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/gfp.h>
  17#include <linux/kernel_stat.h>
  18#include <linux/swap.h>
  19#include <linux/pagemap.h>
  20#include <linux/init.h>
  21#include <linux/highmem.h>
  22#include <linux/vmstat.h>
  23#include <linux/file.h>
  24#include <linux/writeback.h>
  25#include <linux/blkdev.h>
  26#include <linux/buffer_head.h>  /* for try_to_release_page(),
  27                                        buffer_heads_over_limit */
  28#include <linux/mm_inline.h>
  29#include <linux/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/compaction.h>
  36#include <linux/notifier.h>
  37#include <linux/rwsem.h>
  38#include <linux/delay.h>
  39#include <linux/kthread.h>
  40#include <linux/freezer.h>
  41#include <linux/memcontrol.h>
  42#include <linux/delayacct.h>
  43#include <linux/sysctl.h>
  44#include <linux/oom.h>
  45#include <linux/prefetch.h>
  46
  47#include <asm/tlbflush.h>
  48#include <asm/div64.h>
  49
  50#include <linux/swapops.h>
  51
  52#include "internal.h"
  53
  54#define CREATE_TRACE_POINTS
  55#include <trace/events/vmscan.h>
  56
  57/*
  58 * reclaim_mode determines how the inactive list is shrunk
  59 * RECLAIM_MODE_SINGLE: Reclaim only order-0 pages
  60 * RECLAIM_MODE_ASYNC:  Do not block
  61 * RECLAIM_MODE_SYNC:   Allow blocking e.g. call wait_on_page_writeback
  62 * RECLAIM_MODE_LUMPYRECLAIM: For high-order allocations, take a reference
  63 *                      page from the LRU and reclaim all pages within a
  64 *                      naturally aligned range
  65 * RECLAIM_MODE_COMPACTION: For high-order allocations, reclaim a number of
  66 *                      order-0 pages and then compact the zone
  67 */
  68typedef unsigned __bitwise__ reclaim_mode_t;
  69#define RECLAIM_MODE_SINGLE             ((__force reclaim_mode_t)0x01u)
  70#define RECLAIM_MODE_ASYNC              ((__force reclaim_mode_t)0x02u)
  71#define RECLAIM_MODE_SYNC               ((__force reclaim_mode_t)0x04u)
  72#define RECLAIM_MODE_LUMPYRECLAIM       ((__force reclaim_mode_t)0x08u)
  73#define RECLAIM_MODE_COMPACTION         ((__force reclaim_mode_t)0x10u)
  74
  75struct scan_control {
  76        /* Incremented by the number of inactive pages that were scanned */
  77        unsigned long nr_scanned;
  78
  79        /* Number of pages freed so far during a call to shrink_zones() */
  80        unsigned long nr_reclaimed;
  81
  82        /* How many pages shrink_list() should reclaim */
  83        unsigned long nr_to_reclaim;
  84
  85        unsigned long hibernation_mode;
  86
  87        /* This context's GFP mask */
  88        gfp_t gfp_mask;
  89
  90        int may_writepage;
  91
  92        /* Can mapped pages be reclaimed? */
  93        int may_unmap;
  94
  95        /* Can pages be swapped as part of reclaim? */
  96        int may_swap;
  97
  98        int order;
  99
 100        /*
 101         * Intend to reclaim enough continuous memory rather than reclaim
 102         * enough amount of memory. i.e, mode for high order allocation.
 103         */
 104        reclaim_mode_t reclaim_mode;
 105
 106        /* Which cgroup do we reclaim from */
 107        struct mem_cgroup *mem_cgroup;
 108
 109        /*
 110         * Nodemask of nodes allowed by the caller. If NULL, all nodes
 111         * are scanned.
 112         */
 113        nodemask_t      *nodemask;
 114};
 115
 116#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
 117
 118#ifdef ARCH_HAS_PREFETCH
 119#define prefetch_prev_lru_page(_page, _base, _field)                    \
 120        do {                                                            \
 121                if ((_page)->lru.prev != _base) {                       \
 122                        struct page *prev;                              \
 123                                                                        \
 124                        prev = lru_to_page(&(_page->lru));              \
 125                        prefetch(&prev->_field);                        \
 126                }                                                       \
 127        } while (0)
 128#else
 129#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
 130#endif
 131
 132#ifdef ARCH_HAS_PREFETCHW
 133#define prefetchw_prev_lru_page(_page, _base, _field)                   \
 134        do {                                                            \
 135                if ((_page)->lru.prev != _base) {                       \
 136                        struct page *prev;                              \
 137                                                                        \
 138                        prev = lru_to_page(&(_page->lru));              \
 139                        prefetchw(&prev->_field);                       \
 140                }                                                       \
 141        } while (0)
 142#else
 143#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
 144#endif
 145
 146/*
 147 * From 0 .. 100.  Higher means more swappy.
 148 */
 149int vm_swappiness = 60;
 150long vm_total_pages;    /* The total number of pages which the VM controls */
 151
 152static LIST_HEAD(shrinker_list);
 153static DECLARE_RWSEM(shrinker_rwsem);
 154
 155#ifdef CONFIG_CGROUP_MEM_RES_CTLR
 156#define scanning_global_lru(sc) (!(sc)->mem_cgroup)
 157#else
 158#define scanning_global_lru(sc) (1)
 159#endif
 160
 161static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
 162                                                  struct scan_control *sc)
 163{
 164        if (!scanning_global_lru(sc))
 165                return mem_cgroup_get_reclaim_stat(sc->mem_cgroup, zone);
 166
 167        return &zone->reclaim_stat;
 168}
 169
 170static unsigned long zone_nr_lru_pages(struct zone *zone,
 171                                struct scan_control *sc, enum lru_list lru)
 172{
 173        if (!scanning_global_lru(sc))
 174                return mem_cgroup_zone_nr_lru_pages(sc->mem_cgroup,
 175                                zone_to_nid(zone), zone_idx(zone), BIT(lru));
 176
 177        return zone_page_state(zone, NR_LRU_BASE + lru);
 178}
 179
 180
 181/*
 182 * Add a shrinker callback to be called from the vm
 183 */
 184void register_shrinker(struct shrinker *shrinker)
 185{
 186        shrinker->nr = 0;
 187        down_write(&shrinker_rwsem);
 188        list_add_tail(&shrinker->list, &shrinker_list);
 189        up_write(&shrinker_rwsem);
 190}
 191EXPORT_SYMBOL(register_shrinker);
 192
 193/*
 194 * Remove one
 195 */
 196void unregister_shrinker(struct shrinker *shrinker)
 197{
 198        down_write(&shrinker_rwsem);
 199        list_del(&shrinker->list);
 200        up_write(&shrinker_rwsem);
 201}
 202EXPORT_SYMBOL(unregister_shrinker);
 203
 204static inline int do_shrinker_shrink(struct shrinker *shrinker,
 205                                     struct shrink_control *sc,
 206                                     unsigned long nr_to_scan)
 207{
 208        sc->nr_to_scan = nr_to_scan;
 209        return (*shrinker->shrink)(shrinker, sc);
 210}
 211
 212#define SHRINK_BATCH 128
 213/*
 214 * Call the shrink functions to age shrinkable caches
 215 *
 216 * Here we assume it costs one seek to replace a lru page and that it also
 217 * takes a seek to recreate a cache object.  With this in mind we age equal
 218 * percentages of the lru and ageable caches.  This should balance the seeks
 219 * generated by these structures.
 220 *
 221 * If the vm encountered mapped pages on the LRU it increase the pressure on
 222 * slab to avoid swapping.
 223 *
 224 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
 225 *
 226 * `lru_pages' represents the number of on-LRU pages in all the zones which
 227 * are eligible for the caller's allocation attempt.  It is used for balancing
 228 * slab reclaim versus page reclaim.
 229 *
 230 * Returns the number of slab objects which we shrunk.
 231 */
 232unsigned long shrink_slab(struct shrink_control *shrink,
 233                          unsigned long nr_pages_scanned,
 234                          unsigned long lru_pages)
 235{
 236        struct shrinker *shrinker;
 237        unsigned long ret = 0;
 238
 239        if (nr_pages_scanned == 0)
 240                nr_pages_scanned = SWAP_CLUSTER_MAX;
 241
 242        if (!down_read_trylock(&shrinker_rwsem)) {
 243                /* Assume we'll be able to shrink next time */
 244                ret = 1;
 245                goto out;
 246        }
 247
 248        list_for_each_entry(shrinker, &shrinker_list, list) {
 249                unsigned long long delta;
 250                unsigned long total_scan;
 251                unsigned long max_pass;
 252                int shrink_ret = 0;
 253                long nr;
 254                long new_nr;
 255                long batch_size = shrinker->batch ? shrinker->batch
 256                                                  : SHRINK_BATCH;
 257
 258                /*
 259                 * copy the current shrinker scan count into a local variable
 260                 * and zero it so that other concurrent shrinker invocations
 261                 * don't also do this scanning work.
 262                 */
 263                do {
 264                        nr = shrinker->nr;
 265                } while (cmpxchg(&shrinker->nr, nr, 0) != nr);
 266
 267                total_scan = nr;
 268                max_pass = do_shrinker_shrink(shrinker, shrink, 0);
 269                delta = (4 * nr_pages_scanned) / shrinker->seeks;
 270                delta *= max_pass;
 271                do_div(delta, lru_pages + 1);
 272                total_scan += delta;
 273                if (total_scan < 0) {
 274                        printk(KERN_ERR "shrink_slab: %pF negative objects to "
 275                               "delete nr=%ld\n",
 276                               shrinker->shrink, total_scan);
 277                        total_scan = max_pass;
 278                }
 279
 280                /*
 281                 * We need to avoid excessive windup on filesystem shrinkers
 282                 * due to large numbers of GFP_NOFS allocations causing the
 283                 * shrinkers to return -1 all the time. This results in a large
 284                 * nr being built up so when a shrink that can do some work
 285                 * comes along it empties the entire cache due to nr >>>
 286                 * max_pass.  This is bad for sustaining a working set in
 287                 * memory.
 288                 *
 289                 * Hence only allow the shrinker to scan the entire cache when
 290                 * a large delta change is calculated directly.
 291                 */
 292                if (delta < max_pass / 4)
 293                        total_scan = min(total_scan, max_pass / 2);
 294
 295                /*
 296                 * Avoid risking looping forever due to too large nr value:
 297                 * never try to free more than twice the estimate number of
 298                 * freeable entries.
 299                 */
 300                if (total_scan > max_pass * 2)
 301                        total_scan = max_pass * 2;
 302
 303                trace_mm_shrink_slab_start(shrinker, shrink, nr,
 304                                        nr_pages_scanned, lru_pages,
 305                                        max_pass, delta, total_scan);
 306
 307                while (total_scan >= batch_size) {
 308                        int nr_before;
 309
 310                        nr_before = do_shrinker_shrink(shrinker, shrink, 0);
 311                        shrink_ret = do_shrinker_shrink(shrinker, shrink,
 312                                                        batch_size);
 313                        if (shrink_ret == -1)
 314                                break;
 315                        if (shrink_ret < nr_before)
 316                                ret += nr_before - shrink_ret;
 317                        count_vm_events(SLABS_SCANNED, batch_size);
 318                        total_scan -= batch_size;
 319
 320                        cond_resched();
 321                }
 322
 323                /*
 324                 * move the unused scan count back into the shrinker in a
 325                 * manner that handles concurrent updates. If we exhausted the
 326                 * scan, there is no need to do an update.
 327                 */
 328                do {
 329                        nr = shrinker->nr;
 330                        new_nr = total_scan + nr;
 331                        if (total_scan <= 0)
 332                                break;
 333                } while (cmpxchg(&shrinker->nr, nr, new_nr) != nr);
 334
 335                trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
 336        }
 337        up_read(&shrinker_rwsem);
 338out:
 339        cond_resched();
 340        return ret;
 341}
 342
 343static void set_reclaim_mode(int priority, struct scan_control *sc,
 344                                   bool sync)
 345{
 346        reclaim_mode_t syncmode = sync ? RECLAIM_MODE_SYNC : RECLAIM_MODE_ASYNC;
 347
 348        /*
 349         * Initially assume we are entering either lumpy reclaim or
 350         * reclaim/compaction.Depending on the order, we will either set the
 351         * sync mode or just reclaim order-0 pages later.
 352         */
 353        if (COMPACTION_BUILD)
 354                sc->reclaim_mode = RECLAIM_MODE_COMPACTION;
 355        else
 356                sc->reclaim_mode = RECLAIM_MODE_LUMPYRECLAIM;
 357
 358        /*
 359         * Avoid using lumpy reclaim or reclaim/compaction if possible by
 360         * restricting when its set to either costly allocations or when
 361         * under memory pressure
 362         */
 363        if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
 364                sc->reclaim_mode |= syncmode;
 365        else if (sc->order && priority < DEF_PRIORITY - 2)
 366                sc->reclaim_mode |= syncmode;
 367        else
 368                sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
 369}
 370
 371static void reset_reclaim_mode(struct scan_control *sc)
 372{
 373        sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
 374}
 375
 376static inline int is_page_cache_freeable(struct page *page)
 377{
 378        /*
 379         * A freeable page cache page is referenced only by the caller
 380         * that isolated the page, the page cache radix tree and
 381         * optional buffer heads at page->private.
 382         */
 383        return page_count(page) - page_has_private(page) == 2;
 384}
 385
 386static int may_write_to_queue(struct backing_dev_info *bdi,
 387                              struct scan_control *sc)
 388{
 389        if (current->flags & PF_SWAPWRITE)
 390                return 1;
 391        if (!bdi_write_congested(bdi))
 392                return 1;
 393        if (bdi == current->backing_dev_info)
 394                return 1;
 395
 396        /* lumpy reclaim for hugepage often need a lot of write */
 397        if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
 398                return 1;
 399        return 0;
 400}
 401
 402/*
 403 * We detected a synchronous write error writing a page out.  Probably
 404 * -ENOSPC.  We need to propagate that into the address_space for a subsequent
 405 * fsync(), msync() or close().
 406 *
 407 * The tricky part is that after writepage we cannot touch the mapping: nothing
 408 * prevents it from being freed up.  But we have a ref on the page and once
 409 * that page is locked, the mapping is pinned.
 410 *
 411 * We're allowed to run sleeping lock_page() here because we know the caller has
 412 * __GFP_FS.
 413 */
 414static void handle_write_error(struct address_space *mapping,
 415                                struct page *page, int error)
 416{
 417        lock_page(page);
 418        if (page_mapping(page) == mapping)
 419                mapping_set_error(mapping, error);
 420        unlock_page(page);
 421}
 422
 423/* possible outcome of pageout() */
 424typedef enum {
 425        /* failed to write page out, page is locked */
 426        PAGE_KEEP,
 427        /* move page to the active list, page is locked */
 428        PAGE_ACTIVATE,
 429        /* page has been sent to the disk successfully, page is unlocked */
 430        PAGE_SUCCESS,
 431        /* page is clean and locked */
 432        PAGE_CLEAN,
 433} pageout_t;
 434
 435/*
 436 * pageout is called by shrink_page_list() for each dirty page.
 437 * Calls ->writepage().
 438 */
 439static pageout_t pageout(struct page *page, struct address_space *mapping,
 440                         struct scan_control *sc)
 441{
 442        /*
 443         * If the page is dirty, only perform writeback if that write
 444         * will be non-blocking.  To prevent this allocation from being
 445         * stalled by pagecache activity.  But note that there may be
 446         * stalls if we need to run get_block().  We could test
 447         * PagePrivate for that.
 448         *
 449         * If this process is currently in __generic_file_aio_write() against
 450         * this page's queue, we can perform writeback even if that
 451         * will block.
 452         *
 453         * If the page is swapcache, write it back even if that would
 454         * block, for some throttling. This happens by accident, because
 455         * swap_backing_dev_info is bust: it doesn't reflect the
 456         * congestion state of the swapdevs.  Easy to fix, if needed.
 457         */
 458        if (!is_page_cache_freeable(page))
 459                return PAGE_KEEP;
 460        if (!mapping) {
 461                /*
 462                 * Some data journaling orphaned pages can have
 463                 * page->mapping == NULL while being dirty with clean buffers.
 464                 */
 465                if (page_has_private(page)) {
 466                        if (try_to_free_buffers(page)) {
 467                                ClearPageDirty(page);
 468                                printk("%s: orphaned page\n", __func__);
 469                                return PAGE_CLEAN;
 470                        }
 471                }
 472                return PAGE_KEEP;
 473        }
 474        if (mapping->a_ops->writepage == NULL)
 475                return PAGE_ACTIVATE;
 476        if (!may_write_to_queue(mapping->backing_dev_info, sc))
 477                return PAGE_KEEP;
 478
 479        if (clear_page_dirty_for_io(page)) {
 480                int res;
 481                struct writeback_control wbc = {
 482                        .sync_mode = WB_SYNC_NONE,
 483                        .nr_to_write = SWAP_CLUSTER_MAX,
 484                        .range_start = 0,
 485                        .range_end = LLONG_MAX,
 486                        .for_reclaim = 1,
 487                };
 488
 489                SetPageReclaim(page);
 490                res = mapping->a_ops->writepage(page, &wbc);
 491                if (res < 0)
 492                        handle_write_error(mapping, page, res);
 493                if (res == AOP_WRITEPAGE_ACTIVATE) {
 494                        ClearPageReclaim(page);
 495                        return PAGE_ACTIVATE;
 496                }
 497
 498                /*
 499                 * Wait on writeback if requested to. This happens when
 500                 * direct reclaiming a large contiguous area and the
 501                 * first attempt to free a range of pages fails.
 502                 */
 503                if (PageWriteback(page) &&
 504                    (sc->reclaim_mode & RECLAIM_MODE_SYNC))
 505                        wait_on_page_writeback(page);
 506
 507                if (!PageWriteback(page)) {
 508                        /* synchronous write or broken a_ops? */
 509                        ClearPageReclaim(page);
 510                }
 511                trace_mm_vmscan_writepage(page,
 512                        trace_reclaim_flags(page, sc->reclaim_mode));
 513                inc_zone_page_state(page, NR_VMSCAN_WRITE);
 514                return PAGE_SUCCESS;
 515        }
 516
 517        return PAGE_CLEAN;
 518}
 519
 520/*
 521 * Same as remove_mapping, but if the page is removed from the mapping, it
 522 * gets returned with a refcount of 0.
 523 */
 524static int __remove_mapping(struct address_space *mapping, struct page *page)
 525{
 526        BUG_ON(!PageLocked(page));
 527        BUG_ON(mapping != page_mapping(page));
 528
 529        spin_lock_irq(&mapping->tree_lock);
 530        /*
 531         * The non racy check for a busy page.
 532         *
 533         * Must be careful with the order of the tests. When someone has
 534         * a ref to the page, it may be possible that they dirty it then
 535         * drop the reference. So if PageDirty is tested before page_count
 536         * here, then the following race may occur:
 537         *
 538         * get_user_pages(&page);
 539         * [user mapping goes away]
 540         * write_to(page);
 541         *                              !PageDirty(page)    [good]
 542         * SetPageDirty(page);
 543         * put_page(page);
 544         *                              !page_count(page)   [good, discard it]
 545         *
 546         * [oops, our write_to data is lost]
 547         *
 548         * Reversing the order of the tests ensures such a situation cannot
 549         * escape unnoticed. The smp_rmb is needed to ensure the page->flags
 550         * load is not satisfied before that of page->_count.
 551         *
 552         * Note that if SetPageDirty is always performed via set_page_dirty,
 553         * and thus under tree_lock, then this ordering is not required.
 554         */
 555        if (!page_freeze_refs(page, 2))
 556                goto cannot_free;
 557        /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
 558        if (unlikely(PageDirty(page))) {
 559                page_unfreeze_refs(page, 2);
 560                goto cannot_free;
 561        }
 562
 563        if (PageSwapCache(page)) {
 564                swp_entry_t swap = { .val = page_private(page) };
 565                __delete_from_swap_cache(page);
 566                spin_unlock_irq(&mapping->tree_lock);
 567                swapcache_free(swap, page);
 568        } else {
 569                void (*freepage)(struct page *);
 570
 571                freepage = mapping->a_ops->freepage;
 572
 573                __delete_from_page_cache(page);
 574                spin_unlock_irq(&mapping->tree_lock);
 575                mem_cgroup_uncharge_cache_page(page);
 576
 577                if (freepage != NULL)
 578                        freepage(page);
 579        }
 580
 581        return 1;
 582
 583cannot_free:
 584        spin_unlock_irq(&mapping->tree_lock);
 585        return 0;
 586}
 587
 588/*
 589 * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
 590 * someone else has a ref on the page, abort and return 0.  If it was
 591 * successfully detached, return 1.  Assumes the caller has a single ref on
 592 * this page.
 593 */
 594int remove_mapping(struct address_space *mapping, struct page *page)
 595{
 596        if (__remove_mapping(mapping, page)) {
 597                /*
 598                 * Unfreezing the refcount with 1 rather than 2 effectively
 599                 * drops the pagecache ref for us without requiring another
 600                 * atomic operation.
 601                 */
 602                page_unfreeze_refs(page, 1);
 603                return 1;
 604        }
 605        return 0;
 606}
 607
 608/**
 609 * putback_lru_page - put previously isolated page onto appropriate LRU list
 610 * @page: page to be put back to appropriate lru list
 611 *
 612 * Add previously isolated @page to appropriate LRU list.
 613 * Page may still be unevictable for other reasons.
 614 *
 615 * lru_lock must not be held, interrupts must be enabled.
 616 */
 617void putback_lru_page(struct page *page)
 618{
 619        int lru;
 620        int active = !!TestClearPageActive(page);
 621        int was_unevictable = PageUnevictable(page);
 622
 623        VM_BUG_ON(PageLRU(page));
 624
 625redo:
 626        ClearPageUnevictable(page);
 627
 628        if (page_evictable(page, NULL)) {
 629                /*
 630                 * For evictable pages, we can use the cache.
 631                 * In event of a race, worst case is we end up with an
 632                 * unevictable page on [in]active list.
 633                 * We know how to handle that.
 634                 */
 635                lru = active + page_lru_base_type(page);
 636                lru_cache_add_lru(page, lru);
 637        } else {
 638                /*
 639                 * Put unevictable pages directly on zone's unevictable
 640                 * list.
 641                 */
 642                lru = LRU_UNEVICTABLE;
 643                add_page_to_unevictable_list(page);
 644                /*
 645                 * When racing with an mlock clearing (page is
 646                 * unlocked), make sure that if the other thread does
 647                 * not observe our setting of PG_lru and fails
 648                 * isolation, we see PG_mlocked cleared below and move
 649                 * the page back to the evictable list.
 650                 *
 651                 * The other side is TestClearPageMlocked().
 652                 */
 653                smp_mb();
 654        }
 655
 656        /*
 657         * page's status can change while we move it among lru. If an evictable
 658         * page is on unevictable list, it never be freed. To avoid that,
 659         * check after we added it to the list, again.
 660         */
 661        if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) {
 662                if (!isolate_lru_page(page)) {
 663                        put_page(page);
 664                        goto redo;
 665                }
 666                /* This means someone else dropped this page from LRU
 667                 * So, it will be freed or putback to LRU again. There is
 668                 * nothing to do here.
 669                 */
 670        }
 671
 672        if (was_unevictable && lru != LRU_UNEVICTABLE)
 673                count_vm_event(UNEVICTABLE_PGRESCUED);
 674        else if (!was_unevictable && lru == LRU_UNEVICTABLE)
 675                count_vm_event(UNEVICTABLE_PGCULLED);
 676
 677        put_page(page);         /* drop ref from isolate */
 678}
 679
 680enum page_references {
 681        PAGEREF_RECLAIM,
 682        PAGEREF_RECLAIM_CLEAN,
 683        PAGEREF_KEEP,
 684        PAGEREF_ACTIVATE,
 685};
 686
 687static enum page_references page_check_references(struct page *page,
 688                                                  struct scan_control *sc)
 689{
 690        int referenced_ptes, referenced_page;
 691        unsigned long vm_flags;
 692
 693        referenced_ptes = page_referenced(page, 1, sc->mem_cgroup, &vm_flags);
 694        referenced_page = TestClearPageReferenced(page);
 695
 696        /* Lumpy reclaim - ignore references */
 697        if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM)
 698                return PAGEREF_RECLAIM;
 699
 700        /*
 701         * Mlock lost the isolation race with us.  Let try_to_unmap()
 702         * move the page to the unevictable list.
 703         */
 704        if (vm_flags & VM_LOCKED)
 705                return PAGEREF_RECLAIM;
 706
 707        if (referenced_ptes) {
 708                if (PageAnon(page))
 709                        return PAGEREF_ACTIVATE;
 710                /*
 711                 * All mapped pages start out with page table
 712                 * references from the instantiating fault, so we need
 713                 * to look twice if a mapped file page is used more
 714                 * than once.
 715                 *
 716                 * Mark it and spare it for another trip around the
 717                 * inactive list.  Another page table reference will
 718                 * lead to its activation.
 719                 *
 720                 * Note: the mark is set for activated pages as well
 721                 * so that recently deactivated but used pages are
 722                 * quickly recovered.
 723                 */
 724                SetPageReferenced(page);
 725
 726                if (referenced_page)
 727                        return PAGEREF_ACTIVATE;
 728
 729                return PAGEREF_KEEP;
 730        }
 731
 732        /* Reclaim if clean, defer dirty pages to writeback */
 733        if (referenced_page && !PageSwapBacked(page))
 734                return PAGEREF_RECLAIM_CLEAN;
 735
 736        return PAGEREF_RECLAIM;
 737}
 738
 739static noinline_for_stack void free_page_list(struct list_head *free_pages)
 740{
 741        struct pagevec freed_pvec;
 742        struct page *page, *tmp;
 743
 744        pagevec_init(&freed_pvec, 1);
 745
 746        list_for_each_entry_safe(page, tmp, free_pages, lru) {
 747                list_del(&page->lru);
 748                if (!pagevec_add(&freed_pvec, page)) {
 749                        __pagevec_free(&freed_pvec);
 750                        pagevec_reinit(&freed_pvec);
 751                }
 752        }
 753
 754        pagevec_free(&freed_pvec);
 755}
 756
 757/*
 758 * shrink_page_list() returns the number of reclaimed pages
 759 */
 760static unsigned long shrink_page_list(struct list_head *page_list,
 761                                      struct zone *zone,
 762                                      struct scan_control *sc)
 763{
 764        LIST_HEAD(ret_pages);
 765        LIST_HEAD(free_pages);
 766        int pgactivate = 0;
 767        unsigned long nr_dirty = 0;
 768        unsigned long nr_congested = 0;
 769        unsigned long nr_reclaimed = 0;
 770
 771        cond_resched();
 772
 773        while (!list_empty(page_list)) {
 774                enum page_references references;
 775                struct address_space *mapping;
 776                struct page *page;
 777                int may_enter_fs;
 778
 779                cond_resched();
 780
 781                page = lru_to_page(page_list);
 782                list_del(&page->lru);
 783
 784                if (!trylock_page(page))
 785                        goto keep;
 786
 787                VM_BUG_ON(PageActive(page));
 788                VM_BUG_ON(page_zone(page) != zone);
 789
 790                sc->nr_scanned++;
 791
 792                if (unlikely(!page_evictable(page, NULL)))
 793                        goto cull_mlocked;
 794
 795                if (!sc->may_unmap && page_mapped(page))
 796                        goto keep_locked;
 797
 798                /* Double the slab pressure for mapped and swapcache pages */
 799                if (page_mapped(page) || PageSwapCache(page))
 800                        sc->nr_scanned++;
 801
 802                may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
 803                        (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 804
 805                if (PageWriteback(page)) {
 806                        /*
 807                         * Synchronous reclaim is performed in two passes,
 808                         * first an asynchronous pass over the list to
 809                         * start parallel writeback, and a second synchronous
 810                         * pass to wait for the IO to complete.  Wait here
 811                         * for any page for which writeback has already
 812                         * started.
 813                         */
 814                        if ((sc->reclaim_mode & RECLAIM_MODE_SYNC) &&
 815                            may_enter_fs)
 816                                wait_on_page_writeback(page);
 817                        else {
 818                                unlock_page(page);
 819                                goto keep_lumpy;
 820                        }
 821                }
 822
 823                references = page_check_references(page, sc);
 824                switch (references) {
 825                case PAGEREF_ACTIVATE:
 826                        goto activate_locked;
 827                case PAGEREF_KEEP:
 828                        goto keep_locked;
 829                case PAGEREF_RECLAIM:
 830                case PAGEREF_RECLAIM_CLEAN:
 831                        ; /* try to reclaim the page below */
 832                }
 833
 834                /*
 835                 * Anonymous process memory has backing store?
 836                 * Try to allocate it some swap space here.
 837                 */
 838                if (PageAnon(page) && !PageSwapCache(page)) {
 839                        if (!(sc->gfp_mask & __GFP_IO))
 840                                goto keep_locked;
 841                        if (!add_to_swap(page))
 842                                goto activate_locked;
 843                        may_enter_fs = 1;
 844                }
 845
 846                mapping = page_mapping(page);
 847
 848                /*
 849                 * The page is mapped into the page tables of one or more
 850                 * processes. Try to unmap it here.
 851                 */
 852                if (page_mapped(page) && mapping) {
 853                        switch (try_to_unmap(page, TTU_UNMAP)) {
 854                        case SWAP_FAIL:
 855                                goto activate_locked;
 856                        case SWAP_AGAIN:
 857                                goto keep_locked;
 858                        case SWAP_MLOCK:
 859                                goto cull_mlocked;
 860                        case SWAP_SUCCESS:
 861                                ; /* try to free the page below */
 862                        }
 863                }
 864
 865                if (PageDirty(page)) {
 866                        nr_dirty++;
 867
 868                        if (references == PAGEREF_RECLAIM_CLEAN)
 869                                goto keep_locked;
 870                        if (!may_enter_fs)
 871                                goto keep_locked;
 872                        if (!sc->may_writepage)
 873                                goto keep_locked;
 874
 875                        /* Page is dirty, try to write it out here */
 876                        switch (pageout(page, mapping, sc)) {
 877                        case PAGE_KEEP:
 878                                nr_congested++;
 879                                goto keep_locked;
 880                        case PAGE_ACTIVATE:
 881                                goto activate_locked;
 882                        case PAGE_SUCCESS:
 883                                if (PageWriteback(page))
 884                                        goto keep_lumpy;
 885                                if (PageDirty(page))
 886                                        goto keep;
 887
 888                                /*
 889                                 * A synchronous write - probably a ramdisk.  Go
 890                                 * ahead and try to reclaim the page.
 891                                 */
 892                                if (!trylock_page(page))
 893                                        goto keep;
 894                                if (PageDirty(page) || PageWriteback(page))
 895                                        goto keep_locked;
 896                                mapping = page_mapping(page);
 897                        case PAGE_CLEAN:
 898                                ; /* try to free the page below */
 899                        }
 900                }
 901
 902                /*
 903                 * If the page has buffers, try to free the buffer mappings
 904                 * associated with this page. If we succeed we try to free
 905                 * the page as well.
 906                 *
 907                 * We do this even if the page is PageDirty().
 908                 * try_to_release_page() does not perform I/O, but it is
 909                 * possible for a page to have PageDirty set, but it is actually
 910                 * clean (all its buffers are clean).  This happens if the
 911                 * buffers were written out directly, with submit_bh(). ext3
 912                 * will do this, as well as the blockdev mapping.
 913                 * try_to_release_page() will discover that cleanness and will
 914                 * drop the buffers and mark the page clean - it can be freed.
 915                 *
 916                 * Rarely, pages can have buffers and no ->mapping.  These are
 917                 * the pages which were not successfully invalidated in
 918                 * truncate_complete_page().  We try to drop those buffers here
 919                 * and if that worked, and the page is no longer mapped into
 920                 * process address space (page_count == 1) it can be freed.
 921                 * Otherwise, leave the page on the LRU so it is swappable.
 922                 */
 923                if (page_has_private(page)) {
 924                        if (!try_to_release_page(page, sc->gfp_mask))
 925                                goto activate_locked;
 926                        if (!mapping && page_count(page) == 1) {
 927                                unlock_page(page);
 928                                if (put_page_testzero(page))
 929                                        goto free_it;
 930                                else {
 931                                        /*
 932                                         * rare race with speculative reference.
 933                                         * the speculative reference will free
 934                                         * this page shortly, so we may
 935                                         * increment nr_reclaimed here (and
 936                                         * leave it off the LRU).
 937                                         */
 938                                        nr_reclaimed++;
 939                                        continue;
 940                                }
 941                        }
 942                }
 943
 944                if (!mapping || !__remove_mapping(mapping, page))
 945                        goto keep_locked;
 946
 947                /*
 948                 * At this point, we have no other references and there is
 949                 * no way to pick any more up (removed from LRU, removed
 950                 * from pagecache). Can use non-atomic bitops now (and
 951                 * we obviously don't have to worry about waking up a process
 952                 * waiting on the page lock, because there are no references.
 953                 */
 954                __clear_page_locked(page);
 955free_it:
 956                nr_reclaimed++;
 957
 958                /*
 959                 * Is there need to periodically free_page_list? It would
 960                 * appear not as the counts should be low
 961                 */
 962                list_add(&page->lru, &free_pages);
 963                continue;
 964
 965cull_mlocked:
 966                if (PageSwapCache(page))
 967                        try_to_free_swap(page);
 968                unlock_page(page);
 969                putback_lru_page(page);
 970                reset_reclaim_mode(sc);
 971                continue;
 972
 973activate_locked:
 974                /* Not a candidate for swapping, so reclaim swap space. */
 975                if (PageSwapCache(page) && vm_swap_full())
 976                        try_to_free_swap(page);
 977                VM_BUG_ON(PageActive(page));
 978                SetPageActive(page);
 979                pgactivate++;
 980keep_locked:
 981                unlock_page(page);
 982keep:
 983                reset_reclaim_mode(sc);
 984keep_lumpy:
 985                list_add(&page->lru, &ret_pages);
 986                VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
 987        }
 988
 989        /*
 990         * Tag a zone as congested if all the dirty pages encountered were
 991         * backed by a congested BDI. In this case, reclaimers should just
 992         * back off and wait for congestion to clear because further reclaim
 993         * will encounter the same problem
 994         */
 995        if (nr_dirty && nr_dirty == nr_congested && scanning_global_lru(sc))
 996                zone_set_flag(zone, ZONE_CONGESTED);
 997
 998        free_page_list(&free_pages);
 999
1000        list_splice(&ret_pages, page_list);
1001        count_vm_events(PGACTIVATE, pgactivate);
1002        return nr_reclaimed;
1003}
1004
1005/*
1006 * Attempt to remove the specified page from its LRU.  Only take this page
1007 * if it is of the appropriate PageActive status.  Pages which are being
1008 * freed elsewhere are also ignored.
1009 *
1010 * page:        page to consider
1011 * mode:        one of the LRU isolation modes defined above
1012 *
1013 * returns 0 on success, -ve errno on failure.
1014 */
1015int __isolate_lru_page(struct page *page, int mode, int file)
1016{
1017        int ret = -EINVAL;
1018
1019        /* Only take pages on the LRU. */
1020        if (!PageLRU(page))
1021                return ret;
1022
1023        /*
1024         * When checking the active state, we need to be sure we are
1025         * dealing with comparible boolean values.  Take the logical not
1026         * of each.
1027         */
1028        if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode))
1029                return ret;
1030
1031        if (mode != ISOLATE_BOTH && page_is_file_cache(page) != file)
1032                return ret;
1033
1034        /*
1035         * When this function is being called for lumpy reclaim, we
1036         * initially look into all LRU pages, active, inactive and
1037         * unevictable; only give shrink_page_list evictable pages.
1038         */
1039        if (PageUnevictable(page))
1040                return ret;
1041
1042        ret = -EBUSY;
1043
1044        if (likely(get_page_unless_zero(page))) {
1045                /*
1046                 * Be careful not to clear PageLRU until after we're
1047                 * sure the page is not being freed elsewhere -- the
1048                 * page release code relies on it.
1049                 */
1050                ClearPageLRU(page);
1051                ret = 0;
1052        }
1053
1054        return ret;
1055}
1056
1057/*
1058 * zone->lru_lock is heavily contended.  Some of the functions that
1059 * shrink the lists perform better by taking out a batch of pages
1060 * and working on them outside the LRU lock.
1061 *
1062 * For pagecache intensive workloads, this function is the hottest
1063 * spot in the kernel (apart from copy_*_user functions).
1064 *
1065 * Appropriate locks must be held before calling this function.
1066 *
1067 * @nr_to_scan: The number of pages to look through on the list.
1068 * @src:        The LRU list to pull pages off.
1069 * @dst:        The temp list to put pages on to.
1070 * @scanned:    The number of pages that were scanned.
1071 * @order:      The caller's attempted allocation order
1072 * @mode:       One of the LRU isolation modes
1073 * @file:       True [1] if isolating file [!anon] pages
1074 *
1075 * returns how many pages were moved onto *@dst.
1076 */
1077static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1078                struct list_head *src, struct list_head *dst,
1079                unsigned long *scanned, int order, int mode, int file)
1080{
1081        unsigned long nr_taken = 0;
1082        unsigned long nr_lumpy_taken = 0;
1083        unsigned long nr_lumpy_dirty = 0;
1084        unsigned long nr_lumpy_failed = 0;
1085        unsigned long scan;
1086
1087        for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1088                struct page *page;
1089                unsigned long pfn;
1090                unsigned long end_pfn;
1091                unsigned long page_pfn;
1092                int zone_id;
1093
1094                page = lru_to_page(src);
1095                prefetchw_prev_lru_page(page, src, flags);
1096
1097                VM_BUG_ON(!PageLRU(page));
1098
1099                switch (__isolate_lru_page(page, mode, file)) {
1100                case 0:
1101                        list_move(&page->lru, dst);
1102                        mem_cgroup_del_lru(page);
1103                        nr_taken += hpage_nr_pages(page);
1104                        break;
1105
1106                case -EBUSY:
1107                        /* else it is being freed elsewhere */
1108                        list_move(&page->lru, src);
1109                        mem_cgroup_rotate_lru_list(page, page_lru(page));
1110                        continue;
1111
1112                default:
1113                        BUG();
1114                }
1115
1116                if (!order)
1117                        continue;
1118
1119                /*
1120                 * Attempt to take all pages in the order aligned region
1121                 * surrounding the tag page.  Only take those pages of
1122                 * the same active state as that tag page.  We may safely
1123                 * round the target page pfn down to the requested order
1124                 * as the mem_map is guaranteed valid out to MAX_ORDER,
1125                 * where that page is in a different zone we will detect
1126                 * it from its zone id and abort this block scan.
1127                 */
1128                zone_id = page_zone_id(page);
1129                page_pfn = page_to_pfn(page);
1130                pfn = page_pfn & ~((1 << order) - 1);
1131                end_pfn = pfn + (1 << order);
1132                for (; pfn < end_pfn; pfn++) {
1133                        struct page *cursor_page;
1134
1135                        /* The target page is in the block, ignore it. */
1136                        if (unlikely(pfn == page_pfn))
1137                                continue;
1138
1139                        /* Avoid holes within the zone. */
1140                        if (unlikely(!pfn_valid_within(pfn)))
1141                                break;
1142
1143                        cursor_page = pfn_to_page(pfn);
1144
1145                        /* Check that we have not crossed a zone boundary. */
1146                        if (unlikely(page_zone_id(cursor_page) != zone_id))
1147                                break;
1148
1149                        /*
1150                         * If we don't have enough swap space, reclaiming of
1151                         * anon page which don't already have a swap slot is
1152                         * pointless.
1153                         */
1154                        if (nr_swap_pages <= 0 && PageAnon(cursor_page) &&
1155                            !PageSwapCache(cursor_page))
1156                                break;
1157
1158                        if (__isolate_lru_page(cursor_page, mode, file) == 0) {
1159                                list_move(&cursor_page->lru, dst);
1160                                mem_cgroup_del_lru(cursor_page);
1161                                nr_taken += hpage_nr_pages(page);
1162                                nr_lumpy_taken++;
1163                                if (PageDirty(cursor_page))
1164                                        nr_lumpy_dirty++;
1165                                scan++;
1166                        } else {
1167                                /*
1168                                 * Check if the page is freed already.
1169                                 *
1170                                 * We can't use page_count() as that
1171                                 * requires compound_head and we don't
1172                                 * have a pin on the page here. If a
1173                                 * page is tail, we may or may not
1174                                 * have isolated the head, so assume
1175                                 * it's not free, it'd be tricky to
1176                                 * track the head status without a
1177                                 * page pin.
1178                                 */
1179                                if (!PageTail(cursor_page) &&
1180                                    !atomic_read(&cursor_page->_count))
1181                                        continue;
1182                                break;
1183                        }
1184                }
1185
1186                /* If we break out of the loop above, lumpy reclaim failed */
1187                if (pfn < end_pfn)
1188                        nr_lumpy_failed++;
1189        }
1190
1191        *scanned = scan;
1192
1193        trace_mm_vmscan_lru_isolate(order,
1194                        nr_to_scan, scan,
1195                        nr_taken,
1196                        nr_lumpy_taken, nr_lumpy_dirty, nr_lumpy_failed,
1197                        mode);
1198        return nr_taken;
1199}
1200
1201static unsigned long isolate_pages_global(unsigned long nr,
1202                                        struct list_head *dst,
1203                                        unsigned long *scanned, int order,
1204                                        int mode, struct zone *z,
1205                                        int active, int file)
1206{
1207        int lru = LRU_BASE;
1208        if (active)
1209                lru += LRU_ACTIVE;
1210        if (file)
1211                lru += LRU_FILE;
1212        return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order,
1213                                                                mode, file);
1214}
1215
1216/*
1217 * clear_active_flags() is a helper for shrink_active_list(), clearing
1218 * any active bits from the pages in the list.
1219 */
1220static unsigned long clear_active_flags(struct list_head *page_list,
1221                                        unsigned int *count)
1222{
1223        int nr_active = 0;
1224        int lru;
1225        struct page *page;
1226
1227        list_for_each_entry(page, page_list, lru) {
1228                int numpages = hpage_nr_pages(page);
1229                lru = page_lru_base_type(page);
1230                if (PageActive(page)) {
1231                        lru += LRU_ACTIVE;
1232                        ClearPageActive(page);
1233                        nr_active += numpages;
1234                }
1235                if (count)
1236                        count[lru] += numpages;
1237        }
1238
1239        return nr_active;
1240}
1241
1242/**
1243 * isolate_lru_page - tries to isolate a page from its LRU list
1244 * @page: page to isolate from its LRU list
1245 *
1246 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1247 * vmstat statistic corresponding to whatever LRU list the page was on.
1248 *
1249 * Returns 0 if the page was removed from an LRU list.
1250 * Returns -EBUSY if the page was not on an LRU list.
1251 *
1252 * The returned page will have PageLRU() cleared.  If it was found on
1253 * the active list, it will have PageActive set.  If it was found on
1254 * the unevictable list, it will have the PageUnevictable bit set. That flag
1255 * may need to be cleared by the caller before letting the page go.
1256 *
1257 * The vmstat statistic corresponding to the list on which the page was
1258 * found will be decremented.
1259 *
1260 * Restrictions:
1261 * (1) Must be called with an elevated refcount on the page. This is a
1262 *     fundamentnal difference from isolate_lru_pages (which is called
1263 *     without a stable reference).
1264 * (2) the lru_lock must not be held.
1265 * (3) interrupts must be enabled.
1266 */
1267int isolate_lru_page(struct page *page)
1268{
1269        int ret = -EBUSY;
1270
1271        VM_BUG_ON(!page_count(page));
1272
1273        if (PageLRU(page)) {
1274                struct zone *zone = page_zone(page);
1275
1276                spin_lock_irq(&zone->lru_lock);
1277                if (PageLRU(page)) {
1278                        int lru = page_lru(page);
1279                        ret = 0;
1280                        get_page(page);
1281                        ClearPageLRU(page);
1282
1283                        del_page_from_lru_list(zone, page, lru);
1284                }
1285                spin_unlock_irq(&zone->lru_lock);
1286        }
1287        return ret;
1288}
1289
1290/*
1291 * Are there way too many processes in the direct reclaim path already?
1292 */
1293static int too_many_isolated(struct zone *zone, int file,
1294                struct scan_control *sc)
1295{
1296        unsigned long inactive, isolated;
1297
1298        if (current_is_kswapd())
1299                return 0;
1300
1301        if (!scanning_global_lru(sc))
1302                return 0;
1303
1304        if (file) {
1305                inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1306                isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1307        } else {
1308                inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1309                isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1310        }
1311
1312        return isolated > inactive;
1313}
1314
1315/*
1316 * TODO: Try merging with migrations version of putback_lru_pages
1317 */
1318static noinline_for_stack void
1319putback_lru_pages(struct zone *zone, struct scan_control *sc,
1320                                unsigned long nr_anon, unsigned long nr_file,
1321                                struct list_head *page_list)
1322{
1323        struct page *page;
1324        struct pagevec pvec;
1325        struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1326
1327        pagevec_init(&pvec, 1);
1328
1329        /*
1330         * Put back any unfreeable pages.
1331         */
1332        spin_lock(&zone->lru_lock);
1333        while (!list_empty(page_list)) {
1334                int lru;
1335                page = lru_to_page(page_list);
1336                VM_BUG_ON(PageLRU(page));
1337                list_del(&page->lru);
1338                if (unlikely(!page_evictable(page, NULL))) {
1339                        spin_unlock_irq(&zone->lru_lock);
1340                        putback_lru_page(page);
1341                        spin_lock_irq(&zone->lru_lock);
1342                        continue;
1343                }
1344                SetPageLRU(page);
1345                lru = page_lru(page);
1346                add_page_to_lru_list(zone, page, lru);
1347                if (is_active_lru(lru)) {
1348                        int file = is_file_lru(lru);
1349                        int numpages = hpage_nr_pages(page);
1350                        reclaim_stat->recent_rotated[file] += numpages;
1351                }
1352                if (!pagevec_add(&pvec, page)) {
1353                        spin_unlock_irq(&zone->lru_lock);
1354                        __pagevec_release(&pvec);
1355                        spin_lock_irq(&zone->lru_lock);
1356                }
1357        }
1358        __mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon);
1359        __mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file);
1360
1361        spin_unlock_irq(&zone->lru_lock);
1362        pagevec_release(&pvec);
1363}
1364
1365static noinline_for_stack void update_isolated_counts(struct zone *zone,
1366                                        struct scan_control *sc,
1367                                        unsigned long *nr_anon,
1368                                        unsigned long *nr_file,
1369                                        struct list_head *isolated_list)
1370{
1371        unsigned long nr_active;
1372        unsigned int count[NR_LRU_LISTS] = { 0, };
1373        struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1374
1375        nr_active = clear_active_flags(isolated_list, count);
1376        __count_vm_events(PGDEACTIVATE, nr_active);
1377
1378        __mod_zone_page_state(zone, NR_ACTIVE_FILE,
1379                              -count[LRU_ACTIVE_FILE]);
1380        __mod_zone_page_state(zone, NR_INACTIVE_FILE,
1381                              -count[LRU_INACTIVE_FILE]);
1382        __mod_zone_page_state(zone, NR_ACTIVE_ANON,
1383                              -count[LRU_ACTIVE_ANON]);
1384        __mod_zone_page_state(zone, NR_INACTIVE_ANON,
1385                              -count[LRU_INACTIVE_ANON]);
1386
1387        *nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
1388        *nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
1389        __mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon);
1390        __mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file);
1391
1392        reclaim_stat->recent_scanned[0] += *nr_anon;
1393        reclaim_stat->recent_scanned[1] += *nr_file;
1394}
1395
1396/*
1397 * Returns true if the caller should wait to clean dirty/writeback pages.
1398 *
1399 * If we are direct reclaiming for contiguous pages and we do not reclaim
1400 * everything in the list, try again and wait for writeback IO to complete.
1401 * This will stall high-order allocations noticeably. Only do that when really
1402 * need to free the pages under high memory pressure.
1403 */
1404static inline bool should_reclaim_stall(unsigned long nr_taken,
1405                                        unsigned long nr_freed,
1406                                        int priority,
1407                                        struct scan_control *sc)
1408{
1409        int lumpy_stall_priority;
1410
1411        /* kswapd should not stall on sync IO */
1412        if (current_is_kswapd())
1413                return false;
1414
1415        /* Only stall on lumpy reclaim */
1416        if (sc->reclaim_mode & RECLAIM_MODE_SINGLE)
1417                return false;
1418
1419        /* If we have relaimed everything on the isolated list, no stall */
1420        if (nr_freed == nr_taken)
1421                return false;
1422
1423        /*
1424         * For high-order allocations, there are two stall thresholds.
1425         * High-cost allocations stall immediately where as lower
1426         * order allocations such as stacks require the scanning
1427         * priority to be much higher before stalling.
1428         */
1429        if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
1430                lumpy_stall_priority = DEF_PRIORITY;
1431        else
1432                lumpy_stall_priority = DEF_PRIORITY / 3;
1433
1434        return priority <= lumpy_stall_priority;
1435}
1436
1437/*
1438 * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
1439 * of reclaimed pages
1440 */
1441static noinline_for_stack unsigned long
1442shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone,
1443                        struct scan_control *sc, int priority, int file)
1444{
1445        LIST_HEAD(page_list);
1446        unsigned long nr_scanned;
1447        unsigned long nr_reclaimed = 0;
1448        unsigned long nr_taken;
1449        unsigned long nr_anon;
1450        unsigned long nr_file;
1451
1452        while (unlikely(too_many_isolated(zone, file, sc))) {
1453                congestion_wait(BLK_RW_ASYNC, HZ/10);
1454
1455                /* We are about to die and free our memory. Return now. */
1456                if (fatal_signal_pending(current))
1457                        return SWAP_CLUSTER_MAX;
1458        }
1459
1460        set_reclaim_mode(priority, sc, false);
1461        lru_add_drain();
1462        spin_lock_irq(&zone->lru_lock);
1463
1464        if (scanning_global_lru(sc)) {
1465                nr_taken = isolate_pages_global(nr_to_scan,
1466                        &page_list, &nr_scanned, sc->order,
1467                        sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ?
1468                                        ISOLATE_BOTH : ISOLATE_INACTIVE,
1469                        zone, 0, file);
1470                zone->pages_scanned += nr_scanned;
1471                if (current_is_kswapd())
1472                        __count_zone_vm_events(PGSCAN_KSWAPD, zone,
1473                                               nr_scanned);
1474                else
1475                        __count_zone_vm_events(PGSCAN_DIRECT, zone,
1476                                               nr_scanned);
1477        } else {
1478                nr_taken = mem_cgroup_isolate_pages(nr_to_scan,
1479                        &page_list, &nr_scanned, sc->order,
1480                        sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ?
1481                                        ISOLATE_BOTH : ISOLATE_INACTIVE,
1482                        zone, sc->mem_cgroup,
1483                        0, file);
1484                /*
1485                 * mem_cgroup_isolate_pages() keeps track of
1486                 * scanned pages on its own.
1487                 */
1488        }
1489
1490        if (nr_taken == 0) {
1491                spin_unlock_irq(&zone->lru_lock);
1492                return 0;
1493        }
1494
1495        update_isolated_counts(zone, sc, &nr_anon, &nr_file, &page_list);
1496
1497        spin_unlock_irq(&zone->lru_lock);
1498
1499        nr_reclaimed = shrink_page_list(&page_list, zone, sc);
1500
1501        /* Check if we should syncronously wait for writeback */
1502        if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) {
1503                set_reclaim_mode(priority, sc, true);
1504                nr_reclaimed += shrink_page_list(&page_list, zone, sc);
1505        }
1506
1507        local_irq_disable();
1508        if (current_is_kswapd())
1509                __count_vm_events(KSWAPD_STEAL, nr_reclaimed);
1510        __count_zone_vm_events(PGSTEAL, zone, nr_reclaimed);
1511
1512        putback_lru_pages(zone, sc, nr_anon, nr_file, &page_list);
1513
1514        trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1515                zone_idx(zone),
1516                nr_scanned, nr_reclaimed,
1517                priority,
1518                trace_shrink_flags(file, sc->reclaim_mode));
1519        return nr_reclaimed;
1520}
1521
1522/*
1523 * This moves pages from the active list to the inactive list.
1524 *
1525 * We move them the other way if the page is referenced by one or more
1526 * processes, from rmap.
1527 *
1528 * If the pages are mostly unmapped, the processing is fast and it is
1529 * appropriate to hold zone->lru_lock across the whole operation.  But if
1530 * the pages are mapped, the processing is slow (page_referenced()) so we
1531 * should drop zone->lru_lock around each page.  It's impossible to balance
1532 * this, so instead we remove the pages from the LRU while processing them.
1533 * It is safe to rely on PG_active against the non-LRU pages in here because
1534 * nobody will play with that bit on a non-LRU page.
1535 *
1536 * The downside is that we have to touch page->_count against each page.
1537 * But we had to alter page->flags anyway.
1538 */
1539
1540static void move_active_pages_to_lru(struct zone *zone,
1541                                     struct list_head *list,
1542                                     enum lru_list lru)
1543{
1544        unsigned long pgmoved = 0;
1545        struct pagevec pvec;
1546        struct page *page;
1547
1548        pagevec_init(&pvec, 1);
1549
1550        while (!list_empty(list)) {
1551                page = lru_to_page(list);
1552
1553                VM_BUG_ON(PageLRU(page));
1554                SetPageLRU(page);
1555
1556                list_move(&page->lru, &zone->lru[lru].list);
1557                mem_cgroup_add_lru_list(page, lru);
1558                pgmoved += hpage_nr_pages(page);
1559
1560                if (!pagevec_add(&pvec, page) || list_empty(list)) {
1561                        spin_unlock_irq(&zone->lru_lock);
1562                        if (buffer_heads_over_limit)
1563                                pagevec_strip(&pvec);
1564                        __pagevec_release(&pvec);
1565                        spin_lock_irq(&zone->lru_lock);
1566                }
1567        }
1568        __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1569        if (!is_active_lru(lru))
1570                __count_vm_events(PGDEACTIVATE, pgmoved);
1571}
1572
1573static void shrink_active_list(unsigned long nr_pages, struct zone *zone,
1574                        struct scan_control *sc, int priority, int file)
1575{
1576        unsigned long nr_taken;
1577        unsigned long pgscanned;
1578        unsigned long vm_flags;
1579        LIST_HEAD(l_hold);      /* The pages which were snipped off */
1580        LIST_HEAD(l_active);
1581        LIST_HEAD(l_inactive);
1582        struct page *page;
1583        struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1584        unsigned long nr_rotated = 0;
1585
1586        lru_add_drain();
1587        spin_lock_irq(&zone->lru_lock);
1588        if (scanning_global_lru(sc)) {
1589                nr_taken = isolate_pages_global(nr_pages, &l_hold,
1590                                                &pgscanned, sc->order,
1591                                                ISOLATE_ACTIVE, zone,
1592                                                1, file);
1593                zone->pages_scanned += pgscanned;
1594        } else {
1595                nr_taken = mem_cgroup_isolate_pages(nr_pages, &l_hold,
1596                                                &pgscanned, sc->order,
1597                                                ISOLATE_ACTIVE, zone,
1598                                                sc->mem_cgroup, 1, file);
1599                /*
1600                 * mem_cgroup_isolate_pages() keeps track of
1601                 * scanned pages on its own.
1602                 */
1603        }
1604
1605        reclaim_stat->recent_scanned[file] += nr_taken;
1606
1607        __count_zone_vm_events(PGREFILL, zone, pgscanned);
1608        if (file)
1609                __mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken);
1610        else
1611                __mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken);
1612        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1613        spin_unlock_irq(&zone->lru_lock);
1614
1615        while (!list_empty(&l_hold)) {
1616                cond_resched();
1617                page = lru_to_page(&l_hold);
1618                list_del(&page->lru);
1619
1620                if (unlikely(!page_evictable(page, NULL))) {
1621                        putback_lru_page(page);
1622                        continue;
1623                }
1624
1625                if (page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) {
1626                        nr_rotated += hpage_nr_pages(page);
1627                        /*
1628                         * Identify referenced, file-backed active pages and
1629                         * give them one more trip around the active list. So
1630                         * that executable code get better chances to stay in
1631                         * memory under moderate memory pressure.  Anon pages
1632                         * are not likely to be evicted by use-once streaming
1633                         * IO, plus JVM can create lots of anon VM_EXEC pages,
1634                         * so we ignore them here.
1635                         */
1636                        if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1637                                list_add(&page->lru, &l_active);
1638                                continue;
1639                        }
1640                }
1641
1642                ClearPageActive(page);  /* we are de-activating */
1643                list_add(&page->lru, &l_inactive);
1644        }
1645
1646        /*
1647         * Move pages back to the lru list.
1648         */
1649        spin_lock_irq(&zone->lru_lock);
1650        /*
1651         * Count referenced pages from currently used mappings as rotated,
1652         * even though only some of them are actually re-activated.  This
1653         * helps balance scan pressure between file and anonymous pages in
1654         * get_scan_ratio.
1655         */
1656        reclaim_stat->recent_rotated[file] += nr_rotated;
1657
1658        move_active_pages_to_lru(zone, &l_active,
1659                                                LRU_ACTIVE + file * LRU_FILE);
1660        move_active_pages_to_lru(zone, &l_inactive,
1661                                                LRU_BASE   + file * LRU_FILE);
1662        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1663        spin_unlock_irq(&zone->lru_lock);
1664}
1665
1666#ifdef CONFIG_SWAP
1667static int inactive_anon_is_low_global(struct zone *zone)
1668{
1669        unsigned long active, inactive;
1670
1671        active = zone_page_state(zone, NR_ACTIVE_ANON);
1672        inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1673
1674        if (inactive * zone->inactive_ratio < active)
1675                return 1;
1676
1677        return 0;
1678}
1679
1680/**
1681 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1682 * @zone: zone to check
1683 * @sc:   scan control of this context
1684 *
1685 * Returns true if the zone does not have enough inactive anon pages,
1686 * meaning some active anon pages need to be deactivated.
1687 */
1688static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc)
1689{
1690        int low;
1691
1692        /*
1693         * If we don't have swap space, anonymous page deactivation
1694         * is pointless.
1695         */
1696        if (!total_swap_pages)
1697                return 0;
1698
1699        if (scanning_global_lru(sc))
1700                low = inactive_anon_is_low_global(zone);
1701        else
1702                low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup);
1703        return low;
1704}
1705#else
1706static inline int inactive_anon_is_low(struct zone *zone,
1707                                        struct scan_control *sc)
1708{
1709        return 0;
1710}
1711#endif
1712
1713static int inactive_file_is_low_global(struct zone *zone)
1714{
1715        unsigned long active, inactive;
1716
1717        active = zone_page_state(zone, NR_ACTIVE_FILE);
1718        inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1719
1720        return (active > inactive);
1721}
1722
1723/**
1724 * inactive_file_is_low - check if file pages need to be deactivated
1725 * @zone: zone to check
1726 * @sc:   scan control of this context
1727 *
1728 * When the system is doing streaming IO, memory pressure here
1729 * ensures that active file pages get deactivated, until more
1730 * than half of the file pages are on the inactive list.
1731 *
1732 * Once we get to that situation, protect the system's working
1733 * set from being evicted by disabling active file page aging.
1734 *
1735 * This uses a different ratio than the anonymous pages, because
1736 * the page cache uses a use-once replacement algorithm.
1737 */
1738static int inactive_file_is_low(struct zone *zone, struct scan_control *sc)
1739{
1740        int low;
1741
1742        if (scanning_global_lru(sc))
1743                low = inactive_file_is_low_global(zone);
1744        else
1745                low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup);
1746        return low;
1747}
1748
1749static int inactive_list_is_low(struct zone *zone, struct scan_control *sc,
1750                                int file)
1751{
1752        if (file)
1753                return inactive_file_is_low(zone, sc);
1754        else
1755                return inactive_anon_is_low(zone, sc);
1756}
1757
1758static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1759        struct zone *zone, struct scan_control *sc, int priority)
1760{
1761        int file = is_file_lru(lru);
1762
1763        if (is_active_lru(lru)) {
1764                if (inactive_list_is_low(zone, sc, file))
1765                    shrink_active_list(nr_to_scan, zone, sc, priority, file);
1766                return 0;
1767        }
1768
1769        return shrink_inactive_list(nr_to_scan, zone, sc, priority, file);
1770}
1771
1772static int vmscan_swappiness(struct scan_control *sc)
1773{
1774        if (scanning_global_lru(sc))
1775                return vm_swappiness;
1776        return mem_cgroup_swappiness(sc->mem_cgroup);
1777}
1778
1779/*
1780 * Determine how aggressively the anon and file LRU lists should be
1781 * scanned.  The relative value of each set of LRU lists is determined
1782 * by looking at the fraction of the pages scanned we did rotate back
1783 * onto the active list instead of evict.
1784 *
1785 * nr[0] = anon pages to scan; nr[1] = file pages to scan
1786 */
1787static void get_scan_count(struct zone *zone, struct scan_control *sc,
1788                                        unsigned long *nr, int priority)
1789{
1790        unsigned long anon, file, free;
1791        unsigned long anon_prio, file_prio;
1792        unsigned long ap, fp;
1793        struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
1794        u64 fraction[2], denominator;
1795        enum lru_list l;
1796        int noswap = 0;
1797        bool force_scan = false;
1798        unsigned long nr_force_scan[2];
1799
1800        /* kswapd does zone balancing and needs to scan this zone */
1801        if (scanning_global_lru(sc) && current_is_kswapd())
1802                force_scan = true;
1803        /* memcg may have small limit and need to avoid priority drop */
1804        if (!scanning_global_lru(sc))
1805                force_scan = true;
1806
1807        /* If we have no swap space, do not bother scanning anon pages. */
1808        if (!sc->may_swap || (nr_swap_pages <= 0)) {
1809                noswap = 1;
1810                fraction[0] = 0;
1811                fraction[1] = 1;
1812                denominator = 1;
1813                nr_force_scan[0] = 0;
1814                nr_force_scan[1] = SWAP_CLUSTER_MAX;
1815                goto out;
1816        }
1817
1818        anon  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
1819                zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
1820        file  = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
1821                zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
1822
1823        if (scanning_global_lru(sc)) {
1824                free  = zone_page_state(zone, NR_FREE_PAGES);
1825                /* If we have very few page cache pages,
1826                   force-scan anon pages. */
1827                if (unlikely(file + free <= high_wmark_pages(zone))) {
1828                        fraction[0] = 1;
1829                        fraction[1] = 0;
1830                        denominator = 1;
1831                        nr_force_scan[0] = SWAP_CLUSTER_MAX;
1832                        nr_force_scan[1] = 0;
1833                        goto out;
1834                }
1835        }
1836
1837        /*
1838         * With swappiness at 100, anonymous and file have the same priority.
1839         * This scanning priority is essentially the inverse of IO cost.
1840         */
1841        anon_prio = vmscan_swappiness(sc);
1842        file_prio = 200 - vmscan_swappiness(sc);
1843
1844        /*
1845         * OK, so we have swap space and a fair amount of page cache
1846         * pages.  We use the recently rotated / recently scanned
1847         * ratios to determine how valuable each cache is.
1848         *
1849         * Because workloads change over time (and to avoid overflow)
1850         * we keep these statistics as a floating average, which ends
1851         * up weighing recent references more than old ones.
1852         *
1853         * anon in [0], file in [1]
1854         */
1855        spin_lock_irq(&zone->lru_lock);
1856        if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1857                reclaim_stat->recent_scanned[0] /= 2;
1858                reclaim_stat->recent_rotated[0] /= 2;
1859        }
1860
1861        if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1862                reclaim_stat->recent_scanned[1] /= 2;
1863                reclaim_stat->recent_rotated[1] /= 2;
1864        }
1865
1866        /*
1867         * The amount of pressure on anon vs file pages is inversely
1868         * proportional to the fraction of recently scanned pages on
1869         * each list that were recently referenced and in active use.
1870         */
1871        ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1);
1872        ap /= reclaim_stat->recent_rotated[0] + 1;
1873
1874        fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1);
1875        fp /= reclaim_stat->recent_rotated[1] + 1;
1876        spin_unlock_irq(&zone->lru_lock);
1877
1878        fraction[0] = ap;
1879        fraction[1] = fp;
1880        denominator = ap + fp + 1;
1881        if (force_scan) {
1882                unsigned long scan = SWAP_CLUSTER_MAX;
1883                nr_force_scan[0] = div64_u64(scan * ap, denominator);
1884                nr_force_scan[1] = div64_u64(scan * fp, denominator);
1885        }
1886out:
1887        for_each_evictable_lru(l) {
1888                int file = is_file_lru(l);
1889                unsigned long scan;
1890
1891                scan = zone_nr_lru_pages(zone, sc, l);
1892                if (priority || noswap) {
1893                        scan >>= priority;
1894                        scan = div64_u64(scan * fraction[file], denominator);
1895                }
1896
1897                /*
1898                 * If zone is small or memcg is small, nr[l] can be 0.
1899                 * This results no-scan on this priority and priority drop down.
1900                 * For global direct reclaim, it can visit next zone and tend
1901                 * not to have problems. For global kswapd, it's for zone
1902                 * balancing and it need to scan a small amounts. When using
1903                 * memcg, priority drop can cause big latency. So, it's better
1904                 * to scan small amount. See may_noscan above.
1905                 */
1906                if (!scan && force_scan)
1907                        scan = nr_force_scan[file];
1908                nr[l] = scan;
1909        }
1910}
1911
1912/*
1913 * Reclaim/compaction depends on a number of pages being freed. To avoid
1914 * disruption to the system, a small number of order-0 pages continue to be
1915 * rotated and reclaimed in the normal fashion. However, by the time we get
1916 * back to the allocator and call try_to_compact_zone(), we ensure that
1917 * there are enough free pages for it to be likely successful
1918 */
1919static inline bool should_continue_reclaim(struct zone *zone,
1920                                        unsigned long nr_reclaimed,
1921                                        unsigned long nr_scanned,
1922                                        struct scan_control *sc)
1923{
1924        unsigned long pages_for_compaction;
1925        unsigned long inactive_lru_pages;
1926
1927        /* If not in reclaim/compaction mode, stop */
1928        if (!(sc->reclaim_mode & RECLAIM_MODE_COMPACTION))
1929                return false;
1930
1931        /* Consider stopping depending on scan and reclaim activity */
1932        if (sc->gfp_mask & __GFP_REPEAT) {
1933                /*
1934                 * For __GFP_REPEAT allocations, stop reclaiming if the
1935                 * full LRU list has been scanned and we are still failing
1936                 * to reclaim pages. This full LRU scan is potentially
1937                 * expensive but a __GFP_REPEAT caller really wants to succeed
1938                 */
1939                if (!nr_reclaimed && !nr_scanned)
1940                        return false;
1941        } else {
1942                /*
1943                 * For non-__GFP_REPEAT allocations which can presumably
1944                 * fail without consequence, stop if we failed to reclaim
1945                 * any pages from the last SWAP_CLUSTER_MAX number of
1946                 * pages that were scanned. This will return to the
1947                 * caller faster at the risk reclaim/compaction and
1948                 * the resulting allocation attempt fails
1949                 */
1950                if (!nr_reclaimed)
1951                        return false;
1952        }
1953
1954        /*
1955         * If we have not reclaimed enough pages for compaction and the
1956         * inactive lists are large enough, continue reclaiming
1957         */
1958        pages_for_compaction = (2UL << sc->order);
1959        inactive_lru_pages = zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON) +
1960                                zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
1961        if (sc->nr_reclaimed < pages_for_compaction &&
1962                        inactive_lru_pages > pages_for_compaction)
1963                return true;
1964
1965        /* If compaction would go ahead or the allocation would succeed, stop */
1966        switch (compaction_suitable(zone, sc->order)) {
1967        case COMPACT_PARTIAL:
1968        case COMPACT_CONTINUE:
1969                return false;
1970        default:
1971                return true;
1972        }
1973}
1974
1975/*
1976 * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1977 */
1978static void shrink_zone(int priority, struct zone *zone,
1979                                struct scan_control *sc)
1980{
1981        unsigned long nr[NR_LRU_LISTS];
1982        unsigned long nr_to_scan;
1983        enum lru_list l;
1984        unsigned long nr_reclaimed, nr_scanned;
1985        unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1986
1987restart:
1988        nr_reclaimed = 0;
1989        nr_scanned = sc->nr_scanned;
1990        get_scan_count(zone, sc, nr, priority);
1991
1992        while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1993                                        nr[LRU_INACTIVE_FILE]) {
1994                for_each_evictable_lru(l) {
1995                        if (nr[l]) {
1996                                nr_to_scan = min_t(unsigned long,
1997                                                   nr[l], SWAP_CLUSTER_MAX);
1998                                nr[l] -= nr_to_scan;
1999
2000                                nr_reclaimed += shrink_list(l, nr_to_scan,
2001                                                            zone, sc, priority);
2002                        }
2003                }
2004                /*
2005                 * On large memory systems, scan >> priority can become
2006                 * really large. This is fine for the starting priority;
2007                 * we want to put equal scanning pressure on each zone.
2008                 * However, if the VM has a harder time of freeing pages,
2009                 * with multiple processes reclaiming pages, the total
2010                 * freeing target can get unreasonably large.
2011                 */
2012                if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)
2013                        break;
2014        }
2015        sc->nr_reclaimed += nr_reclaimed;
2016
2017        /*
2018         * Even if we did not try to evict anon pages at all, we want to
2019         * rebalance the anon lru active/inactive ratio.
2020         */
2021        if (inactive_anon_is_low(zone, sc))
2022                shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0);
2023
2024        /* reclaim/compaction might need reclaim to continue */
2025        if (should_continue_reclaim(zone, nr_reclaimed,
2026                                        sc->nr_scanned - nr_scanned, sc))
2027                goto restart;
2028
2029        throttle_vm_writeout(sc->gfp_mask);
2030}
2031
2032/*
2033 * This is the direct reclaim path, for page-allocating processes.  We only
2034 * try to reclaim pages from zones which will satisfy the caller's allocation
2035 * request.
2036 *
2037 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
2038 * Because:
2039 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
2040 *    allocation or
2041 * b) The target zone may be at high_wmark_pages(zone) but the lower zones
2042 *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
2043 *    zone defense algorithm.
2044 *
2045 * If a zone is deemed to be full of pinned pages then just give it a light
2046 * scan then give up on it.
2047 */
2048static void shrink_zones(int priority, struct zonelist *zonelist,
2049                                        struct scan_control *sc)
2050{
2051        struct zoneref *z;
2052        struct zone *zone;
2053        unsigned long nr_soft_reclaimed;
2054        unsigned long nr_soft_scanned;
2055
2056        for_each_zone_zonelist_nodemask(zone, z, zonelist,
2057                                        gfp_zone(sc->gfp_mask), sc->nodemask) {
2058                if (!populated_zone(zone))
2059                        continue;
2060                /*
2061                 * Take care memory controller reclaiming has small influence
2062                 * to global LRU.
2063                 */
2064                if (scanning_global_lru(sc)) {
2065                        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2066                                continue;
2067                        if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2068                                continue;       /* Let kswapd poll it */
2069                        /*
2070                         * This steals pages from memory cgroups over softlimit
2071                         * and returns the number of reclaimed pages and
2072                         * scanned pages. This works for global memory pressure
2073                         * and balancing, not for a memcg's limit.
2074                         */
2075                        nr_soft_scanned = 0;
2076                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2077                                                sc->order, sc->gfp_mask,
2078                                                &nr_soft_scanned);
2079                        sc->nr_reclaimed += nr_soft_reclaimed;
2080                        sc->nr_scanned += nr_soft_scanned;
2081                        /* need some check for avoid more shrink_zone() */
2082                }
2083
2084                shrink_zone(priority, zone, sc);
2085        }
2086}
2087
2088static bool zone_reclaimable(struct zone *zone)
2089{
2090        return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
2091}
2092
2093/* All zones in zonelist are unreclaimable? */
2094static bool all_unreclaimable(struct zonelist *zonelist,
2095                struct scan_control *sc)
2096{
2097        struct zoneref *z;
2098        struct zone *zone;
2099
2100        for_each_zone_zonelist_nodemask(zone, z, zonelist,
2101                        gfp_zone(sc->gfp_mask), sc->nodemask) {
2102                if (!populated_zone(zone))
2103                        continue;
2104                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2105                        continue;
2106                if (!zone->all_unreclaimable)
2107                        return false;
2108        }
2109
2110        return true;
2111}
2112
2113/*
2114 * This is the main entry point to direct page reclaim.
2115 *
2116 * If a full scan of the inactive list fails to free enough memory then we
2117 * are "out of memory" and something needs to be killed.
2118 *
2119 * If the caller is !__GFP_FS then the probability of a failure is reasonably
2120 * high - the zone may be full of dirty or under-writeback pages, which this
2121 * caller can't do much about.  We kick the writeback threads and take explicit
2122 * naps in the hope that some of these pages can be written.  But if the
2123 * allocating task holds filesystem locks which prevent writeout this might not
2124 * work, and the allocation attempt will fail.
2125 *
2126 * returns:     0, if no pages reclaimed
2127 *              else, the number of pages reclaimed
2128 */
2129static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2130                                        struct scan_control *sc,
2131                                        struct shrink_control *shrink)
2132{
2133        int priority;
2134        unsigned long total_scanned = 0;
2135        struct reclaim_state *reclaim_state = current->reclaim_state;
2136        struct zoneref *z;
2137        struct zone *zone;
2138        unsigned long writeback_threshold;
2139
2140        get_mems_allowed();
2141        delayacct_freepages_start();
2142
2143        if (scanning_global_lru(sc))
2144                count_vm_event(ALLOCSTALL);
2145
2146        for (priority = DEF_PRIORITY; priority >= 0; priority--) {
2147                sc->nr_scanned = 0;
2148                if (!priority)
2149                        disable_swap_token(sc->mem_cgroup);
2150                shrink_zones(priority, zonelist, sc);
2151                /*
2152                 * Don't shrink slabs when reclaiming memory from
2153                 * over limit cgroups
2154                 */
2155                if (scanning_global_lru(sc)) {
2156                        unsigned long lru_pages = 0;
2157                        for_each_zone_zonelist(zone, z, zonelist,
2158                                        gfp_zone(sc->gfp_mask)) {
2159                                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2160                                        continue;
2161
2162                                lru_pages += zone_reclaimable_pages(zone);
2163                        }
2164
2165                        shrink_slab(shrink, sc->nr_scanned, lru_pages);
2166                        if (reclaim_state) {
2167                                sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2168                                reclaim_state->reclaimed_slab = 0;
2169                        }
2170                }
2171                total_scanned += sc->nr_scanned;
2172                if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2173                        goto out;
2174
2175                /*
2176                 * Try to write back as many pages as we just scanned.  This
2177                 * tends to cause slow streaming writers to write data to the
2178                 * disk smoothly, at the dirtying rate, which is nice.   But
2179                 * that's undesirable in laptop mode, where we *want* lumpy
2180                 * writeout.  So in laptop mode, write out the whole world.
2181                 */
2182                writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2183                if (total_scanned > writeback_threshold) {
2184                        wakeup_flusher_threads(laptop_mode ? 0 : total_scanned);
2185                        sc->may_writepage = 1;
2186                }
2187
2188                /* Take a nap, wait for some writeback to complete */
2189                if (!sc->hibernation_mode && sc->nr_scanned &&
2190                    priority < DEF_PRIORITY - 2) {
2191                        struct zone *preferred_zone;
2192
2193                        first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
2194                                                &cpuset_current_mems_allowed,
2195                                                &preferred_zone);
2196                        wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
2197                }
2198        }
2199
2200out:
2201        delayacct_freepages_end();
2202        put_mems_allowed();
2203
2204        if (sc->nr_reclaimed)
2205                return sc->nr_reclaimed;
2206
2207        /*
2208         * As hibernation is going on, kswapd is freezed so that it can't mark
2209         * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2210         * check.
2211         */
2212        if (oom_killer_disabled)
2213                return 0;
2214
2215        /* top priority shrink_zones still had more to do? don't OOM, then */
2216        if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc))
2217                return 1;
2218
2219        return 0;
2220}
2221
2222unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2223                                gfp_t gfp_mask, nodemask_t *nodemask)
2224{
2225        unsigned long nr_reclaimed;
2226        struct scan_control sc = {
2227                .gfp_mask = gfp_mask,
2228                .may_writepage = !laptop_mode,
2229                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2230                .may_unmap = 1,
2231                .may_swap = 1,
2232                .order = order,
2233                .mem_cgroup = NULL,
2234                .nodemask = nodemask,
2235        };
2236        struct shrink_control shrink = {
2237                .gfp_mask = sc.gfp_mask,
2238        };
2239
2240        trace_mm_vmscan_direct_reclaim_begin(order,
2241                                sc.may_writepage,
2242                                gfp_mask);
2243
2244        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2245
2246        trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2247
2248        return nr_reclaimed;
2249}
2250
2251#ifdef CONFIG_CGROUP_MEM_RES_CTLR
2252
2253unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem,
2254                                                gfp_t gfp_mask, bool noswap,
2255                                                struct zone *zone,
2256                                                unsigned long *nr_scanned)
2257{
2258        struct scan_control sc = {
2259                .nr_scanned = 0,
2260                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2261                .may_writepage = !laptop_mode,
2262                .may_unmap = 1,
2263                .may_swap = !noswap,
2264                .order = 0,
2265                .mem_cgroup = mem,
2266        };
2267
2268        sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2269                        (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2270
2271        trace_mm_vmscan_memcg_softlimit_reclaim_begin(0,
2272                                                      sc.may_writepage,
2273                                                      sc.gfp_mask);
2274
2275        /*
2276         * NOTE: Although we can get the priority field, using it
2277         * here is not a good idea, since it limits the pages we can scan.
2278         * if we don't reclaim here, the shrink_zone from balance_pgdat
2279         * will pick up pages from other mem cgroup's as well. We hack
2280         * the priority and make it zero.
2281         */
2282        shrink_zone(0, zone, &sc);
2283
2284        trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2285
2286        *nr_scanned = sc.nr_scanned;
2287        return sc.nr_reclaimed;
2288}
2289
2290unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
2291                                           gfp_t gfp_mask,
2292                                           bool noswap)
2293{
2294        struct zonelist *zonelist;
2295        unsigned long nr_reclaimed;
2296        int nid;
2297        struct scan_control sc = {
2298                .may_writepage = !laptop_mode,
2299                .may_unmap = 1,
2300                .may_swap = !noswap,
2301                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2302                .order = 0,
2303                .mem_cgroup = mem_cont,
2304                .nodemask = NULL, /* we don't care the placement */
2305                .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2306                                (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2307        };
2308        struct shrink_control shrink = {
2309                .gfp_mask = sc.gfp_mask,
2310        };
2311
2312        /*
2313         * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2314         * take care of from where we get pages. So the node where we start the
2315         * scan does not need to be the current node.
2316         */
2317        nid = mem_cgroup_select_victim_node(mem_cont);
2318
2319        zonelist = NODE_DATA(nid)->node_zonelists;
2320
2321        trace_mm_vmscan_memcg_reclaim_begin(0,
2322                                            sc.may_writepage,
2323                                            sc.gfp_mask);
2324
2325        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2326
2327        trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2328
2329        return nr_reclaimed;
2330}
2331#endif
2332
2333/*
2334 * pgdat_balanced is used when checking if a node is balanced for high-order
2335 * allocations. Only zones that meet watermarks and are in a zone allowed
2336 * by the callers classzone_idx are added to balanced_pages. The total of
2337 * balanced pages must be at least 25% of the zones allowed by classzone_idx
2338 * for the node to be considered balanced. Forcing all zones to be balanced
2339 * for high orders can cause excessive reclaim when there are imbalanced zones.
2340 * The choice of 25% is due to
2341 *   o a 16M DMA zone that is balanced will not balance a zone on any
2342 *     reasonable sized machine
2343 *   o On all other machines, the top zone must be at least a reasonable
2344 *     percentage of the middle zones. For example, on 32-bit x86, highmem
2345 *     would need to be at least 256M for it to be balance a whole node.
2346 *     Similarly, on x86-64 the Normal zone would need to be at least 1G
2347 *     to balance a node on its own. These seemed like reasonable ratios.
2348 */
2349static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
2350                                                int classzone_idx)
2351{
2352        unsigned long present_pages = 0;
2353        int i;
2354
2355        for (i = 0; i <= classzone_idx; i++)
2356                present_pages += pgdat->node_zones[i].present_pages;
2357
2358        /* A special case here: if zone has no page, we think it's balanced */
2359        return balanced_pages >= (present_pages >> 2);
2360}
2361
2362/* is kswapd sleeping prematurely? */
2363static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
2364                                        int classzone_idx)
2365{
2366        int i;
2367        unsigned long balanced = 0;
2368        bool all_zones_ok = true;
2369
2370        /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2371        if (remaining)
2372                return true;
2373
2374        /* Check the watermark levels */
2375        for (i = 0; i <= classzone_idx; i++) {
2376                struct zone *zone = pgdat->node_zones + i;
2377
2378                if (!populated_zone(zone))
2379                        continue;
2380
2381                /*
2382                 * balance_pgdat() skips over all_unreclaimable after
2383                 * DEF_PRIORITY. Effectively, it considers them balanced so
2384                 * they must be considered balanced here as well if kswapd
2385                 * is to sleep
2386                 */
2387                if (zone->all_unreclaimable) {
2388                        balanced += zone->present_pages;
2389                        continue;
2390                }
2391
2392                if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
2393                                                        i, 0))
2394                        all_zones_ok = false;
2395                else
2396                        balanced += zone->present_pages;
2397        }
2398
2399        /*
2400         * For high-order requests, the balanced zones must contain at least
2401         * 25% of the nodes pages for kswapd to sleep. For order-0, all zones
2402         * must be balanced
2403         */
2404        if (order)
2405                return !pgdat_balanced(pgdat, balanced, classzone_idx);
2406        else
2407                return !all_zones_ok;
2408}
2409
2410/*
2411 * For kswapd, balance_pgdat() will work across all this node's zones until
2412 * they are all at high_wmark_pages(zone).
2413 *
2414 * Returns the final order kswapd was reclaiming at
2415 *
2416 * There is special handling here for zones which are full of pinned pages.
2417 * This can happen if the pages are all mlocked, or if they are all used by
2418 * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
2419 * What we do is to detect the case where all pages in the zone have been
2420 * scanned twice and there has been zero successful reclaim.  Mark the zone as
2421 * dead and from now on, only perform a short scan.  Basically we're polling
2422 * the zone for when the problem goes away.
2423 *
2424 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
2425 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2426 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2427 * lower zones regardless of the number of free pages in the lower zones. This
2428 * interoperates with the page allocator fallback scheme to ensure that aging
2429 * of pages is balanced across the zones.
2430 */
2431static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2432                                                        int *classzone_idx)
2433{
2434        int all_zones_ok;
2435        unsigned long balanced;
2436        int priority;
2437        int i;
2438        int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
2439        unsigned long total_scanned;
2440        struct reclaim_state *reclaim_state = current->reclaim_state;
2441        unsigned long nr_soft_reclaimed;
2442        unsigned long nr_soft_scanned;
2443        struct scan_control sc = {
2444                .gfp_mask = GFP_KERNEL,
2445                .may_unmap = 1,
2446                .may_swap = 1,
2447                /*
2448                 * kswapd doesn't want to be bailed out while reclaim. because
2449                 * we want to put equal scanning pressure on each zone.
2450                 */
2451                .nr_to_reclaim = ULONG_MAX,
2452                .order = order,
2453                .mem_cgroup = NULL,
2454        };
2455        struct shrink_control shrink = {
2456                .gfp_mask = sc.gfp_mask,
2457        };
2458loop_again:
2459        total_scanned = 0;
2460        sc.nr_reclaimed = 0;
2461        sc.may_writepage = !laptop_mode;
2462        count_vm_event(PAGEOUTRUN);
2463
2464        for (priority = DEF_PRIORITY; priority >= 0; priority--) {
2465                unsigned long lru_pages = 0;
2466                int has_under_min_watermark_zone = 0;
2467
2468                /* The swap token gets in the way of swapout... */
2469                if (!priority)
2470                        disable_swap_token(NULL);
2471
2472                all_zones_ok = 1;
2473                balanced = 0;
2474
2475                /*
2476                 * Scan in the highmem->dma direction for the highest
2477                 * zone which needs scanning
2478                 */
2479                for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2480                        struct zone *zone = pgdat->node_zones + i;
2481
2482                        if (!populated_zone(zone))
2483                                continue;
2484
2485                        if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2486                                continue;
2487
2488                        /*
2489                         * Do some background aging of the anon list, to give
2490                         * pages a chance to be referenced before reclaiming.
2491                         */
2492                        if (inactive_anon_is_low(zone, &sc))
2493                                shrink_active_list(SWAP_CLUSTER_MAX, zone,
2494                                                        &sc, priority, 0);
2495
2496                        if (!zone_watermark_ok_safe(zone, order,
2497                                        high_wmark_pages(zone), 0, 0)) {
2498                                end_zone = i;
2499                                break;
2500                        } else {
2501                                /* If balanced, clear the congested flag */
2502                                zone_clear_flag(zone, ZONE_CONGESTED);
2503                        }
2504                }
2505                if (i < 0)
2506                        goto out;
2507
2508                for (i = 0; i <= end_zone; i++) {
2509                        struct zone *zone = pgdat->node_zones + i;
2510
2511                        lru_pages += zone_reclaimable_pages(zone);
2512                }
2513
2514                /*
2515                 * Now scan the zone in the dma->highmem direction, stopping
2516                 * at the last zone which needs scanning.
2517                 *
2518                 * We do this because the page allocator works in the opposite
2519                 * direction.  This prevents the page allocator from allocating
2520                 * pages behind kswapd's direction of progress, which would
2521                 * cause too much scanning of the lower zones.
2522                 */
2523                for (i = 0; i <= end_zone; i++) {
2524                        struct zone *zone = pgdat->node_zones + i;
2525                        int nr_slab;
2526                        unsigned long balance_gap;
2527
2528                        if (!populated_zone(zone))
2529                                continue;
2530
2531                        if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2532                                continue;
2533
2534                        sc.nr_scanned = 0;
2535
2536                        nr_soft_scanned = 0;
2537                        /*
2538                         * Call soft limit reclaim before calling shrink_zone.
2539                         */
2540                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2541                                                        order, sc.gfp_mask,
2542                                                        &nr_soft_scanned);
2543                        sc.nr_reclaimed += nr_soft_reclaimed;
2544                        total_scanned += nr_soft_scanned;
2545
2546                        /*
2547                         * We put equal pressure on every zone, unless
2548                         * one zone has way too many pages free
2549                         * already. The "too many pages" is defined
2550                         * as the high wmark plus a "gap" where the
2551                         * gap is either the low watermark or 1%
2552                         * of the zone, whichever is smaller.
2553                         */
2554                        balance_gap = min(low_wmark_pages(zone),
2555                                (zone->present_pages +
2556                                        KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2557                                KSWAPD_ZONE_BALANCE_GAP_RATIO);
2558                        if (!zone_watermark_ok_safe(zone, order,
2559                                        high_wmark_pages(zone) + balance_gap,
2560                                        end_zone, 0)) {
2561                                shrink_zone(priority, zone, &sc);
2562
2563                                reclaim_state->reclaimed_slab = 0;
2564                                nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages);
2565                                sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2566                                total_scanned += sc.nr_scanned;
2567
2568                                if (nr_slab == 0 && !zone_reclaimable(zone))
2569                                        zone->all_unreclaimable = 1;
2570                        }
2571
2572                        /*
2573                         * If we've done a decent amount of scanning and
2574                         * the reclaim ratio is low, start doing writepage
2575                         * even in laptop mode
2576                         */
2577                        if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2578                            total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
2579                                sc.may_writepage = 1;
2580
2581                        if (zone->all_unreclaimable) {
2582                                if (end_zone && end_zone == i)
2583                                        end_zone--;
2584                                continue;
2585                        }
2586
2587                        if (!zone_watermark_ok_safe(zone, order,
2588                                        high_wmark_pages(zone), end_zone, 0)) {
2589                                all_zones_ok = 0;
2590                                /*
2591                                 * We are still under min water mark.  This
2592                                 * means that we have a GFP_ATOMIC allocation
2593                                 * failure risk. Hurry up!
2594                                 */
2595                                if (!zone_watermark_ok_safe(zone, order,
2596                                            min_wmark_pages(zone), end_zone, 0))
2597                                        has_under_min_watermark_zone = 1;
2598                        } else {
2599                                /*
2600                                 * If a zone reaches its high watermark,
2601                                 * consider it to be no longer congested. It's
2602                                 * possible there are dirty pages backed by
2603                                 * congested BDIs but as pressure is relieved,
2604                                 * spectulatively avoid congestion waits
2605                                 */
2606                                zone_clear_flag(zone, ZONE_CONGESTED);
2607                                if (i <= *classzone_idx)
2608                                        balanced += zone->present_pages;
2609                        }
2610
2611                }
2612                if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
2613                        break;          /* kswapd: all done */
2614                /*
2615                 * OK, kswapd is getting into trouble.  Take a nap, then take
2616                 * another pass across the zones.
2617                 */
2618                if (total_scanned && (priority < DEF_PRIORITY - 2)) {
2619                        if (has_under_min_watermark_zone)
2620                                count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
2621                        else
2622                                congestion_wait(BLK_RW_ASYNC, HZ/10);
2623                }
2624
2625                /*
2626                 * We do this so kswapd doesn't build up large priorities for
2627                 * example when it is freeing in parallel with allocators. It
2628                 * matches the direct reclaim path behaviour in terms of impact
2629                 * on zone->*_priority.
2630                 */
2631                if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2632                        break;
2633        }
2634out:
2635
2636        /*
2637         * order-0: All zones must meet high watermark for a balanced node
2638         * high-order: Balanced zones must make up at least 25% of the node
2639         *             for the node to be balanced
2640         */
2641        if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) {
2642                cond_resched();
2643
2644                try_to_freeze();
2645
2646                /*
2647                 * Fragmentation may mean that the system cannot be
2648                 * rebalanced for high-order allocations in all zones.
2649                 * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2650                 * it means the zones have been fully scanned and are still
2651                 * not balanced. For high-order allocations, there is
2652                 * little point trying all over again as kswapd may
2653                 * infinite loop.
2654                 *
2655                 * Instead, recheck all watermarks at order-0 as they
2656                 * are the most important. If watermarks are ok, kswapd will go
2657                 * back to sleep. High-order users can still perform direct
2658                 * reclaim if they wish.
2659                 */
2660                if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2661                        order = sc.order = 0;
2662
2663                goto loop_again;
2664        }
2665
2666        /*
2667         * If kswapd was reclaiming at a higher order, it has the option of
2668         * sleeping without all zones being balanced. Before it does, it must
2669         * ensure that the watermarks for order-0 on *all* zones are met and
2670         * that the congestion flags are cleared. The congestion flag must
2671         * be cleared as kswapd is the only mechanism that clears the flag
2672         * and it is potentially going to sleep here.
2673         */
2674        if (order) {
2675                for (i = 0; i <= end_zone; i++) {
2676                        struct zone *zone = pgdat->node_zones + i;
2677
2678                        if (!populated_zone(zone))
2679                                continue;
2680
2681                        if (zone->all_unreclaimable && priority != DEF_PRIORITY)
2682                                continue;
2683
2684                        /* Confirm the zone is balanced for order-0 */
2685                        if (!zone_watermark_ok(zone, 0,
2686                                        high_wmark_pages(zone), 0, 0)) {
2687                                order = sc.order = 0;
2688                                goto loop_again;
2689                        }
2690
2691                        /* If balanced, clear the congested flag */
2692                        zone_clear_flag(zone, ZONE_CONGESTED);
2693                }
2694        }
2695
2696        /*
2697         * Return the order we were reclaiming at so sleeping_prematurely()
2698         * makes a decision on the order we were last reclaiming at. However,
2699         * if another caller entered the allocator slow path while kswapd
2700         * was awake, order will remain at the higher level
2701         */
2702        *classzone_idx = end_zone;
2703        return order;
2704}
2705
2706static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
2707{
2708        long remaining = 0;
2709        DEFINE_WAIT(wait);
2710
2711        if (freezing(current) || kthread_should_stop())
2712                return;
2713
2714        prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2715
2716        /* Try to sleep for a short interval */
2717        if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
2718                remaining = schedule_timeout(HZ/10);
2719                finish_wait(&pgdat->kswapd_wait, &wait);
2720                prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2721        }
2722
2723        /*
2724         * After a short sleep, check if it was a premature sleep. If not, then
2725         * go fully to sleep until explicitly woken up.
2726         */
2727        if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
2728                trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
2729
2730                /*
2731                 * vmstat counters are not perfectly accurate and the estimated
2732                 * value for counters such as NR_FREE_PAGES can deviate from the
2733                 * true value by nr_online_cpus * threshold. To avoid the zone
2734                 * watermarks being breached while under pressure, we reduce the
2735                 * per-cpu vmstat threshold while kswapd is awake and restore
2736                 * them before going back to sleep.
2737                 */
2738                set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
2739                schedule();
2740                set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
2741        } else {
2742                if (remaining)
2743                        count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2744                else
2745                        count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2746        }
2747        finish_wait(&pgdat->kswapd_wait, &wait);
2748}
2749
2750/*
2751 * The background pageout daemon, started as a kernel thread
2752 * from the init process.
2753 *
2754 * This basically trickles out pages so that we have _some_
2755 * free memory available even if there is no other activity
2756 * that frees anything up. This is needed for things like routing
2757 * etc, where we otherwise might have all activity going on in
2758 * asynchronous contexts that cannot page things out.
2759 *
2760 * If there are applications that are active memory-allocators
2761 * (most normal use), this basically shouldn't matter.
2762 */
2763static int kswapd(void *p)
2764{
2765        unsigned long order, new_order;
2766        int classzone_idx, new_classzone_idx;
2767        pg_data_t *pgdat = (pg_data_t*)p;
2768        struct task_struct *tsk = current;
2769
2770        struct reclaim_state reclaim_state = {
2771                .reclaimed_slab = 0,
2772        };
2773        const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2774
2775        lockdep_set_current_reclaim_state(GFP_KERNEL);
2776
2777        if (!cpumask_empty(cpumask))
2778                set_cpus_allowed_ptr(tsk, cpumask);
2779        current->reclaim_state = &reclaim_state;
2780
2781        /*
2782         * Tell the memory management that we're a "memory allocator",
2783         * and that if we need more memory we should get access to it
2784         * regardless (see "__alloc_pages()"). "kswapd" should
2785         * never get caught in the normal page freeing logic.
2786         *
2787         * (Kswapd normally doesn't need memory anyway, but sometimes
2788         * you need a small amount of memory in order to be able to
2789         * page out something else, and this flag essentially protects
2790         * us from recursively trying to free more memory as we're
2791         * trying to free the first piece of memory in the first place).
2792         */
2793        tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2794        set_freezable();
2795
2796        order = new_order = 0;
2797        classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
2798        for ( ; ; ) {
2799                int ret;
2800
2801                /*
2802                 * If the last balance_pgdat was unsuccessful it's unlikely a
2803                 * new request of a similar or harder type will succeed soon
2804                 * so consider going to sleep on the basis we reclaimed at
2805                 */
2806                if (classzone_idx >= new_classzone_idx && order == new_order) {
2807                        new_order = pgdat->kswapd_max_order;
2808                        new_classzone_idx = pgdat->classzone_idx;
2809                        pgdat->kswapd_max_order =  0;
2810                        pgdat->classzone_idx = pgdat->nr_zones - 1;
2811                }
2812
2813                if (order < new_order || classzone_idx > new_classzone_idx) {
2814                        /*
2815                         * Don't sleep if someone wants a larger 'order'
2816                         * allocation or has tigher zone constraints
2817                         */
2818                        order = new_order;
2819                        classzone_idx = new_classzone_idx;
2820                } else {
2821                        kswapd_try_to_sleep(pgdat, order, classzone_idx);
2822                        order = pgdat->kswapd_max_order;
2823                        classzone_idx = pgdat->classzone_idx;
2824                        pgdat->kswapd_max_order = 0;
2825                        pgdat->classzone_idx = pgdat->nr_zones - 1;
2826                }
2827
2828                ret = try_to_freeze();
2829                if (kthread_should_stop())
2830                        break;
2831
2832                /*
2833                 * We can speed up thawing tasks if we don't call balance_pgdat
2834                 * after returning from the refrigerator
2835                 */
2836                if (!ret) {
2837                        trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
2838                        order = balance_pgdat(pgdat, order, &classzone_idx);
2839                }
2840        }
2841        return 0;
2842}
2843
2844/*
2845 * A zone is low on free memory, so wake its kswapd task to service it.
2846 */
2847void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
2848{
2849        pg_data_t *pgdat;
2850
2851        if (!populated_zone(zone))
2852                return;
2853
2854        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2855                return;
2856        pgdat = zone->zone_pgdat;
2857        if (pgdat->kswapd_max_order < order) {
2858                pgdat->kswapd_max_order = order;
2859                pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
2860        }
2861        if (!waitqueue_active(&pgdat->kswapd_wait))
2862                return;
2863        if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
2864                return;
2865
2866        trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
2867        wake_up_interruptible(&pgdat->kswapd_wait);
2868}
2869
2870/*
2871 * The reclaimable count would be mostly accurate.
2872 * The less reclaimable pages may be
2873 * - mlocked pages, which will be moved to unevictable list when encountered
2874 * - mapped pages, which may require several travels to be reclaimed
2875 * - dirty pages, which is not "instantly" reclaimable
2876 */
2877unsigned long global_reclaimable_pages(void)
2878{
2879        int nr;
2880
2881        nr = global_page_state(NR_ACTIVE_FILE) +
2882             global_page_state(NR_INACTIVE_FILE);
2883
2884        if (nr_swap_pages > 0)
2885                nr += global_page_state(NR_ACTIVE_ANON) +
2886                      global_page_state(NR_INACTIVE_ANON);
2887
2888        return nr;
2889}
2890
2891unsigned long zone_reclaimable_pages(struct zone *zone)
2892{
2893        int nr;
2894
2895        nr = zone_page_state(zone, NR_ACTIVE_FILE) +
2896             zone_page_state(zone, NR_INACTIVE_FILE);
2897
2898        if (nr_swap_pages > 0)
2899                nr += zone_page_state(zone, NR_ACTIVE_ANON) +
2900                      zone_page_state(zone, NR_INACTIVE_ANON);
2901
2902        return nr;
2903}
2904
2905#ifdef CONFIG_HIBERNATION
2906/*
2907 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
2908 * freed pages.
2909 *
2910 * Rather than trying to age LRUs the aim is to preserve the overall
2911 * LRU order by reclaiming preferentially
2912 * inactive > active > active referenced > active mapped
2913 */
2914unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
2915{
2916        struct reclaim_state reclaim_state;
2917        struct scan_control sc = {
2918                .gfp_mask = GFP_HIGHUSER_MOVABLE,
2919                .may_swap = 1,
2920                .may_unmap = 1,
2921                .may_writepage = 1,
2922                .nr_to_reclaim = nr_to_reclaim,
2923                .hibernation_mode = 1,
2924                .order = 0,
2925        };
2926        struct shrink_control shrink = {
2927                .gfp_mask = sc.gfp_mask,
2928        };
2929        struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
2930        struct task_struct *p = current;
2931        unsigned long nr_reclaimed;
2932
2933        p->flags |= PF_MEMALLOC;
2934        lockdep_set_current_reclaim_state(sc.gfp_mask);
2935        reclaim_state.reclaimed_slab = 0;
2936        p->reclaim_state = &reclaim_state;
2937
2938        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2939
2940        p->reclaim_state = NULL;
2941        lockdep_clear_current_reclaim_state();
2942        p->flags &= ~PF_MEMALLOC;
2943
2944        return nr_reclaimed;
2945}
2946#endif /* CONFIG_HIBERNATION */
2947
2948/* It's optimal to keep kswapds on the same CPUs as their memory, but
2949   not required for correctness.  So if the last cpu in a node goes
2950   away, we get changed to run anywhere: as the first one comes back,
2951   restore their cpu bindings. */
2952static int __devinit cpu_callback(struct notifier_block *nfb,
2953                                  unsigned long action, void *hcpu)
2954{
2955        int nid;
2956
2957        if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
2958                for_each_node_state(nid, N_HIGH_MEMORY) {
2959                        pg_data_t *pgdat = NODE_DATA(nid);
2960                        const struct cpumask *mask;
2961
2962                        mask = cpumask_of_node(pgdat->node_id);
2963
2964                        if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2965                                /* One of our CPUs online: restore mask */
2966                                set_cpus_allowed_ptr(pgdat->kswapd, mask);
2967                }
2968        }
2969        return NOTIFY_OK;
2970}
2971
2972/*
2973 * This kswapd start function will be called by init and node-hot-add.
2974 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
2975 */
2976int kswapd_run(int nid)
2977{
2978        pg_data_t *pgdat = NODE_DATA(nid);
2979        int ret = 0;
2980
2981        if (pgdat->kswapd)
2982                return 0;
2983
2984        pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
2985        if (IS_ERR(pgdat->kswapd)) {
2986                /* failure at boot is fatal */
2987                BUG_ON(system_state == SYSTEM_BOOTING);
2988                printk("Failed to start kswapd on node %d\n",nid);
2989                ret = -1;
2990        }
2991        return ret;
2992}
2993
2994/*
2995 * Called by memory hotplug when all memory in a node is offlined.
2996 */
2997void kswapd_stop(int nid)
2998{
2999        struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3000
3001        if (kswapd)
3002                kthread_stop(kswapd);
3003}
3004
3005static int __init kswapd_init(void)
3006{
3007        int nid;
3008
3009        swap_setup();
3010        for_each_node_state(nid, N_HIGH_MEMORY)
3011                kswapd_run(nid);
3012        hotcpu_notifier(cpu_callback, 0);
3013        return 0;
3014}
3015
3016module_init(kswapd_init)
3017
3018#ifdef CONFIG_NUMA
3019/*
3020 * Zone reclaim mode
3021 *
3022 * If non-zero call zone_reclaim when the number of free pages falls below
3023 * the watermarks.
3024 */
3025int zone_reclaim_mode __read_mostly;
3026
3027#define RECLAIM_OFF 0
3028#define RECLAIM_ZONE (1<<0)     /* Run shrink_inactive_list on the zone */
3029#define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
3030#define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
3031
3032/*
3033 * Priority for ZONE_RECLAIM. This determines the fraction of pages
3034 * of a node considered for each zone_reclaim. 4 scans 1/16th of
3035 * a zone.
3036 */
3037#define ZONE_RECLAIM_PRIORITY 4
3038
3039/*
3040 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
3041 * occur.
3042 */
3043int sysctl_min_unmapped_ratio = 1;
3044
3045/*
3046 * If the number of slab pages in a zone grows beyond this percentage then
3047 * slab reclaim needs to occur.
3048 */
3049int sysctl_min_slab_ratio = 5;
3050
3051static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3052{
3053        unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3054        unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3055                zone_page_state(zone, NR_ACTIVE_FILE);
3056
3057        /*
3058         * It's possible for there to be more file mapped pages than
3059         * accounted for by the pages on the file LRU lists because
3060         * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3061         */
3062        return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3063}
3064
3065/* Work out how many page cache pages we can reclaim in this reclaim_mode */
3066static long zone_pagecache_reclaimable(struct zone *zone)
3067{
3068        long nr_pagecache_reclaimable;
3069        long delta = 0;
3070
3071        /*
3072         * If RECLAIM_SWAP is set, then all file pages are considered
3073         * potentially reclaimable. Otherwise, we have to worry about
3074         * pages like swapcache and zone_unmapped_file_pages() provides
3075         * a better estimate
3076         */
3077        if (zone_reclaim_mode & RECLAIM_SWAP)
3078                nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3079        else
3080                nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3081
3082        /* If we can't clean pages, remove dirty pages from consideration */
3083        if (!(zone_reclaim_mode & RECLAIM_WRITE))
3084                delta += zone_page_state(zone, NR_FILE_DIRTY);
3085
3086        /* Watch for any possible underflows due to delta */
3087        if (unlikely(delta > nr_pagecache_reclaimable))
3088                delta = nr_pagecache_reclaimable;
3089
3090        return nr_pagecache_reclaimable - delta;
3091}
3092
3093/*
3094 * Try to free up some pages from this zone through reclaim.
3095 */
3096static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3097{
3098        /* Minimum pages needed in order to stay on node */
3099        const unsigned long nr_pages = 1 << order;
3100        struct task_struct *p = current;
3101        struct reclaim_state reclaim_state;
3102        int priority;
3103        struct scan_control sc = {
3104                .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3105                .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3106                .may_swap = 1,
3107                .nr_to_reclaim = max_t(unsigned long, nr_pages,
3108                                       SWAP_CLUSTER_MAX),
3109                .gfp_mask = gfp_mask,
3110                .order = order,
3111        };
3112        struct shrink_control shrink = {
3113                .gfp_mask = sc.gfp_mask,
3114        };
3115        unsigned long nr_slab_pages0, nr_slab_pages1;
3116
3117        cond_resched();
3118        /*
3119         * We need to be able to allocate from the reserves for RECLAIM_SWAP
3120         * and we also need to be able to write out pages for RECLAIM_WRITE
3121         * and RECLAIM_SWAP.
3122         */
3123        p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3124        lockdep_set_current_reclaim_state(gfp_mask);
3125        reclaim_state.reclaimed_slab = 0;
3126        p->reclaim_state = &reclaim_state;
3127
3128        if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3129                /*
3130                 * Free memory by calling shrink zone with increasing
3131                 * priorities until we have enough memory freed.
3132                 */
3133                priority = ZONE_RECLAIM_PRIORITY;
3134                do {
3135                        shrink_zone(priority, zone, &sc);
3136                        priority--;
3137                } while (priority >= 0 && sc.nr_reclaimed < nr_pages);
3138        }
3139
3140        nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3141        if (nr_slab_pages0 > zone->min_slab_pages) {
3142                /*
3143                 * shrink_slab() does not currently allow us to determine how
3144                 * many pages were freed in this zone. So we take the current
3145                 * number of slab pages and shake the slab until it is reduced
3146                 * by the same nr_pages that we used for reclaiming unmapped
3147                 * pages.
3148                 *
3149                 * Note that shrink_slab will free memory on all zones and may
3150                 * take a long time.
3151                 */
3152                for (;;) {
3153                        unsigned long lru_pages = zone_reclaimable_pages(zone);
3154
3155                        /* No reclaimable slab or very low memory pressure */
3156                        if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3157                                break;
3158
3159                        /* Freed enough memory */
3160                        nr_slab_pages1 = zone_page_state(zone,
3161                                                        NR_SLAB_RECLAIMABLE);
3162                        if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3163                                break;
3164                }
3165
3166                /*
3167                 * Update nr_reclaimed by the number of slab pages we
3168                 * reclaimed from this zone.
3169                 */
3170                nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3171                if (nr_slab_pages1 < nr_slab_pages0)
3172                        sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3173        }
3174
3175        p->reclaim_state = NULL;
3176        current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3177        lockdep_clear_current_reclaim_state();
3178        return sc.nr_reclaimed >= nr_pages;
3179}
3180
3181int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3182{
3183        int node_id;
3184        int ret;
3185
3186        /*
3187         * Zone reclaim reclaims unmapped file backed pages and
3188         * slab pages if we are over the defined limits.
3189         *
3190         * A small portion of unmapped file backed pages is needed for
3191         * file I/O otherwise pages read by file I/O will be immediately
3192         * thrown out if the zone is overallocated. So we do not reclaim
3193         * if less than a specified percentage of the zone is used by
3194         * unmapped file backed pages.
3195         */
3196        if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3197            zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3198                return ZONE_RECLAIM_FULL;
3199
3200        if (zone->all_unreclaimable)
3201                return ZONE_RECLAIM_FULL;
3202
3203        /*
3204         * Do not scan if the allocation should not be delayed.
3205         */
3206        if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3207                return ZONE_RECLAIM_NOSCAN;
3208
3209        /*
3210         * Only run zone reclaim on the local zone or on zones that do not
3211         * have associated processors. This will favor the local processor
3212         * over remote processors and spread off node memory allocations
3213         * as wide as possible.
3214         */
3215        node_id = zone_to_nid(zone);
3216        if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3217                return ZONE_RECLAIM_NOSCAN;
3218
3219        if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3220                return ZONE_RECLAIM_NOSCAN;
3221
3222        ret = __zone_reclaim(zone, gfp_mask, order);
3223        zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3224
3225        if (!ret)
3226                count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3227
3228        return ret;
3229}
3230#endif
3231
3232/*
3233 * page_evictable - test whether a page is evictable
3234 * @page: the page to test
3235 * @vma: the VMA in which the page is or will be mapped, may be NULL
3236 *
3237 * Test whether page is evictable--i.e., should be placed on active/inactive
3238 * lists vs unevictable list.  The vma argument is !NULL when called from the
3239 * fault path to determine how to instantate a new page.
3240 *
3241 * Reasons page might not be evictable:
3242 * (1) page's mapping marked unevictable
3243 * (2) page is part of an mlocked VMA
3244 *
3245 */
3246int page_evictable(struct page *page, struct vm_area_struct *vma)
3247{
3248
3249        if (mapping_unevictable(page_mapping(page)))
3250                return 0;
3251
3252        if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page)))
3253                return 0;
3254
3255        return 1;
3256}
3257
3258/**
3259 * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list
3260 * @page: page to check evictability and move to appropriate lru list
3261 * @zone: zone page is in
3262 *
3263 * Checks a page for evictability and moves the page to the appropriate
3264 * zone lru list.
3265 *
3266 * Restrictions: zone->lru_lock must be held, page must be on LRU and must
3267 * have PageUnevictable set.
3268 */
3269static void check_move_unevictable_page(struct page *page, struct zone *zone)
3270{
3271        VM_BUG_ON(PageActive(page));
3272
3273retry:
3274        ClearPageUnevictable(page);
3275        if (page_evictable(page, NULL)) {
3276                enum lru_list l = page_lru_base_type(page);
3277
3278                __dec_zone_state(zone, NR_UNEVICTABLE);
3279                list_move(&page->lru, &zone->lru[l].list);
3280                mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l);
3281                __inc_zone_state(zone, NR_INACTIVE_ANON + l);
3282                __count_vm_event(UNEVICTABLE_PGRESCUED);
3283        } else {
3284                /*
3285                 * rotate unevictable list
3286                 */
3287                SetPageUnevictable(page);
3288                list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list);
3289                mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE);
3290                if (page_evictable(page, NULL))
3291                        goto retry;
3292        }
3293}
3294
3295/**
3296 * scan_mapping_unevictable_pages - scan an address space for evictable pages
3297 * @mapping: struct address_space to scan for evictable pages
3298 *
3299 * Scan all pages in mapping.  Check unevictable pages for
3300 * evictability and move them to the appropriate zone lru list.
3301 */
3302void scan_mapping_unevictable_pages(struct address_space *mapping)
3303{
3304        pgoff_t next = 0;
3305        pgoff_t end   = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >>
3306                         PAGE_CACHE_SHIFT;
3307        struct zone *zone;
3308        struct pagevec pvec;
3309
3310        if (mapping->nrpages == 0)
3311                return;
3312
3313        pagevec_init(&pvec, 0);
3314        while (next < end &&
3315                pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) {
3316                int i;
3317                int pg_scanned = 0;
3318
3319                zone = NULL;
3320
3321                for (i = 0; i < pagevec_count(&pvec); i++) {
3322                        struct page *page = pvec.pages[i];
3323                        pgoff_t page_index = page->index;
3324                        struct zone *pagezone = page_zone(page);
3325
3326                        pg_scanned++;
3327                        if (page_index > next)
3328                                next = page_index;
3329                        next++;
3330
3331                        if (pagezone != zone) {
3332                                if (zone)
3333                                        spin_unlock_irq(&zone->lru_lock);
3334                                zone = pagezone;
3335                                spin_lock_irq(&zone->lru_lock);
3336                        }
3337
3338                        if (PageLRU(page) && PageUnevictable(page))
3339                                check_move_unevictable_page(page, zone);
3340                }
3341                if (zone)
3342                        spin_unlock_irq(&zone->lru_lock);
3343                pagevec_release(&pvec);
3344
3345                count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned);
3346        }
3347
3348}
3349
3350/**
3351 * scan_zone_unevictable_pages - check unevictable list for evictable pages
3352 * @zone - zone of which to scan the unevictable list
3353 *
3354 * Scan @zone's unevictable LRU lists to check for pages that have become
3355 * evictable.  Move those that have to @zone's inactive list where they
3356 * become candidates for reclaim, unless shrink_inactive_zone() decides
3357 * to reactivate them.  Pages that are still unevictable are rotated
3358 * back onto @zone's unevictable list.
3359 */
3360#define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */
3361static void scan_zone_unevictable_pages(struct zone *zone)
3362{
3363        struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list;
3364        unsigned long scan;
3365        unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE);
3366
3367        while (nr_to_scan > 0) {
3368                unsigned long batch_size = min(nr_to_scan,
3369                                                SCAN_UNEVICTABLE_BATCH_SIZE);
3370
3371                spin_lock_irq(&zone->lru_lock);
3372                for (scan = 0;  scan < batch_size; scan++) {
3373                        struct page *page = lru_to_page(l_unevictable);
3374
3375                        if (!trylock_page(page))
3376                                continue;
3377
3378                        prefetchw_prev_lru_page(page, l_unevictable, flags);
3379
3380                        if (likely(PageLRU(page) && PageUnevictable(page)))
3381                                check_move_unevictable_page(page, zone);
3382
3383                        unlock_page(page);
3384                }
3385                spin_unlock_irq(&zone->lru_lock);
3386
3387                nr_to_scan -= batch_size;
3388        }
3389}
3390
3391
3392/**
3393 * scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages
3394 *
3395 * A really big hammer:  scan all zones' unevictable LRU lists to check for
3396 * pages that have become evictable.  Move those back to the zones'
3397 * inactive list where they become candidates for reclaim.
3398 * This occurs when, e.g., we have unswappable pages on the unevictable lists,
3399 * and we add swap to the system.  As such, it runs in the context of a task
3400 * that has possibly/probably made some previously unevictable pages
3401 * evictable.
3402 */
3403static void scan_all_zones_unevictable_pages(void)
3404{
3405        struct zone *zone;
3406
3407        for_each_zone(zone) {
3408                scan_zone_unevictable_pages(zone);
3409        }
3410}
3411
3412/*
3413 * scan_unevictable_pages [vm] sysctl handler.  On demand re-scan of
3414 * all nodes' unevictable lists for evictable pages
3415 */
3416unsigned long scan_unevictable_pages;
3417
3418int scan_unevictable_handler(struct ctl_table *table, int write,
3419                           void __user *buffer,
3420                           size_t *length, loff_t *ppos)
3421{
3422        proc_doulongvec_minmax(table, write, buffer, length, ppos);
3423
3424        if (write && *(unsigned long *)table->data)
3425                scan_all_zones_unevictable_pages();
3426
3427        scan_unevictable_pages = 0;
3428        return 0;
3429}
3430
3431#ifdef CONFIG_NUMA
3432/*
3433 * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
3434 * a specified node's per zone unevictable lists for evictable pages.
3435 */
3436
3437static ssize_t read_scan_unevictable_node(struct sys_device *dev,
3438                                          struct sysdev_attribute *attr,
3439                                          char *buf)
3440{
3441        return sprintf(buf, "0\n");     /* always zero; should fit... */
3442}
3443
3444static ssize_t write_scan_unevictable_node(struct sys_device *dev,
3445                                           struct sysdev_attribute *attr,
3446                                        const char *buf, size_t count)
3447{
3448        struct zone *node_zones = NODE_DATA(dev->id)->node_zones;
3449        struct zone *zone;
3450        unsigned long res;
3451        unsigned long req = strict_strtoul(buf, 10, &res);
3452
3453        if (!req)
3454                return 1;       /* zero is no-op */
3455
3456        for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
3457                if (!populated_zone(zone))
3458                        continue;
3459                scan_zone_unevictable_pages(zone);
3460        }
3461        return 1;
3462}
3463
3464
3465static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3466                        read_scan_unevictable_node,
3467                        write_scan_unevictable_node);
3468
3469int scan_unevictable_register_node(struct node *node)
3470{
3471        return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages);
3472}
3473
3474void scan_unevictable_unregister_node(struct node *node)
3475{
3476        sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages);
3477}
3478#endif
3479
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