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Root/mm/vmscan.c

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/backing-dev.h>
30	#include <linux/rmap.h>
31	#include <linux/topology.h>
32	#include <linux/cpu.h>
33	#include <linux/cpuset.h>
34	#include <linux/compaction.h>
35	#include <linux/notifier.h>
36	#include <linux/rwsem.h>
37	#include <linux/delay.h>
38	#include <linux/kthread.h>
39	#include <linux/freezer.h>
40	#include <linux/memcontrol.h>
41	#include <linux/delayacct.h>
42	#include <linux/sysctl.h>
43	#include <linux/oom.h>
44	#include <linux/prefetch.h>
45
46	#include <asm/tlbflush.h>
47	#include <asm/div64.h>
48
49	#include <linux/swapops.h>
50
51	#include "internal.h"
52
53	#define CREATE_TRACE_POINTS
54	#include <trace/events/vmscan.h>
55
56	struct scan_control {
57	/* Incremented by the number of inactive pages that were scanned */
58	unsigned long nr_scanned;
59
60	/* Number of pages freed so far during a call to shrink_zones() */
61	unsigned long nr_reclaimed;
62
63	/* How many pages shrink_list() should reclaim */
64	unsigned long nr_to_reclaim;
65
66	unsigned long hibernation_mode;
67
68	/* This context's GFP mask */
69	gfp_t gfp_mask;
70
71	int may_writepage;
72
73	/* Can mapped pages be reclaimed? */
74	int may_unmap;
75
76	/* Can pages be swapped as part of reclaim? */
77	int may_swap;
78
79	int order;
80
81	/* Scan (total_size >> priority) pages at once */
82	int priority;
83
84	/*
85	* The memory cgroup that hit its limit and as a result is the
86	* primary target of this reclaim invocation.
87	*/
88	struct mem_cgroup *target_mem_cgroup;
89
90	/*
91	* Nodemask of nodes allowed by the caller. If NULL, all nodes
92	* are scanned.
93	*/
94	nodemask_t *nodemask;
95	};
96
97	#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
98
99	#ifdef ARCH_HAS_PREFETCH
100	#define prefetch_prev_lru_page(_page, _base, _field) \
101	do { \
102	if ((_page)->lru.prev != _base) { \
103	struct page *prev; \
104	\
105	prev = lru_to_page(&(_page->lru)); \
106	prefetch(&prev->_field); \
107	} \
108	} while (0)
109	#else
110	#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
111	#endif
112
113	#ifdef ARCH_HAS_PREFETCHW
114	#define prefetchw_prev_lru_page(_page, _base, _field) \
115	do { \
116	if ((_page)->lru.prev != _base) { \
117	struct page *prev; \
118	\
119	prev = lru_to_page(&(_page->lru)); \
120	prefetchw(&prev->_field); \
121	} \
122	} while (0)
123	#else
124	#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
125	#endif
126
127	/*
128	* From 0 .. 100. Higher means more swappy.
129	*/
130	int vm_swappiness = 60;
131	long vm_total_pages; /* The total number of pages which the VM controls */
132
133	static LIST_HEAD(shrinker_list);
134	static DECLARE_RWSEM(shrinker_rwsem);
135
136	#ifdef CONFIG_MEMCG
137	static bool global_reclaim(struct scan_control *sc)
138	{
139	return !sc->target_mem_cgroup;
140	}
141	#else
142	static bool global_reclaim(struct scan_control *sc)
143	{
144	return true;
145	}
146	#endif
147
148	static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
149	{
150	if (!mem_cgroup_disabled())
151	return mem_cgroup_get_lru_size(lruvec, lru);
152
153	return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);
154	}
155
156	/*
157	* Add a shrinker callback to be called from the vm
158	*/
159	void register_shrinker(struct shrinker *shrinker)
160	{
161	atomic_long_set(&shrinker->nr_in_batch, 0);
162	down_write(&shrinker_rwsem);
163	list_add_tail(&shrinker->list, &shrinker_list);
164	up_write(&shrinker_rwsem);
165	}
166	EXPORT_SYMBOL(register_shrinker);
167
168	/*
169	* Remove one
170	*/
171	void unregister_shrinker(struct shrinker *shrinker)
172	{
173	down_write(&shrinker_rwsem);
174	list_del(&shrinker->list);
175	up_write(&shrinker_rwsem);
176	}
177	EXPORT_SYMBOL(unregister_shrinker);
178
179	static inline int do_shrinker_shrink(struct shrinker *shrinker,
180	struct shrink_control *sc,
181	unsigned long nr_to_scan)
182	{
183	sc->nr_to_scan = nr_to_scan;
184	return (*shrinker->shrink)(shrinker, sc);
185	}
186
187	#define SHRINK_BATCH 128
188	/*
189	* Call the shrink functions to age shrinkable caches
190	*
191	* Here we assume it costs one seek to replace a lru page and that it also
192	* takes a seek to recreate a cache object. With this in mind we age equal
193	* percentages of the lru and ageable caches. This should balance the seeks
194	* generated by these structures.
195	*
196	* If the vm encountered mapped pages on the LRU it increase the pressure on
197	* slab to avoid swapping.
198	*
199	* We do weird things to avoid (scannedseeksentries) overflowing 32 bits.
200	*
201	* `lru_pages' represents the number of on-LRU pages in all the zones which
202	* are eligible for the caller's allocation attempt. It is used for balancing
203	* slab reclaim versus page reclaim.
204	*
205	* Returns the number of slab objects which we shrunk.
206	*/
207	unsigned long shrink_slab(struct shrink_control *shrink,
208	unsigned long nr_pages_scanned,
209	unsigned long lru_pages)
210	{
211	struct shrinker *shrinker;
212	unsigned long ret = 0;
213
214	if (nr_pages_scanned == 0)
215	nr_pages_scanned = SWAP_CLUSTER_MAX;
216
217	if (!down_read_trylock(&shrinker_rwsem)) {
218	/* Assume we'll be able to shrink next time */
219	ret = 1;
220	goto out;
221	}
222
223	list_for_each_entry(shrinker, &shrinker_list, list) {
224	unsigned long long delta;
225	long total_scan;
226	long max_pass;
227	int shrink_ret = 0;
228	long nr;
229	long new_nr;
230	long batch_size = shrinker->batch ? shrinker->batch
231	: SHRINK_BATCH;
232
233	max_pass = do_shrinker_shrink(shrinker, shrink, 0);
234	if (max_pass <= 0)
235	continue;
236
237	/*
238	* copy the current shrinker scan count into a local variable
239	* and zero it so that other concurrent shrinker invocations
240	* don't also do this scanning work.
241	*/
242	nr = atomic_long_xchg(&shrinker->nr_in_batch, 0);
243
244	total_scan = nr;
245	delta = (4 * nr_pages_scanned) / shrinker->seeks;
246	delta *= max_pass;
247	do_div(delta, lru_pages + 1);
248	total_scan += delta;
249	if (total_scan < 0) {
250	printk(KERN_ERR "shrink_slab: %pF negative objects to "
251	"delete nr=%ld\n",
252	shrinker->shrink, total_scan);
253	total_scan = max_pass;
254	}
255
256	/*
257	* We need to avoid excessive windup on filesystem shrinkers
258	* due to large numbers of GFP_NOFS allocations causing the
259	* shrinkers to return -1 all the time. This results in a large
260	* nr being built up so when a shrink that can do some work
261	* comes along it empties the entire cache due to nr >>>
262	* max_pass. This is bad for sustaining a working set in
263	* memory.
264	*
265	* Hence only allow the shrinker to scan the entire cache when
266	* a large delta change is calculated directly.
267	*/
268	if (delta < max_pass / 4)
269	total_scan = min(total_scan, max_pass / 2);
270
271	/*
272	* Avoid risking looping forever due to too large nr value:
273	* never try to free more than twice the estimate number of
274	* freeable entries.
275	*/
276	if (total_scan > max_pass * 2)
277	total_scan = max_pass * 2;
278
279	trace_mm_shrink_slab_start(shrinker, shrink, nr,
280	nr_pages_scanned, lru_pages,
281	max_pass, delta, total_scan);
282
283	while (total_scan >= batch_size) {
284	int nr_before;
285
286	nr_before = do_shrinker_shrink(shrinker, shrink, 0);
287	shrink_ret = do_shrinker_shrink(shrinker, shrink,
288	batch_size);
289	if (shrink_ret == -1)
290	break;
291	if (shrink_ret < nr_before)
292	ret += nr_before - shrink_ret;
293	count_vm_events(SLABS_SCANNED, batch_size);
294	total_scan -= batch_size;
295
296	cond_resched();
297	}
298
299	/*
300	* move the unused scan count back into the shrinker in a
301	* manner that handles concurrent updates. If we exhausted the
302	* scan, there is no need to do an update.
303	*/
304	if (total_scan > 0)
305	new_nr = atomic_long_add_return(total_scan,
306	&shrinker->nr_in_batch);
307	else
308	new_nr = atomic_long_read(&shrinker->nr_in_batch);
309
310	trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
311	}
312	up_read(&shrinker_rwsem);
313	out:
314	cond_resched();
315	return ret;
316	}
317
318	static inline int is_page_cache_freeable(struct page *page)
319	{
320	/*
321	* A freeable page cache page is referenced only by the caller
322	* that isolated the page, the page cache radix tree and
323	* optional buffer heads at page->private.
324	*/
325	return page_count(page) - page_has_private(page) == 2;
326	}
327
328	static int may_write_to_queue(struct backing_dev_info *bdi,
329	struct scan_control *sc)
330	{
331	if (current->flags & PF_SWAPWRITE)
332	return 1;
333	if (!bdi_write_congested(bdi))
334	return 1;
335	if (bdi == current->backing_dev_info)
336	return 1;
337	return 0;
338	}
339
340	/*
341	* We detected a synchronous write error writing a page out. Probably
342	* -ENOSPC. We need to propagate that into the address_space for a subsequent
343	* fsync(), msync() or close().
344	*
345	* The tricky part is that after writepage we cannot touch the mapping: nothing
346	* prevents it from being freed up. But we have a ref on the page and once
347	* that page is locked, the mapping is pinned.
348	*
349	* We're allowed to run sleeping lock_page() here because we know the caller has
350	* __GFP_FS.
351	*/
352	static void handle_write_error(struct address_space *mapping,
353	struct page *page, int error)
354	{
355	lock_page(page);
356	if (page_mapping(page) == mapping)
357	mapping_set_error(mapping, error);
358	unlock_page(page);
359	}
360
361	/* possible outcome of pageout() */
362	typedef enum {
363	/* failed to write page out, page is locked */
364	PAGE_KEEP,
365	/* move page to the active list, page is locked */
366	PAGE_ACTIVATE,
367	/* page has been sent to the disk successfully, page is unlocked */
368	PAGE_SUCCESS,
369	/* page is clean and locked */
370	PAGE_CLEAN,
371	} pageout_t;
372
373	/*
374	* pageout is called by shrink_page_list() for each dirty page.
375	* Calls ->writepage().
376	*/
377	static pageout_t pageout(struct page page, struct address_space mapping,
378	struct scan_control *sc)
379	{
380	/*
381	* If the page is dirty, only perform writeback if that write
382	* will be non-blocking. To prevent this allocation from being
383	* stalled by pagecache activity. But note that there may be
384	* stalls if we need to run get_block(). We could test
385	* PagePrivate for that.
386	*
387	* If this process is currently in __generic_file_aio_write() against
388	* this page's queue, we can perform writeback even if that
389	* will block.
390	*
391	* If the page is swapcache, write it back even if that would
392	* block, for some throttling. This happens by accident, because
393	* swap_backing_dev_info is bust: it doesn't reflect the
394	* congestion state of the swapdevs. Easy to fix, if needed.
395	*/
396	if (!is_page_cache_freeable(page))
397	return PAGE_KEEP;
398	if (!mapping) {
399	/*
400	* Some data journaling orphaned pages can have
401	* page->mapping == NULL while being dirty with clean buffers.
402	*/
403	if (page_has_private(page)) {
404	if (try_to_free_buffers(page)) {
405	ClearPageDirty(page);
406	printk("%s: orphaned page\n", __func__);
407	return PAGE_CLEAN;
408	}
409	}
410	return PAGE_KEEP;
411	}
412	if (mapping->a_ops->writepage == NULL)
413	return PAGE_ACTIVATE;
414	if (!may_write_to_queue(mapping->backing_dev_info, sc))
415	return PAGE_KEEP;
416
417	if (clear_page_dirty_for_io(page)) {
418	int res;
419	struct writeback_control wbc = {
420	.sync_mode = WB_SYNC_NONE,
421	.nr_to_write = SWAP_CLUSTER_MAX,
422	.range_start = 0,
423	.range_end = LLONG_MAX,
424	.for_reclaim = 1,
425	};
426
427	SetPageReclaim(page);
428	res = mapping->a_ops->writepage(page, &wbc);
429	if (res < 0)
430	handle_write_error(mapping, page, res);
431	if (res == AOP_WRITEPAGE_ACTIVATE) {
432	ClearPageReclaim(page);
433	return PAGE_ACTIVATE;
434	}
435
436	if (!PageWriteback(page)) {
437	/* synchronous write or broken a_ops? */
438	ClearPageReclaim(page);
439	}
440	trace_mm_vmscan_writepage(page, trace_reclaim_flags(page));
441	inc_zone_page_state(page, NR_VMSCAN_WRITE);
442	return PAGE_SUCCESS;
443	}
444
445	return PAGE_CLEAN;
446	}
447
448	/*
449	* Same as remove_mapping, but if the page is removed from the mapping, it
450	* gets returned with a refcount of 0.
451	*/
452	static int __remove_mapping(struct address_space mapping, struct page page)
453	{
454	BUG_ON(!PageLocked(page));
455	BUG_ON(mapping != page_mapping(page));
456
457	spin_lock_irq(&mapping->tree_lock);
458	/*
459	* The non racy check for a busy page.
460	*
461	* Must be careful with the order of the tests. When someone has
462	* a ref to the page, it may be possible that they dirty it then
463	* drop the reference. So if PageDirty is tested before page_count
464	* here, then the following race may occur:
465	*
466	* get_user_pages(&page);
467	* [user mapping goes away]
468	* write_to(page);
469	* !PageDirty(page) [good]
470	* SetPageDirty(page);
471	* put_page(page);
472	* !page_count(page) [good, discard it]
473	*
474	* [oops, our write_to data is lost]
475	*
476	* Reversing the order of the tests ensures such a situation cannot
477	* escape unnoticed. The smp_rmb is needed to ensure the page->flags
478	* load is not satisfied before that of page->_count.
479	*
480	* Note that if SetPageDirty is always performed via set_page_dirty,
481	* and thus under tree_lock, then this ordering is not required.
482	*/
483	if (!page_freeze_refs(page, 2))
484	goto cannot_free;
485	/* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
486	if (unlikely(PageDirty(page))) {
487	page_unfreeze_refs(page, 2);
488	goto cannot_free;
489	}
490
491	if (PageSwapCache(page)) {
492	swp_entry_t swap = { .val = page_private(page) };
493	__delete_from_swap_cache(page);
494	spin_unlock_irq(&mapping->tree_lock);
495	swapcache_free(swap, page);
496	} else {
497	void (freepage)(struct page );
498
499	freepage = mapping->a_ops->freepage;
500
501	__delete_from_page_cache(page);
502	spin_unlock_irq(&mapping->tree_lock);
503	mem_cgroup_uncharge_cache_page(page);
504
505	if (freepage != NULL)
506	freepage(page);
507	}
508
509	return 1;
510
511	cannot_free:
512	spin_unlock_irq(&mapping->tree_lock);
513	return 0;
514	}
515
516	/*
517	* Attempt to detach a locked page from its ->mapping. If it is dirty or if
518	* someone else has a ref on the page, abort and return 0. If it was
519	* successfully detached, return 1. Assumes the caller has a single ref on
520	* this page.
521	*/
522	int remove_mapping(struct address_space mapping, struct page page)
523	{
524	if (__remove_mapping(mapping, page)) {
525	/*
526	* Unfreezing the refcount with 1 rather than 2 effectively
527	* drops the pagecache ref for us without requiring another
528	* atomic operation.
529	*/
530	page_unfreeze_refs(page, 1);
531	return 1;
532	}
533	return 0;
534	}
535
536	/**
537	* putback_lru_page - put previously isolated page onto appropriate LRU list
538	* @page: page to be put back to appropriate lru list
539	*
540	* Add previously isolated @page to appropriate LRU list.
541	* Page may still be unevictable for other reasons.
542	*
543	* lru_lock must not be held, interrupts must be enabled.
544	*/
545	void putback_lru_page(struct page *page)
546	{
547	int lru;
548	int active = !!TestClearPageActive(page);
549	int was_unevictable = PageUnevictable(page);
550
551	VM_BUG_ON(PageLRU(page));
552
553	redo:
554	ClearPageUnevictable(page);
555
556	if (page_evictable(page, NULL)) {
557	/*
558	* For evictable pages, we can use the cache.
559	* In event of a race, worst case is we end up with an
560	* unevictable page on [in]active list.
561	* We know how to handle that.
562	*/
563	lru = active + page_lru_base_type(page);
564	lru_cache_add_lru(page, lru);
565	} else {
566	/*
567	* Put unevictable pages directly on zone's unevictable
568	* list.
569	*/
570	lru = LRU_UNEVICTABLE;
571	add_page_to_unevictable_list(page);
572	/*
573	* When racing with an mlock or AS_UNEVICTABLE clearing
574	* (page is unlocked) make sure that if the other thread
575	* does not observe our setting of PG_lru and fails
576	* isolation/check_move_unevictable_pages,
577	* we see PG_mlocked/AS_UNEVICTABLE cleared below and move
578	* the page back to the evictable list.
579	*
580	* The other side is TestClearPageMlocked() or shmem_lock().
581	*/
582	smp_mb();
583	}
584
585	/*
586	* page's status can change while we move it among lru. If an evictable
587	* page is on unevictable list, it never be freed. To avoid that,
588	* check after we added it to the list, again.
589	*/
590	if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) {
591	if (!isolate_lru_page(page)) {
592	put_page(page);
593	goto redo;
594	}
595	/* This means someone else dropped this page from LRU
596	* So, it will be freed or putback to LRU again. There is
597	* nothing to do here.
598	*/
599	}
600
601	if (was_unevictable && lru != LRU_UNEVICTABLE)
602	count_vm_event(UNEVICTABLE_PGRESCUED);
603	else if (!was_unevictable && lru == LRU_UNEVICTABLE)
604	count_vm_event(UNEVICTABLE_PGCULLED);
605
606	put_page(page); /* drop ref from isolate */
607	}
608
609	enum page_references {
610	PAGEREF_RECLAIM,
611	PAGEREF_RECLAIM_CLEAN,
612	PAGEREF_KEEP,
613	PAGEREF_ACTIVATE,
614	};
615
616	static enum page_references page_check_references(struct page *page,
617	struct scan_control *sc)
618	{
619	int referenced_ptes, referenced_page;
620	unsigned long vm_flags;
621
622	referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
623	&vm_flags);
624	referenced_page = TestClearPageReferenced(page);
625
626	/*
627	* Mlock lost the isolation race with us. Let try_to_unmap()
628	* move the page to the unevictable list.
629	*/
630	if (vm_flags & VM_LOCKED)
631	return PAGEREF_RECLAIM;
632
633	if (referenced_ptes) {
634	if (PageSwapBacked(page))
635	return PAGEREF_ACTIVATE;
636	/*
637	* All mapped pages start out with page table
638	* references from the instantiating fault, so we need
639	* to look twice if a mapped file page is used more
640	* than once.
641	*
642	* Mark it and spare it for another trip around the
643	* inactive list. Another page table reference will
644	* lead to its activation.
645	*
646	* Note: the mark is set for activated pages as well
647	* so that recently deactivated but used pages are
648	* quickly recovered.
649	*/
650	SetPageReferenced(page);
651
652	if (referenced_page \|\| referenced_ptes > 1)
653	return PAGEREF_ACTIVATE;
654
655	/*
656	* Activate file-backed executable pages after first usage.
657	*/
658	if (vm_flags & VM_EXEC)
659	return PAGEREF_ACTIVATE;
660
661	return PAGEREF_KEEP;
662	}
663
664	/* Reclaim if clean, defer dirty pages to writeback */
665	if (referenced_page && !PageSwapBacked(page))
666	return PAGEREF_RECLAIM_CLEAN;
667
668	return PAGEREF_RECLAIM;
669	}
670
671	/*
672	* shrink_page_list() returns the number of reclaimed pages
673	*/
674	static unsigned long shrink_page_list(struct list_head *page_list,
675	struct zone *zone,
676	struct scan_control *sc,
677	unsigned long *ret_nr_dirty,
678	unsigned long *ret_nr_writeback)
679	{
680	LIST_HEAD(ret_pages);
681	LIST_HEAD(free_pages);
682	int pgactivate = 0;
683	unsigned long nr_dirty = 0;
684	unsigned long nr_congested = 0;
685	unsigned long nr_reclaimed = 0;
686	unsigned long nr_writeback = 0;
687
688	cond_resched();
689
690	mem_cgroup_uncharge_start();
691	while (!list_empty(page_list)) {
692	enum page_references references;
693	struct address_space *mapping;
694	struct page *page;
695	int may_enter_fs;
696
697	cond_resched();
698
699	page = lru_to_page(page_list);
700	list_del(&page->lru);
701
702	if (!trylock_page(page))
703	goto keep;
704
705	VM_BUG_ON(PageActive(page));
706	VM_BUG_ON(page_zone(page) != zone);
707
708	sc->nr_scanned++;
709
710	if (unlikely(!page_evictable(page, NULL)))
711	goto cull_mlocked;
712
713	if (!sc->may_unmap && page_mapped(page))
714	goto keep_locked;
715
716	/* Double the slab pressure for mapped and swapcache pages */
717	if (page_mapped(page) \|\| PageSwapCache(page))
718	sc->nr_scanned++;
719
720	may_enter_fs = (sc->gfp_mask & __GFP_FS) \|\|
721	(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
722
723	if (PageWriteback(page)) {
724	/*
725	* memcg doesn't have any dirty pages throttling so we
726	* could easily OOM just because too many pages are in
727	* writeback and there is nothing else to reclaim.
728	*
729	* Check __GFP_IO, certainly because a loop driver
730	* thread might enter reclaim, and deadlock if it waits
731	* on a page for which it is needed to do the write
732	* (loop masks off __GFP_IO\|__GFP_FS for this reason);
733	* but more thought would probably show more reasons.
734	*
735	* Don't require __GFP_FS, since we're not going into
736	* the FS, just waiting on its writeback completion.
737	* Worryingly, ext4 gfs2 and xfs allocate pages with
738	* grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so
739	* testing may_enter_fs here is liable to OOM on them.
740	*/
741	if (global_reclaim(sc) \|\|
742	!PageReclaim(page) \|\| !(sc->gfp_mask & __GFP_IO)) {
743	/*
744	* This is slightly racy - end_page_writeback()
745	* might have just cleared PageReclaim, then
746	* setting PageReclaim here end up interpreted
747	* as PageReadahead - but that does not matter
748	* enough to care. What we do want is for this
749	* page to have PageReclaim set next time memcg
750	* reclaim reaches the tests above, so it will
751	* then wait_on_page_writeback() to avoid OOM;
752	* and it's also appropriate in global reclaim.
753	*/
754	SetPageReclaim(page);
755	nr_writeback++;
756	goto keep_locked;
757	}
758	wait_on_page_writeback(page);
759	}
760
761	references = page_check_references(page, sc);
762	switch (references) {
763	case PAGEREF_ACTIVATE:
764	goto activate_locked;
765	case PAGEREF_KEEP:
766	goto keep_locked;
767	case PAGEREF_RECLAIM:
768	case PAGEREF_RECLAIM_CLEAN:
769	; /* try to reclaim the page below */
770	}
771
772	/*
773	* Anonymous process memory has backing store?
774	* Try to allocate it some swap space here.
775	*/
776	if (PageAnon(page) && !PageSwapCache(page)) {
777	if (!(sc->gfp_mask & __GFP_IO))
778	goto keep_locked;
779	if (!add_to_swap(page))
780	goto activate_locked;
781	may_enter_fs = 1;
782	}
783
784	mapping = page_mapping(page);
785
786	/*
787	* The page is mapped into the page tables of one or more
788	* processes. Try to unmap it here.
789	*/
790	if (page_mapped(page) && mapping) {
791	switch (try_to_unmap(page, TTU_UNMAP)) {
792	case SWAP_FAIL:
793	goto activate_locked;
794	case SWAP_AGAIN:
795	goto keep_locked;
796	case SWAP_MLOCK:
797	goto cull_mlocked;
798	case SWAP_SUCCESS:
799	; /* try to free the page below */
800	}
801	}
802
803	if (PageDirty(page)) {
804	nr_dirty++;
805
806	/*
807	* Only kswapd can writeback filesystem pages to
808	* avoid risk of stack overflow but do not writeback
809	* unless under significant pressure.
810	*/
811	if (page_is_file_cache(page) &&
812	(!current_is_kswapd() \|\|
813	sc->priority >= DEF_PRIORITY - 2)) {
814	/*
815	* Immediately reclaim when written back.
816	* Similar in principal to deactivate_page()
817	* except we already have the page isolated
818	* and know it's dirty
819	*/
820	inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
821	SetPageReclaim(page);
822
823	goto keep_locked;
824	}
825
826	if (references == PAGEREF_RECLAIM_CLEAN)
827	goto keep_locked;
828	if (!may_enter_fs)
829	goto keep_locked;
830	if (!sc->may_writepage)
831	goto keep_locked;
832
833	/* Page is dirty, try to write it out here */
834	switch (pageout(page, mapping, sc)) {
835	case PAGE_KEEP:
836	nr_congested++;
837	goto keep_locked;
838	case PAGE_ACTIVATE:
839	goto activate_locked;
840	case PAGE_SUCCESS:
841	if (PageWriteback(page))
842	goto keep;
843	if (PageDirty(page))
844	goto keep;
845
846	/*
847	* A synchronous write - probably a ramdisk. Go
848	* ahead and try to reclaim the page.
849	*/
850	if (!trylock_page(page))
851	goto keep;
852	if (PageDirty(page) \|\| PageWriteback(page))
853	goto keep_locked;
854	mapping = page_mapping(page);
855	case PAGE_CLEAN:
856	; /* try to free the page below */
857	}
858	}
859
860	/*
861	* If the page has buffers, try to free the buffer mappings
862	* associated with this page. If we succeed we try to free
863	* the page as well.
864	*
865	* We do this even if the page is PageDirty().
866	* try_to_release_page() does not perform I/O, but it is
867	* possible for a page to have PageDirty set, but it is actually
868	* clean (all its buffers are clean). This happens if the
869	* buffers were written out directly, with submit_bh(). ext3
870	* will do this, as well as the blockdev mapping.
871	* try_to_release_page() will discover that cleanness and will
872	* drop the buffers and mark the page clean - it can be freed.
873	*
874	* Rarely, pages can have buffers and no ->mapping. These are
875	* the pages which were not successfully invalidated in
876	* truncate_complete_page(). We try to drop those buffers here
877	* and if that worked, and the page is no longer mapped into
878	* process address space (page_count == 1) it can be freed.
879	* Otherwise, leave the page on the LRU so it is swappable.
880	*/
881	if (page_has_private(page)) {
882	if (!try_to_release_page(page, sc->gfp_mask))
883	goto activate_locked;
884	if (!mapping && page_count(page) == 1) {
885	unlock_page(page);
886	if (put_page_testzero(page))
887	goto free_it;
888	else {
889	/*
890	* rare race with speculative reference.
891	* the speculative reference will free
892	* this page shortly, so we may
893	* increment nr_reclaimed here (and
894	* leave it off the LRU).
895	*/
896	nr_reclaimed++;
897	continue;
898	}
899	}
900	}
901
902	if (!mapping \|\| !__remove_mapping(mapping, page))
903	goto keep_locked;
904
905	/*
906	* At this point, we have no other references and there is
907	* no way to pick any more up (removed from LRU, removed
908	* from pagecache). Can use non-atomic bitops now (and
909	* we obviously don't have to worry about waking up a process
910	* waiting on the page lock, because there are no references.
911	*/
912	__clear_page_locked(page);
913	free_it:
914	nr_reclaimed++;
915
916	/*
917	* Is there need to periodically free_page_list? It would
918	* appear not as the counts should be low
919	*/
920	list_add(&page->lru, &free_pages);
921	continue;
922
923	cull_mlocked:
924	if (PageSwapCache(page))
925	try_to_free_swap(page);
926	unlock_page(page);
927	putback_lru_page(page);
928	continue;
929
930	activate_locked:
931	/* Not a candidate for swapping, so reclaim swap space. */
932	if (PageSwapCache(page) && vm_swap_full())
933	try_to_free_swap(page);
934	VM_BUG_ON(PageActive(page));
935	SetPageActive(page);
936	pgactivate++;
937	keep_locked:
938	unlock_page(page);
939	keep:
940	list_add(&page->lru, &ret_pages);
941	VM_BUG_ON(PageLRU(page) \|\| PageUnevictable(page));
942	}
943
944	/*
945	* Tag a zone as congested if all the dirty pages encountered were
946	* backed by a congested BDI. In this case, reclaimers should just
947	* back off and wait for congestion to clear because further reclaim
948	* will encounter the same problem
949	*/
950	if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
951	zone_set_flag(zone, ZONE_CONGESTED);
952
953	free_hot_cold_page_list(&free_pages, 1);
954
955	list_splice(&ret_pages, page_list);
956	count_vm_events(PGACTIVATE, pgactivate);
957	mem_cgroup_uncharge_end();
958	*ret_nr_dirty += nr_dirty;
959	*ret_nr_writeback += nr_writeback;
960	return nr_reclaimed;
961	}
962
963	/*
964	* Attempt to remove the specified page from its LRU. Only take this page
965	* if it is of the appropriate PageActive status. Pages which are being
966	* freed elsewhere are also ignored.
967	*
968	* page: page to consider
969	* mode: one of the LRU isolation modes defined above
970	*
971	* returns 0 on success, -ve errno on failure.
972	*/
973	int __isolate_lru_page(struct page *page, isolate_mode_t mode)
974	{
975	int ret = -EINVAL;
976
977	/* Only take pages on the LRU. */
978	if (!PageLRU(page))
979	return ret;
980
981	/* Do not give back unevictable pages for compaction */
982	if (PageUnevictable(page))
983	return ret;
984
985	ret = -EBUSY;
986
987	/*
988	* To minimise LRU disruption, the caller can indicate that it only
989	* wants to isolate pages it will be able to operate on without
990	* blocking - clean pages for the most part.
991	*
992	* ISOLATE_CLEAN means that only clean pages should be isolated. This
993	* is used by reclaim when it is cannot write to backing storage
994	*
995	* ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
996	* that it is possible to migrate without blocking
997	*/
998	if (mode & (ISOLATE_CLEAN\|ISOLATE_ASYNC_MIGRATE)) {
999	/* All the caller can do on PageWriteback is block */
1000	if (PageWriteback(page))
1001	return ret;
1002
1003	if (PageDirty(page)) {
1004	struct address_space *mapping;
1005
1006	/* ISOLATE_CLEAN means only clean pages */
1007	if (mode & ISOLATE_CLEAN)
1008	return ret;
1009
1010	/*
1011	* Only pages without mappings or that have a
1012	* ->migratepage callback are possible to migrate
1013	* without blocking
1014	*/
1015	mapping = page_mapping(page);
1016	if (mapping && !mapping->a_ops->migratepage)
1017	return ret;
1018	}
1019	}
1020
1021	if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1022	return ret;
1023
1024	if (likely(get_page_unless_zero(page))) {
1025	/*
1026	* Be careful not to clear PageLRU until after we're
1027	* sure the page is not being freed elsewhere -- the
1028	* page release code relies on it.
1029	*/
1030	ClearPageLRU(page);
1031	ret = 0;
1032	}
1033
1034	return ret;
1035	}
1036
1037	/*
1038	* zone->lru_lock is heavily contended. Some of the functions that
1039	* shrink the lists perform better by taking out a batch of pages
1040	* and working on them outside the LRU lock.
1041	*
1042	* For pagecache intensive workloads, this function is the hottest
1043	* spot in the kernel (apart from copy_*_user functions).
1044	*
1045	* Appropriate locks must be held before calling this function.
1046	*
1047	* @nr_to_scan: The number of pages to look through on the list.
1048	* @lruvec: The LRU vector to pull pages from.
1049	* @dst: The temp list to put pages on to.
1050	* @nr_scanned: The number of pages that were scanned.
1051	* @sc: The scan_control struct for this reclaim session
1052	* @mode: One of the LRU isolation modes
1053	* @lru: LRU list id for isolating
1054	*
1055	* returns how many pages were moved onto *@dst.
1056	*/
1057	static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1058	struct lruvec lruvec, struct list_head dst,
1059	unsigned long nr_scanned, struct scan_control sc,
1060	isolate_mode_t mode, enum lru_list lru)
1061	{
1062	struct list_head *src = &lruvec->lists[lru];
1063	unsigned long nr_taken = 0;
1064	unsigned long scan;
1065
1066	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1067	struct page *page;
1068	int nr_pages;
1069
1070	page = lru_to_page(src);
1071	prefetchw_prev_lru_page(page, src, flags);
1072
1073	VM_BUG_ON(!PageLRU(page));
1074
1075	switch (__isolate_lru_page(page, mode)) {
1076	case 0:
1077	nr_pages = hpage_nr_pages(page);
1078	mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
1079	list_move(&page->lru, dst);
1080	nr_taken += nr_pages;
1081	break;
1082
1083	case -EBUSY:
1084	/* else it is being freed elsewhere */
1085	list_move(&page->lru, src);
1086	continue;
1087
1088	default:
1089	BUG();
1090	}
1091	}
1092
1093	*nr_scanned = scan;
1094	trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
1095	nr_taken, mode, is_file_lru(lru));
1096	return nr_taken;
1097	}
1098
1099	/**
1100	* isolate_lru_page - tries to isolate a page from its LRU list
1101	* @page: page to isolate from its LRU list
1102	*
1103	* Isolates a @page from an LRU list, clears PageLRU and adjusts the
1104	* vmstat statistic corresponding to whatever LRU list the page was on.
1105	*
1106	* Returns 0 if the page was removed from an LRU list.
1107	* Returns -EBUSY if the page was not on an LRU list.
1108	*
1109	* The returned page will have PageLRU() cleared. If it was found on
1110	* the active list, it will have PageActive set. If it was found on
1111	* the unevictable list, it will have the PageUnevictable bit set. That flag
1112	* may need to be cleared by the caller before letting the page go.
1113	*
1114	* The vmstat statistic corresponding to the list on which the page was
1115	* found will be decremented.
1116	*
1117	* Restrictions:
1118	* (1) Must be called with an elevated refcount on the page. This is a
1119	* fundamentnal difference from isolate_lru_pages (which is called
1120	* without a stable reference).
1121	* (2) the lru_lock must not be held.
1122	* (3) interrupts must be enabled.
1123	*/
1124	int isolate_lru_page(struct page *page)
1125	{
1126	int ret = -EBUSY;
1127
1128	VM_BUG_ON(!page_count(page));
1129
1130	if (PageLRU(page)) {
1131	struct zone *zone = page_zone(page);
1132	struct lruvec *lruvec;
1133
1134	spin_lock_irq(&zone->lru_lock);
1135	lruvec = mem_cgroup_page_lruvec(page, zone);
1136	if (PageLRU(page)) {
1137	int lru = page_lru(page);
1138	get_page(page);
1139	ClearPageLRU(page);
1140	del_page_from_lru_list(page, lruvec, lru);
1141	ret = 0;
1142	}
1143	spin_unlock_irq(&zone->lru_lock);
1144	}
1145	return ret;
1146	}
1147
1148	/*
1149	* Are there way too many processes in the direct reclaim path already?
1150	*/
1151	static int too_many_isolated(struct zone *zone, int file,
1152	struct scan_control *sc)
1153	{
1154	unsigned long inactive, isolated;
1155
1156	if (current_is_kswapd())
1157	return 0;
1158
1159	if (!global_reclaim(sc))
1160	return 0;
1161
1162	if (file) {
1163	inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1164	isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1165	} else {
1166	inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1167	isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1168	}
1169
1170	return isolated > inactive;
1171	}
1172
1173	static noinline_for_stack void
1174	putback_inactive_pages(struct lruvec lruvec, struct list_head page_list)
1175	{
1176	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1177	struct zone *zone = lruvec_zone(lruvec);
1178	LIST_HEAD(pages_to_free);
1179
1180	/*
1181	* Put back any unfreeable pages.
1182	*/
1183	while (!list_empty(page_list)) {
1184	struct page *page = lru_to_page(page_list);
1185	int lru;
1186
1187	VM_BUG_ON(PageLRU(page));
1188	list_del(&page->lru);
1189	if (unlikely(!page_evictable(page, NULL))) {
1190	spin_unlock_irq(&zone->lru_lock);
1191	putback_lru_page(page);
1192	spin_lock_irq(&zone->lru_lock);
1193	continue;
1194	}
1195
1196	lruvec = mem_cgroup_page_lruvec(page, zone);
1197
1198	SetPageLRU(page);
1199	lru = page_lru(page);
1200	add_page_to_lru_list(page, lruvec, lru);
1201
1202	if (is_active_lru(lru)) {
1203	int file = is_file_lru(lru);
1204	int numpages = hpage_nr_pages(page);
1205	reclaim_stat->recent_rotated[file] += numpages;
1206	}
1207	if (put_page_testzero(page)) {
1208	__ClearPageLRU(page);
1209	__ClearPageActive(page);
1210	del_page_from_lru_list(page, lruvec, lru);
1211
1212	if (unlikely(PageCompound(page))) {
1213	spin_unlock_irq(&zone->lru_lock);
1214	(*get_compound_page_dtor(page))(page);
1215	spin_lock_irq(&zone->lru_lock);
1216	} else
1217	list_add(&page->lru, &pages_to_free);
1218	}
1219	}
1220
1221	/*
1222	* To save our caller's stack, now use input list for pages to free.
1223	*/
1224	list_splice(&pages_to_free, page_list);
1225	}
1226
1227	/*
1228	* shrink_inactive_list() is a helper for shrink_zone(). It returns the number
1229	* of reclaimed pages
1230	*/
1231	static noinline_for_stack unsigned long
1232	shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1233	struct scan_control *sc, enum lru_list lru)
1234	{
1235	LIST_HEAD(page_list);
1236	unsigned long nr_scanned;
1237	unsigned long nr_reclaimed = 0;
1238	unsigned long nr_taken;
1239	unsigned long nr_dirty = 0;
1240	unsigned long nr_writeback = 0;
1241	isolate_mode_t isolate_mode = 0;
1242	int file = is_file_lru(lru);
1243	struct zone *zone = lruvec_zone(lruvec);
1244	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1245
1246	while (unlikely(too_many_isolated(zone, file, sc))) {
1247	congestion_wait(BLK_RW_ASYNC, HZ/10);
1248
1249	/* We are about to die and free our memory. Return now. */
1250	if (fatal_signal_pending(current))
1251	return SWAP_CLUSTER_MAX;
1252	}
1253
1254	lru_add_drain();
1255
1256	if (!sc->may_unmap)
1257	isolate_mode \|= ISOLATE_UNMAPPED;
1258	if (!sc->may_writepage)
1259	isolate_mode \|= ISOLATE_CLEAN;
1260
1261	spin_lock_irq(&zone->lru_lock);
1262
1263	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1264	&nr_scanned, sc, isolate_mode, lru);
1265
1266	__mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1267	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1268
1269	if (global_reclaim(sc)) {
1270	zone->pages_scanned += nr_scanned;
1271	if (current_is_kswapd())
1272	__count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1273	else
1274	__count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1275	}
1276	spin_unlock_irq(&zone->lru_lock);
1277
1278	if (nr_taken == 0)
1279	return 0;
1280
1281	nr_reclaimed = shrink_page_list(&page_list, zone, sc,
1282	&nr_dirty, &nr_writeback);
1283
1284	spin_lock_irq(&zone->lru_lock);
1285
1286	reclaim_stat->recent_scanned[file] += nr_taken;
1287
1288	if (global_reclaim(sc)) {
1289	if (current_is_kswapd())
1290	__count_zone_vm_events(PGSTEAL_KSWAPD, zone,
1291	nr_reclaimed);
1292	else
1293	__count_zone_vm_events(PGSTEAL_DIRECT, zone,
1294	nr_reclaimed);
1295	}
1296
1297	putback_inactive_pages(lruvec, &page_list);
1298
1299	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1300
1301	spin_unlock_irq(&zone->lru_lock);
1302
1303	free_hot_cold_page_list(&page_list, 1);
1304
1305	/*
1306	* If reclaim is isolating dirty pages under writeback, it implies
1307	* that the long-lived page allocation rate is exceeding the page
1308	* laundering rate. Either the global limits are not being effective
1309	* at throttling processes due to the page distribution throughout
1310	* zones or there is heavy usage of a slow backing device. The
1311	* only option is to throttle from reclaim context which is not ideal
1312	* as there is no guarantee the dirtying process is throttled in the
1313	* same way balance_dirty_pages() manages.
1314	*
1315	* This scales the number of dirty pages that must be under writeback
1316	* before throttling depending on priority. It is a simple backoff
1317	* function that has the most effect in the range DEF_PRIORITY to
1318	* DEF_PRIORITY-2 which is the priority reclaim is considered to be
1319	* in trouble and reclaim is considered to be in trouble.
1320	*
1321	* DEF_PRIORITY 100% isolated pages must be PageWriteback to throttle
1322	* DEF_PRIORITY-1 50% must be PageWriteback
1323	* DEF_PRIORITY-2 25% must be PageWriteback, kswapd in trouble
1324	* ...
1325	* DEF_PRIORITY-6 For SWAP_CLUSTER_MAX isolated pages, throttle if any
1326	* isolated page is PageWriteback
1327	*/
1328	if (nr_writeback && nr_writeback >=
1329	(nr_taken >> (DEF_PRIORITY - sc->priority)))
1330	wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
1331
1332	trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1333	zone_idx(zone),
1334	nr_scanned, nr_reclaimed,
1335	sc->priority,
1336	trace_shrink_flags(file));
1337	return nr_reclaimed;
1338	}
1339
1340	/*
1341	* This moves pages from the active list to the inactive list.
1342	*
1343	* We move them the other way if the page is referenced by one or more
1344	* processes, from rmap.
1345	*
1346	* If the pages are mostly unmapped, the processing is fast and it is
1347	* appropriate to hold zone->lru_lock across the whole operation. But if
1348	* the pages are mapped, the processing is slow (page_referenced()) so we
1349	* should drop zone->lru_lock around each page. It's impossible to balance
1350	* this, so instead we remove the pages from the LRU while processing them.
1351	* It is safe to rely on PG_active against the non-LRU pages in here because
1352	* nobody will play with that bit on a non-LRU page.
1353	*
1354	* The downside is that we have to touch page->_count against each page.
1355	* But we had to alter page->flags anyway.
1356	*/
1357
1358	static void move_active_pages_to_lru(struct lruvec *lruvec,
1359	struct list_head *list,
1360	struct list_head *pages_to_free,
1361	enum lru_list lru)
1362	{
1363	struct zone *zone = lruvec_zone(lruvec);
1364	unsigned long pgmoved = 0;
1365	struct page *page;
1366	int nr_pages;
1367
1368	while (!list_empty(list)) {
1369	page = lru_to_page(list);
1370	lruvec = mem_cgroup_page_lruvec(page, zone);
1371
1372	VM_BUG_ON(PageLRU(page));
1373	SetPageLRU(page);
1374
1375	nr_pages = hpage_nr_pages(page);
1376	mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1377	list_move(&page->lru, &lruvec->lists[lru]);
1378	pgmoved += nr_pages;
1379
1380	if (put_page_testzero(page)) {
1381	__ClearPageLRU(page);
1382	__ClearPageActive(page);
1383	del_page_from_lru_list(page, lruvec, lru);
1384
1385	if (unlikely(PageCompound(page))) {
1386	spin_unlock_irq(&zone->lru_lock);
1387	(*get_compound_page_dtor(page))(page);
1388	spin_lock_irq(&zone->lru_lock);
1389	} else
1390	list_add(&page->lru, pages_to_free);
1391	}
1392	}
1393	__mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1394	if (!is_active_lru(lru))
1395	__count_vm_events(PGDEACTIVATE, pgmoved);
1396	}
1397
1398	static void shrink_active_list(unsigned long nr_to_scan,
1399	struct lruvec *lruvec,
1400	struct scan_control *sc,
1401	enum lru_list lru)
1402	{
1403	unsigned long nr_taken;
1404	unsigned long nr_scanned;
1405	unsigned long vm_flags;
1406	LIST_HEAD(l_hold); /* The pages which were snipped off */
1407	LIST_HEAD(l_active);
1408	LIST_HEAD(l_inactive);
1409	struct page *page;
1410	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1411	unsigned long nr_rotated = 0;
1412	isolate_mode_t isolate_mode = 0;
1413	int file = is_file_lru(lru);
1414	struct zone *zone = lruvec_zone(lruvec);
1415
1416	lru_add_drain();
1417
1418	if (!sc->may_unmap)
1419	isolate_mode \|= ISOLATE_UNMAPPED;
1420	if (!sc->may_writepage)
1421	isolate_mode \|= ISOLATE_CLEAN;
1422
1423	spin_lock_irq(&zone->lru_lock);
1424
1425	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1426	&nr_scanned, sc, isolate_mode, lru);
1427	if (global_reclaim(sc))
1428	zone->pages_scanned += nr_scanned;
1429
1430	reclaim_stat->recent_scanned[file] += nr_taken;
1431
1432	__count_zone_vm_events(PGREFILL, zone, nr_scanned);
1433	__mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1434	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1435	spin_unlock_irq(&zone->lru_lock);
1436
1437	while (!list_empty(&l_hold)) {
1438	cond_resched();
1439	page = lru_to_page(&l_hold);
1440	list_del(&page->lru);
1441
1442	if (unlikely(!page_evictable(page, NULL))) {
1443	putback_lru_page(page);
1444	continue;
1445	}
1446
1447	if (unlikely(buffer_heads_over_limit)) {
1448	if (page_has_private(page) && trylock_page(page)) {
1449	if (page_has_private(page))
1450	try_to_release_page(page, 0);
1451	unlock_page(page);
1452	}
1453	}
1454
1455	if (page_referenced(page, 0, sc->target_mem_cgroup,
1456	&vm_flags)) {
1457	nr_rotated += hpage_nr_pages(page);
1458	/*
1459	* Identify referenced, file-backed active pages and
1460	* give them one more trip around the active list. So
1461	* that executable code get better chances to stay in
1462	* memory under moderate memory pressure. Anon pages
1463	* are not likely to be evicted by use-once streaming
1464	* IO, plus JVM can create lots of anon VM_EXEC pages,
1465	* so we ignore them here.
1466	*/
1467	if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1468	list_add(&page->lru, &l_active);
1469	continue;
1470	}
1471	}
1472
1473	ClearPageActive(page); /* we are de-activating */
1474	list_add(&page->lru, &l_inactive);
1475	}
1476
1477	/*
1478	* Move pages back to the lru list.
1479	*/
1480	spin_lock_irq(&zone->lru_lock);
1481	/*
1482	* Count referenced pages from currently used mappings as rotated,
1483	* even though only some of them are actually re-activated. This
1484	* helps balance scan pressure between file and anonymous pages in
1485	* get_scan_ratio.
1486	*/
1487	reclaim_stat->recent_rotated[file] += nr_rotated;
1488
1489	move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1490	move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1491	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1492	spin_unlock_irq(&zone->lru_lock);
1493
1494	free_hot_cold_page_list(&l_hold, 1);
1495	}
1496
1497	#ifdef CONFIG_SWAP
1498	static int inactive_anon_is_low_global(struct zone *zone)
1499	{
1500	unsigned long active, inactive;
1501
1502	active = zone_page_state(zone, NR_ACTIVE_ANON);
1503	inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1504
1505	if (inactive * zone->inactive_ratio < active)
1506	return 1;
1507
1508	return 0;
1509	}
1510
1511	/**
1512	* inactive_anon_is_low - check if anonymous pages need to be deactivated
1513	* @lruvec: LRU vector to check
1514	*
1515	* Returns true if the zone does not have enough inactive anon pages,
1516	* meaning some active anon pages need to be deactivated.
1517	*/
1518	static int inactive_anon_is_low(struct lruvec *lruvec)
1519	{
1520	/*
1521	* If we don't have swap space, anonymous page deactivation
1522	* is pointless.
1523	*/
1524	if (!total_swap_pages)
1525	return 0;
1526
1527	if (!mem_cgroup_disabled())
1528	return mem_cgroup_inactive_anon_is_low(lruvec);
1529
1530	return inactive_anon_is_low_global(lruvec_zone(lruvec));
1531	}
1532	#else
1533	static inline int inactive_anon_is_low(struct lruvec *lruvec)
1534	{
1535	return 0;
1536	}
1537	#endif
1538
1539	static int inactive_file_is_low_global(struct zone *zone)
1540	{
1541	unsigned long active, inactive;
1542
1543	active = zone_page_state(zone, NR_ACTIVE_FILE);
1544	inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1545
1546	return (active > inactive);
1547	}
1548
1549	/**
1550	* inactive_file_is_low - check if file pages need to be deactivated
1551	* @lruvec: LRU vector to check
1552	*
1553	* When the system is doing streaming IO, memory pressure here
1554	* ensures that active file pages get deactivated, until more
1555	* than half of the file pages are on the inactive list.
1556	*
1557	* Once we get to that situation, protect the system's working
1558	* set from being evicted by disabling active file page aging.
1559	*
1560	* This uses a different ratio than the anonymous pages, because
1561	* the page cache uses a use-once replacement algorithm.
1562	*/
1563	static int inactive_file_is_low(struct lruvec *lruvec)
1564	{
1565	if (!mem_cgroup_disabled())
1566	return mem_cgroup_inactive_file_is_low(lruvec);
1567
1568	return inactive_file_is_low_global(lruvec_zone(lruvec));
1569	}
1570
1571	static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1572	{
1573	if (is_file_lru(lru))
1574	return inactive_file_is_low(lruvec);
1575	else
1576	return inactive_anon_is_low(lruvec);
1577	}
1578
1579	static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1580	struct lruvec lruvec, struct scan_control sc)
1581	{
1582	if (is_active_lru(lru)) {
1583	if (inactive_list_is_low(lruvec, lru))
1584	shrink_active_list(nr_to_scan, lruvec, sc, lru);
1585	return 0;
1586	}
1587
1588	return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1589	}
1590
1591	static int vmscan_swappiness(struct scan_control *sc)
1592	{
1593	if (global_reclaim(sc))
1594	return vm_swappiness;
1595	return mem_cgroup_swappiness(sc->target_mem_cgroup);
1596	}
1597
1598	/*
1599	* Determine how aggressively the anon and file LRU lists should be
1600	* scanned. The relative value of each set of LRU lists is determined
1601	* by looking at the fraction of the pages scanned we did rotate back
1602	* onto the active list instead of evict.
1603	*
1604	* nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
1605	* nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
1606	*/
1607	static void get_scan_count(struct lruvec lruvec, struct scan_control sc,
1608	unsigned long *nr)
1609	{
1610	unsigned long anon, file, free;
1611	unsigned long anon_prio, file_prio;
1612	unsigned long ap, fp;
1613	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1614	u64 fraction[2], denominator;
1615	enum lru_list lru;
1616	int noswap = 0;
1617	bool force_scan = false;
1618	struct zone *zone = lruvec_zone(lruvec);
1619
1620	/*
1621	* If the zone or memcg is small, nr[l] can be 0. This
1622	* results in no scanning on this priority and a potential
1623	* priority drop. Global direct reclaim can go to the next
1624	* zone and tends to have no problems. Global kswapd is for
1625	* zone balancing and it needs to scan a minimum amount. When
1626	* reclaiming for a memcg, a priority drop can cause high
1627	* latencies, so it's better to scan a minimum amount there as
1628	* well.
1629	*/
1630	if (current_is_kswapd() && zone->all_unreclaimable)
1631	force_scan = true;
1632	if (!global_reclaim(sc))
1633	force_scan = true;
1634
1635	/* If we have no swap space, do not bother scanning anon pages. */
1636	if (!sc->may_swap \|\| (nr_swap_pages <= 0)) {
1637	noswap = 1;
1638	fraction[0] = 0;
1639	fraction[1] = 1;
1640	denominator = 1;
1641	goto out;
1642	}
1643
1644	anon = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
1645	get_lru_size(lruvec, LRU_INACTIVE_ANON);
1646	file = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
1647	get_lru_size(lruvec, LRU_INACTIVE_FILE);
1648
1649	if (global_reclaim(sc)) {
1650	free = zone_page_state(zone, NR_FREE_PAGES);
1651	/* If we have very few page cache pages,
1652	force-scan anon pages. */
1653	if (unlikely(file + free <= high_wmark_pages(zone))) {
1654	fraction[0] = 1;
1655	fraction[1] = 0;
1656	denominator = 1;
1657	goto out;
1658	}
1659	}
1660
1661	/*
1662	* With swappiness at 100, anonymous and file have the same priority.
1663	* This scanning priority is essentially the inverse of IO cost.
1664	*/
1665	anon_prio = vmscan_swappiness(sc);
1666	file_prio = 200 - anon_prio;
1667
1668	/*
1669	* OK, so we have swap space and a fair amount of page cache
1670	* pages. We use the recently rotated / recently scanned
1671	* ratios to determine how valuable each cache is.
1672	*
1673	* Because workloads change over time (and to avoid overflow)
1674	* we keep these statistics as a floating average, which ends
1675	* up weighing recent references more than old ones.
1676	*
1677	* anon in [0], file in [1]
1678	*/
1679	spin_lock_irq(&zone->lru_lock);
1680	if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1681	reclaim_stat->recent_scanned[0] /= 2;
1682	reclaim_stat->recent_rotated[0] /= 2;
1683	}
1684
1685	if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1686	reclaim_stat->recent_scanned[1] /= 2;
1687	reclaim_stat->recent_rotated[1] /= 2;
1688	}
1689
1690	/*
1691	* The amount of pressure on anon vs file pages is inversely
1692	* proportional to the fraction of recently scanned pages on
1693	* each list that were recently referenced and in active use.
1694	*/
1695	ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1696	ap /= reclaim_stat->recent_rotated[0] + 1;
1697
1698	fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
1699	fp /= reclaim_stat->recent_rotated[1] + 1;
1700	spin_unlock_irq(&zone->lru_lock);
1701
1702	fraction[0] = ap;
1703	fraction[1] = fp;
1704	denominator = ap + fp + 1;
1705	out:
1706	for_each_evictable_lru(lru) {
1707	int file = is_file_lru(lru);
1708	unsigned long scan;
1709
1710	scan = get_lru_size(lruvec, lru);
1711	if (sc->priority \|\| noswap \|\| !vmscan_swappiness(sc)) {
1712	scan >>= sc->priority;
1713	if (!scan && force_scan)
1714	scan = SWAP_CLUSTER_MAX;
1715	scan = div64_u64(scan * fraction[file], denominator);
1716	}
1717	nr[lru] = scan;
1718	}
1719	}
1720
1721	/* Use reclaim/compaction for costly allocs or under memory pressure */
1722	static bool in_reclaim_compaction(struct scan_control *sc)
1723	{
1724	if (COMPACTION_BUILD && sc->order &&
1725	(sc->order > PAGE_ALLOC_COSTLY_ORDER \|\|
1726	sc->priority < DEF_PRIORITY - 2))
1727	return true;
1728
1729	return false;
1730	}
1731
1732	/*
1733	* Reclaim/compaction is used for high-order allocation requests. It reclaims
1734	* order-0 pages before compacting the zone. should_continue_reclaim() returns
1735	* true if more pages should be reclaimed such that when the page allocator
1736	* calls try_to_compact_zone() that it will have enough free pages to succeed.
1737	* It will give up earlier than that if there is difficulty reclaiming pages.
1738	*/
1739	static inline bool should_continue_reclaim(struct lruvec *lruvec,
1740	unsigned long nr_reclaimed,
1741	unsigned long nr_scanned,
1742	struct scan_control *sc)
1743	{
1744	unsigned long pages_for_compaction;
1745	unsigned long inactive_lru_pages;
1746
1747	/* If not in reclaim/compaction mode, stop */
1748	if (!in_reclaim_compaction(sc))
1749	return false;
1750
1751	/* Consider stopping depending on scan and reclaim activity */
1752	if (sc->gfp_mask & __GFP_REPEAT) {
1753	/*
1754	* For __GFP_REPEAT allocations, stop reclaiming if the
1755	* full LRU list has been scanned and we are still failing
1756	* to reclaim pages. This full LRU scan is potentially
1757	* expensive but a __GFP_REPEAT caller really wants to succeed
1758	*/
1759	if (!nr_reclaimed && !nr_scanned)
1760	return false;
1761	} else {
1762	/*
1763	* For non-__GFP_REPEAT allocations which can presumably
1764	* fail without consequence, stop if we failed to reclaim
1765	* any pages from the last SWAP_CLUSTER_MAX number of
1766	* pages that were scanned. This will return to the
1767	* caller faster at the risk reclaim/compaction and
1768	* the resulting allocation attempt fails
1769	*/
1770	if (!nr_reclaimed)
1771	return false;
1772	}
1773
1774	/*
1775	* If we have not reclaimed enough pages for compaction and the
1776	* inactive lists are large enough, continue reclaiming
1777	*/
1778	pages_for_compaction = (2UL << sc->order);
1779	inactive_lru_pages = get_lru_size(lruvec, LRU_INACTIVE_FILE);
1780	if (nr_swap_pages > 0)
1781	inactive_lru_pages += get_lru_size(lruvec, LRU_INACTIVE_ANON);
1782	if (sc->nr_reclaimed < pages_for_compaction &&
1783	inactive_lru_pages > pages_for_compaction)
1784	return true;
1785
1786	/* If compaction would go ahead or the allocation would succeed, stop */
1787	switch (compaction_suitable(lruvec_zone(lruvec), sc->order)) {
1788	case COMPACT_PARTIAL:
1789	case COMPACT_CONTINUE:
1790	return false;
1791	default:
1792	return true;
1793	}
1794	}
1795
1796	/*
1797	* This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
1798	*/
1799	static void shrink_lruvec(struct lruvec lruvec, struct scan_control sc)
1800	{
1801	unsigned long nr[NR_LRU_LISTS];
1802	unsigned long nr_to_scan;
1803	enum lru_list lru;
1804	unsigned long nr_reclaimed, nr_scanned;
1805	unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1806	struct blk_plug plug;
1807
1808	restart:
1809	nr_reclaimed = 0;
1810	nr_scanned = sc->nr_scanned;
1811	get_scan_count(lruvec, sc, nr);
1812
1813	blk_start_plug(&plug);
1814	while (nr[LRU_INACTIVE_ANON] \|\| nr[LRU_ACTIVE_FILE] \|\|
1815	nr[LRU_INACTIVE_FILE]) {
1816	for_each_evictable_lru(lru) {
1817	if (nr[lru]) {
1818	nr_to_scan = min_t(unsigned long,
1819	nr[lru], SWAP_CLUSTER_MAX);
1820	nr[lru] -= nr_to_scan;
1821
1822	nr_reclaimed += shrink_list(lru, nr_to_scan,
1823	lruvec, sc);
1824	}
1825	}
1826	/*
1827	* On large memory systems, scan >> priority can become
1828	* really large. This is fine for the starting priority;
1829	* we want to put equal scanning pressure on each zone.
1830	* However, if the VM has a harder time of freeing pages,
1831	* with multiple processes reclaiming pages, the total
1832	* freeing target can get unreasonably large.
1833	*/
1834	if (nr_reclaimed >= nr_to_reclaim &&
1835	sc->priority < DEF_PRIORITY)
1836	break;
1837	}
1838	blk_finish_plug(&plug);
1839	sc->nr_reclaimed += nr_reclaimed;
1840
1841	/*
1842	* Even if we did not try to evict anon pages at all, we want to
1843	* rebalance the anon lru active/inactive ratio.
1844	*/
1845	if (inactive_anon_is_low(lruvec))
1846	shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
1847	sc, LRU_ACTIVE_ANON);
1848
1849	/* reclaim/compaction might need reclaim to continue */
1850	if (should_continue_reclaim(lruvec, nr_reclaimed,
1851	sc->nr_scanned - nr_scanned, sc))
1852	goto restart;
1853
1854	throttle_vm_writeout(sc->gfp_mask);
1855	}
1856
1857	static void shrink_zone(struct zone zone, struct scan_control sc)
1858	{
1859	struct mem_cgroup *root = sc->target_mem_cgroup;
1860	struct mem_cgroup_reclaim_cookie reclaim = {
1861	.zone = zone,
1862	.priority = sc->priority,
1863	};
1864	struct mem_cgroup *memcg;
1865
1866	memcg = mem_cgroup_iter(root, NULL, &reclaim);
1867	do {
1868	struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
1869
1870	shrink_lruvec(lruvec, sc);
1871
1872	/*
1873	* Limit reclaim has historically picked one memcg and
1874	* scanned it with decreasing priority levels until
1875	* nr_to_reclaim had been reclaimed. This priority
1876	* cycle is thus over after a single memcg.
1877	*
1878	* Direct reclaim and kswapd, on the other hand, have
1879	* to scan all memory cgroups to fulfill the overall
1880	* scan target for the zone.
1881	*/
1882	if (!global_reclaim(sc)) {
1883	mem_cgroup_iter_break(root, memcg);
1884	break;
1885	}
1886	memcg = mem_cgroup_iter(root, memcg, &reclaim);
1887	} while (memcg);
1888	}
1889
1890	/* Returns true if compaction should go ahead for a high-order request */
1891	static inline bool compaction_ready(struct zone zone, struct scan_control sc)
1892	{
1893	unsigned long balance_gap, watermark;
1894	bool watermark_ok;
1895
1896	/* Do not consider compaction for orders reclaim is meant to satisfy */
1897	if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
1898	return false;
1899
1900	/*
1901	* Compaction takes time to run and there are potentially other
1902	* callers using the pages just freed. Continue reclaiming until
1903	* there is a buffer of free pages available to give compaction
1904	* a reasonable chance of completing and allocating the page
1905	*/
1906	balance_gap = min(low_wmark_pages(zone),
1907	(zone->present_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
1908	KSWAPD_ZONE_BALANCE_GAP_RATIO);
1909	watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
1910	watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
1911
1912	/*
1913	* If compaction is deferred, reclaim up to a point where
1914	* compaction will have a chance of success when re-enabled
1915	*/
1916	if (compaction_deferred(zone, sc->order))
1917	return watermark_ok;
1918
1919	/* If compaction is not ready to start, keep reclaiming */
1920	if (!compaction_suitable(zone, sc->order))
1921	return false;
1922
1923	return watermark_ok;
1924	}
1925
1926	/*
1927	* This is the direct reclaim path, for page-allocating processes. We only
1928	* try to reclaim pages from zones which will satisfy the caller's allocation
1929	* request.
1930	*
1931	* We reclaim from a zone even if that zone is over high_wmark_pages(zone).
1932	* Because:
1933	* a) The caller may be trying to free extra pages to satisfy a higher-order
1934	* allocation or
1935	* b) The target zone may be at high_wmark_pages(zone) but the lower zones
1936	* must go over high_wmark_pages(zone) to satisfy the `incremental min'
1937	* zone defense algorithm.
1938	*
1939	* If a zone is deemed to be full of pinned pages then just give it a light
1940	* scan then give up on it.
1941	*
1942	* This function returns true if a zone is being reclaimed for a costly
1943	* high-order allocation and compaction is ready to begin. This indicates to
1944	* the caller that it should consider retrying the allocation instead of
1945	* further reclaim.
1946	*/
1947	static bool shrink_zones(struct zonelist zonelist, struct scan_control sc)
1948	{
1949	struct zoneref *z;
1950	struct zone *zone;
1951	unsigned long nr_soft_reclaimed;
1952	unsigned long nr_soft_scanned;
1953	bool aborted_reclaim = false;
1954
1955	/*
1956	* If the number of buffer_heads in the machine exceeds the maximum
1957	* allowed level, force direct reclaim to scan the highmem zone as
1958	* highmem pages could be pinning lowmem pages storing buffer_heads
1959	*/
1960	if (buffer_heads_over_limit)
1961	sc->gfp_mask \|= __GFP_HIGHMEM;
1962
1963	for_each_zone_zonelist_nodemask(zone, z, zonelist,
1964	gfp_zone(sc->gfp_mask), sc->nodemask) {
1965	if (!populated_zone(zone))
1966	continue;
1967	/*
1968	* Take care memory controller reclaiming has small influence
1969	* to global LRU.
1970	*/
1971	if (global_reclaim(sc)) {
1972	if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1973	continue;
1974	if (zone->all_unreclaimable &&
1975	sc->priority != DEF_PRIORITY)
1976	continue; /* Let kswapd poll it */
1977	if (COMPACTION_BUILD) {
1978	/*
1979	* If we already have plenty of memory free for
1980	* compaction in this zone, don't free any more.
1981	* Even though compaction is invoked for any
1982	* non-zero order, only frequent costly order
1983	* reclamation is disruptive enough to become a
1984	* noticeable problem, like transparent huge
1985	* page allocations.
1986	*/
1987	if (compaction_ready(zone, sc)) {
1988	aborted_reclaim = true;
1989	continue;
1990	}
1991	}
1992	/*
1993	* This steals pages from memory cgroups over softlimit
1994	* and returns the number of reclaimed pages and
1995	* scanned pages. This works for global memory pressure
1996	* and balancing, not for a memcg's limit.
1997	*/
1998	nr_soft_scanned = 0;
1999	nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2000	sc->order, sc->gfp_mask,
2001	&nr_soft_scanned);
2002	sc->nr_reclaimed += nr_soft_reclaimed;
2003	sc->nr_scanned += nr_soft_scanned;
2004	/* need some check for avoid more shrink_zone() */
2005	}
2006
2007	shrink_zone(zone, sc);
2008	}
2009
2010	return aborted_reclaim;
2011	}
2012
2013	static bool zone_reclaimable(struct zone *zone)
2014	{
2015	return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
2016	}
2017
2018	/* All zones in zonelist are unreclaimable? */
2019	static bool all_unreclaimable(struct zonelist *zonelist,
2020	struct scan_control *sc)
2021	{
2022	struct zoneref *z;
2023	struct zone *zone;
2024
2025	for_each_zone_zonelist_nodemask(zone, z, zonelist,
2026	gfp_zone(sc->gfp_mask), sc->nodemask) {
2027	if (!populated_zone(zone))
2028	continue;
2029	if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2030	continue;
2031	if (!zone->all_unreclaimable)
2032	return false;
2033	}
2034
2035	return true;
2036	}
2037
2038	/*
2039	* This is the main entry point to direct page reclaim.
2040	*
2041	* If a full scan of the inactive list fails to free enough memory then we
2042	* are "out of memory" and something needs to be killed.
2043	*
2044	* If the caller is !__GFP_FS then the probability of a failure is reasonably
2045	* high - the zone may be full of dirty or under-writeback pages, which this
2046	* caller can't do much about. We kick the writeback threads and take explicit
2047	* naps in the hope that some of these pages can be written. But if the
2048	* allocating task holds filesystem locks which prevent writeout this might not
2049	* work, and the allocation attempt will fail.
2050	*
2051	* returns: 0, if no pages reclaimed
2052	* else, the number of pages reclaimed
2053	*/
2054	static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2055	struct scan_control *sc,
2056	struct shrink_control *shrink)
2057	{
2058	unsigned long total_scanned = 0;
2059	struct reclaim_state *reclaim_state = current->reclaim_state;
2060	struct zoneref *z;
2061	struct zone *zone;
2062	unsigned long writeback_threshold;
2063	bool aborted_reclaim;
2064
2065	delayacct_freepages_start();
2066
2067	if (global_reclaim(sc))
2068	count_vm_event(ALLOCSTALL);
2069
2070	do {
2071	sc->nr_scanned = 0;
2072	aborted_reclaim = shrink_zones(zonelist, sc);
2073
2074	/*
2075	* Don't shrink slabs when reclaiming memory from
2076	* over limit cgroups
2077	*/
2078	if (global_reclaim(sc)) {
2079	unsigned long lru_pages = 0;
2080	for_each_zone_zonelist(zone, z, zonelist,
2081	gfp_zone(sc->gfp_mask)) {
2082	if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2083	continue;
2084
2085	lru_pages += zone_reclaimable_pages(zone);
2086	}
2087
2088	shrink_slab(shrink, sc->nr_scanned, lru_pages);
2089	if (reclaim_state) {
2090	sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2091	reclaim_state->reclaimed_slab = 0;
2092	}
2093	}
2094	total_scanned += sc->nr_scanned;
2095	if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2096	goto out;
2097
2098	/*
2099	* Try to write back as many pages as we just scanned. This
2100	* tends to cause slow streaming writers to write data to the
2101	* disk smoothly, at the dirtying rate, which is nice. But
2102	* that's undesirable in laptop mode, where we want lumpy
2103	* writeout. So in laptop mode, write out the whole world.
2104	*/
2105	writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2106	if (total_scanned > writeback_threshold) {
2107	wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2108	WB_REASON_TRY_TO_FREE_PAGES);
2109	sc->may_writepage = 1;
2110	}
2111
2112	/* Take a nap, wait for some writeback to complete */
2113	if (!sc->hibernation_mode && sc->nr_scanned &&
2114	sc->priority < DEF_PRIORITY - 2) {
2115	struct zone *preferred_zone;
2116
2117	first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
2118	&cpuset_current_mems_allowed,
2119	&preferred_zone);
2120	wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
2121	}
2122	} while (--sc->priority >= 0);
2123
2124	out:
2125	delayacct_freepages_end();
2126
2127	if (sc->nr_reclaimed)
2128	return sc->nr_reclaimed;
2129
2130	/*
2131	* As hibernation is going on, kswapd is freezed so that it can't mark
2132	* the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2133	* check.
2134	*/
2135	if (oom_killer_disabled)
2136	return 0;
2137
2138	/* Aborted reclaim to try compaction? don't OOM, then */
2139	if (aborted_reclaim)
2140	return 1;
2141
2142	/* top priority shrink_zones still had more to do? don't OOM, then */
2143	if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2144	return 1;
2145
2146	return 0;
2147	}
2148
2149	static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2150	{
2151	struct zone *zone;
2152	unsigned long pfmemalloc_reserve = 0;
2153	unsigned long free_pages = 0;
2154	int i;
2155	bool wmark_ok;
2156
2157	for (i = 0; i <= ZONE_NORMAL; i++) {
2158	zone = &pgdat->node_zones[i];
2159	pfmemalloc_reserve += min_wmark_pages(zone);
2160	free_pages += zone_page_state(zone, NR_FREE_PAGES);
2161	}
2162
2163	wmark_ok = free_pages > pfmemalloc_reserve / 2;
2164
2165	/* kswapd must be awake if processes are being throttled */
2166	if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2167	pgdat->classzone_idx = min(pgdat->classzone_idx,
2168	(enum zone_type)ZONE_NORMAL);
2169	wake_up_interruptible(&pgdat->kswapd_wait);
2170	}
2171
2172	return wmark_ok;
2173	}
2174
2175	/*
2176	* Throttle direct reclaimers if backing storage is backed by the network
2177	* and the PFMEMALLOC reserve for the preferred node is getting dangerously
2178	* depleted. kswapd will continue to make progress and wake the processes
2179	* when the low watermark is reached
2180	*/
2181	static void throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2182	nodemask_t *nodemask)
2183	{
2184	struct zone *zone;
2185	int high_zoneidx = gfp_zone(gfp_mask);
2186	pg_data_t *pgdat;
2187
2188	/*
2189	* Kernel threads should not be throttled as they may be indirectly
2190	* responsible for cleaning pages necessary for reclaim to make forward
2191	* progress. kjournald for example may enter direct reclaim while
2192	* committing a transaction where throttling it could forcing other
2193	* processes to block on log_wait_commit().
2194	*/
2195	if (current->flags & PF_KTHREAD)
2196	return;
2197
2198	/* Check if the pfmemalloc reserves are ok */
2199	first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
2200	pgdat = zone->zone_pgdat;
2201	if (pfmemalloc_watermark_ok(pgdat))
2202	return;
2203
2204	/* Account for the throttling */
2205	count_vm_event(PGSCAN_DIRECT_THROTTLE);
2206
2207	/*
2208	* If the caller cannot enter the filesystem, it's possible that it
2209	* is due to the caller holding an FS lock or performing a journal
2210	* transaction in the case of a filesystem like ext[3\|4]. In this case,
2211	* it is not safe to block on pfmemalloc_wait as kswapd could be
2212	* blocked waiting on the same lock. Instead, throttle for up to a
2213	* second before continuing.
2214	*/
2215	if (!(gfp_mask & __GFP_FS)) {
2216	wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2217	pfmemalloc_watermark_ok(pgdat), HZ);
2218	return;
2219	}
2220
2221	/* Throttle until kswapd wakes the process */
2222	wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2223	pfmemalloc_watermark_ok(pgdat));
2224	}
2225
2226	unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2227	gfp_t gfp_mask, nodemask_t *nodemask)
2228	{
2229	unsigned long nr_reclaimed;
2230	struct scan_control sc = {
2231	.gfp_mask = gfp_mask,
2232	.may_writepage = !laptop_mode,
2233	.nr_to_reclaim = SWAP_CLUSTER_MAX,
2234	.may_unmap = 1,
2235	.may_swap = 1,
2236	.order = order,
2237	.priority = DEF_PRIORITY,
2238	.target_mem_cgroup = NULL,
2239	.nodemask = nodemask,
2240	};
2241	struct shrink_control shrink = {
2242	.gfp_mask = sc.gfp_mask,
2243	};
2244
2245	throttle_direct_reclaim(gfp_mask, zonelist, nodemask);
2246
2247	/*
2248	* Do not enter reclaim if fatal signal is pending. 1 is returned so
2249	* that the page allocator does not consider triggering OOM
2250	*/
2251	if (fatal_signal_pending(current))
2252	return 1;
2253
2254	trace_mm_vmscan_direct_reclaim_begin(order,
2255	sc.may_writepage,
2256	gfp_mask);
2257
2258	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2259
2260	trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2261
2262	return nr_reclaimed;
2263	}
2264
2265	#ifdef CONFIG_MEMCG
2266
2267	unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2268	gfp_t gfp_mask, bool noswap,
2269	struct zone *zone,
2270	unsigned long *nr_scanned)
2271	{
2272	struct scan_control sc = {
2273	.nr_scanned = 0,
2274	.nr_to_reclaim = SWAP_CLUSTER_MAX,
2275	.may_writepage = !laptop_mode,
2276	.may_unmap = 1,
2277	.may_swap = !noswap,
2278	.order = 0,
2279	.priority = 0,
2280	.target_mem_cgroup = memcg,
2281	};
2282	struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2283
2284	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) \|
2285	(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2286
2287	trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2288	sc.may_writepage,
2289	sc.gfp_mask);
2290
2291	/*
2292	* NOTE: Although we can get the priority field, using it
2293	* here is not a good idea, since it limits the pages we can scan.
2294	* if we don't reclaim here, the shrink_zone from balance_pgdat
2295	* will pick up pages from other mem cgroup's as well. We hack
2296	* the priority and make it zero.
2297	*/
2298	shrink_lruvec(lruvec, &sc);
2299
2300	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2301
2302	*nr_scanned = sc.nr_scanned;
2303	return sc.nr_reclaimed;
2304	}
2305
2306	unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
2307	gfp_t gfp_mask,
2308	bool noswap)
2309	{
2310	struct zonelist *zonelist;
2311	unsigned long nr_reclaimed;
2312	int nid;
2313	struct scan_control sc = {
2314	.may_writepage = !laptop_mode,
2315	.may_unmap = 1,
2316	.may_swap = !noswap,
2317	.nr_to_reclaim = SWAP_CLUSTER_MAX,
2318	.order = 0,
2319	.priority = DEF_PRIORITY,
2320	.target_mem_cgroup = memcg,
2321	.nodemask = NULL, /* we don't care the placement */
2322	.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) \|
2323	(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2324	};
2325	struct shrink_control shrink = {
2326	.gfp_mask = sc.gfp_mask,
2327	};
2328
2329	/*
2330	* Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2331	* take care of from where we get pages. So the node where we start the
2332	* scan does not need to be the current node.
2333	*/
2334	nid = mem_cgroup_select_victim_node(memcg);
2335
2336	zonelist = NODE_DATA(nid)->node_zonelists;
2337
2338	trace_mm_vmscan_memcg_reclaim_begin(0,
2339	sc.may_writepage,
2340	sc.gfp_mask);
2341
2342	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2343
2344	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2345
2346	return nr_reclaimed;
2347	}
2348	#endif
2349
2350	static void age_active_anon(struct zone zone, struct scan_control sc)
2351	{
2352	struct mem_cgroup *memcg;
2353
2354	if (!total_swap_pages)
2355	return;
2356
2357	memcg = mem_cgroup_iter(NULL, NULL, NULL);
2358	do {
2359	struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2360
2361	if (inactive_anon_is_low(lruvec))
2362	shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2363	sc, LRU_ACTIVE_ANON);
2364
2365	memcg = mem_cgroup_iter(NULL, memcg, NULL);
2366	} while (memcg);
2367	}
2368
2369	/*
2370	* pgdat_balanced is used when checking if a node is balanced for high-order
2371	* allocations. Only zones that meet watermarks and are in a zone allowed
2372	* by the callers classzone_idx are added to balanced_pages. The total of
2373	* balanced pages must be at least 25% of the zones allowed by classzone_idx
2374	* for the node to be considered balanced. Forcing all zones to be balanced
2375	* for high orders can cause excessive reclaim when there are imbalanced zones.
2376	* The choice of 25% is due to
2377	* o a 16M DMA zone that is balanced will not balance a zone on any
2378	* reasonable sized machine
2379	* o On all other machines, the top zone must be at least a reasonable
2380	* percentage of the middle zones. For example, on 32-bit x86, highmem
2381	* would need to be at least 256M for it to be balance a whole node.
2382	* Similarly, on x86-64 the Normal zone would need to be at least 1G
2383	* to balance a node on its own. These seemed like reasonable ratios.
2384	*/
2385	static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
2386	int classzone_idx)
2387	{
2388	unsigned long present_pages = 0;
2389	int i;
2390
2391	for (i = 0; i <= classzone_idx; i++)
2392	present_pages += pgdat->node_zones[i].present_pages;
2393
2394	/* A special case here: if zone has no page, we think it's balanced */
2395	return balanced_pages >= (present_pages >> 2);
2396	}
2397
2398	/*
2399	* Prepare kswapd for sleeping. This verifies that there are no processes
2400	* waiting in throttle_direct_reclaim() and that watermarks have been met.
2401	*
2402	* Returns true if kswapd is ready to sleep
2403	*/
2404	static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
2405	int classzone_idx)
2406	{
2407	int i;
2408	unsigned long balanced = 0;
2409	bool all_zones_ok = true;
2410
2411	/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2412	if (remaining)
2413	return false;
2414
2415	/*
2416	* There is a potential race between when kswapd checks its watermarks
2417	* and a process gets throttled. There is also a potential race if
2418	* processes get throttled, kswapd wakes, a large process exits therby
2419	* balancing the zones that causes kswapd to miss a wakeup. If kswapd
2420	* is going to sleep, no process should be sleeping on pfmemalloc_wait
2421	* so wake them now if necessary. If necessary, processes will wake
2422	* kswapd and get throttled again
2423	*/
2424	if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
2425	wake_up(&pgdat->pfmemalloc_wait);
2426	return false;
2427	}
2428
2429	/* Check the watermark levels */
2430	for (i = 0; i <= classzone_idx; i++) {
2431	struct zone *zone = pgdat->node_zones + i;
2432
2433	if (!populated_zone(zone))
2434	continue;
2435
2436	/*
2437	* balance_pgdat() skips over all_unreclaimable after
2438	* DEF_PRIORITY. Effectively, it considers them balanced so
2439	* they must be considered balanced here as well if kswapd
2440	* is to sleep
2441	*/
2442	if (zone->all_unreclaimable) {
2443	balanced += zone->present_pages;
2444	continue;
2445	}
2446
2447	if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
2448	i, 0))
2449	all_zones_ok = false;
2450	else
2451	balanced += zone->present_pages;
2452	}
2453
2454	/*
2455	* For high-order requests, the balanced zones must contain at least
2456	* 25% of the nodes pages for kswapd to sleep. For order-0, all zones
2457	* must be balanced
2458	*/
2459	if (order)
2460	return pgdat_balanced(pgdat, balanced, classzone_idx);
2461	else
2462	return all_zones_ok;
2463	}
2464
2465	/*
2466	* For kswapd, balance_pgdat() will work across all this node's zones until
2467	* they are all at high_wmark_pages(zone).
2468	*
2469	* Returns the final order kswapd was reclaiming at
2470	*
2471	* There is special handling here for zones which are full of pinned pages.
2472	* This can happen if the pages are all mlocked, or if they are all used by
2473	* device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
2474	* What we do is to detect the case where all pages in the zone have been
2475	* scanned twice and there has been zero successful reclaim. Mark the zone as
2476	* dead and from now on, only perform a short scan. Basically we're polling
2477	* the zone for when the problem goes away.
2478	*
2479	* kswapd scans the zones in the highmem->normal->dma direction. It skips
2480	* zones which have free_pages > high_wmark_pages(zone), but once a zone is
2481	* found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2482	* lower zones regardless of the number of free pages in the lower zones. This
2483	* interoperates with the page allocator fallback scheme to ensure that aging
2484	* of pages is balanced across the zones.
2485	*/
2486	static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2487	int *classzone_idx)
2488	{
2489	int all_zones_ok;
2490	unsigned long balanced;
2491	int i;
2492	int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
2493	unsigned long total_scanned;
2494	struct reclaim_state *reclaim_state = current->reclaim_state;
2495	unsigned long nr_soft_reclaimed;
2496	unsigned long nr_soft_scanned;
2497	struct scan_control sc = {
2498	.gfp_mask = GFP_KERNEL,
2499	.may_unmap = 1,
2500	.may_swap = 1,
2501	/*
2502	* kswapd doesn't want to be bailed out while reclaim. because
2503	* we want to put equal scanning pressure on each zone.
2504	*/
2505	.nr_to_reclaim = ULONG_MAX,
2506	.order = order,
2507	.target_mem_cgroup = NULL,
2508	};
2509	struct shrink_control shrink = {
2510	.gfp_mask = sc.gfp_mask,
2511	};
2512	loop_again:
2513	total_scanned = 0;
2514	sc.priority = DEF_PRIORITY;
2515	sc.nr_reclaimed = 0;
2516	sc.may_writepage = !laptop_mode;
2517	count_vm_event(PAGEOUTRUN);
2518
2519	do {
2520	unsigned long lru_pages = 0;
2521	int has_under_min_watermark_zone = 0;
2522
2523	all_zones_ok = 1;
2524	balanced = 0;
2525
2526	/*
2527	* Scan in the highmem->dma direction for the highest
2528	* zone which needs scanning
2529	*/
2530	for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2531	struct zone *zone = pgdat->node_zones + i;
2532
2533	if (!populated_zone(zone))
2534	continue;
2535
2536	if (zone->all_unreclaimable &&
2537	sc.priority != DEF_PRIORITY)
2538	continue;
2539
2540	/*
2541	* Do some background aging of the anon list, to give
2542	* pages a chance to be referenced before reclaiming.
2543	*/
2544	age_active_anon(zone, &sc);
2545
2546	/*
2547	* If the number of buffer_heads in the machine
2548	* exceeds the maximum allowed level and this node
2549	* has a highmem zone, force kswapd to reclaim from
2550	* it to relieve lowmem pressure.
2551	*/
2552	if (buffer_heads_over_limit && is_highmem_idx(i)) {
2553	end_zone = i;
2554	break;
2555	}
2556
2557	if (!zone_watermark_ok_safe(zone, order,
2558	high_wmark_pages(zone), 0, 0)) {
2559	end_zone = i;
2560	break;
2561	} else {
2562	/* If balanced, clear the congested flag */
2563	zone_clear_flag(zone, ZONE_CONGESTED);
2564	}
2565	}
2566	if (i < 0)
2567	goto out;
2568
2569	for (i = 0; i <= end_zone; i++) {
2570	struct zone *zone = pgdat->node_zones + i;
2571
2572	lru_pages += zone_reclaimable_pages(zone);
2573	}
2574
2575	/*
2576	* Now scan the zone in the dma->highmem direction, stopping
2577	* at the last zone which needs scanning.
2578	*
2579	* We do this because the page allocator works in the opposite
2580	* direction. This prevents the page allocator from allocating
2581	* pages behind kswapd's direction of progress, which would
2582	* cause too much scanning of the lower zones.
2583	*/
2584	for (i = 0; i <= end_zone; i++) {
2585	struct zone *zone = pgdat->node_zones + i;
2586	int nr_slab, testorder;
2587	unsigned long balance_gap;
2588
2589	if (!populated_zone(zone))
2590	continue;
2591
2592	if (zone->all_unreclaimable &&
2593	sc.priority != DEF_PRIORITY)
2594	continue;
2595
2596	sc.nr_scanned = 0;
2597
2598	nr_soft_scanned = 0;
2599	/*
2600	* Call soft limit reclaim before calling shrink_zone.
2601	*/
2602	nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2603	order, sc.gfp_mask,
2604	&nr_soft_scanned);
2605	sc.nr_reclaimed += nr_soft_reclaimed;
2606	total_scanned += nr_soft_scanned;
2607
2608	/*
2609	* We put equal pressure on every zone, unless
2610	* one zone has way too many pages free
2611	* already. The "too many pages" is defined
2612	* as the high wmark plus a "gap" where the
2613	* gap is either the low watermark or 1%
2614	* of the zone, whichever is smaller.
2615	*/
2616	balance_gap = min(low_wmark_pages(zone),
2617	(zone->present_pages +
2618	KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2619	KSWAPD_ZONE_BALANCE_GAP_RATIO);
2620	/*
2621	* Kswapd reclaims only single pages with compaction
2622	* enabled. Trying too hard to reclaim until contiguous
2623	* free pages have become available can hurt performance
2624	* by evicting too much useful data from memory.
2625	* Do not reclaim more than needed for compaction.
2626	*/
2627	testorder = order;
2628	if (COMPACTION_BUILD && order &&
2629	compaction_suitable(zone, order) !=
2630	COMPACT_SKIPPED)
2631	testorder = 0;
2632
2633	if ((buffer_heads_over_limit && is_highmem_idx(i)) \|\|
2634	!zone_watermark_ok_safe(zone, testorder,
2635	high_wmark_pages(zone) + balance_gap,
2636	end_zone, 0)) {
2637	shrink_zone(zone, &sc);
2638
2639	reclaim_state->reclaimed_slab = 0;
2640	nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages);
2641	sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2642	total_scanned += sc.nr_scanned;
2643
2644	if (nr_slab == 0 && !zone_reclaimable(zone))
2645	zone->all_unreclaimable = 1;
2646	}
2647
2648	/*
2649	* If we've done a decent amount of scanning and
2650	* the reclaim ratio is low, start doing writepage
2651	* even in laptop mode
2652	*/
2653	if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2654	total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
2655	sc.may_writepage = 1;
2656
2657	if (zone->all_unreclaimable) {
2658	if (end_zone && end_zone == i)
2659	end_zone--;
2660	continue;
2661	}
2662
2663	if (!zone_watermark_ok_safe(zone, testorder,
2664	high_wmark_pages(zone), end_zone, 0)) {
2665	all_zones_ok = 0;
2666	/*
2667	* We are still under min water mark. This
2668	* means that we have a GFP_ATOMIC allocation
2669	* failure risk. Hurry up!
2670	*/
2671	if (!zone_watermark_ok_safe(zone, order,
2672	min_wmark_pages(zone), end_zone, 0))
2673	has_under_min_watermark_zone = 1;
2674	} else {
2675	/*
2676	* If a zone reaches its high watermark,
2677	* consider it to be no longer congested. It's
2678	* possible there are dirty pages backed by
2679	* congested BDIs but as pressure is relieved,
2680	* speculatively avoid congestion waits
2681	*/
2682	zone_clear_flag(zone, ZONE_CONGESTED);
2683	if (i <= *classzone_idx)
2684	balanced += zone->present_pages;
2685	}
2686
2687	}
2688
2689	/*
2690	* If the low watermark is met there is no need for processes
2691	* to be throttled on pfmemalloc_wait as they should not be
2692	* able to safely make forward progress. Wake them
2693	*/
2694	if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
2695	pfmemalloc_watermark_ok(pgdat))
2696	wake_up(&pgdat->pfmemalloc_wait);
2697
2698	if (all_zones_ok \|\| (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
2699	break; /* kswapd: all done */
2700	/*
2701	* OK, kswapd is getting into trouble. Take a nap, then take
2702	* another pass across the zones.
2703	*/
2704	if (total_scanned && (sc.priority < DEF_PRIORITY - 2)) {
2705	if (has_under_min_watermark_zone)
2706	count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
2707	else
2708	congestion_wait(BLK_RW_ASYNC, HZ/10);
2709	}
2710
2711	/*
2712	* We do this so kswapd doesn't build up large priorities for
2713	* example when it is freeing in parallel with allocators. It
2714	* matches the direct reclaim path behaviour in terms of impact
2715	* on zone->*_priority.
2716	*/
2717	if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2718	break;
2719	} while (--sc.priority >= 0);
2720	out:
2721
2722	/*
2723	* order-0: All zones must meet high watermark for a balanced node
2724	* high-order: Balanced zones must make up at least 25% of the node
2725	* for the node to be balanced
2726	*/
2727	if (!(all_zones_ok \|\| (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) {
2728	cond_resched();
2729
2730	try_to_freeze();
2731
2732	/*
2733	* Fragmentation may mean that the system cannot be
2734	* rebalanced for high-order allocations in all zones.
2735	* At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2736	* it means the zones have been fully scanned and are still
2737	* not balanced. For high-order allocations, there is
2738	* little point trying all over again as kswapd may
2739	* infinite loop.
2740	*
2741	* Instead, recheck all watermarks at order-0 as they
2742	* are the most important. If watermarks are ok, kswapd will go
2743	* back to sleep. High-order users can still perform direct
2744	* reclaim if they wish.
2745	*/
2746	if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2747	order = sc.order = 0;
2748
2749	goto loop_again;
2750	}
2751
2752	/*
2753	* If kswapd was reclaiming at a higher order, it has the option of
2754	* sleeping without all zones being balanced. Before it does, it must
2755	* ensure that the watermarks for order-0 on all zones are met and
2756	* that the congestion flags are cleared. The congestion flag must
2757	* be cleared as kswapd is the only mechanism that clears the flag
2758	* and it is potentially going to sleep here.
2759	*/
2760	if (order) {
2761	int zones_need_compaction = 1;
2762
2763	for (i = 0; i <= end_zone; i++) {
2764	struct zone *zone = pgdat->node_zones + i;
2765
2766	if (!populated_zone(zone))
2767	continue;
2768
2769	if (zone->all_unreclaimable &&
2770	sc.priority != DEF_PRIORITY)
2771	continue;
2772
2773	/* Would compaction fail due to lack of free memory? */
2774	if (COMPACTION_BUILD &&
2775	compaction_suitable(zone, order) == COMPACT_SKIPPED)
2776	goto loop_again;
2777
2778	/* Confirm the zone is balanced for order-0 */
2779	if (!zone_watermark_ok(zone, 0,
2780	high_wmark_pages(zone), 0, 0)) {
2781	order = sc.order = 0;
2782	goto loop_again;
2783	}
2784
2785	/* Check if the memory needs to be defragmented. */
2786	if (zone_watermark_ok(zone, order,
2787	low_wmark_pages(zone), *classzone_idx, 0))
2788	zones_need_compaction = 0;
2789
2790	/* If balanced, clear the congested flag */
2791	zone_clear_flag(zone, ZONE_CONGESTED);
2792	}
2793
2794	if (zones_need_compaction)
2795	compact_pgdat(pgdat, order);
2796	}
2797
2798	/*
2799	* Return the order we were reclaiming at so prepare_kswapd_sleep()
2800	* makes a decision on the order we were last reclaiming at. However,
2801	* if another caller entered the allocator slow path while kswapd
2802	* was awake, order will remain at the higher level
2803	*/
2804	*classzone_idx = end_zone;
2805	return order;
2806	}
2807
2808	static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
2809	{
2810	long remaining = 0;
2811	DEFINE_WAIT(wait);
2812
2813	if (freezing(current) \|\| kthread_should_stop())
2814	return;
2815
2816	prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2817
2818	/* Try to sleep for a short interval */
2819	if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2820	remaining = schedule_timeout(HZ/10);
2821	finish_wait(&pgdat->kswapd_wait, &wait);
2822	prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2823	}
2824
2825	/*
2826	* After a short sleep, check if it was a premature sleep. If not, then
2827	* go fully to sleep until explicitly woken up.
2828	*/
2829	if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2830	trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
2831
2832	/*
2833	* vmstat counters are not perfectly accurate and the estimated
2834	* value for counters such as NR_FREE_PAGES can deviate from the
2835	* true value by nr_online_cpus * threshold. To avoid the zone
2836	* watermarks being breached while under pressure, we reduce the
2837	* per-cpu vmstat threshold while kswapd is awake and restore
2838	* them before going back to sleep.
2839	*/
2840	set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
2841
2842	if (!kthread_should_stop())
2843	schedule();
2844
2845	set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
2846	} else {
2847	if (remaining)
2848	count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2849	else
2850	count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2851	}
2852	finish_wait(&pgdat->kswapd_wait, &wait);
2853	}
2854
2855	/*
2856	* The background pageout daemon, started as a kernel thread
2857	* from the init process.
2858	*
2859	* This basically trickles out pages so that we have _some_
2860	* free memory available even if there is no other activity
2861	* that frees anything up. This is needed for things like routing
2862	* etc, where we otherwise might have all activity going on in
2863	* asynchronous contexts that cannot page things out.
2864	*
2865	* If there are applications that are active memory-allocators
2866	* (most normal use), this basically shouldn't matter.
2867	*/
2868	static int kswapd(void *p)
2869	{
2870	unsigned long order, new_order;
2871	unsigned balanced_order;
2872	int classzone_idx, new_classzone_idx;
2873	int balanced_classzone_idx;
2874	pg_data_t pgdat = (pg_data_t)p;
2875	struct task_struct *tsk = current;
2876
2877	struct reclaim_state reclaim_state = {
2878	.reclaimed_slab = 0,
2879	};
2880	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2881
2882	lockdep_set_current_reclaim_state(GFP_KERNEL);
2883
2884	if (!cpumask_empty(cpumask))
2885	set_cpus_allowed_ptr(tsk, cpumask);
2886	current->reclaim_state = &reclaim_state;
2887
2888	/*
2889	* Tell the memory management that we're a "memory allocator",
2890	* and that if we need more memory we should get access to it
2891	* regardless (see "__alloc_pages()"). "kswapd" should
2892	* never get caught in the normal page freeing logic.
2893	*
2894	* (Kswapd normally doesn't need memory anyway, but sometimes
2895	* you need a small amount of memory in order to be able to
2896	* page out something else, and this flag essentially protects
2897	* us from recursively trying to free more memory as we're
2898	* trying to free the first piece of memory in the first place).
2899	*/
2900	tsk->flags \|= PF_MEMALLOC \| PF_SWAPWRITE \| PF_KSWAPD;
2901	set_freezable();
2902
2903	order = new_order = 0;
2904	balanced_order = 0;
2905	classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
2906	balanced_classzone_idx = classzone_idx;
2907	for ( ; ; ) {
2908	int ret;
2909
2910	/*
2911	* If the last balance_pgdat was unsuccessful it's unlikely a
2912	* new request of a similar or harder type will succeed soon
2913	* so consider going to sleep on the basis we reclaimed at
2914	*/
2915	if (balanced_classzone_idx >= new_classzone_idx &&
2916	balanced_order == new_order) {
2917	new_order = pgdat->kswapd_max_order;
2918	new_classzone_idx = pgdat->classzone_idx;
2919	pgdat->kswapd_max_order = 0;
2920	pgdat->classzone_idx = pgdat->nr_zones - 1;
2921	}
2922
2923	if (order < new_order \|\| classzone_idx > new_classzone_idx) {
2924	/*
2925	* Don't sleep if someone wants a larger 'order'
2926	* allocation or has tigher zone constraints
2927	*/
2928	order = new_order;
2929	classzone_idx = new_classzone_idx;
2930	} else {
2931	kswapd_try_to_sleep(pgdat, balanced_order,
2932	balanced_classzone_idx);
2933	order = pgdat->kswapd_max_order;
2934	classzone_idx = pgdat->classzone_idx;
2935	new_order = order;
2936	new_classzone_idx = classzone_idx;
2937	pgdat->kswapd_max_order = 0;
2938	pgdat->classzone_idx = pgdat->nr_zones - 1;
2939	}
2940
2941	ret = try_to_freeze();
2942	if (kthread_should_stop())
2943	break;
2944
2945	/*
2946	* We can speed up thawing tasks if we don't call balance_pgdat
2947	* after returning from the refrigerator
2948	*/
2949	if (!ret) {
2950	trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
2951	balanced_classzone_idx = classzone_idx;
2952	balanced_order = balance_pgdat(pgdat, order,
2953	&balanced_classzone_idx);
2954	}
2955	}
2956	return 0;
2957	}
2958
2959	/*
2960	* A zone is low on free memory, so wake its kswapd task to service it.
2961	*/
2962	void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
2963	{
2964	pg_data_t *pgdat;
2965
2966	if (!populated_zone(zone))
2967	return;
2968
2969	if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2970	return;
2971	pgdat = zone->zone_pgdat;
2972	if (pgdat->kswapd_max_order < order) {
2973	pgdat->kswapd_max_order = order;
2974	pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
2975	}
2976	if (!waitqueue_active(&pgdat->kswapd_wait))
2977	return;
2978	if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
2979	return;
2980
2981	trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
2982	wake_up_interruptible(&pgdat->kswapd_wait);
2983	}
2984
2985	/*
2986	* The reclaimable count would be mostly accurate.
2987	* The less reclaimable pages may be
2988	* - mlocked pages, which will be moved to unevictable list when encountered
2989	* - mapped pages, which may require several travels to be reclaimed
2990	* - dirty pages, which is not "instantly" reclaimable
2991	*/
2992	unsigned long global_reclaimable_pages(void)
2993	{
2994	int nr;
2995
2996	nr = global_page_state(NR_ACTIVE_FILE) +
2997	global_page_state(NR_INACTIVE_FILE);
2998
2999	if (nr_swap_pages > 0)
3000	nr += global_page_state(NR_ACTIVE_ANON) +
3001	global_page_state(NR_INACTIVE_ANON);
3002
3003	return nr;
3004	}
3005
3006	unsigned long zone_reclaimable_pages(struct zone *zone)
3007	{
3008	int nr;
3009
3010	nr = zone_page_state(zone, NR_ACTIVE_FILE) +
3011	zone_page_state(zone, NR_INACTIVE_FILE);
3012
3013	if (nr_swap_pages > 0)
3014	nr += zone_page_state(zone, NR_ACTIVE_ANON) +
3015	zone_page_state(zone, NR_INACTIVE_ANON);
3016
3017	return nr;
3018	}
3019
3020	#ifdef CONFIG_HIBERNATION
3021	/*
3022	* Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3023	* freed pages.
3024	*
3025	* Rather than trying to age LRUs the aim is to preserve the overall
3026	* LRU order by reclaiming preferentially
3027	* inactive > active > active referenced > active mapped
3028	*/
3029	unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3030	{
3031	struct reclaim_state reclaim_state;
3032	struct scan_control sc = {
3033	.gfp_mask = GFP_HIGHUSER_MOVABLE,
3034	.may_swap = 1,
3035	.may_unmap = 1,
3036	.may_writepage = 1,
3037	.nr_to_reclaim = nr_to_reclaim,
3038	.hibernation_mode = 1,
3039	.order = 0,
3040	.priority = DEF_PRIORITY,
3041	};
3042	struct shrink_control shrink = {
3043	.gfp_mask = sc.gfp_mask,
3044	};
3045	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3046	struct task_struct *p = current;
3047	unsigned long nr_reclaimed;
3048
3049	p->flags \|= PF_MEMALLOC;
3050	lockdep_set_current_reclaim_state(sc.gfp_mask);
3051	reclaim_state.reclaimed_slab = 0;
3052	p->reclaim_state = &reclaim_state;
3053
3054	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
3055
3056	p->reclaim_state = NULL;
3057	lockdep_clear_current_reclaim_state();
3058	p->flags &= ~PF_MEMALLOC;
3059
3060	return nr_reclaimed;
3061	}
3062	#endif /* CONFIG_HIBERNATION */
3063
3064	/* It's optimal to keep kswapds on the same CPUs as their memory, but
3065	not required for correctness. So if the last cpu in a node goes
3066	away, we get changed to run anywhere: as the first one comes back,
3067	restore their cpu bindings. */
3068	static int __devinit cpu_callback(struct notifier_block *nfb,
3069	unsigned long action, void *hcpu)
3070	{
3071	int nid;
3072
3073	if (action == CPU_ONLINE \|\| action == CPU_ONLINE_FROZEN) {
3074	for_each_node_state(nid, N_HIGH_MEMORY) {
3075	pg_data_t *pgdat = NODE_DATA(nid);
3076	const struct cpumask *mask;
3077
3078	mask = cpumask_of_node(pgdat->node_id);
3079
3080	if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3081	/* One of our CPUs online: restore mask */
3082	set_cpus_allowed_ptr(pgdat->kswapd, mask);
3083	}
3084	}
3085	return NOTIFY_OK;
3086	}
3087
3088	/*
3089	* This kswapd start function will be called by init and node-hot-add.
3090	* On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3091	*/
3092	int kswapd_run(int nid)
3093	{
3094	pg_data_t *pgdat = NODE_DATA(nid);
3095	int ret = 0;
3096
3097	if (pgdat->kswapd)
3098	return 0;
3099
3100	pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3101	if (IS_ERR(pgdat->kswapd)) {
3102	/* failure at boot is fatal */
3103	BUG_ON(system_state == SYSTEM_BOOTING);
3104	printk("Failed to start kswapd on node %d\n",nid);
3105	ret = -1;
3106	}
3107	return ret;
3108	}
3109
3110	/*
3111	* Called by memory hotplug when all memory in a node is offlined. Caller must
3112	* hold lock_memory_hotplug().
3113	*/
3114	void kswapd_stop(int nid)
3115	{
3116	struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3117
3118	if (kswapd) {
3119	kthread_stop(kswapd);
3120	NODE_DATA(nid)->kswapd = NULL;
3121	}
3122	}
3123
3124	static int __init kswapd_init(void)
3125	{
3126	int nid;
3127
3128	swap_setup();
3129	for_each_node_state(nid, N_HIGH_MEMORY)
3130	kswapd_run(nid);
3131	hotcpu_notifier(cpu_callback, 0);
3132	return 0;
3133	}
3134
3135	module_init(kswapd_init)
3136
3137	#ifdef CONFIG_NUMA
3138	/*
3139	* Zone reclaim mode
3140	*
3141	* If non-zero call zone_reclaim when the number of free pages falls below
3142	* the watermarks.
3143	*/
3144	int zone_reclaim_mode __read_mostly;
3145
3146	#define RECLAIM_OFF 0
3147	#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
3148	#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
3149	#define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
3150
3151	/*
3152	* Priority for ZONE_RECLAIM. This determines the fraction of pages
3153	* of a node considered for each zone_reclaim. 4 scans 1/16th of
3154	* a zone.
3155	*/
3156	#define ZONE_RECLAIM_PRIORITY 4
3157
3158	/*
3159	* Percentage of pages in a zone that must be unmapped for zone_reclaim to
3160	* occur.
3161	*/
3162	int sysctl_min_unmapped_ratio = 1;
3163
3164	/*
3165	* If the number of slab pages in a zone grows beyond this percentage then
3166	* slab reclaim needs to occur.
3167	*/
3168	int sysctl_min_slab_ratio = 5;
3169
3170	static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3171	{
3172	unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3173	unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3174	zone_page_state(zone, NR_ACTIVE_FILE);
3175
3176	/*
3177	* It's possible for there to be more file mapped pages than
3178	* accounted for by the pages on the file LRU lists because
3179	* tmpfs pages accounted for as ANON can also be FILE_MAPPED
3180	*/
3181	return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3182	}
3183
3184	/* Work out how many page cache pages we can reclaim in this reclaim_mode */
3185	static long zone_pagecache_reclaimable(struct zone *zone)
3186	{
3187	long nr_pagecache_reclaimable;
3188	long delta = 0;
3189
3190	/*
3191	* If RECLAIM_SWAP is set, then all file pages are considered
3192	* potentially reclaimable. Otherwise, we have to worry about
3193	* pages like swapcache and zone_unmapped_file_pages() provides
3194	* a better estimate
3195	*/
3196	if (zone_reclaim_mode & RECLAIM_SWAP)
3197	nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3198	else
3199	nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3200
3201	/* If we can't clean pages, remove dirty pages from consideration */
3202	if (!(zone_reclaim_mode & RECLAIM_WRITE))
3203	delta += zone_page_state(zone, NR_FILE_DIRTY);
3204
3205	/* Watch for any possible underflows due to delta */
3206	if (unlikely(delta > nr_pagecache_reclaimable))
3207	delta = nr_pagecache_reclaimable;
3208
3209	return nr_pagecache_reclaimable - delta;
3210	}
3211
3212	/*
3213	* Try to free up some pages from this zone through reclaim.
3214	*/
3215	static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3216	{
3217	/* Minimum pages needed in order to stay on node */
3218	const unsigned long nr_pages = 1 << order;
3219	struct task_struct *p = current;
3220	struct reclaim_state reclaim_state;
3221	struct scan_control sc = {
3222	.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3223	.may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3224	.may_swap = 1,
3225	.nr_to_reclaim = max_t(unsigned long, nr_pages,
3226	SWAP_CLUSTER_MAX),
3227	.gfp_mask = gfp_mask,
3228	.order = order,
3229	.priority = ZONE_RECLAIM_PRIORITY,
3230	};
3231	struct shrink_control shrink = {
3232	.gfp_mask = sc.gfp_mask,
3233	};
3234	unsigned long nr_slab_pages0, nr_slab_pages1;
3235
3236	cond_resched();
3237	/*
3238	* We need to be able to allocate from the reserves for RECLAIM_SWAP
3239	* and we also need to be able to write out pages for RECLAIM_WRITE
3240	* and RECLAIM_SWAP.
3241	*/
3242	p->flags \|= PF_MEMALLOC \| PF_SWAPWRITE;
3243	lockdep_set_current_reclaim_state(gfp_mask);
3244	reclaim_state.reclaimed_slab = 0;
3245	p->reclaim_state = &reclaim_state;
3246
3247	if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3248	/*
3249	* Free memory by calling shrink zone with increasing
3250	* priorities until we have enough memory freed.
3251	*/
3252	do {
3253	shrink_zone(zone, &sc);
3254	} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3255	}
3256
3257	nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3258	if (nr_slab_pages0 > zone->min_slab_pages) {
3259	/*
3260	* shrink_slab() does not currently allow us to determine how
3261	* many pages were freed in this zone. So we take the current
3262	* number of slab pages and shake the slab until it is reduced
3263	* by the same nr_pages that we used for reclaiming unmapped
3264	* pages.
3265	*
3266	* Note that shrink_slab will free memory on all zones and may
3267	* take a long time.
3268	*/
3269	for (;;) {
3270	unsigned long lru_pages = zone_reclaimable_pages(zone);
3271
3272	/* No reclaimable slab or very low memory pressure */
3273	if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3274	break;
3275
3276	/* Freed enough memory */
3277	nr_slab_pages1 = zone_page_state(zone,
3278	NR_SLAB_RECLAIMABLE);
3279	if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3280	break;
3281	}
3282
3283	/*
3284	* Update nr_reclaimed by the number of slab pages we
3285	* reclaimed from this zone.
3286	*/
3287	nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3288	if (nr_slab_pages1 < nr_slab_pages0)
3289	sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3290	}
3291
3292	p->reclaim_state = NULL;
3293	current->flags &= ~(PF_MEMALLOC \| PF_SWAPWRITE);
3294	lockdep_clear_current_reclaim_state();
3295	return sc.nr_reclaimed >= nr_pages;
3296	}
3297
3298	int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3299	{
3300	int node_id;
3301	int ret;
3302
3303	/*
3304	* Zone reclaim reclaims unmapped file backed pages and
3305	* slab pages if we are over the defined limits.
3306	*
3307	* A small portion of unmapped file backed pages is needed for
3308	* file I/O otherwise pages read by file I/O will be immediately
3309	* thrown out if the zone is overallocated. So we do not reclaim
3310	* if less than a specified percentage of the zone is used by
3311	* unmapped file backed pages.
3312	*/
3313	if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3314	zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3315	return ZONE_RECLAIM_FULL;
3316
3317	if (zone->all_unreclaimable)
3318	return ZONE_RECLAIM_FULL;
3319
3320	/*
3321	* Do not scan if the allocation should not be delayed.
3322	*/
3323	if (!(gfp_mask & __GFP_WAIT) \|\| (current->flags & PF_MEMALLOC))
3324	return ZONE_RECLAIM_NOSCAN;
3325
3326	/*
3327	* Only run zone reclaim on the local zone or on zones that do not
3328	* have associated processors. This will favor the local processor
3329	* over remote processors and spread off node memory allocations
3330	* as wide as possible.
3331	*/
3332	node_id = zone_to_nid(zone);
3333	if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3334	return ZONE_RECLAIM_NOSCAN;
3335
3336	if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3337	return ZONE_RECLAIM_NOSCAN;
3338
3339	ret = __zone_reclaim(zone, gfp_mask, order);
3340	zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3341
3342	if (!ret)
3343	count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3344
3345	return ret;
3346	}
3347	#endif
3348
3349	/*
3350	* page_evictable - test whether a page is evictable
3351	* @page: the page to test
3352	* @vma: the VMA in which the page is or will be mapped, may be NULL
3353	*
3354	* Test whether page is evictable--i.e., should be placed on active/inactive
3355	* lists vs unevictable list. The vma argument is !NULL when called from the
3356	* fault path to determine how to instantate a new page.
3357	*
3358	* Reasons page might not be evictable:
3359	* (1) page's mapping marked unevictable
3360	* (2) page is part of an mlocked VMA
3361	*
3362	*/
3363	int page_evictable(struct page page, struct vm_area_struct vma)
3364	{
3365
3366	if (mapping_unevictable(page_mapping(page)))
3367	return 0;
3368
3369	if (PageMlocked(page) \|\| (vma && mlocked_vma_newpage(vma, page)))
3370	return 0;
3371
3372	return 1;
3373	}
3374
3375	#ifdef CONFIG_SHMEM
3376	/**
3377	* check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3378	* @pages: array of pages to check
3379	* @nr_pages: number of pages to check
3380	*
3381	* Checks pages for evictability and moves them to the appropriate lru list.
3382	*
3383	* This function is only used for SysV IPC SHM_UNLOCK.
3384	*/
3385	void check_move_unevictable_pages(struct page **pages, int nr_pages)
3386	{
3387	struct lruvec *lruvec;
3388	struct zone *zone = NULL;
3389	int pgscanned = 0;
3390	int pgrescued = 0;
3391	int i;
3392
3393	for (i = 0; i < nr_pages; i++) {
3394	struct page *page = pages[i];
3395	struct zone *pagezone;
3396
3397	pgscanned++;
3398	pagezone = page_zone(page);
3399	if (pagezone != zone) {
3400	if (zone)
3401	spin_unlock_irq(&zone->lru_lock);
3402	zone = pagezone;
3403	spin_lock_irq(&zone->lru_lock);
3404	}
3405	lruvec = mem_cgroup_page_lruvec(page, zone);
3406
3407	if (!PageLRU(page) \|\| !PageUnevictable(page))
3408	continue;
3409
3410	if (page_evictable(page, NULL)) {
3411	enum lru_list lru = page_lru_base_type(page);
3412
3413	VM_BUG_ON(PageActive(page));
3414	ClearPageUnevictable(page);
3415	del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3416	add_page_to_lru_list(page, lruvec, lru);
3417	pgrescued++;
3418	}
3419	}
3420
3421	if (zone) {
3422	__count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3423	__count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3424	spin_unlock_irq(&zone->lru_lock);
3425	}
3426	}
3427	#endif /* CONFIG_SHMEM */
3428
3429	static void warn_scan_unevictable_pages(void)
3430	{
3431	printk_once(KERN_WARNING
3432	"%s: The scan_unevictable_pages sysctl/node-interface has been "
3433	"disabled for lack of a legitimate use case. If you have "
3434	"one, please send an email to linux-mm@kvack.org.\n",
3435	current->comm);
3436	}
3437
3438	/*
3439	* scan_unevictable_pages [vm] sysctl handler. On demand re-scan of
3440	* all nodes' unevictable lists for evictable pages
3441	*/
3442	unsigned long scan_unevictable_pages;
3443
3444	int scan_unevictable_handler(struct ctl_table *table, int write,
3445	void __user *buffer,
3446	size_t length, loff_t ppos)
3447	{
3448	warn_scan_unevictable_pages();
3449	proc_doulongvec_minmax(table, write, buffer, length, ppos);
3450	scan_unevictable_pages = 0;
3451	return 0;
3452	}
3453
3454	#ifdef CONFIG_NUMA
3455	/*
3456	* per node 'scan_unevictable_pages' attribute. On demand re-scan of
3457	* a specified node's per zone unevictable lists for evictable pages.
3458	*/
3459
3460	static ssize_t read_scan_unevictable_node(struct device *dev,
3461	struct device_attribute *attr,
3462	char *buf)
3463	{
3464	warn_scan_unevictable_pages();
3465	return sprintf(buf, "0\n"); /* always zero; should fit... */
3466	}
3467
3468	static ssize_t write_scan_unevictable_node(struct device *dev,
3469	struct device_attribute *attr,
3470	const char *buf, size_t count)
3471	{
3472	warn_scan_unevictable_pages();
3473	return 1;
3474	}
3475
3476
3477	static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO \| S_IWUSR,
3478	read_scan_unevictable_node,
3479	write_scan_unevictable_node);
3480
3481	int scan_unevictable_register_node(struct node *node)
3482	{
3483	return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages);
3484	}
3485
3486	void scan_unevictable_unregister_node(struct node *node)
3487	{
3488	device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages);
3489	}
3490	#endif
3491

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