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1/*
2 * linux/mm/vmscan.c
3 *
4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
5 *
6 * Swap reorganised 29.12.95, Stephen Tweedie.
7 * kswapd added: 7.1.96 sct
8 * Removed kswapd_ctl limits, and swap out as many pages as needed
9 * to bring the system back to freepages.high: 2.4.97, Rik van Riel.
10 * Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
11 * Multiqueue VM started 5.8.00, Rik van Riel.
12 */
13
14#include <linux/mm.h>
15#include <linux/module.h>
16#include <linux/slab.h>
17#include <linux/kernel_stat.h>
18#include <linux/swap.h>
19#include <linux/pagemap.h>
20#include <linux/init.h>
21#include <linux/highmem.h>
22#include <linux/file.h>
23#include <linux/writeback.h>
24#include <linux/blkdev.h>
25#include <linux/buffer_head.h> /* for try_to_release_page(),
26 buffer_heads_over_limit */
27#include <linux/mm_inline.h>
28#include <linux/pagevec.h>
29#include <linux/backing-dev.h>
30#include <linux/rmap.h>
31#include <linux/topology.h>
32#include <linux/cpu.h>
33#include <linux/cpuset.h>
34#include <linux/notifier.h>
35#include <linux/rwsem.h>
36
37#include <asm/tlbflush.h>
38#include <asm/div64.h>
39
40#include <linux/swapops.h>
41
42/* possible outcome of pageout() */
43typedef enum {
44 /* failed to write page out, page is locked */
45 PAGE_KEEP,
46 /* move page to the active list, page is locked */
47 PAGE_ACTIVATE,
48 /* page has been sent to the disk successfully, page is unlocked */
49 PAGE_SUCCESS,
50 /* page is clean and locked */
51 PAGE_CLEAN,
52} pageout_t;
53
54struct scan_control {
55 /* Ask refill_inactive_zone, or shrink_cache to scan this many pages */
56 unsigned long nr_to_scan;
57
58 /* Incremented by the number of inactive pages that were scanned */
59 unsigned long nr_scanned;
60
61 /* Incremented by the number of pages reclaimed */
62 unsigned long nr_reclaimed;
63
64 unsigned long nr_mapped; /* From page_state */
65
66 /* How many pages shrink_cache() should reclaim */
67 int nr_to_reclaim;
68
69 /* Ask shrink_caches, or shrink_zone to scan at this priority */
70 unsigned int priority;
71
72 /* This context's GFP mask */
73 unsigned int gfp_mask;
74
75 int may_writepage;
76
77 /* This context's SWAP_CLUSTER_MAX. If freeing memory for
78 * suspend, we effectively ignore SWAP_CLUSTER_MAX.
79 * In this context, it doesn't matter that we scan the
80 * whole list at once. */
81 int swap_cluster_max;
82};
83
84/*
85 * The list of shrinker callbacks used by to apply pressure to
86 * ageable caches.
87 */
88struct shrinker {
89 shrinker_t shrinker;
90 struct list_head list;
91 int seeks; /* seeks to recreate an obj */
92 long nr; /* objs pending delete */
93};
94
95#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
96
97#ifdef ARCH_HAS_PREFETCH
98#define prefetch_prev_lru_page(_page, _base, _field) \
99 do { \
100 if ((_page)->lru.prev != _base) { \
101 struct page *prev; \
102 \
103 prev = lru_to_page(&(_page->lru)); \
104 prefetch(&prev->_field); \
105 } \
106 } while (0)
107#else
108#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
109#endif
110
111#ifdef ARCH_HAS_PREFETCHW
112#define prefetchw_prev_lru_page(_page, _base, _field) \
113 do { \
114 if ((_page)->lru.prev != _base) { \
115 struct page *prev; \
116 \
117 prev = lru_to_page(&(_page->lru)); \
118 prefetchw(&prev->_field); \
119 } \
120 } while (0)
121#else
122#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
123#endif
124
125/*
126 * From 0 .. 100. Higher means more swappy.
127 */
128int vm_swappiness = 60;
129static long total_memory;
130
131static LIST_HEAD(shrinker_list);
132static DECLARE_RWSEM(shrinker_rwsem);
133
134/*
135 * Add a shrinker callback to be called from the vm
136 */
137struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
138{
139 struct shrinker *shrinker;
140
141 shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
142 if (shrinker) {
143 shrinker->shrinker = theshrinker;
144 shrinker->seeks = seeks;
145 shrinker->nr = 0;
146 down_write(&shrinker_rwsem);
147 list_add_tail(&shrinker->list, &shrinker_list);
148 up_write(&shrinker_rwsem);
149 }
150 return shrinker;
151}
152EXPORT_SYMBOL(set_shrinker);
153
154/*
155 * Remove one
156 */
157void remove_shrinker(struct shrinker *shrinker)
158{
159 down_write(&shrinker_rwsem);
160 list_del(&shrinker->list);
161 up_write(&shrinker_rwsem);
162 kfree(shrinker);
163}
164EXPORT_SYMBOL(remove_shrinker);
165
166#define SHRINK_BATCH 128
167/*
168 * Call the shrink functions to age shrinkable caches
169 *
170 * Here we assume it costs one seek to replace a lru page and that it also
171 * takes a seek to recreate a cache object. With this in mind we age equal
172 * percentages of the lru and ageable caches. This should balance the seeks
173 * generated by these structures.
174 *
175 * If the vm encounted mapped pages on the LRU it increase the pressure on
176 * slab to avoid swapping.
177 *
178 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
179 *
180 * `lru_pages' represents the number of on-LRU pages in all the zones which
181 * are eligible for the caller's allocation attempt. It is used for balancing
182 * slab reclaim versus page reclaim.
183 */
184static int shrink_slab(unsigned long scanned, unsigned int gfp_mask,
185 unsigned long lru_pages)
186{
187 struct shrinker *shrinker;
188
189 if (scanned == 0)
190 scanned = SWAP_CLUSTER_MAX;
191
192 if (!down_read_trylock(&shrinker_rwsem))
193 return 0;
194
195 list_for_each_entry(shrinker, &shrinker_list, list) {
196 unsigned long long delta;
197 unsigned long total_scan;
198
199 delta = (4 * scanned) / shrinker->seeks;
200 delta *= (*shrinker->shrinker)(0, gfp_mask);
201 do_div(delta, lru_pages + 1);
202 shrinker->nr += delta;
203 if (shrinker->nr < 0)
204 shrinker->nr = LONG_MAX; /* It wrapped! */
205
206 total_scan = shrinker->nr;
207 shrinker->nr = 0;
208
209 while (total_scan >= SHRINK_BATCH) {
210 long this_scan = SHRINK_BATCH;
211 int shrink_ret;
212
213 shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
214 if (shrink_ret == -1)
215 break;
216 mod_page_state(slabs_scanned, this_scan);
217 total_scan -= this_scan;
218
219 cond_resched();
220 }
221
222 shrinker->nr += total_scan;
223 }
224 up_read(&shrinker_rwsem);
225 return 0;
226}
227
228/* Called without lock on whether page is mapped, so answer is unstable */
229static inline int page_mapping_inuse(struct page *page)
230{
231 struct address_space *mapping;
232
233 /* Page is in somebody's page tables. */
234 if (page_mapped(page))
235 return 1;
236
237 /* Be more reluctant to reclaim swapcache than pagecache */
238 if (PageSwapCache(page))
239 return 1;
240
241 mapping = page_mapping(page);
242 if (!mapping)
243 return 0;
244
245 /* File is mmap'd by somebody? */
246 return mapping_mapped(mapping);
247}
248
249static inline int is_page_cache_freeable(struct page *page)
250{
251 return page_count(page) - !!PagePrivate(page) == 2;
252}
253
254static int may_write_to_queue(struct backing_dev_info *bdi)
255{
256 if (current_is_kswapd())
257 return 1;
258 if (current_is_pdflush()) /* This is unlikely, but why not... */
259 return 1;
260 if (!bdi_write_congested(bdi))
261 return 1;
262 if (bdi == current->backing_dev_info)
263 return 1;
264 return 0;
265}
266
267/*
268 * We detected a synchronous write error writing a page out. Probably
269 * -ENOSPC. We need to propagate that into the address_space for a subsequent
270 * fsync(), msync() or close().
271 *
272 * The tricky part is that after writepage we cannot touch the mapping: nothing
273 * prevents it from being freed up. But we have a ref on the page and once
274 * that page is locked, the mapping is pinned.
275 *
276 * We're allowed to run sleeping lock_page() here because we know the caller has
277 * __GFP_FS.
278 */
279static void handle_write_error(struct address_space *mapping,
280 struct page *page, int error)
281{
282 lock_page(page);
283 if (page_mapping(page) == mapping) {
284 if (error == -ENOSPC)
285 set_bit(AS_ENOSPC, &mapping->flags);
286 else
287 set_bit(AS_EIO, &mapping->flags);
288 }
289 unlock_page(page);
290}
291
292/*
293 * pageout is called by shrink_list() for each dirty page. Calls ->writepage().
294 */
295static pageout_t pageout(struct page *page, struct address_space *mapping)
296{
297 /*
298 * If the page is dirty, only perform writeback if that write
299 * will be non-blocking. To prevent this allocation from being
300 * stalled by pagecache activity. But note that there may be
301 * stalls if we need to run get_block(). We could test
302 * PagePrivate for that.
303 *
304 * If this process is currently in generic_file_write() against
305 * this page's queue, we can perform writeback even if that
306 * will block.
307 *
308 * If the page is swapcache, write it back even if that would
309 * block, for some throttling. This happens by accident, because
310 * swap_backing_dev_info is bust: it doesn't reflect the
311 * congestion state of the swapdevs. Easy to fix, if needed.
312 * See swapfile.c:page_queue_congested().
313 */
314 if (!is_page_cache_freeable(page))
315 return PAGE_KEEP;
316 if (!mapping) {
317 /*
318 * Some data journaling orphaned pages can have
319 * page->mapping == NULL while being dirty with clean buffers.
320 */
321 if (PageDirty(page) && PagePrivate(page)) {
322 if (try_to_free_buffers(page)) {
323 ClearPageDirty(page);
324 printk("%s: orphaned page\n", __FUNCTION__);
325 return PAGE_CLEAN;
326 }
327 }
328 return PAGE_KEEP;
329 }
330 if (mapping->a_ops->writepage == NULL)
331 return PAGE_ACTIVATE;
332 if (!may_write_to_queue(mapping->backing_dev_info))
333 return PAGE_KEEP;
334
335 if (clear_page_dirty_for_io(page)) {
336 int res;
337 struct writeback_control wbc = {
338 .sync_mode = WB_SYNC_NONE,
339 .nr_to_write = SWAP_CLUSTER_MAX,
340 .nonblocking = 1,
341 .for_reclaim = 1,
342 };
343
344 SetPageReclaim(page);
345 res = mapping->a_ops->writepage(page, &wbc);
346 if (res < 0)
347 handle_write_error(mapping, page, res);
348 if (res == WRITEPAGE_ACTIVATE) {
349 ClearPageReclaim(page);
350 return PAGE_ACTIVATE;
351 }
352 if (!PageWriteback(page)) {
353 /* synchronous write or broken a_ops? */
354 ClearPageReclaim(page);
355 }
356
357 return PAGE_SUCCESS;
358 }
359
360 return PAGE_CLEAN;
361}
362
363/*
364 * shrink_list adds the number of reclaimed pages to sc->nr_reclaimed
365 */
366static int shrink_list(struct list_head *page_list, struct scan_control *sc)
367{
368 LIST_HEAD(ret_pages);
369 struct pagevec freed_pvec;
370 int pgactivate = 0;
371 int reclaimed = 0;
372
373 cond_resched();
374
375 pagevec_init(&freed_pvec, 1);
376 while (!list_empty(page_list)) {
377 struct address_space *mapping;
378 struct page *page;
379 int may_enter_fs;
380 int referenced;
381
382 cond_resched();
383
384 page = lru_to_page(page_list);
385 list_del(&page->lru);
386
387 if (TestSetPageLocked(page))
388 goto keep;
389
390 BUG_ON(PageActive(page));
391
392 sc->nr_scanned++;
393 /* Double the slab pressure for mapped and swapcache pages */
394 if (page_mapped(page) || PageSwapCache(page))
395 sc->nr_scanned++;
396
397 if (PageWriteback(page))
398 goto keep_locked;
399
400 referenced = page_referenced(page, 1, sc->priority <= 0);
401 /* In active use or really unfreeable? Activate it. */
402 if (referenced && page_mapping_inuse(page))
403 goto activate_locked;
404
405#ifdef CONFIG_SWAP
406 /*
407 * Anonymous process memory has backing store?
408 * Try to allocate it some swap space here.
409 */
410 if (PageAnon(page) && !PageSwapCache(page)) {
411 if (!add_to_swap(page))
412 goto activate_locked;
413 }
414#endif /* CONFIG_SWAP */
415
416 mapping = page_mapping(page);
417 may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
418 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
419
420 /*
421 * The page is mapped into the page tables of one or more
422 * processes. Try to unmap it here.
423 */
424 if (page_mapped(page) && mapping) {
425 switch (try_to_unmap(page)) {
426 case SWAP_FAIL:
427 goto activate_locked;
428 case SWAP_AGAIN:
429 goto keep_locked;
430 case SWAP_SUCCESS:
431 ; /* try to free the page below */
432 }
433 }
434
435 if (PageDirty(page)) {
436 if (referenced)
437 goto keep_locked;
438 if (!may_enter_fs)
439 goto keep_locked;
440 if (laptop_mode && !sc->may_writepage)
441 goto keep_locked;
442
443 /* Page is dirty, try to write it out here */
444 switch(pageout(page, mapping)) {
445 case PAGE_KEEP:
446 goto keep_locked;
447 case PAGE_ACTIVATE:
448 goto activate_locked;
449 case PAGE_SUCCESS:
450 if (PageWriteback(page) || PageDirty(page))
451 goto keep;
452 /*
453 * A synchronous write - probably a ramdisk. Go
454 * ahead and try to reclaim the page.
455 */
456 if (TestSetPageLocked(page))
457 goto keep;
458 if (PageDirty(page) || PageWriteback(page))
459 goto keep_locked;
460 mapping = page_mapping(page);
461 case PAGE_CLEAN:
462 ; /* try to free the page below */
463 }
464 }
465
466 /*
467 * If the page has buffers, try to free the buffer mappings
468 * associated with this page. If we succeed we try to free
469 * the page as well.
470 *
471 * We do this even if the page is PageDirty().
472 * try_to_release_page() does not perform I/O, but it is
473 * possible for a page to have PageDirty set, but it is actually
474 * clean (all its buffers are clean). This happens if the
475 * buffers were written out directly, with submit_bh(). ext3
476 * will do this, as well as the blockdev mapping.
477 * try_to_release_page() will discover that cleanness and will
478 * drop the buffers and mark the page clean - it can be freed.
479 *
480 * Rarely, pages can have buffers and no ->mapping. These are
481 * the pages which were not successfully invalidated in
482 * truncate_complete_page(). We try to drop those buffers here
483 * and if that worked, and the page is no longer mapped into
484 * process address space (page_count == 1) it can be freed.
485 * Otherwise, leave the page on the LRU so it is swappable.
486 */
487 if (PagePrivate(page)) {
488 if (!try_to_release_page(page, sc->gfp_mask))
489 goto activate_locked;
490 if (!mapping && page_count(page) == 1)
491 goto free_it;
492 }
493
494 if (!mapping)
495 goto keep_locked; /* truncate got there first */
496
497 write_lock_irq(&mapping->tree_lock);
498
499 /*
500 * The non-racy check for busy page. It is critical to check
501 * PageDirty _after_ making sure that the page is freeable and
502 * not in use by anybody. (pagecache + us == 2)
503 */
504 if (page_count(page) != 2 || PageDirty(page)) {
505 write_unlock_irq(&mapping->tree_lock);
506 goto keep_locked;
507 }
508
509#ifdef CONFIG_SWAP
510 if (PageSwapCache(page)) {
511 swp_entry_t swap = { .val = page->private };
512 __delete_from_swap_cache(page);
513 write_unlock_irq(&mapping->tree_lock);
514 swap_free(swap);
515 __put_page(page); /* The pagecache ref */
516 goto free_it;
517 }
518#endif /* CONFIG_SWAP */
519
520 __remove_from_page_cache(page);
521 write_unlock_irq(&mapping->tree_lock);
522 __put_page(page);
523
524free_it:
525 unlock_page(page);
526 reclaimed++;
527 if (!pagevec_add(&freed_pvec, page))
528 __pagevec_release_nonlru(&freed_pvec);
529 continue;
530
531activate_locked:
532 SetPageActive(page);
533 pgactivate++;
534keep_locked:
535 unlock_page(page);
536keep:
537 list_add(&page->lru, &ret_pages);
538 BUG_ON(PageLRU(page));
539 }
540 list_splice(&ret_pages, page_list);
541 if (pagevec_count(&freed_pvec))
542 __pagevec_release_nonlru(&freed_pvec);
543 mod_page_state(pgactivate, pgactivate);
544 sc->nr_reclaimed += reclaimed;
545 return reclaimed;
546}
547
548/*
549 * zone->lru_lock is heavily contended. Some of the functions that
550 * shrink the lists perform better by taking out a batch of pages
551 * and working on them outside the LRU lock.
552 *
553 * For pagecache intensive workloads, this function is the hottest
554 * spot in the kernel (apart from copy_*_user functions).
555 *
556 * Appropriate locks must be held before calling this function.
557 *
558 * @nr_to_scan: The number of pages to look through on the list.
559 * @src: The LRU list to pull pages off.
560 * @dst: The temp list to put pages on to.
561 * @scanned: The number of pages that were scanned.
562 *
563 * returns how many pages were moved onto *@dst.
564 */
565static int isolate_lru_pages(int nr_to_scan, struct list_head *src,
566 struct list_head *dst, int *scanned)
567{
568 int nr_taken = 0;
569 struct page *page;
570 int scan = 0;
571
572 while (scan++ < nr_to_scan && !list_empty(src)) {
573 page = lru_to_page(src);
574 prefetchw_prev_lru_page(page, src, flags);
575
576 if (!TestClearPageLRU(page))
577 BUG();
578 list_del(&page->lru);
579 if (get_page_testone(page)) {
580 /*
581 * It is being freed elsewhere
582 */
583 __put_page(page);
584 SetPageLRU(page);
585 list_add(&page->lru, src);
586 continue;
587 } else {
588 list_add(&page->lru, dst);
589 nr_taken++;
590 }
591 }
592
593 *scanned = scan;
594 return nr_taken;
595}
596
597/*
598 * shrink_cache() adds the number of pages reclaimed to sc->nr_reclaimed
599 */
600static void shrink_cache(struct zone *zone, struct scan_control *sc)
601{
602 LIST_HEAD(page_list);
603 struct pagevec pvec;
604 int max_scan = sc->nr_to_scan;
605
606 pagevec_init(&pvec, 1);
607
608 lru_add_drain();
609 spin_lock_irq(&zone->lru_lock);
610 while (max_scan > 0) {
611 struct page *page;
612 int nr_taken;
613 int nr_scan;
614 int nr_freed;
615
616 nr_taken = isolate_lru_pages(sc->swap_cluster_max,
617 &zone->inactive_list,
618 &page_list, &nr_scan);
619 zone->nr_inactive -= nr_taken;
620 zone->pages_scanned += nr_scan;
621 spin_unlock_irq(&zone->lru_lock);
622
623 if (nr_taken == 0)
624 goto done;
625
626 max_scan -= nr_scan;
627 if (current_is_kswapd())
628 mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
629 else
630 mod_page_state_zone(zone, pgscan_direct, nr_scan);
631 nr_freed = shrink_list(&page_list, sc);
632 if (current_is_kswapd())
633 mod_page_state(kswapd_steal, nr_freed);
634 mod_page_state_zone(zone, pgsteal, nr_freed);
635 sc->nr_to_reclaim -= nr_freed;
636
637 spin_lock_irq(&zone->lru_lock);
638 /*
639 * Put back any unfreeable pages.
640 */
641 while (!list_empty(&page_list)) {
642 page = lru_to_page(&page_list);
643 if (TestSetPageLRU(page))
644 BUG();
645 list_del(&page->lru);
646 if (PageActive(page))
647 add_page_to_active_list(zone, page);
648 else
649 add_page_to_inactive_list(zone, page);
650 if (!pagevec_add(&pvec, page)) {
651 spin_unlock_irq(&zone->lru_lock);
652 __pagevec_release(&pvec);
653 spin_lock_irq(&zone->lru_lock);
654 }
655 }
656 }
657 spin_unlock_irq(&zone->lru_lock);
658done:
659 pagevec_release(&pvec);
660}
661
662/*
663 * This moves pages from the active list to the inactive list.
664 *
665 * We move them the other way if the page is referenced by one or more
666 * processes, from rmap.
667 *
668 * If the pages are mostly unmapped, the processing is fast and it is
669 * appropriate to hold zone->lru_lock across the whole operation. But if
670 * the pages are mapped, the processing is slow (page_referenced()) so we
671 * should drop zone->lru_lock around each page. It's impossible to balance
672 * this, so instead we remove the pages from the LRU while processing them.
673 * It is safe to rely on PG_active against the non-LRU pages in here because
674 * nobody will play with that bit on a non-LRU page.
675 *
676 * The downside is that we have to touch page->_count against each page.
677 * But we had to alter page->flags anyway.
678 */
679static void
680refill_inactive_zone(struct zone *zone, struct scan_control *sc)
681{
682 int pgmoved;
683 int pgdeactivate = 0;
684 int pgscanned;
685 int nr_pages = sc->nr_to_scan;
686 LIST_HEAD(l_hold); /* The pages which were snipped off */
687 LIST_HEAD(l_inactive); /* Pages to go onto the inactive_list */
688 LIST_HEAD(l_active); /* Pages to go onto the active_list */
689 struct page *page;
690 struct pagevec pvec;
691 int reclaim_mapped = 0;
692 long mapped_ratio;
693 long distress;
694 long swap_tendency;
695
696 lru_add_drain();
697 spin_lock_irq(&zone->lru_lock);
698 pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
699 &l_hold, &pgscanned);
700 zone->pages_scanned += pgscanned;
701 zone->nr_active -= pgmoved;
702 spin_unlock_irq(&zone->lru_lock);
703
704 /*
705 * `distress' is a measure of how much trouble we're having reclaiming
706 * pages. 0 -> no problems. 100 -> great trouble.
707 */
708 distress = 100 >> zone->prev_priority;
709
710 /*
711 * The point of this algorithm is to decide when to start reclaiming
712 * mapped memory instead of just pagecache. Work out how much memory
713 * is mapped.
714 */
715 mapped_ratio = (sc->nr_mapped * 100) / total_memory;
716
717 /*
718 * Now decide how much we really want to unmap some pages. The mapped
719 * ratio is downgraded - just because there's a lot of mapped memory
720 * doesn't necessarily mean that page reclaim isn't succeeding.
721 *
722 * The distress ratio is important - we don't want to start going oom.
723 *
724 * A 100% value of vm_swappiness overrides this algorithm altogether.
725 */
726 swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
727
728 /*
729 * Now use this metric to decide whether to start moving mapped memory
730 * onto the inactive list.
731 */
732 if (swap_tendency >= 100)
733 reclaim_mapped = 1;
734
735 while (!list_empty(&l_hold)) {
736 cond_resched();
737 page = lru_to_page(&l_hold);
738 list_del(&page->lru);
739 if (page_mapped(page)) {
740 if (!reclaim_mapped ||
741 (total_swap_pages == 0 && PageAnon(page)) ||
742 page_referenced(page, 0, sc->priority <= 0)) {
743 list_add(&page->lru, &l_active);
744 continue;
745 }
746 }
747 list_add(&page->lru, &l_inactive);
748 }
749
750 pagevec_init(&pvec, 1);
751 pgmoved = 0;
752 spin_lock_irq(&zone->lru_lock);
753 while (!list_empty(&l_inactive)) {
754 page = lru_to_page(&l_inactive);
755 prefetchw_prev_lru_page(page, &l_inactive, flags);
756 if (TestSetPageLRU(page))
757 BUG();
758 if (!TestClearPageActive(page))
759 BUG();
760 list_move(&page->lru, &zone->inactive_list);
761 pgmoved++;
762 if (!pagevec_add(&pvec, page)) {
763 zone->nr_inactive += pgmoved;
764 spin_unlock_irq(&zone->lru_lock);
765 pgdeactivate += pgmoved;
766 pgmoved = 0;
767 if (buffer_heads_over_limit)
768 pagevec_strip(&pvec);
769 __pagevec_release(&pvec);
770 spin_lock_irq(&zone->lru_lock);
771 }
772 }
773 zone->nr_inactive += pgmoved;
774 pgdeactivate += pgmoved;
775 if (buffer_heads_over_limit) {
776 spin_unlock_irq(&zone->lru_lock);
777 pagevec_strip(&pvec);
778 spin_lock_irq(&zone->lru_lock);
779 }
780
781 pgmoved = 0;
782 while (!list_empty(&l_active)) {
783 page = lru_to_page(&l_active);
784 prefetchw_prev_lru_page(page, &l_active, flags);
785 if (TestSetPageLRU(page))
786 BUG();
787 BUG_ON(!PageActive(page));
788 list_move(&page->lru, &zone->active_list);
789 pgmoved++;
790 if (!pagevec_add(&pvec, page)) {
791 zone->nr_active += pgmoved;
792 pgmoved = 0;
793 spin_unlock_irq(&zone->lru_lock);
794 __pagevec_release(&pvec);
795 spin_lock_irq(&zone->lru_lock);
796 }
797 }
798 zone->nr_active += pgmoved;
799 spin_unlock_irq(&zone->lru_lock);
800 pagevec_release(&pvec);
801
802 mod_page_state_zone(zone, pgrefill, pgscanned);
803 mod_page_state(pgdeactivate, pgdeactivate);
804}
805
806/*
807 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim.
808 */
809static void
810shrink_zone(struct zone *zone, struct scan_control *sc)
811{
812 unsigned long nr_active;
813 unsigned long nr_inactive;
814
815 /*
816 * Add one to `nr_to_scan' just to make sure that the kernel will
817 * slowly sift through the active list.
818 */
819 zone->nr_scan_active += (zone->nr_active >> sc->priority) + 1;
820 nr_active = zone->nr_scan_active;
821 if (nr_active >= sc->swap_cluster_max)
822 zone->nr_scan_active = 0;
823 else
824 nr_active = 0;
825
826 zone->nr_scan_inactive += (zone->nr_inactive >> sc->priority) + 1;
827 nr_inactive = zone->nr_scan_inactive;
828 if (nr_inactive >= sc->swap_cluster_max)
829 zone->nr_scan_inactive = 0;
830 else
831 nr_inactive = 0;
832
833 sc->nr_to_reclaim = sc->swap_cluster_max;
834
835 while (nr_active || nr_inactive) {
836 if (nr_active) {
837 sc->nr_to_scan = min(nr_active,
838 (unsigned long)sc->swap_cluster_max);
839 nr_active -= sc->nr_to_scan;
840 refill_inactive_zone(zone, sc);
841 }
842
843 if (nr_inactive) {
844 sc->nr_to_scan = min(nr_inactive,
845 (unsigned long)sc->swap_cluster_max);
846 nr_inactive -= sc->nr_to_scan;
847 shrink_cache(zone, sc);
848 if (sc->nr_to_reclaim <= 0)
849 break;
850 }
851 }
852
853 throttle_vm_writeout();
854}
855
856/*
857 * This is the direct reclaim path, for page-allocating processes. We only
858 * try to reclaim pages from zones which will satisfy the caller's allocation
859 * request.
860 *
861 * We reclaim from a zone even if that zone is over pages_high. Because:
862 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
863 * allocation or
864 * b) The zones may be over pages_high but they must go *over* pages_high to
865 * satisfy the `incremental min' zone defense algorithm.
866 *
867 * Returns the number of reclaimed pages.
868 *
869 * If a zone is deemed to be full of pinned pages then just give it a light
870 * scan then give up on it.
871 */
872static void
873shrink_caches(struct zone **zones, struct scan_control *sc)
874{
875 int i;
876
877 for (i = 0; zones[i] != NULL; i++) {
878 struct zone *zone = zones[i];
879
880 if (zone->present_pages == 0)
881 continue;
882
883 if (!cpuset_zone_allowed(zone))
884 continue;
885
886 zone->temp_priority = sc->priority;
887 if (zone->prev_priority > sc->priority)
888 zone->prev_priority = sc->priority;
889
890 if (zone->all_unreclaimable && sc->priority != DEF_PRIORITY)
891 continue; /* Let kswapd poll it */
892
893 shrink_zone(zone, sc);
894 }
895}
896
897/*
898 * This is the main entry point to direct page reclaim.
899 *
900 * If a full scan of the inactive list fails to free enough memory then we
901 * are "out of memory" and something needs to be killed.
902 *
903 * If the caller is !__GFP_FS then the probability of a failure is reasonably
904 * high - the zone may be full of dirty or under-writeback pages, which this
905 * caller can't do much about. We kick pdflush and take explicit naps in the
906 * hope that some of these pages can be written. But if the allocating task
907 * holds filesystem locks which prevent writeout this might not work, and the
908 * allocation attempt will fail.
909 */
910int try_to_free_pages(struct zone **zones,
911 unsigned int gfp_mask, unsigned int order)
912{
913 int priority;
914 int ret = 0;
915 int total_scanned = 0, total_reclaimed = 0;
916 struct reclaim_state *reclaim_state = current->reclaim_state;
917 struct scan_control sc;
918 unsigned long lru_pages = 0;
919 int i;
920
921 sc.gfp_mask = gfp_mask;
922 sc.may_writepage = 0;
923
924 inc_page_state(allocstall);
925
926 for (i = 0; zones[i] != NULL; i++) {
927 struct zone *zone = zones[i];
928
929 if (!cpuset_zone_allowed(zone))
930 continue;
931
932 zone->temp_priority = DEF_PRIORITY;
933 lru_pages += zone->nr_active + zone->nr_inactive;
934 }
935
936 for (priority = DEF_PRIORITY; priority >= 0; priority--) {
937 sc.nr_mapped = read_page_state(nr_mapped);
938 sc.nr_scanned = 0;
939 sc.nr_reclaimed = 0;
940 sc.priority = priority;
941 sc.swap_cluster_max = SWAP_CLUSTER_MAX;
942 shrink_caches(zones, &sc);
943 shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
944 if (reclaim_state) {
945 sc.nr_reclaimed += reclaim_state->reclaimed_slab;
946 reclaim_state->reclaimed_slab = 0;
947 }
948 total_scanned += sc.nr_scanned;
949 total_reclaimed += sc.nr_reclaimed;
950 if (total_reclaimed >= sc.swap_cluster_max) {
951 ret = 1;
952 goto out;
953 }
954
955 /*
956 * Try to write back as many pages as we just scanned. This
957 * tends to cause slow streaming writers to write data to the
958 * disk smoothly, at the dirtying rate, which is nice. But
959 * that's undesirable in laptop mode, where we *want* lumpy
960 * writeout. So in laptop mode, write out the whole world.
961 */
962 if (total_scanned > sc.swap_cluster_max + sc.swap_cluster_max/2) {
963 wakeup_bdflush(laptop_mode ? 0 : total_scanned);
964 sc.may_writepage = 1;
965 }
966
967 /* Take a nap, wait for some writeback to complete */
968 if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
969 blk_congestion_wait(WRITE, HZ/10);
970 }
971out:
972 for (i = 0; zones[i] != 0; i++) {
973 struct zone *zone = zones[i];
974
975 if (!cpuset_zone_allowed(zone))
976 continue;
977
978 zone->prev_priority = zone->temp_priority;
979 }
980 return ret;
981}
982
983/*
984 * For kswapd, balance_pgdat() will work across all this node's zones until
985 * they are all at pages_high.
986 *
987 * If `nr_pages' is non-zero then it is the number of pages which are to be
988 * reclaimed, regardless of the zone occupancies. This is a software suspend
989 * special.
990 *
991 * Returns the number of pages which were actually freed.
992 *
993 * There is special handling here for zones which are full of pinned pages.
994 * This can happen if the pages are all mlocked, or if they are all used by
995 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb.
996 * What we do is to detect the case where all pages in the zone have been
997 * scanned twice and there has been zero successful reclaim. Mark the zone as
998 * dead and from now on, only perform a short scan. Basically we're polling
999 * the zone for when the problem goes away.
1000 *
1001 * kswapd scans the zones in the highmem->normal->dma direction. It skips
1002 * zones which have free_pages > pages_high, but once a zone is found to have
1003 * free_pages <= pages_high, we scan that zone and the lower zones regardless
1004 * of the number of free pages in the lower zones. This interoperates with
1005 * the page allocator fallback scheme to ensure that aging of pages is balanced
1006 * across the zones.
1007 */
1008static int balance_pgdat(pg_data_t *pgdat, int nr_pages, int order)
1009{
1010 int to_free = nr_pages;
1011 int all_zones_ok;
1012 int priority;
1013 int i;
1014 int total_scanned, total_reclaimed;
1015 struct reclaim_state *reclaim_state = current->reclaim_state;
1016 struct scan_control sc;
1017
1018loop_again:
1019 total_scanned = 0;
1020 total_reclaimed = 0;
1021 sc.gfp_mask = GFP_KERNEL;
1022 sc.may_writepage = 0;
1023 sc.nr_mapped = read_page_state(nr_mapped);
1024
1025 inc_page_state(pageoutrun);
1026
1027 for (i = 0; i < pgdat->nr_zones; i++) {
1028 struct zone *zone = pgdat->node_zones + i;
1029
1030 zone->temp_priority = DEF_PRIORITY;
1031 }
1032
1033 for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1034 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */
1035 unsigned long lru_pages = 0;
1036
1037 all_zones_ok = 1;
1038
1039 if (nr_pages == 0) {
1040 /*
1041 * Scan in the highmem->dma direction for the highest
1042 * zone which needs scanning
1043 */
1044 for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1045 struct zone *zone = pgdat->node_zones + i;
1046
1047 if (zone->present_pages == 0)
1048 continue;
1049
1050 if (zone->all_unreclaimable &&
1051 priority != DEF_PRIORITY)
1052 continue;
1053
1054 if (!zone_watermark_ok(zone, order,
1055 zone->pages_high, 0, 0, 0)) {
1056 end_zone = i;
1057 goto scan;
1058 }
1059 }
1060 goto out;
1061 } else {
1062 end_zone = pgdat->nr_zones - 1;
1063 }
1064scan:
1065 for (i = 0; i <= end_zone; i++) {
1066 struct zone *zone = pgdat->node_zones + i;
1067
1068 lru_pages += zone->nr_active + zone->nr_inactive;
1069 }
1070
1071 /*
1072 * Now scan the zone in the dma->highmem direction, stopping
1073 * at the last zone which needs scanning.
1074 *
1075 * We do this because the page allocator works in the opposite
1076 * direction. This prevents the page allocator from allocating
1077 * pages behind kswapd's direction of progress, which would
1078 * cause too much scanning of the lower zones.
1079 */
1080 for (i = 0; i <= end_zone; i++) {
1081 struct zone *zone = pgdat->node_zones + i;
1082
1083 if (zone->present_pages == 0)
1084 continue;
1085
1086 if (zone->all_unreclaimable && priority != DEF_PRIORITY)
1087 continue;
1088
1089 if (nr_pages == 0) { /* Not software suspend */
1090 if (!zone_watermark_ok(zone, order,
1091 zone->pages_high, end_zone, 0, 0))
1092 all_zones_ok = 0;
1093 }
1094 zone->temp_priority = priority;
1095 if (zone->prev_priority > priority)
1096 zone->prev_priority = priority;
1097 sc.nr_scanned = 0;
1098 sc.nr_reclaimed = 0;
1099 sc.priority = priority;
1100 sc.swap_cluster_max = nr_pages? nr_pages : SWAP_CLUSTER_MAX;
1101 shrink_zone(zone, &sc);
1102 reclaim_state->reclaimed_slab = 0;
1103 shrink_slab(sc.nr_scanned, GFP_KERNEL, lru_pages);
1104 sc.nr_reclaimed += reclaim_state->reclaimed_slab;
1105 total_reclaimed += sc.nr_reclaimed;
1106 total_scanned += sc.nr_scanned;
1107 if (zone->all_unreclaimable)
1108 continue;
1109 if (zone->pages_scanned >= (zone->nr_active +
1110 zone->nr_inactive) * 4)
1111 zone->all_unreclaimable = 1;
1112 /*
1113 * If we've done a decent amount of scanning and
1114 * the reclaim ratio is low, start doing writepage
1115 * even in laptop mode
1116 */
1117 if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1118 total_scanned > total_reclaimed+total_reclaimed/2)
1119 sc.may_writepage = 1;
1120 }
1121 if (nr_pages && to_free > total_reclaimed)
1122 continue; /* swsusp: need to do more work */
1123 if (all_zones_ok)
1124 break; /* kswapd: all done */
1125 /*
1126 * OK, kswapd is getting into trouble. Take a nap, then take
1127 * another pass across the zones.
1128 */
1129 if (total_scanned && priority < DEF_PRIORITY - 2)
1130 blk_congestion_wait(WRITE, HZ/10);
1131
1132 /*
1133 * We do this so kswapd doesn't build up large priorities for
1134 * example when it is freeing in parallel with allocators. It
1135 * matches the direct reclaim path behaviour in terms of impact
1136 * on zone->*_priority.
1137 */
1138 if ((total_reclaimed >= SWAP_CLUSTER_MAX) && (!nr_pages))
1139 break;
1140 }
1141out:
1142 for (i = 0; i < pgdat->nr_zones; i++) {
1143 struct zone *zone = pgdat->node_zones + i;
1144
1145 zone->prev_priority = zone->temp_priority;
1146 }
1147 if (!all_zones_ok) {
1148 cond_resched();
1149 goto loop_again;
1150 }
1151
1152 return total_reclaimed;
1153}
1154
1155/*
1156 * The background pageout daemon, started as a kernel thread
1157 * from the init process.
1158 *
1159 * This basically trickles out pages so that we have _some_
1160 * free memory available even if there is no other activity
1161 * that frees anything up. This is needed for things like routing
1162 * etc, where we otherwise might have all activity going on in
1163 * asynchronous contexts that cannot page things out.
1164 *
1165 * If there are applications that are active memory-allocators
1166 * (most normal use), this basically shouldn't matter.
1167 */
1168static int kswapd(void *p)
1169{
1170 unsigned long order;
1171 pg_data_t *pgdat = (pg_data_t*)p;
1172 struct task_struct *tsk = current;
1173 DEFINE_WAIT(wait);
1174 struct reclaim_state reclaim_state = {
1175 .reclaimed_slab = 0,
1176 };
1177 cpumask_t cpumask;
1178
1179 daemonize("kswapd%d", pgdat->node_id);
1180 cpumask = node_to_cpumask(pgdat->node_id);
1181 if (!cpus_empty(cpumask))
1182 set_cpus_allowed(tsk, cpumask);
1183 current->reclaim_state = &reclaim_state;
1184
1185 /*
1186 * Tell the memory management that we're a "memory allocator",
1187 * and that if we need more memory we should get access to it
1188 * regardless (see "__alloc_pages()"). "kswapd" should
1189 * never get caught in the normal page freeing logic.
1190 *
1191 * (Kswapd normally doesn't need memory anyway, but sometimes
1192 * you need a small amount of memory in order to be able to
1193 * page out something else, and this flag essentially protects
1194 * us from recursively trying to free more memory as we're
1195 * trying to free the first piece of memory in the first place).
1196 */
1197 tsk->flags |= PF_MEMALLOC|PF_KSWAPD;
1198
1199 order = 0;
1200 for ( ; ; ) {
1201 unsigned long new_order;
1202 if (current->flags & PF_FREEZE)
1203 refrigerator(PF_FREEZE);
1204
1205 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1206 new_order = pgdat->kswapd_max_order;
1207 pgdat->kswapd_max_order = 0;
1208 if (order < new_order) {
1209 /*
1210 * Don't sleep if someone wants a larger 'order'
1211 * allocation
1212 */
1213 order = new_order;
1214 } else {
1215 schedule();
1216 order = pgdat->kswapd_max_order;
1217 }
1218 finish_wait(&pgdat->kswapd_wait, &wait);
1219
1220 balance_pgdat(pgdat, 0, order);
1221 }
1222 return 0;
1223}
1224
1225/*
1226 * A zone is low on free memory, so wake its kswapd task to service it.
1227 */
1228void wakeup_kswapd(struct zone *zone, int order)
1229{
1230 pg_data_t *pgdat;
1231
1232 if (zone->present_pages == 0)
1233 return;
1234
1235 pgdat = zone->zone_pgdat;
1236 if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0, 0))
1237 return;
1238 if (pgdat->kswapd_max_order < order)
1239 pgdat->kswapd_max_order = order;
1240 if (!cpuset_zone_allowed(zone))
1241 return;
1242 if (!waitqueue_active(&zone->zone_pgdat->kswapd_wait))
1243 return;
1244 wake_up_interruptible(&zone->zone_pgdat->kswapd_wait);
1245}
1246
1247#ifdef CONFIG_PM
1248/*
1249 * Try to free `nr_pages' of memory, system-wide. Returns the number of freed
1250 * pages.
1251 */
1252int shrink_all_memory(int nr_pages)
1253{
1254 pg_data_t *pgdat;
1255 int nr_to_free = nr_pages;
1256 int ret = 0;
1257 struct reclaim_state reclaim_state = {
1258 .reclaimed_slab = 0,
1259 };
1260
1261 current->reclaim_state = &reclaim_state;
1262 for_each_pgdat(pgdat) {
1263 int freed;
1264 freed = balance_pgdat(pgdat, nr_to_free, 0);
1265 ret += freed;
1266 nr_to_free -= freed;
1267 if (nr_to_free <= 0)
1268 break;
1269 }
1270 current->reclaim_state = NULL;
1271 return ret;
1272}
1273#endif
1274
1275#ifdef CONFIG_HOTPLUG_CPU
1276/* It's optimal to keep kswapds on the same CPUs as their memory, but
1277 not required for correctness. So if the last cpu in a node goes
1278 away, we get changed to run anywhere: as the first one comes back,
1279 restore their cpu bindings. */
1280static int __devinit cpu_callback(struct notifier_block *nfb,
1281 unsigned long action,
1282 void *hcpu)
1283{
1284 pg_data_t *pgdat;
1285 cpumask_t mask;
1286
1287 if (action == CPU_ONLINE) {
1288 for_each_pgdat(pgdat) {
1289 mask = node_to_cpumask(pgdat->node_id);
1290 if (any_online_cpu(mask) != NR_CPUS)
1291 /* One of our CPUs online: restore mask */
1292 set_cpus_allowed(pgdat->kswapd, mask);
1293 }
1294 }
1295 return NOTIFY_OK;
1296}
1297#endif /* CONFIG_HOTPLUG_CPU */
1298
1299static int __init kswapd_init(void)
1300{
1301 pg_data_t *pgdat;
1302 swap_setup();
1303 for_each_pgdat(pgdat)
1304 pgdat->kswapd
1305 = find_task_by_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL));
1306 total_memory = nr_free_pagecache_pages();
1307 hotcpu_notifier(cpu_callback, 0);
1308 return 0;
1309}
1310
1311module_init(kswapd_init)
generated by cgit v1.2.2 (git 2.25.0) at 2024-12-15 09:04:57 -0500