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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/vmpressure.h>
23	#include <linux/vmstat.h>
24	#include <linux/file.h>
25	#include <linux/writeback.h>
26	#include <linux/blkdev.h>
27	#include <linux/buffer_head.h> /* for try_to_release_page(),
28	buffer_heads_over_limit */
29	#include <linux/mm_inline.h>
30	#include <linux/backing-dev.h>
31	#include <linux/rmap.h>
32	#include <linux/topology.h>
33	#include <linux/cpu.h>
34	#include <linux/cpuset.h>
35	#include <linux/compaction.h>
36	#include <linux/notifier.h>
37	#include <linux/rwsem.h>
38	#include <linux/delay.h>
39	#include <linux/kthread.h>
40	#include <linux/freezer.h>
41	#include <linux/memcontrol.h>
42	#include <linux/delayacct.h>
43	#include <linux/sysctl.h>
44	#include <linux/oom.h>
45	#include <linux/prefetch.h>
46
47	#include <asm/tlbflush.h>
48	#include <asm/div64.h>
49
50	#include <linux/swapops.h>
51	#include <linux/balloon_compaction.h>
52
53	#include "internal.h"
54
55	#define CREATE_TRACE_POINTS
56	#include <trace/events/vmscan.h>
57
58	struct scan_control {
59	/* Incremented by the number of inactive pages that were scanned */
60	unsigned long nr_scanned;
61
62	/* Number of pages freed so far during a call to shrink_zones() */
63	unsigned long nr_reclaimed;
64
65	/* How many pages shrink_list() should reclaim */
66	unsigned long nr_to_reclaim;
67
68	unsigned long hibernation_mode;
69
70	/* This context's GFP mask */
71	gfp_t gfp_mask;
72
73	int may_writepage;
74
75	/* Can mapped pages be reclaimed? */
76	int may_unmap;
77
78	/* Can pages be swapped as part of reclaim? */
79	int may_swap;
80
81	int order;
82
83	/* Scan (total_size >> priority) pages at once */
84	int priority;
85
86	/*
87	* The memory cgroup that hit its limit and as a result is the
88	* primary target of this reclaim invocation.
89	*/
90	struct mem_cgroup *target_mem_cgroup;
91
92	/*
93	* Nodemask of nodes allowed by the caller. If NULL, all nodes
94	* are scanned.
95	*/
96	nodemask_t *nodemask;
97	};
98
99	#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
100
101	#ifdef ARCH_HAS_PREFETCH
102	#define prefetch_prev_lru_page(_page, _base, _field) \
103	do { \
104	if ((_page)->lru.prev != _base) { \
105	struct page *prev; \
106	\
107	prev = lru_to_page(&(_page->lru)); \
108	prefetch(&prev->_field); \
109	} \
110	} while (0)
111	#else
112	#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
113	#endif
114
115	#ifdef ARCH_HAS_PREFETCHW
116	#define prefetchw_prev_lru_page(_page, _base, _field) \
117	do { \
118	if ((_page)->lru.prev != _base) { \
119	struct page *prev; \
120	\
121	prev = lru_to_page(&(_page->lru)); \
122	prefetchw(&prev->_field); \
123	} \
124	} while (0)
125	#else
126	#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
127	#endif
128
129	/*
130	* From 0 .. 100. Higher means more swappy.
131	*/
132	int vm_swappiness = 60;
133	unsigned long vm_total_pages; /* The total number of pages which the VM controls */
134
135	static LIST_HEAD(shrinker_list);
136	static DECLARE_RWSEM(shrinker_rwsem);
137
138	#ifdef CONFIG_MEMCG
139	static bool global_reclaim(struct scan_control *sc)
140	{
141	return !sc->target_mem_cgroup;
142	}
143	#else
144	static bool global_reclaim(struct scan_control *sc)
145	{
146	return true;
147	}
148	#endif
149
150	unsigned long zone_reclaimable_pages(struct zone *zone)
151	{
152	int nr;
153
154	nr = zone_page_state(zone, NR_ACTIVE_FILE) +
155	zone_page_state(zone, NR_INACTIVE_FILE);
156
157	if (get_nr_swap_pages() > 0)
158	nr += zone_page_state(zone, NR_ACTIVE_ANON) +
159	zone_page_state(zone, NR_INACTIVE_ANON);
160
161	return nr;
162	}
163
164	bool zone_reclaimable(struct zone *zone)
165	{
166	return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
167	}
168
169	static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
170	{
171	if (!mem_cgroup_disabled())
172	return mem_cgroup_get_lru_size(lruvec, lru);
173
174	return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);
175	}
176
177	/*
178	* Add a shrinker callback to be called from the vm.
179	*/
180	int register_shrinker(struct shrinker *shrinker)
181	{
182	size_t size = sizeof(*shrinker->nr_deferred);
183
184	/*
185	* If we only have one possible node in the system anyway, save
186	* ourselves the trouble and disable NUMA aware behavior. This way we
187	* will save memory and some small loop time later.
188	*/
189	if (nr_node_ids == 1)
190	shrinker->flags &= ~SHRINKER_NUMA_AWARE;
191
192	if (shrinker->flags & SHRINKER_NUMA_AWARE)
193	size *= nr_node_ids;
194
195	shrinker->nr_deferred = kzalloc(size, GFP_KERNEL);
196	if (!shrinker->nr_deferred)
197	return -ENOMEM;
198
199	down_write(&shrinker_rwsem);
200	list_add_tail(&shrinker->list, &shrinker_list);
201	up_write(&shrinker_rwsem);
202	return 0;
203	}
204	EXPORT_SYMBOL(register_shrinker);
205
206	/*
207	* Remove one
208	*/
209	void unregister_shrinker(struct shrinker *shrinker)
210	{
211	down_write(&shrinker_rwsem);
212	list_del(&shrinker->list);
213	up_write(&shrinker_rwsem);
214	kfree(shrinker->nr_deferred);
215	}
216	EXPORT_SYMBOL(unregister_shrinker);
217
218	#define SHRINK_BATCH 128
219
220	static unsigned long
221	shrink_slab_node(struct shrink_control shrinkctl, struct shrinker shrinker,
222	unsigned long nr_pages_scanned, unsigned long lru_pages)
223	{
224	unsigned long freed = 0;
225	unsigned long long delta;
226	long total_scan;
227	long max_pass;
228	long nr;
229	long new_nr;
230	int nid = shrinkctl->nid;
231	long batch_size = shrinker->batch ? shrinker->batch
232	: SHRINK_BATCH;
233
234	max_pass = shrinker->count_objects(shrinker, shrinkctl);
235	if (max_pass == 0)
236	return 0;
237
238	/*
239	* copy the current shrinker scan count into a local variable
240	* and zero it so that other concurrent shrinker invocations
241	* don't also do this scanning work.
242	*/
243	nr = atomic_long_xchg(&shrinker->nr_deferred[nid], 0);
244
245	total_scan = nr;
246	delta = (4 * nr_pages_scanned) / shrinker->seeks;
247	delta *= max_pass;
248	do_div(delta, lru_pages + 1);
249	total_scan += delta;
250	if (total_scan < 0) {
251	printk(KERN_ERR
252	"shrink_slab: %pF negative objects to delete nr=%ld\n",
253	shrinker->scan_objects, total_scan);
254	total_scan = max_pass;
255	}
256
257	/*
258	* We need to avoid excessive windup on filesystem shrinkers
259	* due to large numbers of GFP_NOFS allocations causing the
260	* shrinkers to return -1 all the time. This results in a large
261	* nr being built up so when a shrink that can do some work
262	* comes along it empties the entire cache due to nr >>>
263	* max_pass. This is bad for sustaining a working set in
264	* memory.
265	*
266	* Hence only allow the shrinker to scan the entire cache when
267	* a large delta change is calculated directly.
268	*/
269	if (delta < max_pass / 4)
270	total_scan = min(total_scan, max_pass / 2);
271
272	/*
273	* Avoid risking looping forever due to too large nr value:
274	* never try to free more than twice the estimate number of
275	* freeable entries.
276	*/
277	if (total_scan > max_pass * 2)
278	total_scan = max_pass * 2;
279
280	trace_mm_shrink_slab_start(shrinker, shrinkctl, nr,
281	nr_pages_scanned, lru_pages,
282	max_pass, delta, total_scan);
283
284	while (total_scan >= batch_size) {
285	unsigned long ret;
286
287	shrinkctl->nr_to_scan = batch_size;
288	ret = shrinker->scan_objects(shrinker, shrinkctl);
289	if (ret == SHRINK_STOP)
290	break;
291	freed += ret;
292
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_deferred[nid]);
307	else
308	new_nr = atomic_long_read(&shrinker->nr_deferred[nid]);
309
310	trace_mm_shrink_slab_end(shrinker, freed, nr, new_nr);
311	return freed;
312	}
313
314	/*
315	* Call the shrink functions to age shrinkable caches
316	*
317	* Here we assume it costs one seek to replace a lru page and that it also
318	* takes a seek to recreate a cache object. With this in mind we age equal
319	* percentages of the lru and ageable caches. This should balance the seeks
320	* generated by these structures.
321	*
322	* If the vm encountered mapped pages on the LRU it increase the pressure on
323	* slab to avoid swapping.
324	*
325	* We do weird things to avoid (scannedseeksentries) overflowing 32 bits.
326	*
327	* `lru_pages' represents the number of on-LRU pages in all the zones which
328	* are eligible for the caller's allocation attempt. It is used for balancing
329	* slab reclaim versus page reclaim.
330	*
331	* Returns the number of slab objects which we shrunk.
332	*/
333	unsigned long shrink_slab(struct shrink_control *shrinkctl,
334	unsigned long nr_pages_scanned,
335	unsigned long lru_pages)
336	{
337	struct shrinker *shrinker;
338	unsigned long freed = 0;
339
340	if (nr_pages_scanned == 0)
341	nr_pages_scanned = SWAP_CLUSTER_MAX;
342
343	if (!down_read_trylock(&shrinker_rwsem)) {
344	/*
345	* If we would return 0, our callers would understand that we
346	* have nothing else to shrink and give up trying. By returning
347	* 1 we keep it going and assume we'll be able to shrink next
348	* time.
349	*/
350	freed = 1;
351	goto out;
352	}
353
354	list_for_each_entry(shrinker, &shrinker_list, list) {
355	for_each_node_mask(shrinkctl->nid, shrinkctl->nodes_to_scan) {
356	if (!node_online(shrinkctl->nid))
357	continue;
358
359	if (!(shrinker->flags & SHRINKER_NUMA_AWARE) &&
360	(shrinkctl->nid != 0))
361	break;
362
363	freed += shrink_slab_node(shrinkctl, shrinker,
364	nr_pages_scanned, lru_pages);
365
366	}
367	}
368	up_read(&shrinker_rwsem);
369	out:
370	cond_resched();
371	return freed;
372	}
373
374	static inline int is_page_cache_freeable(struct page *page)
375	{
376	/*
377	* A freeable page cache page is referenced only by the caller
378	* that isolated the page, the page cache radix tree and
379	* optional buffer heads at page->private.
380	*/
381	return page_count(page) - page_has_private(page) == 2;
382	}
383
384	static int may_write_to_queue(struct backing_dev_info *bdi,
385	struct scan_control *sc)
386	{
387	if (current->flags & PF_SWAPWRITE)
388	return 1;
389	if (!bdi_write_congested(bdi))
390	return 1;
391	if (bdi == current->backing_dev_info)
392	return 1;
393	return 0;
394	}
395
396	/*
397	* We detected a synchronous write error writing a page out. Probably
398	* -ENOSPC. We need to propagate that into the address_space for a subsequent
399	* fsync(), msync() or close().
400	*
401	* The tricky part is that after writepage we cannot touch the mapping: nothing
402	* prevents it from being freed up. But we have a ref on the page and once
403	* that page is locked, the mapping is pinned.
404	*
405	* We're allowed to run sleeping lock_page() here because we know the caller has
406	* __GFP_FS.
407	*/
408	static void handle_write_error(struct address_space *mapping,
409	struct page *page, int error)
410	{
411	lock_page(page);
412	if (page_mapping(page) == mapping)
413	mapping_set_error(mapping, error);
414	unlock_page(page);
415	}
416
417	/* possible outcome of pageout() */
418	typedef enum {
419	/* failed to write page out, page is locked */
420	PAGE_KEEP,
421	/* move page to the active list, page is locked */
422	PAGE_ACTIVATE,
423	/* page has been sent to the disk successfully, page is unlocked */
424	PAGE_SUCCESS,
425	/* page is clean and locked */
426	PAGE_CLEAN,
427	} pageout_t;
428
429	/*
430	* pageout is called by shrink_page_list() for each dirty page.
431	* Calls ->writepage().
432	*/
433	static pageout_t pageout(struct page page, struct address_space mapping,
434	struct scan_control *sc)
435	{
436	/*
437	* If the page is dirty, only perform writeback if that write
438	* will be non-blocking. To prevent this allocation from being
439	* stalled by pagecache activity. But note that there may be
440	* stalls if we need to run get_block(). We could test
441	* PagePrivate for that.
442	*
443	* If this process is currently in __generic_file_aio_write() against
444	* this page's queue, we can perform writeback even if that
445	* will block.
446	*
447	* If the page is swapcache, write it back even if that would
448	* block, for some throttling. This happens by accident, because
449	* swap_backing_dev_info is bust: it doesn't reflect the
450	* congestion state of the swapdevs. Easy to fix, if needed.
451	*/
452	if (!is_page_cache_freeable(page))
453	return PAGE_KEEP;
454	if (!mapping) {
455	/*
456	* Some data journaling orphaned pages can have
457	* page->mapping == NULL while being dirty with clean buffers.
458	*/
459	if (page_has_private(page)) {
460	if (try_to_free_buffers(page)) {
461	ClearPageDirty(page);
462	printk("%s: orphaned page\n", __func__);
463	return PAGE_CLEAN;
464	}
465	}
466	return PAGE_KEEP;
467	}
468	if (mapping->a_ops->writepage == NULL)
469	return PAGE_ACTIVATE;
470	if (!may_write_to_queue(mapping->backing_dev_info, sc))
471	return PAGE_KEEP;
472
473	if (clear_page_dirty_for_io(page)) {
474	int res;
475	struct writeback_control wbc = {
476	.sync_mode = WB_SYNC_NONE,
477	.nr_to_write = SWAP_CLUSTER_MAX,
478	.range_start = 0,
479	.range_end = LLONG_MAX,
480	.for_reclaim = 1,
481	};
482
483	SetPageReclaim(page);
484	res = mapping->a_ops->writepage(page, &wbc);
485	if (res < 0)
486	handle_write_error(mapping, page, res);
487	if (res == AOP_WRITEPAGE_ACTIVATE) {
488	ClearPageReclaim(page);
489	return PAGE_ACTIVATE;
490	}
491
492	if (!PageWriteback(page)) {
493	/* synchronous write or broken a_ops? */
494	ClearPageReclaim(page);
495	}
496	trace_mm_vmscan_writepage(page, trace_reclaim_flags(page));
497	inc_zone_page_state(page, NR_VMSCAN_WRITE);
498	return PAGE_SUCCESS;
499	}
500
501	return PAGE_CLEAN;
502	}
503
504	/*
505	* Same as remove_mapping, but if the page is removed from the mapping, it
506	* gets returned with a refcount of 0.
507	*/
508	static int __remove_mapping(struct address_space mapping, struct page page)
509	{
510	BUG_ON(!PageLocked(page));
511	BUG_ON(mapping != page_mapping(page));
512
513	spin_lock_irq(&mapping->tree_lock);
514	/*
515	* The non racy check for a busy page.
516	*
517	* Must be careful with the order of the tests. When someone has
518	* a ref to the page, it may be possible that they dirty it then
519	* drop the reference. So if PageDirty is tested before page_count
520	* here, then the following race may occur:
521	*
522	* get_user_pages(&page);
523	* [user mapping goes away]
524	* write_to(page);
525	* !PageDirty(page) [good]
526	* SetPageDirty(page);
527	* put_page(page);
528	* !page_count(page) [good, discard it]
529	*
530	* [oops, our write_to data is lost]
531	*
532	* Reversing the order of the tests ensures such a situation cannot
533	* escape unnoticed. The smp_rmb is needed to ensure the page->flags
534	* load is not satisfied before that of page->_count.
535	*
536	* Note that if SetPageDirty is always performed via set_page_dirty,
537	* and thus under tree_lock, then this ordering is not required.
538	*/
539	if (!page_freeze_refs(page, 2))
540	goto cannot_free;
541	/* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
542	if (unlikely(PageDirty(page))) {
543	page_unfreeze_refs(page, 2);
544	goto cannot_free;
545	}
546
547	if (PageSwapCache(page)) {
548	swp_entry_t swap = { .val = page_private(page) };
549	__delete_from_swap_cache(page);
550	spin_unlock_irq(&mapping->tree_lock);
551	swapcache_free(swap, page);
552	} else {
553	void (freepage)(struct page );
554
555	freepage = mapping->a_ops->freepage;
556
557	__delete_from_page_cache(page);
558	spin_unlock_irq(&mapping->tree_lock);
559	mem_cgroup_uncharge_cache_page(page);
560
561	if (freepage != NULL)
562	freepage(page);
563	}
564
565	return 1;
566
567	cannot_free:
568	spin_unlock_irq(&mapping->tree_lock);
569	return 0;
570	}
571
572	/*
573	* Attempt to detach a locked page from its ->mapping. If it is dirty or if
574	* someone else has a ref on the page, abort and return 0. If it was
575	* successfully detached, return 1. Assumes the caller has a single ref on
576	* this page.
577	*/
578	int remove_mapping(struct address_space mapping, struct page page)
579	{
580	if (__remove_mapping(mapping, page)) {
581	/*
582	* Unfreezing the refcount with 1 rather than 2 effectively
583	* drops the pagecache ref for us without requiring another
584	* atomic operation.
585	*/
586	page_unfreeze_refs(page, 1);
587	return 1;
588	}
589	return 0;
590	}
591
592	/**
593	* putback_lru_page - put previously isolated page onto appropriate LRU list
594	* @page: page to be put back to appropriate lru list
595	*
596	* Add previously isolated @page to appropriate LRU list.
597	* Page may still be unevictable for other reasons.
598	*
599	* lru_lock must not be held, interrupts must be enabled.
600	*/
601	void putback_lru_page(struct page *page)
602	{
603	bool is_unevictable;
604	int was_unevictable = PageUnevictable(page);
605
606	VM_BUG_ON(PageLRU(page));
607
608	redo:
609	ClearPageUnevictable(page);
610
611	if (page_evictable(page)) {
612	/*
613	* For evictable pages, we can use the cache.
614	* In event of a race, worst case is we end up with an
615	* unevictable page on [in]active list.
616	* We know how to handle that.
617	*/
618	is_unevictable = false;
619	lru_cache_add(page);
620	} else {
621	/*
622	* Put unevictable pages directly on zone's unevictable
623	* list.
624	*/
625	is_unevictable = true;
626	add_page_to_unevictable_list(page);
627	/*
628	* When racing with an mlock or AS_UNEVICTABLE clearing
629	* (page is unlocked) make sure that if the other thread
630	* does not observe our setting of PG_lru and fails
631	* isolation/check_move_unevictable_pages,
632	* we see PG_mlocked/AS_UNEVICTABLE cleared below and move
633	* the page back to the evictable list.
634	*
635	* The other side is TestClearPageMlocked() or shmem_lock().
636	*/
637	smp_mb();
638	}
639
640	/*
641	* page's status can change while we move it among lru. If an evictable
642	* page is on unevictable list, it never be freed. To avoid that,
643	* check after we added it to the list, again.
644	*/
645	if (is_unevictable && page_evictable(page)) {
646	if (!isolate_lru_page(page)) {
647	put_page(page);
648	goto redo;
649	}
650	/* This means someone else dropped this page from LRU
651	* So, it will be freed or putback to LRU again. There is
652	* nothing to do here.
653	*/
654	}
655
656	if (was_unevictable && !is_unevictable)
657	count_vm_event(UNEVICTABLE_PGRESCUED);
658	else if (!was_unevictable && is_unevictable)
659	count_vm_event(UNEVICTABLE_PGCULLED);
660
661	put_page(page); /* drop ref from isolate */
662	}
663
664	enum page_references {
665	PAGEREF_RECLAIM,
666	PAGEREF_RECLAIM_CLEAN,
667	PAGEREF_KEEP,
668	PAGEREF_ACTIVATE,
669	};
670
671	static enum page_references page_check_references(struct page *page,
672	struct scan_control *sc)
673	{
674	int referenced_ptes, referenced_page;
675	unsigned long vm_flags;
676
677	referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
678	&vm_flags);
679	referenced_page = TestClearPageReferenced(page);
680
681	/*
682	* Mlock lost the isolation race with us. Let try_to_unmap()
683	* move the page to the unevictable list.
684	*/
685	if (vm_flags & VM_LOCKED)
686	return PAGEREF_RECLAIM;
687
688	if (referenced_ptes) {
689	if (PageSwapBacked(page))
690	return PAGEREF_ACTIVATE;
691	/*
692	* All mapped pages start out with page table
693	* references from the instantiating fault, so we need
694	* to look twice if a mapped file page is used more
695	* than once.
696	*
697	* Mark it and spare it for another trip around the
698	* inactive list. Another page table reference will
699	* lead to its activation.
700	*
701	* Note: the mark is set for activated pages as well
702	* so that recently deactivated but used pages are
703	* quickly recovered.
704	*/
705	SetPageReferenced(page);
706
707	if (referenced_page \|\| referenced_ptes > 1)
708	return PAGEREF_ACTIVATE;
709
710	/*
711	* Activate file-backed executable pages after first usage.
712	*/
713	if (vm_flags & VM_EXEC)
714	return PAGEREF_ACTIVATE;
715
716	return PAGEREF_KEEP;
717	}
718
719	/* Reclaim if clean, defer dirty pages to writeback */
720	if (referenced_page && !PageSwapBacked(page))
721	return PAGEREF_RECLAIM_CLEAN;
722
723	return PAGEREF_RECLAIM;
724	}
725
726	/* Check if a page is dirty or under writeback */
727	static void page_check_dirty_writeback(struct page *page,
728	bool dirty, bool writeback)
729	{
730	struct address_space *mapping;
731
732	/*
733	* Anonymous pages are not handled by flushers and must be written
734	* from reclaim context. Do not stall reclaim based on them
735	*/
736	if (!page_is_file_cache(page)) {
737	*dirty = false;
738	*writeback = false;
739	return;
740	}
741
742	/* By default assume that the page flags are accurate */
743	*dirty = PageDirty(page);
744	*writeback = PageWriteback(page);
745
746	/* Verify dirty/writeback state if the filesystem supports it */
747	if (!page_has_private(page))
748	return;
749
750	mapping = page_mapping(page);
751	if (mapping && mapping->a_ops->is_dirty_writeback)
752	mapping->a_ops->is_dirty_writeback(page, dirty, writeback);
753	}
754
755	/*
756	* shrink_page_list() returns the number of reclaimed pages
757	*/
758	static unsigned long shrink_page_list(struct list_head *page_list,
759	struct zone *zone,
760	struct scan_control *sc,
761	enum ttu_flags ttu_flags,
762	unsigned long *ret_nr_dirty,
763	unsigned long *ret_nr_unqueued_dirty,
764	unsigned long *ret_nr_congested,
765	unsigned long *ret_nr_writeback,
766	unsigned long *ret_nr_immediate,
767	bool force_reclaim)
768	{
769	LIST_HEAD(ret_pages);
770	LIST_HEAD(free_pages);
771	int pgactivate = 0;
772	unsigned long nr_unqueued_dirty = 0;
773	unsigned long nr_dirty = 0;
774	unsigned long nr_congested = 0;
775	unsigned long nr_reclaimed = 0;
776	unsigned long nr_writeback = 0;
777	unsigned long nr_immediate = 0;
778
779	cond_resched();
780
781	mem_cgroup_uncharge_start();
782	while (!list_empty(page_list)) {
783	struct address_space *mapping;
784	struct page *page;
785	int may_enter_fs;
786	enum page_references references = PAGEREF_RECLAIM_CLEAN;
787	bool dirty, writeback;
788
789	cond_resched();
790
791	page = lru_to_page(page_list);
792	list_del(&page->lru);
793
794	if (!trylock_page(page))
795	goto keep;
796
797	VM_BUG_ON(PageActive(page));
798	VM_BUG_ON(page_zone(page) != zone);
799
800	sc->nr_scanned++;
801
802	if (unlikely(!page_evictable(page)))
803	goto cull_mlocked;
804
805	if (!sc->may_unmap && page_mapped(page))
806	goto keep_locked;
807
808	/* Double the slab pressure for mapped and swapcache pages */
809	if (page_mapped(page) \|\| PageSwapCache(page))
810	sc->nr_scanned++;
811
812	may_enter_fs = (sc->gfp_mask & __GFP_FS) \|\|
813	(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
814
815	/*
816	* The number of dirty pages determines if a zone is marked
817	* reclaim_congested which affects wait_iff_congested. kswapd
818	* will stall and start writing pages if the tail of the LRU
819	* is all dirty unqueued pages.
820	*/
821	page_check_dirty_writeback(page, &dirty, &writeback);
822	if (dirty \|\| writeback)
823	nr_dirty++;
824
825	if (dirty && !writeback)
826	nr_unqueued_dirty++;
827
828	/*
829	* Treat this page as congested if the underlying BDI is or if
830	* pages are cycling through the LRU so quickly that the
831	* pages marked for immediate reclaim are making it to the
832	* end of the LRU a second time.
833	*/
834	mapping = page_mapping(page);
835	if ((mapping && bdi_write_congested(mapping->backing_dev_info)) \|\|
836	(writeback && PageReclaim(page)))
837	nr_congested++;
838
839	/*
840	* If a page at the tail of the LRU is under writeback, there
841	* are three cases to consider.
842	*
843	* 1) If reclaim is encountering an excessive number of pages
844	* under writeback and this page is both under writeback and
845	* PageReclaim then it indicates that pages are being queued
846	* for IO but are being recycled through the LRU before the
847	* IO can complete. Waiting on the page itself risks an
848	* indefinite stall if it is impossible to writeback the
849	* page due to IO error or disconnected storage so instead
850	* note that the LRU is being scanned too quickly and the
851	* caller can stall after page list has been processed.
852	*
853	* 2) Global reclaim encounters a page, memcg encounters a
854	* page that is not marked for immediate reclaim or
855	* the caller does not have __GFP_IO. In this case mark
856	* the page for immediate reclaim and continue scanning.
857	*
858	* __GFP_IO is checked because a loop driver thread might
859	* enter reclaim, and deadlock if it waits on a page for
860	* which it is needed to do the write (loop masks off
861	* __GFP_IO\|__GFP_FS for this reason); but more thought
862	* would probably show more reasons.
863	*
864	* Don't require __GFP_FS, since we're not going into the
865	* FS, just waiting on its writeback completion. Worryingly,
866	* ext4 gfs2 and xfs allocate pages with
867	* grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so testing
868	* may_enter_fs here is liable to OOM on them.
869	*
870	* 3) memcg encounters a page that is not already marked
871	* PageReclaim. memcg does not have any dirty pages
872	* throttling so we could easily OOM just because too many
873	* pages are in writeback and there is nothing else to
874	* reclaim. Wait for the writeback to complete.
875	*/
876	if (PageWriteback(page)) {
877	/* Case 1 above */
878	if (current_is_kswapd() &&
879	PageReclaim(page) &&
880	zone_is_reclaim_writeback(zone)) {
881	nr_immediate++;
882	goto keep_locked;
883
884	/* Case 2 above */
885	} else if (global_reclaim(sc) \|\|
886	!PageReclaim(page) \|\| !(sc->gfp_mask & __GFP_IO)) {
887	/*
888	* This is slightly racy - end_page_writeback()
889	* might have just cleared PageReclaim, then
890	* setting PageReclaim here end up interpreted
891	* as PageReadahead - but that does not matter
892	* enough to care. What we do want is for this
893	* page to have PageReclaim set next time memcg
894	* reclaim reaches the tests above, so it will
895	* then wait_on_page_writeback() to avoid OOM;
896	* and it's also appropriate in global reclaim.
897	*/
898	SetPageReclaim(page);
899	nr_writeback++;
900
901	goto keep_locked;
902
903	/* Case 3 above */
904	} else {
905	wait_on_page_writeback(page);
906	}
907	}
908
909	if (!force_reclaim)
910	references = page_check_references(page, sc);
911
912	switch (references) {
913	case PAGEREF_ACTIVATE:
914	goto activate_locked;
915	case PAGEREF_KEEP:
916	goto keep_locked;
917	case PAGEREF_RECLAIM:
918	case PAGEREF_RECLAIM_CLEAN:
919	; /* try to reclaim the page below */
920	}
921
922	/*
923	* Anonymous process memory has backing store?
924	* Try to allocate it some swap space here.
925	*/
926	if (PageAnon(page) && !PageSwapCache(page)) {
927	if (!(sc->gfp_mask & __GFP_IO))
928	goto keep_locked;
929	if (!add_to_swap(page, page_list))
930	goto activate_locked;
931	may_enter_fs = 1;
932
933	/* Adding to swap updated mapping */
934	mapping = page_mapping(page);
935	}
936
937	/*
938	* The page is mapped into the page tables of one or more
939	* processes. Try to unmap it here.
940	*/
941	if (page_mapped(page) && mapping) {
942	switch (try_to_unmap(page, ttu_flags)) {
943	case SWAP_FAIL:
944	goto activate_locked;
945	case SWAP_AGAIN:
946	goto keep_locked;
947	case SWAP_MLOCK:
948	goto cull_mlocked;
949	case SWAP_SUCCESS:
950	; /* try to free the page below */
951	}
952	}
953
954	if (PageDirty(page)) {
955	/*
956	* Only kswapd can writeback filesystem pages to
957	* avoid risk of stack overflow but only writeback
958	* if many dirty pages have been encountered.
959	*/
960	if (page_is_file_cache(page) &&
961	(!current_is_kswapd() \|\|
962	!zone_is_reclaim_dirty(zone))) {
963	/*
964	* Immediately reclaim when written back.
965	* Similar in principal to deactivate_page()
966	* except we already have the page isolated
967	* and know it's dirty
968	*/
969	inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
970	SetPageReclaim(page);
971
972	goto keep_locked;
973	}
974
975	if (references == PAGEREF_RECLAIM_CLEAN)
976	goto keep_locked;
977	if (!may_enter_fs)
978	goto keep_locked;
979	if (!sc->may_writepage)
980	goto keep_locked;
981
982	/* Page is dirty, try to write it out here */
983	switch (pageout(page, mapping, sc)) {
984	case PAGE_KEEP:
985	goto keep_locked;
986	case PAGE_ACTIVATE:
987	goto activate_locked;
988	case PAGE_SUCCESS:
989	if (PageWriteback(page))
990	goto keep;
991	if (PageDirty(page))
992	goto keep;
993
994	/*
995	* A synchronous write - probably a ramdisk. Go
996	* ahead and try to reclaim the page.
997	*/
998	if (!trylock_page(page))
999	goto keep;
1000	if (PageDirty(page) \|\| PageWriteback(page))
1001	goto keep_locked;
1002	mapping = page_mapping(page);
1003	case PAGE_CLEAN:
1004	; /* try to free the page below */
1005	}
1006	}
1007
1008	/*
1009	* If the page has buffers, try to free the buffer mappings
1010	* associated with this page. If we succeed we try to free
1011	* the page as well.
1012	*
1013	* We do this even if the page is PageDirty().
1014	* try_to_release_page() does not perform I/O, but it is
1015	* possible for a page to have PageDirty set, but it is actually
1016	* clean (all its buffers are clean). This happens if the
1017	* buffers were written out directly, with submit_bh(). ext3
1018	* will do this, as well as the blockdev mapping.
1019	* try_to_release_page() will discover that cleanness and will
1020	* drop the buffers and mark the page clean - it can be freed.
1021	*
1022	* Rarely, pages can have buffers and no ->mapping. These are
1023	* the pages which were not successfully invalidated in
1024	* truncate_complete_page(). We try to drop those buffers here
1025	* and if that worked, and the page is no longer mapped into
1026	* process address space (page_count == 1) it can be freed.
1027	* Otherwise, leave the page on the LRU so it is swappable.
1028	*/
1029	if (page_has_private(page)) {
1030	if (!try_to_release_page(page, sc->gfp_mask))
1031	goto activate_locked;
1032	if (!mapping && page_count(page) == 1) {
1033	unlock_page(page);
1034	if (put_page_testzero(page))
1035	goto free_it;
1036	else {
1037	/*
1038	* rare race with speculative reference.
1039	* the speculative reference will free
1040	* this page shortly, so we may
1041	* increment nr_reclaimed here (and
1042	* leave it off the LRU).
1043	*/
1044	nr_reclaimed++;
1045	continue;
1046	}
1047	}
1048	}
1049
1050	if (!mapping \|\| !__remove_mapping(mapping, page))
1051	goto keep_locked;
1052
1053	/*
1054	* At this point, we have no other references and there is
1055	* no way to pick any more up (removed from LRU, removed
1056	* from pagecache). Can use non-atomic bitops now (and
1057	* we obviously don't have to worry about waking up a process
1058	* waiting on the page lock, because there are no references.
1059	*/
1060	__clear_page_locked(page);
1061	free_it:
1062	nr_reclaimed++;
1063
1064	/*
1065	* Is there need to periodically free_page_list? It would
1066	* appear not as the counts should be low
1067	*/
1068	list_add(&page->lru, &free_pages);
1069	continue;
1070
1071	cull_mlocked:
1072	if (PageSwapCache(page))
1073	try_to_free_swap(page);
1074	unlock_page(page);
1075	putback_lru_page(page);
1076	continue;
1077
1078	activate_locked:
1079	/* Not a candidate for swapping, so reclaim swap space. */
1080	if (PageSwapCache(page) && vm_swap_full())
1081	try_to_free_swap(page);
1082	VM_BUG_ON(PageActive(page));
1083	SetPageActive(page);
1084	pgactivate++;
1085	keep_locked:
1086	unlock_page(page);
1087	keep:
1088	list_add(&page->lru, &ret_pages);
1089	VM_BUG_ON(PageLRU(page) \|\| PageUnevictable(page));
1090	}
1091
1092	free_hot_cold_page_list(&free_pages, 1);
1093
1094	list_splice(&ret_pages, page_list);
1095	count_vm_events(PGACTIVATE, pgactivate);
1096	mem_cgroup_uncharge_end();
1097	*ret_nr_dirty += nr_dirty;
1098	*ret_nr_congested += nr_congested;
1099	*ret_nr_unqueued_dirty += nr_unqueued_dirty;
1100	*ret_nr_writeback += nr_writeback;
1101	*ret_nr_immediate += nr_immediate;
1102	return nr_reclaimed;
1103	}
1104
1105	unsigned long reclaim_clean_pages_from_list(struct zone *zone,
1106	struct list_head *page_list)
1107	{
1108	struct scan_control sc = {
1109	.gfp_mask = GFP_KERNEL,
1110	.priority = DEF_PRIORITY,
1111	.may_unmap = 1,
1112	};
1113	unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
1114	struct page page, next;
1115	LIST_HEAD(clean_pages);
1116
1117	list_for_each_entry_safe(page, next, page_list, lru) {
1118	if (page_is_file_cache(page) && !PageDirty(page) &&
1119	!isolated_balloon_page(page)) {
1120	ClearPageActive(page);
1121	list_move(&page->lru, &clean_pages);
1122	}
1123	}
1124
1125	ret = shrink_page_list(&clean_pages, zone, &sc,
1126	TTU_UNMAP\|TTU_IGNORE_ACCESS,
1127	&dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true);
1128	list_splice(&clean_pages, page_list);
1129	__mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
1130	return ret;
1131	}
1132
1133	/*
1134	* Attempt to remove the specified page from its LRU. Only take this page
1135	* if it is of the appropriate PageActive status. Pages which are being
1136	* freed elsewhere are also ignored.
1137	*
1138	* page: page to consider
1139	* mode: one of the LRU isolation modes defined above
1140	*
1141	* returns 0 on success, -ve errno on failure.
1142	*/
1143	int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1144	{
1145	int ret = -EINVAL;
1146
1147	/* Only take pages on the LRU. */
1148	if (!PageLRU(page))
1149	return ret;
1150
1151	/* Compaction should not handle unevictable pages but CMA can do so */
1152	if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1153	return ret;
1154
1155	ret = -EBUSY;
1156
1157	/*
1158	* To minimise LRU disruption, the caller can indicate that it only
1159	* wants to isolate pages it will be able to operate on without
1160	* blocking - clean pages for the most part.
1161	*
1162	* ISOLATE_CLEAN means that only clean pages should be isolated. This
1163	* is used by reclaim when it is cannot write to backing storage
1164	*
1165	* ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1166	* that it is possible to migrate without blocking
1167	*/
1168	if (mode & (ISOLATE_CLEAN\|ISOLATE_ASYNC_MIGRATE)) {
1169	/* All the caller can do on PageWriteback is block */
1170	if (PageWriteback(page))
1171	return ret;
1172
1173	if (PageDirty(page)) {
1174	struct address_space *mapping;
1175
1176	/* ISOLATE_CLEAN means only clean pages */
1177	if (mode & ISOLATE_CLEAN)
1178	return ret;
1179
1180	/*
1181	* Only pages without mappings or that have a
1182	* ->migratepage callback are possible to migrate
1183	* without blocking
1184	*/
1185	mapping = page_mapping(page);
1186	if (mapping && !mapping->a_ops->migratepage)
1187	return ret;
1188	}
1189	}
1190
1191	if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1192	return ret;
1193
1194	if (likely(get_page_unless_zero(page))) {
1195	/*
1196	* Be careful not to clear PageLRU until after we're
1197	* sure the page is not being freed elsewhere -- the
1198	* page release code relies on it.
1199	*/
1200	ClearPageLRU(page);
1201	ret = 0;
1202	}
1203
1204	return ret;
1205	}
1206
1207	/*
1208	* zone->lru_lock is heavily contended. Some of the functions that
1209	* shrink the lists perform better by taking out a batch of pages
1210	* and working on them outside the LRU lock.
1211	*
1212	* For pagecache intensive workloads, this function is the hottest
1213	* spot in the kernel (apart from copy_*_user functions).
1214	*
1215	* Appropriate locks must be held before calling this function.
1216	*
1217	* @nr_to_scan: The number of pages to look through on the list.
1218	* @lruvec: The LRU vector to pull pages from.
1219	* @dst: The temp list to put pages on to.
1220	* @nr_scanned: The number of pages that were scanned.
1221	* @sc: The scan_control struct for this reclaim session
1222	* @mode: One of the LRU isolation modes
1223	* @lru: LRU list id for isolating
1224	*
1225	* returns how many pages were moved onto *@dst.
1226	*/
1227	static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1228	struct lruvec lruvec, struct list_head dst,
1229	unsigned long nr_scanned, struct scan_control sc,
1230	isolate_mode_t mode, enum lru_list lru)
1231	{
1232	struct list_head *src = &lruvec->lists[lru];
1233	unsigned long nr_taken = 0;
1234	unsigned long scan;
1235
1236	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1237	struct page *page;
1238	int nr_pages;
1239
1240	page = lru_to_page(src);
1241	prefetchw_prev_lru_page(page, src, flags);
1242
1243	VM_BUG_ON(!PageLRU(page));
1244
1245	switch (__isolate_lru_page(page, mode)) {
1246	case 0:
1247	nr_pages = hpage_nr_pages(page);
1248	mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
1249	list_move(&page->lru, dst);
1250	nr_taken += nr_pages;
1251	break;
1252
1253	case -EBUSY:
1254	/* else it is being freed elsewhere */
1255	list_move(&page->lru, src);
1256	continue;
1257
1258	default:
1259	BUG();
1260	}
1261	}
1262
1263	*nr_scanned = scan;
1264	trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
1265	nr_taken, mode, is_file_lru(lru));
1266	return nr_taken;
1267	}
1268
1269	/**
1270	* isolate_lru_page - tries to isolate a page from its LRU list
1271	* @page: page to isolate from its LRU list
1272	*
1273	* Isolates a @page from an LRU list, clears PageLRU and adjusts the
1274	* vmstat statistic corresponding to whatever LRU list the page was on.
1275	*
1276	* Returns 0 if the page was removed from an LRU list.
1277	* Returns -EBUSY if the page was not on an LRU list.
1278	*
1279	* The returned page will have PageLRU() cleared. If it was found on
1280	* the active list, it will have PageActive set. If it was found on
1281	* the unevictable list, it will have the PageUnevictable bit set. That flag
1282	* may need to be cleared by the caller before letting the page go.
1283	*
1284	* The vmstat statistic corresponding to the list on which the page was
1285	* found will be decremented.
1286	*
1287	* Restrictions:
1288	* (1) Must be called with an elevated refcount on the page. This is a
1289	* fundamentnal difference from isolate_lru_pages (which is called
1290	* without a stable reference).
1291	* (2) the lru_lock must not be held.
1292	* (3) interrupts must be enabled.
1293	*/
1294	int isolate_lru_page(struct page *page)
1295	{
1296	int ret = -EBUSY;
1297
1298	VM_BUG_ON(!page_count(page));
1299
1300	if (PageLRU(page)) {
1301	struct zone *zone = page_zone(page);
1302	struct lruvec *lruvec;
1303
1304	spin_lock_irq(&zone->lru_lock);
1305	lruvec = mem_cgroup_page_lruvec(page, zone);
1306	if (PageLRU(page)) {
1307	int lru = page_lru(page);
1308	get_page(page);
1309	ClearPageLRU(page);
1310	del_page_from_lru_list(page, lruvec, lru);
1311	ret = 0;
1312	}
1313	spin_unlock_irq(&zone->lru_lock);
1314	}
1315	return ret;
1316	}
1317
1318	/*
1319	* A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
1320	* then get resheduled. When there are massive number of tasks doing page
1321	* allocation, such sleeping direct reclaimers may keep piling up on each CPU,
1322	* the LRU list will go small and be scanned faster than necessary, leading to
1323	* unnecessary swapping, thrashing and OOM.
1324	*/
1325	static int too_many_isolated(struct zone *zone, int file,
1326	struct scan_control *sc)
1327	{
1328	unsigned long inactive, isolated;
1329
1330	if (current_is_kswapd())
1331	return 0;
1332
1333	if (!global_reclaim(sc))
1334	return 0;
1335
1336	if (file) {
1337	inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1338	isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1339	} else {
1340	inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1341	isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1342	}
1343
1344	/*
1345	* GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
1346	* won't get blocked by normal direct-reclaimers, forming a circular
1347	* deadlock.
1348	*/
1349	if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS)
1350	inactive >>= 3;
1351
1352	return isolated > inactive;
1353	}
1354
1355	static noinline_for_stack void
1356	putback_inactive_pages(struct lruvec lruvec, struct list_head page_list)
1357	{
1358	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1359	struct zone *zone = lruvec_zone(lruvec);
1360	LIST_HEAD(pages_to_free);
1361
1362	/*
1363	* Put back any unfreeable pages.
1364	*/
1365	while (!list_empty(page_list)) {
1366	struct page *page = lru_to_page(page_list);
1367	int lru;
1368
1369	VM_BUG_ON(PageLRU(page));
1370	list_del(&page->lru);
1371	if (unlikely(!page_evictable(page))) {
1372	spin_unlock_irq(&zone->lru_lock);
1373	putback_lru_page(page);
1374	spin_lock_irq(&zone->lru_lock);
1375	continue;
1376	}
1377
1378	lruvec = mem_cgroup_page_lruvec(page, zone);
1379
1380	SetPageLRU(page);
1381	lru = page_lru(page);
1382	add_page_to_lru_list(page, lruvec, lru);
1383
1384	if (is_active_lru(lru)) {
1385	int file = is_file_lru(lru);
1386	int numpages = hpage_nr_pages(page);
1387	reclaim_stat->recent_rotated[file] += numpages;
1388	}
1389	if (put_page_testzero(page)) {
1390	__ClearPageLRU(page);
1391	__ClearPageActive(page);
1392	del_page_from_lru_list(page, lruvec, lru);
1393
1394	if (unlikely(PageCompound(page))) {
1395	spin_unlock_irq(&zone->lru_lock);
1396	(*get_compound_page_dtor(page))(page);
1397	spin_lock_irq(&zone->lru_lock);
1398	} else
1399	list_add(&page->lru, &pages_to_free);
1400	}
1401	}
1402
1403	/*
1404	* To save our caller's stack, now use input list for pages to free.
1405	*/
1406	list_splice(&pages_to_free, page_list);
1407	}
1408
1409	/*
1410	* shrink_inactive_list() is a helper for shrink_zone(). It returns the number
1411	* of reclaimed pages
1412	*/
1413	static noinline_for_stack unsigned long
1414	shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1415	struct scan_control *sc, enum lru_list lru)
1416	{
1417	LIST_HEAD(page_list);
1418	unsigned long nr_scanned;
1419	unsigned long nr_reclaimed = 0;
1420	unsigned long nr_taken;
1421	unsigned long nr_dirty = 0;
1422	unsigned long nr_congested = 0;
1423	unsigned long nr_unqueued_dirty = 0;
1424	unsigned long nr_writeback = 0;
1425	unsigned long nr_immediate = 0;
1426	isolate_mode_t isolate_mode = 0;
1427	int file = is_file_lru(lru);
1428	struct zone *zone = lruvec_zone(lruvec);
1429	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1430
1431	while (unlikely(too_many_isolated(zone, file, sc))) {
1432	congestion_wait(BLK_RW_ASYNC, HZ/10);
1433
1434	/* We are about to die and free our memory. Return now. */
1435	if (fatal_signal_pending(current))
1436	return SWAP_CLUSTER_MAX;
1437	}
1438
1439	lru_add_drain();
1440
1441	if (!sc->may_unmap)
1442	isolate_mode \|= ISOLATE_UNMAPPED;
1443	if (!sc->may_writepage)
1444	isolate_mode \|= ISOLATE_CLEAN;
1445
1446	spin_lock_irq(&zone->lru_lock);
1447
1448	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1449	&nr_scanned, sc, isolate_mode, lru);
1450
1451	__mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1452	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1453
1454	if (global_reclaim(sc)) {
1455	zone->pages_scanned += nr_scanned;
1456	if (current_is_kswapd())
1457	__count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1458	else
1459	__count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1460	}
1461	spin_unlock_irq(&zone->lru_lock);
1462
1463	if (nr_taken == 0)
1464	return 0;
1465
1466	nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
1467	&nr_dirty, &nr_unqueued_dirty, &nr_congested,
1468	&nr_writeback, &nr_immediate,
1469	false);
1470
1471	spin_lock_irq(&zone->lru_lock);
1472
1473	reclaim_stat->recent_scanned[file] += nr_taken;
1474
1475	if (global_reclaim(sc)) {
1476	if (current_is_kswapd())
1477	__count_zone_vm_events(PGSTEAL_KSWAPD, zone,
1478	nr_reclaimed);
1479	else
1480	__count_zone_vm_events(PGSTEAL_DIRECT, zone,
1481	nr_reclaimed);
1482	}
1483
1484	putback_inactive_pages(lruvec, &page_list);
1485
1486	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1487
1488	spin_unlock_irq(&zone->lru_lock);
1489
1490	free_hot_cold_page_list(&page_list, 1);
1491
1492	/*
1493	* If reclaim is isolating dirty pages under writeback, it implies
1494	* that the long-lived page allocation rate is exceeding the page
1495	* laundering rate. Either the global limits are not being effective
1496	* at throttling processes due to the page distribution throughout
1497	* zones or there is heavy usage of a slow backing device. The
1498	* only option is to throttle from reclaim context which is not ideal
1499	* as there is no guarantee the dirtying process is throttled in the
1500	* same way balance_dirty_pages() manages.
1501	*
1502	* Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number
1503	* of pages under pages flagged for immediate reclaim and stall if any
1504	* are encountered in the nr_immediate check below.
1505	*/
1506	if (nr_writeback && nr_writeback == nr_taken)
1507	zone_set_flag(zone, ZONE_WRITEBACK);
1508
1509	/*
1510	* memcg will stall in page writeback so only consider forcibly
1511	* stalling for global reclaim
1512	*/
1513	if (global_reclaim(sc)) {
1514	/*
1515	* Tag a zone as congested if all the dirty pages scanned were
1516	* backed by a congested BDI and wait_iff_congested will stall.
1517	*/
1518	if (nr_dirty && nr_dirty == nr_congested)
1519	zone_set_flag(zone, ZONE_CONGESTED);
1520
1521	/*
1522	* If dirty pages are scanned that are not queued for IO, it
1523	* implies that flushers are not keeping up. In this case, flag
1524	* the zone ZONE_TAIL_LRU_DIRTY and kswapd will start writing
1525	* pages from reclaim context. It will forcibly stall in the
1526	* next check.
1527	*/
1528	if (nr_unqueued_dirty == nr_taken)
1529	zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY);
1530
1531	/*
1532	* In addition, if kswapd scans pages marked marked for
1533	* immediate reclaim and under writeback (nr_immediate), it
1534	* implies that pages are cycling through the LRU faster than
1535	* they are written so also forcibly stall.
1536	*/
1537	if (nr_unqueued_dirty == nr_taken \|\| nr_immediate)
1538	congestion_wait(BLK_RW_ASYNC, HZ/10);
1539	}
1540
1541	/*
1542	* Stall direct reclaim for IO completions if underlying BDIs or zone
1543	* is congested. Allow kswapd to continue until it starts encountering
1544	* unqueued dirty pages or cycling through the LRU too quickly.
1545	*/
1546	if (!sc->hibernation_mode && !current_is_kswapd())
1547	wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
1548
1549	trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1550	zone_idx(zone),
1551	nr_scanned, nr_reclaimed,
1552	sc->priority,
1553	trace_shrink_flags(file));
1554	return nr_reclaimed;
1555	}
1556
1557	/*
1558	* This moves pages from the active list to the inactive list.
1559	*
1560	* We move them the other way if the page is referenced by one or more
1561	* processes, from rmap.
1562	*
1563	* If the pages are mostly unmapped, the processing is fast and it is
1564	* appropriate to hold zone->lru_lock across the whole operation. But if
1565	* the pages are mapped, the processing is slow (page_referenced()) so we
1566	* should drop zone->lru_lock around each page. It's impossible to balance
1567	* this, so instead we remove the pages from the LRU while processing them.
1568	* It is safe to rely on PG_active against the non-LRU pages in here because
1569	* nobody will play with that bit on a non-LRU page.
1570	*
1571	* The downside is that we have to touch page->_count against each page.
1572	* But we had to alter page->flags anyway.
1573	*/
1574
1575	static void move_active_pages_to_lru(struct lruvec *lruvec,
1576	struct list_head *list,
1577	struct list_head *pages_to_free,
1578	enum lru_list lru)
1579	{
1580	struct zone *zone = lruvec_zone(lruvec);
1581	unsigned long pgmoved = 0;
1582	struct page *page;
1583	int nr_pages;
1584
1585	while (!list_empty(list)) {
1586	page = lru_to_page(list);
1587	lruvec = mem_cgroup_page_lruvec(page, zone);
1588
1589	VM_BUG_ON(PageLRU(page));
1590	SetPageLRU(page);
1591
1592	nr_pages = hpage_nr_pages(page);
1593	mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1594	list_move(&page->lru, &lruvec->lists[lru]);
1595	pgmoved += nr_pages;
1596
1597	if (put_page_testzero(page)) {
1598	__ClearPageLRU(page);
1599	__ClearPageActive(page);
1600	del_page_from_lru_list(page, lruvec, lru);
1601
1602	if (unlikely(PageCompound(page))) {
1603	spin_unlock_irq(&zone->lru_lock);
1604	(*get_compound_page_dtor(page))(page);
1605	spin_lock_irq(&zone->lru_lock);
1606	} else
1607	list_add(&page->lru, pages_to_free);
1608	}
1609	}
1610	__mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1611	if (!is_active_lru(lru))
1612	__count_vm_events(PGDEACTIVATE, pgmoved);
1613	}
1614
1615	static void shrink_active_list(unsigned long nr_to_scan,
1616	struct lruvec *lruvec,
1617	struct scan_control *sc,
1618	enum lru_list lru)
1619	{
1620	unsigned long nr_taken;
1621	unsigned long nr_scanned;
1622	unsigned long vm_flags;
1623	LIST_HEAD(l_hold); /* The pages which were snipped off */
1624	LIST_HEAD(l_active);
1625	LIST_HEAD(l_inactive);
1626	struct page *page;
1627	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1628	unsigned long nr_rotated = 0;
1629	isolate_mode_t isolate_mode = 0;
1630	int file = is_file_lru(lru);
1631	struct zone *zone = lruvec_zone(lruvec);
1632
1633	lru_add_drain();
1634
1635	if (!sc->may_unmap)
1636	isolate_mode \|= ISOLATE_UNMAPPED;
1637	if (!sc->may_writepage)
1638	isolate_mode \|= ISOLATE_CLEAN;
1639
1640	spin_lock_irq(&zone->lru_lock);
1641
1642	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1643	&nr_scanned, sc, isolate_mode, lru);
1644	if (global_reclaim(sc))
1645	zone->pages_scanned += nr_scanned;
1646
1647	reclaim_stat->recent_scanned[file] += nr_taken;
1648
1649	__count_zone_vm_events(PGREFILL, zone, nr_scanned);
1650	__mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1651	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1652	spin_unlock_irq(&zone->lru_lock);
1653
1654	while (!list_empty(&l_hold)) {
1655	cond_resched();
1656	page = lru_to_page(&l_hold);
1657	list_del(&page->lru);
1658
1659	if (unlikely(!page_evictable(page))) {
1660	putback_lru_page(page);
1661	continue;
1662	}
1663
1664	if (unlikely(buffer_heads_over_limit)) {
1665	if (page_has_private(page) && trylock_page(page)) {
1666	if (page_has_private(page))
1667	try_to_release_page(page, 0);
1668	unlock_page(page);
1669	}
1670	}
1671
1672	if (page_referenced(page, 0, sc->target_mem_cgroup,
1673	&vm_flags)) {
1674	nr_rotated += hpage_nr_pages(page);
1675	/*
1676	* Identify referenced, file-backed active pages and
1677	* give them one more trip around the active list. So
1678	* that executable code get better chances to stay in
1679	* memory under moderate memory pressure. Anon pages
1680	* are not likely to be evicted by use-once streaming
1681	* IO, plus JVM can create lots of anon VM_EXEC pages,
1682	* so we ignore them here.
1683	*/
1684	if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1685	list_add(&page->lru, &l_active);
1686	continue;
1687	}
1688	}
1689
1690	ClearPageActive(page); /* we are de-activating */
1691	list_add(&page->lru, &l_inactive);
1692	}
1693
1694	/*
1695	* Move pages back to the lru list.
1696	*/
1697	spin_lock_irq(&zone->lru_lock);
1698	/*
1699	* Count referenced pages from currently used mappings as rotated,
1700	* even though only some of them are actually re-activated. This
1701	* helps balance scan pressure between file and anonymous pages in
1702	* get_scan_ratio.
1703	*/
1704	reclaim_stat->recent_rotated[file] += nr_rotated;
1705
1706	move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1707	move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1708	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1709	spin_unlock_irq(&zone->lru_lock);
1710
1711	free_hot_cold_page_list(&l_hold, 1);
1712	}
1713
1714	#ifdef CONFIG_SWAP
1715	static int inactive_anon_is_low_global(struct zone *zone)
1716	{
1717	unsigned long active, inactive;
1718
1719	active = zone_page_state(zone, NR_ACTIVE_ANON);
1720	inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1721
1722	if (inactive * zone->inactive_ratio < active)
1723	return 1;
1724
1725	return 0;
1726	}
1727
1728	/**
1729	* inactive_anon_is_low - check if anonymous pages need to be deactivated
1730	* @lruvec: LRU vector to check
1731	*
1732	* Returns true if the zone does not have enough inactive anon pages,
1733	* meaning some active anon pages need to be deactivated.
1734	*/
1735	static int inactive_anon_is_low(struct lruvec *lruvec)
1736	{
1737	/*
1738	* If we don't have swap space, anonymous page deactivation
1739	* is pointless.
1740	*/
1741	if (!total_swap_pages)
1742	return 0;
1743
1744	if (!mem_cgroup_disabled())
1745	return mem_cgroup_inactive_anon_is_low(lruvec);
1746
1747	return inactive_anon_is_low_global(lruvec_zone(lruvec));
1748	}
1749	#else
1750	static inline int inactive_anon_is_low(struct lruvec *lruvec)
1751	{
1752	return 0;
1753	}
1754	#endif
1755
1756	/**
1757	* inactive_file_is_low - check if file pages need to be deactivated
1758	* @lruvec: LRU vector to check
1759	*
1760	* When the system is doing streaming IO, memory pressure here
1761	* ensures that active file pages get deactivated, until more
1762	* than half of the file pages are on the inactive list.
1763	*
1764	* Once we get to that situation, protect the system's working
1765	* set from being evicted by disabling active file page aging.
1766	*
1767	* This uses a different ratio than the anonymous pages, because
1768	* the page cache uses a use-once replacement algorithm.
1769	*/
1770	static int inactive_file_is_low(struct lruvec *lruvec)
1771	{
1772	unsigned long inactive;
1773	unsigned long active;
1774
1775	inactive = get_lru_size(lruvec, LRU_INACTIVE_FILE);
1776	active = get_lru_size(lruvec, LRU_ACTIVE_FILE);
1777
1778	return active > inactive;
1779	}
1780
1781	static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1782	{
1783	if (is_file_lru(lru))
1784	return inactive_file_is_low(lruvec);
1785	else
1786	return inactive_anon_is_low(lruvec);
1787	}
1788
1789	static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1790	struct lruvec lruvec, struct scan_control sc)
1791	{
1792	if (is_active_lru(lru)) {
1793	if (inactive_list_is_low(lruvec, lru))
1794	shrink_active_list(nr_to_scan, lruvec, sc, lru);
1795	return 0;
1796	}
1797
1798	return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1799	}
1800
1801	static int vmscan_swappiness(struct scan_control *sc)
1802	{
1803	if (global_reclaim(sc))
1804	return vm_swappiness;
1805	return mem_cgroup_swappiness(sc->target_mem_cgroup);
1806	}
1807
1808	enum scan_balance {
1809	SCAN_EQUAL,
1810	SCAN_FRACT,
1811	SCAN_ANON,
1812	SCAN_FILE,
1813	};
1814
1815	/*
1816	* Determine how aggressively the anon and file LRU lists should be
1817	* scanned. The relative value of each set of LRU lists is determined
1818	* by looking at the fraction of the pages scanned we did rotate back
1819	* onto the active list instead of evict.
1820	*
1821	* nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
1822	* nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
1823	*/
1824	static void get_scan_count(struct lruvec lruvec, struct scan_control sc,
1825	unsigned long *nr)
1826	{
1827	struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1828	u64 fraction[2];
1829	u64 denominator = 0; /* gcc */
1830	struct zone *zone = lruvec_zone(lruvec);
1831	unsigned long anon_prio, file_prio;
1832	enum scan_balance scan_balance;
1833	unsigned long anon, file, free;
1834	bool force_scan = false;
1835	unsigned long ap, fp;
1836	enum lru_list lru;
1837
1838	/*
1839	* If the zone or memcg is small, nr[l] can be 0. This
1840	* results in no scanning on this priority and a potential
1841	* priority drop. Global direct reclaim can go to the next
1842	* zone and tends to have no problems. Global kswapd is for
1843	* zone balancing and it needs to scan a minimum amount. When
1844	* reclaiming for a memcg, a priority drop can cause high
1845	* latencies, so it's better to scan a minimum amount there as
1846	* well.
1847	*/
1848	if (current_is_kswapd() && !zone_reclaimable(zone))
1849	force_scan = true;
1850	if (!global_reclaim(sc))
1851	force_scan = true;
1852
1853	/* If we have no swap space, do not bother scanning anon pages. */
1854	if (!sc->may_swap \|\| (get_nr_swap_pages() <= 0)) {
1855	scan_balance = SCAN_FILE;
1856	goto out;
1857	}
1858
1859	/*
1860	* Global reclaim will swap to prevent OOM even with no
1861	* swappiness, but memcg users want to use this knob to
1862	* disable swapping for individual groups completely when
1863	* using the memory controller's swap limit feature would be
1864	* too expensive.
1865	*/
1866	if (!global_reclaim(sc) && !vmscan_swappiness(sc)) {
1867	scan_balance = SCAN_FILE;
1868	goto out;
1869	}
1870
1871	/*
1872	* Do not apply any pressure balancing cleverness when the
1873	* system is close to OOM, scan both anon and file equally
1874	* (unless the swappiness setting disagrees with swapping).
1875	*/
1876	if (!sc->priority && vmscan_swappiness(sc)) {
1877	scan_balance = SCAN_EQUAL;
1878	goto out;
1879	}
1880
1881	anon = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
1882	get_lru_size(lruvec, LRU_INACTIVE_ANON);
1883	file = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
1884	get_lru_size(lruvec, LRU_INACTIVE_FILE);
1885
1886	/*
1887	* If it's foreseeable that reclaiming the file cache won't be
1888	* enough to get the zone back into a desirable shape, we have
1889	* to swap. Better start now and leave the - probably heavily
1890	* thrashing - remaining file pages alone.
1891	*/
1892	if (global_reclaim(sc)) {
1893	free = zone_page_state(zone, NR_FREE_PAGES);
1894	if (unlikely(file + free <= high_wmark_pages(zone))) {
1895	scan_balance = SCAN_ANON;
1896	goto out;
1897	}
1898	}
1899
1900	/*
1901	* There is enough inactive page cache, do not reclaim
1902	* anything from the anonymous working set right now.
1903	*/
1904	if (!inactive_file_is_low(lruvec)) {
1905	scan_balance = SCAN_FILE;
1906	goto out;
1907	}
1908
1909	scan_balance = SCAN_FRACT;
1910
1911	/*
1912	* With swappiness at 100, anonymous and file have the same priority.
1913	* This scanning priority is essentially the inverse of IO cost.
1914	*/
1915	anon_prio = vmscan_swappiness(sc);
1916	file_prio = 200 - anon_prio;
1917
1918	/*
1919	* OK, so we have swap space and a fair amount of page cache
1920	* pages. We use the recently rotated / recently scanned
1921	* ratios to determine how valuable each cache is.
1922	*
1923	* Because workloads change over time (and to avoid overflow)
1924	* we keep these statistics as a floating average, which ends
1925	* up weighing recent references more than old ones.
1926	*
1927	* anon in [0], file in [1]
1928	*/
1929	spin_lock_irq(&zone->lru_lock);
1930	if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1931	reclaim_stat->recent_scanned[0] /= 2;
1932	reclaim_stat->recent_rotated[0] /= 2;
1933	}
1934
1935	if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1936	reclaim_stat->recent_scanned[1] /= 2;
1937	reclaim_stat->recent_rotated[1] /= 2;
1938	}
1939
1940	/*
1941	* The amount of pressure on anon vs file pages is inversely
1942	* proportional to the fraction of recently scanned pages on
1943	* each list that were recently referenced and in active use.
1944	*/
1945	ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1946	ap /= reclaim_stat->recent_rotated[0] + 1;
1947
1948	fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
1949	fp /= reclaim_stat->recent_rotated[1] + 1;
1950	spin_unlock_irq(&zone->lru_lock);
1951
1952	fraction[0] = ap;
1953	fraction[1] = fp;
1954	denominator = ap + fp + 1;
1955	out:
1956	for_each_evictable_lru(lru) {
1957	int file = is_file_lru(lru);
1958	unsigned long size;
1959	unsigned long scan;
1960
1961	size = get_lru_size(lruvec, lru);
1962	scan = size >> sc->priority;
1963
1964	if (!scan && force_scan)
1965	scan = min(size, SWAP_CLUSTER_MAX);
1966
1967	switch (scan_balance) {
1968	case SCAN_EQUAL:
1969	/* Scan lists relative to size */
1970	break;
1971	case SCAN_FRACT:
1972	/*
1973	* Scan types proportional to swappiness and
1974	* their relative recent reclaim efficiency.
1975	*/
1976	scan = div64_u64(scan * fraction[file], denominator);
1977	break;
1978	case SCAN_FILE:
1979	case SCAN_ANON:
1980	/* Scan one type exclusively */
1981	if ((scan_balance == SCAN_FILE) != file)
1982	scan = 0;
1983	break;
1984	default:
1985	/* Look ma, no brain */
1986	BUG();
1987	}
1988	nr[lru] = scan;
1989	}
1990	}
1991
1992	/*
1993	* This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
1994	*/
1995	static void shrink_lruvec(struct lruvec lruvec, struct scan_control sc)
1996	{
1997	unsigned long nr[NR_LRU_LISTS];
1998	unsigned long targets[NR_LRU_LISTS];
1999	unsigned long nr_to_scan;
2000	enum lru_list lru;
2001	unsigned long nr_reclaimed = 0;
2002	unsigned long nr_to_reclaim = sc->nr_to_reclaim;
2003	struct blk_plug plug;
2004	bool scan_adjusted = false;
2005
2006	get_scan_count(lruvec, sc, nr);
2007
2008	/* Record the original scan target for proportional adjustments later */
2009	memcpy(targets, nr, sizeof(nr));
2010
2011	blk_start_plug(&plug);
2012	while (nr[LRU_INACTIVE_ANON] \|\| nr[LRU_ACTIVE_FILE] \|\|
2013	nr[LRU_INACTIVE_FILE]) {
2014	unsigned long nr_anon, nr_file, percentage;
2015	unsigned long nr_scanned;
2016
2017	for_each_evictable_lru(lru) {
2018	if (nr[lru]) {
2019	nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
2020	nr[lru] -= nr_to_scan;
2021
2022	nr_reclaimed += shrink_list(lru, nr_to_scan,
2023	lruvec, sc);
2024	}
2025	}
2026
2027	if (nr_reclaimed < nr_to_reclaim \|\| scan_adjusted)
2028	continue;
2029
2030	/*
2031	* For global direct reclaim, reclaim only the number of pages
2032	* requested. Less care is taken to scan proportionally as it
2033	* is more important to minimise direct reclaim stall latency
2034	* than it is to properly age the LRU lists.
2035	*/
2036	if (global_reclaim(sc) && !current_is_kswapd())
2037	break;
2038
2039	/*
2040	* For kswapd and memcg, reclaim at least the number of pages
2041	* requested. Ensure that the anon and file LRUs shrink
2042	* proportionally what was requested by get_scan_count(). We
2043	* stop reclaiming one LRU and reduce the amount scanning
2044	* proportional to the original scan target.
2045	*/
2046	nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE];
2047	nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON];
2048
2049	if (nr_file > nr_anon) {
2050	unsigned long scan_target = targets[LRU_INACTIVE_ANON] +
2051	targets[LRU_ACTIVE_ANON] + 1;
2052	lru = LRU_BASE;
2053	percentage = nr_anon * 100 / scan_target;
2054	} else {
2055	unsigned long scan_target = targets[LRU_INACTIVE_FILE] +
2056	targets[LRU_ACTIVE_FILE] + 1;
2057	lru = LRU_FILE;
2058	percentage = nr_file * 100 / scan_target;
2059	}
2060
2061	/* Stop scanning the smaller of the LRU */
2062	nr[lru] = 0;
2063	nr[lru + LRU_ACTIVE] = 0;
2064
2065	/*
2066	* Recalculate the other LRU scan count based on its original
2067	* scan target and the percentage scanning already complete
2068	*/
2069	lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE;
2070	nr_scanned = targets[lru] - nr[lru];
2071	nr[lru] = targets[lru] * (100 - percentage) / 100;
2072	nr[lru] -= min(nr[lru], nr_scanned);
2073
2074	lru += LRU_ACTIVE;
2075	nr_scanned = targets[lru] - nr[lru];
2076	nr[lru] = targets[lru] * (100 - percentage) / 100;
2077	nr[lru] -= min(nr[lru], nr_scanned);
2078
2079	scan_adjusted = true;
2080	}
2081	blk_finish_plug(&plug);
2082	sc->nr_reclaimed += nr_reclaimed;
2083
2084	/*
2085	* Even if we did not try to evict anon pages at all, we want to
2086	* rebalance the anon lru active/inactive ratio.
2087	*/
2088	if (inactive_anon_is_low(lruvec))
2089	shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2090	sc, LRU_ACTIVE_ANON);
2091
2092	throttle_vm_writeout(sc->gfp_mask);
2093	}
2094
2095	/* Use reclaim/compaction for costly allocs or under memory pressure */
2096	static bool in_reclaim_compaction(struct scan_control *sc)
2097	{
2098	if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2099	(sc->order > PAGE_ALLOC_COSTLY_ORDER \|\|
2100	sc->priority < DEF_PRIORITY - 2))
2101	return true;
2102
2103	return false;
2104	}
2105
2106	/*
2107	* Reclaim/compaction is used for high-order allocation requests. It reclaims
2108	* order-0 pages before compacting the zone. should_continue_reclaim() returns
2109	* true if more pages should be reclaimed such that when the page allocator
2110	* calls try_to_compact_zone() that it will have enough free pages to succeed.
2111	* It will give up earlier than that if there is difficulty reclaiming pages.
2112	*/
2113	static inline bool should_continue_reclaim(struct zone *zone,
2114	unsigned long nr_reclaimed,
2115	unsigned long nr_scanned,
2116	struct scan_control *sc)
2117	{
2118	unsigned long pages_for_compaction;
2119	unsigned long inactive_lru_pages;
2120
2121	/* If not in reclaim/compaction mode, stop */
2122	if (!in_reclaim_compaction(sc))
2123	return false;
2124
2125	/* Consider stopping depending on scan and reclaim activity */
2126	if (sc->gfp_mask & __GFP_REPEAT) {
2127	/*
2128	* For __GFP_REPEAT allocations, stop reclaiming if the
2129	* full LRU list has been scanned and we are still failing
2130	* to reclaim pages. This full LRU scan is potentially
2131	* expensive but a __GFP_REPEAT caller really wants to succeed
2132	*/
2133	if (!nr_reclaimed && !nr_scanned)
2134	return false;
2135	} else {
2136	/*
2137	* For non-__GFP_REPEAT allocations which can presumably
2138	* fail without consequence, stop if we failed to reclaim
2139	* any pages from the last SWAP_CLUSTER_MAX number of
2140	* pages that were scanned. This will return to the
2141	* caller faster at the risk reclaim/compaction and
2142	* the resulting allocation attempt fails
2143	*/
2144	if (!nr_reclaimed)
2145	return false;
2146	}
2147
2148	/*
2149	* If we have not reclaimed enough pages for compaction and the
2150	* inactive lists are large enough, continue reclaiming
2151	*/
2152	pages_for_compaction = (2UL << sc->order);
2153	inactive_lru_pages = zone_page_state(zone, NR_INACTIVE_FILE);
2154	if (get_nr_swap_pages() > 0)
2155	inactive_lru_pages += zone_page_state(zone, NR_INACTIVE_ANON);
2156	if (sc->nr_reclaimed < pages_for_compaction &&
2157	inactive_lru_pages > pages_for_compaction)
2158	return true;
2159
2160	/* If compaction would go ahead or the allocation would succeed, stop */
2161	switch (compaction_suitable(zone, sc->order)) {
2162	case COMPACT_PARTIAL:
2163	case COMPACT_CONTINUE:
2164	return false;
2165	default:
2166	return true;
2167	}
2168	}
2169
2170	static void shrink_zone(struct zone zone, struct scan_control sc)
2171	{
2172	unsigned long nr_reclaimed, nr_scanned;
2173
2174	do {
2175	struct mem_cgroup *root = sc->target_mem_cgroup;
2176	struct mem_cgroup_reclaim_cookie reclaim = {
2177	.zone = zone,
2178	.priority = sc->priority,
2179	};
2180	struct mem_cgroup *memcg;
2181
2182	nr_reclaimed = sc->nr_reclaimed;
2183	nr_scanned = sc->nr_scanned;
2184
2185	memcg = mem_cgroup_iter(root, NULL, &reclaim);
2186	do {
2187	struct lruvec *lruvec;
2188
2189	lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2190
2191	shrink_lruvec(lruvec, sc);
2192
2193	/*
2194	* Direct reclaim and kswapd have to scan all memory
2195	* cgroups to fulfill the overall scan target for the
2196	* zone.
2197	*
2198	* Limit reclaim, on the other hand, only cares about
2199	* nr_to_reclaim pages to be reclaimed and it will
2200	* retry with decreasing priority if one round over the
2201	* whole hierarchy is not sufficient.
2202	*/
2203	if (!global_reclaim(sc) &&
2204	sc->nr_reclaimed >= sc->nr_to_reclaim) {
2205	mem_cgroup_iter_break(root, memcg);
2206	break;
2207	}
2208	memcg = mem_cgroup_iter(root, memcg, &reclaim);
2209	} while (memcg);
2210
2211	vmpressure(sc->gfp_mask, sc->target_mem_cgroup,
2212	sc->nr_scanned - nr_scanned,
2213	sc->nr_reclaimed - nr_reclaimed);
2214
2215	} while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed,
2216	sc->nr_scanned - nr_scanned, sc));
2217	}
2218
2219	/* Returns true if compaction should go ahead for a high-order request */
2220	static inline bool compaction_ready(struct zone zone, struct scan_control sc)
2221	{
2222	unsigned long balance_gap, watermark;
2223	bool watermark_ok;
2224
2225	/* Do not consider compaction for orders reclaim is meant to satisfy */
2226	if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
2227	return false;
2228
2229	/*
2230	* Compaction takes time to run and there are potentially other
2231	* callers using the pages just freed. Continue reclaiming until
2232	* there is a buffer of free pages available to give compaction
2233	* a reasonable chance of completing and allocating the page
2234	*/
2235	balance_gap = min(low_wmark_pages(zone),
2236	(zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2237	KSWAPD_ZONE_BALANCE_GAP_RATIO);
2238	watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
2239	watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
2240
2241	/*
2242	* If compaction is deferred, reclaim up to a point where
2243	* compaction will have a chance of success when re-enabled
2244	*/
2245	if (compaction_deferred(zone, sc->order))
2246	return watermark_ok;
2247
2248	/* If compaction is not ready to start, keep reclaiming */
2249	if (!compaction_suitable(zone, sc->order))
2250	return false;
2251
2252	return watermark_ok;
2253	}
2254
2255	/*
2256	* This is the direct reclaim path, for page-allocating processes. We only
2257	* try to reclaim pages from zones which will satisfy the caller's allocation
2258	* request.
2259	*
2260	* We reclaim from a zone even if that zone is over high_wmark_pages(zone).
2261	* Because:
2262	* a) The caller may be trying to free extra pages to satisfy a higher-order
2263	* allocation or
2264	* b) The target zone may be at high_wmark_pages(zone) but the lower zones
2265	* must go over high_wmark_pages(zone) to satisfy the `incremental min'
2266	* zone defense algorithm.
2267	*
2268	* If a zone is deemed to be full of pinned pages then just give it a light
2269	* scan then give up on it.
2270	*
2271	* This function returns true if a zone is being reclaimed for a costly
2272	* high-order allocation and compaction is ready to begin. This indicates to
2273	* the caller that it should consider retrying the allocation instead of
2274	* further reclaim.
2275	*/
2276	static bool shrink_zones(struct zonelist zonelist, struct scan_control sc)
2277	{
2278	struct zoneref *z;
2279	struct zone *zone;
2280	unsigned long nr_soft_reclaimed;
2281	unsigned long nr_soft_scanned;
2282	bool aborted_reclaim = false;
2283
2284	/*
2285	* If the number of buffer_heads in the machine exceeds the maximum
2286	* allowed level, force direct reclaim to scan the highmem zone as
2287	* highmem pages could be pinning lowmem pages storing buffer_heads
2288	*/
2289	if (buffer_heads_over_limit)
2290	sc->gfp_mask \|= __GFP_HIGHMEM;
2291
2292	for_each_zone_zonelist_nodemask(zone, z, zonelist,
2293	gfp_zone(sc->gfp_mask), sc->nodemask) {
2294	if (!populated_zone(zone))
2295	continue;
2296	/*
2297	* Take care memory controller reclaiming has small influence
2298	* to global LRU.
2299	*/
2300	if (global_reclaim(sc)) {
2301	if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2302	continue;
2303	if (sc->priority != DEF_PRIORITY &&
2304	!zone_reclaimable(zone))
2305	continue; /* Let kswapd poll it */
2306	if (IS_ENABLED(CONFIG_COMPACTION)) {
2307	/*
2308	* If we already have plenty of memory free for
2309	* compaction in this zone, don't free any more.
2310	* Even though compaction is invoked for any
2311	* non-zero order, only frequent costly order
2312	* reclamation is disruptive enough to become a
2313	* noticeable problem, like transparent huge
2314	* page allocations.
2315	*/
2316	if (compaction_ready(zone, sc)) {
2317	aborted_reclaim = true;
2318	continue;
2319	}
2320	}
2321	/*
2322	* This steals pages from memory cgroups over softlimit
2323	* and returns the number of reclaimed pages and
2324	* scanned pages. This works for global memory pressure
2325	* and balancing, not for a memcg's limit.
2326	*/
2327	nr_soft_scanned = 0;
2328	nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2329	sc->order, sc->gfp_mask,
2330	&nr_soft_scanned);
2331	sc->nr_reclaimed += nr_soft_reclaimed;
2332	sc->nr_scanned += nr_soft_scanned;
2333	/* need some check for avoid more shrink_zone() */
2334	}
2335
2336	shrink_zone(zone, sc);
2337	}
2338
2339	return aborted_reclaim;
2340	}
2341
2342	/* All zones in zonelist are unreclaimable? */
2343	static bool all_unreclaimable(struct zonelist *zonelist,
2344	struct scan_control *sc)
2345	{
2346	struct zoneref *z;
2347	struct zone *zone;
2348
2349	for_each_zone_zonelist_nodemask(zone, z, zonelist,
2350	gfp_zone(sc->gfp_mask), sc->nodemask) {
2351	if (!populated_zone(zone))
2352	continue;
2353	if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2354	continue;
2355	if (zone_reclaimable(zone))
2356	return false;
2357	}
2358
2359	return true;
2360	}
2361
2362	/*
2363	* This is the main entry point to direct page reclaim.
2364	*
2365	* If a full scan of the inactive list fails to free enough memory then we
2366	* are "out of memory" and something needs to be killed.
2367	*
2368	* If the caller is !__GFP_FS then the probability of a failure is reasonably
2369	* high - the zone may be full of dirty or under-writeback pages, which this
2370	* caller can't do much about. We kick the writeback threads and take explicit
2371	* naps in the hope that some of these pages can be written. But if the
2372	* allocating task holds filesystem locks which prevent writeout this might not
2373	* work, and the allocation attempt will fail.
2374	*
2375	* returns: 0, if no pages reclaimed
2376	* else, the number of pages reclaimed
2377	*/
2378	static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2379	struct scan_control *sc,
2380	struct shrink_control *shrink)
2381	{
2382	unsigned long total_scanned = 0;
2383	struct reclaim_state *reclaim_state = current->reclaim_state;
2384	struct zoneref *z;
2385	struct zone *zone;
2386	unsigned long writeback_threshold;
2387	bool aborted_reclaim;
2388
2389	delayacct_freepages_start();
2390
2391	if (global_reclaim(sc))
2392	count_vm_event(ALLOCSTALL);
2393
2394	do {
2395	vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
2396	sc->priority);
2397	sc->nr_scanned = 0;
2398	aborted_reclaim = shrink_zones(zonelist, sc);
2399
2400	/*
2401	* Don't shrink slabs when reclaiming memory from over limit
2402	* cgroups but do shrink slab at least once when aborting
2403	* reclaim for compaction to avoid unevenly scanning file/anon
2404	* LRU pages over slab pages.
2405	*/
2406	if (global_reclaim(sc)) {
2407	unsigned long lru_pages = 0;
2408
2409	nodes_clear(shrink->nodes_to_scan);
2410	for_each_zone_zonelist(zone, z, zonelist,
2411	gfp_zone(sc->gfp_mask)) {
2412	if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2413	continue;
2414
2415	lru_pages += zone_reclaimable_pages(zone);
2416	node_set(zone_to_nid(zone),
2417	shrink->nodes_to_scan);
2418	}
2419
2420	shrink_slab(shrink, sc->nr_scanned, lru_pages);
2421	if (reclaim_state) {
2422	sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2423	reclaim_state->reclaimed_slab = 0;
2424	}
2425	}
2426	total_scanned += sc->nr_scanned;
2427	if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2428	goto out;
2429
2430	/*
2431	* If we're getting trouble reclaiming, start doing
2432	* writepage even in laptop mode.
2433	*/
2434	if (sc->priority < DEF_PRIORITY - 2)
2435	sc->may_writepage = 1;
2436
2437	/*
2438	* Try to write back as many pages as we just scanned. This
2439	* tends to cause slow streaming writers to write data to the
2440	* disk smoothly, at the dirtying rate, which is nice. But
2441	* that's undesirable in laptop mode, where we want lumpy
2442	* writeout. So in laptop mode, write out the whole world.
2443	*/
2444	writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2445	if (total_scanned > writeback_threshold) {
2446	wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2447	WB_REASON_TRY_TO_FREE_PAGES);
2448	sc->may_writepage = 1;
2449	}
2450	} while (--sc->priority >= 0 && !aborted_reclaim);
2451
2452	out:
2453	delayacct_freepages_end();
2454
2455	if (sc->nr_reclaimed)
2456	return sc->nr_reclaimed;
2457
2458	/*
2459	* As hibernation is going on, kswapd is freezed so that it can't mark
2460	* the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2461	* check.
2462	*/
2463	if (oom_killer_disabled)
2464	return 0;
2465
2466	/* Aborted reclaim to try compaction? don't OOM, then */
2467	if (aborted_reclaim)
2468	return 1;
2469
2470	/* top priority shrink_zones still had more to do? don't OOM, then */
2471	if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2472	return 1;
2473
2474	return 0;
2475	}
2476
2477	static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2478	{
2479	struct zone *zone;
2480	unsigned long pfmemalloc_reserve = 0;
2481	unsigned long free_pages = 0;
2482	int i;
2483	bool wmark_ok;
2484
2485	for (i = 0; i <= ZONE_NORMAL; i++) {
2486	zone = &pgdat->node_zones[i];
2487	pfmemalloc_reserve += min_wmark_pages(zone);
2488	free_pages += zone_page_state(zone, NR_FREE_PAGES);
2489	}
2490
2491	wmark_ok = free_pages > pfmemalloc_reserve / 2;
2492
2493	/* kswapd must be awake if processes are being throttled */
2494	if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2495	pgdat->classzone_idx = min(pgdat->classzone_idx,
2496	(enum zone_type)ZONE_NORMAL);
2497	wake_up_interruptible(&pgdat->kswapd_wait);
2498	}
2499
2500	return wmark_ok;
2501	}
2502
2503	/*
2504	* Throttle direct reclaimers if backing storage is backed by the network
2505	* and the PFMEMALLOC reserve for the preferred node is getting dangerously
2506	* depleted. kswapd will continue to make progress and wake the processes
2507	* when the low watermark is reached.
2508	*
2509	* Returns true if a fatal signal was delivered during throttling. If this
2510	* happens, the page allocator should not consider triggering the OOM killer.
2511	*/
2512	static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2513	nodemask_t *nodemask)
2514	{
2515	struct zone *zone;
2516	int high_zoneidx = gfp_zone(gfp_mask);
2517	pg_data_t *pgdat;
2518
2519	/*
2520	* Kernel threads should not be throttled as they may be indirectly
2521	* responsible for cleaning pages necessary for reclaim to make forward
2522	* progress. kjournald for example may enter direct reclaim while
2523	* committing a transaction where throttling it could forcing other
2524	* processes to block on log_wait_commit().
2525	*/
2526	if (current->flags & PF_KTHREAD)
2527	goto out;
2528
2529	/*
2530	* If a fatal signal is pending, this process should not throttle.
2531	* It should return quickly so it can exit and free its memory
2532	*/
2533	if (fatal_signal_pending(current))
2534	goto out;
2535
2536	/* Check if the pfmemalloc reserves are ok */
2537	first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
2538	pgdat = zone->zone_pgdat;
2539	if (pfmemalloc_watermark_ok(pgdat))
2540	goto out;
2541
2542	/* Account for the throttling */
2543	count_vm_event(PGSCAN_DIRECT_THROTTLE);
2544
2545	/*
2546	* If the caller cannot enter the filesystem, it's possible that it
2547	* is due to the caller holding an FS lock or performing a journal
2548	* transaction in the case of a filesystem like ext[3\|4]. In this case,
2549	* it is not safe to block on pfmemalloc_wait as kswapd could be
2550	* blocked waiting on the same lock. Instead, throttle for up to a
2551	* second before continuing.
2552	*/
2553	if (!(gfp_mask & __GFP_FS)) {
2554	wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2555	pfmemalloc_watermark_ok(pgdat), HZ);
2556
2557	goto check_pending;
2558	}
2559
2560	/* Throttle until kswapd wakes the process */
2561	wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2562	pfmemalloc_watermark_ok(pgdat));
2563
2564	check_pending:
2565	if (fatal_signal_pending(current))
2566	return true;
2567
2568	out:
2569	return false;
2570	}
2571
2572	unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2573	gfp_t gfp_mask, nodemask_t *nodemask)
2574	{
2575	unsigned long nr_reclaimed;
2576	struct scan_control sc = {
2577	.gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
2578	.may_writepage = !laptop_mode,
2579	.nr_to_reclaim = SWAP_CLUSTER_MAX,
2580	.may_unmap = 1,
2581	.may_swap = 1,
2582	.order = order,
2583	.priority = DEF_PRIORITY,
2584	.target_mem_cgroup = NULL,
2585	.nodemask = nodemask,
2586	};
2587	struct shrink_control shrink = {
2588	.gfp_mask = sc.gfp_mask,
2589	};
2590
2591	/*
2592	* Do not enter reclaim if fatal signal was delivered while throttled.
2593	* 1 is returned so that the page allocator does not OOM kill at this
2594	* point.
2595	*/
2596	if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2597	return 1;
2598
2599	trace_mm_vmscan_direct_reclaim_begin(order,
2600	sc.may_writepage,
2601	gfp_mask);
2602
2603	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2604
2605	trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2606
2607	return nr_reclaimed;
2608	}
2609
2610	#ifdef CONFIG_MEMCG
2611
2612	unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2613	gfp_t gfp_mask, bool noswap,
2614	struct zone *zone,
2615	unsigned long *nr_scanned)
2616	{
2617	struct scan_control sc = {
2618	.nr_scanned = 0,
2619	.nr_to_reclaim = SWAP_CLUSTER_MAX,
2620	.may_writepage = !laptop_mode,
2621	.may_unmap = 1,
2622	.may_swap = !noswap,
2623	.order = 0,
2624	.priority = 0,
2625	.target_mem_cgroup = memcg,
2626	};
2627	struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2628
2629	sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) \|
2630	(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2631
2632	trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2633	sc.may_writepage,
2634	sc.gfp_mask);
2635
2636	/*
2637	* NOTE: Although we can get the priority field, using it
2638	* here is not a good idea, since it limits the pages we can scan.
2639	* if we don't reclaim here, the shrink_zone from balance_pgdat
2640	* will pick up pages from other mem cgroup's as well. We hack
2641	* the priority and make it zero.
2642	*/
2643	shrink_lruvec(lruvec, &sc);
2644
2645	trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2646
2647	*nr_scanned = sc.nr_scanned;
2648	return sc.nr_reclaimed;
2649	}
2650
2651	unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
2652	gfp_t gfp_mask,
2653	bool noswap)
2654	{
2655	struct zonelist *zonelist;
2656	unsigned long nr_reclaimed;
2657	int nid;
2658	struct scan_control sc = {
2659	.may_writepage = !laptop_mode,
2660	.may_unmap = 1,
2661	.may_swap = !noswap,
2662	.nr_to_reclaim = SWAP_CLUSTER_MAX,
2663	.order = 0,
2664	.priority = DEF_PRIORITY,
2665	.target_mem_cgroup = memcg,
2666	.nodemask = NULL, /* we don't care the placement */
2667	.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) \|
2668	(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2669	};
2670	struct shrink_control shrink = {
2671	.gfp_mask = sc.gfp_mask,
2672	};
2673
2674	/*
2675	* Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2676	* take care of from where we get pages. So the node where we start the
2677	* scan does not need to be the current node.
2678	*/
2679	nid = mem_cgroup_select_victim_node(memcg);
2680
2681	zonelist = NODE_DATA(nid)->node_zonelists;
2682
2683	trace_mm_vmscan_memcg_reclaim_begin(0,
2684	sc.may_writepage,
2685	sc.gfp_mask);
2686
2687	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2688
2689	trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2690
2691	return nr_reclaimed;
2692	}
2693	#endif
2694
2695	static void age_active_anon(struct zone zone, struct scan_control sc)
2696	{
2697	struct mem_cgroup *memcg;
2698
2699	if (!total_swap_pages)
2700	return;
2701
2702	memcg = mem_cgroup_iter(NULL, NULL, NULL);
2703	do {
2704	struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2705
2706	if (inactive_anon_is_low(lruvec))
2707	shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2708	sc, LRU_ACTIVE_ANON);
2709
2710	memcg = mem_cgroup_iter(NULL, memcg, NULL);
2711	} while (memcg);
2712	}
2713
2714	static bool zone_balanced(struct zone *zone, int order,
2715	unsigned long balance_gap, int classzone_idx)
2716	{
2717	if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) +
2718	balance_gap, classzone_idx, 0))
2719	return false;
2720
2721	if (IS_ENABLED(CONFIG_COMPACTION) && order &&
2722	!compaction_suitable(zone, order))
2723	return false;
2724
2725	return true;
2726	}
2727
2728	/*
2729	* pgdat_balanced() is used when checking if a node is balanced.
2730	*
2731	* For order-0, all zones must be balanced!
2732	*
2733	* For high-order allocations only zones that meet watermarks and are in a
2734	* zone allowed by the callers classzone_idx are added to balanced_pages. The
2735	* total of balanced pages must be at least 25% of the zones allowed by
2736	* classzone_idx for the node to be considered balanced. Forcing all zones to
2737	* be balanced for high orders can cause excessive reclaim when there are
2738	* imbalanced zones.
2739	* The choice of 25% is due to
2740	* o a 16M DMA zone that is balanced will not balance a zone on any
2741	* reasonable sized machine
2742	* o On all other machines, the top zone must be at least a reasonable
2743	* percentage of the middle zones. For example, on 32-bit x86, highmem
2744	* would need to be at least 256M for it to be balance a whole node.
2745	* Similarly, on x86-64 the Normal zone would need to be at least 1G
2746	* to balance a node on its own. These seemed like reasonable ratios.
2747	*/
2748	static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
2749	{
2750	unsigned long managed_pages = 0;
2751	unsigned long balanced_pages = 0;
2752	int i;
2753
2754	/* Check the watermark levels */
2755	for (i = 0; i <= classzone_idx; i++) {
2756	struct zone *zone = pgdat->node_zones + i;
2757
2758	if (!populated_zone(zone))
2759	continue;
2760
2761	managed_pages += zone->managed_pages;
2762
2763	/*
2764	* A special case here:
2765	*
2766	* balance_pgdat() skips over all_unreclaimable after
2767	* DEF_PRIORITY. Effectively, it considers them balanced so
2768	* they must be considered balanced here as well!
2769	*/
2770	if (!zone_reclaimable(zone)) {
2771	balanced_pages += zone->managed_pages;
2772	continue;
2773	}
2774
2775	if (zone_balanced(zone, order, 0, i))
2776	balanced_pages += zone->managed_pages;
2777	else if (!order)
2778	return false;
2779	}
2780
2781	if (order)
2782	return balanced_pages >= (managed_pages >> 2);
2783	else
2784	return true;
2785	}
2786
2787	/*
2788	* Prepare kswapd for sleeping. This verifies that there are no processes
2789	* waiting in throttle_direct_reclaim() and that watermarks have been met.
2790	*
2791	* Returns true if kswapd is ready to sleep
2792	*/
2793	static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
2794	int classzone_idx)
2795	{
2796	/* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2797	if (remaining)
2798	return false;
2799
2800	/*
2801	* There is a potential race between when kswapd checks its watermarks
2802	* and a process gets throttled. There is also a potential race if
2803	* processes get throttled, kswapd wakes, a large process exits therby
2804	* balancing the zones that causes kswapd to miss a wakeup. If kswapd
2805	* is going to sleep, no process should be sleeping on pfmemalloc_wait
2806	* so wake them now if necessary. If necessary, processes will wake
2807	* kswapd and get throttled again
2808	*/
2809	if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
2810	wake_up(&pgdat->pfmemalloc_wait);
2811	return false;
2812	}
2813
2814	return pgdat_balanced(pgdat, order, classzone_idx);
2815	}
2816
2817	/*
2818	* kswapd shrinks the zone by the number of pages required to reach
2819	* the high watermark.
2820	*
2821	* Returns true if kswapd scanned at least the requested number of pages to
2822	* reclaim or if the lack of progress was due to pages under writeback.
2823	* This is used to determine if the scanning priority needs to be raised.
2824	*/
2825	static bool kswapd_shrink_zone(struct zone *zone,
2826	int classzone_idx,
2827	struct scan_control *sc,
2828	unsigned long lru_pages,
2829	unsigned long *nr_attempted)
2830	{
2831	int testorder = sc->order;
2832	unsigned long balance_gap;
2833	struct reclaim_state *reclaim_state = current->reclaim_state;
2834	struct shrink_control shrink = {
2835	.gfp_mask = sc->gfp_mask,
2836	};
2837	bool lowmem_pressure;
2838
2839	/* Reclaim above the high watermark. */
2840	sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone));
2841
2842	/*
2843	* Kswapd reclaims only single pages with compaction enabled. Trying
2844	* too hard to reclaim until contiguous free pages have become
2845	* available can hurt performance by evicting too much useful data
2846	* from memory. Do not reclaim more than needed for compaction.
2847	*/
2848	if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
2849	compaction_suitable(zone, sc->order) !=
2850	COMPACT_SKIPPED)
2851	testorder = 0;
2852
2853	/*
2854	* We put equal pressure on every zone, unless one zone has way too
2855	* many pages free already. The "too many pages" is defined as the
2856	* high wmark plus a "gap" where the gap is either the low
2857	* watermark or 1% of the zone, whichever is smaller.
2858	*/
2859	balance_gap = min(low_wmark_pages(zone),
2860	(zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2861	KSWAPD_ZONE_BALANCE_GAP_RATIO);
2862
2863	/*
2864	* If there is no low memory pressure or the zone is balanced then no
2865	* reclaim is necessary
2866	*/
2867	lowmem_pressure = (buffer_heads_over_limit && is_highmem(zone));
2868	if (!lowmem_pressure && zone_balanced(zone, testorder,
2869	balance_gap, classzone_idx))
2870	return true;
2871
2872	shrink_zone(zone, sc);
2873	nodes_clear(shrink.nodes_to_scan);
2874	node_set(zone_to_nid(zone), shrink.nodes_to_scan);
2875
2876	reclaim_state->reclaimed_slab = 0;
2877	shrink_slab(&shrink, sc->nr_scanned, lru_pages);
2878	sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2879
2880	/* Account for the number of pages attempted to reclaim */
2881	*nr_attempted += sc->nr_to_reclaim;
2882
2883	zone_clear_flag(zone, ZONE_WRITEBACK);
2884
2885	/*
2886	* If a zone reaches its high watermark, consider it to be no longer
2887	* congested. It's possible there are dirty pages backed by congested
2888	* BDIs but as pressure is relieved, speculatively avoid congestion
2889	* waits.
2890	*/
2891	if (zone_reclaimable(zone) &&
2892	zone_balanced(zone, testorder, 0, classzone_idx)) {
2893	zone_clear_flag(zone, ZONE_CONGESTED);
2894	zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY);
2895	}
2896
2897	return sc->nr_scanned >= sc->nr_to_reclaim;
2898	}
2899
2900	/*
2901	* For kswapd, balance_pgdat() will work across all this node's zones until
2902	* they are all at high_wmark_pages(zone).
2903	*
2904	* Returns the final order kswapd was reclaiming at
2905	*
2906	* There is special handling here for zones which are full of pinned pages.
2907	* This can happen if the pages are all mlocked, or if they are all used by
2908	* device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
2909	* What we do is to detect the case where all pages in the zone have been
2910	* scanned twice and there has been zero successful reclaim. Mark the zone as
2911	* dead and from now on, only perform a short scan. Basically we're polling
2912	* the zone for when the problem goes away.
2913	*
2914	* kswapd scans the zones in the highmem->normal->dma direction. It skips
2915	* zones which have free_pages > high_wmark_pages(zone), but once a zone is
2916	* found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2917	* lower zones regardless of the number of free pages in the lower zones. This
2918	* interoperates with the page allocator fallback scheme to ensure that aging
2919	* of pages is balanced across the zones.
2920	*/
2921	static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2922	int *classzone_idx)
2923	{
2924	int i;
2925	int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
2926	unsigned long nr_soft_reclaimed;
2927	unsigned long nr_soft_scanned;
2928	struct scan_control sc = {
2929	.gfp_mask = GFP_KERNEL,
2930	.priority = DEF_PRIORITY,
2931	.may_unmap = 1,
2932	.may_swap = 1,
2933	.may_writepage = !laptop_mode,
2934	.order = order,
2935	.target_mem_cgroup = NULL,
2936	};
2937	count_vm_event(PAGEOUTRUN);
2938
2939	do {
2940	unsigned long lru_pages = 0;
2941	unsigned long nr_attempted = 0;
2942	bool raise_priority = true;
2943	bool pgdat_needs_compaction = (order > 0);
2944
2945	sc.nr_reclaimed = 0;
2946
2947	/*
2948	* Scan in the highmem->dma direction for the highest
2949	* zone which needs scanning
2950	*/
2951	for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2952	struct zone *zone = pgdat->node_zones + i;
2953
2954	if (!populated_zone(zone))
2955	continue;
2956
2957	if (sc.priority != DEF_PRIORITY &&
2958	!zone_reclaimable(zone))
2959	continue;
2960
2961	/*
2962	* Do some background aging of the anon list, to give
2963	* pages a chance to be referenced before reclaiming.
2964	*/
2965	age_active_anon(zone, &sc);
2966
2967	/*
2968	* If the number of buffer_heads in the machine
2969	* exceeds the maximum allowed level and this node
2970	* has a highmem zone, force kswapd to reclaim from
2971	* it to relieve lowmem pressure.
2972	*/
2973	if (buffer_heads_over_limit && is_highmem_idx(i)) {
2974	end_zone = i;
2975	break;
2976	}
2977
2978	if (!zone_balanced(zone, order, 0, 0)) {
2979	end_zone = i;
2980	break;
2981	} else {
2982	/*
2983	* If balanced, clear the dirty and congested
2984	* flags
2985	*/
2986	zone_clear_flag(zone, ZONE_CONGESTED);
2987	zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY);
2988	}
2989	}
2990
2991	if (i < 0)
2992	goto out;
2993
2994	for (i = 0; i <= end_zone; i++) {
2995	struct zone *zone = pgdat->node_zones + i;
2996
2997	if (!populated_zone(zone))
2998	continue;
2999
3000	lru_pages += zone_reclaimable_pages(zone);
3001
3002	/*
3003	* If any zone is currently balanced then kswapd will
3004	* not call compaction as it is expected that the
3005	* necessary pages are already available.
3006	*/
3007	if (pgdat_needs_compaction &&
3008	zone_watermark_ok(zone, order,
3009	low_wmark_pages(zone),
3010	*classzone_idx, 0))
3011	pgdat_needs_compaction = false;
3012	}
3013
3014	/*
3015	* If we're getting trouble reclaiming, start doing writepage
3016	* even in laptop mode.
3017	*/
3018	if (sc.priority < DEF_PRIORITY - 2)
3019	sc.may_writepage = 1;
3020
3021	/*
3022	* Now scan the zone in the dma->highmem direction, stopping
3023	* at the last zone which needs scanning.
3024	*
3025	* We do this because the page allocator works in the opposite
3026	* direction. This prevents the page allocator from allocating
3027	* pages behind kswapd's direction of progress, which would
3028	* cause too much scanning of the lower zones.
3029	*/
3030	for (i = 0; i <= end_zone; i++) {
3031	struct zone *zone = pgdat->node_zones + i;
3032
3033	if (!populated_zone(zone))
3034	continue;
3035
3036	if (sc.priority != DEF_PRIORITY &&
3037	!zone_reclaimable(zone))
3038	continue;
3039
3040	sc.nr_scanned = 0;
3041
3042	nr_soft_scanned = 0;
3043	/*
3044	* Call soft limit reclaim before calling shrink_zone.
3045	*/
3046	nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
3047	order, sc.gfp_mask,
3048	&nr_soft_scanned);
3049	sc.nr_reclaimed += nr_soft_reclaimed;
3050
3051	/*
3052	* There should be no need to raise the scanning
3053	* priority if enough pages are already being scanned
3054	* that that high watermark would be met at 100%
3055	* efficiency.
3056	*/
3057	if (kswapd_shrink_zone(zone, end_zone, &sc,
3058	lru_pages, &nr_attempted))
3059	raise_priority = false;
3060	}
3061
3062	/*
3063	* If the low watermark is met there is no need for processes
3064	* to be throttled on pfmemalloc_wait as they should not be
3065	* able to safely make forward progress. Wake them
3066	*/
3067	if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
3068	pfmemalloc_watermark_ok(pgdat))
3069	wake_up(&pgdat->pfmemalloc_wait);
3070
3071	/*
3072	* Fragmentation may mean that the system cannot be rebalanced
3073	* for high-order allocations in all zones. If twice the
3074	* allocation size has been reclaimed and the zones are still
3075	* not balanced then recheck the watermarks at order-0 to
3076	* prevent kswapd reclaiming excessively. Assume that a
3077	* process requested a high-order can direct reclaim/compact.
3078	*/
3079	if (order && sc.nr_reclaimed >= 2UL << order)
3080	order = sc.order = 0;
3081
3082	/* Check if kswapd should be suspending */
3083	if (try_to_freeze() \|\| kthread_should_stop())
3084	break;
3085
3086	/*
3087	* Compact if necessary and kswapd is reclaiming at least the
3088	* high watermark number of pages as requsted
3089	*/
3090	if (pgdat_needs_compaction && sc.nr_reclaimed > nr_attempted)
3091	compact_pgdat(pgdat, order);
3092
3093	/*
3094	* Raise priority if scanning rate is too low or there was no
3095	* progress in reclaiming pages
3096	*/
3097	if (raise_priority \|\| !sc.nr_reclaimed)
3098	sc.priority--;
3099	} while (sc.priority >= 1 &&
3100	!pgdat_balanced(pgdat, order, *classzone_idx));
3101
3102	out:
3103	/*
3104	* Return the order we were reclaiming at so prepare_kswapd_sleep()
3105	* makes a decision on the order we were last reclaiming at. However,
3106	* if another caller entered the allocator slow path while kswapd
3107	* was awake, order will remain at the higher level
3108	*/
3109	*classzone_idx = end_zone;
3110	return order;
3111	}
3112
3113	static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
3114	{
3115	long remaining = 0;
3116	DEFINE_WAIT(wait);
3117
3118	if (freezing(current) \|\| kthread_should_stop())
3119	return;
3120
3121	prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3122
3123	/* Try to sleep for a short interval */
3124	if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
3125	remaining = schedule_timeout(HZ/10);
3126	finish_wait(&pgdat->kswapd_wait, &wait);
3127	prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
3128	}
3129
3130	/*
3131	* After a short sleep, check if it was a premature sleep. If not, then
3132	* go fully to sleep until explicitly woken up.
3133	*/
3134	if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
3135	trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
3136
3137	/*
3138	* vmstat counters are not perfectly accurate and the estimated
3139	* value for counters such as NR_FREE_PAGES can deviate from the
3140	* true value by nr_online_cpus * threshold. To avoid the zone
3141	* watermarks being breached while under pressure, we reduce the
3142	* per-cpu vmstat threshold while kswapd is awake and restore
3143	* them before going back to sleep.
3144	*/
3145	set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
3146
3147	/*
3148	* Compaction records what page blocks it recently failed to
3149	* isolate pages from and skips them in the future scanning.
3150	* When kswapd is going to sleep, it is reasonable to assume
3151	* that pages and compaction may succeed so reset the cache.
3152	*/
3153	reset_isolation_suitable(pgdat);
3154
3155	if (!kthread_should_stop())
3156	schedule();
3157
3158	set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
3159	} else {
3160	if (remaining)
3161	count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
3162	else
3163	count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
3164	}
3165	finish_wait(&pgdat->kswapd_wait, &wait);
3166	}
3167
3168	/*
3169	* The background pageout daemon, started as a kernel thread
3170	* from the init process.
3171	*
3172	* This basically trickles out pages so that we have _some_
3173	* free memory available even if there is no other activity
3174	* that frees anything up. This is needed for things like routing
3175	* etc, where we otherwise might have all activity going on in
3176	* asynchronous contexts that cannot page things out.
3177	*
3178	* If there are applications that are active memory-allocators
3179	* (most normal use), this basically shouldn't matter.
3180	*/
3181	static int kswapd(void *p)
3182	{
3183	unsigned long order, new_order;
3184	unsigned balanced_order;
3185	int classzone_idx, new_classzone_idx;
3186	int balanced_classzone_idx;
3187	pg_data_t pgdat = (pg_data_t)p;
3188	struct task_struct *tsk = current;
3189
3190	struct reclaim_state reclaim_state = {
3191	.reclaimed_slab = 0,
3192	};
3193	const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
3194
3195	lockdep_set_current_reclaim_state(GFP_KERNEL);
3196
3197	if (!cpumask_empty(cpumask))
3198	set_cpus_allowed_ptr(tsk, cpumask);
3199	current->reclaim_state = &reclaim_state;
3200
3201	/*
3202	* Tell the memory management that we're a "memory allocator",
3203	* and that if we need more memory we should get access to it
3204	* regardless (see "__alloc_pages()"). "kswapd" should
3205	* never get caught in the normal page freeing logic.
3206	*
3207	* (Kswapd normally doesn't need memory anyway, but sometimes
3208	* you need a small amount of memory in order to be able to
3209	* page out something else, and this flag essentially protects
3210	* us from recursively trying to free more memory as we're
3211	* trying to free the first piece of memory in the first place).
3212	*/
3213	tsk->flags \|= PF_MEMALLOC \| PF_SWAPWRITE \| PF_KSWAPD;
3214	set_freezable();
3215
3216	order = new_order = 0;
3217	balanced_order = 0;
3218	classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
3219	balanced_classzone_idx = classzone_idx;
3220	for ( ; ; ) {
3221	bool ret;
3222
3223	/*
3224	* If the last balance_pgdat was unsuccessful it's unlikely a
3225	* new request of a similar or harder type will succeed soon
3226	* so consider going to sleep on the basis we reclaimed at
3227	*/
3228	if (balanced_classzone_idx >= new_classzone_idx &&
3229	balanced_order == new_order) {
3230	new_order = pgdat->kswapd_max_order;
3231	new_classzone_idx = pgdat->classzone_idx;
3232	pgdat->kswapd_max_order = 0;
3233	pgdat->classzone_idx = pgdat->nr_zones - 1;
3234	}
3235
3236	if (order < new_order \|\| classzone_idx > new_classzone_idx) {
3237	/*
3238	* Don't sleep if someone wants a larger 'order'
3239	* allocation or has tigher zone constraints
3240	*/
3241	order = new_order;
3242	classzone_idx = new_classzone_idx;
3243	} else {
3244	kswapd_try_to_sleep(pgdat, balanced_order,
3245	balanced_classzone_idx);
3246	order = pgdat->kswapd_max_order;
3247	classzone_idx = pgdat->classzone_idx;
3248	new_order = order;
3249	new_classzone_idx = classzone_idx;
3250	pgdat->kswapd_max_order = 0;
3251	pgdat->classzone_idx = pgdat->nr_zones - 1;
3252	}
3253
3254	ret = try_to_freeze();
3255	if (kthread_should_stop())
3256	break;
3257
3258	/*
3259	* We can speed up thawing tasks if we don't call balance_pgdat
3260	* after returning from the refrigerator
3261	*/
3262	if (!ret) {
3263	trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
3264	balanced_classzone_idx = classzone_idx;
3265	balanced_order = balance_pgdat(pgdat, order,
3266	&balanced_classzone_idx);
3267	}
3268	}
3269
3270	current->reclaim_state = NULL;
3271	return 0;
3272	}
3273
3274	/*
3275	* A zone is low on free memory, so wake its kswapd task to service it.
3276	*/
3277	void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
3278	{
3279	pg_data_t *pgdat;
3280
3281	if (!populated_zone(zone))
3282	return;
3283
3284	if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
3285	return;
3286	pgdat = zone->zone_pgdat;
3287	if (pgdat->kswapd_max_order < order) {
3288	pgdat->kswapd_max_order = order;
3289	pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
3290	}
3291	if (!waitqueue_active(&pgdat->kswapd_wait))
3292	return;
3293	if (zone_balanced(zone, order, 0, 0))
3294	return;
3295
3296	trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3297	wake_up_interruptible(&pgdat->kswapd_wait);
3298	}
3299
3300	/*
3301	* The reclaimable count would be mostly accurate.
3302	* The less reclaimable pages may be
3303	* - mlocked pages, which will be moved to unevictable list when encountered
3304	* - mapped pages, which may require several travels to be reclaimed
3305	* - dirty pages, which is not "instantly" reclaimable
3306	*/
3307	unsigned long global_reclaimable_pages(void)
3308	{
3309	int nr;
3310
3311	nr = global_page_state(NR_ACTIVE_FILE) +
3312	global_page_state(NR_INACTIVE_FILE);
3313
3314	if (get_nr_swap_pages() > 0)
3315	nr += global_page_state(NR_ACTIVE_ANON) +
3316	global_page_state(NR_INACTIVE_ANON);
3317
3318	return nr;
3319	}
3320
3321	#ifdef CONFIG_HIBERNATION
3322	/*
3323	* Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3324	* freed pages.
3325	*
3326	* Rather than trying to age LRUs the aim is to preserve the overall
3327	* LRU order by reclaiming preferentially
3328	* inactive > active > active referenced > active mapped
3329	*/
3330	unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3331	{
3332	struct reclaim_state reclaim_state;
3333	struct scan_control sc = {
3334	.gfp_mask = GFP_HIGHUSER_MOVABLE,
3335	.may_swap = 1,
3336	.may_unmap = 1,
3337	.may_writepage = 1,
3338	.nr_to_reclaim = nr_to_reclaim,
3339	.hibernation_mode = 1,
3340	.order = 0,
3341	.priority = DEF_PRIORITY,
3342	};
3343	struct shrink_control shrink = {
3344	.gfp_mask = sc.gfp_mask,
3345	};
3346	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3347	struct task_struct *p = current;
3348	unsigned long nr_reclaimed;
3349
3350	p->flags \|= PF_MEMALLOC;
3351	lockdep_set_current_reclaim_state(sc.gfp_mask);
3352	reclaim_state.reclaimed_slab = 0;
3353	p->reclaim_state = &reclaim_state;
3354
3355	nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
3356
3357	p->reclaim_state = NULL;
3358	lockdep_clear_current_reclaim_state();
3359	p->flags &= ~PF_MEMALLOC;
3360
3361	return nr_reclaimed;
3362	}
3363	#endif /* CONFIG_HIBERNATION */
3364
3365	/* It's optimal to keep kswapds on the same CPUs as their memory, but
3366	not required for correctness. So if the last cpu in a node goes
3367	away, we get changed to run anywhere: as the first one comes back,
3368	restore their cpu bindings. */
3369	static int cpu_callback(struct notifier_block *nfb, unsigned long action,
3370	void *hcpu)
3371	{
3372	int nid;
3373
3374	if (action == CPU_ONLINE \|\| action == CPU_ONLINE_FROZEN) {
3375	for_each_node_state(nid, N_MEMORY) {
3376	pg_data_t *pgdat = NODE_DATA(nid);
3377	const struct cpumask *mask;
3378
3379	mask = cpumask_of_node(pgdat->node_id);
3380
3381	if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3382	/* One of our CPUs online: restore mask */
3383	set_cpus_allowed_ptr(pgdat->kswapd, mask);
3384	}
3385	}
3386	return NOTIFY_OK;
3387	}
3388
3389	/*
3390	* This kswapd start function will be called by init and node-hot-add.
3391	* On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3392	*/
3393	int kswapd_run(int nid)
3394	{
3395	pg_data_t *pgdat = NODE_DATA(nid);
3396	int ret = 0;
3397
3398	if (pgdat->kswapd)
3399	return 0;
3400
3401	pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3402	if (IS_ERR(pgdat->kswapd)) {
3403	/* failure at boot is fatal */
3404	BUG_ON(system_state == SYSTEM_BOOTING);
3405	pr_err("Failed to start kswapd on node %d\n", nid);
3406	ret = PTR_ERR(pgdat->kswapd);
3407	pgdat->kswapd = NULL;
3408	}
3409	return ret;
3410	}
3411
3412	/*
3413	* Called by memory hotplug when all memory in a node is offlined. Caller must
3414	* hold lock_memory_hotplug().
3415	*/
3416	void kswapd_stop(int nid)
3417	{
3418	struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3419
3420	if (kswapd) {
3421	kthread_stop(kswapd);
3422	NODE_DATA(nid)->kswapd = NULL;
3423	}
3424	}
3425
3426	static int __init kswapd_init(void)
3427	{
3428	int nid;
3429
3430	swap_setup();
3431	for_each_node_state(nid, N_MEMORY)
3432	kswapd_run(nid);
3433	hotcpu_notifier(cpu_callback, 0);
3434	return 0;
3435	}
3436
3437	module_init(kswapd_init)
3438
3439	#ifdef CONFIG_NUMA
3440	/*
3441	* Zone reclaim mode
3442	*
3443	* If non-zero call zone_reclaim when the number of free pages falls below
3444	* the watermarks.
3445	*/
3446	int zone_reclaim_mode __read_mostly;
3447
3448	#define RECLAIM_OFF 0
3449	#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */
3450	#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */
3451	#define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */
3452
3453	/*
3454	* Priority for ZONE_RECLAIM. This determines the fraction of pages
3455	* of a node considered for each zone_reclaim. 4 scans 1/16th of
3456	* a zone.
3457	*/
3458	#define ZONE_RECLAIM_PRIORITY 4
3459
3460	/*
3461	* Percentage of pages in a zone that must be unmapped for zone_reclaim to
3462	* occur.
3463	*/
3464	int sysctl_min_unmapped_ratio = 1;
3465
3466	/*
3467	* If the number of slab pages in a zone grows beyond this percentage then
3468	* slab reclaim needs to occur.
3469	*/
3470	int sysctl_min_slab_ratio = 5;
3471
3472	static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3473	{
3474	unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3475	unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3476	zone_page_state(zone, NR_ACTIVE_FILE);
3477
3478	/*
3479	* It's possible for there to be more file mapped pages than
3480	* accounted for by the pages on the file LRU lists because
3481	* tmpfs pages accounted for as ANON can also be FILE_MAPPED
3482	*/
3483	return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3484	}
3485
3486	/* Work out how many page cache pages we can reclaim in this reclaim_mode */
3487	static long zone_pagecache_reclaimable(struct zone *zone)
3488	{
3489	long nr_pagecache_reclaimable;
3490	long delta = 0;
3491
3492	/*
3493	* If RECLAIM_SWAP is set, then all file pages are considered
3494	* potentially reclaimable. Otherwise, we have to worry about
3495	* pages like swapcache and zone_unmapped_file_pages() provides
3496	* a better estimate
3497	*/
3498	if (zone_reclaim_mode & RECLAIM_SWAP)
3499	nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3500	else
3501	nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3502
3503	/* If we can't clean pages, remove dirty pages from consideration */
3504	if (!(zone_reclaim_mode & RECLAIM_WRITE))
3505	delta += zone_page_state(zone, NR_FILE_DIRTY);
3506
3507	/* Watch for any possible underflows due to delta */
3508	if (unlikely(delta > nr_pagecache_reclaimable))
3509	delta = nr_pagecache_reclaimable;
3510
3511	return nr_pagecache_reclaimable - delta;
3512	}
3513
3514	/*
3515	* Try to free up some pages from this zone through reclaim.
3516	*/
3517	static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3518	{
3519	/* Minimum pages needed in order to stay on node */
3520	const unsigned long nr_pages = 1 << order;
3521	struct task_struct *p = current;
3522	struct reclaim_state reclaim_state;
3523	struct scan_control sc = {
3524	.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3525	.may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3526	.may_swap = 1,
3527	.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3528	.gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
3529	.order = order,
3530	.priority = ZONE_RECLAIM_PRIORITY,
3531	};
3532	struct shrink_control shrink = {
3533	.gfp_mask = sc.gfp_mask,
3534	};
3535	unsigned long nr_slab_pages0, nr_slab_pages1;
3536
3537	cond_resched();
3538	/*
3539	* We need to be able to allocate from the reserves for RECLAIM_SWAP
3540	* and we also need to be able to write out pages for RECLAIM_WRITE
3541	* and RECLAIM_SWAP.
3542	*/
3543	p->flags \|= PF_MEMALLOC \| PF_SWAPWRITE;
3544	lockdep_set_current_reclaim_state(gfp_mask);
3545	reclaim_state.reclaimed_slab = 0;
3546	p->reclaim_state = &reclaim_state;
3547
3548	if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3549	/*
3550	* Free memory by calling shrink zone with increasing
3551	* priorities until we have enough memory freed.
3552	*/
3553	do {
3554	shrink_zone(zone, &sc);
3555	} while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3556	}
3557
3558	nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3559	if (nr_slab_pages0 > zone->min_slab_pages) {
3560	/*
3561	* shrink_slab() does not currently allow us to determine how
3562	* many pages were freed in this zone. So we take the current
3563	* number of slab pages and shake the slab until it is reduced
3564	* by the same nr_pages that we used for reclaiming unmapped
3565	* pages.
3566	*/
3567	nodes_clear(shrink.nodes_to_scan);
3568	node_set(zone_to_nid(zone), shrink.nodes_to_scan);
3569	for (;;) {
3570	unsigned long lru_pages = zone_reclaimable_pages(zone);
3571
3572	/* No reclaimable slab or very low memory pressure */
3573	if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3574	break;
3575
3576	/* Freed enough memory */
3577	nr_slab_pages1 = zone_page_state(zone,
3578	NR_SLAB_RECLAIMABLE);
3579	if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3580	break;
3581	}
3582
3583	/*
3584	* Update nr_reclaimed by the number of slab pages we
3585	* reclaimed from this zone.
3586	*/
3587	nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3588	if (nr_slab_pages1 < nr_slab_pages0)
3589	sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3590	}
3591
3592	p->reclaim_state = NULL;
3593	current->flags &= ~(PF_MEMALLOC \| PF_SWAPWRITE);
3594	lockdep_clear_current_reclaim_state();
3595	return sc.nr_reclaimed >= nr_pages;
3596	}
3597
3598	int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3599	{
3600	int node_id;
3601	int ret;
3602
3603	/*
3604	* Zone reclaim reclaims unmapped file backed pages and
3605	* slab pages if we are over the defined limits.
3606	*
3607	* A small portion of unmapped file backed pages is needed for
3608	* file I/O otherwise pages read by file I/O will be immediately
3609	* thrown out if the zone is overallocated. So we do not reclaim
3610	* if less than a specified percentage of the zone is used by
3611	* unmapped file backed pages.
3612	*/
3613	if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3614	zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3615	return ZONE_RECLAIM_FULL;
3616
3617	if (!zone_reclaimable(zone))
3618	return ZONE_RECLAIM_FULL;
3619
3620	/*
3621	* Do not scan if the allocation should not be delayed.
3622	*/
3623	if (!(gfp_mask & __GFP_WAIT) \|\| (current->flags & PF_MEMALLOC))
3624	return ZONE_RECLAIM_NOSCAN;
3625
3626	/*
3627	* Only run zone reclaim on the local zone or on zones that do not
3628	* have associated processors. This will favor the local processor
3629	* over remote processors and spread off node memory allocations
3630	* as wide as possible.
3631	*/
3632	node_id = zone_to_nid(zone);
3633	if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3634	return ZONE_RECLAIM_NOSCAN;
3635
3636	if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3637	return ZONE_RECLAIM_NOSCAN;
3638
3639	ret = __zone_reclaim(zone, gfp_mask, order);
3640	zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3641
3642	if (!ret)
3643	count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3644
3645	return ret;
3646	}
3647	#endif
3648
3649	/*
3650	* page_evictable - test whether a page is evictable
3651	* @page: the page to test
3652	*
3653	* Test whether page is evictable--i.e., should be placed on active/inactive
3654	* lists vs unevictable list.
3655	*
3656	* Reasons page might not be evictable:
3657	* (1) page's mapping marked unevictable
3658	* (2) page is part of an mlocked VMA
3659	*
3660	*/
3661	int page_evictable(struct page *page)
3662	{
3663	return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
3664	}
3665
3666	#ifdef CONFIG_SHMEM
3667	/**
3668	* check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3669	* @pages: array of pages to check
3670	* @nr_pages: number of pages to check
3671	*
3672	* Checks pages for evictability and moves them to the appropriate lru list.
3673	*
3674	* This function is only used for SysV IPC SHM_UNLOCK.
3675	*/
3676	void check_move_unevictable_pages(struct page **pages, int nr_pages)
3677	{
3678	struct lruvec *lruvec;
3679	struct zone *zone = NULL;
3680	int pgscanned = 0;
3681	int pgrescued = 0;
3682	int i;
3683
3684	for (i = 0; i < nr_pages; i++) {
3685	struct page *page = pages[i];
3686	struct zone *pagezone;
3687
3688	pgscanned++;
3689	pagezone = page_zone(page);
3690	if (pagezone != zone) {
3691	if (zone)
3692	spin_unlock_irq(&zone->lru_lock);
3693	zone = pagezone;
3694	spin_lock_irq(&zone->lru_lock);
3695	}
3696	lruvec = mem_cgroup_page_lruvec(page, zone);
3697
3698	if (!PageLRU(page) \|\| !PageUnevictable(page))
3699	continue;
3700
3701	if (page_evictable(page)) {
3702	enum lru_list lru = page_lru_base_type(page);
3703
3704	VM_BUG_ON(PageActive(page));
3705	ClearPageUnevictable(page);
3706	del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3707	add_page_to_lru_list(page, lruvec, lru);
3708	pgrescued++;
3709	}
3710	}
3711
3712	if (zone) {
3713	__count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3714	__count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3715	spin_unlock_irq(&zone->lru_lock);
3716	}
3717	}
3718	#endif /* CONFIG_SHMEM */
3719
3720	static void warn_scan_unevictable_pages(void)
3721	{
3722	printk_once(KERN_WARNING
3723	"%s: The scan_unevictable_pages sysctl/node-interface has been "
3724	"disabled for lack of a legitimate use case. If you have "
3725	"one, please send an email to linux-mm@kvack.org.\n",
3726	current->comm);
3727	}
3728
3729	/*
3730	* scan_unevictable_pages [vm] sysctl handler. On demand re-scan of
3731	* all nodes' unevictable lists for evictable pages
3732	*/
3733	unsigned long scan_unevictable_pages;
3734
3735	int scan_unevictable_handler(struct ctl_table *table, int write,
3736	void __user *buffer,
3737	size_t length, loff_t ppos)
3738	{
3739	warn_scan_unevictable_pages();
3740	proc_doulongvec_minmax(table, write, buffer, length, ppos);
3741	scan_unevictable_pages = 0;
3742	return 0;
3743	}
3744
3745	#ifdef CONFIG_NUMA
3746	/*
3747	* per node 'scan_unevictable_pages' attribute. On demand re-scan of
3748	* a specified node's per zone unevictable lists for evictable pages.
3749	*/
3750
3751	static ssize_t read_scan_unevictable_node(struct device *dev,
3752	struct device_attribute *attr,
3753	char *buf)
3754	{
3755	warn_scan_unevictable_pages();
3756	return sprintf(buf, "0\n"); /* always zero; should fit... */
3757	}
3758
3759	static ssize_t write_scan_unevictable_node(struct device *dev,
3760	struct device_attribute *attr,
3761	const char *buf, size_t count)
3762	{
3763	warn_scan_unevictable_pages();
3764	return 1;
3765	}
3766
3767
3768	static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO \| S_IWUSR,
3769	read_scan_unevictable_node,
3770	write_scan_unevictable_node);
3771
3772	int scan_unevictable_register_node(struct node *node)
3773	{
3774	return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages);
3775	}
3776
3777	void scan_unevictable_unregister_node(struct node *node)
3778	{
3779	device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages);
3780	}
3781	#endif
3782

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