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[/] [test_project/] [trunk/] [linux_sd_driver/] [mm/] [vmscan.c] - Blame information for rev 81

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1 62 marcus.erl
/*
2
 *  linux/mm/vmscan.c
3
 *
4
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
5
 *
6
 *  Swap reorganised 29.12.95, Stephen Tweedie.
7
 *  kswapd added: 7.1.96  sct
8
 *  Removed kswapd_ctl limits, and swap out as many pages as needed
9
 *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
10
 *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
11
 *  Multiqueue VM started 5.8.00, Rik van Riel.
12
 */
13
 
14
#include <linux/mm.h>
15
#include <linux/module.h>
16
#include <linux/slab.h>
17
#include <linux/kernel_stat.h>
18
#include <linux/swap.h>
19
#include <linux/pagemap.h>
20
#include <linux/init.h>
21
#include <linux/highmem.h>
22
#include <linux/vmstat.h>
23
#include <linux/file.h>
24
#include <linux/writeback.h>
25
#include <linux/blkdev.h>
26
#include <linux/buffer_head.h>  /* for try_to_release_page(),
27
                                        buffer_heads_over_limit */
28
#include <linux/mm_inline.h>
29
#include <linux/pagevec.h>
30
#include <linux/backing-dev.h>
31
#include <linux/rmap.h>
32
#include <linux/topology.h>
33
#include <linux/cpu.h>
34
#include <linux/cpuset.h>
35
#include <linux/notifier.h>
36
#include <linux/rwsem.h>
37
#include <linux/delay.h>
38
#include <linux/kthread.h>
39
#include <linux/freezer.h>
40
 
41
#include <asm/tlbflush.h>
42
#include <asm/div64.h>
43
 
44
#include <linux/swapops.h>
45
 
46
#include "internal.h"
47
 
48
struct scan_control {
49
        /* Incremented by the number of inactive pages that were scanned */
50
        unsigned long nr_scanned;
51
 
52
        /* This context's GFP mask */
53
        gfp_t gfp_mask;
54
 
55
        int may_writepage;
56
 
57
        /* Can pages be swapped as part of reclaim? */
58
        int may_swap;
59
 
60
        /* This context's SWAP_CLUSTER_MAX. If freeing memory for
61
         * suspend, we effectively ignore SWAP_CLUSTER_MAX.
62
         * In this context, it doesn't matter that we scan the
63
         * whole list at once. */
64
        int swap_cluster_max;
65
 
66
        int swappiness;
67
 
68
        int all_unreclaimable;
69
 
70
        int order;
71
};
72
 
73
#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
74
 
75
#ifdef ARCH_HAS_PREFETCH
76
#define prefetch_prev_lru_page(_page, _base, _field)                    \
77
        do {                                                            \
78
                if ((_page)->lru.prev != _base) {                       \
79
                        struct page *prev;                              \
80
                                                                        \
81
                        prev = lru_to_page(&(_page->lru));              \
82
                        prefetch(&prev->_field);                        \
83
                }                                                       \
84
        } while (0)
85
#else
86
#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
87
#endif
88
 
89
#ifdef ARCH_HAS_PREFETCHW
90
#define prefetchw_prev_lru_page(_page, _base, _field)                   \
91
        do {                                                            \
92
                if ((_page)->lru.prev != _base) {                       \
93
                        struct page *prev;                              \
94
                                                                        \
95
                        prev = lru_to_page(&(_page->lru));              \
96
                        prefetchw(&prev->_field);                       \
97
                }                                                       \
98
        } while (0)
99
#else
100
#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
101
#endif
102
 
103
/*
104
 * From 0 .. 100.  Higher means more swappy.
105
 */
106
int vm_swappiness = 60;
107
long vm_total_pages;    /* The total number of pages which the VM controls */
108
 
109
static LIST_HEAD(shrinker_list);
110
static DECLARE_RWSEM(shrinker_rwsem);
111
 
112
/*
113
 * Add a shrinker callback to be called from the vm
114
 */
115
void register_shrinker(struct shrinker *shrinker)
116
{
117
        shrinker->nr = 0;
118
        down_write(&shrinker_rwsem);
119
        list_add_tail(&shrinker->list, &shrinker_list);
120
        up_write(&shrinker_rwsem);
121
}
122
EXPORT_SYMBOL(register_shrinker);
123
 
124
/*
125
 * Remove one
126
 */
127
void unregister_shrinker(struct shrinker *shrinker)
128
{
129
        down_write(&shrinker_rwsem);
130
        list_del(&shrinker->list);
131
        up_write(&shrinker_rwsem);
132
}
133
EXPORT_SYMBOL(unregister_shrinker);
134
 
135
#define SHRINK_BATCH 128
136
/*
137
 * Call the shrink functions to age shrinkable caches
138
 *
139
 * Here we assume it costs one seek to replace a lru page and that it also
140
 * takes a seek to recreate a cache object.  With this in mind we age equal
141
 * percentages of the lru and ageable caches.  This should balance the seeks
142
 * generated by these structures.
143
 *
144
 * If the vm encountered mapped pages on the LRU it increase the pressure on
145
 * slab to avoid swapping.
146
 *
147
 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
148
 *
149
 * `lru_pages' represents the number of on-LRU pages in all the zones which
150
 * are eligible for the caller's allocation attempt.  It is used for balancing
151
 * slab reclaim versus page reclaim.
152
 *
153
 * Returns the number of slab objects which we shrunk.
154
 */
155
unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
156
                        unsigned long lru_pages)
157
{
158
        struct shrinker *shrinker;
159
        unsigned long ret = 0;
160
 
161
        if (scanned == 0)
162
                scanned = SWAP_CLUSTER_MAX;
163
 
164
        if (!down_read_trylock(&shrinker_rwsem))
165
                return 1;       /* Assume we'll be able to shrink next time */
166
 
167
        list_for_each_entry(shrinker, &shrinker_list, list) {
168
                unsigned long long delta;
169
                unsigned long total_scan;
170
                unsigned long max_pass = (*shrinker->shrink)(0, gfp_mask);
171
 
172
                delta = (4 * scanned) / shrinker->seeks;
173
                delta *= max_pass;
174
                do_div(delta, lru_pages + 1);
175
                shrinker->nr += delta;
176
                if (shrinker->nr < 0) {
177
                        printk(KERN_ERR "%s: nr=%ld\n",
178
                                        __FUNCTION__, shrinker->nr);
179
                        shrinker->nr = max_pass;
180
                }
181
 
182
                /*
183
                 * Avoid risking looping forever due to too large nr value:
184
                 * never try to free more than twice the estimate number of
185
                 * freeable entries.
186
                 */
187
                if (shrinker->nr > max_pass * 2)
188
                        shrinker->nr = max_pass * 2;
189
 
190
                total_scan = shrinker->nr;
191
                shrinker->nr = 0;
192
 
193
                while (total_scan >= SHRINK_BATCH) {
194
                        long this_scan = SHRINK_BATCH;
195
                        int shrink_ret;
196
                        int nr_before;
197
 
198
                        nr_before = (*shrinker->shrink)(0, gfp_mask);
199
                        shrink_ret = (*shrinker->shrink)(this_scan, gfp_mask);
200
                        if (shrink_ret == -1)
201
                                break;
202
                        if (shrink_ret < nr_before)
203
                                ret += nr_before - shrink_ret;
204
                        count_vm_events(SLABS_SCANNED, this_scan);
205
                        total_scan -= this_scan;
206
 
207
                        cond_resched();
208
                }
209
 
210
                shrinker->nr += total_scan;
211
        }
212
        up_read(&shrinker_rwsem);
213
        return ret;
214
}
215
 
216
/* Called without lock on whether page is mapped, so answer is unstable */
217
static inline int page_mapping_inuse(struct page *page)
218
{
219
        struct address_space *mapping;
220
 
221
        /* Page is in somebody's page tables. */
222
        if (page_mapped(page))
223
                return 1;
224
 
225
        /* Be more reluctant to reclaim swapcache than pagecache */
226
        if (PageSwapCache(page))
227
                return 1;
228
 
229
        mapping = page_mapping(page);
230
        if (!mapping)
231
                return 0;
232
 
233
        /* File is mmap'd by somebody? */
234
        return mapping_mapped(mapping);
235
}
236
 
237
static inline int is_page_cache_freeable(struct page *page)
238
{
239
        return page_count(page) - !!PagePrivate(page) == 2;
240
}
241
 
242
static int may_write_to_queue(struct backing_dev_info *bdi)
243
{
244
        if (current->flags & PF_SWAPWRITE)
245
                return 1;
246
        if (!bdi_write_congested(bdi))
247
                return 1;
248
        if (bdi == current->backing_dev_info)
249
                return 1;
250
        return 0;
251
}
252
 
253
/*
254
 * We detected a synchronous write error writing a page out.  Probably
255
 * -ENOSPC.  We need to propagate that into the address_space for a subsequent
256
 * fsync(), msync() or close().
257
 *
258
 * The tricky part is that after writepage we cannot touch the mapping: nothing
259
 * prevents it from being freed up.  But we have a ref on the page and once
260
 * that page is locked, the mapping is pinned.
261
 *
262
 * We're allowed to run sleeping lock_page() here because we know the caller has
263
 * __GFP_FS.
264
 */
265
static void handle_write_error(struct address_space *mapping,
266
                                struct page *page, int error)
267
{
268
        lock_page(page);
269
        if (page_mapping(page) == mapping)
270
                mapping_set_error(mapping, error);
271
        unlock_page(page);
272
}
273
 
274
/* Request for sync pageout. */
275
enum pageout_io {
276
        PAGEOUT_IO_ASYNC,
277
        PAGEOUT_IO_SYNC,
278
};
279
 
280
/* possible outcome of pageout() */
281
typedef enum {
282
        /* failed to write page out, page is locked */
283
        PAGE_KEEP,
284
        /* move page to the active list, page is locked */
285
        PAGE_ACTIVATE,
286
        /* page has been sent to the disk successfully, page is unlocked */
287
        PAGE_SUCCESS,
288
        /* page is clean and locked */
289
        PAGE_CLEAN,
290
} pageout_t;
291
 
292
/*
293
 * pageout is called by shrink_page_list() for each dirty page.
294
 * Calls ->writepage().
295
 */
296
static pageout_t pageout(struct page *page, struct address_space *mapping,
297
                                                enum pageout_io sync_writeback)
298
{
299
        /*
300
         * If the page is dirty, only perform writeback if that write
301
         * will be non-blocking.  To prevent this allocation from being
302
         * stalled by pagecache activity.  But note that there may be
303
         * stalls if we need to run get_block().  We could test
304
         * PagePrivate for that.
305
         *
306
         * If this process is currently in generic_file_write() against
307
         * this page's queue, we can perform writeback even if that
308
         * will block.
309
         *
310
         * If the page is swapcache, write it back even if that would
311
         * block, for some throttling. This happens by accident, because
312
         * swap_backing_dev_info is bust: it doesn't reflect the
313
         * congestion state of the swapdevs.  Easy to fix, if needed.
314
         * See swapfile.c:page_queue_congested().
315
         */
316
        if (!is_page_cache_freeable(page))
317
                return PAGE_KEEP;
318
        if (!mapping) {
319
                /*
320
                 * Some data journaling orphaned pages can have
321
                 * page->mapping == NULL while being dirty with clean buffers.
322
                 */
323
                if (PagePrivate(page)) {
324
                        if (try_to_free_buffers(page)) {
325
                                ClearPageDirty(page);
326
                                printk("%s: orphaned page\n", __FUNCTION__);
327
                                return PAGE_CLEAN;
328
                        }
329
                }
330
                return PAGE_KEEP;
331
        }
332
        if (mapping->a_ops->writepage == NULL)
333
                return PAGE_ACTIVATE;
334
        if (!may_write_to_queue(mapping->backing_dev_info))
335
                return PAGE_KEEP;
336
 
337
        if (clear_page_dirty_for_io(page)) {
338
                int res;
339
                struct writeback_control wbc = {
340
                        .sync_mode = WB_SYNC_NONE,
341
                        .nr_to_write = SWAP_CLUSTER_MAX,
342
                        .range_start = 0,
343
                        .range_end = LLONG_MAX,
344
                        .nonblocking = 1,
345
                        .for_reclaim = 1,
346
                };
347
 
348
                SetPageReclaim(page);
349
                res = mapping->a_ops->writepage(page, &wbc);
350
                if (res < 0)
351
                        handle_write_error(mapping, page, res);
352
                if (res == AOP_WRITEPAGE_ACTIVATE) {
353
                        ClearPageReclaim(page);
354
                        return PAGE_ACTIVATE;
355
                }
356
 
357
                /*
358
                 * Wait on writeback if requested to. This happens when
359
                 * direct reclaiming a large contiguous area and the
360
                 * first attempt to free a range of pages fails.
361
                 */
362
                if (PageWriteback(page) && sync_writeback == PAGEOUT_IO_SYNC)
363
                        wait_on_page_writeback(page);
364
 
365
                if (!PageWriteback(page)) {
366
                        /* synchronous write or broken a_ops? */
367
                        ClearPageReclaim(page);
368
                }
369
                inc_zone_page_state(page, NR_VMSCAN_WRITE);
370
                return PAGE_SUCCESS;
371
        }
372
 
373
        return PAGE_CLEAN;
374
}
375
 
376
/*
377
 * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
378
 * someone else has a ref on the page, abort and return 0.  If it was
379
 * successfully detached, return 1.  Assumes the caller has a single ref on
380
 * this page.
381
 */
382
int remove_mapping(struct address_space *mapping, struct page *page)
383
{
384
        BUG_ON(!PageLocked(page));
385
        BUG_ON(mapping != page_mapping(page));
386
 
387
        write_lock_irq(&mapping->tree_lock);
388
        /*
389
         * The non racy check for a busy page.
390
         *
391
         * Must be careful with the order of the tests. When someone has
392
         * a ref to the page, it may be possible that they dirty it then
393
         * drop the reference. So if PageDirty is tested before page_count
394
         * here, then the following race may occur:
395
         *
396
         * get_user_pages(&page);
397
         * [user mapping goes away]
398
         * write_to(page);
399
         *                              !PageDirty(page)    [good]
400
         * SetPageDirty(page);
401
         * put_page(page);
402
         *                              !page_count(page)   [good, discard it]
403
         *
404
         * [oops, our write_to data is lost]
405
         *
406
         * Reversing the order of the tests ensures such a situation cannot
407
         * escape unnoticed. The smp_rmb is needed to ensure the page->flags
408
         * load is not satisfied before that of page->_count.
409
         *
410
         * Note that if SetPageDirty is always performed via set_page_dirty,
411
         * and thus under tree_lock, then this ordering is not required.
412
         */
413
        if (unlikely(page_count(page) != 2))
414
                goto cannot_free;
415
        smp_rmb();
416
        if (unlikely(PageDirty(page)))
417
                goto cannot_free;
418
 
419
        if (PageSwapCache(page)) {
420
                swp_entry_t swap = { .val = page_private(page) };
421
                __delete_from_swap_cache(page);
422
                write_unlock_irq(&mapping->tree_lock);
423
                swap_free(swap);
424
                __put_page(page);       /* The pagecache ref */
425
                return 1;
426
        }
427
 
428
        __remove_from_page_cache(page);
429
        write_unlock_irq(&mapping->tree_lock);
430
        __put_page(page);
431
        return 1;
432
 
433
cannot_free:
434
        write_unlock_irq(&mapping->tree_lock);
435
        return 0;
436
}
437
 
438
/*
439
 * shrink_page_list() returns the number of reclaimed pages
440
 */
441
static unsigned long shrink_page_list(struct list_head *page_list,
442
                                        struct scan_control *sc,
443
                                        enum pageout_io sync_writeback)
444
{
445
        LIST_HEAD(ret_pages);
446
        struct pagevec freed_pvec;
447
        int pgactivate = 0;
448
        unsigned long nr_reclaimed = 0;
449
 
450
        cond_resched();
451
 
452
        pagevec_init(&freed_pvec, 1);
453
        while (!list_empty(page_list)) {
454
                struct address_space *mapping;
455
                struct page *page;
456
                int may_enter_fs;
457
                int referenced;
458
 
459
                cond_resched();
460
 
461
                page = lru_to_page(page_list);
462
                list_del(&page->lru);
463
 
464
                if (TestSetPageLocked(page))
465
                        goto keep;
466
 
467
                VM_BUG_ON(PageActive(page));
468
 
469
                sc->nr_scanned++;
470
 
471
                if (!sc->may_swap && page_mapped(page))
472
                        goto keep_locked;
473
 
474
                /* Double the slab pressure for mapped and swapcache pages */
475
                if (page_mapped(page) || PageSwapCache(page))
476
                        sc->nr_scanned++;
477
 
478
                may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
479
                        (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
480
 
481
                if (PageWriteback(page)) {
482
                        /*
483
                         * Synchronous reclaim is performed in two passes,
484
                         * first an asynchronous pass over the list to
485
                         * start parallel writeback, and a second synchronous
486
                         * pass to wait for the IO to complete.  Wait here
487
                         * for any page for which writeback has already
488
                         * started.
489
                         */
490
                        if (sync_writeback == PAGEOUT_IO_SYNC && may_enter_fs)
491
                                wait_on_page_writeback(page);
492
                        else
493
                                goto keep_locked;
494
                }
495
 
496
                referenced = page_referenced(page, 1);
497
                /* In active use or really unfreeable?  Activate it. */
498
                if (sc->order <= PAGE_ALLOC_COSTLY_ORDER &&
499
                                        referenced && page_mapping_inuse(page))
500
                        goto activate_locked;
501
 
502
#ifdef CONFIG_SWAP
503
                /*
504
                 * Anonymous process memory has backing store?
505
                 * Try to allocate it some swap space here.
506
                 */
507
                if (PageAnon(page) && !PageSwapCache(page))
508
                        if (!add_to_swap(page, GFP_ATOMIC))
509
                                goto activate_locked;
510
#endif /* CONFIG_SWAP */
511
 
512
                mapping = page_mapping(page);
513
 
514
                /*
515
                 * The page is mapped into the page tables of one or more
516
                 * processes. Try to unmap it here.
517
                 */
518
                if (page_mapped(page) && mapping) {
519
                        switch (try_to_unmap(page, 0)) {
520
                        case SWAP_FAIL:
521
                                goto activate_locked;
522
                        case SWAP_AGAIN:
523
                                goto keep_locked;
524
                        case SWAP_SUCCESS:
525
                                ; /* try to free the page below */
526
                        }
527
                }
528
 
529
                if (PageDirty(page)) {
530
                        if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced)
531
                                goto keep_locked;
532
                        if (!may_enter_fs)
533
                                goto keep_locked;
534
                        if (!sc->may_writepage)
535
                                goto keep_locked;
536
 
537
                        /* Page is dirty, try to write it out here */
538
                        switch (pageout(page, mapping, sync_writeback)) {
539
                        case PAGE_KEEP:
540
                                goto keep_locked;
541
                        case PAGE_ACTIVATE:
542
                                goto activate_locked;
543
                        case PAGE_SUCCESS:
544
                                if (PageWriteback(page) || PageDirty(page))
545
                                        goto keep;
546
                                /*
547
                                 * A synchronous write - probably a ramdisk.  Go
548
                                 * ahead and try to reclaim the page.
549
                                 */
550
                                if (TestSetPageLocked(page))
551
                                        goto keep;
552
                                if (PageDirty(page) || PageWriteback(page))
553
                                        goto keep_locked;
554
                                mapping = page_mapping(page);
555
                        case PAGE_CLEAN:
556
                                ; /* try to free the page below */
557
                        }
558
                }
559
 
560
                /*
561
                 * If the page has buffers, try to free the buffer mappings
562
                 * associated with this page. If we succeed we try to free
563
                 * the page as well.
564
                 *
565
                 * We do this even if the page is PageDirty().
566
                 * try_to_release_page() does not perform I/O, but it is
567
                 * possible for a page to have PageDirty set, but it is actually
568
                 * clean (all its buffers are clean).  This happens if the
569
                 * buffers were written out directly, with submit_bh(). ext3
570
                 * will do this, as well as the blockdev mapping.
571
                 * try_to_release_page() will discover that cleanness and will
572
                 * drop the buffers and mark the page clean - it can be freed.
573
                 *
574
                 * Rarely, pages can have buffers and no ->mapping.  These are
575
                 * the pages which were not successfully invalidated in
576
                 * truncate_complete_page().  We try to drop those buffers here
577
                 * and if that worked, and the page is no longer mapped into
578
                 * process address space (page_count == 1) it can be freed.
579
                 * Otherwise, leave the page on the LRU so it is swappable.
580
                 */
581
                if (PagePrivate(page)) {
582
                        if (!try_to_release_page(page, sc->gfp_mask))
583
                                goto activate_locked;
584
                        if (!mapping && page_count(page) == 1)
585
                                goto free_it;
586
                }
587
 
588
                if (!mapping || !remove_mapping(mapping, page))
589
                        goto keep_locked;
590
 
591
free_it:
592
                unlock_page(page);
593
                nr_reclaimed++;
594
                if (!pagevec_add(&freed_pvec, page))
595
                        __pagevec_release_nonlru(&freed_pvec);
596
                continue;
597
 
598
activate_locked:
599
                SetPageActive(page);
600
                pgactivate++;
601
keep_locked:
602
                unlock_page(page);
603
keep:
604
                list_add(&page->lru, &ret_pages);
605
                VM_BUG_ON(PageLRU(page));
606
        }
607
        list_splice(&ret_pages, page_list);
608
        if (pagevec_count(&freed_pvec))
609
                __pagevec_release_nonlru(&freed_pvec);
610
        count_vm_events(PGACTIVATE, pgactivate);
611
        return nr_reclaimed;
612
}
613
 
614
/* LRU Isolation modes. */
615
#define ISOLATE_INACTIVE 0      /* Isolate inactive pages. */
616
#define ISOLATE_ACTIVE 1        /* Isolate active pages. */
617
#define ISOLATE_BOTH 2          /* Isolate both active and inactive pages. */
618
 
619
/*
620
 * Attempt to remove the specified page from its LRU.  Only take this page
621
 * if it is of the appropriate PageActive status.  Pages which are being
622
 * freed elsewhere are also ignored.
623
 *
624
 * page:        page to consider
625
 * mode:        one of the LRU isolation modes defined above
626
 *
627
 * returns 0 on success, -ve errno on failure.
628
 */
629
static int __isolate_lru_page(struct page *page, int mode)
630
{
631
        int ret = -EINVAL;
632
 
633
        /* Only take pages on the LRU. */
634
        if (!PageLRU(page))
635
                return ret;
636
 
637
        /*
638
         * When checking the active state, we need to be sure we are
639
         * dealing with comparible boolean values.  Take the logical not
640
         * of each.
641
         */
642
        if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode))
643
                return ret;
644
 
645
        ret = -EBUSY;
646
        if (likely(get_page_unless_zero(page))) {
647
                /*
648
                 * Be careful not to clear PageLRU until after we're
649
                 * sure the page is not being freed elsewhere -- the
650
                 * page release code relies on it.
651
                 */
652
                ClearPageLRU(page);
653
                ret = 0;
654
        }
655
 
656
        return ret;
657
}
658
 
659
/*
660
 * zone->lru_lock is heavily contended.  Some of the functions that
661
 * shrink the lists perform better by taking out a batch of pages
662
 * and working on them outside the LRU lock.
663
 *
664
 * For pagecache intensive workloads, this function is the hottest
665
 * spot in the kernel (apart from copy_*_user functions).
666
 *
667
 * Appropriate locks must be held before calling this function.
668
 *
669
 * @nr_to_scan: The number of pages to look through on the list.
670
 * @src:        The LRU list to pull pages off.
671
 * @dst:        The temp list to put pages on to.
672
 * @scanned:    The number of pages that were scanned.
673
 * @order:      The caller's attempted allocation order
674
 * @mode:       One of the LRU isolation modes
675
 *
676
 * returns how many pages were moved onto *@dst.
677
 */
678
static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
679
                struct list_head *src, struct list_head *dst,
680
                unsigned long *scanned, int order, int mode)
681
{
682
        unsigned long nr_taken = 0;
683
        unsigned long scan;
684
 
685
        for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
686
                struct page *page;
687
                unsigned long pfn;
688
                unsigned long end_pfn;
689
                unsigned long page_pfn;
690
                int zone_id;
691
 
692
                page = lru_to_page(src);
693
                prefetchw_prev_lru_page(page, src, flags);
694
 
695
                VM_BUG_ON(!PageLRU(page));
696
 
697
                switch (__isolate_lru_page(page, mode)) {
698
                case 0:
699
                        list_move(&page->lru, dst);
700
                        nr_taken++;
701
                        break;
702
 
703
                case -EBUSY:
704
                        /* else it is being freed elsewhere */
705
                        list_move(&page->lru, src);
706
                        continue;
707
 
708
                default:
709
                        BUG();
710
                }
711
 
712
                if (!order)
713
                        continue;
714
 
715
                /*
716
                 * Attempt to take all pages in the order aligned region
717
                 * surrounding the tag page.  Only take those pages of
718
                 * the same active state as that tag page.  We may safely
719
                 * round the target page pfn down to the requested order
720
                 * as the mem_map is guarenteed valid out to MAX_ORDER,
721
                 * where that page is in a different zone we will detect
722
                 * it from its zone id and abort this block scan.
723
                 */
724
                zone_id = page_zone_id(page);
725
                page_pfn = page_to_pfn(page);
726
                pfn = page_pfn & ~((1 << order) - 1);
727
                end_pfn = pfn + (1 << order);
728
                for (; pfn < end_pfn; pfn++) {
729
                        struct page *cursor_page;
730
 
731
                        /* The target page is in the block, ignore it. */
732
                        if (unlikely(pfn == page_pfn))
733
                                continue;
734
 
735
                        /* Avoid holes within the zone. */
736
                        if (unlikely(!pfn_valid_within(pfn)))
737
                                break;
738
 
739
                        cursor_page = pfn_to_page(pfn);
740
                        /* Check that we have not crossed a zone boundary. */
741
                        if (unlikely(page_zone_id(cursor_page) != zone_id))
742
                                continue;
743
                        switch (__isolate_lru_page(cursor_page, mode)) {
744
                        case 0:
745
                                list_move(&cursor_page->lru, dst);
746
                                nr_taken++;
747
                                scan++;
748
                                break;
749
 
750
                        case -EBUSY:
751
                                /* else it is being freed elsewhere */
752
                                list_move(&cursor_page->lru, src);
753
                        default:
754
                                break;
755
                        }
756
                }
757
        }
758
 
759
        *scanned = scan;
760
        return nr_taken;
761
}
762
 
763
/*
764
 * clear_active_flags() is a helper for shrink_active_list(), clearing
765
 * any active bits from the pages in the list.
766
 */
767
static unsigned long clear_active_flags(struct list_head *page_list)
768
{
769
        int nr_active = 0;
770
        struct page *page;
771
 
772
        list_for_each_entry(page, page_list, lru)
773
                if (PageActive(page)) {
774
                        ClearPageActive(page);
775
                        nr_active++;
776
                }
777
 
778
        return nr_active;
779
}
780
 
781
/*
782
 * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
783
 * of reclaimed pages
784
 */
785
static unsigned long shrink_inactive_list(unsigned long max_scan,
786
                                struct zone *zone, struct scan_control *sc)
787
{
788
        LIST_HEAD(page_list);
789
        struct pagevec pvec;
790
        unsigned long nr_scanned = 0;
791
        unsigned long nr_reclaimed = 0;
792
 
793
        pagevec_init(&pvec, 1);
794
 
795
        lru_add_drain();
796
        spin_lock_irq(&zone->lru_lock);
797
        do {
798
                struct page *page;
799
                unsigned long nr_taken;
800
                unsigned long nr_scan;
801
                unsigned long nr_freed;
802
                unsigned long nr_active;
803
 
804
                nr_taken = isolate_lru_pages(sc->swap_cluster_max,
805
                             &zone->inactive_list,
806
                             &page_list, &nr_scan, sc->order,
807
                             (sc->order > PAGE_ALLOC_COSTLY_ORDER)?
808
                                             ISOLATE_BOTH : ISOLATE_INACTIVE);
809
                nr_active = clear_active_flags(&page_list);
810
                __count_vm_events(PGDEACTIVATE, nr_active);
811
 
812
                __mod_zone_page_state(zone, NR_ACTIVE, -nr_active);
813
                __mod_zone_page_state(zone, NR_INACTIVE,
814
                                                -(nr_taken - nr_active));
815
                zone->pages_scanned += nr_scan;
816
                spin_unlock_irq(&zone->lru_lock);
817
 
818
                nr_scanned += nr_scan;
819
                nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
820
 
821
                /*
822
                 * If we are direct reclaiming for contiguous pages and we do
823
                 * not reclaim everything in the list, try again and wait
824
                 * for IO to complete. This will stall high-order allocations
825
                 * but that should be acceptable to the caller
826
                 */
827
                if (nr_freed < nr_taken && !current_is_kswapd() &&
828
                                        sc->order > PAGE_ALLOC_COSTLY_ORDER) {
829
                        congestion_wait(WRITE, HZ/10);
830
 
831
                        /*
832
                         * The attempt at page out may have made some
833
                         * of the pages active, mark them inactive again.
834
                         */
835
                        nr_active = clear_active_flags(&page_list);
836
                        count_vm_events(PGDEACTIVATE, nr_active);
837
 
838
                        nr_freed += shrink_page_list(&page_list, sc,
839
                                                        PAGEOUT_IO_SYNC);
840
                }
841
 
842
                nr_reclaimed += nr_freed;
843
                local_irq_disable();
844
                if (current_is_kswapd()) {
845
                        __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scan);
846
                        __count_vm_events(KSWAPD_STEAL, nr_freed);
847
                } else
848
                        __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scan);
849
                __count_zone_vm_events(PGSTEAL, zone, nr_freed);
850
 
851
                if (nr_taken == 0)
852
                        goto done;
853
 
854
                spin_lock(&zone->lru_lock);
855
                /*
856
                 * Put back any unfreeable pages.
857
                 */
858
                while (!list_empty(&page_list)) {
859
                        page = lru_to_page(&page_list);
860
                        VM_BUG_ON(PageLRU(page));
861
                        SetPageLRU(page);
862
                        list_del(&page->lru);
863
                        if (PageActive(page))
864
                                add_page_to_active_list(zone, page);
865
                        else
866
                                add_page_to_inactive_list(zone, page);
867
                        if (!pagevec_add(&pvec, page)) {
868
                                spin_unlock_irq(&zone->lru_lock);
869
                                __pagevec_release(&pvec);
870
                                spin_lock_irq(&zone->lru_lock);
871
                        }
872
                }
873
        } while (nr_scanned < max_scan);
874
        spin_unlock(&zone->lru_lock);
875
done:
876
        local_irq_enable();
877
        pagevec_release(&pvec);
878
        return nr_reclaimed;
879
}
880
 
881
/*
882
 * We are about to scan this zone at a certain priority level.  If that priority
883
 * level is smaller (ie: more urgent) than the previous priority, then note
884
 * that priority level within the zone.  This is done so that when the next
885
 * process comes in to scan this zone, it will immediately start out at this
886
 * priority level rather than having to build up its own scanning priority.
887
 * Here, this priority affects only the reclaim-mapped threshold.
888
 */
889
static inline void note_zone_scanning_priority(struct zone *zone, int priority)
890
{
891
        if (priority < zone->prev_priority)
892
                zone->prev_priority = priority;
893
}
894
 
895
static inline int zone_is_near_oom(struct zone *zone)
896
{
897
        return zone->pages_scanned >= (zone_page_state(zone, NR_ACTIVE)
898
                                + zone_page_state(zone, NR_INACTIVE))*3;
899
}
900
 
901
/*
902
 * This moves pages from the active list to the inactive list.
903
 *
904
 * We move them the other way if the page is referenced by one or more
905
 * processes, from rmap.
906
 *
907
 * If the pages are mostly unmapped, the processing is fast and it is
908
 * appropriate to hold zone->lru_lock across the whole operation.  But if
909
 * the pages are mapped, the processing is slow (page_referenced()) so we
910
 * should drop zone->lru_lock around each page.  It's impossible to balance
911
 * this, so instead we remove the pages from the LRU while processing them.
912
 * It is safe to rely on PG_active against the non-LRU pages in here because
913
 * nobody will play with that bit on a non-LRU page.
914
 *
915
 * The downside is that we have to touch page->_count against each page.
916
 * But we had to alter page->flags anyway.
917
 */
918
static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
919
                                struct scan_control *sc, int priority)
920
{
921
        unsigned long pgmoved;
922
        int pgdeactivate = 0;
923
        unsigned long pgscanned;
924
        LIST_HEAD(l_hold);      /* The pages which were snipped off */
925
        LIST_HEAD(l_inactive);  /* Pages to go onto the inactive_list */
926
        LIST_HEAD(l_active);    /* Pages to go onto the active_list */
927
        struct page *page;
928
        struct pagevec pvec;
929
        int reclaim_mapped = 0;
930
 
931
        if (sc->may_swap) {
932
                long mapped_ratio;
933
                long distress;
934
                long swap_tendency;
935
                long imbalance;
936
 
937
                if (zone_is_near_oom(zone))
938
                        goto force_reclaim_mapped;
939
 
940
                /*
941
                 * `distress' is a measure of how much trouble we're having
942
                 * reclaiming pages.  0 -> no problems.  100 -> great trouble.
943
                 */
944
                distress = 100 >> min(zone->prev_priority, priority);
945
 
946
                /*
947
                 * The point of this algorithm is to decide when to start
948
                 * reclaiming mapped memory instead of just pagecache.  Work out
949
                 * how much memory
950
                 * is mapped.
951
                 */
952
                mapped_ratio = ((global_page_state(NR_FILE_MAPPED) +
953
                                global_page_state(NR_ANON_PAGES)) * 100) /
954
                                        vm_total_pages;
955
 
956
                /*
957
                 * Now decide how much we really want to unmap some pages.  The
958
                 * mapped ratio is downgraded - just because there's a lot of
959
                 * mapped memory doesn't necessarily mean that page reclaim
960
                 * isn't succeeding.
961
                 *
962
                 * The distress ratio is important - we don't want to start
963
                 * going oom.
964
                 *
965
                 * A 100% value of vm_swappiness overrides this algorithm
966
                 * altogether.
967
                 */
968
                swap_tendency = mapped_ratio / 2 + distress + sc->swappiness;
969
 
970
                /*
971
                 * If there's huge imbalance between active and inactive
972
                 * (think active 100 times larger than inactive) we should
973
                 * become more permissive, or the system will take too much
974
                 * cpu before it start swapping during memory pressure.
975
                 * Distress is about avoiding early-oom, this is about
976
                 * making swappiness graceful despite setting it to low
977
                 * values.
978
                 *
979
                 * Avoid div by zero with nr_inactive+1, and max resulting
980
                 * value is vm_total_pages.
981
                 */
982
                imbalance  = zone_page_state(zone, NR_ACTIVE);
983
                imbalance /= zone_page_state(zone, NR_INACTIVE) + 1;
984
 
985
                /*
986
                 * Reduce the effect of imbalance if swappiness is low,
987
                 * this means for a swappiness very low, the imbalance
988
                 * must be much higher than 100 for this logic to make
989
                 * the difference.
990
                 *
991
                 * Max temporary value is vm_total_pages*100.
992
                 */
993
                imbalance *= (vm_swappiness + 1);
994
                imbalance /= 100;
995
 
996
                /*
997
                 * If not much of the ram is mapped, makes the imbalance
998
                 * less relevant, it's high priority we refill the inactive
999
                 * list with mapped pages only in presence of high ratio of
1000
                 * mapped pages.
1001
                 *
1002
                 * Max temporary value is vm_total_pages*100.
1003
                 */
1004
                imbalance *= mapped_ratio;
1005
                imbalance /= 100;
1006
 
1007
                /* apply imbalance feedback to swap_tendency */
1008
                swap_tendency += imbalance;
1009
 
1010
                /*
1011
                 * Now use this metric to decide whether to start moving mapped
1012
                 * memory onto the inactive list.
1013
                 */
1014
                if (swap_tendency >= 100)
1015
force_reclaim_mapped:
1016
                        reclaim_mapped = 1;
1017
        }
1018
 
1019
        lru_add_drain();
1020
        spin_lock_irq(&zone->lru_lock);
1021
        pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
1022
                            &l_hold, &pgscanned, sc->order, ISOLATE_ACTIVE);
1023
        zone->pages_scanned += pgscanned;
1024
        __mod_zone_page_state(zone, NR_ACTIVE, -pgmoved);
1025
        spin_unlock_irq(&zone->lru_lock);
1026
 
1027
        while (!list_empty(&l_hold)) {
1028
                cond_resched();
1029
                page = lru_to_page(&l_hold);
1030
                list_del(&page->lru);
1031
                if (page_mapped(page)) {
1032
                        if (!reclaim_mapped ||
1033
                            (total_swap_pages == 0 && PageAnon(page)) ||
1034
                            page_referenced(page, 0)) {
1035
                                list_add(&page->lru, &l_active);
1036
                                continue;
1037
                        }
1038
                }
1039
                list_add(&page->lru, &l_inactive);
1040
        }
1041
 
1042
        pagevec_init(&pvec, 1);
1043
        pgmoved = 0;
1044
        spin_lock_irq(&zone->lru_lock);
1045
        while (!list_empty(&l_inactive)) {
1046
                page = lru_to_page(&l_inactive);
1047
                prefetchw_prev_lru_page(page, &l_inactive, flags);
1048
                VM_BUG_ON(PageLRU(page));
1049
                SetPageLRU(page);
1050
                VM_BUG_ON(!PageActive(page));
1051
                ClearPageActive(page);
1052
 
1053
                list_move(&page->lru, &zone->inactive_list);
1054
                pgmoved++;
1055
                if (!pagevec_add(&pvec, page)) {
1056
                        __mod_zone_page_state(zone, NR_INACTIVE, pgmoved);
1057
                        spin_unlock_irq(&zone->lru_lock);
1058
                        pgdeactivate += pgmoved;
1059
                        pgmoved = 0;
1060
                        if (buffer_heads_over_limit)
1061
                                pagevec_strip(&pvec);
1062
                        __pagevec_release(&pvec);
1063
                        spin_lock_irq(&zone->lru_lock);
1064
                }
1065
        }
1066
        __mod_zone_page_state(zone, NR_INACTIVE, pgmoved);
1067
        pgdeactivate += pgmoved;
1068
        if (buffer_heads_over_limit) {
1069
                spin_unlock_irq(&zone->lru_lock);
1070
                pagevec_strip(&pvec);
1071
                spin_lock_irq(&zone->lru_lock);
1072
        }
1073
 
1074
        pgmoved = 0;
1075
        while (!list_empty(&l_active)) {
1076
                page = lru_to_page(&l_active);
1077
                prefetchw_prev_lru_page(page, &l_active, flags);
1078
                VM_BUG_ON(PageLRU(page));
1079
                SetPageLRU(page);
1080
                VM_BUG_ON(!PageActive(page));
1081
                list_move(&page->lru, &zone->active_list);
1082
                pgmoved++;
1083
                if (!pagevec_add(&pvec, page)) {
1084
                        __mod_zone_page_state(zone, NR_ACTIVE, pgmoved);
1085
                        pgmoved = 0;
1086
                        spin_unlock_irq(&zone->lru_lock);
1087
                        __pagevec_release(&pvec);
1088
                        spin_lock_irq(&zone->lru_lock);
1089
                }
1090
        }
1091
        __mod_zone_page_state(zone, NR_ACTIVE, pgmoved);
1092
 
1093
        __count_zone_vm_events(PGREFILL, zone, pgscanned);
1094
        __count_vm_events(PGDEACTIVATE, pgdeactivate);
1095
        spin_unlock_irq(&zone->lru_lock);
1096
 
1097
        pagevec_release(&pvec);
1098
}
1099
 
1100
/*
1101
 * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1102
 */
1103
static unsigned long shrink_zone(int priority, struct zone *zone,
1104
                                struct scan_control *sc)
1105
{
1106
        unsigned long nr_active;
1107
        unsigned long nr_inactive;
1108
        unsigned long nr_to_scan;
1109
        unsigned long nr_reclaimed = 0;
1110
 
1111
        /*
1112
         * Add one to `nr_to_scan' just to make sure that the kernel will
1113
         * slowly sift through the active list.
1114
         */
1115
        zone->nr_scan_active +=
1116
                (zone_page_state(zone, NR_ACTIVE) >> priority) + 1;
1117
        nr_active = zone->nr_scan_active;
1118
        if (nr_active >= sc->swap_cluster_max)
1119
                zone->nr_scan_active = 0;
1120
        else
1121
                nr_active = 0;
1122
 
1123
        zone->nr_scan_inactive +=
1124
                (zone_page_state(zone, NR_INACTIVE) >> priority) + 1;
1125
        nr_inactive = zone->nr_scan_inactive;
1126
        if (nr_inactive >= sc->swap_cluster_max)
1127
                zone->nr_scan_inactive = 0;
1128
        else
1129
                nr_inactive = 0;
1130
 
1131
        while (nr_active || nr_inactive) {
1132
                if (nr_active) {
1133
                        nr_to_scan = min(nr_active,
1134
                                        (unsigned long)sc->swap_cluster_max);
1135
                        nr_active -= nr_to_scan;
1136
                        shrink_active_list(nr_to_scan, zone, sc, priority);
1137
                }
1138
 
1139
                if (nr_inactive) {
1140
                        nr_to_scan = min(nr_inactive,
1141
                                        (unsigned long)sc->swap_cluster_max);
1142
                        nr_inactive -= nr_to_scan;
1143
                        nr_reclaimed += shrink_inactive_list(nr_to_scan, zone,
1144
                                                                sc);
1145
                }
1146
        }
1147
 
1148
        throttle_vm_writeout(sc->gfp_mask);
1149
        return nr_reclaimed;
1150
}
1151
 
1152
/*
1153
 * This is the direct reclaim path, for page-allocating processes.  We only
1154
 * try to reclaim pages from zones which will satisfy the caller's allocation
1155
 * request.
1156
 *
1157
 * We reclaim from a zone even if that zone is over pages_high.  Because:
1158
 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1159
 *    allocation or
1160
 * b) The zones may be over pages_high but they must go *over* pages_high to
1161
 *    satisfy the `incremental min' zone defense algorithm.
1162
 *
1163
 * Returns the number of reclaimed pages.
1164
 *
1165
 * If a zone is deemed to be full of pinned pages then just give it a light
1166
 * scan then give up on it.
1167
 */
1168
static unsigned long shrink_zones(int priority, struct zone **zones,
1169
                                        struct scan_control *sc)
1170
{
1171
        unsigned long nr_reclaimed = 0;
1172
        int i;
1173
 
1174
        sc->all_unreclaimable = 1;
1175
        for (i = 0; zones[i] != NULL; i++) {
1176
                struct zone *zone = zones[i];
1177
 
1178
                if (!populated_zone(zone))
1179
                        continue;
1180
 
1181
                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1182
                        continue;
1183
 
1184
                note_zone_scanning_priority(zone, priority);
1185
 
1186
                if (zone_is_all_unreclaimable(zone) && priority != DEF_PRIORITY)
1187
                        continue;       /* Let kswapd poll it */
1188
 
1189
                sc->all_unreclaimable = 0;
1190
 
1191
                nr_reclaimed += shrink_zone(priority, zone, sc);
1192
        }
1193
        return nr_reclaimed;
1194
}
1195
 
1196
/*
1197
 * This is the main entry point to direct page reclaim.
1198
 *
1199
 * If a full scan of the inactive list fails to free enough memory then we
1200
 * are "out of memory" and something needs to be killed.
1201
 *
1202
 * If the caller is !__GFP_FS then the probability of a failure is reasonably
1203
 * high - the zone may be full of dirty or under-writeback pages, which this
1204
 * caller can't do much about.  We kick pdflush and take explicit naps in the
1205
 * hope that some of these pages can be written.  But if the allocating task
1206
 * holds filesystem locks which prevent writeout this might not work, and the
1207
 * allocation attempt will fail.
1208
 */
1209
unsigned long try_to_free_pages(struct zone **zones, int order, gfp_t gfp_mask)
1210
{
1211
        int priority;
1212
        int ret = 0;
1213
        unsigned long total_scanned = 0;
1214
        unsigned long nr_reclaimed = 0;
1215
        struct reclaim_state *reclaim_state = current->reclaim_state;
1216
        unsigned long lru_pages = 0;
1217
        int i;
1218
        struct scan_control sc = {
1219
                .gfp_mask = gfp_mask,
1220
                .may_writepage = !laptop_mode,
1221
                .swap_cluster_max = SWAP_CLUSTER_MAX,
1222
                .may_swap = 1,
1223
                .swappiness = vm_swappiness,
1224
                .order = order,
1225
        };
1226
 
1227
        count_vm_event(ALLOCSTALL);
1228
 
1229
        for (i = 0; zones[i] != NULL; i++) {
1230
                struct zone *zone = zones[i];
1231
 
1232
                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1233
                        continue;
1234
 
1235
                lru_pages += zone_page_state(zone, NR_ACTIVE)
1236
                                + zone_page_state(zone, NR_INACTIVE);
1237
        }
1238
 
1239
        for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1240
                sc.nr_scanned = 0;
1241
                if (!priority)
1242
                        disable_swap_token();
1243
                nr_reclaimed += shrink_zones(priority, zones, &sc);
1244
                shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
1245
                if (reclaim_state) {
1246
                        nr_reclaimed += reclaim_state->reclaimed_slab;
1247
                        reclaim_state->reclaimed_slab = 0;
1248
                }
1249
                total_scanned += sc.nr_scanned;
1250
                if (nr_reclaimed >= sc.swap_cluster_max) {
1251
                        ret = 1;
1252
                        goto out;
1253
                }
1254
 
1255
                /*
1256
                 * Try to write back as many pages as we just scanned.  This
1257
                 * tends to cause slow streaming writers to write data to the
1258
                 * disk smoothly, at the dirtying rate, which is nice.   But
1259
                 * that's undesirable in laptop mode, where we *want* lumpy
1260
                 * writeout.  So in laptop mode, write out the whole world.
1261
                 */
1262
                if (total_scanned > sc.swap_cluster_max +
1263
                                        sc.swap_cluster_max / 2) {
1264
                        wakeup_pdflush(laptop_mode ? 0 : total_scanned);
1265
                        sc.may_writepage = 1;
1266
                }
1267
 
1268
                /* Take a nap, wait for some writeback to complete */
1269
                if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
1270
                        congestion_wait(WRITE, HZ/10);
1271
        }
1272
        /* top priority shrink_caches still had more to do? don't OOM, then */
1273
        if (!sc.all_unreclaimable)
1274
                ret = 1;
1275
out:
1276
        /*
1277
         * Now that we've scanned all the zones at this priority level, note
1278
         * that level within the zone so that the next thread which performs
1279
         * scanning of this zone will immediately start out at this priority
1280
         * level.  This affects only the decision whether or not to bring
1281
         * mapped pages onto the inactive list.
1282
         */
1283
        if (priority < 0)
1284
                priority = 0;
1285
        for (i = 0; zones[i] != NULL; i++) {
1286
                struct zone *zone = zones[i];
1287
 
1288
                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1289
                        continue;
1290
 
1291
                zone->prev_priority = priority;
1292
        }
1293
        return ret;
1294
}
1295
 
1296
/*
1297
 * For kswapd, balance_pgdat() will work across all this node's zones until
1298
 * they are all at pages_high.
1299
 *
1300
 * Returns the number of pages which were actually freed.
1301
 *
1302
 * There is special handling here for zones which are full of pinned pages.
1303
 * This can happen if the pages are all mlocked, or if they are all used by
1304
 * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
1305
 * What we do is to detect the case where all pages in the zone have been
1306
 * scanned twice and there has been zero successful reclaim.  Mark the zone as
1307
 * dead and from now on, only perform a short scan.  Basically we're polling
1308
 * the zone for when the problem goes away.
1309
 *
1310
 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
1311
 * zones which have free_pages > pages_high, but once a zone is found to have
1312
 * free_pages <= pages_high, we scan that zone and the lower zones regardless
1313
 * of the number of free pages in the lower zones.  This interoperates with
1314
 * the page allocator fallback scheme to ensure that aging of pages is balanced
1315
 * across the zones.
1316
 */
1317
static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
1318
{
1319
        int all_zones_ok;
1320
        int priority;
1321
        int i;
1322
        unsigned long total_scanned;
1323
        unsigned long nr_reclaimed;
1324
        struct reclaim_state *reclaim_state = current->reclaim_state;
1325
        struct scan_control sc = {
1326
                .gfp_mask = GFP_KERNEL,
1327
                .may_swap = 1,
1328
                .swap_cluster_max = SWAP_CLUSTER_MAX,
1329
                .swappiness = vm_swappiness,
1330
                .order = order,
1331
        };
1332
        /*
1333
         * temp_priority is used to remember the scanning priority at which
1334
         * this zone was successfully refilled to free_pages == pages_high.
1335
         */
1336
        int temp_priority[MAX_NR_ZONES];
1337
 
1338
loop_again:
1339
        total_scanned = 0;
1340
        nr_reclaimed = 0;
1341
        sc.may_writepage = !laptop_mode;
1342
        count_vm_event(PAGEOUTRUN);
1343
 
1344
        for (i = 0; i < pgdat->nr_zones; i++)
1345
                temp_priority[i] = DEF_PRIORITY;
1346
 
1347
        for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1348
                int end_zone = 0;        /* Inclusive.  0 = ZONE_DMA */
1349
                unsigned long lru_pages = 0;
1350
 
1351
                /* The swap token gets in the way of swapout... */
1352
                if (!priority)
1353
                        disable_swap_token();
1354
 
1355
                all_zones_ok = 1;
1356
 
1357
                /*
1358
                 * Scan in the highmem->dma direction for the highest
1359
                 * zone which needs scanning
1360
                 */
1361
                for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1362
                        struct zone *zone = pgdat->node_zones + i;
1363
 
1364
                        if (!populated_zone(zone))
1365
                                continue;
1366
 
1367
                        if (zone_is_all_unreclaimable(zone) &&
1368
                            priority != DEF_PRIORITY)
1369
                                continue;
1370
 
1371
                        if (!zone_watermark_ok(zone, order, zone->pages_high,
1372
                                               0, 0)) {
1373
                                end_zone = i;
1374
                                break;
1375
                        }
1376
                }
1377
                if (i < 0)
1378
                        goto out;
1379
 
1380
                for (i = 0; i <= end_zone; i++) {
1381
                        struct zone *zone = pgdat->node_zones + i;
1382
 
1383
                        lru_pages += zone_page_state(zone, NR_ACTIVE)
1384
                                        + zone_page_state(zone, NR_INACTIVE);
1385
                }
1386
 
1387
                /*
1388
                 * Now scan the zone in the dma->highmem direction, stopping
1389
                 * at the last zone which needs scanning.
1390
                 *
1391
                 * We do this because the page allocator works in the opposite
1392
                 * direction.  This prevents the page allocator from allocating
1393
                 * pages behind kswapd's direction of progress, which would
1394
                 * cause too much scanning of the lower zones.
1395
                 */
1396
                for (i = 0; i <= end_zone; i++) {
1397
                        struct zone *zone = pgdat->node_zones + i;
1398
                        int nr_slab;
1399
 
1400
                        if (!populated_zone(zone))
1401
                                continue;
1402
 
1403
                        if (zone_is_all_unreclaimable(zone) &&
1404
                                        priority != DEF_PRIORITY)
1405
                                continue;
1406
 
1407
                        if (!zone_watermark_ok(zone, order, zone->pages_high,
1408
                                               end_zone, 0))
1409
                                all_zones_ok = 0;
1410
                        temp_priority[i] = priority;
1411
                        sc.nr_scanned = 0;
1412
                        note_zone_scanning_priority(zone, priority);
1413
                        /*
1414
                         * We put equal pressure on every zone, unless one
1415
                         * zone has way too many pages free already.
1416
                         */
1417
                        if (!zone_watermark_ok(zone, order, 8*zone->pages_high,
1418
                                                end_zone, 0))
1419
                                nr_reclaimed += shrink_zone(priority, zone, &sc);
1420
                        reclaim_state->reclaimed_slab = 0;
1421
                        nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
1422
                                                lru_pages);
1423
                        nr_reclaimed += reclaim_state->reclaimed_slab;
1424
                        total_scanned += sc.nr_scanned;
1425
                        if (zone_is_all_unreclaimable(zone))
1426
                                continue;
1427
                        if (nr_slab == 0 && zone->pages_scanned >=
1428
                                (zone_page_state(zone, NR_ACTIVE)
1429
                                + zone_page_state(zone, NR_INACTIVE)) * 6)
1430
                                        zone_set_flag(zone,
1431
                                                      ZONE_ALL_UNRECLAIMABLE);
1432
                        /*
1433
                         * If we've done a decent amount of scanning and
1434
                         * the reclaim ratio is low, start doing writepage
1435
                         * even in laptop mode
1436
                         */
1437
                        if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1438
                            total_scanned > nr_reclaimed + nr_reclaimed / 2)
1439
                                sc.may_writepage = 1;
1440
                }
1441
                if (all_zones_ok)
1442
                        break;          /* kswapd: all done */
1443
                /*
1444
                 * OK, kswapd is getting into trouble.  Take a nap, then take
1445
                 * another pass across the zones.
1446
                 */
1447
                if (total_scanned && priority < DEF_PRIORITY - 2)
1448
                        congestion_wait(WRITE, HZ/10);
1449
 
1450
                /*
1451
                 * We do this so kswapd doesn't build up large priorities for
1452
                 * example when it is freeing in parallel with allocators. It
1453
                 * matches the direct reclaim path behaviour in terms of impact
1454
                 * on zone->*_priority.
1455
                 */
1456
                if (nr_reclaimed >= SWAP_CLUSTER_MAX)
1457
                        break;
1458
        }
1459
out:
1460
        /*
1461
         * Note within each zone the priority level at which this zone was
1462
         * brought into a happy state.  So that the next thread which scans this
1463
         * zone will start out at that priority level.
1464
         */
1465
        for (i = 0; i < pgdat->nr_zones; i++) {
1466
                struct zone *zone = pgdat->node_zones + i;
1467
 
1468
                zone->prev_priority = temp_priority[i];
1469
        }
1470
        if (!all_zones_ok) {
1471
                cond_resched();
1472
 
1473
                try_to_freeze();
1474
 
1475
                goto loop_again;
1476
        }
1477
 
1478
        return nr_reclaimed;
1479
}
1480
 
1481
/*
1482
 * The background pageout daemon, started as a kernel thread
1483
 * from the init process.
1484
 *
1485
 * This basically trickles out pages so that we have _some_
1486
 * free memory available even if there is no other activity
1487
 * that frees anything up. This is needed for things like routing
1488
 * etc, where we otherwise might have all activity going on in
1489
 * asynchronous contexts that cannot page things out.
1490
 *
1491
 * If there are applications that are active memory-allocators
1492
 * (most normal use), this basically shouldn't matter.
1493
 */
1494
static int kswapd(void *p)
1495
{
1496
        unsigned long order;
1497
        pg_data_t *pgdat = (pg_data_t*)p;
1498
        struct task_struct *tsk = current;
1499
        DEFINE_WAIT(wait);
1500
        struct reclaim_state reclaim_state = {
1501
                .reclaimed_slab = 0,
1502
        };
1503
        cpumask_t cpumask;
1504
 
1505
        cpumask = node_to_cpumask(pgdat->node_id);
1506
        if (!cpus_empty(cpumask))
1507
                set_cpus_allowed(tsk, cpumask);
1508
        current->reclaim_state = &reclaim_state;
1509
 
1510
        /*
1511
         * Tell the memory management that we're a "memory allocator",
1512
         * and that if we need more memory we should get access to it
1513
         * regardless (see "__alloc_pages()"). "kswapd" should
1514
         * never get caught in the normal page freeing logic.
1515
         *
1516
         * (Kswapd normally doesn't need memory anyway, but sometimes
1517
         * you need a small amount of memory in order to be able to
1518
         * page out something else, and this flag essentially protects
1519
         * us from recursively trying to free more memory as we're
1520
         * trying to free the first piece of memory in the first place).
1521
         */
1522
        tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
1523
        set_freezable();
1524
 
1525
        order = 0;
1526
        for ( ; ; ) {
1527
                unsigned long new_order;
1528
 
1529
                prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1530
                new_order = pgdat->kswapd_max_order;
1531
                pgdat->kswapd_max_order = 0;
1532
                if (order < new_order) {
1533
                        /*
1534
                         * Don't sleep if someone wants a larger 'order'
1535
                         * allocation
1536
                         */
1537
                        order = new_order;
1538
                } else {
1539
                        if (!freezing(current))
1540
                                schedule();
1541
 
1542
                        order = pgdat->kswapd_max_order;
1543
                }
1544
                finish_wait(&pgdat->kswapd_wait, &wait);
1545
 
1546
                if (!try_to_freeze()) {
1547
                        /* We can speed up thawing tasks if we don't call
1548
                         * balance_pgdat after returning from the refrigerator
1549
                         */
1550
                        balance_pgdat(pgdat, order);
1551
                }
1552
        }
1553
        return 0;
1554
}
1555
 
1556
/*
1557
 * A zone is low on free memory, so wake its kswapd task to service it.
1558
 */
1559
void wakeup_kswapd(struct zone *zone, int order)
1560
{
1561
        pg_data_t *pgdat;
1562
 
1563
        if (!populated_zone(zone))
1564
                return;
1565
 
1566
        pgdat = zone->zone_pgdat;
1567
        if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0))
1568
                return;
1569
        if (pgdat->kswapd_max_order < order)
1570
                pgdat->kswapd_max_order = order;
1571
        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1572
                return;
1573
        if (!waitqueue_active(&pgdat->kswapd_wait))
1574
                return;
1575
        wake_up_interruptible(&pgdat->kswapd_wait);
1576
}
1577
 
1578
#ifdef CONFIG_PM
1579
/*
1580
 * Helper function for shrink_all_memory().  Tries to reclaim 'nr_pages' pages
1581
 * from LRU lists system-wide, for given pass and priority, and returns the
1582
 * number of reclaimed pages
1583
 *
1584
 * For pass > 3 we also try to shrink the LRU lists that contain a few pages
1585
 */
1586
static unsigned long shrink_all_zones(unsigned long nr_pages, int prio,
1587
                                      int pass, struct scan_control *sc)
1588
{
1589
        struct zone *zone;
1590
        unsigned long nr_to_scan, ret = 0;
1591
 
1592
        for_each_zone(zone) {
1593
 
1594
                if (!populated_zone(zone))
1595
                        continue;
1596
 
1597
                if (zone_is_all_unreclaimable(zone) && prio != DEF_PRIORITY)
1598
                        continue;
1599
 
1600
                /* For pass = 0 we don't shrink the active list */
1601
                if (pass > 0) {
1602
                        zone->nr_scan_active +=
1603
                                (zone_page_state(zone, NR_ACTIVE) >> prio) + 1;
1604
                        if (zone->nr_scan_active >= nr_pages || pass > 3) {
1605
                                zone->nr_scan_active = 0;
1606
                                nr_to_scan = min(nr_pages,
1607
                                        zone_page_state(zone, NR_ACTIVE));
1608
                                shrink_active_list(nr_to_scan, zone, sc, prio);
1609
                        }
1610
                }
1611
 
1612
                zone->nr_scan_inactive +=
1613
                        (zone_page_state(zone, NR_INACTIVE) >> prio) + 1;
1614
                if (zone->nr_scan_inactive >= nr_pages || pass > 3) {
1615
                        zone->nr_scan_inactive = 0;
1616
                        nr_to_scan = min(nr_pages,
1617
                                zone_page_state(zone, NR_INACTIVE));
1618
                        ret += shrink_inactive_list(nr_to_scan, zone, sc);
1619
                        if (ret >= nr_pages)
1620
                                return ret;
1621
                }
1622
        }
1623
 
1624
        return ret;
1625
}
1626
 
1627
static unsigned long count_lru_pages(void)
1628
{
1629
        return global_page_state(NR_ACTIVE) + global_page_state(NR_INACTIVE);
1630
}
1631
 
1632
/*
1633
 * Try to free `nr_pages' of memory, system-wide, and return the number of
1634
 * freed pages.
1635
 *
1636
 * Rather than trying to age LRUs the aim is to preserve the overall
1637
 * LRU order by reclaiming preferentially
1638
 * inactive > active > active referenced > active mapped
1639
 */
1640
unsigned long shrink_all_memory(unsigned long nr_pages)
1641
{
1642
        unsigned long lru_pages, nr_slab;
1643
        unsigned long ret = 0;
1644
        int pass;
1645
        struct reclaim_state reclaim_state;
1646
        struct scan_control sc = {
1647
                .gfp_mask = GFP_KERNEL,
1648
                .may_swap = 0,
1649
                .swap_cluster_max = nr_pages,
1650
                .may_writepage = 1,
1651
                .swappiness = vm_swappiness,
1652
        };
1653
 
1654
        current->reclaim_state = &reclaim_state;
1655
 
1656
        lru_pages = count_lru_pages();
1657
        nr_slab = global_page_state(NR_SLAB_RECLAIMABLE);
1658
        /* If slab caches are huge, it's better to hit them first */
1659
        while (nr_slab >= lru_pages) {
1660
                reclaim_state.reclaimed_slab = 0;
1661
                shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
1662
                if (!reclaim_state.reclaimed_slab)
1663
                        break;
1664
 
1665
                ret += reclaim_state.reclaimed_slab;
1666
                if (ret >= nr_pages)
1667
                        goto out;
1668
 
1669
                nr_slab -= reclaim_state.reclaimed_slab;
1670
        }
1671
 
1672
        /*
1673
         * We try to shrink LRUs in 5 passes:
1674
         * 0 = Reclaim from inactive_list only
1675
         * 1 = Reclaim from active list but don't reclaim mapped
1676
         * 2 = 2nd pass of type 1
1677
         * 3 = Reclaim mapped (normal reclaim)
1678
         * 4 = 2nd pass of type 3
1679
         */
1680
        for (pass = 0; pass < 5; pass++) {
1681
                int prio;
1682
 
1683
                /* Force reclaiming mapped pages in the passes #3 and #4 */
1684
                if (pass > 2) {
1685
                        sc.may_swap = 1;
1686
                        sc.swappiness = 100;
1687
                }
1688
 
1689
                for (prio = DEF_PRIORITY; prio >= 0; prio--) {
1690
                        unsigned long nr_to_scan = nr_pages - ret;
1691
 
1692
                        sc.nr_scanned = 0;
1693
                        ret += shrink_all_zones(nr_to_scan, prio, pass, &sc);
1694
                        if (ret >= nr_pages)
1695
                                goto out;
1696
 
1697
                        reclaim_state.reclaimed_slab = 0;
1698
                        shrink_slab(sc.nr_scanned, sc.gfp_mask,
1699
                                        count_lru_pages());
1700
                        ret += reclaim_state.reclaimed_slab;
1701
                        if (ret >= nr_pages)
1702
                                goto out;
1703
 
1704
                        if (sc.nr_scanned && prio < DEF_PRIORITY - 2)
1705
                                congestion_wait(WRITE, HZ / 10);
1706
                }
1707
        }
1708
 
1709
        /*
1710
         * If ret = 0, we could not shrink LRUs, but there may be something
1711
         * in slab caches
1712
         */
1713
        if (!ret) {
1714
                do {
1715
                        reclaim_state.reclaimed_slab = 0;
1716
                        shrink_slab(nr_pages, sc.gfp_mask, count_lru_pages());
1717
                        ret += reclaim_state.reclaimed_slab;
1718
                } while (ret < nr_pages && reclaim_state.reclaimed_slab > 0);
1719
        }
1720
 
1721
out:
1722
        current->reclaim_state = NULL;
1723
 
1724
        return ret;
1725
}
1726
#endif
1727
 
1728
/* It's optimal to keep kswapds on the same CPUs as their memory, but
1729
   not required for correctness.  So if the last cpu in a node goes
1730
   away, we get changed to run anywhere: as the first one comes back,
1731
   restore their cpu bindings. */
1732
static int __devinit cpu_callback(struct notifier_block *nfb,
1733
                                  unsigned long action, void *hcpu)
1734
{
1735
        pg_data_t *pgdat;
1736
        cpumask_t mask;
1737
        int nid;
1738
 
1739
        if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
1740
                for_each_node_state(nid, N_HIGH_MEMORY) {
1741
                        pgdat = NODE_DATA(nid);
1742
                        mask = node_to_cpumask(pgdat->node_id);
1743
                        if (any_online_cpu(mask) != NR_CPUS)
1744
                                /* One of our CPUs online: restore mask */
1745
                                set_cpus_allowed(pgdat->kswapd, mask);
1746
                }
1747
        }
1748
        return NOTIFY_OK;
1749
}
1750
 
1751
/*
1752
 * This kswapd start function will be called by init and node-hot-add.
1753
 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
1754
 */
1755
int kswapd_run(int nid)
1756
{
1757
        pg_data_t *pgdat = NODE_DATA(nid);
1758
        int ret = 0;
1759
 
1760
        if (pgdat->kswapd)
1761
                return 0;
1762
 
1763
        pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
1764
        if (IS_ERR(pgdat->kswapd)) {
1765
                /* failure at boot is fatal */
1766
                BUG_ON(system_state == SYSTEM_BOOTING);
1767
                printk("Failed to start kswapd on node %d\n",nid);
1768
                ret = -1;
1769
        }
1770
        return ret;
1771
}
1772
 
1773
static int __init kswapd_init(void)
1774
{
1775
        int nid;
1776
 
1777
        swap_setup();
1778
        for_each_node_state(nid, N_HIGH_MEMORY)
1779
                kswapd_run(nid);
1780
        hotcpu_notifier(cpu_callback, 0);
1781
        return 0;
1782
}
1783
 
1784
module_init(kswapd_init)
1785
 
1786
#ifdef CONFIG_NUMA
1787
/*
1788
 * Zone reclaim mode
1789
 *
1790
 * If non-zero call zone_reclaim when the number of free pages falls below
1791
 * the watermarks.
1792
 */
1793
int zone_reclaim_mode __read_mostly;
1794
 
1795
#define RECLAIM_OFF 0
1796
#define RECLAIM_ZONE (1<<0)     /* Run shrink_cache on the zone */
1797
#define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
1798
#define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
1799
 
1800
/*
1801
 * Priority for ZONE_RECLAIM. This determines the fraction of pages
1802
 * of a node considered for each zone_reclaim. 4 scans 1/16th of
1803
 * a zone.
1804
 */
1805
#define ZONE_RECLAIM_PRIORITY 4
1806
 
1807
/*
1808
 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
1809
 * occur.
1810
 */
1811
int sysctl_min_unmapped_ratio = 1;
1812
 
1813
/*
1814
 * If the number of slab pages in a zone grows beyond this percentage then
1815
 * slab reclaim needs to occur.
1816
 */
1817
int sysctl_min_slab_ratio = 5;
1818
 
1819
/*
1820
 * Try to free up some pages from this zone through reclaim.
1821
 */
1822
static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1823
{
1824
        /* Minimum pages needed in order to stay on node */
1825
        const unsigned long nr_pages = 1 << order;
1826
        struct task_struct *p = current;
1827
        struct reclaim_state reclaim_state;
1828
        int priority;
1829
        unsigned long nr_reclaimed = 0;
1830
        struct scan_control sc = {
1831
                .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
1832
                .may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP),
1833
                .swap_cluster_max = max_t(unsigned long, nr_pages,
1834
                                        SWAP_CLUSTER_MAX),
1835
                .gfp_mask = gfp_mask,
1836
                .swappiness = vm_swappiness,
1837
        };
1838
        unsigned long slab_reclaimable;
1839
 
1840
        disable_swap_token();
1841
        cond_resched();
1842
        /*
1843
         * We need to be able to allocate from the reserves for RECLAIM_SWAP
1844
         * and we also need to be able to write out pages for RECLAIM_WRITE
1845
         * and RECLAIM_SWAP.
1846
         */
1847
        p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
1848
        reclaim_state.reclaimed_slab = 0;
1849
        p->reclaim_state = &reclaim_state;
1850
 
1851
        if (zone_page_state(zone, NR_FILE_PAGES) -
1852
                zone_page_state(zone, NR_FILE_MAPPED) >
1853
                zone->min_unmapped_pages) {
1854
                /*
1855
                 * Free memory by calling shrink zone with increasing
1856
                 * priorities until we have enough memory freed.
1857
                 */
1858
                priority = ZONE_RECLAIM_PRIORITY;
1859
                do {
1860
                        note_zone_scanning_priority(zone, priority);
1861
                        nr_reclaimed += shrink_zone(priority, zone, &sc);
1862
                        priority--;
1863
                } while (priority >= 0 && nr_reclaimed < nr_pages);
1864
        }
1865
 
1866
        slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
1867
        if (slab_reclaimable > zone->min_slab_pages) {
1868
                /*
1869
                 * shrink_slab() does not currently allow us to determine how
1870
                 * many pages were freed in this zone. So we take the current
1871
                 * number of slab pages and shake the slab until it is reduced
1872
                 * by the same nr_pages that we used for reclaiming unmapped
1873
                 * pages.
1874
                 *
1875
                 * Note that shrink_slab will free memory on all zones and may
1876
                 * take a long time.
1877
                 */
1878
                while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
1879
                        zone_page_state(zone, NR_SLAB_RECLAIMABLE) >
1880
                                slab_reclaimable - nr_pages)
1881
                        ;
1882
 
1883
                /*
1884
                 * Update nr_reclaimed by the number of slab pages we
1885
                 * reclaimed from this zone.
1886
                 */
1887
                nr_reclaimed += slab_reclaimable -
1888
                        zone_page_state(zone, NR_SLAB_RECLAIMABLE);
1889
        }
1890
 
1891
        p->reclaim_state = NULL;
1892
        current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
1893
        return nr_reclaimed >= nr_pages;
1894
}
1895
 
1896
int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1897
{
1898
        int node_id;
1899
        int ret;
1900
 
1901
        /*
1902
         * Zone reclaim reclaims unmapped file backed pages and
1903
         * slab pages if we are over the defined limits.
1904
         *
1905
         * A small portion of unmapped file backed pages is needed for
1906
         * file I/O otherwise pages read by file I/O will be immediately
1907
         * thrown out if the zone is overallocated. So we do not reclaim
1908
         * if less than a specified percentage of the zone is used by
1909
         * unmapped file backed pages.
1910
         */
1911
        if (zone_page_state(zone, NR_FILE_PAGES) -
1912
            zone_page_state(zone, NR_FILE_MAPPED) <= zone->min_unmapped_pages
1913
            && zone_page_state(zone, NR_SLAB_RECLAIMABLE)
1914
                        <= zone->min_slab_pages)
1915
                return 0;
1916
 
1917
        if (zone_is_all_unreclaimable(zone))
1918
                return 0;
1919
 
1920
        /*
1921
         * Do not scan if the allocation should not be delayed.
1922
         */
1923
        if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
1924
                        return 0;
1925
 
1926
        /*
1927
         * Only run zone reclaim on the local zone or on zones that do not
1928
         * have associated processors. This will favor the local processor
1929
         * over remote processors and spread off node memory allocations
1930
         * as wide as possible.
1931
         */
1932
        node_id = zone_to_nid(zone);
1933
        if (node_state(node_id, N_CPU) && node_id != numa_node_id())
1934
                return 0;
1935
 
1936
        if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
1937
                return 0;
1938
        ret = __zone_reclaim(zone, gfp_mask, order);
1939
        zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
1940
 
1941
        return ret;
1942
}
1943
#endif

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