space *mapping,
441 			 struct scan_control *sc)
442 {
443 	/*
444 	 * If the page is dirty, only perform writeback if that write
445 	 * will be non-blocking.  To prevent this allocation from being
446 	 * stalled by pagecache activity.  But note that there may be
447 	 * stalls if we need to run get_block().  We could test
448 	 * PagePrivate for that.
449 	 *
450 	 * If this process is currently in __generic_file_aio_write() against
451 	 * this page's queue, we can perform writeback even if that
452 	 * will block.
453 	 *
454 	 * If the page is swapcache, write it back even if that would
455 	 * block, for some throttling. This happens by accident, because
456 	 * swap_backing_dev_info is bust: it doesn't reflect the
457 	 * congestion state of the swapdevs.  Easy to fix, if needed.
458 	 */
459 	if (!is_page_cache_freeable(page))
460 		return PAGE_KEEP;
461 	if (!mapping) {
462 		/*
463 		 * Some data journaling orphaned pages can have
464 		 * page->mapping == NULL while being dirty with clean buffers.
465 		 */
466 		if (page_has_private(page)) {
467 			if (try_to_free_buffers(page)) {
468 				ClearPageDirty(page);
469 				printk("%s: orphaned page\n", __func__);
470 				return PAGE_CLEAN;
471 			}
472 		}
473 		return PAGE_KEEP;
474 	}
475 	if (mapping->a_ops->writepage == NULL)
476 		return PAGE_ACTIVATE;
477 	if (!may_write_to_queue(mapping->backing_dev_info, sc))
478 		return PAGE_KEEP;
479 
480 	if (clear_page_dirty_for_io(page)) {
481 		int res;
482 		struct writeback_control wbc = {
483 			.sync_mode = WB_SYNC_NONE,
484 			.nr_to_write = SWAP_CLUSTER_MAX,
485 			.range_start = 0,
486 			.range_end = LLONG_MAX,
487 			.for_reclaim = 1,
488 		};
489 
490 		SetPageReclaim(page);
491 		res = mapping->a_ops->writepage(page, &wbc);
492 		if (res < 0)
493 			handle_write_error(mapping, page, res);
494 		if (res == AOP_WRITEPAGE_ACTIVATE) {
495 			ClearPageReclaim(page);
496 			return PAGE_ACTIVATE;
497 		}
498 
499 		/*
500 		 * Wait on writeback if requested to. This happens when
501 		 * direct reclaiming a large contiguous area and the
502 		 * first attempt to free a range of pages fails.
503 		 */
504 		if (PageWriteback(page) &&
505 		    (sc->reclaim_mode & RECLAIM_MODE_SYNC))
506 			wait_on_page_writeback(page);
507 
508 		if (!PageWriteback(page)) {
509 			/* synchronous write or broken a_ops? */
510 			ClearPageReclaim(page);
511 		}
512 		trace_mm_vmscan_writepage(page,
513 			trace_reclaim_flags(page, sc->reclaim_mode));
514 		inc_zone_page_state(page, NR_VMSCAN_WRITE);
515 		return PAGE_SUCCESS;
516 	}
517 
518 	return PAGE_CLEAN;
519 }
520 
521 /*
522  * Same as remove_mapping, but if the page is removed from the mapping, it
523  * gets returned with a refcount of 0.
524  */
525 static int __remove_mapping(struct address_space *mapping, struct page *page)
526 {
527 	BUG_ON(!PageLocked(page));
528 	BUG_ON(mapping != page_mapping(page));
529 
530 	spin_lock_irq(&mapping->tree_lock);
531 	/*
532 	 * The non racy check for a busy page.
533 	 *
534 	 * Must be careful with the order of the tests. When someone has
535 	 * a ref to the page, it may be possible that they dirty it then
536 	 * drop the reference. So if PageDirty is tested before page_count
537 	 * here, then the following race may occur:
538 	 *
539 	 * get_user_pages(&page);
540 	 * [user mapping goes away]
541 	 * write_to(page);
542 	 *				!PageDirty(page)    [good]
543 	 * SetPageDirty(page);
544 	 * put_page(page);
545 	 *				!page_count(page)   [good, discard it]
546 	 *
547 	 * [oops, our write_to data is lost]
548 	 *
549 	 * Reversing the order of the tests ensures such a situation cannot
550 	 * escape unnoticed. The smp_rmb is needed to ensure the page->flags
551 	 * load is not satisfied before that of page->_count.
552 	 *
553 	 * Note that if SetPageDirty is always performed via set_page_dirty,
554 	 * and thus under tree_lock, then this ordering is not required.
555 	 */
556 	if (!page_freeze_refs(page, 2))
557 		goto cannot_free;
558 	/* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
559 	if (unlikely(PageDirty(page))) {
560 		page_unfreeze_refs(page, 2);
561 		goto cannot_free;
562 	}
563 
564 	if (PageSwapCache(page)) {
565 		swp_entry_t swap = { .val = page_private(page) };
566 		__delete_from_swap_cache(page);
567 		spin_unlock_irq(&mapping->tree_lock);
568 		swapcache_free(swap, page);
569 	} else {
570 		void (*freepage)(struct page *);
571 
572 		freepage = mapping->a_ops->freepage;
573 
574 		__delete_from_page_cache(page);
575 		spin_unlock_irq(&mapping->tree_lock);
576 		mem_cgroup_uncharge_cache_page(page);
577 
578 		if (freepage != NULL)
579 			freepage(page);
580 	}
581 
582 	return 1;
583 
584 cannot_free:
585 	spin_unlock_irq(&mapping->tree_lock);
586 	return 0;
587 }
588 
589 /*
590  * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
591  * someone else has a ref on the page, abort and return 0.  If it was
592  * successfully detached, return 1.  Assumes the caller has a single ref on
593  * this page.
594  */
595 int remove_mapping(struct address_space *mapping, struct page *page)
596 {
597 	if (__remove_mapping(mapping, page)) {
598 		/*
599 		 * Unfreezing the refcount with 1 rather than 2 effectively
600 		 * drops the pagecache ref for us without requiring another
601 		 * atomic operation.
602 		 */
603 		page_unfreeze_refs(page, 1);
604 		return 1;
605 	}
606 	return 0;
607 }
608 
609 /**
610  * putback_lru_page - put previously isolated page onto appropriate LRU list
611  * @page: page to be put back to appropriate lru list
612  *
613  * Add previously isolated @page to appropriate LRU list.
614  * Page may still be unevictable for other reasons.
615  *
616  * lru_lock must not be held, interrupts must be enabled.
617  */
618 void putback_lru_page(struct page *page)
619 {
620 	int lru;
621 	int active = !!TestClearPageActive(page);
622 	int was_unevictable = PageUnevictable(page);
623 
624 	VM_BUG_ON(PageLRU(page));
625 
626 redo:
627 	ClearPageUnevictable(page);
628 
629 	if (page_evictable(page, NULL)) {
630 		/*
631 		 * For evictable pages, we can use the cache.
632 		 * In event of a race, worst case is we end up with an
633 		 * unevictable page on [in]active list.
634 		 * We know how to handle that.
635 		 */
636 		lru = active + page_lru_base_type(page);
637 		lru_cache_add_lru(page, lru);
638 	} else {
639 		/*
640 		 * Put unevictable pages directly on zone's unevictable
641 		 * list.
642 		 */
643 		lru = LRU_UNEVICTABLE;
644 		add_page_to_unevictable_list(page);
645 		/*
646 		 * When racing with an mlock clearing (page is
647 		 * unlocked), make sure that if the other thread does
648 		 * not observe our setting of PG_lru and fails
649 		 * isolation, we see PG_mlocked cleared below and move
650 		 * the page back to the evictable list.
651 		 *
652 		 * The other side is TestClearPageMlocked().
653 		 */
654 		smp_mb();
655 	}
656 
657 	/*
658 	 * page's status can change while we move it among lru. If an evictable
659 	 * page is on unevictable list, it never be freed. To avoid that,
660 	 * check after we added it to the list, again.
661 	 */
662 	if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) {
663 		if (!isolate_lru_page(page)) {
664 			put_page(page);
665 			goto redo;
666 		}
667 		/* This means someone else dropped this page from LRU
668 		 * So, it will be freed or putback to LRU again. There is
669 		 * nothing to do here.
670 		 */
671 	}
672 
673 	if (was_unevictable && lru != LRU_UNEVICTABLE)
674 		count_vm_event(UNEVICTABLE_PGRESCUED);
675 	else if (!was_unevictable && lru == LRU_UNEVICTABLE)
676 		count_vm_event(UNEVICTABLE_PGCULLED);
677 
678 	put_page(page);		/* drop ref from isolate */
679 }
680 
681 enum page_references {
682 	PAGEREF_RECLAIM,
683 	PAGEREF_RECLAIM_CLEAN,
684 	PAGEREF_KEEP,
685 	PAGEREF_ACTIVATE,
686 };
687 
688 static enum page_references page_check_references(struct page *page,
689 						  struct scan_control *sc)
690 {
691 	int referenced_ptes, referenced_page;
692 	unsigned long vm_flags;
693 
694 	referenced_ptes = page_referenced(page, 1, sc->mem_cgroup, &vm_flags);
695 	referenced_page = TestClearPageReferenced(page);
696 
697 	/* Lumpy reclaim - ignore references */
698 	if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM)
699 		return PAGEREF_RECLAIM;
700 
701 	/*
702 	 * Mlock lost the isolation race with us.  Let try_to_unmap()
703 	 * move the page to the unevictable list.
704 	 */
705 	if (vm_flags & VM_LOCKED)
706 		return PAGEREF_RECLAIM;
707 
708 	if (referenced_ptes) {
709 		if (PageAnon(page))
710 			return PAGEREF_ACTIVATE;
711 		/*
712 		 * All mapped pages start out with page table
713 		 * references from the instantiating fault, so we need
714 		 * to look twice if a mapped file page is used more
715 		 * than once.
716 		 *
717 		 * Mark it and spare it for another trip around the
718 		 * inactive list.  Another page table reference will
719 		 * lead to its activation.
720 		 *
721 		 * Note: the mark is set for activated pages as well
722 		 * so that recently deactivated but used pages are
723 		 * quickly recovered.
724 		 */
725 		SetPageReferenced(page);
726 
727 		if (referenced_page)
728 			return PAGEREF_ACTIVATE;
729 
730 		return PAGEREF_KEEP;
731 	}
732 
733 	/* Reclaim if clean, defer dirty pages to writeback */
734 	if (referenced_page && !PageSwapBacked(page))
735 		return PAGEREF_RECLAIM_CLEAN;
736 
737 	return PAGEREF_RECLAIM;
738 }
739 
740 static noinline_for_stack void free_page_list(struct list_head *free_pages)
741 {
742 	struct pagevec freed_pvec;
743 	struct page *page, *tmp;
744 
745 	pagevec_init(&freed_pvec, 1);
746 
747 	list_for_each_entry_safe(page, tmp, free_pages, lru) {
748 		list_del(&page->lru);
749 		if (!pagevec_add(&freed_pvec, page)) {
750 			__pagevec_free(&freed_pvec);
751 			pagevec_reinit(&freed_pvec);
752 		}
753 	}
754 
755 	pagevec_free(&freed_pvec);
756 }
757 
758 /*
759  * shrink_page_list() returns the number of reclaimed pages
760  */
761 static unsigned long shrink_page_list(struct list_head *page_list,
762 				      struct zone *zone,
763 				      struct scan_control *sc)
764 {
765 	LIST_HEAD(ret_pages);
766 	LIST_HEAD(free_pages);
767 	int pgactivate = 0;
768 	unsigned long nr_dirty = 0;
769 	unsigned long nr_congested = 0;
770 	unsigned long nr_reclaimed = 0;
771 
772 	cond_resched();
773 
774 	while (!list_empty(page_list)) {
775 		enum page_references references;
776 		struct address_space *mapping;
777 		struct page *page;
778 		int may_enter_fs;
779 
780 		cond_resched();
781 
782 		page = lru_to_page(page_list);
783 		list_del(&page->lru);
784 
785 		if (!trylock_page(page))
786 			goto keep;
787 
788 		VM_BUG_ON(PageActive(page));
789 		VM_BUG_ON(page_zone(page) != zone);
790 
791 		sc->nr_scanned++;
792 
793 		if (unlikely(!page_evictable(page, NULL)))
794 			goto cull_mlocked;
795 
796 		if (!sc->may_unmap && page_mapped(page))
797 			goto keep_locked;
798 
799 		/* Double the slab pressure for mapped and swapcache pages */
800 		if (page_mapped(page) || PageSwapCache(page))
801 			sc->nr_scanned++;
802 
803 		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
804 			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
805 
806 		if (PageWriteback(page)) {
807 			/*
808 			 * Synchronous reclaim is performed in two passes,
809 			 * first an asynchronous pass over the list to
810 			 * start parallel writeback, and a second synchronous
811 			 * pass to wait for the IO to complete.  Wait here
812 			 * for any page for which writeback has already
813 			 * started.
814 			 */
815 			if ((sc->reclaim_mode & RECLAIM_MODE_SYNC) &&
816 			    may_enter_fs)
817 				wait_on_page_writeback(page);
818 			else {
819 				unlock_page(page);
820 				goto keep_lumpy;
821 			}
822 		}
823 
824 		references = page_check_references(page, sc);
825 		switch (references) {
826 		case PAGEREF_ACTIVATE:
827 			goto activate_locked;
828 		case PAGEREF_KEEP:
829 			goto keep_locked;
830 		case PAGEREF_RECLAIM:
831 		case PAGEREF_RECLAIM_CLEAN:
832 			; /* try to reclaim the page below */
833 		}
834 
835 		/*
836 		 * Anonymous process memory has backing store?
837 		 * Try to allocate it some swap space here.
838 		 */
839 		if (PageAnon(page) && !PageSwapCache(page)) {
840 			if (!(sc->gfp_mask & __GFP_IO))
841 				goto keep_locked;
842 			if (!add_to_swap(page))
843 				goto activate_locked;
844 			may_enter_fs = 1;
845 		}
846 
847 		mapping = page_mapping(page);
848 
849 		/*
850 		 * The page is mapped into the page tables of one or more
851 		 * processes. Try to unmap it here.
852 		 */
853 		if (page_mapped(page) && mapping) {
854 			switch (try_to_unmap(page, TTU_UNMAP)) {
855 			case SWAP_FAIL:
856 				goto activate_locked;
857 			case SWAP_AGAIN:
858 				goto keep_locked;
859 			case SWAP_MLOCK:
860 				goto cull_mlocked;
861 			case SWAP_SUCCESS:
862 				; /* try to free the page below */
863 			}
864 		}
865 
866 		if (PageDirty(page)) {
867 			nr_dirty++;
868 
869 			if (references == PAGEREF_RECLAIM_CLEAN)
870 				goto keep_locked;
871 			if (!may_enter_fs)
872 				goto keep_locked;
873 			if (!sc->may_writepage)
874 				goto keep_locked;
875 
876 			/* Page is dirty, try to write it out here */
877 			switch (pageout(page, mapping, sc)) {
878 			case PAGE_KEEP:
879 				nr_congested++;
880 				goto keep_locked;
881 			case PAGE_ACTIVATE:
882 				goto activate_locked;
883 			case PAGE_SUCCESS:
884 				if (PageWriteback(page))
885 					goto keep_lumpy;
886 				if (PageDirty(page))
887 					goto keep;
888 
889 				/*
890 				 * A synchronous write - probably a ramdisk.  Go
891 				 * ahead and try to reclaim the page.
892 				 */
893 				if (!trylock_page(page))
894 					goto keep;
895 				if (PageDirty(page) || PageWriteback(page))
896 					goto keep_locked;
897 				mapping = page_mapping(page);
898 			case PAGE_CLEAN:
899 				; /* try to free the page below */
900 			}
901 		}
902 
903 		/*
904 		 * If the page has buffers, try to free the buffer mappings
905 		 * associated with this page. If we succeed we try to free
906 		 * the page as well.
907 		 *
908 		 * We do this even if the page is PageDirty().
909 		 * try_to_release_page() does not perform I/O, but it is
910 		 * possible for a page to have PageDirty set, but it is actually
911 		 * clean (all its buffers are clean).  This happens if the
912 		 * buffers were written out directly, with submit_bh(). ext3
913 		 * will do this, as well as the blockdev mapping.
914 		 * try_to_release_page() will discover that cleanness and will
915 		 * drop the buffers and mark the page clean - it can be freed.
916 		 *
917 		 * Rarely, pages can have buffers and no ->mapping.  These are
918 		 * the pages which were not successfully invalidated in
919 		 * truncate_complete_page().  We try to drop those buffers here
920 		 * and if that worked, and the page is no longer mapped into
921 		 * process address space (page_count == 1) it can be freed.
922 		 * Otherwise, leave the page on the LRU so it is swappable.
923 		 */
924 		if (page_has_private(page)) {
925 			if (!try_to_release_page(page, sc->gfp_mask))
926 				goto activate_locked;
927 			if (!mapping && page_count(page) == 1) {
928 				unlock_page(page);
929 				if (put_page_testzero(page))
930 					goto free_it;
931 				else {
932 					/*
933 					 * rare race with speculative reference.
934 					 * the speculative reference will free
935 					 * this page shortly, so we may
936 					 * increment nr_reclaimed here (and
937 					 * leave it off the LRU).
938 					 */
939 					nr_reclaimed++;
940 					continue;
941 				}
942 			}
943 		}
944 
945 		if (!mapping || !__remove_mapping(mapping, page))
946 			goto keep_locked;
947 
948 		/*
949 		 * At this point, we have no other references and there is
950 		 * no way to pick any more up (removed from LRU, removed
951 		 * from pagecache). Can use non-atomic bitops now (and
952 		 * we obviously don't have to worry about waking up a process
953 		 * waiting on the page lock, because there are no references.
954 		 */
955 		__clear_page_locked(page);
956 free_it:
957 		nr_reclaimed++;
958 
959 		/*
960 		 * Is there need to periodically free_page_list? It would
961 		 * appear not as the counts should be low
962 		 */
963 		list_add(&page->lru, &free_pages);
964 		continue;
965 
966 cull_mlocked:
967 		if (PageSwapCache(page))
968 			try_to_free_swap(page);
969 		unlock_page(page);
970 		putback_lru_page(page);
971 		reset_reclaim_mode(sc);
972 		continue;
973 
974 activate_locked:
975 		/* Not a candidate for swapping, so reclaim swap space. */
976 		if (PageSwapCache(page) && vm_swap_full())
977 			try_to_free_swap(page);
978 		VM_BUG_ON(PageActive(page));
979 		SetPageActive(page);
980 		pgactivate++;
981 keep_locked:
982 		unlock_page(page);
983 keep:
984 		reset_reclaim_mode(sc);
985 keep_lumpy:
986 		list_add(&page->lru, &ret_pages);
987 		VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
988 	}
989 
990 	/*
991 	 * Tag a zone as congested if all the dirty pages encountered were
992 	 * backed by a congested BDI. In this case, reclaimers should just
993 	 * back off and wait for congestion to clear because further reclaim
994 	 * will encounter the same problem
995 	 */
996 	if (nr_dirty && nr_dirty == nr_congested && scanning_global_lru(sc))
997 		zone_set_flag(zone, ZONE_CONGESTED);
998 
999 	free_page_list(&free_pages);
1000 
1001 	list_splice(&ret_pages, page_list);
1002 	count_vm_events(PGACTIVATE, pgactivate);
1003 	return nr_reclaimed;
1004 }
1005 
1006 /*
1007  * Attempt to remove the specified page from its LRU.  Only take this page
1008  * if it is of the appropriate PageActive status.  Pages which are being
1009  * freed elsewhere are also ignored.
1010  *
1011  * page:	page to consider
1012  * mode:	one of the LRU isolation modes defined above
1013  *
1014  * returns 0 on success, -ve errno on failure.
1015  */
1016 int __isolate_lru_page(struct page *page, int mode, int file)
1017 {
1018 	int ret = -EINVAL;
1019 
1020 	/* Only take pages on the LRU. */
1021 	if (!PageLRU(page))
1022 		return ret;
1023 
1024 	/*
1025 	 * When checking the active state, we need to be sure we are
1026 	 * dealing with comparible boolean values.  Take the logical not
1027 	 * of each.
1028 	 */
1029 	if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode))
1030 		return ret;
1031 
1032 	if (mode != ISOLATE_BOTH && page_is_file_cache(page) != file)
1033 		return ret;
1034 
1035 	/*
1036 	 * When this function is being called for lumpy reclaim, we
1037 	 * initially look into all LRU pages, active, inactive and
1038 	 * unevictable; only give shrink_page_list evictable pages.
1039 	 */
1040 	if (PageUnevictable(page))
1041 		return ret;
1042 
1043 	ret = -EBUSY;
1044 
1045 	if (likely(get_page_unless_zero(page))) {
1046 		/*
1047 		 * Be careful not to clear PageLRU until after we're
1048 		 * sure the page is not being freed elsewhere -- the
1049 		 * page release code relies on it.
1050 		 */
1051 		ClearPageLRU(page);
1052 		ret = 0;
1053 	}
1054 
1055 	return ret;
1056 }
1057 
1058 /*
1059  * zone->lru_lock is heavily contended.  Some of the functions that
1060  * shrink the lists perform better by taking out a batch of pages
1061  * and working on them outside the LRU lock.
1062  *
1063  * For pagecache intensive workloads, this function is the hottest
1064  * spot in the kernel (apart from copy_*_user functions).
1065  *
1066  * Appropriate locks must be held before calling this function.
1067  *
1068  * @nr_to_scan:	The number of pages to look through on the list.
1069  * @src:	The LRU list to pull pages off.
1070  * @dst:	The temp list to put pages on to.
1071  * @scanned:	The number of pages that were scanned.
1072  * @order:	The caller's attempted allocation order
1073  * @mode:	One of the LRU isolation modes
1074  * @file:	True [1] if isolating file [!anon] pages
1075  *
1076  * returns how many pages were moved onto *@dst.
1077  */
1078 static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1079 		struct list_head *src, struct list_head *dst,
1080 		unsigned long *scanned, int order, int mode, int file)
1081 {
1082 	unsigned long nr_taken = 0;
1083 	unsigned long nr_lumpy_taken = 0;
1084 	unsigned long nr_lumpy_dirty = 0;
1085 	unsigned long nr_lumpy_failed = 0;
1086 	unsigned long scan;
1087 
1088 	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1089 		struct page *page;
1090 		unsigned long pfn;
1091 		unsigned long end_pfn;
1092 		unsigned long page_pfn;
1093 		int zone_id;
1094 
1095 		page = lru_to_page(src);
1096 		prefetchw_prev_lru_page(page, src, flags);
1097 
1098 		VM_BUG_ON(!PageLRU(page));
1099 
1100 		switch (__isolate_lru_page(page, mode, file)) {
1101 		case 0:
1102 			list_move(&page->lru, dst);
1103 			mem_cgroup_del_lru(page);
1104 			nr_taken += hpage_nr_pages(page);
1105 			break;
1106 
1107 		case -EBUSY:
1108 			/* else it is being freed elsewhere */
1109 			list_move(&page->lru, src);
1110 			mem_cgroup_rotate_lru_list(page, page_lru(page));
1111 			continue;
1112 
1113 		default:
1114 			BUG();
1115 		}
1116 
1117 		if (!order)
1118 			continue;
1119 
1120 		/*
1121 		 * Attempt to take all pages in the order aligned region
1122 		 * surrounding the tag page.  Only take those pages of
1123 		 * the same active state as that tag page.  We may safely
1124 		 * round the target page pfn down to the requested order
1125 		 * as the mem_map is guaranteed valid out to MAX_ORDER,
1126 		 * where that page is in a different zone we will detect
1127 		 * it from its zone id and abort this block scan.
1128 		 */
1129 		zone_id = page_zone_id(page);
1130 		page_pfn = page_to_pfn(page);
1131 		pfn = page_pfn & ~((1 << order) - 1);
1132 		end_pfn = pfn + (1 << order);
1133 		for (; pfn < end_pfn; pfn++) {
1134 			struct page *cursor_page;
1135 
1136 			/* The target page is in the block, ignore it. */
1137 			if (unlikely(pfn == page_pfn))
1138 				continue;
1139 
1140 			/* Avoid holes within the zone. */
1141 			if (unlikely(!pfn_valid_within(pfn)))
1142 				break;
1143 
1144 			cursor_page = pfn_to_page(pfn);
1145 
1146 			/* Check that we have not crossed a zone boundary. */
1147 			if (unlikely(page_zone_id(cursor_page) != zone_id))
1148 				break;
1149 
1150 			/*
1151 			 * If we don't have enough swap space, reclaiming of
1152 			 * anon page which don't already have a swap slot is
1153 			 * pointless.
1154 			 */
1155 			if (nr_swap_pages <= 0 && PageAnon(cursor_page) &&
1156 			    !PageSwapCache(cursor_page))
1157 				break;
1158 
1159 			if (__isolate_lru_page(cursor_page, mode, file) == 0) {
1160 				list_move(&cursor_page->lru, dst);
1161 				mem_cgroup_del_lru(cursor_page);
1162 				nr_taken += hpage_nr_pages(page);
1163 				nr_lumpy_taken++;
1164 				if (PageDirty(cursor_page))
1165 					nr_lumpy_dirty++;
1166 				scan++;
1167 			} else {
1168 				/*
1169 				 * Check if the page is freed already.
1170 				 *
1171 				 * We can't use page_count() as that
1172 				 * requires compound_head and we don't
1173 				 * have a pin on the page here. If a
1174 				 * page is tail, we may or may not
1175 				 * have isolated the head, so assume
1176 				 * it's not free, it'd be tricky to
1177 				 * track the head status without a
1178 				 * page pin.
1179 				 */
1180 				if (!PageTail(cursor_page) &&
1181 				    !atomic_read(&cursor_page->_count))
1182 					continue;
1183 				break;
1184 			}
1185 		}
1186 
1187 		/* If we break out of the loop above, lumpy reclaim failed */
1188 		if (pfn < end_pfn)
1189 			nr_lumpy_failed++;
1190 	}
1191 
1192 	*scanned = scan;
1193 
1194 	trace_mm_vmscan_lru_isolate(order,
1195 			nr_to_scan, scan,
1196 			nr_taken,
1197 			nr_lumpy_taken, nr_lumpy_dirty, nr_lumpy_failed,
1198 			mode);
1199 	return nr_taken;
1200 }
1201 
1202 static unsigned long isolate_pages_global(unsigned long nr,
1203 					struct list_head *dst,
1204 					unsigned long *scanned, int order,
1205 					int mode, struct zone *z,
1206 					int active, int file)
1207 {
1208 	int lru = LRU_BASE;
1209 	if (active)
1210 		lru += LRU_ACTIVE;
1211 	if (file)
1212 		lru += LRU_FILE;
1213 	return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order,
1214 								mode, file);
1215 }
1216 
1217 /*
1218  * clear_active_flags() is a helper for shrink_active_list(), clearing
1219  * any active bits from the pages in the list.
1220  */
1221 static unsigned long clear_active_flags(struct list_head *page_list,
1222 					unsigned int *count)
1223 {
1224 	int nr_active = 0;
1225 	int lru;
1226 	struct page *page;
1227 
1228 	list_for_each_entry(page, page_list, lru) {
1229 		int numpages = hpage_nr_pages(page);
1230 		lru = page_lru_base_type(page);
1231 		if (PageActive(page)) {
1232 			lru += LRU_ACTIVE;
1233 			ClearPageActive(page);
1234 			nr_active += numpages;
1235 		}
1236 		if (count)
1237 			count[lru] += numpages;
1238 	}
1239 
1240 	return nr_active;
1241 }
1242 
1243 /**
1244  * isolate_lru_page - tries to isolate a page from its LRU list
1245  * @page: page to isolate from its LRU list
1246  *
1247  * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1248  * vmstat statistic corresponding to whatever LRU list the page was on.
1249  *
1250  * Returns 0 if the page was removed from an LRU list.
1251  * Returns -EBUSY if the page was not on an LRU list.
1252  *
1253  * The returned page will have PageLRU() cleared.  If it was found on
1254  * the active list, it will have PageActive set.  If it was found on
1255  * the unevictable list, it will have the PageUnevictable bit set. That flag
1256  * may need to be cleared by the caller before letting the page go.
1257  *
1258  * The vmstat statistic corresponding to the list on which the page was
1259  * found will be decremented.
1260  *
1261  * Restrictions:
1262  * (1) Must be called with an elevated refcount on the page. This is a
1263  *     fundamentnal difference from isolate_lru_pages (which is called
1264  *     without a stable reference).
1265  * (2) the lru_lock must not be held.
1266  * (3) interrupts must be enabled.
1267  */
1268 int isolate_lru_page(struct page *page)
1269 {
1270 	int ret = -EBUSY;
1271 
1272 	VM_BUG_ON(!page_count(page));
1273 
1274 	if (PageLRU(page)) {
1275 		struct zone *zone = page_zone(page);
1276 
1277 		spin_lock_irq(&zone->lru_lock);
1278 		if (PageLRU(page)) {
1279 			int lru = page_lru(page);
1280 			ret = 0;
1281 			get_page(page);
1282 			ClearPageLRU(page);
1283 
1284 			del_page_from_lru_list(zone, page, lru);
1285 		}
1286 		spin_unlock_irq(&zone->lru_lock);
1287 	}
1288 	return ret;
1289 }
1290 
1291 /*
1292  * Are there way too many processes in the direct reclaim path already?
1293  */
1294 static int too_many_isolated(struct zone *zone, int file,
1295 		struct scan_control *sc)
1296 {
1297 	unsigned long inactive, isolated;
1298 
1299 	if (current_is_kswapd())
1300 		return 0;
1301 
1302 	if (!scanning_global_lru(sc))
1303 		return 0;
1304 
1305 	if (file) {
1306 		inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1307 		isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1308 	} else {
1309 		inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1310 		isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1311 	}
1312 
1313 	return isolated > inactive;
1314 }
1315 
1316 /*
1317  * TODO: Try merging with migrations version of putback_lru_pages
1318  */
1319 static noinline_for_stack void
1320 putback_lru_pages(struct zone *zone, struct scan_control *sc,
1321 				unsigned long nr_anon, unsigned long nr_file,
1322 				struct list_head *page_list)
1323 {
1324 	struct page *page;
1325 	struct pagevec pvec;
1326 	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1327 
1328 	pagevec_init(&pvec, 1);
1329 
1330 	/*
1331 	 * Put back any unfreeable pages.
1332 	 */
1333 	spin_lock(&zone->lru_lock);
1334 	while (!list_empty(page_list)) {
1335 		int lru;
1336 		page = lru_to_page(page_list);
1337 		VM_BUG_ON(PageLRU(page));
1338 		list_del(&page->lru);
1339 		if (unlikely(!page_evictable(page, NULL))) {
1340 			spin_unlock_irq(&zone->lru_lock);
1341 			putback_lru_page(page);
1342 			spin_lock_irq(&zone->lru_lock);
1343 			continue;
1344 		}
1345 		SetPageLRU(page);
1346 		lru = page_lru(page);
1347 		add_page_to_lru_list(zone, page, lru);
1348 		if (is_active_lru(lru)) {
1349 			int file = is_file_lru(lru);
1350 			int numpages = hpage_nr_pages(page);
1351 			reclaim_stat->recent_rotated[file] += numpages;
1352 		}
1353 		if (!pagevec_add(&pvec, page)) {
1354 			spin_unlock_irq(&zone->lru_lock);
1355 			__pagevec_release(&pvec);
1356 			spin_lock_irq(&zone->lru_lock);
1357 		}
1358 	}
1359 	__mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon);
1360 	__mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file);
1361 
1362 	spin_unlock_irq(&zone->lru_lock);
1363 	pagevec_release(&pvec);
1364 }
1365 
1366 static noinline_for_stack void update_isolated_counts(struct zone *zone,
1367 					struct scan_control *sc,
1368 					unsigned long *nr_anon,
1369 					unsigned long *nr_file,
1370 					struct list_head *isolated_list)
1371 {
1372 	unsigned long nr_active;
1373 	unsigned int count[NR_LRU_LISTS] = { 0, };
1374 	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1375 
1376 	nr_active = clear_active_flags(isolated_list, count);
1377 	__count_vm_events(PGDEACTIVATE, nr_active);
1378 
1379 	__mod_zone_page_state(zone, NR_ACTIVE_FILE,
1380 			      -count[LRU_ACTIVE_FILE]);
1381 	__mod_zone_page_state(zone, NR_INACTIVE_FILE,
1382 			      -count[LRU_INACTIVE_FILE]);
1383 	__mod_zone_page_state(zone, NR_ACTIVE_ANON,
1384 			      -count[LRU_ACTIVE_ANON]);
1385 	__mod_zone_page_state(zone, NR_INACTIVE_ANON,
1386 			      -count[LRU_INACTIVE_ANON]);
1387 
1388 	*nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
1389 	*nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
1390 	__mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon);
1391 	__mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file);
1392 
1393 	reclaim_stat->recent_scanned[0] += *nr_anon;
1394 	reclaim_stat->recent_scanned[1] += *nr_file;
1395 }
1396 
1397 /*
1398  * Returns true if the caller should wait to clean dirty/writeback pages.
1399  *
1400  * If we are direct reclaiming for contiguous pages and we do not reclaim
1401  * everything in the list, try again and wait for writeback IO to complete.
1402  * This will stall high-order allocations noticeably. Only do that when really
1403  * need to free the pages under high memory pressure.
1404  */
1405 static inline bool should_reclaim_stall(unsigned long nr_taken,
1406 					unsigned long nr_freed,
1407 					int priority,
1408 					struct scan_control *sc)
1409 {
1410 	int lumpy_stall_priority;
1411 
1412 	/* kswapd should not stall on sync IO */
1413 	if (current_is_kswapd())
1414 		return false;
1415 
1416 	/* Only stall on lumpy reclaim */
1417 	if (sc->reclaim_mode & RECLAIM_MODE_SINGLE)
1418 		return false;
1419 
1420 	/* If we have relaimed everything on the isolated list, no stall */
1421 	if (nr_freed == nr_taken)
1422 		return false;
1423 
1424 	/*
1425 	 * For high-order allocations, there are two stall thresholds.
1426 	 * High-cost allocations stall immediately where as lower
1427 	 * order allocations such as stacks require the scanning
1428 	 * priority to be much higher before stalling.
1429 	 */
1430 	if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
1431 		lumpy_stall_priority = DEF_PRIORITY;
1432 	else
1433 		lumpy_stall_priority = DEF_PRIORITY / 3;
1434 
1435 	return priority <= lumpy_stall_priority;
1436 }
1437 
1438 /*
1439  * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
1440  * of reclaimed pages
1441  */
1442 static noinline_for_stack unsigned long
1443 shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
1444 			struct scan_control *sc, int priority, int file)
1445 {
1446 	LIST_HEAD(page_list);
1447 	unsigned long nr_scanned;
1448 	unsigned long nr_reclaimed = 0;
1449 	unsigned long nr_taken;
1450 	unsigned long nr_anon;
1451 	unsigned long nr_file;
1452 
1453 	while (unlikely(too_many_isolated(zone, file, sc))) {
1454 		congestion_wait(BLK_RW_ASYNC, HZ/10);
1455 
1456 		/* We are about to die and free our memory. Return now. */
1457 		if (fatal_signal_pending(current))
1458 			return SWAP_CLUSTER_MAX;
1459 	}
1460 
1461 	set_reclaim_mode(priority, sc, false);
1462 	lru_add_drain();
1463 	spin_lock_irq(&zone->lru_lock);
1464 
1465 	if (scanning_global_lru(sc)) {
1466 		nr_taken = isolate_pages_global(nr_to_scan,
1467 			&page_list, &nr_scanned, sc->order,
1468 			sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ?
1469 					ISOLATE_BOTH : ISOLATE_INACTIVE,
1470 			zone, 0, file);
1471 		zone->pages_scanned += nr_scanned;
1472 		if (current_is_kswapd())
1473 			__count_zone_vm_events(PGSCAN_KSWAPD, zone,
1474 					       nr_scanned);
1475 		else
1476 			__count_zone_vm_events(PGSCAN_DIRECT, zone,
1477 					       nr_scanned);
1478 	} else {
1479 		nr_taken = mem_cgroup_isolate_pages(nr_to_scan,
1480 			&page_list, &nr_scanned, sc->order,
1481 			sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ?
1482 					ISOLATE_BOTH : ISOLATE_INACTIVE,
1483 			zone, sc->mem_cgroup,
1484 			0, file);
1485 		/*
1486 		 * mem_cgroup_isolate_pages() keeps track of
1487 		 * scanned pages on its own.
1488 		 */
1489 	}
1490 
1491 	if (nr_taken == 0) {
1492 		spin_unlock_irq(&zone->lru_lock);
1493 		return 0;
1494 	}
1495 
1496 	update_isolated_counts(zone, sc, &nr_anon, &nr_file, &page_list);
1497 
1498 	spin_unlock_irq(&zone->lru_lock);
1499 
1500 	nr_reclaimed = shrink_page_list(&page_list, zone, sc);
1501 
1502 	/* Check if we should syncronously wait for writeback */
1503 	if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) {
1504 		set_reclaim_mode(priority, sc, true);
1505 		nr_reclaimed += shrink_page_list(&page_list, zone, sc);
1506 	}
1507 
1508 	local_irq_disable();
1509 	if (current_is_kswapd())
1510 		__count_vm_events(KSWAPD_STEAL, nr_reclaimed);
1511 	__count_zone_vm_events(PGSTEAL, zone, nr_reclaimed);
1512 
1513 	putback_lru_pages(zone, sc, nr_anon, nr_file, &page_list);
1514 
1515 	trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1516 		zone_idx(zone),
1517 		nr_scanned, nr_reclaimed,
1518 		priority,
1519 		trace_shrink_flags(file, sc->reclaim_mode));
1520 	return nr_reclaimed;
1521 }
1522 
1523 /*
1524  * This moves pages from the active list to the inactive list.
1525  *
1526  * We move them the other way if the page is referenced by one or more
1527  * processes, from rmap.
1528  *
1529  * If the pages are mostly unmapped, the processing is fast and it is
1530  * appropriate to hold zone->lru_lock across the whole operation.  But if
1531  * the pages are mapped, the processing is slow (page_referenced()) so we
1532  * should drop zone->lru_lock around each page.  It's impossible to balance
1533  * this, so instead we remove the pages from the LRU while processing them.
1534  * It is safe to rely on PG_active against the non-LRU pages in here because
1535  * nobody will play with that bit on a non-LRU page.
1536  *
1537  * The downside is that we have to touch page->_count against each page.
1538  * But we had to alter page->flags anyway.
1539  */
1540 
1541 static void move_active_pages_to_lru(struct zone *zone,
1542 				     struct list_head *list,
1543 				     enum lru_list lru)
1544 {
1545 	unsigned long pgmoved = 0;
1546 	struct pagevec pvec;
1547 	struct page *page;
1548 
1549 	pagevec_init(&pvec, 1);
1550 
1551 	while (!list_empty(list)) {
1552 		page = lru_to_page(list);
1553 
1554 		VM_BUG_ON(PageLRU(page));
1555 		SetPageLRU(page);
1556 
1557 		list_move(&page->lru, &zone->lru[lru].list);
1558 		mem_cgroup_add_lru_list(page, lru);
1559 		pgmoved += hpage_nr_pages(page);
1560 
1561 		if (!pagevec_add(&pvec, page) || list_empty(list)) {
1562 			spin_unlock_irq(&zone->lru_lock);
1563 			if (buffer_heads_over_limit)
1564 				pagevec_strip(&pvec);
1565 			__pagevec_release(&pvec);
1566 			spin_lock_irq(&zone->lru_lock);
1567 		}
1568 	}
1569 	__mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1570 	if (!is_active_lru(lru))
1571 		__count_vm_events(PGDEACTIVATE, pgmoved);
1572 }
1573 
1574 static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
1575 			struct scan_control *sc, int priority, int file)
1576 {
1577 	unsigned long nr_taken;
1578 	unsigned long pgscanned;
1579 	unsigned long vm_flags;
1580 	LIST_HEAD(l_hold);	/* The pages which were snipped off */
1581 	LIST_HEAD(l_active);
1582 	LIST_HEAD(l_inactive);
1583 	struct page *page;
1584 	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1585 	unsigned long nr_rotated = 0;
1586 
1587 	lru_add_drain();
1588 	spin_lock_irq(&zone->lru_lock);
1589 	if (scanning_global_lru(sc)) {
1590 		nr_taken = isolate_pages_global(nr_pages, &l_hold,
1591 						&pgscanned, sc->order,
1592 						ISOLATE_ACTIVE, zone,
1593 						1, file);
1594 		zone->pages_scanned += pgscanned;
1595 	} else {
1596 		nr_taken = mem_cgroup_isolate_pages(nr_pages, &l_hold,
1597 						&pgscanned, sc->order,
1598 						ISOLATE_ACTIVE, zone,
1599 						sc->mem_cgroup, 1, file);
1600 		/*
1601 		 * mem_cgroup_isolate_pages() keeps track of
1602 		 * scanned pages on its own.
1603 		 */
1604 	}
1605 
1606 	reclaim_stat->recent_scanned[file] += nr_taken;
1607 
1608 	__count_zone_vm_events(PGREFILL, zone, pgscanned);
1609 	if (file)
1610 		__mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken);
1611 	else
1612 		__mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken);
1613 	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1614 	spin_unlock_irq(&zone->lru_lock);
1615 
1616 	while (!list_empty(&l_hold)) {
1617 		cond_resched();
1618 		page = lru_to_page(&l_hold);
1619 		list_del(&page->lru);
1620 
1621 		if (unlikely(!page_evictable(page, NULL))) {
1622 			putback_lru_page(page);
1623 			continue;
1624 		}
1625 
1626 		if (page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
1627 			nr_rotated += hpage_nr_pages(page);
1628 			/*
1629 			 * Identify referenced, file-backed active pages and
1630 			 * give them one more trip around the active list. So
1631 			 * that executable code get better chances to stay in
1632 			 * memory under moderate memory pressure.  Anon pages
1633 			 * are not likely to be evicted by use-once streaming
1634 			 * IO, plus JVM can create lots of anon VM_EXEC pages,
1635 			 * so we ignore them here.
1636 			 */
1637 			if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1638 				list_add(&page->lru, &l_active);
1639 				continue;
1640 			}
1641 		}
1642 
1643 		ClearPageActive(page);	/* we are de-activating */
1644 		list_add(&page->lru, &l_inactive);
1645 	}
1646 
1647 	/*
1648 	 * Move pages back to the lru list.
1649 	 */
1650 	spin_lock_irq(&zone->lru_lock);
1651 	/*
1652 	 * Count referenced pages from currently used mappings as rotated,
1653 	 * even though only some of them are actually re-activated.  This
1654 	 * helps balance scan pressure between file and anonymous pages in
1655 	 * get_scan_ratio.
1656 	 */
1657 	reclaim_stat->recent_rotated[file] += nr_rotated;
1658 
1659 	move_active_pages_to_lru(zone, &l_active,
1660 						LRU_ACTIVE + file * LRU_FILE);
1661 	move_active_pages_to_lru(zone, &l_inactive,
1662 						LRU_BASE   + file * LRU_FILE);
1663 	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1664 	spin_unlock_irq(&zone->lru_lock);
1665 }
1666 
1667 #ifdef CONFIG_SWAP
1668 static int inactive_anon_is_low_global(struct zone *zone)
1669 {
1670 	unsigned long active, inactive;
1671 
1672 	active = zone_page_state(zone, NR_ACTIVE_ANON);
1673 	inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1674 
1675 	if (inactive * zone->inactive_ratio < active)
1676 		return 1;
1677 
1678 	return 0;
1679 }
1680 
1681 /**
1682  * inactive_anon_is_low - check if anonymous pages need to be deactivated
1683  * @zone: zone to check
1684  * @sc:   scan control of this context
1685  *
1686  * Returns true if the zone does not have enough inactive anon pages,
1687  * meaning some active anon pages need to be deactivated.
1688  */
1689 static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc)
1690 {
1691 	int low;
1692 
1693 	/*
1694 	 * If we don't have swap space, anonymous page deactivation
1695 	 * is pointless.
1696 	 */
1697 	if (!total_swap_pages)
1698 		return 0;
1699 
1700 	if (scanning_global_lru(sc))
1701 		low = inactive_anon_is_low_global(zone);
1702 	else
1703 		low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup);
1704 	return low;
1705 }
1706 #else
1707 static inline int inactive_anon_is_low(struct zone *zone,
1708 					struct scan_control *sc)
1709 {
1710 	return 0;
1711 }
1712 #endif
1713 
1714 static int inactive_file_is_low_global(struct zone *zone)
1715 {
1716 	unsigned long active, inactive;
1717 
1718 	active = zone_page_state(zone, NR_ACTIVE_FILE);
1719 	inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1720 
1721 	return (active > inactive);
1722 }
1723 
1724 /**
1725  * inactive_file_is_low - check if file pages need to be deactivated
1726  * @zone: zone to check
1727  * @sc:   scan control of this context
1728  *
1729  * When the system is doing streaming IO, memory pressure here
1730  * ensures that active file pages get deactivated, until more
1731  * than half of the file pages are on the inactive list.
1732  *
1733  * Once we get to that situation, protect the system's working
1734  * set from being evicted by disabling active file page aging.
1735  *
1736  * This uses a different ratio than the anonymous pages, because
1737  * the page cache uses a use-once replacement algorithm.
1738  */
1739 static int inactive_file_is_low(struct zone *zone, struct scan_control *sc)
1740 {
1741 	int low;
1742 
1743 	if (scanning_global_lru(sc))
1744 		low = inactive_file_is_low_global(zone);
1745 	else
1746 		low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup);
1747 	return low;
1748 }
1749 
1750 static int inactive_list_is_low(struct zone *zone, struct scan_control *sc,
1751 				int file)
1752 {
1753 	if (file)
1754 		return inactive_file_is_low(zone, sc);
1755 	else
1756 		return inactive_anon_is_low(zone, sc);
1757 }
1758 
1759 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1760 	struct zone *zone, struct scan_control *sc, int priority)
1761 {
1762 	int file = is_file_lru(lru);
1763 
1764 	if (is_active_lru(lru)) {
1765 		if (inactive_list_is_low(zone, sc, file))
1766 		    shrink_active_list(nr_to_scan, zone, sc, priority, file);
1767 		return 0;
1768 	}
1769 
1770 	return shrink_inactive_list(nr_to_scan, zone, sc, priority, file);
1771 }
1772 
1773 /*
1774  * Determine how aggressively the anon and file LRU lists should be
1775  * scanned.  The relative value of each set of LRU lists is determined
1776  * by looking at the fraction of the pages scanned we did rotate back
1777  * onto the active list instead of evict.
1778  *
1779  * nr[0] = anon pages to scan; nr[1] = file pages to scan
1780  */
1781 static void get_scan_count(struct zone *zone, struct scan_control *sc,
1782 					unsigned long *nr, int priority)
1783 {
1784 	unsigned long anon, file, free;
1785 	unsigned long anon_prio, file_prio;
1786 	unsigned long ap, fp;
1787 	struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1788 	u64 fraction[2], denominator;
1789 	enum lru_list l;
1790 	int noswap = 0;
1791 	int force_scan = 0;
1792 
1793 
1794 	anon  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
1795 		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
1796 	file  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
1797 		zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
1798 
1799 	if (((anon + file) >> priority) < SWAP_CLUSTER_MAX) {
1800 		/* kswapd does zone balancing and need to scan this zone */
1801 		if (scanning_global_lru(sc) && current_is_kswapd())
1802 			force_scan = 1;
1803 		/* memcg may have small limit and need to avoid priority drop */
1804 		if (!scanning_global_lru(sc))
1805 			force_scan = 1;
1806 	}
1807 
1808 	/* If we have no swap space, do not bother scanning anon pages. */
1809 	if (!sc->may_swap || (nr_swap_pages <= 0)) {
1810 		noswap = 1;
1811 		fraction[0] = 0;
1812 		fraction[1] = 1;
1813 		denominator = 1;
1814 		goto out;
1815 	}
1816 
1817 	if (scanning_global_lru(sc)) {
1818 		free  = zone_page_state(zone, NR_FREE_PAGES);
1819 		/* If we have very few page cache pages,
1820 		   force-scan anon pages. */
1821 		if (unlikely(file + free <= high_wmark_pages(zone))) {
1822 			fraction[0] = 1;
1823 			fraction[1] = 0;
1824 			denominator = 1;
1825 			goto out;
1826 		}
1827 	}
1828 
1829 	/*
1830 	 * With swappiness at 100, anonymous and file have the same priority.
1831 	 * This scanning priority is essentially the inverse of IO cost.
1832 	 */
1833 	anon_prio = sc->swappiness;
1834 	file_prio = 200 - sc->swappiness;
1835 
1836 	/*
1837 	 * OK, so we have swap space and a fair amount of page cache
1838 	 * pages.  We use the recently rotated / recently scanned
1839 	 * ratios to determine how valuable each cache is.
1840 	 *
1841 	 * Because workloads change over time (and to avoid overflow)
1842 	 * we keep these statistics as a floating average, which ends
1843 	 * up weighing recent references more than old ones.
1844 	 *
1845 	 * anon in [0], file in [1]
1846 	 */
1847 	spin_lock_irq(&zone->lru_lock);
1848 	if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1849 		reclaim_stat->recent_scanned[0] /= 2;
1850 		reclaim_stat->recent_rotated[0] /= 2;
1851 	}
1852 
1853 	if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1854 		reclaim_stat->recent_scanned[1] /= 2;
1855 		reclaim_stat->recent_rotated[1] /= 2;
1856 	}
1857 
1858 	/*
1859 	 * The amount of pressure on anon vs file pages is inversely
1860 	 * proportional to the fraction of recently scanned pages on
1861 	 * each list that were recently referenced and in active use.
1862 	 */
1863 	ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1);
1864 	ap /= reclaim_stat->recent_rotated[0] + 1;
1865 
1866 	fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
1867 	fp /= reclaim_stat->recent_rotated[1] + 1;
1868 	spin_unlock_irq(&zone->lru_lock);
1869 
1870 	fraction[0] = ap;
1871 	fraction[1] = fp;
1872 	denominator = ap + fp + 1;
1873 out:
1874 	for_each_evictable_lru(l) {
1875 		int file = is_file_lru(l);
1876 		unsigned long scan;
1877 
1878 		scan = zone_nr_lru_pages(zone, sc, l);
1879 		if (priority || noswap) {
1880 			scan >>= priority;
1881 			scan = div64_u64(scan * fraction[file], denominator);
1882 		}
1883 
1884 		/*
1885 		 * If zone is small or memcg is small, nr[l] can be 0.
1886 		 * This results no-scan on this priority and priority drop down.
1887 		 * For global direct reclaim, it can visit next zone and tend
1888 		 * not to have problems. For global kswapd, it's for zone
1889 		 * balancing and it need to scan a small amounts. When using
1890 		 * memcg, priority drop can cause big latency. So, it's better
1891 		 * to scan small amount. See may_noscan above.
1892 		 */
1893 		if (!scan && force_scan) {
1894 			if (file)
1895 				scan = SWAP_CLUSTER_MAX;
1896 			else if (!noswap)
1897 				scan = SWAP_CLUSTER_MAX;
1898 		}
1899 		nr[l] = scan;
1900 	}
1901 }
1902 
1903 /*
1904  * Reclaim/compaction depends on a number of pages being freed. To avoid
1905  * disruption to the system, a small number of order-0 pages continue to be
1906  * rotated and reclaimed in the normal fashion. However, by the time we get
1907  * back to the allocator and call try_to_compact_zone(), we ensure that
1908  * there are enough free pages for it to be likely successful
1909  */
1910 static inline bool should_continue_reclaim(struct zone *zone,
1911 					unsigned long nr_reclaimed,
1912 					unsigned long nr_scanned,
1913 					struct scan_control *sc)
1914 {
1915 	unsigned long pages_for_compaction;
1916 	unsigned long inactive_lru_pages;
1917 
1918 	/* If not in reclaim/compaction mode, stop */
1919 	if (!(sc->reclaim_mode & RECLAIM_MODE_COMPACTION))
1920 		return false;
1921 
1922 	/* Consider stopping depending on scan and reclaim activity */
1923 	if (sc->gfp_mask & __GFP_REPEAT) {
1924 		/*
1925 		 * For __GFP_REPEAT allocations, stop reclaiming if the
1926 		 * full LRU list has been scanned and we are still failing
1927 		 * to reclaim pages. This full LRU scan is potentially
1928 		 * expensive but a __GFP_REPEAT caller really wants to succeed
1929 		 */
1930 		if (!nr_reclaimed && !nr_scanned)
1931 			return false;
1932 	} else {
1933 		/*
1934 		 * For non-__GFP_REPEAT allocations which can presumably
1935 		 * fail without consequence, stop if we failed to reclaim
1936 		 * any pages from the last SWAP_CLUSTER_MAX number of
1937 		 * pages that were scanned. This will return to the
1938 		 * caller faster at the risk reclaim/compaction and
1939 		 * the resulting allocation attempt fails
1940 		 */
1941 		if (!nr_reclaimed)
1942 			return false;
1943 	}
1944 
1945 	/*
1946 	 * If we have not reclaimed enough pages for compaction and the
1947 	 * inactive lists are large enough, continue reclaiming
1948 	 */
1949 	pages_for_compaction = (2UL << sc->order);
1950 	inactive_lru_pages = zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON) +
1951 				zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
1952 	if (sc->nr_reclaimed < pages_for_compaction &&
1953 			inactive_lru_pages > pages_for_compaction)
1954 		return true;
1955 
1956 	/* If compaction would go ahead or the allocation would succeed, stop */
1957 	switch (compaction_suitable(zone, sc->order)) {
1958 	case COMPACT_PARTIAL:
1959 	case COMPACT_CONTINUE:
1960 		return false;
1961 	default:
1962 		return true;
1963 	}
1964 }
1965 
1966 /*
1967  * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1968  */
1969 static void shrink_zone(int priority, struct zone *zone,
1970 				struct scan_control *sc)
1971 {
1972 	unsigned long nr[NR_LRU_LISTS];
1973 	unsigned long nr_to_scan;
1974 	enum lru_list l;
1975 	unsigned long nr_reclaimed, nr_scanned;
1976 	unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1977 
1978 restart:
1979 	nr_reclaimed = 0;
1980 	nr_scanned = sc->nr_scanned;
1981 	get_scan_count(zone, sc, nr, priority);
1982 
1983 	while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1984 					nr[LRU_INACTIVE_FILE]) {
1985 		for_each_evictable_lru(l) {
1986 			if (nr[l]) {
1987 				nr_to_scan = min_t(unsigned long,
1988 						   nr[l], SWAP_CLUSTER_MAX);
1989 				nr[l] -= nr_to_scan;
1990 
1991 				nr_reclaimed += shrink_list(l, nr_to_scan,
1992 							    zone, sc, priority);
1993 			}
1994 		}
1995 		/*
1996 		 * On large memory systems, scan >> priority can become
1997 		 * really large. This is fine for the starting priority;
1998 		 * we want to put equal scanning pressure on each zone.
1999 		 * However, if the VM has a harder time of freeing pages,
2000 		 * with multiple processes reclaiming pages, the total
2001 		 * freeing target can get unreasonably large.
2002 		 */
2003 		if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)
2004 			break;
2005 	}
2006 	sc->nr_reclaimed += nr_reclaimed;
2007 
2008 	/*
2009 	 * Even if we did not try to evict anon pages at all, we want to
2010 	 * rebalance the anon lru active/inactive ratio.
2011 	 */
2012 	if (inactive_anon_is_low(zone, sc))
2013 		shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);
2014 
2015 	/* reclaim/compaction might need reclaim to continue */
2016 	if (should_continue_reclaim(zone, nr_reclaimed,
2017 					sc->nr_scanned - nr_scanned, sc))
2018 		goto restart;
2019 
2020 	throttle_vm_writeout(sc->gfp_mask);
2021 }
2022 
2023 /*
2024  * This is the direct reclaim path, for page-allocating processes.  We only
2025  * try to reclaim pages from zones which will satisfy the caller's allocation
2026  * request.
2027  *
2028  * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
2029  * Because:
2030  * a) The caller may be trying to free *extra* pages to satisfy a higher-order
2031  *    allocation or
2032  * b) The target zone may be at high_wmark_pages(zone) but the lower zones
2033  *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
2034  *    zone defense algorithm.
2035  *
2036  * If a zone is deemed to be full of pinned pages then just give it a light
2037  * scan then give up on it.
2038  */
2039 static void shrink_zones(int priority, struct zonelist *zonelist,
2040 					struct scan_control *sc)
2041 {
2042 	struct zoneref *z;
2043 	struct zone *zone;
2044 	unsigned long nr_soft_reclaimed;
2045 	unsigned long nr_soft_scanned;
2046 
2047 	for_each_zone_zonelist_nodemask(zone, z, zonelist,
2048 					gfp_zone(sc->gfp_mask), sc->nodemask) {
2049 		if (!populated_zone(zone))
2050 			continue;
2051 		/*
2052 		 * Take care memory controller reclaiming has small influence
2053 		 * to global LRU.
2054 		 */
2055 		if (scanning_global_lru(sc)) {
2056 			if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2057 				continue;
2058 			if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2059 				continue;	/* Let kswapd poll it */
2060 			/*
2061 			 * This steals pages from memory cgroups over softlimit
2062 			 * and returns the number of reclaimed pages and
2063 			 * scanned pages. This works for global memory pressure
2064 			 * and balancing, not for a memcg's limit.
2065 			 */
2066 			nr_soft_scanned = 0;
2067 			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2068 						sc->order, sc->gfp_mask,
2069 						&nr_soft_scanned);
2070 			sc->nr_reclaimed += nr_soft_reclaimed;
2071 			sc->nr_scanned += nr_soft_scanned;
2072 			/* need some check for avoid more shrink_zone() */
2073 		}
2074 
2075 		shrink_zone(priority, zone, sc);
2076 	}
2077 }
2078 
2079 static bool zone_reclaimable(struct zone *zone)
2080 {
2081 	return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
2082 }
2083 
2084 /* All zones in zonelist are unreclaimable? */
2085 static bool all_unreclaimable(struct zonelist *zonelist,
2086 		struct scan_control *sc)
2087 {
2088 	struct zoneref *z;
2089 	struct zone *zone;
2090 
2091 	for_each_zone_zonelist_nodemask(zone, z, zonelist,
2092 			gfp_zone(sc->gfp_mask), sc->nodemask) {
2093 		if (!populated_zone(zone))
2094 			continue;
2095 		if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2096 			continue;
2097 		if (!zone->all_unreclaimable)
2098 			return false;
2099 	}
2100 
2101 	return true;
2102 }
2103 
2104 /*
2105  * This is the main entry point to direct page reclaim.
2106  *
2107  * If a full scan of the inactive list fails to free enough memory then we
2108  * are "out of memory" and something needs to be killed.
2109  *
2110  * If the caller is !__GFP_FS then the probability of a failure is reasonably
2111  * high - the zone may be full of dirty or under-writeback pages, which this
2112  * caller can't do much about.  We kick the writeback threads and take explicit
2113  * naps in the hope that some of these pages can be written.  But if the
2114  * allocating task holds filesystem locks which prevent writeout this might not
2115  * work, and the allocation attempt will fail.
2116  *
2117  * returns:	0, if no pages reclaimed
2118  * 		else, the number of pages reclaimed
2119  */
2120 static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2121 					struct scan_control *sc,
2122 					struct shrink_control *shrink)
2123 {
2124 	int priority;
2125 	unsigned long total_scanned = 0;
2126 	struct reclaim_state *reclaim_state = current->reclaim_state;
2127 	struct zoneref *z;
2128 	struct zone *zone;
2129 	unsigned long writeback_threshold;
2130 
2131 	get_mems_allowed();
2132 	delayacct_freepages_start();
2133 
2134 	if (scanning_global_lru(sc))
2135 		count_vm_event(ALLOCSTALL);
2136 
2137 	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
2138 		sc->nr_scanned = 0;
2139 		if (!priority)
2140 			disable_swap_token(sc->mem_cgroup);
2141 		shrink_zones(priority, zonelist, sc);
2142 		/*
2143 		 * Don't shrink slabs when reclaiming memory from
2144 		 * over limit cgroups
2145 		 */
2146 		if (scanning_global_lru(sc)) {
2147 			unsigned long lru_pages = 0;
2148 			for_each_zone_zonelist(zone, z, zonelist,
2149 					gfp_zone(sc->gfp_mask)) {
2150 				if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2151 					continue;
2152 
2153 				lru_pages += zone_reclaimable_pages(zone);
2154 			}
2155 
2156 			shrink_slab(shrink, sc->nr_scanned, lru_pages);
2157 			if (reclaim_state) {
2158 				sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2159 				reclaim_state->reclaimed_slab = 0;
2160 			}
2161 		}
2162 		total_scanned += sc->nr_scanned;
2163 		if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2164 			goto out;
2165 
2166 		/*
2167 		 * Try to write back as many pages as we just scanned.  This
2168 		 * tends to cause slow streaming writers to write data to the
2169 		 * disk smoothly, at the dirtying rate, which is nice.   But
2170 		 * that's undesirable in laptop mode, where we *want* lumpy
2171 		 * writeout.  So in laptop mode, write out the whole world.
2172 		 */
2173 		writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2174 		if (total_scanned > writeback_threshold) {
2175 			wakeup_flusher_threads(laptop_mode ? 0 : total_scanned);
2176 			sc->may_writepage = 1;
2177 		}
2178 
2179 		/* Take a nap, wait for some writeback to complete */
2180 		if (!sc->hibernation_mode && sc->nr_scanned &&
2181 		    priority < DEF_PRIORITY - 2) {
2182 			struct zone *preferred_zone;
2183 
2184 			first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
2185 						&cpuset_current_mems_allowed,
2186 						&preferred_zone);
2187 			wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
2188 		}
2189 	}
2190 
2191 out:
2192 	delayacct_freepages_end();
2193 	put_mems_allowed();
2194 
2195 	if (sc->nr_reclaimed)
2196 		return sc->nr_reclaimed;
2197 
2198 	/*
2199 	 * As hibernation is going on, kswapd is freezed so that it can't mark
2200 	 * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2201 	 * check.
2202 	 */
2203 	if (oom_killer_disabled)
2204 		return 0;
2205 
2206 	/* top priority shrink_zones still had more to do? don't OOM, then */
2207 	if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc))
2208 		return 1;
2209 
2210 	return 0;
2211 }
2212 
2213 unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2214 				gfp_t gfp_mask, nodemask_t *nodemask)
2215 {
2216 	unsigned long nr_reclaimed;
2217 	struct scan_control sc = {
2218 		.gfp_mask = gfp_mask,
2219 		.may_writepage = !laptop_mode,
2220 		.nr_to_reclaim = SWAP_CLUSTER_MAX,
2221 		.may_unmap = 1,
2222 		.may_swap = 1,
2223 		.swappiness = vm_swappiness,
2224 		.order = order,
2225 		.mem_cgroup = NULL,
2226 		.nodemask = nodemask,
2227 	};
2228 	struct shrink_control shrink = {
2229 		.gfp_mask = sc.gfp_mask,
2230 	};
2231 
2232 	trace_mm_vmscan_direct_reclaim_begin(order,
2233 				sc.may_writepage,
2234 				gfp_mask);
2235 
2236 	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2237 
2238 	trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2239 
2240 	return nr_reclaimed;
2241 }
2242 
2243 #ifdef CONFIG_CGROUP_MEM_RES_CTLR
2244 
2245 unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
2246 						gfp_t gfp_mask, bool noswap,
2247 						unsigned int swappiness,
2248 						struct zone *zone,
2249 						unsigned long *nr_scanned)
2250 {
2251 	struct scan_control sc = {
2252 		.nr_scanned = 0,
2253 		.nr_to_reclaim = SWAP_CLUSTER_MAX,
2254 		.may_writepage = !laptop_mode,
2255 		.may_unmap = 1,
2256 		.may_swap = !noswap,
2257 		.swappiness = swappiness,
2258 		.order = 0,
2259 		.mem_cgroup = mem,
2260 	};
2261 
2262 	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2263 			(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2264 
2265 	trace_mm_vmscan_memcg_softlimit_reclaim_begin(0,
2266 						      sc.may_writepage,
2267 						      sc.gfp_mask);
2268 
2269 	/*
2270 	 * NOTE: Although we can get the priority field, using it
2271 	 * here is not a good idea, since it limits the pages we can scan.
2272 	 * if we don't reclaim here, the shrink_zone from balance_pgdat
2273 	 * will pick up pages from other mem cgroup's as well. We hack
2274 	 * the priority and make it zero.
2275 	 */
2276 	shrink_zone(0, zone, &sc);
2277 
2278 	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2279 
2280 	*nr_scanned = sc.nr_scanned;
2281 	return sc.nr_reclaimed;
2282 }
2283 
2284 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
2285 					   gfp_t gfp_mask,
2286 					   bool noswap,
2287 					   unsigned int swappiness)
2288 {
2289 	struct zonelist *zonelist;
2290 	unsigned long nr_reclaimed;
2291 	int nid;
2292 	struct scan_control sc = {
2293 		.may_writepage = !laptop_mode,
2294 		.may_unmap = 1,
2295 		.may_swap = !noswap,
2296 		.nr_to_reclaim = SWAP_CLUSTER_MAX,
2297 		.swappiness = swappiness,
2298 		.order = 0,
2299 		.mem_cgroup = mem_cont,
2300 		.nodemask = NULL, /* we don't care the placement */
2301 		.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2302 				(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2303 	};
2304 	struct shrink_control shrink = {
2305 		.gfp_mask = sc.gfp_mask,
2306 	};
2307 
2308 	/*
2309 	 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2310 	 * take care of from where we get pages. So the node where we start the
2311 	 * scan does not need to be the current node.
2312 	 */
2313 	nid = mem_cgroup_select_victim_node(mem_cont);
2314 
2315 	zonelist = NODE_DATA(nid)->node_zonelists;
2316 
2317 	trace_mm_vmscan_memcg_reclaim_begin(0,
2318 					    sc.may_writepage,
2319 					    sc.gfp_mask);
2320 
2321 	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2322 
2323 	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2324 
2325 	return nr_reclaimed;
2326 }
2327 #endif
2328 
2329 /*
2330  * pgdat_balanced is used when checking if a node is balanced for high-order
2331  * allocations. Only zones that meet watermarks and are in a zone allowed
2332  * by the callers classzone_idx are added to balanced_pages. The total of
2333  * balanced pages must be at least 25% of the zones allowed by classzone_idx
2334  * for the node to be considered balanced. Forcing all zones to be balanced
2335  * for high orders can cause excessive reclaim when there are imbalanced zones.
2336  * The choice of 25% is due to
2337  *   o a 16M DMA zone that is balanced will not balance a zone on any
2338  *     reasonable sized machine
2339  *   o On all other machines, the top zone must be at least a reasonable
2340  *     percentage of the middle zones. For example, on 32-bit x86, highmem
2341  *     would need to be at least 256M for it to be balance a whole node.
2342  *     Similarly, on x86-64 the Normal zone would need to be at least 1G
2343  *     to balance a node on its own. These seemed like reasonable ratios.
2344  */
2345 static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
2346 						int classzone_idx)
2347 {
2348 	unsigned long present_pages = 0;
2349 	int i;
2350 
2351 	for (i = 0; i <= classzone_idx; i++)
2352 		present_pages += pgdat->node_zones[i].present_pages;
2353 
2354 	/* A special case here: if zone has no page, we think it's balanced */
2355 	return balanced_pages >= (present_pages >> 2);
2356 }
2357 
2358 /* is kswapd sleeping prematurely? */
2359 static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
2360 					int classzone_idx)
2361 {
2362 	int i;
2363 	unsigned long balanced = 0;
2364 	bool all_zones_ok = true;
2365 
2366 	/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2367 	if (remaining)
2368 		return true;
2369 
2370 	/* Check the watermark levels */
2371 	for (i = 0; i <= classzone_idx; i++) {
2372 		struct zone *zone = pgdat->node_zones + i;
2373 
2374 		if (!populated_zone(zone))
2375 			continue;
2376 
2377 		/*
2378 		 * balance_pgdat() skips over all_unreclaimable after
2379 		 * DEF_PRIORITY. Effectively, it considers them balanced so
2380 		 * they must be considered balanced here as well if kswapd
2381 		 * is to sleep
2382 		 */
2383 		if (zone->all_unreclaimable) {
2384 			balanced += zone->present_pages;
2385 			continue;
2386 		}
2387 
2388 		if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
2389 							i, 0))
2390 			all_zones_ok = false;
2391 		else
2392 			balanced += zone->present_pages;
2393 	}
2394 
2395 	/*
2396 	 * For high-order requests, the balanced zones must contain at least
2397 	 * 25% of the nodes pages for kswapd to sleep. For order-0, all zones
2398 	 * must be balanced
2399 	 */
2400 	if (order)
2401 		return !pgdat_balanced(pgdat, balanced, classzone_idx);
2402 	else
2403 		return !all_zones_ok;
2404 }
2405 
2406 /*
2407  * For kswapd, balance_pgdat() will work across all this node's zones until
2408  * they are all at high_wmark_pages(zone).
2409  *
2410  * Returns the final order kswapd was reclaiming at
2411  *
2412  * There is special handling here for zones which are full of pinned pages.
2413  * This can happen if the pages are all mlocked, or if they are all used by
2414  * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
2415  * What we do is to detect the case where all pages in the zone have been
2416  * scanned twice and there has been zero successful reclaim.  Mark the zone as
2417  * dead and from now on, only perform a short scan.  Basically we're polling
2418  * the zone for when the problem goes away.
2419  *
2420  * kswapd scans the zones in the highmem->normal->dma direction.  It skips
2421  * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2422  * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2423  * lower zones regardless of the number of free pages in the lower zones. This
2424  * interoperates with the page allocator fallback scheme to ensure that aging
2425  * of pages is balanced across the zones.
2426  */
2427 static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2428 							int *classzone_idx)
2429 {
2430 	int all_zones_ok;
2431 	unsigned long balanced;
2432 	int priority;
2433 	int i;
2434 	int end_zone = 0;	/* Inclusive.  0 = ZONE_DMA */
2435 	unsigned long total_scanned;
2436 	struct reclaim_state *reclaim_state = current->reclaim_state;
2437 	unsigned long nr_soft_reclaimed;
2438 	unsigned long nr_soft_scanned;
2439 	struct scan_control sc = {
2440 		.gfp_mask = GFP_KERNEL,
2441 		.may_unmap = 1,
2442 		.may_swap = 1,
2443 		/*
2444 		 * kswapd doesn't want to be bailed out while reclaim. because
2445 		 * we want to put equal scanning pressure on each zone.
2446 		 */
2447 		.nr_to_reclaim = ULONG_MAX,
2448 		.swappiness = vm_swappiness,
2449 		.order = order,
2450 		.mem_cgroup = NULL,
2451 	};
2452 	struct shrink_control shrink = {
2453 		.gfp_mask = sc.gfp_mask,
2454 	};
2455 loop_again:
2456 	total_scanned = 0;
2457 	sc.nr_reclaimed = 0;
2458 	sc.may_writepage = !laptop_mode;
2459 	count_vm_event(PAGEOUTRUN);
2460 
2461 	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
2462 		unsigned long lru_pages = 0;
2463 		int has_under_min_watermark_zone = 0;
2464 
2465 		/* The swap token gets in the way of swapout... */
2466 		if (!priority)
2467 			disable_swap_token(NULL);
2468 
2469 		all_zones_ok = 1;
2470 		balanced = 0;
2471 
2472 		/*
2473 		 * Scan in the highmem->dma direction for the highest
2474 		 * zone which needs scanning
2475 		 */
2476 		for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2477 			struct zone *zone = pgdat->node_zones + i;
2478 
2479 			if (!populated_zone(zone))
2480 				continue;
2481 
2482 			if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2483 				continue;
2484 
2485 			/*
2486 			 * Do some background aging of the anon list, to give
2487 			 * pages a chance to be referenced before reclaiming.
2488 			 */
2489 			if (inactive_anon_is_low(zone, &sc))
2490 				shrink_active_list(SWAP_CLUSTER_MAX, zone,
2491 							&sc, priority, 0);
2492 
2493 			if (!zone_watermark_ok_safe(zone, order,
2494 					high_wmark_pages(zone), 0, 0)) {
2495 				end_zone = i;
2496 				break;
2497 			}
2498 		}
2499 		if (i < 0)
2500 			goto out;
2501 
2502 		for (i = 0; i <= end_zone; i++) {
2503 			struct zone *zone = pgdat->node_zones + i;
2504 
2505 			lru_pages += zone_reclaimable_pages(zone);
2506 		}
2507 
2508 		/*
2509 		 * Now scan the zone in the dma->highmem direction, stopping
2510 		 * at the last zone which needs scanning.
2511 		 *
2512 		 * We do this because the page allocator works in the opposite
2513 		 * direction.  This prevents the page allocator from allocating
2514 		 * pages behind kswapd's direction of progress, which would
2515 		 * cause too much scanning of the lower zones.
2516 		 */
2517 		for (i = 0; i <= end_zone; i++) {
2518 			struct zone *zone = pgdat->node_zones + i;
2519 			int nr_slab;
2520 			unsigned long balance_gap;
2521 
2522 			if (!populated_zone(zone))
2523 				continue;
2524 
2525 			if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2526 				continue;
2527 
2528 			sc.nr_scanned = 0;
2529 
2530 			nr_soft_scanned = 0;
2531 			/*
2532 			 * Call soft limit reclaim before calling shrink_zone.
2533 			 */
2534 			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2535 							order, sc.gfp_mask,
2536 							&nr_soft_scanned);
2537 			sc.nr_reclaimed += nr_soft_reclaimed;
2538 			total_scanned += nr_soft_scanned;
2539 
2540 			/*
2541 			 * We put equal pressure on every zone, unless
2542 			 * one zone has way too many pages free
2543 			 * already. The "too many pages" is defined
2544 			 * as the high wmark plus a "gap" where the
2545 			 * gap is either the low watermark or 1%
2546 			 * of the zone, whichever is smaller.
2547 			 */
2548 			balance_gap = min(low_wmark_pages(zone),
2549 				(zone->present_pages +
2550 					KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2551 				KSWAPD_ZONE_BALANCE_GAP_RATIO);
2552 			if (!zone_watermark_ok_safe(zone, order,
2553 					high_wmark_pages(zone) + balance_gap,
2554 					end_zone, 0)) {
2555 				shrink_zone(priority, zone, &sc);
2556 
2557 				reclaim_state->reclaimed_slab = 0;
2558 				nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages);
2559 				sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2560 				total_scanned += sc.nr_scanned;
2561 
2562 				if (nr_slab == 0 && !zone_reclaimable(zone))
2563 					zone->all_unreclaimable = 1;
2564 			}
2565 
2566 			/*
2567 			 * If we've done a decent amount of scanning and
2568 			 * the reclaim ratio is low, start doing writepage
2569 			 * even in laptop mode
2570 			 */
2571 			if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2572 			    total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
2573 				sc.may_writepage = 1;
2574 
2575 			if (zone->all_unreclaimable) {
2576 				if (end_zone && end_zone == i)
2577 					end_zone--;
2578 				continue;
2579 			}
2580 
2581 			if (!zone_watermark_ok_safe(zone, order,
2582 					high_wmark_pages(zone), end_zone, 0)) {
2583 				all_zones_ok = 0;
2584 				/*
2585 				 * We are still under min water mark.  This
2586 				 * means that we have a GFP_ATOMIC allocation
2587 				 * failure risk. Hurry up!
2588 				 */
2589 				if (!zone_watermark_ok_safe(zone, order,
2590 					    min_wmark_pages(zone), end_zone, 0))
2591 					has_under_min_watermark_zone = 1;
2592 			} else {
2593 				/*
2594 				 * If a zone reaches its high watermark,
2595 				 * consider it to be no longer congested. It's
2596 				 * possible there are dirty pages backed by
2597 				 * congested BDIs but as pressure is relieved,
2598 				 * spectulatively avoid congestion waits
2599 				 */
2600 				zone_clear_flag(zone, ZONE_CONGESTED);
2601 				if (i <= *classzone_idx)
2602 					balanced += zone->present_pages;
2603 			}
2604 
2605 		}
2606 		if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
2607 			break;		/* kswapd: all done */
2608 		/*
2609 		 * OK, kswapd is getting into trouble.  Take a nap, then take
2610 		 * another pass across the zones.
2611 		 */
2612 		if (total_scanned && (priority < DEF_PRIORITY - 2)) {
2613 			if (has_under_min_watermark_zone)
2614 				count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
2615 			else
2616 				congestion_wait(BLK_RW_ASYNC, HZ/10);
2617 		}
2618 
2619 		/*
2620 		 * We do this so kswapd doesn't build up large priorities for
2621 		 * example when it is freeing in parallel with allocators. It
2622 		 * matches the direct reclaim path behaviour in terms of impact
2623 		 * on zone->*_priority.
2624 		 */
2625 		if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2626 			break;
2627 	}
2628 out:
2629 
2630 	/*
2631 	 * order-0: All zones must meet high watermark for a balanced node
2632 	 * high-order: Balanced zones must make up at least 25% of the node
2633 	 *             for the node to be balanced
2634 	 */
2635 	if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) {
2636 		cond_resched();
2637 
2638 		try_to_freeze();
2639 
2640 		/*
2641 		 * Fragmentation may mean that the system cannot be
2642 		 * rebalanced for high-order allocations in all zones.
2643 		 * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2644 		 * it means the zones have been fully scanned and are still
2645 		 * not balanced. For high-order allocations, there is
2646 		 * little point trying all over again as kswapd may
2647 		 * infinite loop.
2648 		 *
2649 		 * Instead, recheck all watermarks at order-0 as they
2650 		 * are the most important. If watermarks are ok, kswapd will go
2651 		 * back to sleep. High-order users can still perform direct
2652 		 * reclaim if they wish.
2653 		 */
2654 		if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2655 			order = sc.order = 0;
2656 
2657 		goto loop_again;
2658 	}
2659 
2660 	/*
2661 	 * If kswapd was reclaiming at a higher order, it has the option of
2662 	 * sleeping without all zones being balanced. Before it does, it must
2663 	 * ensure that the watermarks for order-0 on *all* zones are met and
2664 	 * that the congestion flags are cleared. The congestion flag must
2665 	 * be cleared as kswapd is the only mechanism that clears the flag
2666 	 * and it is potentially going to sleep here.
2667 	 */
2668 	if (order) {
2669 		for (i = 0; i <= end_zone; i++) {
2670 			struct zone *zone = pgdat->node_zones + i;
2671 
2672 			if (!populated_zone(zone))
2673 				continue;
2674 
2675 			if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2676 				continue;
2677 
2678 			/* Confirm the zone is balanced for order-0 */
2679 			if (!zone_watermark_ok(zone, 0,
2680 					high_wmark_pages(zone), 0, 0)) {
2681 				order = sc.order = 0;
2682 				goto loop_again;
2683 			}
2684 
2685 			/* If balanced, clear the congested flag */
2686 			zone_clear_flag(zone, ZONE_CONGESTED);
2687 		}
2688 	}
2689 
2690 	/*
2691 	 * Return the order we were reclaiming at so sleeping_prematurely()
2692 	 * makes a decision on the order we were last reclaiming at. However,
2693 	 * if another caller entered the allocator slow path while kswapd
2694 	 * was awake, order will remain at the higher level
2695 	 */
2696 	*classzone_idx = end_zone;
2697 	return order;
2698 }
2699 
2700 static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
2701 {
2702 	long remaining = 0;
2703 	DEFINE_WAIT(wait);
2704 
2705 	if (freezing(current) || kthread_should_stop())
2706 		return;
2707 
2708 	prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2709 
2710 	/* Try to sleep for a short interval */
2711 	if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
2712 		remaining = schedule_timeout(HZ/10);
2713 		finish_wait(&pgdat->kswapd_wait, &wait);
2714 		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2715 	}
2716 
2717 	/*
2718 	 * After a short sleep, check if it was a premature sleep. If not, then
2719 	 * go fully to sleep until explicitly woken up.
2720 	 */
2721 	if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
2722 		trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
2723 
2724 		/*
2725 		 * vmstat counters are not perfectly accurate and the estimated
2726 		 * value for counters such as NR_FREE_PAGES can deviate from the
2727 		 * true value by nr_online_cpus * threshold. To avoid the zone
2728 		 * watermarks being breached while under pressure, we reduce the
2729 		 * per-cpu vmstat threshold while kswapd is awake and restore
2730 		 * them before going back to sleep.
2731 		 */
2732 		set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
2733 		schedule();
2734 		set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
2735 	} else {
2736 		if (remaining)
2737 			count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2738 		else
2739 			count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2740 	}
2741 	finish_wait(&pgdat->kswapd_wait, &wait);
2742 }
2743 
2744 /*
2745  * The background pageout daemon, started as a kernel thread
2746  * from the init process.
2747  *
2748  * This basically trickles out pages so that we have _some_
2749  * free memory available even if there is no other activity
2750  * that frees anything up. This is needed for things like routing
2751  * etc, where we otherwise might have all activity going on in
2752  * asynchronous contexts that cannot page things out.
2753  *
2754  * If there are applications that are active memory-allocators
2755  * (most normal use), this basically shouldn't matter.
2756  */
2757 static int kswapd(void *p)
2758 {
2759 	unsigned long order, new_order;
2760 	int classzone_idx, new_classzone_idx;
2761 	pg_data_t *pgdat = (pg_data_t*)p;
2762 	struct task_struct *tsk = current;
2763 
2764 	struct reclaim_state reclaim_state = {
2765 		.reclaimed_slab = 0,
2766 	};
2767 	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2768 
2769 	lockdep_set_current_reclaim_state(GFP_KERNEL);
2770 
2771 	if (!cpumask_empty(cpumask))
2772 		set_cpus_allowed_ptr(tsk, cpumask);
2773 	current->reclaim_state = &reclaim_state;
2774 
2775 	/*
2776 	 * Tell the memory management that we're a "memory allocator",
2777 	 * and that if we need more memory we should get access to it
2778 	 * regardless (see "__alloc_pages()"). "kswapd" should
2779 	 * never get caught in the normal page freeing logic.
2780 	 *
2781 	 * (Kswapd normally doesn't need memory anyway, but sometimes
2782 	 * you need a small amount of memory in order to be able to
2783 	 * page out something else, and this flag essentially protects
2784 	 * us from recursively trying to free more memory as we're
2785 	 * trying to free the first piece of memory in the first place).
2786 	 */
2787 	tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2788 	set_freezable();
2789 
2790 	order = new_order = 0;
2791 	classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
2792 	for ( ; ; ) {
2793 		int ret;
2794 
2795 		/*
2796 		 * If the last balance_pgdat was unsuccessful it's unlikely a
2797 		 * new request of a similar or harder type will succeed soon
2798 		 * so consider going to sleep on the basis we reclaimed at
2799 		 */
2800 		if (classzone_idx >= new_classzone_idx && order == new_order) {
2801 			new_order = pgdat->kswapd_max_order;
2802 			new_classzone_idx = pgdat->classzone_idx;
2803 			pgdat->kswapd_max_order =  0;
2804 			pgdat->classzone_idx = pgdat->nr_zones - 1;
2805 		}
2806 
2807 		if (order < new_order || classzone_idx > new_classzone_idx) {
2808 			/*
2809 			 * Don't sleep if someone wants a larger 'order'
2810 			 * allocation or has tigher zone constraints
2811 			 */
2812 			order = new_order;
2813 			classzone_idx = new_classzone_idx;
2814 		} else {
2815 			kswapd_try_to_sleep(pgdat, order, classzone_idx);
2816 			order = pgdat->kswapd_max_order;
2817 			classzone_idx = pgdat->classzone_idx;
2818 			pgdat->kswapd_max_order = 0;
2819 			pgdat->classzone_idx = pgdat->nr_zones - 1;
2820 		}
2821 
2822 		ret = try_to_freeze();
2823 		if (kthread_should_stop())
2824 			break;
2825 
2826 		/*
2827 		 * We can speed up thawing tasks if we don't call balance_pgdat
2828 		 * after returning from the refrigerator
2829 		 */
2830 		if (!ret) {
2831 			trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
2832 			order = balance_pgdat(pgdat, order, &classzone_idx);
2833 		}
2834 	}
2835 	return 0;
2836 }
2837 
2838 /*
2839  * A zone is low on free memory, so wake its kswapd task to service it.
2840  */
2841 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
2842 {
2843 	pg_data_t *pgdat;
2844 
2845 	if (!populated_zone(zone))
2846 		return;
2847 
2848 	if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2849 		return;
2850 	pgdat = zone->zone_pgdat;
2851 	if (pgdat->kswapd_max_order < order) {
2852 		pgdat->kswapd_max_order = order;
2853 		pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
2854 	}
2855 	if (!waitqueue_active(&pgdat->kswapd_wait))
2856 		return;
2857 	if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
2858 		return;
2859 
2860 	trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
2861 	wake_up_interruptible(&pgdat->kswapd_wait);
2862 }
2863 
2864 /*
2865  * The reclaimable count would be mostly accurate.
2866  * The less reclaimable pages may be
2867  * - mlocked pages, which will be moved to unevictable list when encountered
2868  * - mapped pages, which may require several travels to be reclaimed
2869  * - dirty pages, which is not "instantly" reclaimable
2870  */
2871 unsigned long global_reclaimable_pages(void)
2872 {
2873 	int nr;
2874 
2875 	nr = global_page_state(NR_ACTIVE_FILE) +
2876 	     global_page_state(NR_INACTIVE_FILE);
2877 
2878 	if (nr_swap_pages > 0)
2879 		nr += global_page_state(NR_ACTIVE_ANON) +
2880 		      global_page_state(NR_INACTIVE_ANON);
2881 
2882 	return nr;
2883 }
2884 
2885 unsigned long zone_reclaimable_pages(struct zone *zone)
2886 {
2887 	int nr;
2888 
2889 	nr = zone_page_state(zone, NR_ACTIVE_FILE) +
2890 	     zone_page_state(zone, NR_INACTIVE_FILE);
2891 
2892 	if (nr_swap_pages > 0)
2893 		nr += zone_page_state(zone, NR_ACTIVE_ANON) +
2894 		      zone_page_state(zone, NR_INACTIVE_ANON);
2895 
2896 	return nr;
2897 }
2898 
2899 #ifdef CONFIG_HIBERNATION
2900 /*
2901  * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
2902  * freed pages.
2903  *
2904  * Rather than trying to age LRUs the aim is to preserve the overall
2905  * LRU order by reclaiming preferentially
2906  * inactive > active > active referenced > active mapped
2907  */
2908 unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
2909 {
2910 	struct reclaim_state reclaim_state;
2911 	struct scan_control sc = {
2912 		.gfp_mask = GFP_HIGHUSER_MOVABLE,
2913 		.may_swap = 1,
2914 		.may_unmap = 1,
2915 		.may_writepage = 1,
2916 		.nr_to_reclaim = nr_to_reclaim,
2917 		.hibernation_mode = 1,
2918 		.swappiness = vm_swappiness,
2919 		.order = 0,
2920 	};
2921 	struct shrink_control shrink = {
2922 		.gfp_mask = sc.gfp_mask,
2923 	};
2924 	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
2925 	struct task_struct *p = current;
2926 	unsigned long nr_reclaimed;
2927 
2928 	p->flags |= PF_MEMALLOC;
2929 	lockdep_set_current_reclaim_state(sc.gfp_mask);
2930 	reclaim_state.reclaimed_slab = 0;
2931 	p->reclaim_state = &reclaim_state;
2932 
2933 	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2934 
2935 	p->reclaim_state = NULL;
2936 	lockdep_clear_current_reclaim_state();
2937 	p->flags &= ~PF_MEMALLOC;
2938 
2939 	return nr_reclaimed;
2940 }
2941 #endif /* CONFIG_HIBERNATION */
2942 
2943 /* It's optimal to keep kswapds on the same CPUs as their memory, but
2944    not required for correctness.  So if the last cpu in a node goes
2945    away, we get changed to run anywhere: as the first one comes back,
2946    restore their cpu bindings. */
2947 static int __devinit cpu_callback(struct notifier_block *nfb,
2948 				  unsigned long action, void *hcpu)
2949 {
2950 	int nid;
2951 
2952 	if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
2953 		for_each_node_state(nid, N_HIGH_MEMORY) {
2954 			pg_data_t *pgdat = NODE_DATA(nid);
2955 			const struct cpumask *mask;
2956 
2957 			mask = cpumask_of_node(pgdat->node_id);
2958 
2959 			if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2960 				/* One of our CPUs online: restore mask */
2961 				set_cpus_allowed_ptr(pgdat->kswapd, mask);
2962 		}
2963 	}
2964 	return NOTIFY_OK;
2965 }
2966 
2967 /*
2968  * This kswapd start function will be called by init and node-hot-add.
2969  * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
2970  */
2971 int kswapd_run(int nid)
2972 {
2973 	pg_data_t *pgdat = NODE_DATA(nid);
2974 	int ret = 0;
2975 
2976 	if (pgdat->kswapd)
2977 		return 0;
2978 
2979 	pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
2980 	if (IS_ERR(pgdat->kswapd)) {
2981 		/* failure at boot is fatal */
2982 		BUG_ON(system_state == SYSTEM_BOOTING);
2983 		printk("Failed to start kswapd on node %d\n",nid);
2984 		ret = -1;
2985 	}
2986 	return ret;
2987 }
2988 
2989 /*
2990  * Called by memory hotplug when all memory in a node is offlined.
2991  */
2992 void kswapd_stop(int nid)
2993 {
2994 	struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
2995 
2996 	if (kswapd)
2997 		kthread_stop(kswapd);
2998 }
2999 
3000 static int __init kswapd_init(void)
3001 {
3002 	int nid;
3003 
3004 	swap_setup();
3005 	for_each_node_state(nid, N_HIGH_MEMORY)
3006  		kswapd_run(nid);
3007 	hotcpu_notifier(cpu_callback, 0);
3008 	return 0;
3009 }
3010 
3011 module_init(kswapd_init)
3012 
3013 #ifdef CONFIG_NUMA
3014 /*
3015  * Zone reclaim mode
3016  *
3017  * If non-zero call zone_reclaim when the number of free pages falls below
3018  * the watermarks.
3019  */
3020 int zone_reclaim_mode __read_mostly;
3021 
3022 #define RECLAIM_OFF 0
3023 #define RECLAIM_ZONE (1<<0)	/* Run shrink_inactive_list on the zone */
3024 #define RECLAIM_WRITE (1<<1)	/* Writeout pages during reclaim */
3025 #define RECLAIM_SWAP (1<<2)	/* Swap pages out during reclaim */
3026 
3027 /*
3028  * Priority for ZONE_RECLAIM. This determines the fraction of pages
3029  * of a node considered for each zone_reclaim. 4 scans 1/16th of
3030  * a zone.
3031  */
3032 #define ZONE_RECLAIM_PRIORITY 4
3033 
3034 /*
3035  * Percentage of pages in a zone that must be unmapped for zone_reclaim to
3036  * occur.
3037  */
3038 int sysctl_min_unmapped_ratio = 1;
3039 
3040 /*
3041  * If the number of slab pages in a zone grows beyond this percentage then
3042  * slab reclaim needs to occur.
3043  */
3044 int sysctl_min_slab_ratio = 5;
3045 
3046 static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3047 {
3048 	unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3049 	unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3050 		zone_page_state(zone, NR_ACTIVE_FILE);
3051 
3052 	/*
3053 	 * It's possible for there to be more file mapped pages than
3054 	 * accounted for by the pages on the file LRU lists because
3055 	 * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3056 	 */
3057 	return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3058 }
3059 
3060 /* Work out how many page cache pages we can reclaim in this reclaim_mode */
3061 static long zone_pagecache_reclaimable(struct zone *zone)
3062 {
3063 	long nr_pagecache_reclaimable;
3064 	long delta = 0;
3065 
3066 	/*
3067 	 * If RECLAIM_SWAP is set, then all file pages are considered
3068 	 * potentially reclaimable. Otherwise, we have to worry about
3069 	 * pages like swapcache and zone_unmapped_file_pages() provides
3070 	 * a better estimate
3071 	 */
3072 	if (zone_reclaim_mode & RECLAIM_SWAP)
3073 		nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3074 	else
3075 		nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3076 
3077 	/* If we can't clean pages, remove dirty pages from consideration */
3078 	if (!(zone_reclaim_mode & RECLAIM_WRITE))
3079 		delta += zone_page_state(zone, NR_FILE_DIRTY);
3080 
3081 	/* Watch for any possible underflows due to delta */
3082 	if (unlikely(delta > nr_pagecache_reclaimable))
3083 		delta = nr_pagecache_reclaimable;
3084 
3085 	return nr_pagecache_reclaimable - delta;
3086 }
3087 
3088 /*
3089  * Try to free up some pages from this zone through reclaim.
3090  */
3091 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3092 {
3093 	/* Minimum pages needed in order to stay on node */
3094 	const unsigned long nr_pages = 1 << order;
3095 	struct task_struct *p = current;
3096 	struct reclaim_state reclaim_state;
3097 	int priority;
3098 	struct scan_control sc = {
3099 		.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3100 		.may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3101 		.may_swap = 1,
3102 		.nr_to_reclaim = max_t(unsigned long, nr_pages,
3103 				       SWAP_CLUSTER_MAX),
3104 		.gfp_mask = gfp_mask,
3105 		.swappiness = vm_swappiness,
3106 		.order = order,
3107 	};
3108 	struct shrink_control shrink = {
3109 		.gfp_mask = sc.gfp_mask,
3110 	};
3111 	unsigned long nr_slab_pages0, nr_slab_pages1;
3112 
3113 	cond_resched();
3114 	/*
3115 	 * We need to be able to allocate from the reserves for RECLAIM_SWAP
3116 	 * and we also need to be able to write out pages for RECLAIM_WRITE
3117 	 * and RECLAIM_SWAP.
3118 	 */
3119 	p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3120 	lockdep_set_current_reclaim_state(gfp_mask);
3121 	reclaim_state.reclaimed_slab = 0;
3122 	p->reclaim_state = &reclaim_state;
3123 
3124 	if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3125 		/*
3126 		 * Free memory by calling shrink zone with increasing
3127 		 * priorities until we have enough memory freed.
3128 		 */
3129 		priority = ZONE_RECLAIM_PRIORITY;
3130 		do {
3131 			shrink_zone(priority, zone, &sc);
3132 			priority--;
3133 		} while (priority >= 0 && sc.nr_reclaimed < nr_pages);
3134 	}
3135 
3136 	nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3137 	if (nr_slab_pages0 > zone->min_slab_pages) {
3138 		/*
3139 		 * shrink_slab() does not currently allow us to determine how
3140 		 * many pages were freed in this zone. So we take the current
3141 		 * number of slab pages and shake the slab until it is reduced
3142 		 * by the same nr_pages that we used for reclaiming unmapped
3143 		 * pages.
3144 		 *
3145 		 * Note that shrink_slab will free memory on all zones and may
3146 		 * take a long time.
3147 		 */
3148 		for (;;) {
3149 			unsigned long lru_pages = zone_reclaimable_pages(zone);
3150 
3151 			/* No reclaimable slab or very low memory pressure */
3152 			if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3153 				break;
3154 
3155 			/* Freed enough memory */
3156 			nr_slab_pages1 = zone_page_state(zone,
3157 							NR_SLAB_RECLAIMABLE);
3158 			if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3159 				break;
3160 		}
3161 
3162 		/*
3163 		 * Update nr_reclaimed by the number of slab pages we
3164 		 * reclaimed from this zone.
3165 		 */
3166 		nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3167 		if (nr_slab_pages1 < nr_slab_pages0)
3168 			sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3169 	}
3170 
3171 	p->reclaim_state = NULL;
3172 	current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3173 	lockdep_clear_current_reclaim_state();
3174 	return sc.nr_reclaimed >= nr_pages;
3175 }
3176 
3177 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3178 {
3179 	int node_id;
3180 	int ret;
3181 
3182 	/*
3183 	 * Zone reclaim reclaims unmapped file backed pages and
3184 	 * slab pages if we are over the defined limits.
3185 	 *
3186 	 * A small portion of unmapped file backed pages is needed for
3187 	 * file I/O otherwise pages read by file I/O will be immediately
3188 	 * thrown out if the zone is overallocated. So we do not reclaim
3189 	 * if less than a specified percentage of the zone is used by
3190 	 * unmapped file backed pages.
3191 	 */
3192 	if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3193 	    zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3194 		return ZONE_RECLAIM_FULL;
3195 
3196 	if (zone->all_unreclaimable)
3197 		return ZONE_RECLAIM_FULL;
3198 
3199 	/*
3200 	 * Do not scan if the allocation should not be delayed.
3201 	 */
3202 	if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3203 		return ZONE_RECLAIM_NOSCAN;
3204 
3205 	/*
3206 	 * Only run zone reclaim on the local zone or on zones that do not
3207 	 * have associated processors. This will favor the local processor
3208 	 * over remote processors and spread off node memory allocations
3209 	 * as wide as possible.
3210 	 */
3211 	node_id = zone_to_nid(zone);
3212 	if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3213 		return ZONE_RECLAIM_NOSCAN;
3214 
3215 	if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3216 		return ZONE_RECLAIM_NOSCAN;
3217 
3218 	ret = __zone_reclaim(zone, gfp_mask, order);
3219 	zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3220 
3221 	if (!ret)
3222 		count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3223 
3224 	return ret;
3225 }
3226 #endif
3227 
3228 /*
3229  * page_evictable - test whether a page is evictable
3230  * @page: the page to test
3231  * @vma: the VMA in which the page is or will be mapped, may be NULL
3232  *
3233  * Test whether page is evictable--i.e., should be placed on active/inactive
3234  * lists vs unevictable list.  The vma argument is !NULL when called from the
3235  * fault path to determine how to instantate a new page.
3236  *
3237  * Reasons page might not be evictable:
3238  * (1) page's mapping marked unevictable
3239  * (2) page is part of an mlocked VMA
3240  *
3241  */
3242 int page_evictable(struct page *page, struct vm_area_struct *vma)
3243 {
3244 
3245 	if (mapping_unevictable(page_mapping(page)))
3246 		return 0;
3247 
3248 	if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
3249 		return 0;
3250 
3251 	return 1;
3252 }
3253 
3254 /**
3255  * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list
3256  * @page: page to check evictability and move to appropriate lru list
3257  * @zone: zone page is in
3258  *
3259  * Checks a page for evictability and moves the page to the appropriate
3260  * zone lru list.
3261  *
3262  * Restrictions: zone->lru_lock must be held, page must be on LRU and must
3263  * have PageUnevictable set.
3264  */
3265 static void check_move_unevictable_page(struct page *page, struct zone *zone)
3266 {
3267 	VM_BUG_ON(PageActive(page));
3268 
3269 retry:
3270 	ClearPageUnevictable(page);
3271 	if (page_evictable(page, NULL)) {
3272 		enum lru_list l = page_lru_base_type(page);
3273 
3274 		__dec_zone_state(zone, NR_UNEVICTABLE);
3275 		list_move(&page->lru, &zone->lru[l].list);
3276 		mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l);
3277 		__inc_zone_state(zone, NR_INACTIVE_ANON + l);
3278 		__count_vm_event(UNEVICTABLE_PGRESCUED);
3279 	} else {
3280 		/*
3281 		 * rotate unevictable list
3282 		 */
3283 		SetPageUnevictable(page);
3284 		list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list);
3285 		mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE);
3286 		if (page_evictable(page, NULL))
3287 			goto retry;
3288 	}
3289 }
3290 
3291 /**
3292  * scan_mapping_unevictable_pages - scan an address space for evictable pages
3293  * @mapping: struct address_space to scan for evictable pages
3294  *
3295  * Scan all pages in mapping.  Check unevictable pages for
3296  * evictability and move them to the appropriate zone lru list.
3297  */
3298 void scan_mapping_unevictable_pages(struct address_space *mapping)
3299 {
3300 	pgoff_t next = 0;
3301 	pgoff_t end   = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >>
3302 			 PAGE_CACHE_SHIFT;
3303 	struct zone *zone;
3304 	struct pagevec pvec;
3305 
3306 	if (mapping->nrpages == 0)
3307 		return;
3308 
3309 	pagevec_init(&pvec, 0);
3310 	while (next < end &&
3311 		pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
3312 		int i;
3313 		int pg_scanned = 0;
3314 
3315 		zone = NULL;
3316 
3317 		for (i = 0; i < pagevec_count(&pvec); i++) {
3318 			struct page *page = pvec.pages[i];
3319 			pgoff_t page_index = page->index;
3320 			struct zone *pagezone = page_zone(page);
3321 
3322 			pg_scanned++;
3323 			if (page_index > next)
3324 				next = page_index;
3325 			next++;
3326 
3327 			if (pagezone != zone) {
3328 				if (zone)
3329 					spin_unlock_irq(&zone->lru_lock);
3330 				zone = pagezone;
3331 				spin_lock_irq(&zone->lru_lock);
3332 			}
3333 
3334 			if (PageLRU(page) && PageUnevictable(page))
3335 				check_move_unevictable_page(page, zone);
3336 		}
3337 		if (zone)
3338 			spin_unlock_irq(&zone->lru_lock);
3339 		pagevec_release(&pvec);
3340 
3341 		count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
3342 	}
3343 
3344 }
3345 
3346 /**
3347  * scan_zone_unevictable_pages - check unevictable list for evictable pages
3348  * @zone - zone of which to scan the unevictable list
3349  *
3350  * Scan @zone's unevictable LRU lists to check for pages that have become
3351  * evictable.  Move those that have to @zone's inactive list where they
3352  * become candidates for reclaim, unless shrink_inactive_zone() decides
3353  * to reactivate them.  Pages that are still unevictable are rotated
3354  * back onto @zone's unevictable list.
3355  */
3356 #define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */
3357 static void scan_zone_unevictable_pages(struct zone *zone)
3358 {
3359 	struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list;
3360 	unsigned long scan;
3361 	unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE);
3362 
3363 	while (nr_to_scan > 0) {
3364 		unsigned long batch_size = min(nr_to_scan,
3365 						SCAN_UNEVICTABLE_BATCH_SIZE);
3366 
3367 		spin_lock_irq(&zone->lru_lock);
3368 		for (scan = 0;  scan < batch_size; scan++) {
3369 			struct page *page = lru_to_page(l_unevictable);
3370 
3371 			if (!trylock_page(page))
3372 				continue;
3373 
3374 			prefetchw_prev_lru_page(page, l_unevictable, flags);
3375 
3376 			if (likely(PageLRU(page) && PageUnevictable(page)))
3377 				check_move_unevictable_page(page, zone);
3378 
3379 			unlock_page(page);
3380 		}
3381 		spin_unlock_irq(&zone->lru_lock);
3382 
3383 		nr_to_scan -= batch_size;
3384 	}
3385 }
3386 
3387 
3388 /**
3389  * scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages
3390  *
3391  * A really big hammer:  scan all zones' unevictable LRU lists to check for
3392  * pages that have become evictable.  Move those back to the zones'
3393  * inactive list where they become candidates for reclaim.
3394  * This occurs when, e.g., we have unswappable pages on the unevictable lists,
3395  * and we add swap to the system.  As such, it runs in the context of a task
3396  * that has possibly/probably made some previously unevictable pages
3397  * evictable.
3398  */
3399 static void scan_all_zones_unevictable_pages(void)
3400 {
3401 	struct zone *zone;
3402 
3403 	for_each_zone(zone) {
3404 		scan_zone_unevictable_pages(zone);
3405 	}
3406 }
3407 
3408 /*
3409  * scan_unevictable_pages [vm] sysctl handler.  On demand re-scan of
3410  * all nodes' unevictable lists for evictable pages
3411  */
3412 unsigned long scan_unevictable_pages;
3413 
3414 int scan_unevictable_handler(struct ctl_table *table, int write,
3415 			   void __user *buffer,
3416 			   size_t *length, loff_t *ppos)
3417 {
3418 	proc_doulongvec_minmax(table, write, buffer, length, ppos);
3419 
3420 	if (write && *(unsigned long *)table->data)
3421 		scan_all_zones_unevictable_pages();
3422 
3423 	scan_unevictable_pages = 0;
3424 	return 0;
3425 }
3426 
3427 #ifdef CONFIG_NUMA
3428 /*
3429  * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
3430  * a specified node's per zone unevictable lists for evictable pages.
3431  */
3432 
3433 static ssize_t read_scan_unevictable_node(struct sys_device *dev,
3434 					  struct sysdev_attribute *attr,
3435 					  char *buf)
3436 {
3437 	return sprintf(buf, "0\n");	/* always zero; should fit... */
3438 }
3439 
3440 static ssize_t write_scan_unevictable_node(struct sys_device *dev,
3441 					   struct sysdev_attribute *attr,
3442 					const char *buf, size_t count)
3443 {
3444 	struct zone *node_zones = NODE_DATA(dev->id)->node_zones;
3445 	struct zone *zone;
3446 	unsigned long res;
3447 	unsigned long req = strict_strtoul(buf, 10, &res);
3448 
3449 	if (!req)
3450 		return 1;	/* zero is no-op */
3451 
3452 	for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
3453 		if (!populated_zone(zone))
3454 			continue;
3455 		scan_zone_unevictable_pages(zone);
3456 	}
3457 	return 1;
3458 }
3459 
3460 
3461 static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3462 			read_scan_unevictable_node,
3463 			write_scan_unevictable_node);
3464 
3465 int scan_unevictable_register_node(struct node *node)
3466 {
3467 	return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages);
3468 }
3469 
3470 void scan_unevictable_unregister_node(struct node *node)
3471 {
3472 	sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages);
3473 }
3474 #endif
3475