linux/mm/vmscan.c
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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/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#include <linux/memcontrol.h>
  41
  42#include <asm/tlbflush.h>
  43#include <asm/div64.h>
  44
  45#include <linux/swapops.h>
  46
  47#include "internal.h"
  48
  49struct scan_control {
  50        /* Incremented by the number of inactive pages that were scanned */
  51        unsigned long nr_scanned;
  52
  53        /* This context's GFP mask */
  54        gfp_t gfp_mask;
  55
  56        int may_writepage;
  57
  58        /* Can pages be swapped as part of reclaim? */
  59        int may_swap;
  60
  61        /* This context's SWAP_CLUSTER_MAX. If freeing memory for
  62         * suspend, we effectively ignore SWAP_CLUSTER_MAX.
  63         * In this context, it doesn't matter that we scan the
  64         * whole list at once. */
  65        int swap_cluster_max;
  66
  67        int swappiness;
  68
  69        int all_unreclaimable;
  70
  71        int order;
  72
  73        /* Which cgroup do we reclaim from */
  74        struct mem_cgroup *mem_cgroup;
  75
  76        /* Pluggable isolate pages callback */
  77        unsigned long (*isolate_pages)(unsigned long nr, struct list_head *dst,
  78                        unsigned long *scanned, int order, int mode,
  79                        struct zone *z, struct mem_cgroup *mem_cont,
  80                        int active);
  81};
  82
  83#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
  84
  85#ifdef ARCH_HAS_PREFETCH
  86#define prefetch_prev_lru_page(_page, _base, _field)                    \
  87        do {                                                            \
  88                if ((_page)->lru.prev != _base) {                       \
  89                        struct page *prev;                              \
  90                                                                        \
  91                        prev = lru_to_page(&(_page->lru));              \
  92                        prefetch(&prev->_field);                        \
  93                }                                                       \
  94        } while (0)
  95#else
  96#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
  97#endif
  98
  99#ifdef ARCH_HAS_PREFETCHW
 100#define prefetchw_prev_lru_page(_page, _base, _field)                   \
 101        do {                                                            \
 102                if ((_page)->lru.prev != _base) {                       \
 103                        struct page *prev;                              \
 104                                                                        \
 105                        prev = lru_to_page(&(_page->lru));              \
 106                        prefetchw(&prev->_field);                       \
 107                }                                                       \
 108        } while (0)
 109#else
 110#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
 111#endif
 112
 113/*
 114 * From 0 .. 100.  Higher means more swappy.
 115 */
 116int vm_swappiness = 60;
 117long vm_total_pages;    /* The total number of pages which the VM controls */
 118
 119static LIST_HEAD(shrinker_list);
 120static DECLARE_RWSEM(shrinker_rwsem);
 121
 122#ifdef CONFIG_CGROUP_MEM_RES_CTLR
 123#define scan_global_lru(sc)     (!(sc)->mem_cgroup)
 124#else
 125#define scan_global_lru(sc)     (1)
 126#endif
 127
 128/*
 129 * Add a shrinker callback to be called from the vm
 130 */
 131void register_shrinker(struct shrinker *shrinker)
 132{
 133        shrinker->nr = 0;
 134        down_write(&shrinker_rwsem);
 135        list_add_tail(&shrinker->list, &shrinker_list);
 136        up_write(&shrinker_rwsem);
 137}
 138EXPORT_SYMBOL(register_shrinker);
 139
 140/*
 141 * Remove one
 142 */
 143void unregister_shrinker(struct shrinker *shrinker)
 144{
 145        down_write(&shrinker_rwsem);
 146        list_del(&shrinker->list);
 147        up_write(&shrinker_rwsem);
 148}
 149EXPORT_SYMBOL(unregister_shrinker);
 150
 151#define SHRINK_BATCH 128
 152/*
 153 * Call the shrink functions to age shrinkable caches
 154 *
 155 * Here we assume it costs one seek to replace a lru page and that it also
 156 * takes a seek to recreate a cache object.  With this in mind we age equal
 157 * percentages of the lru and ageable caches.  This should balance the seeks
 158 * generated by these structures.
 159 *
 160 * If the vm encountered mapped pages on the LRU it increase the pressure on
 161 * slab to avoid swapping.
 162 *
 163 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
 164 *
 165 * `lru_pages' represents the number of on-LRU pages in all the zones which
 166 * are eligible for the caller's allocation attempt.  It is used for balancing
 167 * slab reclaim versus page reclaim.
 168 *
 169 * Returns the number of slab objects which we shrunk.
 170 */
 171unsigned long shrink_slab(unsigned long scanned, gfp_t gfp_mask,
 172                        unsigned long lru_pages)
 173{
 174        struct shrinker *shrinker;
 175        unsigned long ret = 0;
 176
 177        if (scanned == 0)
 178                scanned = SWAP_CLUSTER_MAX;
 179
 180        if (!down_read_trylock(&shrinker_rwsem))
 181                return 1;       /* Assume we'll be able to shrink next time */
 182
 183        list_for_each_entry(shrinker, &shrinker_list, list) {
 184                unsigned long long delta;
 185                unsigned long total_scan;
 186                unsigned long max_pass = (*shrinker->shrink)(0, gfp_mask);
 187
 188                delta = (4 * scanned) / shrinker->seeks;
 189                delta *= max_pass;
 190                do_div(delta, lru_pages + 1);
 191                shrinker->nr += delta;
 192                if (shrinker->nr < 0) {
 193                        printk(KERN_ERR "%s: nr=%ld\n",
 194                                        __func__, shrinker->nr);
 195                        shrinker->nr = max_pass;
 196                }
 197
 198                /*
 199                 * Avoid risking looping forever due to too large nr value:
 200                 * never try to free more than twice the estimate number of
 201                 * freeable entries.
 202                 */
 203                if (shrinker->nr > max_pass * 2)
 204                        shrinker->nr = max_pass * 2;
 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                        int nr_before;
 213
 214                        nr_before = (*shrinker->shrink)(0, gfp_mask);
 215                        shrink_ret = (*shrinker->shrink)(this_scan, gfp_mask);
 216                        if (shrink_ret == -1)
 217                                break;
 218                        if (shrink_ret < nr_before)
 219                                ret += nr_before - shrink_ret;
 220                        count_vm_events(SLABS_SCANNED, this_scan);
 221                        total_scan -= this_scan;
 222
 223                        cond_resched();
 224                }
 225
 226                shrinker->nr += total_scan;
 227        }
 228        up_read(&shrinker_rwsem);
 229        return ret;
 230}
 231
 232/* Called without lock on whether page is mapped, so answer is unstable */
 233static inline int page_mapping_inuse(struct page *page)
 234{
 235        struct address_space *mapping;
 236
 237        /* Page is in somebody's page tables. */
 238        if (page_mapped(page))
 239                return 1;
 240
 241        /* Be more reluctant to reclaim swapcache than pagecache */
 242        if (PageSwapCache(page))
 243                return 1;
 244
 245        mapping = page_mapping(page);
 246        if (!mapping)
 247                return 0;
 248
 249        /* File is mmap'd by somebody? */
 250        return mapping_mapped(mapping);
 251}
 252
 253static inline int is_page_cache_freeable(struct page *page)
 254{
 255        return page_count(page) - !!PagePrivate(page) == 2;
 256}
 257
 258static int may_write_to_queue(struct backing_dev_info *bdi)
 259{
 260        if (current->flags & PF_SWAPWRITE)
 261                return 1;
 262        if (!bdi_write_congested(bdi))
 263                return 1;
 264        if (bdi == current->backing_dev_info)
 265                return 1;
 266        return 0;
 267}
 268
 269/*
 270 * We detected a synchronous write error writing a page out.  Probably
 271 * -ENOSPC.  We need to propagate that into the address_space for a subsequent
 272 * fsync(), msync() or close().
 273 *
 274 * The tricky part is that after writepage we cannot touch the mapping: nothing
 275 * prevents it from being freed up.  But we have a ref on the page and once
 276 * that page is locked, the mapping is pinned.
 277 *
 278 * We're allowed to run sleeping lock_page() here because we know the caller has
 279 * __GFP_FS.
 280 */
 281static void handle_write_error(struct address_space *mapping,
 282                                struct page *page, int error)
 283{
 284        lock_page(page);
 285        if (page_mapping(page) == mapping)
 286                mapping_set_error(mapping, error);
 287        unlock_page(page);
 288}
 289
 290/* Request for sync pageout. */
 291enum pageout_io {
 292        PAGEOUT_IO_ASYNC,
 293        PAGEOUT_IO_SYNC,
 294};
 295
 296/* possible outcome of pageout() */
 297typedef enum {
 298        /* failed to write page out, page is locked */
 299        PAGE_KEEP,
 300        /* move page to the active list, page is locked */
 301        PAGE_ACTIVATE,
 302        /* page has been sent to the disk successfully, page is unlocked */
 303        PAGE_SUCCESS,
 304        /* page is clean and locked */
 305        PAGE_CLEAN,
 306} pageout_t;
 307
 308/*
 309 * pageout is called by shrink_page_list() for each dirty page.
 310 * Calls ->writepage().
 311 */
 312static pageout_t pageout(struct page *page, struct address_space *mapping,
 313                                                enum pageout_io sync_writeback)
 314{
 315        /*
 316         * If the page is dirty, only perform writeback if that write
 317         * will be non-blocking.  To prevent this allocation from being
 318         * stalled by pagecache activity.  But note that there may be
 319         * stalls if we need to run get_block().  We could test
 320         * PagePrivate for that.
 321         *
 322         * If this process is currently in generic_file_write() against
 323         * this page's queue, we can perform writeback even if that
 324         * will block.
 325         *
 326         * If the page is swapcache, write it back even if that would
 327         * block, for some throttling. This happens by accident, because
 328         * swap_backing_dev_info is bust: it doesn't reflect the
 329         * congestion state of the swapdevs.  Easy to fix, if needed.
 330         * See swapfile.c:page_queue_congested().
 331         */
 332        if (!is_page_cache_freeable(page))
 333                return PAGE_KEEP;
 334        if (!mapping) {
 335                /*
 336                 * Some data journaling orphaned pages can have
 337                 * page->mapping == NULL while being dirty with clean buffers.
 338                 */
 339                if (PagePrivate(page)) {
 340                        if (try_to_free_buffers(page)) {
 341                                ClearPageDirty(page);
 342                                printk("%s: orphaned page\n", __func__);
 343                                return PAGE_CLEAN;
 344                        }
 345                }
 346                return PAGE_KEEP;
 347        }
 348        if (mapping->a_ops->writepage == NULL)
 349                return PAGE_ACTIVATE;
 350        if (!may_write_to_queue(mapping->backing_dev_info))
 351                return PAGE_KEEP;
 352
 353        if (clear_page_dirty_for_io(page)) {
 354                int res;
 355                struct writeback_control wbc = {
 356                        .sync_mode = WB_SYNC_NONE,
 357                        .nr_to_write = SWAP_CLUSTER_MAX,
 358                        .range_start = 0,
 359                        .range_end = LLONG_MAX,
 360                        .nonblocking = 1,
 361                        .for_reclaim = 1,
 362                };
 363
 364                SetPageReclaim(page);
 365                res = mapping->a_ops->writepage(page, &wbc);
 366                if (res < 0)
 367                        handle_write_error(mapping, page, res);
 368                if (res == AOP_WRITEPAGE_ACTIVATE) {
 369                        ClearPageReclaim(page);
 370                        return PAGE_ACTIVATE;
 371                }
 372
 373                /*
 374                 * Wait on writeback if requested to. This happens when
 375                 * direct reclaiming a large contiguous area and the
 376                 * first attempt to free a range of pages fails.
 377                 */
 378                if (PageWriteback(page) && sync_writeback == PAGEOUT_IO_SYNC)
 379                        wait_on_page_writeback(page);
 380
 381                if (!PageWriteback(page)) {
 382                        /* synchronous write or broken a_ops? */
 383                        ClearPageReclaim(page);
 384                }
 385                inc_zone_page_state(page, NR_VMSCAN_WRITE);
 386                return PAGE_SUCCESS;
 387        }
 388
 389        return PAGE_CLEAN;
 390}
 391
 392/*
 393 * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
 394 * someone else has a ref on the page, abort and return 0.  If it was
 395 * successfully detached, return 1.  Assumes the caller has a single ref on
 396 * this page.
 397 */
 398int remove_mapping(struct address_space *mapping, struct page *page)
 399{
 400        BUG_ON(!PageLocked(page));
 401        BUG_ON(mapping != page_mapping(page));
 402
 403        write_lock_irq(&mapping->tree_lock);
 404        /*
 405         * The non racy check for a busy page.
 406         *
 407         * Must be careful with the order of the tests. When someone has
 408         * a ref to the page, it may be possible that they dirty it then
 409         * drop the reference. So if PageDirty is tested before page_count
 410         * here, then the following race may occur:
 411         *
 412         * get_user_pages(&page);
 413         * [user mapping goes away]
 414         * write_to(page);
 415         *                              !PageDirty(page)    [good]
 416         * SetPageDirty(page);
 417         * put_page(page);
 418         *                              !page_count(page)   [good, discard it]
 419         *
 420         * [oops, our write_to data is lost]
 421         *
 422         * Reversing the order of the tests ensures such a situation cannot
 423         * escape unnoticed. The smp_rmb is needed to ensure the page->flags
 424         * load is not satisfied before that of page->_count.
 425         *
 426         * Note that if SetPageDirty is always performed via set_page_dirty,
 427         * and thus under tree_lock, then this ordering is not required.
 428         */
 429        if (unlikely(page_count(page) != 2))
 430                goto cannot_free;
 431        smp_rmb();
 432        if (unlikely(PageDirty(page)))
 433                goto cannot_free;
 434
 435        if (PageSwapCache(page)) {
 436                swp_entry_t swap = { .val = page_private(page) };
 437                __delete_from_swap_cache(page);
 438                write_unlock_irq(&mapping->tree_lock);
 439                swap_free(swap);
 440                __put_page(page);       /* The pagecache ref */
 441                return 1;
 442        }
 443
 444        __remove_from_page_cache(page);
 445        write_unlock_irq(&mapping->tree_lock);
 446        __put_page(page);
 447        return 1;
 448
 449cannot_free:
 450        write_unlock_irq(&mapping->tree_lock);
 451        return 0;
 452}
 453
 454/*
 455 * shrink_page_list() returns the number of reclaimed pages
 456 */
 457static unsigned long shrink_page_list(struct list_head *page_list,
 458                                        struct scan_control *sc,
 459                                        enum pageout_io sync_writeback)
 460{
 461        LIST_HEAD(ret_pages);
 462        struct pagevec freed_pvec;
 463        int pgactivate = 0;
 464        unsigned long nr_reclaimed = 0;
 465
 466        cond_resched();
 467
 468        pagevec_init(&freed_pvec, 1);
 469        while (!list_empty(page_list)) {
 470                struct address_space *mapping;
 471                struct page *page;
 472                int may_enter_fs;
 473                int referenced;
 474
 475                cond_resched();
 476
 477                page = lru_to_page(page_list);
 478                list_del(&page->lru);
 479
 480                if (TestSetPageLocked(page))
 481                        goto keep;
 482
 483                VM_BUG_ON(PageActive(page));
 484
 485                sc->nr_scanned++;
 486
 487                if (!sc->may_swap && page_mapped(page))
 488                        goto keep_locked;
 489
 490                /* Double the slab pressure for mapped and swapcache pages */
 491                if (page_mapped(page) || PageSwapCache(page))
 492                        sc->nr_scanned++;
 493
 494                may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
 495                        (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 496
 497                if (PageWriteback(page)) {
 498                        /*
 499                         * Synchronous reclaim is performed in two passes,
 500                         * first an asynchronous pass over the list to
 501                         * start parallel writeback, and a second synchronous
 502                         * pass to wait for the IO to complete.  Wait here
 503                         * for any page for which writeback has already
 504                         * started.
 505                         */
 506                        if (sync_writeback == PAGEOUT_IO_SYNC && may_enter_fs)
 507                                wait_on_page_writeback(page);
 508                        else
 509                                goto keep_locked;
 510                }
 511
 512                referenced = page_referenced(page, 1, sc->mem_cgroup);
 513                /* In active use or really unfreeable?  Activate it. */
 514                if (sc->order <= PAGE_ALLOC_COSTLY_ORDER &&
 515                                        referenced && page_mapping_inuse(page))
 516                        goto activate_locked;
 517
 518#ifdef CONFIG_SWAP
 519                /*
 520                 * Anonymous process memory has backing store?
 521                 * Try to allocate it some swap space here.
 522                 */
 523                if (PageAnon(page) && !PageSwapCache(page))
 524                        if (!add_to_swap(page, GFP_ATOMIC))
 525                                goto activate_locked;
 526#endif /* CONFIG_SWAP */
 527
 528                mapping = page_mapping(page);
 529
 530                /*
 531                 * The page is mapped into the page tables of one or more
 532                 * processes. Try to unmap it here.
 533                 */
 534                if (page_mapped(page) && mapping) {
 535                        switch (try_to_unmap(page, 0)) {
 536                        case SWAP_FAIL:
 537                                goto activate_locked;
 538                        case SWAP_AGAIN:
 539                                goto keep_locked;
 540                        case SWAP_SUCCESS:
 541                                ; /* try to free the page below */
 542                        }
 543                }
 544
 545                if (PageDirty(page)) {
 546                        if (sc->order <= PAGE_ALLOC_COSTLY_ORDER && referenced)
 547                                goto keep_locked;
 548                        if (!may_enter_fs)
 549                                goto keep_locked;
 550                        if (!sc->may_writepage)
 551                                goto keep_locked;
 552
 553                        /* Page is dirty, try to write it out here */
 554                        switch (pageout(page, mapping, sync_writeback)) {
 555                        case PAGE_KEEP:
 556                                goto keep_locked;
 557                        case PAGE_ACTIVATE:
 558                                goto activate_locked;
 559                        case PAGE_SUCCESS:
 560                                if (PageWriteback(page) || PageDirty(page))
 561                                        goto keep;
 562                                /*
 563                                 * A synchronous write - probably a ramdisk.  Go
 564                                 * ahead and try to reclaim the page.
 565                                 */
 566                                if (TestSetPageLocked(page))
 567                                        goto keep;
 568                                if (PageDirty(page) || PageWriteback(page))
 569                                        goto keep_locked;
 570                                mapping = page_mapping(page);
 571                        case PAGE_CLEAN:
 572                                ; /* try to free the page below */
 573                        }
 574                }
 575
 576                /*
 577                 * If the page has buffers, try to free the buffer mappings
 578                 * associated with this page. If we succeed we try to free
 579                 * the page as well.
 580                 *
 581                 * We do this even if the page is PageDirty().
 582                 * try_to_release_page() does not perform I/O, but it is
 583                 * possible for a page to have PageDirty set, but it is actually
 584                 * clean (all its buffers are clean).  This happens if the
 585                 * buffers were written out directly, with submit_bh(). ext3
 586                 * will do this, as well as the blockdev mapping. 
 587                 * try_to_release_page() will discover that cleanness and will
 588                 * drop the buffers and mark the page clean - it can be freed.
 589                 *
 590                 * Rarely, pages can have buffers and no ->mapping.  These are
 591                 * the pages which were not successfully invalidated in
 592                 * truncate_complete_page().  We try to drop those buffers here
 593                 * and if that worked, and the page is no longer mapped into
 594                 * process address space (page_count == 1) it can be freed.
 595                 * Otherwise, leave the page on the LRU so it is swappable.
 596                 */
 597                if (PagePrivate(page)) {
 598                        if (!try_to_release_page(page, sc->gfp_mask))
 599                                goto activate_locked;
 600                        if (!mapping && page_count(page) == 1)
 601                                goto free_it;
 602                }
 603
 604                if (!mapping || !remove_mapping(mapping, page))
 605                        goto keep_locked;
 606
 607free_it:
 608                unlock_page(page);
 609                nr_reclaimed++;
 610                if (!pagevec_add(&freed_pvec, page))
 611                        __pagevec_release_nonlru(&freed_pvec);
 612                continue;
 613
 614activate_locked:
 615                SetPageActive(page);
 616                pgactivate++;
 617keep_locked:
 618                unlock_page(page);
 619keep:
 620                list_add(&page->lru, &ret_pages);
 621                VM_BUG_ON(PageLRU(page));
 622        }
 623        list_splice(&ret_pages, page_list);
 624        if (pagevec_count(&freed_pvec))
 625                __pagevec_release_nonlru(&freed_pvec);
 626        count_vm_events(PGACTIVATE, pgactivate);
 627        return nr_reclaimed;
 628}
 629
 630/* LRU Isolation modes. */
 631#define ISOLATE_INACTIVE 0      /* Isolate inactive pages. */
 632#define ISOLATE_ACTIVE 1        /* Isolate active pages. */
 633#define ISOLATE_BOTH 2          /* Isolate both active and inactive pages. */
 634
 635/*
 636 * Attempt to remove the specified page from its LRU.  Only take this page
 637 * if it is of the appropriate PageActive status.  Pages which are being
 638 * freed elsewhere are also ignored.
 639 *
 640 * page:        page to consider
 641 * mode:        one of the LRU isolation modes defined above
 642 *
 643 * returns 0 on success, -ve errno on failure.
 644 */
 645int __isolate_lru_page(struct page *page, int mode)
 646{
 647        int ret = -EINVAL;
 648
 649        /* Only take pages on the LRU. */
 650        if (!PageLRU(page))
 651                return ret;
 652
 653        /*
 654         * When checking the active state, we need to be sure we are
 655         * dealing with comparible boolean values.  Take the logical not
 656         * of each.
 657         */
 658        if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode))
 659                return ret;
 660
 661        ret = -EBUSY;
 662        if (likely(get_page_unless_zero(page))) {
 663                /*
 664                 * Be careful not to clear PageLRU until after we're
 665                 * sure the page is not being freed elsewhere -- the
 666                 * page release code relies on it.
 667                 */
 668                ClearPageLRU(page);
 669                ret = 0;
 670        }
 671
 672        return ret;
 673}
 674
 675/*
 676 * zone->lru_lock is heavily contended.  Some of the functions that
 677 * shrink the lists perform better by taking out a batch of pages
 678 * and working on them outside the LRU lock.
 679 *
 680 * For pagecache intensive workloads, this function is the hottest
 681 * spot in the kernel (apart from copy_*_user functions).
 682 *
 683 * Appropriate locks must be held before calling this function.
 684 *
 685 * @nr_to_scan: The number of pages to look through on the list.
 686 * @src:        The LRU list to pull pages off.
 687 * @dst:        The temp list to put pages on to.
 688 * @scanned:    The number of pages that were scanned.
 689 * @order:      The caller's attempted allocation order
 690 * @mode:       One of the LRU isolation modes
 691 *
 692 * returns how many pages were moved onto *@dst.
 693 */
 694static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 695                struct list_head *src, struct list_head *dst,
 696                unsigned long *scanned, int order, int mode)
 697{
 698        unsigned long nr_taken = 0;
 699        unsigned long scan;
 700
 701        for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
 702                struct page *page;
 703                unsigned long pfn;
 704                unsigned long end_pfn;
 705                unsigned long page_pfn;
 706                int zone_id;
 707
 708                page = lru_to_page(src);
 709                prefetchw_prev_lru_page(page, src, flags);
 710
 711                VM_BUG_ON(!PageLRU(page));
 712
 713                switch (__isolate_lru_page(page, mode)) {
 714                case 0:
 715                        list_move(&page->lru, dst);
 716                        nr_taken++;
 717                        break;
 718
 719                case -EBUSY:
 720                        /* else it is being freed elsewhere */
 721                        list_move(&page->lru, src);
 722                        continue;
 723
 724                default:
 725                        BUG();
 726                }
 727
 728                if (!order)
 729                        continue;
 730
 731                /*
 732                 * Attempt to take all pages in the order aligned region
 733                 * surrounding the tag page.  Only take those pages of
 734                 * the same active state as that tag page.  We may safely
 735                 * round the target page pfn down to the requested order
 736                 * as the mem_map is guarenteed valid out to MAX_ORDER,
 737                 * where that page is in a different zone we will detect
 738                 * it from its zone id and abort this block scan.
 739                 */
 740                zone_id = page_zone_id(page);
 741                page_pfn = page_to_pfn(page);
 742                pfn = page_pfn & ~((1 << order) - 1);
 743                end_pfn = pfn + (1 << order);
 744                for (; pfn < end_pfn; pfn++) {
 745                        struct page *cursor_page;
 746
 747                        /* The target page is in the block, ignore it. */
 748                        if (unlikely(pfn == page_pfn))
 749                                continue;
 750
 751                        /* Avoid holes within the zone. */
 752                        if (unlikely(!pfn_valid_within(pfn)))
 753                                break;
 754
 755                        cursor_page = pfn_to_page(pfn);
 756                        /* Check that we have not crossed a zone boundary. */
 757                        if (unlikely(page_zone_id(cursor_page) != zone_id))
 758                                continue;
 759                        switch (__isolate_lru_page(cursor_page, mode)) {
 760                        case 0:
 761                                list_move(&cursor_page->lru, dst);
 762                                nr_taken++;
 763                                scan++;
 764                                break;
 765
 766                        case -EBUSY:
 767                                /* else it is being freed elsewhere */
 768                                list_move(&cursor_page->lru, src);
 769                        default:
 770                                break;
 771                        }
 772                }
 773        }
 774
 775        *scanned = scan;
 776        return nr_taken;
 777}
 778
 779static unsigned long isolate_pages_global(unsigned long nr,
 780                                        struct list_head *dst,
 781                                        unsigned long *scanned, int order,
 782                                        int mode, struct zone *z,
 783                                        struct mem_cgroup *mem_cont,
 784                                        int active)
 785{
 786        if (active)
 787                return isolate_lru_pages(nr, &z->active_list, dst,
 788                                                scanned, order, mode);
 789        else
 790                return isolate_lru_pages(nr, &z->inactive_list, dst,
 791                                                scanned, order, mode);
 792}
 793
 794/*
 795 * clear_active_flags() is a helper for shrink_active_list(), clearing
 796 * any active bits from the pages in the list.
 797 */
 798static unsigned long clear_active_flags(struct list_head *page_list)
 799{
 800        int nr_active = 0;
 801        struct page *page;
 802
 803        list_for_each_entry(page, page_list, lru)
 804                if (PageActive(page)) {
 805                        ClearPageActive(page);
 806                        nr_active++;
 807                }
 808
 809        return nr_active;
 810}
 811
 812/*
 813 * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
 814 * of reclaimed pages
 815 */
 816static unsigned long shrink_inactive_list(unsigned long max_scan,
 817                                struct zone *zone, struct scan_control *sc)
 818{
 819        LIST_HEAD(page_list);
 820        struct pagevec pvec;
 821        unsigned long nr_scanned = 0;
 822        unsigned long nr_reclaimed = 0;
 823
 824        pagevec_init(&pvec, 1);
 825
 826        lru_add_drain();
 827        spin_lock_irq(&zone->lru_lock);
 828        do {
 829                struct page *page;
 830                unsigned long nr_taken;
 831                unsigned long nr_scan;
 832                unsigned long nr_freed;
 833                unsigned long nr_active;
 834
 835                nr_taken = sc->isolate_pages(sc->swap_cluster_max,
 836                             &page_list, &nr_scan, sc->order,
 837                             (sc->order > PAGE_ALLOC_COSTLY_ORDER)?
 838                                             ISOLATE_BOTH : ISOLATE_INACTIVE,
 839                                zone, sc->mem_cgroup, 0);
 840                nr_active = clear_active_flags(&page_list);
 841                __count_vm_events(PGDEACTIVATE, nr_active);
 842
 843                __mod_zone_page_state(zone, NR_ACTIVE, -nr_active);
 844                __mod_zone_page_state(zone, NR_INACTIVE,
 845                                                -(nr_taken - nr_active));
 846                if (scan_global_lru(sc))
 847                        zone->pages_scanned += nr_scan;
 848                spin_unlock_irq(&zone->lru_lock);
 849
 850                nr_scanned += nr_scan;
 851                nr_freed = shrink_page_list(&page_list, sc, PAGEOUT_IO_ASYNC);
 852
 853                /*
 854                 * If we are direct reclaiming for contiguous pages and we do
 855                 * not reclaim everything in the list, try again and wait
 856                 * for IO to complete. This will stall high-order allocations
 857                 * but that should be acceptable to the caller
 858                 */
 859                if (nr_freed < nr_taken && !current_is_kswapd() &&
 860                                        sc->order > PAGE_ALLOC_COSTLY_ORDER) {
 861                        congestion_wait(WRITE, HZ/10);
 862
 863                        /*
 864                         * The attempt at page out may have made some
 865                         * of the pages active, mark them inactive again.
 866                         */
 867                        nr_active = clear_active_flags(&page_list);
 868                        count_vm_events(PGDEACTIVATE, nr_active);
 869
 870                        nr_freed += shrink_page_list(&page_list, sc,
 871                                                        PAGEOUT_IO_SYNC);
 872                }
 873
 874                nr_reclaimed += nr_freed;
 875                local_irq_disable();
 876                if (current_is_kswapd()) {
 877                        __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scan);
 878                        __count_vm_events(KSWAPD_STEAL, nr_freed);
 879                } else if (scan_global_lru(sc))
 880                        __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scan);
 881
 882                __count_zone_vm_events(PGSTEAL, zone, nr_freed);
 883
 884                if (nr_taken == 0)
 885                        goto done;
 886
 887                spin_lock(&zone->lru_lock);
 888                /*
 889                 * Put back any unfreeable pages.
 890                 */
 891                while (!list_empty(&page_list)) {
 892                        page = lru_to_page(&page_list);
 893                        VM_BUG_ON(PageLRU(page));
 894                        SetPageLRU(page);
 895                        list_del(&page->lru);
 896                        if (PageActive(page))
 897                                add_page_to_active_list(zone, page);
 898                        else
 899                                add_page_to_inactive_list(zone, page);
 900                        if (!pagevec_add(&pvec, page)) {
 901                                spin_unlock_irq(&zone->lru_lock);
 902                                __pagevec_release(&pvec);
 903                                spin_lock_irq(&zone->lru_lock);
 904                        }
 905                }
 906        } while (nr_scanned < max_scan);
 907        spin_unlock(&zone->lru_lock);
 908done:
 909        local_irq_enable();
 910        pagevec_release(&pvec);
 911        return nr_reclaimed;
 912}
 913
 914/*
 915 * We are about to scan this zone at a certain priority level.  If that priority
 916 * level is smaller (ie: more urgent) than the previous priority, then note
 917 * that priority level within the zone.  This is done so that when the next
 918 * process comes in to scan this zone, it will immediately start out at this
 919 * priority level rather than having to build up its own scanning priority.
 920 * Here, this priority affects only the reclaim-mapped threshold.
 921 */
 922static inline void note_zone_scanning_priority(struct zone *zone, int priority)
 923{
 924        if (priority < zone->prev_priority)
 925                zone->prev_priority = priority;
 926}
 927
 928static inline int zone_is_near_oom(struct zone *zone)
 929{
 930        return zone->pages_scanned >= (zone_page_state(zone, NR_ACTIVE)
 931                                + zone_page_state(zone, NR_INACTIVE))*3;
 932}
 933
 934/*
 935 * Determine we should try to reclaim mapped pages.
 936 * This is called only when sc->mem_cgroup is NULL.
 937 */
 938static int calc_reclaim_mapped(struct scan_control *sc, struct zone *zone,
 939                                int priority)
 940{
 941        long mapped_ratio;
 942        long distress;
 943        long swap_tendency;
 944        long imbalance;
 945        int reclaim_mapped = 0;
 946        int prev_priority;
 947
 948        if (scan_global_lru(sc) && zone_is_near_oom(zone))
 949                return 1;
 950        /*
 951         * `distress' is a measure of how much trouble we're having
 952         * reclaiming pages.  0 -> no problems.  100 -> great trouble.
 953         */
 954        if (scan_global_lru(sc))
 955                prev_priority = zone->prev_priority;
 956        else
 957                prev_priority = mem_cgroup_get_reclaim_priority(sc->mem_cgroup);
 958
 959        distress = 100 >> min(prev_priority, priority);
 960
 961        /*
 962         * The point of this algorithm is to decide when to start
 963         * reclaiming mapped memory instead of just pagecache.  Work out
 964         * how much memory
 965         * is mapped.
 966         */
 967        if (scan_global_lru(sc))
 968                mapped_ratio = ((global_page_state(NR_FILE_MAPPED) +
 969                                global_page_state(NR_ANON_PAGES)) * 100) /
 970                                        vm_total_pages;
 971        else
 972                mapped_ratio = mem_cgroup_calc_mapped_ratio(sc->mem_cgroup);
 973
 974        /*
 975         * Now decide how much we really want to unmap some pages.  The
 976         * mapped ratio is downgraded - just because there's a lot of
 977         * mapped memory doesn't necessarily mean that page reclaim
 978         * isn't succeeding.
 979         *
 980         * The distress ratio is important - we don't want to start
 981         * going oom.
 982         *
 983         * A 100% value of vm_swappiness overrides this algorithm
 984         * altogether.
 985         */
 986        swap_tendency = mapped_ratio / 2 + distress + sc->swappiness;
 987
 988        /*
 989         * If there's huge imbalance between active and inactive
 990         * (think active 100 times larger than inactive) we should
 991         * become more permissive, or the system will take too much
 992         * cpu before it start swapping during memory pressure.
 993         * Distress is about avoiding early-oom, this is about
 994         * making swappiness graceful despite setting it to low
 995         * values.
 996         *
 997         * Avoid div by zero with nr_inactive+1, and max resulting
 998         * value is vm_total_pages.
 999         */
1000        if (scan_global_lru(sc)) {
1001                imbalance  = zone_page_state(zone, NR_ACTIVE);
1002                imbalance /= zone_page_state(zone, NR_INACTIVE) + 1;
1003        } else
1004                imbalance = mem_cgroup_reclaim_imbalance(sc->mem_cgroup);
1005
1006        /*
1007         * Reduce the effect of imbalance if swappiness is low,
1008         * this means for a swappiness very low, the imbalance
1009         * must be much higher than 100 for this logic to make
1010         * the difference.
1011         *
1012         * Max temporary value is vm_total_pages*100.
1013         */
1014        imbalance *= (vm_swappiness + 1);
1015        imbalance /= 100;
1016
1017        /*
1018         * If not much of the ram is mapped, makes the imbalance
1019         * less relevant, it's high priority we refill the inactive
1020         * list with mapped pages only in presence of high ratio of
1021         * mapped pages.
1022         *
1023         * Max temporary value is vm_total_pages*100.
1024         */
1025        imbalance *= mapped_ratio;
1026        imbalance /= 100;
1027
1028        /* apply imbalance feedback to swap_tendency */
1029        swap_tendency += imbalance;
1030
1031        /*
1032         * Now use this metric to decide whether to start moving mapped
1033         * memory onto the inactive list.
1034         */
1035        if (swap_tendency >= 100)
1036                reclaim_mapped = 1;
1037
1038        return reclaim_mapped;
1039}
1040
1041/*
1042 * This moves pages from the active list to the inactive list.
1043 *
1044 * We move them the other way if the page is referenced by one or more
1045 * processes, from rmap.
1046 *
1047 * If the pages are mostly unmapped, the processing is fast and it is
1048 * appropriate to hold zone->lru_lock across the whole operation.  But if
1049 * the pages are mapped, the processing is slow (page_referenced()) so we
1050 * should drop zone->lru_lock around each page.  It's impossible to balance
1051 * this, so instead we remove the pages from the LRU while processing them.
1052 * It is safe to rely on PG_active against the non-LRU pages in here because
1053 * nobody will play with that bit on a non-LRU page.
1054 *
1055 * The downside is that we have to touch page->_count against each page.
1056 * But we had to alter page->flags anyway.
1057 */
1058
1059
1060static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
1061                                struct scan_control *sc, int priority)
1062{
1063        unsigned long pgmoved;
1064        int pgdeactivate = 0;
1065        unsigned long pgscanned;
1066        LIST_HEAD(l_hold);      /* The pages which were snipped off */
1067        LIST_HEAD(l_inactive);  /* Pages to go onto the inactive_list */
1068        LIST_HEAD(l_active);    /* Pages to go onto the active_list */
1069        struct page *page;
1070        struct pagevec pvec;
1071        int reclaim_mapped = 0;
1072
1073        if (sc->may_swap)
1074                reclaim_mapped = calc_reclaim_mapped(sc, zone, priority);
1075
1076        lru_add_drain();
1077        spin_lock_irq(&zone->lru_lock);
1078        pgmoved = sc->isolate_pages(nr_pages, &l_hold, &pgscanned, sc->order,
1079                                        ISOLATE_ACTIVE, zone,
1080                                        sc->mem_cgroup, 1);
1081        /*
1082         * zone->pages_scanned is used for detect zone's oom
1083         * mem_cgroup remembers nr_scan by itself.
1084         */
1085        if (scan_global_lru(sc))
1086                zone->pages_scanned += pgscanned;
1087
1088        __mod_zone_page_state(zone, NR_ACTIVE, -pgmoved);
1089        spin_unlock_irq(&zone->lru_lock);
1090
1091        while (!list_empty(&l_hold)) {
1092                cond_resched();
1093                page = lru_to_page(&l_hold);
1094                list_del(&page->lru);
1095                if (page_mapped(page)) {
1096                        if (!reclaim_mapped ||
1097                            (total_swap_pages == 0 && PageAnon(page)) ||
1098                            page_referenced(page, 0, sc->mem_cgroup)) {
1099                                list_add(&page->lru, &l_active);
1100                                continue;
1101                        }
1102                }
1103                list_add(&page->lru, &l_inactive);
1104        }
1105
1106        pagevec_init(&pvec, 1);
1107        pgmoved = 0;
1108        spin_lock_irq(&zone->lru_lock);
1109        while (!list_empty(&l_inactive)) {
1110                page = lru_to_page(&l_inactive);
1111                prefetchw_prev_lru_page(page, &l_inactive, flags);
1112                VM_BUG_ON(PageLRU(page));
1113                SetPageLRU(page);
1114                VM_BUG_ON(!PageActive(page));
1115                ClearPageActive(page);
1116
1117                list_move(&page->lru, &zone->inactive_list);
1118                mem_cgroup_move_lists(page, false);
1119                pgmoved++;
1120                if (!pagevec_add(&pvec, page)) {
1121                        __mod_zone_page_state(zone, NR_INACTIVE, pgmoved);
1122                        spin_unlock_irq(&zone->lru_lock);
1123                        pgdeactivate += pgmoved;
1124                        pgmoved = 0;
1125                        if (buffer_heads_over_limit)
1126                                pagevec_strip(&pvec);
1127                        __pagevec_release(&pvec);
1128                        spin_lock_irq(&zone->lru_lock);
1129                }
1130        }
1131        __mod_zone_page_state(zone, NR_INACTIVE, pgmoved);
1132        pgdeactivate += pgmoved;
1133        if (buffer_heads_over_limit) {
1134                spin_unlock_irq(&zone->lru_lock);
1135                pagevec_strip(&pvec);
1136                spin_lock_irq(&zone->lru_lock);
1137        }
1138
1139        pgmoved = 0;
1140        while (!list_empty(&l_active)) {
1141                page = lru_to_page(&l_active);
1142                prefetchw_prev_lru_page(page, &l_active, flags);
1143                VM_BUG_ON(PageLRU(page));
1144                SetPageLRU(page);
1145                VM_BUG_ON(!PageActive(page));
1146
1147                list_move(&page->lru, &zone->active_list);
1148                mem_cgroup_move_lists(page, true);
1149                pgmoved++;
1150                if (!pagevec_add(&pvec, page)) {
1151                        __mod_zone_page_state(zone, NR_ACTIVE, pgmoved);
1152                        pgmoved = 0;
1153                        spin_unlock_irq(&zone->lru_lock);
1154                        __pagevec_release(&pvec);
1155                        spin_lock_irq(&zone->lru_lock);
1156                }
1157        }
1158        __mod_zone_page_state(zone, NR_ACTIVE, pgmoved);
1159
1160        __count_zone_vm_events(PGREFILL, zone, pgscanned);
1161        __count_vm_events(PGDEACTIVATE, pgdeactivate);
1162        spin_unlock_irq(&zone->lru_lock);
1163
1164        pagevec_release(&pvec);
1165}
1166
1167/*
1168 * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1169 */
1170static unsigned long shrink_zone(int priority, struct zone *zone,
1171                                struct scan_control *sc)
1172{
1173        unsigned long nr_active;
1174        unsigned long nr_inactive;
1175        unsigned long nr_to_scan;
1176        unsigned long nr_reclaimed = 0;
1177
1178        if (scan_global_lru(sc)) {
1179                /*
1180                 * Add one to nr_to_scan just to make sure that the kernel
1181                 * will slowly sift through the active list.
1182                 */
1183                zone->nr_scan_active +=
1184                        (zone_page_state(zone, NR_ACTIVE) >> priority) + 1;
1185                nr_active = zone->nr_scan_active;
1186                zone->nr_scan_inactive +=
1187                        (zone_page_state(zone, NR_INACTIVE) >> priority) + 1;
1188                nr_inactive = zone->nr_scan_inactive;
1189                if (nr_inactive >= sc->swap_cluster_max)
1190                        zone->nr_scan_inactive = 0;
1191                else
1192                        nr_inactive = 0;
1193
1194                if (nr_active >= sc->swap_cluster_max)
1195                        zone->nr_scan_active = 0;
1196                else
1197                        nr_active = 0;
1198        } else {
1199                /*
1200                 * This reclaim occurs not because zone memory shortage but
1201                 * because memory controller hits its limit.
1202                 * Then, don't modify zone reclaim related data.
1203                 */
1204                nr_active = mem_cgroup_calc_reclaim_active(sc->mem_cgroup,
1205                                        zone, priority);
1206
1207                nr_inactive = mem_cgroup_calc_reclaim_inactive(sc->mem_cgroup,
1208                                        zone, priority);
1209        }
1210
1211
1212        while (nr_active || nr_inactive) {
1213                if (nr_active) {
1214                        nr_to_scan = min(nr_active,
1215                                        (unsigned long)sc->swap_cluster_max);
1216                        nr_active -= nr_to_scan;
1217                        shrink_active_list(nr_to_scan, zone, sc, priority);
1218                }
1219
1220                if (nr_inactive) {
1221                        nr_to_scan = min(nr_inactive,
1222                                        (unsigned long)sc->swap_cluster_max);
1223                        nr_inactive -= nr_to_scan;
1224                        nr_reclaimed += shrink_inactive_list(nr_to_scan, zone,
1225                                                                sc);
1226                }
1227        }
1228
1229        throttle_vm_writeout(sc->gfp_mask);
1230        return nr_reclaimed;
1231}
1232
1233/*
1234 * This is the direct reclaim path, for page-allocating processes.  We only
1235 * try to reclaim pages from zones which will satisfy the caller's allocation
1236 * request.
1237 *
1238 * We reclaim from a zone even if that zone is over pages_high.  Because:
1239 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1240 *    allocation or
1241 * b) The zones may be over pages_high but they must go *over* pages_high to
1242 *    satisfy the `incremental min' zone defense algorithm.
1243 *
1244 * Returns the number of reclaimed pages.
1245 *
1246 * If a zone is deemed to be full of pinned pages then just give it a light
1247 * scan then give up on it.
1248 */
1249static unsigned long shrink_zones(int priority, struct zonelist *zonelist,
1250                                        struct scan_control *sc)
1251{
1252        enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);
1253        unsigned long nr_reclaimed = 0;
1254        struct zoneref *z;
1255        struct zone *zone;
1256
1257        sc->all_unreclaimable = 1;
1258        for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
1259                if (!populated_zone(zone))
1260                        continue;
1261                /*
1262                 * Take care memory controller reclaiming has small influence
1263                 * to global LRU.
1264                 */
1265                if (scan_global_lru(sc)) {
1266                        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1267                                continue;
1268                        note_zone_scanning_priority(zone, priority);
1269
1270                        if (zone_is_all_unreclaimable(zone) &&
1271                                                priority != DEF_PRIORITY)
1272                                continue;       /* Let kswapd poll it */
1273                        sc->all_unreclaimable = 0;
1274                } else {
1275                        /*
1276                         * Ignore cpuset limitation here. We just want to reduce
1277                         * # of used pages by us regardless of memory shortage.
1278                         */
1279                        sc->all_unreclaimable = 0;
1280                        mem_cgroup_note_reclaim_priority(sc->mem_cgroup,
1281                                                        priority);
1282                }
1283
1284                nr_reclaimed += shrink_zone(priority, zone, sc);
1285        }
1286
1287        return nr_reclaimed;
1288}
1289 
1290/*
1291 * This is the main entry point to direct page reclaim.
1292 *
1293 * If a full scan of the inactive list fails to free enough memory then we
1294 * are "out of memory" and something needs to be killed.
1295 *
1296 * If the caller is !__GFP_FS then the probability of a failure is reasonably
1297 * high - the zone may be full of dirty or under-writeback pages, which this
1298 * caller can't do much about.  We kick pdflush and take explicit naps in the
1299 * hope that some of these pages can be written.  But if the allocating task
1300 * holds filesystem locks which prevent writeout this might not work, and the
1301 * allocation attempt will fail.
1302 *
1303 * returns:     0, if no pages reclaimed
1304 *              else, the number of pages reclaimed
1305 */
1306static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
1307                                        struct scan_control *sc)
1308{
1309        int priority;
1310        unsigned long ret = 0;
1311        unsigned long total_scanned = 0;
1312        unsigned long nr_reclaimed = 0;
1313        struct reclaim_state *reclaim_state = current->reclaim_state;
1314        unsigned long lru_pages = 0;
1315        struct zoneref *z;
1316        struct zone *zone;
1317        enum zone_type high_zoneidx = gfp_zone(sc->gfp_mask);
1318
1319        if (scan_global_lru(sc))
1320                count_vm_event(ALLOCSTALL);
1321        /*
1322         * mem_cgroup will not do shrink_slab.
1323         */
1324        if (scan_global_lru(sc)) {
1325                for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
1326
1327                        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1328                                continue;
1329
1330                        lru_pages += zone_page_state(zone, NR_ACTIVE)
1331                                        + zone_page_state(zone, NR_INACTIVE);
1332                }
1333        }
1334
1335        for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1336                sc->nr_scanned = 0;
1337                if (!priority)
1338                        disable_swap_token();
1339                nr_reclaimed += shrink_zones(priority, zonelist, sc);
1340                /*
1341                 * Don't shrink slabs when reclaiming memory from
1342                 * over limit cgroups
1343                 */
1344                if (scan_global_lru(sc)) {
1345                        shrink_slab(sc->nr_scanned, sc->gfp_mask, lru_pages);
1346                        if (reclaim_state) {
1347                                nr_reclaimed += reclaim_state->reclaimed_slab;
1348                                reclaim_state->reclaimed_slab = 0;
1349                        }
1350                }
1351                total_scanned += sc->nr_scanned;
1352                if (nr_reclaimed >= sc->swap_cluster_max) {
1353                        ret = nr_reclaimed;
1354                        goto out;
1355                }
1356
1357                /*
1358                 * Try to write back as many pages as we just scanned.  This
1359                 * tends to cause slow streaming writers to write data to the
1360                 * disk smoothly, at the dirtying rate, which is nice.   But
1361                 * that's undesirable in laptop mode, where we *want* lumpy
1362                 * writeout.  So in laptop mode, write out the whole world.
1363                 */
1364                if (total_scanned > sc->swap_cluster_max +
1365                                        sc->swap_cluster_max / 2) {
1366                        wakeup_pdflush(laptop_mode ? 0 : total_scanned);
1367                        sc->may_writepage = 1;
1368                }
1369
1370                /* Take a nap, wait for some writeback to complete */
1371                if (sc->nr_scanned && priority < DEF_PRIORITY - 2)
1372                        congestion_wait(WRITE, HZ/10);
1373        }
1374        /* top priority shrink_caches still had more to do? don't OOM, then */
1375        if (!sc->all_unreclaimable && scan_global_lru(sc))
1376                ret = nr_reclaimed;
1377out:
1378        /*
1379         * Now that we've scanned all the zones at this priority level, note
1380         * that level within the zone so that the next thread which performs
1381         * scanning of this zone will immediately start out at this priority
1382         * level.  This affects only the decision whether or not to bring
1383         * mapped pages onto the inactive list.
1384         */
1385        if (priority < 0)
1386                priority = 0;
1387
1388        if (scan_global_lru(sc)) {
1389                for_each_zone_zonelist(zone, z, zonelist, high_zoneidx) {
1390
1391                        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1392                                continue;
1393
1394                        zone->prev_priority = priority;
1395                }
1396        } else
1397                mem_cgroup_record_reclaim_priority(sc->mem_cgroup, priority);
1398
1399        return ret;
1400}
1401
1402unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
1403                                                                gfp_t gfp_mask)
1404{
1405        struct scan_control sc = {
1406                .gfp_mask = gfp_mask,
1407                .may_writepage = !laptop_mode,
1408                .swap_cluster_max = SWAP_CLUSTER_MAX,
1409                .may_swap = 1,
1410                .swappiness = vm_swappiness,
1411                .order = order,
1412                .mem_cgroup = NULL,
1413                .isolate_pages = isolate_pages_global,
1414        };
1415
1416        return do_try_to_free_pages(zonelist, &sc);
1417}
1418
1419#ifdef CONFIG_CGROUP_MEM_RES_CTLR
1420
1421unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
1422                                                gfp_t gfp_mask)
1423{
1424        struct scan_control sc = {
1425                .may_writepage = !laptop_mode,
1426                .may_swap = 1,
1427                .swap_cluster_max = SWAP_CLUSTER_MAX,
1428                .swappiness = vm_swappiness,
1429                .order = 0,
1430                .mem_cgroup = mem_cont,
1431                .isolate_pages = mem_cgroup_isolate_pages,
1432        };
1433        struct zonelist *zonelist;
1434
1435        sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
1436                        (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
1437        zonelist = NODE_DATA(numa_node_id())->node_zonelists;
1438        return do_try_to_free_pages(zonelist, &sc);
1439}
1440#endif
1441
1442/*
1443 * For kswapd, balance_pgdat() will work across all this node's zones until
1444 * they are all at pages_high.
1445 *
1446 * Returns the number of pages which were actually freed.
1447 *
1448 * There is special handling here for zones which are full of pinned pages.
1449 * This can happen if the pages are all mlocked, or if they are all used by
1450 * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
1451 * What we do is to detect the case where all pages in the zone have been
1452 * scanned twice and there has been zero successful reclaim.  Mark the zone as
1453 * dead and from now on, only perform a short scan.  Basically we're polling
1454 * the zone for when the problem goes away.
1455 *
1456 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
1457 * zones which have free_pages > pages_high, but once a zone is found to have
1458 * free_pages <= pages_high, we scan that zone and the lower zones regardless
1459 * of the number of free pages in the lower zones.  This interoperates with
1460 * the page allocator fallback scheme to ensure that aging of pages is balanced
1461 * across the zones.
1462 */
1463static unsigned long balance_pgdat(pg_data_t *pgdat, int order)
1464{
1465        int all_zones_ok;
1466        int priority;
1467        int i;
1468        unsigned long total_scanned;
1469        unsigned long nr_reclaimed;
1470        struct reclaim_state *reclaim_state = current->reclaim_state;
1471        struct scan_control sc = {
1472                .gfp_mask = GFP_KERNEL,
1473                .may_swap = 1,
1474                .swap_cluster_max = SWAP_CLUSTER_MAX,
1475                .swappiness = vm_swappiness,
1476                .order = order,
1477                .mem_cgroup = NULL,
1478                .isolate_pages = isolate_pages_global,
1479        };
1480        /*
1481         * temp_priority is used to remember the scanning priority at which
1482         * this zone was successfully refilled to free_pages == pages_high.
1483         */
1484        int temp_priority[MAX_NR_ZONES];
1485
1486loop_again:
1487        total_scanned = 0;
1488        nr_reclaimed = 0;
1489        sc.may_writepage = !laptop_mode;
1490        count_vm_event(PAGEOUTRUN);
1491
1492        for (i = 0; i < pgdat->nr_zones; i++)
1493                temp_priority[i] = DEF_PRIORITY;
1494
1495        for (priority = DEF_PRIORITY; priority >= 0; priority--) {
1496                int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
1497                unsigned long lru_pages = 0;
1498
1499                /* The swap token gets in the way of swapout... */
1500                if (!priority)
1501                        disable_swap_token();
1502
1503                all_zones_ok = 1;
1504
1505                /*
1506                 * Scan in the highmem->dma direction for the highest
1507                 * zone which needs scanning
1508                 */
1509                for (i = pgdat->nr_zones - 1; i >= 0; i--) {
1510                        struct zone *zone = pgdat->node_zones + i;
1511
1512                        if (!populated_zone(zone))
1513                                continue;
1514
1515                        if (zone_is_all_unreclaimable(zone) &&
1516                            priority != DEF_PRIORITY)
1517                                continue;
1518
1519                        if (!zone_watermark_ok(zone, order, zone->pages_high,
1520                                               0, 0)) {
1521                                end_zone = i;
1522                                break;
1523                        }
1524                }
1525                if (i < 0)
1526                        goto out;
1527
1528                for (i = 0; i <= end_zone; i++) {
1529                        struct zone *zone = pgdat->node_zones + i;
1530
1531                        lru_pages += zone_page_state(zone, NR_ACTIVE)
1532                                        + zone_page_state(zone, NR_INACTIVE);
1533                }
1534
1535                /*
1536                 * Now scan the zone in the dma->highmem direction, stopping
1537                 * at the last zone which needs scanning.
1538                 *
1539                 * We do this because the page allocator works in the opposite
1540                 * direction.  This prevents the page allocator from allocating
1541                 * pages behind kswapd's direction of progress, which would
1542                 * cause too much scanning of the lower zones.
1543                 */
1544                for (i = 0; i <= end_zone; i++) {
1545                        struct zone *zone = pgdat->node_zones + i;
1546                        int nr_slab;
1547
1548                        if (!populated_zone(zone))
1549                                continue;
1550
1551                        if (zone_is_all_unreclaimable(zone) &&
1552                                        priority != DEF_PRIORITY)
1553                                continue;
1554
1555                        if (!zone_watermark_ok(zone, order, zone->pages_high,
1556                                               end_zone, 0))
1557                                all_zones_ok = 0;
1558                        temp_priority[i] = priority;
1559                        sc.nr_scanned = 0;
1560                        note_zone_scanning_priority(zone, priority);
1561                        /*
1562                         * We put equal pressure on every zone, unless one
1563                         * zone has way too many pages free already.
1564                         */
1565                        if (!zone_watermark_ok(zone, order, 8*zone->pages_high,
1566                                                end_zone, 0))
1567                                nr_reclaimed += shrink_zone(priority, zone, &sc);
1568                        reclaim_state->reclaimed_slab = 0;
1569                        nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL,
1570                                                lru_pages);
1571                        nr_reclaimed += reclaim_state->reclaimed_slab;
1572                        total_scanned += sc.nr_scanned;
1573                        if (zone_is_all_unreclaimable(zone))
1574                                continue;
1575                        if (nr_slab == 0 && zone->pages_scanned >=
1576                                (zone_page_state(zone, NR_ACTIVE)
1577                                + zone_page_state(zone, NR_INACTIVE)) * 6)
1578                                        zone_set_flag(zone,
1579                                                      ZONE_ALL_UNRECLAIMABLE);
1580                        /*
1581                         * If we've done a decent amount of scanning and
1582                         * the reclaim ratio is low, start doing writepage
1583                         * even in laptop mode
1584                         */
1585                        if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
1586                            total_scanned > nr_reclaimed + nr_reclaimed / 2)
1587                                sc.may_writepage = 1;
1588                }
1589                if (all_zones_ok)
1590                        break;          /* kswapd: all done */
1591                /*
1592                 * OK, kswapd is getting into trouble.  Take a nap, then take
1593                 * another pass across the zones.
1594                 */
1595                if (total_scanned && priority < DEF_PRIORITY - 2)
1596                        congestion_wait(WRITE, HZ/10);
1597
1598                /*
1599                 * We do this so kswapd doesn't build up large priorities for
1600                 * example when it is freeing in parallel with allocators. It
1601                 * matches the direct reclaim path behaviour in terms of impact
1602                 * on zone->*_priority.
1603                 */
1604                if (nr_reclaimed >= SWAP_CLUSTER_MAX)
1605                        break;
1606        }
1607out:
1608        /*
1609         * Note within each zone the priority level at which this zone was
1610         * brought into a happy state.  So that the next thread which scans this
1611         * zone will start out at that priority level.
1612         */
1613        for (i = 0; i < pgdat->nr_zones; i++) {
1614                struct zone *zone = pgdat->node_zones + i;
1615
1616                zone->prev_priority = temp_priority[i];
1617        }
1618        if (!all_zones_ok) {
1619                cond_resched();
1620
1621                try_to_freeze();
1622
1623                goto loop_again;
1624        }
1625
1626        return nr_reclaimed;
1627}
1628
1629/*
1630 * The background pageout daemon, started as a kernel thread
1631 * from the init process. 
1632 *
1633 * This basically trickles out pages so that we have _some_
1634 * free memory available even if there is no other activity
1635 * that frees anything up. This is needed for things like routing
1636 * etc, where we otherwise might have all activity going on in
1637 * asynchronous contexts that cannot page things out.
1638 *
1639 * If there are applications that are active memory-allocators
1640 * (most normal use), this basically shouldn't matter.
1641 */
1642static int kswapd(void *p)
1643{
1644        unsigned long order;
1645        pg_data_t *pgdat = (pg_data_t*)p;
1646        struct task_struct *tsk = current;
1647        DEFINE_WAIT(wait);
1648        struct reclaim_state reclaim_state = {
1649                .reclaimed_slab = 0,
1650        };
1651        node_to_cpumask_ptr(cpumask, pgdat->node_id);
1652
1653        if (!cpus_empty(*cpumask))
1654                set_cpus_allowed_ptr(tsk, cpumask);
1655        current->reclaim_state = &reclaim_state;
1656
1657        /*
1658         * Tell the memory management that we're a "memory allocator",
1659         * and that if we need more memory we should get access to it
1660         * regardless (see "__alloc_pages()"). "kswapd" should
1661         * never get caught in the normal page freeing logic.
1662         *
1663         * (Kswapd normally doesn't need memory anyway, but sometimes
1664         * you need a small amount of memory in order to be able to
1665         * page out something else, and this flag essentially protects
1666         * us from recursively trying to free more memory as we're
1667         * trying to free the first piece of memory in the first place).
1668         */
1669        tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
1670        set_freezable();
1671
1672        order = 0;
1673        for ( ; ; ) {
1674                unsigned long new_order;
1675
1676                prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
1677                new_order = pgdat->kswapd_max_order;
1678                pgdat->kswapd_max_order = 0;
1679                if (order < new_order) {
1680                        /*
1681                         * Don't sleep if someone wants a larger 'order'
1682                         * allocation
1683                         */
1684                        order = new_order;
1685                } else {
1686                        if (!freezing(current))
1687                                schedule();
1688
1689                        order = pgdat->kswapd_max_order;
1690                }
1691                finish_wait(&pgdat->kswapd_wait, &wait);
1692
1693                if (!try_to_freeze()) {
1694                        /* We can speed up thawing tasks if we don't call
1695                         * balance_pgdat after returning from the refrigerator
1696                         */
1697                        balance_pgdat(pgdat, order);
1698                }
1699        }
1700        return 0;
1701}
1702
1703/*
1704 * A zone is low on free memory, so wake its kswapd task to service it.
1705 */
1706void wakeup_kswapd(struct zone *zone, int order)
1707{
1708        pg_data_t *pgdat;
1709
1710        if (!populated_zone(zone))
1711                return;
1712
1713        pgdat = zone->zone_pgdat;
1714        if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0))
1715                return;
1716        if (pgdat->kswapd_max_order < order)
1717                pgdat->kswapd_max_order = order;
1718        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1719                return;
1720        if (!waitqueue_active(&pgdat->kswapd_wait))
1721                return;
1722        wake_up_interruptible(&pgdat->kswapd_wait);
1723}
1724
1725#ifdef CONFIG_PM
1726/*
1727 * Helper function for shrink_all_memory().  Tries to reclaim 'nr_pages' pages
1728 * from LRU lists system-wide, for given pass and priority, and returns the
1729 * number of reclaimed pages
1730 *
1731 * For pass > 3 we also try to shrink the LRU lists that contain a few pages
1732 */
1733static unsigned long shrink_all_zones(unsigned long nr_pages, int prio,
1734                                      int pass, struct scan_control *sc)
1735{
1736        struct zone *zone;
1737        unsigned long nr_to_scan, ret = 0;
1738
1739        for_each_zone(zone) {
1740
1741                if (!populated_zone(zone))
1742                        continue;
1743
1744                if (zone_is_all_unreclaimable(zone) && prio != DEF_PRIORITY)
1745                        continue;
1746
1747                /* For pass = 0 we don't shrink the active list */
1748                if (pass > 0) {
1749                        zone->nr_scan_active +=
1750                                (zone_page_state(zone, NR_ACTIVE) >> prio) + 1;
1751                        if (zone->nr_scan_active >= nr_pages || pass > 3) {
1752                                zone->nr_scan_active = 0;
1753                                nr_to_scan = min(nr_pages,
1754                                        zone_page_state(zone, NR_ACTIVE));
1755                                shrink_active_list(nr_to_scan, zone, sc, prio);
1756                        }
1757                }
1758
1759                zone->nr_scan_inactive +=
1760                        (zone_page_state(zone, NR_INACTIVE) >> prio) + 1;
1761                if (zone->nr_scan_inactive >= nr_pages || pass > 3) {
1762                        zone->nr_scan_inactive = 0;
1763                        nr_to_scan = min(nr_pages,
1764                                zone_page_state(zone, NR_INACTIVE));
1765                        ret += shrink_inactive_list(nr_to_scan, zone, sc);
1766                        if (ret >= nr_pages)
1767                                return ret;
1768                }
1769        }
1770
1771        return ret;
1772}
1773
1774static unsigned long count_lru_pages(void)
1775{
1776        return global_page_state(NR_ACTIVE) + global_page_state(NR_INACTIVE);
1777}
1778
1779/*
1780 * Try to free `nr_pages' of memory, system-wide, and return the number of
1781 * freed pages.
1782 *
1783 * Rather than trying to age LRUs the aim is to preserve the overall
1784 * LRU order by reclaiming preferentially
1785 * inactive > active > active referenced > active mapped
1786 */
1787unsigned long shrink_all_memory(unsigned long nr_pages)
1788{
1789        unsigned long lru_pages, nr_slab;
1790        unsigned long ret = 0;
1791        int pass;
1792        struct reclaim_state reclaim_state;
1793        struct scan_control sc = {
1794                .gfp_mask = GFP_KERNEL,
1795                .may_swap = 0,
1796                .swap_cluster_max = nr_pages,
1797                .may_writepage = 1,
1798                .swappiness = vm_swappiness,
1799                .isolate_pages = isolate_pages_global,
1800        };
1801
1802        current->reclaim_state = &reclaim_state;
1803
1804        lru_pages = count_lru_pages();
1805        nr_slab = global_page_state(NR_SLAB_RECLAIMABLE);
1806        /* If slab caches are huge, it's better to hit them first */
1807        while (nr_slab >= lru_pages) {
1808                reclaim_state.reclaimed_slab = 0;
1809                shrink_slab(nr_pages, sc.gfp_mask, lru_pages);
1810                if (!reclaim_state.reclaimed_slab)
1811                        break;
1812
1813                ret += reclaim_state.reclaimed_slab;
1814                if (ret >= nr_pages)
1815                        goto out;
1816
1817                nr_slab -= reclaim_state.reclaimed_slab;
1818        }
1819
1820        /*
1821         * We try to shrink LRUs in 5 passes:
1822         * 0 = Reclaim from inactive_list only
1823         * 1 = Reclaim from active list but don't reclaim mapped
1824         * 2 = 2nd pass of type 1
1825         * 3 = Reclaim mapped (normal reclaim)
1826         * 4 = 2nd pass of type 3
1827         */
1828        for (pass = 0; pass < 5; pass++) {
1829                int prio;
1830
1831                /* Force reclaiming mapped pages in the passes #3 and #4 */
1832                if (pass > 2) {
1833                        sc.may_swap = 1;
1834                        sc.swappiness = 100;
1835                }
1836
1837                for (prio = DEF_PRIORITY; prio >= 0; prio--) {
1838                        unsigned long nr_to_scan = nr_pages - ret;
1839
1840                        sc.nr_scanned = 0;
1841                        ret += shrink_all_zones(nr_to_scan, prio, pass, &sc);
1842                        if (ret >= nr_pages)
1843                                goto out;
1844
1845                        reclaim_state.reclaimed_slab = 0;
1846                        shrink_slab(sc.nr_scanned, sc.gfp_mask,
1847                                        count_lru_pages());
1848                        ret += reclaim_state.reclaimed_slab;
1849                        if (ret >= nr_pages)
1850                                goto out;
1851
1852                        if (sc.nr_scanned && prio < DEF_PRIORITY - 2)
1853                                congestion_wait(WRITE, HZ / 10);
1854                }
1855        }
1856
1857        /*
1858         * If ret = 0, we could not shrink LRUs, but there may be something
1859         * in slab caches
1860         */
1861        if (!ret) {
1862                do {
1863                        reclaim_state.reclaimed_slab = 0;
1864                        shrink_slab(nr_pages, sc.gfp_mask, count_lru_pages());
1865                        ret += reclaim_state.reclaimed_slab;
1866                } while (ret < nr_pages && reclaim_state.reclaimed_slab > 0);
1867        }
1868
1869out:
1870        current->reclaim_state = NULL;
1871
1872        return ret;
1873}
1874#endif
1875
1876/* It's optimal to keep kswapds on the same CPUs as their memory, but
1877   not required for correctness.  So if the last cpu in a node goes
1878   away, we get changed to run anywhere: as the first one comes back,
1879   restore their cpu bindings. */
1880static int __devinit cpu_callback(struct notifier_block *nfb,
1881                                  unsigned long action, void *hcpu)
1882{
1883        int nid;
1884
1885        if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
1886                for_each_node_state(nid, N_HIGH_MEMORY) {
1887                        pg_data_t *pgdat = NODE_DATA(nid);
1888                        node_to_cpumask_ptr(mask, pgdat->node_id);
1889
1890                        if (any_online_cpu(*mask) < nr_cpu_ids)
1891                                /* One of our CPUs online: restore mask */
1892                                set_cpus_allowed_ptr(pgdat->kswapd, mask);
1893                }
1894        }
1895        return NOTIFY_OK;
1896}
1897
1898/*
1899 * This kswapd start function will be called by init and node-hot-add.
1900 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
1901 */
1902int kswapd_run(int nid)
1903{
1904        pg_data_t *pgdat = NODE_DATA(nid);
1905        int ret = 0;
1906
1907        if (pgdat->kswapd)
1908                return 0;
1909
1910        pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
1911        if (IS_ERR(pgdat->kswapd)) {
1912                /* failure at boot is fatal */
1913                BUG_ON(system_state == SYSTEM_BOOTING);
1914                printk("Failed to start kswapd on node %d\n",nid);
1915                ret = -1;
1916        }
1917        return ret;
1918}
1919
1920static int __init kswapd_init(void)
1921{
1922        int nid;
1923
1924        swap_setup();
1925        for_each_node_state(nid, N_HIGH_MEMORY)
1926                kswapd_run(nid);
1927        hotcpu_notifier(cpu_callback, 0);
1928        return 0;
1929}
1930
1931module_init(kswapd_init)
1932
1933#ifdef CONFIG_NUMA
1934/*
1935 * Zone reclaim mode
1936 *
1937 * If non-zero call zone_reclaim when the number of free pages falls below
1938 * the watermarks.
1939 */
1940int zone_reclaim_mode __read_mostly;
1941
1942#define RECLAIM_OFF 0
1943#define RECLAIM_ZONE (1<<0)     /* Run shrink_cache on the zone */
1944#define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
1945#define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
1946
1947/*
1948 * Priority for ZONE_RECLAIM. This determines the fraction of pages
1949 * of a node considered for each zone_reclaim. 4 scans 1/16th of
1950 * a zone.
1951 */
1952#define ZONE_RECLAIM_PRIORITY 4
1953
1954/*
1955 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
1956 * occur.
1957 */
1958int sysctl_min_unmapped_ratio = 1;
1959
1960/*
1961 * If the number of slab pages in a zone grows beyond this percentage then
1962 * slab reclaim needs to occur.
1963 */
1964int sysctl_min_slab_ratio = 5;
1965
1966/*
1967 * Try to free up some pages from this zone through reclaim.
1968 */
1969static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
1970{
1971        /* Minimum pages needed in order to stay on node */
1972        const unsigned long nr_pages = 1 << order;
1973        struct task_struct *p = current;
1974        struct reclaim_state reclaim_state;
1975        int priority;
1976        unsigned long nr_reclaimed = 0;
1977        struct scan_control sc = {
1978                .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
1979                .may_swap = !!(zone_reclaim_mode & RECLAIM_SWAP),
1980                .swap_cluster_max = max_t(unsigned long, nr_pages,
1981                                        SWAP_CLUSTER_MAX),
1982                .gfp_mask = gfp_mask,
1983                .swappiness = vm_swappiness,
1984                .isolate_pages = isolate_pages_global,
1985        };
1986        unsigned long slab_reclaimable;
1987
1988        disable_swap_token();
1989        cond_resched();
1990        /*
1991         * We need to be able to allocate from the reserves for RECLAIM_SWAP
1992         * and we also need to be able to write out pages for RECLAIM_WRITE
1993         * and RECLAIM_SWAP.
1994         */
1995        p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
1996        reclaim_state.reclaimed_slab = 0;
1997        p->reclaim_state = &reclaim_state;
1998
1999        if (zone_page_state(zone, NR_FILE_PAGES) -
2000                zone_page_state(zone, NR_FILE_MAPPED) >
2001                zone->min_unmapped_pages) {
2002                /*
2003                 * Free memory by calling shrink zone with increasing
2004                 * priorities until we have enough memory freed.
2005                 */
2006                priority = ZONE_RECLAIM_PRIORITY;
2007                do {
2008                        note_zone_scanning_priority(zone, priority);
2009                        nr_reclaimed += shrink_zone(priority, zone, &sc);
2010                        priority--;
2011                } while (priority >= 0 && nr_reclaimed < nr_pages);
2012        }
2013
2014        slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
2015        if (slab_reclaimable > zone->min_slab_pages) {
2016                /*
2017                 * shrink_slab() does not currently allow us to determine how
2018                 * many pages were freed in this zone. So we take the current
2019                 * number of slab pages and shake the slab until it is reduced
2020                 * by the same nr_pages that we used for reclaiming unmapped
2021                 * pages.
2022                 *
2023                 * Note that shrink_slab will free memory on all zones and may
2024                 * take a long time.
2025                 */
2026                while (shrink_slab(sc.nr_scanned, gfp_mask, order) &&
2027                        zone_page_state(zone, NR_SLAB_RECLAIMABLE) >
2028                                slab_reclaimable - nr_pages)
2029                        ;
2030
2031                /*
2032                 * Update nr_reclaimed by the number of slab pages we
2033                 * reclaimed from this zone.
2034                 */
2035                nr_reclaimed += slab_reclaimable -
2036                        zone_page_state(zone, NR_SLAB_RECLAIMABLE);
2037        }
2038
2039        p->reclaim_state = NULL;
2040        current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
2041        return nr_reclaimed >= nr_pages;
2042}
2043
2044int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
2045{
2046        int node_id;
2047        int ret;
2048
2049        /*
2050         * Zone reclaim reclaims unmapped file backed pages and
2051         * slab pages if we are over the defined limits.
2052         *
2053         * A small portion of unmapped file backed pages is needed for
2054         * file I/O otherwise pages read by file I/O will be immediately
2055         * thrown out if the zone is overallocated. So we do not reclaim
2056         * if less than a specified percentage of the zone is used by
2057         * unmapped file backed pages.
2058         */
2059        if (zone_page_state(zone, NR_FILE_PAGES) -
2060            zone_page_state(zone, NR_FILE_MAPPED) <= zone->min_unmapped_pages
2061            && zone_page_state(zone, NR_SLAB_RECLAIMABLE)
2062                        <= zone->min_slab_pages)
2063                return 0;
2064
2065        if (zone_is_all_unreclaimable(zone))
2066                return 0;
2067
2068        /*
2069         * Do not scan if the allocation should not be delayed.
2070         */
2071        if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
2072                        return 0;
2073
2074        /*
2075         * Only run zone reclaim on the local zone or on zones that do not
2076         * have associated processors. This will favor the local processor
2077         * over remote processors and spread off node memory allocations
2078         * as wide as possible.
2079         */
2080        node_id = zone_to_nid(zone);
2081        if (node_state(node_id, N_CPU) && node_id != numa_node_id())
2082                return 0;
2083
2084        if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
2085                return 0;
2086        ret = __zone_reclaim(zone, gfp_mask, order);
2087        zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
2088
2089        return ret;
2090}
2091#endif
2092