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/backing-dev.h>
  30#include <linux/rmap.h>
  31#include <linux/topology.h>
  32#include <linux/cpu.h>
  33#include <linux/cpuset.h>
  34#include <linux/compaction.h>
  35#include <linux/notifier.h>
  36#include <linux/rwsem.h>
  37#include <linux/delay.h>
  38#include <linux/kthread.h>
  39#include <linux/freezer.h>
  40#include <linux/memcontrol.h>
  41#include <linux/delayacct.h>
  42#include <linux/sysctl.h>
  43#include <linux/oom.h>
  44#include <linux/prefetch.h>
  45
  46#include <asm/tlbflush.h>
  47#include <asm/div64.h>
  48
  49#include <linux/swapops.h>
  50
  51#include "internal.h"
  52
  53#define CREATE_TRACE_POINTS
  54#include <trace/events/vmscan.h>
  55
  56struct scan_control {
  57        /* Incremented by the number of inactive pages that were scanned */
  58        unsigned long nr_scanned;
  59
  60        /* Number of pages freed so far during a call to shrink_zones() */
  61        unsigned long nr_reclaimed;
  62
  63        /* How many pages shrink_list() should reclaim */
  64        unsigned long nr_to_reclaim;
  65
  66        unsigned long hibernation_mode;
  67
  68        /* This context's GFP mask */
  69        gfp_t gfp_mask;
  70
  71        int may_writepage;
  72
  73        /* Can mapped pages be reclaimed? */
  74        int may_unmap;
  75
  76        /* Can pages be swapped as part of reclaim? */
  77        int may_swap;
  78
  79        int order;
  80
  81        /* Scan (total_size >> priority) pages at once */
  82        int priority;
  83
  84        /*
  85         * The memory cgroup that hit its limit and as a result is the
  86         * primary target of this reclaim invocation.
  87         */
  88        struct mem_cgroup *target_mem_cgroup;
  89
  90        /*
  91         * Nodemask of nodes allowed by the caller. If NULL, all nodes
  92         * are scanned.
  93         */
  94        nodemask_t      *nodemask;
  95};
  96
  97#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
  98
  99#ifdef ARCH_HAS_PREFETCH
 100#define prefetch_prev_lru_page(_page, _base, _field)                    \
 101        do {                                                            \
 102                if ((_page)->lru.prev != _base) {                       \
 103                        struct page *prev;                              \
 104                                                                        \
 105                        prev = lru_to_page(&(_page->lru));              \
 106                        prefetch(&prev->_field);                        \
 107                }                                                       \
 108        } while (0)
 109#else
 110#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
 111#endif
 112
 113#ifdef ARCH_HAS_PREFETCHW
 114#define prefetchw_prev_lru_page(_page, _base, _field)                   \
 115        do {                                                            \
 116                if ((_page)->lru.prev != _base) {                       \
 117                        struct page *prev;                              \
 118                                                                        \
 119                        prev = lru_to_page(&(_page->lru));              \
 120                        prefetchw(&prev->_field);                       \
 121                }                                                       \
 122        } while (0)
 123#else
 124#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
 125#endif
 126
 127/*
 128 * From 0 .. 100.  Higher means more swappy.
 129 */
 130int vm_swappiness = 60;
 131long vm_total_pages;    /* The total number of pages which the VM controls */
 132
 133static LIST_HEAD(shrinker_list);
 134static DECLARE_RWSEM(shrinker_rwsem);
 135
 136#ifdef CONFIG_CGROUP_MEM_RES_CTLR
 137static bool global_reclaim(struct scan_control *sc)
 138{
 139        return !sc->target_mem_cgroup;
 140}
 141#else
 142static bool global_reclaim(struct scan_control *sc)
 143{
 144        return true;
 145}
 146#endif
 147
 148static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
 149{
 150        if (!mem_cgroup_disabled())
 151                return mem_cgroup_get_lru_size(lruvec, lru);
 152
 153        return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru);
 154}
 155
 156/*
 157 * Add a shrinker callback to be called from the vm
 158 */
 159void register_shrinker(struct shrinker *shrinker)
 160{
 161        atomic_long_set(&shrinker->nr_in_batch, 0);
 162        down_write(&shrinker_rwsem);
 163        list_add_tail(&shrinker->list, &shrinker_list);
 164        up_write(&shrinker_rwsem);
 165}
 166EXPORT_SYMBOL(register_shrinker);
 167
 168/*
 169 * Remove one
 170 */
 171void unregister_shrinker(struct shrinker *shrinker)
 172{
 173        down_write(&shrinker_rwsem);
 174        list_del(&shrinker->list);
 175        up_write(&shrinker_rwsem);
 176}
 177EXPORT_SYMBOL(unregister_shrinker);
 178
 179static inline int do_shrinker_shrink(struct shrinker *shrinker,
 180                                     struct shrink_control *sc,
 181                                     unsigned long nr_to_scan)
 182{
 183        sc->nr_to_scan = nr_to_scan;
 184        return (*shrinker->shrink)(shrinker, sc);
 185}
 186
 187#define SHRINK_BATCH 128
 188/*
 189 * Call the shrink functions to age shrinkable caches
 190 *
 191 * Here we assume it costs one seek to replace a lru page and that it also
 192 * takes a seek to recreate a cache object.  With this in mind we age equal
 193 * percentages of the lru and ageable caches.  This should balance the seeks
 194 * generated by these structures.
 195 *
 196 * If the vm encountered mapped pages on the LRU it increase the pressure on
 197 * slab to avoid swapping.
 198 *
 199 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
 200 *
 201 * `lru_pages' represents the number of on-LRU pages in all the zones which
 202 * are eligible for the caller's allocation attempt.  It is used for balancing
 203 * slab reclaim versus page reclaim.
 204 *
 205 * Returns the number of slab objects which we shrunk.
 206 */
 207unsigned long shrink_slab(struct shrink_control *shrink,
 208                          unsigned long nr_pages_scanned,
 209                          unsigned long lru_pages)
 210{
 211        struct shrinker *shrinker;
 212        unsigned long ret = 0;
 213
 214        if (nr_pages_scanned == 0)
 215                nr_pages_scanned = SWAP_CLUSTER_MAX;
 216
 217        if (!down_read_trylock(&shrinker_rwsem)) {
 218                /* Assume we'll be able to shrink next time */
 219                ret = 1;
 220                goto out;
 221        }
 222
 223        list_for_each_entry(shrinker, &shrinker_list, list) {
 224                unsigned long long delta;
 225                long total_scan;
 226                long max_pass;
 227                int shrink_ret = 0;
 228                long nr;
 229                long new_nr;
 230                long batch_size = shrinker->batch ? shrinker->batch
 231                                                  : SHRINK_BATCH;
 232
 233                max_pass = do_shrinker_shrink(shrinker, shrink, 0);
 234                if (max_pass <= 0)
 235                        continue;
 236
 237                /*
 238                 * copy the current shrinker scan count into a local variable
 239                 * and zero it so that other concurrent shrinker invocations
 240                 * don't also do this scanning work.
 241                 */
 242                nr = atomic_long_xchg(&shrinker->nr_in_batch, 0);
 243
 244                total_scan = nr;
 245                delta = (4 * nr_pages_scanned) / shrinker->seeks;
 246                delta *= max_pass;
 247                do_div(delta, lru_pages + 1);
 248                total_scan += delta;
 249                if (total_scan < 0) {
 250                        printk(KERN_ERR "shrink_slab: %pF negative objects to "
 251                               "delete nr=%ld\n",
 252                               shrinker->shrink, total_scan);
 253                        total_scan = max_pass;
 254                }
 255
 256                /*
 257                 * We need to avoid excessive windup on filesystem shrinkers
 258                 * due to large numbers of GFP_NOFS allocations causing the
 259                 * shrinkers to return -1 all the time. This results in a large
 260                 * nr being built up so when a shrink that can do some work
 261                 * comes along it empties the entire cache due to nr >>>
 262                 * max_pass.  This is bad for sustaining a working set in
 263                 * memory.
 264                 *
 265                 * Hence only allow the shrinker to scan the entire cache when
 266                 * a large delta change is calculated directly.
 267                 */
 268                if (delta < max_pass / 4)
 269                        total_scan = min(total_scan, max_pass / 2);
 270
 271                /*
 272                 * Avoid risking looping forever due to too large nr value:
 273                 * never try to free more than twice the estimate number of
 274                 * freeable entries.
 275                 */
 276                if (total_scan > max_pass * 2)
 277                        total_scan = max_pass * 2;
 278
 279                trace_mm_shrink_slab_start(shrinker, shrink, nr,
 280                                        nr_pages_scanned, lru_pages,
 281                                        max_pass, delta, total_scan);
 282
 283                while (total_scan >= batch_size) {
 284                        int nr_before;
 285
 286                        nr_before = do_shrinker_shrink(shrinker, shrink, 0);
 287                        shrink_ret = do_shrinker_shrink(shrinker, shrink,
 288                                                        batch_size);
 289                        if (shrink_ret == -1)
 290                                break;
 291                        if (shrink_ret < nr_before)
 292                                ret += nr_before - shrink_ret;
 293                        count_vm_events(SLABS_SCANNED, batch_size);
 294                        total_scan -= batch_size;
 295
 296                        cond_resched();
 297                }
 298
 299                /*
 300                 * move the unused scan count back into the shrinker in a
 301                 * manner that handles concurrent updates. If we exhausted the
 302                 * scan, there is no need to do an update.
 303                 */
 304                if (total_scan > 0)
 305                        new_nr = atomic_long_add_return(total_scan,
 306                                        &shrinker->nr_in_batch);
 307                else
 308                        new_nr = atomic_long_read(&shrinker->nr_in_batch);
 309
 310                trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr);
 311        }
 312        up_read(&shrinker_rwsem);
 313out:
 314        cond_resched();
 315        return ret;
 316}
 317
 318static inline int is_page_cache_freeable(struct page *page)
 319{
 320        /*
 321         * A freeable page cache page is referenced only by the caller
 322         * that isolated the page, the page cache radix tree and
 323         * optional buffer heads at page->private.
 324         */
 325        return page_count(page) - page_has_private(page) == 2;
 326}
 327
 328static int may_write_to_queue(struct backing_dev_info *bdi,
 329                              struct scan_control *sc)
 330{
 331        if (current->flags & PF_SWAPWRITE)
 332                return 1;
 333        if (!bdi_write_congested(bdi))
 334                return 1;
 335        if (bdi == current->backing_dev_info)
 336                return 1;
 337        return 0;
 338}
 339
 340/*
 341 * We detected a synchronous write error writing a page out.  Probably
 342 * -ENOSPC.  We need to propagate that into the address_space for a subsequent
 343 * fsync(), msync() or close().
 344 *
 345 * The tricky part is that after writepage we cannot touch the mapping: nothing
 346 * prevents it from being freed up.  But we have a ref on the page and once
 347 * that page is locked, the mapping is pinned.
 348 *
 349 * We're allowed to run sleeping lock_page() here because we know the caller has
 350 * __GFP_FS.
 351 */
 352static void handle_write_error(struct address_space *mapping,
 353                                struct page *page, int error)
 354{
 355        lock_page(page);
 356        if (page_mapping(page) == mapping)
 357                mapping_set_error(mapping, error);
 358        unlock_page(page);
 359}
 360
 361/* possible outcome of pageout() */
 362typedef enum {
 363        /* failed to write page out, page is locked */
 364        PAGE_KEEP,
 365        /* move page to the active list, page is locked */
 366        PAGE_ACTIVATE,
 367        /* page has been sent to the disk successfully, page is unlocked */
 368        PAGE_SUCCESS,
 369        /* page is clean and locked */
 370        PAGE_CLEAN,
 371} pageout_t;
 372
 373/*
 374 * pageout is called by shrink_page_list() for each dirty page.
 375 * Calls ->writepage().
 376 */
 377static pageout_t pageout(struct page *page, struct address_space *mapping,
 378                         struct scan_control *sc)
 379{
 380        /*
 381         * If the page is dirty, only perform writeback if that write
 382         * will be non-blocking.  To prevent this allocation from being
 383         * stalled by pagecache activity.  But note that there may be
 384         * stalls if we need to run get_block().  We could test
 385         * PagePrivate for that.
 386         *
 387         * If this process is currently in __generic_file_aio_write() against
 388         * this page's queue, we can perform writeback even if that
 389         * will block.
 390         *
 391         * If the page is swapcache, write it back even if that would
 392         * block, for some throttling. This happens by accident, because
 393         * swap_backing_dev_info is bust: it doesn't reflect the
 394         * congestion state of the swapdevs.  Easy to fix, if needed.
 395         */
 396        if (!is_page_cache_freeable(page))
 397                return PAGE_KEEP;
 398        if (!mapping) {
 399                /*
 400                 * Some data journaling orphaned pages can have
 401                 * page->mapping == NULL while being dirty with clean buffers.
 402                 */
 403                if (page_has_private(page)) {
 404                        if (try_to_free_buffers(page)) {
 405                                ClearPageDirty(page);
 406                                printk("%s: orphaned page\n", __func__);
 407                                return PAGE_CLEAN;
 408                        }
 409                }
 410                return PAGE_KEEP;
 411        }
 412        if (mapping->a_ops->writepage == NULL)
 413                return PAGE_ACTIVATE;
 414        if (!may_write_to_queue(mapping->backing_dev_info, sc))
 415                return PAGE_KEEP;
 416
 417        if (clear_page_dirty_for_io(page)) {
 418                int res;
 419                struct writeback_control wbc = {
 420                        .sync_mode = WB_SYNC_NONE,
 421                        .nr_to_write = SWAP_CLUSTER_MAX,
 422                        .range_start = 0,
 423                        .range_end = LLONG_MAX,
 424                        .for_reclaim = 1,
 425                };
 426
 427                SetPageReclaim(page);
 428                res = mapping->a_ops->writepage(page, &wbc);
 429                if (res < 0)
 430                        handle_write_error(mapping, page, res);
 431                if (res == AOP_WRITEPAGE_ACTIVATE) {
 432                        ClearPageReclaim(page);
 433                        return PAGE_ACTIVATE;
 434                }
 435
 436                if (!PageWriteback(page)) {
 437                        /* synchronous write or broken a_ops? */
 438                        ClearPageReclaim(page);
 439                }
 440                trace_mm_vmscan_writepage(page, trace_reclaim_flags(page));
 441                inc_zone_page_state(page, NR_VMSCAN_WRITE);
 442                return PAGE_SUCCESS;
 443        }
 444
 445        return PAGE_CLEAN;
 446}
 447
 448/*
 449 * Same as remove_mapping, but if the page is removed from the mapping, it
 450 * gets returned with a refcount of 0.
 451 */
 452static int __remove_mapping(struct address_space *mapping, struct page *page)
 453{
 454        BUG_ON(!PageLocked(page));
 455        BUG_ON(mapping != page_mapping(page));
 456
 457        spin_lock_irq(&mapping->tree_lock);
 458        /*
 459         * The non racy check for a busy page.
 460         *
 461         * Must be careful with the order of the tests. When someone has
 462         * a ref to the page, it may be possible that they dirty it then
 463         * drop the reference. So if PageDirty is tested before page_count
 464         * here, then the following race may occur:
 465         *
 466         * get_user_pages(&page);
 467         * [user mapping goes away]
 468         * write_to(page);
 469         *                              !PageDirty(page)    [good]
 470         * SetPageDirty(page);
 471         * put_page(page);
 472         *                              !page_count(page)   [good, discard it]
 473         *
 474         * [oops, our write_to data is lost]
 475         *
 476         * Reversing the order of the tests ensures such a situation cannot
 477         * escape unnoticed. The smp_rmb is needed to ensure the page->flags
 478         * load is not satisfied before that of page->_count.
 479         *
 480         * Note that if SetPageDirty is always performed via set_page_dirty,
 481         * and thus under tree_lock, then this ordering is not required.
 482         */
 483        if (!page_freeze_refs(page, 2))
 484                goto cannot_free;
 485        /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
 486        if (unlikely(PageDirty(page))) {
 487                page_unfreeze_refs(page, 2);
 488                goto cannot_free;
 489        }
 490
 491        if (PageSwapCache(page)) {
 492                swp_entry_t swap = { .val = page_private(page) };
 493                __delete_from_swap_cache(page);
 494                spin_unlock_irq(&mapping->tree_lock);
 495                swapcache_free(swap, page);
 496        } else {
 497                void (*freepage)(struct page *);
 498
 499                freepage = mapping->a_ops->freepage;
 500
 501                __delete_from_page_cache(page);
 502                spin_unlock_irq(&mapping->tree_lock);
 503                mem_cgroup_uncharge_cache_page(page);
 504
 505                if (freepage != NULL)
 506                        freepage(page);
 507        }
 508
 509        return 1;
 510
 511cannot_free:
 512        spin_unlock_irq(&mapping->tree_lock);
 513        return 0;
 514}
 515
 516/*
 517 * Attempt to detach a locked page from its ->mapping.  If it is dirty or if
 518 * someone else has a ref on the page, abort and return 0.  If it was
 519 * successfully detached, return 1.  Assumes the caller has a single ref on
 520 * this page.
 521 */
 522int remove_mapping(struct address_space *mapping, struct page *page)
 523{
 524        if (__remove_mapping(mapping, page)) {
 525                /*
 526                 * Unfreezing the refcount with 1 rather than 2 effectively
 527                 * drops the pagecache ref for us without requiring another
 528                 * atomic operation.
 529                 */
 530                page_unfreeze_refs(page, 1);
 531                return 1;
 532        }
 533        return 0;
 534}
 535
 536/**
 537 * putback_lru_page - put previously isolated page onto appropriate LRU list
 538 * @page: page to be put back to appropriate lru list
 539 *
 540 * Add previously isolated @page to appropriate LRU list.
 541 * Page may still be unevictable for other reasons.
 542 *
 543 * lru_lock must not be held, interrupts must be enabled.
 544 */
 545void putback_lru_page(struct page *page)
 546{
 547        int lru;
 548        int active = !!TestClearPageActive(page);
 549        int was_unevictable = PageUnevictable(page);
 550
 551        VM_BUG_ON(PageLRU(page));
 552
 553redo:
 554        ClearPageUnevictable(page);
 555
 556        if (page_evictable(page, NULL)) {
 557                /*
 558                 * For evictable pages, we can use the cache.
 559                 * In event of a race, worst case is we end up with an
 560                 * unevictable page on [in]active list.
 561                 * We know how to handle that.
 562                 */
 563                lru = active + page_lru_base_type(page);
 564                lru_cache_add_lru(page, lru);
 565        } else {
 566                /*
 567                 * Put unevictable pages directly on zone's unevictable
 568                 * list.
 569                 */
 570                lru = LRU_UNEVICTABLE;
 571                add_page_to_unevictable_list(page);
 572                /*
 573                 * When racing with an mlock or AS_UNEVICTABLE clearing
 574                 * (page is unlocked) make sure that if the other thread
 575                 * does not observe our setting of PG_lru and fails
 576                 * isolation/check_move_unevictable_pages,
 577                 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move
 578                 * the page back to the evictable list.
 579                 *
 580                 * The other side is TestClearPageMlocked() or shmem_lock().
 581                 */
 582                smp_mb();
 583        }
 584
 585        /*
 586         * page's status can change while we move it among lru. If an evictable
 587         * page is on unevictable list, it never be freed. To avoid that,
 588         * check after we added it to the list, again.
 589         */
 590        if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) {
 591                if (!isolate_lru_page(page)) {
 592                        put_page(page);
 593                        goto redo;
 594                }
 595                /* This means someone else dropped this page from LRU
 596                 * So, it will be freed or putback to LRU again. There is
 597                 * nothing to do here.
 598                 */
 599        }
 600
 601        if (was_unevictable && lru != LRU_UNEVICTABLE)
 602                count_vm_event(UNEVICTABLE_PGRESCUED);
 603        else if (!was_unevictable && lru == LRU_UNEVICTABLE)
 604                count_vm_event(UNEVICTABLE_PGCULLED);
 605
 606        put_page(page);         /* drop ref from isolate */
 607}
 608
 609enum page_references {
 610        PAGEREF_RECLAIM,
 611        PAGEREF_RECLAIM_CLEAN,
 612        PAGEREF_KEEP,
 613        PAGEREF_ACTIVATE,
 614};
 615
 616static enum page_references page_check_references(struct page *page,
 617                                                  struct scan_control *sc)
 618{
 619        int referenced_ptes, referenced_page;
 620        unsigned long vm_flags;
 621
 622        referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup,
 623                                          &vm_flags);
 624        referenced_page = TestClearPageReferenced(page);
 625
 626        /*
 627         * Mlock lost the isolation race with us.  Let try_to_unmap()
 628         * move the page to the unevictable list.
 629         */
 630        if (vm_flags & VM_LOCKED)
 631                return PAGEREF_RECLAIM;
 632
 633        if (referenced_ptes) {
 634                if (PageSwapBacked(page))
 635                        return PAGEREF_ACTIVATE;
 636                /*
 637                 * All mapped pages start out with page table
 638                 * references from the instantiating fault, so we need
 639                 * to look twice if a mapped file page is used more
 640                 * than once.
 641                 *
 642                 * Mark it and spare it for another trip around the
 643                 * inactive list.  Another page table reference will
 644                 * lead to its activation.
 645                 *
 646                 * Note: the mark is set for activated pages as well
 647                 * so that recently deactivated but used pages are
 648                 * quickly recovered.
 649                 */
 650                SetPageReferenced(page);
 651
 652                if (referenced_page || referenced_ptes > 1)
 653                        return PAGEREF_ACTIVATE;
 654
 655                /*
 656                 * Activate file-backed executable pages after first usage.
 657                 */
 658                if (vm_flags & VM_EXEC)
 659                        return PAGEREF_ACTIVATE;
 660
 661                return PAGEREF_KEEP;
 662        }
 663
 664        /* Reclaim if clean, defer dirty pages to writeback */
 665        if (referenced_page && !PageSwapBacked(page))
 666                return PAGEREF_RECLAIM_CLEAN;
 667
 668        return PAGEREF_RECLAIM;
 669}
 670
 671/*
 672 * shrink_page_list() returns the number of reclaimed pages
 673 */
 674static unsigned long shrink_page_list(struct list_head *page_list,
 675                                      struct zone *zone,
 676                                      struct scan_control *sc,
 677                                      unsigned long *ret_nr_dirty,
 678                                      unsigned long *ret_nr_writeback)
 679{
 680        LIST_HEAD(ret_pages);
 681        LIST_HEAD(free_pages);
 682        int pgactivate = 0;
 683        unsigned long nr_dirty = 0;
 684        unsigned long nr_congested = 0;
 685        unsigned long nr_reclaimed = 0;
 686        unsigned long nr_writeback = 0;
 687
 688        cond_resched();
 689
 690        while (!list_empty(page_list)) {
 691                enum page_references references;
 692                struct address_space *mapping;
 693                struct page *page;
 694                int may_enter_fs;
 695
 696                cond_resched();
 697
 698                page = lru_to_page(page_list);
 699                list_del(&page->lru);
 700
 701                if (!trylock_page(page))
 702                        goto keep;
 703
 704                VM_BUG_ON(PageActive(page));
 705                VM_BUG_ON(page_zone(page) != zone);
 706
 707                sc->nr_scanned++;
 708
 709                if (unlikely(!page_evictable(page, NULL)))
 710                        goto cull_mlocked;
 711
 712                if (!sc->may_unmap && page_mapped(page))
 713                        goto keep_locked;
 714
 715                /* Double the slab pressure for mapped and swapcache pages */
 716                if (page_mapped(page) || PageSwapCache(page))
 717                        sc->nr_scanned++;
 718
 719                may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
 720                        (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 721
 722                if (PageWriteback(page)) {
 723                        /*
 724                         * memcg doesn't have any dirty pages throttling so we
 725                         * could easily OOM just because too many pages are in
 726                         * writeback and there is nothing else to reclaim.
 727                         *
 728                         * Check __GFP_IO, certainly because a loop driver
 729                         * thread might enter reclaim, and deadlock if it waits
 730                         * on a page for which it is needed to do the write
 731                         * (loop masks off __GFP_IO|__GFP_FS for this reason);
 732                         * but more thought would probably show more reasons.
 733                         *
 734                         * Don't require __GFP_FS, since we're not going into
 735                         * the FS, just waiting on its writeback completion.
 736                         * Worryingly, ext4 gfs2 and xfs allocate pages with
 737                         * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so
 738                         * testing may_enter_fs here is liable to OOM on them.
 739                         */
 740                        if (global_reclaim(sc) ||
 741                            !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
 742                                /*
 743                                 * This is slightly racy - end_page_writeback()
 744                                 * might have just cleared PageReclaim, then
 745                                 * setting PageReclaim here end up interpreted
 746                                 * as PageReadahead - but that does not matter
 747                                 * enough to care.  What we do want is for this
 748                                 * page to have PageReclaim set next time memcg
 749                                 * reclaim reaches the tests above, so it will
 750                                 * then wait_on_page_writeback() to avoid OOM;
 751                                 * and it's also appropriate in global reclaim.
 752                                 */
 753                                SetPageReclaim(page);
 754                                nr_writeback++;
 755                                goto keep_locked;
 756                        }
 757                        wait_on_page_writeback(page);
 758                }
 759
 760                references = page_check_references(page, sc);
 761                switch (references) {
 762                case PAGEREF_ACTIVATE:
 763                        goto activate_locked;
 764                case PAGEREF_KEEP:
 765                        goto keep_locked;
 766                case PAGEREF_RECLAIM:
 767                case PAGEREF_RECLAIM_CLEAN:
 768                        ; /* try to reclaim the page below */
 769                }
 770
 771                /*
 772                 * Anonymous process memory has backing store?
 773                 * Try to allocate it some swap space here.
 774                 */
 775                if (PageAnon(page) && !PageSwapCache(page)) {
 776                        if (!(sc->gfp_mask & __GFP_IO))
 777                                goto keep_locked;
 778                        if (!add_to_swap(page))
 779                                goto activate_locked;
 780                        may_enter_fs = 1;
 781                }
 782
 783                mapping = page_mapping(page);
 784
 785                /*
 786                 * The page is mapped into the page tables of one or more
 787                 * processes. Try to unmap it here.
 788                 */
 789                if (page_mapped(page) && mapping) {
 790                        switch (try_to_unmap(page, TTU_UNMAP)) {
 791                        case SWAP_FAIL:
 792                                goto activate_locked;
 793                        case SWAP_AGAIN:
 794                                goto keep_locked;
 795                        case SWAP_MLOCK:
 796                                goto cull_mlocked;
 797                        case SWAP_SUCCESS:
 798                                ; /* try to free the page below */
 799                        }
 800                }
 801
 802                if (PageDirty(page)) {
 803                        nr_dirty++;
 804
 805                        /*
 806                         * Only kswapd can writeback filesystem pages to
 807                         * avoid risk of stack overflow but do not writeback
 808                         * unless under significant pressure.
 809                         */
 810                        if (page_is_file_cache(page) &&
 811                                        (!current_is_kswapd() ||
 812                                         sc->priority >= DEF_PRIORITY - 2)) {
 813                                /*
 814                                 * Immediately reclaim when written back.
 815                                 * Similar in principal to deactivate_page()
 816                                 * except we already have the page isolated
 817                                 * and know it's dirty
 818                                 */
 819                                inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
 820                                SetPageReclaim(page);
 821
 822                                goto keep_locked;
 823                        }
 824
 825                        if (references == PAGEREF_RECLAIM_CLEAN)
 826                                goto keep_locked;
 827                        if (!may_enter_fs)
 828                                goto keep_locked;
 829                        if (!sc->may_writepage)
 830                                goto keep_locked;
 831
 832                        /* Page is dirty, try to write it out here */
 833                        switch (pageout(page, mapping, sc)) {
 834                        case PAGE_KEEP:
 835                                nr_congested++;
 836                                goto keep_locked;
 837                        case PAGE_ACTIVATE:
 838                                goto activate_locked;
 839                        case PAGE_SUCCESS:
 840                                if (PageWriteback(page))
 841                                        goto keep;
 842                                if (PageDirty(page))
 843                                        goto keep;
 844
 845                                /*
 846                                 * A synchronous write - probably a ramdisk.  Go
 847                                 * ahead and try to reclaim the page.
 848                                 */
 849                                if (!trylock_page(page))
 850                                        goto keep;
 851                                if (PageDirty(page) || PageWriteback(page))
 852                                        goto keep_locked;
 853                                mapping = page_mapping(page);
 854                        case PAGE_CLEAN:
 855                                ; /* try to free the page below */
 856                        }
 857                }
 858
 859                /*
 860                 * If the page has buffers, try to free the buffer mappings
 861                 * associated with this page. If we succeed we try to free
 862                 * the page as well.
 863                 *
 864                 * We do this even if the page is PageDirty().
 865                 * try_to_release_page() does not perform I/O, but it is
 866                 * possible for a page to have PageDirty set, but it is actually
 867                 * clean (all its buffers are clean).  This happens if the
 868                 * buffers were written out directly, with submit_bh(). ext3
 869                 * will do this, as well as the blockdev mapping.
 870                 * try_to_release_page() will discover that cleanness and will
 871                 * drop the buffers and mark the page clean - it can be freed.
 872                 *
 873                 * Rarely, pages can have buffers and no ->mapping.  These are
 874                 * the pages which were not successfully invalidated in
 875                 * truncate_complete_page().  We try to drop those buffers here
 876                 * and if that worked, and the page is no longer mapped into
 877                 * process address space (page_count == 1) it can be freed.
 878                 * Otherwise, leave the page on the LRU so it is swappable.
 879                 */
 880                if (page_has_private(page)) {
 881                        if (!try_to_release_page(page, sc->gfp_mask))
 882                                goto activate_locked;
 883                        if (!mapping && page_count(page) == 1) {
 884                                unlock_page(page);
 885                                if (put_page_testzero(page))
 886                                        goto free_it;
 887                                else {
 888                                        /*
 889                                         * rare race with speculative reference.
 890                                         * the speculative reference will free
 891                                         * this page shortly, so we may
 892                                         * increment nr_reclaimed here (and
 893                                         * leave it off the LRU).
 894                                         */
 895                                        nr_reclaimed++;
 896                                        continue;
 897                                }
 898                        }
 899                }
 900
 901                if (!mapping || !__remove_mapping(mapping, page))
 902                        goto keep_locked;
 903
 904                /*
 905                 * At this point, we have no other references and there is
 906                 * no way to pick any more up (removed from LRU, removed
 907                 * from pagecache). Can use non-atomic bitops now (and
 908                 * we obviously don't have to worry about waking up a process
 909                 * waiting on the page lock, because there are no references.
 910                 */
 911                __clear_page_locked(page);
 912free_it:
 913                nr_reclaimed++;
 914
 915                /*
 916                 * Is there need to periodically free_page_list? It would
 917                 * appear not as the counts should be low
 918                 */
 919                list_add(&page->lru, &free_pages);
 920                continue;
 921
 922cull_mlocked:
 923                if (PageSwapCache(page))
 924                        try_to_free_swap(page);
 925                unlock_page(page);
 926                putback_lru_page(page);
 927                continue;
 928
 929activate_locked:
 930                /* Not a candidate for swapping, so reclaim swap space. */
 931                if (PageSwapCache(page) && vm_swap_full())
 932                        try_to_free_swap(page);
 933                VM_BUG_ON(PageActive(page));
 934                SetPageActive(page);
 935                pgactivate++;
 936keep_locked:
 937                unlock_page(page);
 938keep:
 939                list_add(&page->lru, &ret_pages);
 940                VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
 941        }
 942
 943        /*
 944         * Tag a zone as congested if all the dirty pages encountered were
 945         * backed by a congested BDI. In this case, reclaimers should just
 946         * back off and wait for congestion to clear because further reclaim
 947         * will encounter the same problem
 948         */
 949        if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
 950                zone_set_flag(zone, ZONE_CONGESTED);
 951
 952        free_hot_cold_page_list(&free_pages, 1);
 953
 954        list_splice(&ret_pages, page_list);
 955        count_vm_events(PGACTIVATE, pgactivate);
 956        *ret_nr_dirty += nr_dirty;
 957        *ret_nr_writeback += nr_writeback;
 958        return nr_reclaimed;
 959}
 960
 961/*
 962 * Attempt to remove the specified page from its LRU.  Only take this page
 963 * if it is of the appropriate PageActive status.  Pages which are being
 964 * freed elsewhere are also ignored.
 965 *
 966 * page:        page to consider
 967 * mode:        one of the LRU isolation modes defined above
 968 *
 969 * returns 0 on success, -ve errno on failure.
 970 */
 971int __isolate_lru_page(struct page *page, isolate_mode_t mode)
 972{
 973        int ret = -EINVAL;
 974
 975        /* Only take pages on the LRU. */
 976        if (!PageLRU(page))
 977                return ret;
 978
 979        /* Do not give back unevictable pages for compaction */
 980        if (PageUnevictable(page))
 981                return ret;
 982
 983        ret = -EBUSY;
 984
 985        /*
 986         * To minimise LRU disruption, the caller can indicate that it only
 987         * wants to isolate pages it will be able to operate on without
 988         * blocking - clean pages for the most part.
 989         *
 990         * ISOLATE_CLEAN means that only clean pages should be isolated. This
 991         * is used by reclaim when it is cannot write to backing storage
 992         *
 993         * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
 994         * that it is possible to migrate without blocking
 995         */
 996        if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
 997                /* All the caller can do on PageWriteback is block */
 998                if (PageWriteback(page))
 999                        return ret;
1000
1001                if (PageDirty(page)) {
1002                        struct address_space *mapping;
1003
1004                        /* ISOLATE_CLEAN means only clean pages */
1005                        if (mode & ISOLATE_CLEAN)
1006                                return ret;
1007
1008                        /*
1009                         * Only pages without mappings or that have a
1010                         * ->migratepage callback are possible to migrate
1011                         * without blocking
1012                         */
1013                        mapping = page_mapping(page);
1014                        if (mapping && !mapping->a_ops->migratepage)
1015                                return ret;
1016                }
1017        }
1018
1019        if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1020                return ret;
1021
1022        if (likely(get_page_unless_zero(page))) {
1023                /*
1024                 * Be careful not to clear PageLRU until after we're
1025                 * sure the page is not being freed elsewhere -- the
1026                 * page release code relies on it.
1027                 */
1028                ClearPageLRU(page);
1029                ret = 0;
1030        }
1031
1032        return ret;
1033}
1034
1035/*
1036 * zone->lru_lock is heavily contended.  Some of the functions that
1037 * shrink the lists perform better by taking out a batch of pages
1038 * and working on them outside the LRU lock.
1039 *
1040 * For pagecache intensive workloads, this function is the hottest
1041 * spot in the kernel (apart from copy_*_user functions).
1042 *
1043 * Appropriate locks must be held before calling this function.
1044 *
1045 * @nr_to_scan: The number of pages to look through on the list.
1046 * @lruvec:     The LRU vector to pull pages from.
1047 * @dst:        The temp list to put pages on to.
1048 * @nr_scanned: The number of pages that were scanned.
1049 * @sc:         The scan_control struct for this reclaim session
1050 * @mode:       One of the LRU isolation modes
1051 * @lru:        LRU list id for isolating
1052 *
1053 * returns how many pages were moved onto *@dst.
1054 */
1055static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1056                struct lruvec *lruvec, struct list_head *dst,
1057                unsigned long *nr_scanned, struct scan_control *sc,
1058                isolate_mode_t mode, enum lru_list lru)
1059{
1060        struct list_head *src = &lruvec->lists[lru];
1061        unsigned long nr_taken = 0;
1062        unsigned long scan;
1063
1064        for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1065                struct page *page;
1066                int nr_pages;
1067
1068                page = lru_to_page(src);
1069                prefetchw_prev_lru_page(page, src, flags);
1070
1071                VM_BUG_ON(!PageLRU(page));
1072
1073                switch (__isolate_lru_page(page, mode)) {
1074                case 0:
1075                        nr_pages = hpage_nr_pages(page);
1076                        mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
1077                        list_move(&page->lru, dst);
1078                        nr_taken += nr_pages;
1079                        break;
1080
1081                case -EBUSY:
1082                        /* else it is being freed elsewhere */
1083                        list_move(&page->lru, src);
1084                        continue;
1085
1086                default:
1087                        BUG();
1088                }
1089        }
1090
1091        *nr_scanned = scan;
1092        trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
1093                                    nr_taken, mode, is_file_lru(lru));
1094        return nr_taken;
1095}
1096
1097/**
1098 * isolate_lru_page - tries to isolate a page from its LRU list
1099 * @page: page to isolate from its LRU list
1100 *
1101 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1102 * vmstat statistic corresponding to whatever LRU list the page was on.
1103 *
1104 * Returns 0 if the page was removed from an LRU list.
1105 * Returns -EBUSY if the page was not on an LRU list.
1106 *
1107 * The returned page will have PageLRU() cleared.  If it was found on
1108 * the active list, it will have PageActive set.  If it was found on
1109 * the unevictable list, it will have the PageUnevictable bit set. That flag
1110 * may need to be cleared by the caller before letting the page go.
1111 *
1112 * The vmstat statistic corresponding to the list on which the page was
1113 * found will be decremented.
1114 *
1115 * Restrictions:
1116 * (1) Must be called with an elevated refcount on the page. This is a
1117 *     fundamentnal difference from isolate_lru_pages (which is called
1118 *     without a stable reference).
1119 * (2) the lru_lock must not be held.
1120 * (3) interrupts must be enabled.
1121 */
1122int isolate_lru_page(struct page *page)
1123{
1124        int ret = -EBUSY;
1125
1126        VM_BUG_ON(!page_count(page));
1127
1128        if (PageLRU(page)) {
1129                struct zone *zone = page_zone(page);
1130                struct lruvec *lruvec;
1131
1132                spin_lock_irq(&zone->lru_lock);
1133                lruvec = mem_cgroup_page_lruvec(page, zone);
1134                if (PageLRU(page)) {
1135                        int lru = page_lru(page);
1136                        get_page(page);
1137                        ClearPageLRU(page);
1138                        del_page_from_lru_list(page, lruvec, lru);
1139                        ret = 0;
1140                }
1141                spin_unlock_irq(&zone->lru_lock);
1142        }
1143        return ret;
1144}
1145
1146/*
1147 * Are there way too many processes in the direct reclaim path already?
1148 */
1149static int too_many_isolated(struct zone *zone, int file,
1150                struct scan_control *sc)
1151{
1152        unsigned long inactive, isolated;
1153
1154        if (current_is_kswapd())
1155                return 0;
1156
1157        if (!global_reclaim(sc))
1158                return 0;
1159
1160        if (file) {
1161                inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1162                isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1163        } else {
1164                inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1165                isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1166        }
1167
1168        return isolated > inactive;
1169}
1170
1171static noinline_for_stack void
1172putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1173{
1174        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1175        struct zone *zone = lruvec_zone(lruvec);
1176        LIST_HEAD(pages_to_free);
1177
1178        /*
1179         * Put back any unfreeable pages.
1180         */
1181        while (!list_empty(page_list)) {
1182                struct page *page = lru_to_page(page_list);
1183                int lru;
1184
1185                VM_BUG_ON(PageLRU(page));
1186                list_del(&page->lru);
1187                if (unlikely(!page_evictable(page, NULL))) {
1188                        spin_unlock_irq(&zone->lru_lock);
1189                        putback_lru_page(page);
1190                        spin_lock_irq(&zone->lru_lock);
1191                        continue;
1192                }
1193
1194                lruvec = mem_cgroup_page_lruvec(page, zone);
1195
1196                SetPageLRU(page);
1197                lru = page_lru(page);
1198                add_page_to_lru_list(page, lruvec, lru);
1199
1200                if (is_active_lru(lru)) {
1201                        int file = is_file_lru(lru);
1202                        int numpages = hpage_nr_pages(page);
1203                        reclaim_stat->recent_rotated[file] += numpages;
1204                }
1205                if (put_page_testzero(page)) {
1206                        __ClearPageLRU(page);
1207                        __ClearPageActive(page);
1208                        del_page_from_lru_list(page, lruvec, lru);
1209
1210                        if (unlikely(PageCompound(page))) {
1211                                spin_unlock_irq(&zone->lru_lock);
1212                                (*get_compound_page_dtor(page))(page);
1213                                spin_lock_irq(&zone->lru_lock);
1214                        } else
1215                                list_add(&page->lru, &pages_to_free);
1216                }
1217        }
1218
1219        /*
1220         * To save our caller's stack, now use input list for pages to free.
1221         */
1222        list_splice(&pages_to_free, page_list);
1223}
1224
1225/*
1226 * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
1227 * of reclaimed pages
1228 */
1229static noinline_for_stack unsigned long
1230shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1231                     struct scan_control *sc, enum lru_list lru)
1232{
1233        LIST_HEAD(page_list);
1234        unsigned long nr_scanned;
1235        unsigned long nr_reclaimed = 0;
1236        unsigned long nr_taken;
1237        unsigned long nr_dirty = 0;
1238        unsigned long nr_writeback = 0;
1239        isolate_mode_t isolate_mode = 0;
1240        int file = is_file_lru(lru);
1241        struct zone *zone = lruvec_zone(lruvec);
1242        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1243
1244        while (unlikely(too_many_isolated(zone, file, sc))) {
1245                congestion_wait(BLK_RW_ASYNC, HZ/10);
1246
1247                /* We are about to die and free our memory. Return now. */
1248                if (fatal_signal_pending(current))
1249                        return SWAP_CLUSTER_MAX;
1250        }
1251
1252        lru_add_drain();
1253
1254        if (!sc->may_unmap)
1255                isolate_mode |= ISOLATE_UNMAPPED;
1256        if (!sc->may_writepage)
1257                isolate_mode |= ISOLATE_CLEAN;
1258
1259        spin_lock_irq(&zone->lru_lock);
1260
1261        nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1262                                     &nr_scanned, sc, isolate_mode, lru);
1263
1264        __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1265        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1266
1267        if (global_reclaim(sc)) {
1268                zone->pages_scanned += nr_scanned;
1269                if (current_is_kswapd())
1270                        __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1271                else
1272                        __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1273        }
1274        spin_unlock_irq(&zone->lru_lock);
1275
1276        if (nr_taken == 0)
1277                return 0;
1278
1279        nr_reclaimed = shrink_page_list(&page_list, zone, sc,
1280                                                &nr_dirty, &nr_writeback);
1281
1282        spin_lock_irq(&zone->lru_lock);
1283
1284        reclaim_stat->recent_scanned[file] += nr_taken;
1285
1286        if (global_reclaim(sc)) {
1287                if (current_is_kswapd())
1288                        __count_zone_vm_events(PGSTEAL_KSWAPD, zone,
1289                                               nr_reclaimed);
1290                else
1291                        __count_zone_vm_events(PGSTEAL_DIRECT, zone,
1292                                               nr_reclaimed);
1293        }
1294
1295        putback_inactive_pages(lruvec, &page_list);
1296
1297        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1298
1299        spin_unlock_irq(&zone->lru_lock);
1300
1301        free_hot_cold_page_list(&page_list, 1);
1302
1303        /*
1304         * If reclaim is isolating dirty pages under writeback, it implies
1305         * that the long-lived page allocation rate is exceeding the page
1306         * laundering rate. Either the global limits are not being effective
1307         * at throttling processes due to the page distribution throughout
1308         * zones or there is heavy usage of a slow backing device. The
1309         * only option is to throttle from reclaim context which is not ideal
1310         * as there is no guarantee the dirtying process is throttled in the
1311         * same way balance_dirty_pages() manages.
1312         *
1313         * This scales the number of dirty pages that must be under writeback
1314         * before throttling depending on priority. It is a simple backoff
1315         * function that has the most effect in the range DEF_PRIORITY to
1316         * DEF_PRIORITY-2 which is the priority reclaim is considered to be
1317         * in trouble and reclaim is considered to be in trouble.
1318         *
1319         * DEF_PRIORITY   100% isolated pages must be PageWriteback to throttle
1320         * DEF_PRIORITY-1  50% must be PageWriteback
1321         * DEF_PRIORITY-2  25% must be PageWriteback, kswapd in trouble
1322         * ...
1323         * DEF_PRIORITY-6 For SWAP_CLUSTER_MAX isolated pages, throttle if any
1324         *                     isolated page is PageWriteback
1325         */
1326        if (nr_writeback && nr_writeback >=
1327                        (nr_taken >> (DEF_PRIORITY - sc->priority)))
1328                wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
1329
1330        trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1331                zone_idx(zone),
1332                nr_scanned, nr_reclaimed,
1333                sc->priority,
1334                trace_shrink_flags(file));
1335        return nr_reclaimed;
1336}
1337
1338/*
1339 * This moves pages from the active list to the inactive list.
1340 *
1341 * We move them the other way if the page is referenced by one or more
1342 * processes, from rmap.
1343 *
1344 * If the pages are mostly unmapped, the processing is fast and it is
1345 * appropriate to hold zone->lru_lock across the whole operation.  But if
1346 * the pages are mapped, the processing is slow (page_referenced()) so we
1347 * should drop zone->lru_lock around each page.  It's impossible to balance
1348 * this, so instead we remove the pages from the LRU while processing them.
1349 * It is safe to rely on PG_active against the non-LRU pages in here because
1350 * nobody will play with that bit on a non-LRU page.
1351 *
1352 * The downside is that we have to touch page->_count against each page.
1353 * But we had to alter page->flags anyway.
1354 */
1355
1356static void move_active_pages_to_lru(struct lruvec *lruvec,
1357                                     struct list_head *list,
1358                                     struct list_head *pages_to_free,
1359                                     enum lru_list lru)
1360{
1361        struct zone *zone = lruvec_zone(lruvec);
1362        unsigned long pgmoved = 0;
1363        struct page *page;
1364        int nr_pages;
1365
1366        while (!list_empty(list)) {
1367                page = lru_to_page(list);
1368                lruvec = mem_cgroup_page_lruvec(page, zone);
1369
1370                VM_BUG_ON(PageLRU(page));
1371                SetPageLRU(page);
1372
1373                nr_pages = hpage_nr_pages(page);
1374                mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1375                list_move(&page->lru, &lruvec->lists[lru]);
1376                pgmoved += nr_pages;
1377
1378                if (put_page_testzero(page)) {
1379                        __ClearPageLRU(page);
1380                        __ClearPageActive(page);
1381                        del_page_from_lru_list(page, lruvec, lru);
1382
1383                        if (unlikely(PageCompound(page))) {
1384                                spin_unlock_irq(&zone->lru_lock);
1385                                (*get_compound_page_dtor(page))(page);
1386                                spin_lock_irq(&zone->lru_lock);
1387                        } else
1388                                list_add(&page->lru, pages_to_free);
1389                }
1390        }
1391        __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1392        if (!is_active_lru(lru))
1393                __count_vm_events(PGDEACTIVATE, pgmoved);
1394}
1395
1396static void shrink_active_list(unsigned long nr_to_scan,
1397                               struct lruvec *lruvec,
1398                               struct scan_control *sc,
1399                               enum lru_list lru)
1400{
1401        unsigned long nr_taken;
1402        unsigned long nr_scanned;
1403        unsigned long vm_flags;
1404        LIST_HEAD(l_hold);      /* The pages which were snipped off */
1405        LIST_HEAD(l_active);
1406        LIST_HEAD(l_inactive);
1407        struct page *page;
1408        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1409        unsigned long nr_rotated = 0;
1410        isolate_mode_t isolate_mode = 0;
1411        int file = is_file_lru(lru);
1412        struct zone *zone = lruvec_zone(lruvec);
1413
1414        lru_add_drain();
1415
1416        if (!sc->may_unmap)
1417                isolate_mode |= ISOLATE_UNMAPPED;
1418        if (!sc->may_writepage)
1419                isolate_mode |= ISOLATE_CLEAN;
1420
1421        spin_lock_irq(&zone->lru_lock);
1422
1423        nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1424                                     &nr_scanned, sc, isolate_mode, lru);
1425        if (global_reclaim(sc))
1426                zone->pages_scanned += nr_scanned;
1427
1428        reclaim_stat->recent_scanned[file] += nr_taken;
1429
1430        __count_zone_vm_events(PGREFILL, zone, nr_scanned);
1431        __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1432        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1433        spin_unlock_irq(&zone->lru_lock);
1434
1435        while (!list_empty(&l_hold)) {
1436                cond_resched();
1437                page = lru_to_page(&l_hold);
1438                list_del(&page->lru);
1439
1440                if (unlikely(!page_evictable(page, NULL))) {
1441                        putback_lru_page(page);
1442                        continue;
1443                }
1444
1445                if (unlikely(buffer_heads_over_limit)) {
1446                        if (page_has_private(page) && trylock_page(page)) {
1447                                if (page_has_private(page))
1448                                        try_to_release_page(page, 0);
1449                                unlock_page(page);
1450                        }
1451                }
1452
1453                if (page_referenced(page, 0, sc->target_mem_cgroup,
1454                                    &vm_flags)) {
1455                        nr_rotated += hpage_nr_pages(page);
1456                        /*
1457                         * Identify referenced, file-backed active pages and
1458                         * give them one more trip around the active list. So
1459                         * that executable code get better chances to stay in
1460                         * memory under moderate memory pressure.  Anon pages
1461                         * are not likely to be evicted by use-once streaming
1462                         * IO, plus JVM can create lots of anon VM_EXEC pages,
1463                         * so we ignore them here.
1464                         */
1465                        if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1466                                list_add(&page->lru, &l_active);
1467                                continue;
1468                        }
1469                }
1470
1471                ClearPageActive(page);  /* we are de-activating */
1472                list_add(&page->lru, &l_inactive);
1473        }
1474
1475        /*
1476         * Move pages back to the lru list.
1477         */
1478        spin_lock_irq(&zone->lru_lock);
1479        /*
1480         * Count referenced pages from currently used mappings as rotated,
1481         * even though only some of them are actually re-activated.  This
1482         * helps balance scan pressure between file and anonymous pages in
1483         * get_scan_ratio.
1484         */
1485        reclaim_stat->recent_rotated[file] += nr_rotated;
1486
1487        move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1488        move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1489        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1490        spin_unlock_irq(&zone->lru_lock);
1491
1492        free_hot_cold_page_list(&l_hold, 1);
1493}
1494
1495#ifdef CONFIG_SWAP
1496static int inactive_anon_is_low_global(struct zone *zone)
1497{
1498        unsigned long active, inactive;
1499
1500        active = zone_page_state(zone, NR_ACTIVE_ANON);
1501        inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1502
1503        if (inactive * zone->inactive_ratio < active)
1504                return 1;
1505
1506        return 0;
1507}
1508
1509/**
1510 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1511 * @lruvec: LRU vector to check
1512 *
1513 * Returns true if the zone does not have enough inactive anon pages,
1514 * meaning some active anon pages need to be deactivated.
1515 */
1516static int inactive_anon_is_low(struct lruvec *lruvec)
1517{
1518        /*
1519         * If we don't have swap space, anonymous page deactivation
1520         * is pointless.
1521         */
1522        if (!total_swap_pages)
1523                return 0;
1524
1525        if (!mem_cgroup_disabled())
1526                return mem_cgroup_inactive_anon_is_low(lruvec);
1527
1528        return inactive_anon_is_low_global(lruvec_zone(lruvec));
1529}
1530#else
1531static inline int inactive_anon_is_low(struct lruvec *lruvec)
1532{
1533        return 0;
1534}
1535#endif
1536
1537static int inactive_file_is_low_global(struct zone *zone)
1538{
1539        unsigned long active, inactive;
1540
1541        active = zone_page_state(zone, NR_ACTIVE_FILE);
1542        inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1543
1544        return (active > inactive);
1545}
1546
1547/**
1548 * inactive_file_is_low - check if file pages need to be deactivated
1549 * @lruvec: LRU vector to check
1550 *
1551 * When the system is doing streaming IO, memory pressure here
1552 * ensures that active file pages get deactivated, until more
1553 * than half of the file pages are on the inactive list.
1554 *
1555 * Once we get to that situation, protect the system's working
1556 * set from being evicted by disabling active file page aging.
1557 *
1558 * This uses a different ratio than the anonymous pages, because
1559 * the page cache uses a use-once replacement algorithm.
1560 */
1561static int inactive_file_is_low(struct lruvec *lruvec)
1562{
1563        if (!mem_cgroup_disabled())
1564                return mem_cgroup_inactive_file_is_low(lruvec);
1565
1566        return inactive_file_is_low_global(lruvec_zone(lruvec));
1567}
1568
1569static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1570{
1571        if (is_file_lru(lru))
1572                return inactive_file_is_low(lruvec);
1573        else
1574                return inactive_anon_is_low(lruvec);
1575}
1576
1577static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1578                                 struct lruvec *lruvec, struct scan_control *sc)
1579{
1580        if (is_active_lru(lru)) {
1581                if (inactive_list_is_low(lruvec, lru))
1582                        shrink_active_list(nr_to_scan, lruvec, sc, lru);
1583                return 0;
1584        }
1585
1586        return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1587}
1588
1589static int vmscan_swappiness(struct scan_control *sc)
1590{
1591        if (global_reclaim(sc))
1592                return vm_swappiness;
1593        return mem_cgroup_swappiness(sc->target_mem_cgroup);
1594}
1595
1596/*
1597 * Determine how aggressively the anon and file LRU lists should be
1598 * scanned.  The relative value of each set of LRU lists is determined
1599 * by looking at the fraction of the pages scanned we did rotate back
1600 * onto the active list instead of evict.
1601 *
1602 * nr[0] = anon pages to scan; nr[1] = file pages to scan
1603 */
1604static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
1605                           unsigned long *nr)
1606{
1607        unsigned long anon, file, free;
1608        unsigned long anon_prio, file_prio;
1609        unsigned long ap, fp;
1610        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1611        u64 fraction[2], denominator;
1612        enum lru_list lru;
1613        int noswap = 0;
1614        bool force_scan = false;
1615        struct zone *zone = lruvec_zone(lruvec);
1616
1617        /*
1618         * If the zone or memcg is small, nr[l] can be 0.  This
1619         * results in no scanning on this priority and a potential
1620         * priority drop.  Global direct reclaim can go to the next
1621         * zone and tends to have no problems. Global kswapd is for
1622         * zone balancing and it needs to scan a minimum amount. When
1623         * reclaiming for a memcg, a priority drop can cause high
1624         * latencies, so it's better to scan a minimum amount there as
1625         * well.
1626         */
1627        if (current_is_kswapd() && zone->all_unreclaimable)
1628                force_scan = true;
1629        if (!global_reclaim(sc))
1630                force_scan = true;
1631
1632        /* If we have no swap space, do not bother scanning anon pages. */
1633        if (!sc->may_swap || (nr_swap_pages <= 0)) {
1634                noswap = 1;
1635                fraction[0] = 0;
1636                fraction[1] = 1;
1637                denominator = 1;
1638                goto out;
1639        }
1640
1641        anon  = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
1642                get_lru_size(lruvec, LRU_INACTIVE_ANON);
1643        file  = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
1644                get_lru_size(lruvec, LRU_INACTIVE_FILE);
1645
1646        if (global_reclaim(sc)) {
1647                free  = zone_page_state(zone, NR_FREE_PAGES);
1648                /* If we have very few page cache pages,
1649                   force-scan anon pages. */
1650                if (unlikely(file + free <= high_wmark_pages(zone))) {
1651                        fraction[0] = 1;
1652                        fraction[1] = 0;
1653                        denominator = 1;
1654                        goto out;
1655                }
1656        }
1657
1658        /*
1659         * With swappiness at 100, anonymous and file have the same priority.
1660         * This scanning priority is essentially the inverse of IO cost.
1661         */
1662        anon_prio = vmscan_swappiness(sc);
1663        file_prio = 200 - anon_prio;
1664
1665        /*
1666         * OK, so we have swap space and a fair amount of page cache
1667         * pages.  We use the recently rotated / recently scanned
1668         * ratios to determine how valuable each cache is.
1669         *
1670         * Because workloads change over time (and to avoid overflow)
1671         * we keep these statistics as a floating average, which ends
1672         * up weighing recent references more than old ones.
1673         *
1674         * anon in [0], file in [1]
1675         */
1676        spin_lock_irq(&zone->lru_lock);
1677        if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1678                reclaim_stat->recent_scanned[0] /= 2;
1679                reclaim_stat->recent_rotated[0] /= 2;
1680        }
1681
1682        if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1683                reclaim_stat->recent_scanned[1] /= 2;
1684                reclaim_stat->recent_rotated[1] /= 2;
1685        }
1686
1687        /*
1688         * The amount of pressure on anon vs file pages is inversely
1689         * proportional to the fraction of recently scanned pages on
1690         * each list that were recently referenced and in active use.
1691         */
1692        ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1693        ap /= reclaim_stat->recent_rotated[0] + 1;
1694
1695        fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
1696        fp /= reclaim_stat->recent_rotated[1] + 1;
1697        spin_unlock_irq(&zone->lru_lock);
1698
1699        fraction[0] = ap;
1700        fraction[1] = fp;
1701        denominator = ap + fp + 1;
1702out:
1703        for_each_evictable_lru(lru) {
1704                int file = is_file_lru(lru);
1705                unsigned long scan;
1706
1707                scan = get_lru_size(lruvec, lru);
1708                if (sc->priority || noswap || !vmscan_swappiness(sc)) {
1709                        scan >>= sc->priority;
1710                        if (!scan && force_scan)
1711                                scan = SWAP_CLUSTER_MAX;
1712                        scan = div64_u64(scan * fraction[file], denominator);
1713                }
1714                nr[lru] = scan;
1715        }
1716}
1717
1718/* Use reclaim/compaction for costly allocs or under memory pressure */
1719static bool in_reclaim_compaction(struct scan_control *sc)
1720{
1721        if (COMPACTION_BUILD && sc->order &&
1722                        (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
1723                         sc->priority < DEF_PRIORITY - 2))
1724                return true;
1725
1726        return false;
1727}
1728
1729/*
1730 * Reclaim/compaction is used for high-order allocation requests. It reclaims
1731 * order-0 pages before compacting the zone. should_continue_reclaim() returns
1732 * true if more pages should be reclaimed such that when the page allocator
1733 * calls try_to_compact_zone() that it will have enough free pages to succeed.
1734 * It will give up earlier than that if there is difficulty reclaiming pages.
1735 */
1736static inline bool should_continue_reclaim(struct lruvec *lruvec,
1737                                        unsigned long nr_reclaimed,
1738                                        unsigned long nr_scanned,
1739                                        struct scan_control *sc)
1740{
1741        unsigned long pages_for_compaction;
1742        unsigned long inactive_lru_pages;
1743
1744        /* If not in reclaim/compaction mode, stop */
1745        if (!in_reclaim_compaction(sc))
1746                return false;
1747
1748        /* Consider stopping depending on scan and reclaim activity */
1749        if (sc->gfp_mask & __GFP_REPEAT) {
1750                /*
1751                 * For __GFP_REPEAT allocations, stop reclaiming if the
1752                 * full LRU list has been scanned and we are still failing
1753                 * to reclaim pages. This full LRU scan is potentially
1754                 * expensive but a __GFP_REPEAT caller really wants to succeed
1755                 */
1756                if (!nr_reclaimed && !nr_scanned)
1757                        return false;
1758        } else {
1759                /*
1760                 * For non-__GFP_REPEAT allocations which can presumably
1761                 * fail without consequence, stop if we failed to reclaim
1762                 * any pages from the last SWAP_CLUSTER_MAX number of
1763                 * pages that were scanned. This will return to the
1764                 * caller faster at the risk reclaim/compaction and
1765                 * the resulting allocation attempt fails
1766                 */
1767                if (!nr_reclaimed)
1768                        return false;
1769        }
1770
1771        /*
1772         * If we have not reclaimed enough pages for compaction and the
1773         * inactive lists are large enough, continue reclaiming
1774         */
1775        pages_for_compaction = (2UL << sc->order);
1776        inactive_lru_pages = get_lru_size(lruvec, LRU_INACTIVE_FILE);
1777        if (nr_swap_pages > 0)
1778                inactive_lru_pages += get_lru_size(lruvec, LRU_INACTIVE_ANON);
1779        if (sc->nr_reclaimed < pages_for_compaction &&
1780                        inactive_lru_pages > pages_for_compaction)
1781                return true;
1782
1783        /* If compaction would go ahead or the allocation would succeed, stop */
1784        switch (compaction_suitable(lruvec_zone(lruvec), sc->order)) {
1785        case COMPACT_PARTIAL:
1786        case COMPACT_CONTINUE:
1787                return false;
1788        default:
1789                return true;
1790        }
1791}
1792
1793/*
1794 * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1795 */
1796static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
1797{
1798        unsigned long nr[NR_LRU_LISTS];
1799        unsigned long nr_to_scan;
1800        enum lru_list lru;
1801        unsigned long nr_reclaimed, nr_scanned;
1802        unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1803        struct blk_plug plug;
1804
1805restart:
1806        nr_reclaimed = 0;
1807        nr_scanned = sc->nr_scanned;
1808        get_scan_count(lruvec, sc, nr);
1809
1810        blk_start_plug(&plug);
1811        while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1812                                        nr[LRU_INACTIVE_FILE]) {
1813                for_each_evictable_lru(lru) {
1814                        if (nr[lru]) {
1815                                nr_to_scan = min_t(unsigned long,
1816                                                   nr[lru], SWAP_CLUSTER_MAX);
1817                                nr[lru] -= nr_to_scan;
1818
1819                                nr_reclaimed += shrink_list(lru, nr_to_scan,
1820                                                            lruvec, sc);
1821                        }
1822                }
1823                /*
1824                 * On large memory systems, scan >> priority can become
1825                 * really large. This is fine for the starting priority;
1826                 * we want to put equal scanning pressure on each zone.
1827                 * However, if the VM has a harder time of freeing pages,
1828                 * with multiple processes reclaiming pages, the total
1829                 * freeing target can get unreasonably large.
1830                 */
1831                if (nr_reclaimed >= nr_to_reclaim &&
1832                    sc->priority < DEF_PRIORITY)
1833                        break;
1834        }
1835        blk_finish_plug(&plug);
1836        sc->nr_reclaimed += nr_reclaimed;
1837
1838        /*
1839         * Even if we did not try to evict anon pages at all, we want to
1840         * rebalance the anon lru active/inactive ratio.
1841         */
1842        if (inactive_anon_is_low(lruvec))
1843                shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
1844                                   sc, LRU_ACTIVE_ANON);
1845
1846        /* reclaim/compaction might need reclaim to continue */
1847        if (should_continue_reclaim(lruvec, nr_reclaimed,
1848                                    sc->nr_scanned - nr_scanned, sc))
1849                goto restart;
1850
1851        throttle_vm_writeout(sc->gfp_mask);
1852}
1853
1854static void shrink_zone(struct zone *zone, struct scan_control *sc)
1855{
1856        struct mem_cgroup *root = sc->target_mem_cgroup;
1857        struct mem_cgroup_reclaim_cookie reclaim = {
1858                .zone = zone,
1859                .priority = sc->priority,
1860        };
1861        struct mem_cgroup *memcg;
1862
1863        memcg = mem_cgroup_iter(root, NULL, &reclaim);
1864        do {
1865                struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
1866
1867                shrink_lruvec(lruvec, sc);
1868
1869                /*
1870                 * Limit reclaim has historically picked one memcg and
1871                 * scanned it with decreasing priority levels until
1872                 * nr_to_reclaim had been reclaimed.  This priority
1873                 * cycle is thus over after a single memcg.
1874                 *
1875                 * Direct reclaim and kswapd, on the other hand, have
1876                 * to scan all memory cgroups to fulfill the overall
1877                 * scan target for the zone.
1878                 */
1879                if (!global_reclaim(sc)) {
1880                        mem_cgroup_iter_break(root, memcg);
1881                        break;
1882                }
1883                memcg = mem_cgroup_iter(root, memcg, &reclaim);
1884        } while (memcg);
1885}
1886
1887/* Returns true if compaction should go ahead for a high-order request */
1888static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
1889{
1890        unsigned long balance_gap, watermark;
1891        bool watermark_ok;
1892
1893        /* Do not consider compaction for orders reclaim is meant to satisfy */
1894        if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
1895                return false;
1896
1897        /*
1898         * Compaction takes time to run and there are potentially other
1899         * callers using the pages just freed. Continue reclaiming until
1900         * there is a buffer of free pages available to give compaction
1901         * a reasonable chance of completing and allocating the page
1902         */
1903        balance_gap = min(low_wmark_pages(zone),
1904                (zone->present_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
1905                        KSWAPD_ZONE_BALANCE_GAP_RATIO);
1906        watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
1907        watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
1908
1909        /*
1910         * If compaction is deferred, reclaim up to a point where
1911         * compaction will have a chance of success when re-enabled
1912         */
1913        if (compaction_deferred(zone, sc->order))
1914                return watermark_ok;
1915
1916        /* If compaction is not ready to start, keep reclaiming */
1917        if (!compaction_suitable(zone, sc->order))
1918                return false;
1919
1920        return watermark_ok;
1921}
1922
1923/*
1924 * This is the direct reclaim path, for page-allocating processes.  We only
1925 * try to reclaim pages from zones which will satisfy the caller's allocation
1926 * request.
1927 *
1928 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
1929 * Because:
1930 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1931 *    allocation or
1932 * b) The target zone may be at high_wmark_pages(zone) but the lower zones
1933 *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
1934 *    zone defense algorithm.
1935 *
1936 * If a zone is deemed to be full of pinned pages then just give it a light
1937 * scan then give up on it.
1938 *
1939 * This function returns true if a zone is being reclaimed for a costly
1940 * high-order allocation and compaction is ready to begin. This indicates to
1941 * the caller that it should consider retrying the allocation instead of
1942 * further reclaim.
1943 */
1944static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
1945{
1946        struct zoneref *z;
1947        struct zone *zone;
1948        unsigned long nr_soft_reclaimed;
1949        unsigned long nr_soft_scanned;
1950        bool aborted_reclaim = false;
1951
1952        /*
1953         * If the number of buffer_heads in the machine exceeds the maximum
1954         * allowed level, force direct reclaim to scan the highmem zone as
1955         * highmem pages could be pinning lowmem pages storing buffer_heads
1956         */
1957        if (buffer_heads_over_limit)
1958                sc->gfp_mask |= __GFP_HIGHMEM;
1959
1960        for_each_zone_zonelist_nodemask(zone, z, zonelist,
1961                                        gfp_zone(sc->gfp_mask), sc->nodemask) {
1962                if (!populated_zone(zone))
1963                        continue;
1964                /*
1965                 * Take care memory controller reclaiming has small influence
1966                 * to global LRU.
1967                 */
1968                if (global_reclaim(sc)) {
1969                        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1970                                continue;
1971                        if (zone->all_unreclaimable &&
1972                                        sc->priority != DEF_PRIORITY)
1973                                continue;       /* Let kswapd poll it */
1974                        if (COMPACTION_BUILD) {
1975                                /*
1976                                 * If we already have plenty of memory free for
1977                                 * compaction in this zone, don't free any more.
1978                                 * Even though compaction is invoked for any
1979                                 * non-zero order, only frequent costly order
1980                                 * reclamation is disruptive enough to become a
1981                                 * noticeable problem, like transparent huge
1982                                 * page allocations.
1983                                 */
1984                                if (compaction_ready(zone, sc)) {
1985                                        aborted_reclaim = true;
1986                                        continue;
1987                                }
1988                        }
1989                        /*
1990                         * This steals pages from memory cgroups over softlimit
1991                         * and returns the number of reclaimed pages and
1992                         * scanned pages. This works for global memory pressure
1993                         * and balancing, not for a memcg's limit.
1994                         */
1995                        nr_soft_scanned = 0;
1996                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
1997                                                sc->order, sc->gfp_mask,
1998                                                &nr_soft_scanned);
1999                        sc->nr_reclaimed += nr_soft_reclaimed;
2000                        sc->nr_scanned += nr_soft_scanned;
2001                        /* need some check for avoid more shrink_zone() */
2002                }
2003
2004                shrink_zone(zone, sc);
2005        }
2006
2007        return aborted_reclaim;
2008}
2009
2010static bool zone_reclaimable(struct zone *zone)
2011{
2012        return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
2013}
2014
2015/* All zones in zonelist are unreclaimable? */
2016static bool all_unreclaimable(struct zonelist *zonelist,
2017                struct scan_control *sc)
2018{
2019        struct zoneref *z;
2020        struct zone *zone;
2021
2022        for_each_zone_zonelist_nodemask(zone, z, zonelist,
2023                        gfp_zone(sc->gfp_mask), sc->nodemask) {
2024                if (!populated_zone(zone))
2025                        continue;
2026                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2027                        continue;
2028                if (!zone->all_unreclaimable)
2029                        return false;
2030        }
2031
2032        return true;
2033}
2034
2035/*
2036 * This is the main entry point to direct page reclaim.
2037 *
2038 * If a full scan of the inactive list fails to free enough memory then we
2039 * are "out of memory" and something needs to be killed.
2040 *
2041 * If the caller is !__GFP_FS then the probability of a failure is reasonably
2042 * high - the zone may be full of dirty or under-writeback pages, which this
2043 * caller can't do much about.  We kick the writeback threads and take explicit
2044 * naps in the hope that some of these pages can be written.  But if the
2045 * allocating task holds filesystem locks which prevent writeout this might not
2046 * work, and the allocation attempt will fail.
2047 *
2048 * returns:     0, if no pages reclaimed
2049 *              else, the number of pages reclaimed
2050 */
2051static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2052                                        struct scan_control *sc,
2053                                        struct shrink_control *shrink)
2054{
2055        unsigned long total_scanned = 0;
2056        struct reclaim_state *reclaim_state = current->reclaim_state;
2057        struct zoneref *z;
2058        struct zone *zone;
2059        unsigned long writeback_threshold;
2060        bool aborted_reclaim;
2061
2062        delayacct_freepages_start();
2063
2064        if (global_reclaim(sc))
2065                count_vm_event(ALLOCSTALL);
2066
2067        do {
2068                sc->nr_scanned = 0;
2069                aborted_reclaim = shrink_zones(zonelist, sc);
2070
2071                /*
2072                 * Don't shrink slabs when reclaiming memory from
2073                 * over limit cgroups
2074                 */
2075                if (global_reclaim(sc)) {
2076                        unsigned long lru_pages = 0;
2077                        for_each_zone_zonelist(zone, z, zonelist,
2078                                        gfp_zone(sc->gfp_mask)) {
2079                                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2080                                        continue;
2081
2082                                lru_pages += zone_reclaimable_pages(zone);
2083                        }
2084
2085                        shrink_slab(shrink, sc->nr_scanned, lru_pages);
2086                        if (reclaim_state) {
2087                                sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2088                                reclaim_state->reclaimed_slab = 0;
2089                        }
2090                }
2091                total_scanned += sc->nr_scanned;
2092                if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2093                        goto out;
2094
2095                /*
2096                 * Try to write back as many pages as we just scanned.  This
2097                 * tends to cause slow streaming writers to write data to the
2098                 * disk smoothly, at the dirtying rate, which is nice.   But
2099                 * that's undesirable in laptop mode, where we *want* lumpy
2100                 * writeout.  So in laptop mode, write out the whole world.
2101                 */
2102                writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2103                if (total_scanned > writeback_threshold) {
2104                        wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2105                                                WB_REASON_TRY_TO_FREE_PAGES);
2106                        sc->may_writepage = 1;
2107                }
2108
2109                /* Take a nap, wait for some writeback to complete */
2110                if (!sc->hibernation_mode && sc->nr_scanned &&
2111                    sc->priority < DEF_PRIORITY - 2) {
2112                        struct zone *preferred_zone;
2113
2114                        first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
2115                                                &cpuset_current_mems_allowed,
2116                                                &preferred_zone);
2117                        wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
2118                }
2119        } while (--sc->priority >= 0);
2120
2121out:
2122        delayacct_freepages_end();
2123
2124        if (sc->nr_reclaimed)
2125                return sc->nr_reclaimed;
2126
2127        /*
2128         * As hibernation is going on, kswapd is freezed so that it can't mark
2129         * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2130         * check.
2131         */
2132        if (oom_killer_disabled)
2133                return 0;
2134
2135        /* Aborted reclaim to try compaction? don't OOM, then */
2136        if (aborted_reclaim)
2137                return 1;
2138
2139        /* top priority shrink_zones still had more to do? don't OOM, then */
2140        if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2141                return 1;
2142
2143        return 0;
2144}
2145
2146unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2147                                gfp_t gfp_mask, nodemask_t *nodemask)
2148{
2149        unsigned long nr_reclaimed;
2150        struct scan_control sc = {
2151                .gfp_mask = gfp_mask,
2152                .may_writepage = !laptop_mode,
2153                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2154                .may_unmap = 1,
2155                .may_swap = 1,
2156                .order = order,
2157                .priority = DEF_PRIORITY,
2158                .target_mem_cgroup = NULL,
2159                .nodemask = nodemask,
2160        };
2161        struct shrink_control shrink = {
2162                .gfp_mask = sc.gfp_mask,
2163        };
2164
2165        trace_mm_vmscan_direct_reclaim_begin(order,
2166                                sc.may_writepage,
2167                                gfp_mask);
2168
2169        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2170
2171        trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2172
2173        return nr_reclaimed;
2174}
2175
2176#ifdef CONFIG_CGROUP_MEM_RES_CTLR
2177
2178unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2179                                                gfp_t gfp_mask, bool noswap,
2180                                                struct zone *zone,
2181                                                unsigned long *nr_scanned)
2182{
2183        struct scan_control sc = {
2184                .nr_scanned = 0,
2185                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2186                .may_writepage = !laptop_mode,
2187                .may_unmap = 1,
2188                .may_swap = !noswap,
2189                .order = 0,
2190                .priority = 0,
2191                .target_mem_cgroup = memcg,
2192        };
2193        struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2194
2195        sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2196                        (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2197
2198        trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2199                                                      sc.may_writepage,
2200                                                      sc.gfp_mask);
2201
2202        /*
2203         * NOTE: Although we can get the priority field, using it
2204         * here is not a good idea, since it limits the pages we can scan.
2205         * if we don't reclaim here, the shrink_zone from balance_pgdat
2206         * will pick up pages from other mem cgroup's as well. We hack
2207         * the priority and make it zero.
2208         */
2209        shrink_lruvec(lruvec, &sc);
2210
2211        trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2212
2213        *nr_scanned = sc.nr_scanned;
2214        return sc.nr_reclaimed;
2215}
2216
2217unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
2218                                           gfp_t gfp_mask,
2219                                           bool noswap)
2220{
2221        struct zonelist *zonelist;
2222        unsigned long nr_reclaimed;
2223        int nid;
2224        struct scan_control sc = {
2225                .may_writepage = !laptop_mode,
2226                .may_unmap = 1,
2227                .may_swap = !noswap,
2228                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2229                .order = 0,
2230                .priority = DEF_PRIORITY,
2231                .target_mem_cgroup = memcg,
2232                .nodemask = NULL, /* we don't care the placement */
2233                .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2234                                (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2235        };
2236        struct shrink_control shrink = {
2237                .gfp_mask = sc.gfp_mask,
2238        };
2239
2240        /*
2241         * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2242         * take care of from where we get pages. So the node where we start the
2243         * scan does not need to be the current node.
2244         */
2245        nid = mem_cgroup_select_victim_node(memcg);
2246
2247        zonelist = NODE_DATA(nid)->node_zonelists;
2248
2249        trace_mm_vmscan_memcg_reclaim_begin(0,
2250                                            sc.may_writepage,
2251                                            sc.gfp_mask);
2252
2253        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2254
2255        trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2256
2257        return nr_reclaimed;
2258}
2259#endif
2260
2261static void age_active_anon(struct zone *zone, struct scan_control *sc)
2262{
2263        struct mem_cgroup *memcg;
2264
2265        if (!total_swap_pages)
2266                return;
2267
2268        memcg = mem_cgroup_iter(NULL, NULL, NULL);
2269        do {
2270                struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2271
2272                if (inactive_anon_is_low(lruvec))
2273                        shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2274                                           sc, LRU_ACTIVE_ANON);
2275
2276                memcg = mem_cgroup_iter(NULL, memcg, NULL);
2277        } while (memcg);
2278}
2279
2280/*
2281 * pgdat_balanced is used when checking if a node is balanced for high-order
2282 * allocations. Only zones that meet watermarks and are in a zone allowed
2283 * by the callers classzone_idx are added to balanced_pages. The total of
2284 * balanced pages must be at least 25% of the zones allowed by classzone_idx
2285 * for the node to be considered balanced. Forcing all zones to be balanced
2286 * for high orders can cause excessive reclaim when there are imbalanced zones.
2287 * The choice of 25% is due to
2288 *   o a 16M DMA zone that is balanced will not balance a zone on any
2289 *     reasonable sized machine
2290 *   o On all other machines, the top zone must be at least a reasonable
2291 *     percentage of the middle zones. For example, on 32-bit x86, highmem
2292 *     would need to be at least 256M for it to be balance a whole node.
2293 *     Similarly, on x86-64 the Normal zone would need to be at least 1G
2294 *     to balance a node on its own. These seemed like reasonable ratios.
2295 */
2296static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
2297                                                int classzone_idx)
2298{
2299        unsigned long present_pages = 0;
2300        int i;
2301
2302        for (i = 0; i <= classzone_idx; i++)
2303                present_pages += pgdat->node_zones[i].present_pages;
2304
2305        /* A special case here: if zone has no page, we think it's balanced */
2306        return balanced_pages >= (present_pages >> 2);
2307}
2308
2309/* is kswapd sleeping prematurely? */
2310static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining,
2311                                        int classzone_idx)
2312{
2313        int i;
2314        unsigned long balanced = 0;
2315        bool all_zones_ok = true;
2316
2317        /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2318        if (remaining)
2319                return true;
2320
2321        /* Check the watermark levels */
2322        for (i = 0; i <= classzone_idx; i++) {
2323                struct zone *zone = pgdat->node_zones + i;
2324
2325                if (!populated_zone(zone))
2326                        continue;
2327
2328                /*
2329                 * balance_pgdat() skips over all_unreclaimable after
2330                 * DEF_PRIORITY. Effectively, it considers them balanced so
2331                 * they must be considered balanced here as well if kswapd
2332                 * is to sleep
2333                 */
2334                if (zone->all_unreclaimable) {
2335                        balanced += zone->present_pages;
2336                        continue;
2337                }
2338
2339                if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
2340                                                        i, 0))
2341                        all_zones_ok = false;
2342                else
2343                        balanced += zone->present_pages;
2344        }
2345
2346        /*
2347         * For high-order requests, the balanced zones must contain at least
2348         * 25% of the nodes pages for kswapd to sleep. For order-0, all zones
2349         * must be balanced
2350         */
2351        if (order)
2352                return !pgdat_balanced(pgdat, balanced, classzone_idx);
2353        else
2354                return !all_zones_ok;
2355}
2356
2357/*
2358 * For kswapd, balance_pgdat() will work across all this node's zones until
2359 * they are all at high_wmark_pages(zone).
2360 *
2361 * Returns the final order kswapd was reclaiming at
2362 *
2363 * There is special handling here for zones which are full of pinned pages.
2364 * This can happen if the pages are all mlocked, or if they are all used by
2365 * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
2366 * What we do is to detect the case where all pages in the zone have been
2367 * scanned twice and there has been zero successful reclaim.  Mark the zone as
2368 * dead and from now on, only perform a short scan.  Basically we're polling
2369 * the zone for when the problem goes away.
2370 *
2371 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
2372 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2373 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2374 * lower zones regardless of the number of free pages in the lower zones. This
2375 * interoperates with the page allocator fallback scheme to ensure that aging
2376 * of pages is balanced across the zones.
2377 */
2378static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2379                                                        int *classzone_idx)
2380{
2381        int all_zones_ok;
2382        unsigned long balanced;
2383        int i;
2384        int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
2385        unsigned long total_scanned;
2386        struct reclaim_state *reclaim_state = current->reclaim_state;
2387        unsigned long nr_soft_reclaimed;
2388        unsigned long nr_soft_scanned;
2389        struct scan_control sc = {
2390                .gfp_mask = GFP_KERNEL,
2391                .may_unmap = 1,
2392                .may_swap = 1,
2393                /*
2394                 * kswapd doesn't want to be bailed out while reclaim. because
2395                 * we want to put equal scanning pressure on each zone.
2396                 */
2397                .nr_to_reclaim = ULONG_MAX,
2398                .order = order,
2399                .target_mem_cgroup = NULL,
2400        };
2401        struct shrink_control shrink = {
2402                .gfp_mask = sc.gfp_mask,
2403        };
2404loop_again:
2405        total_scanned = 0;
2406        sc.priority = DEF_PRIORITY;
2407        sc.nr_reclaimed = 0;
2408        sc.may_writepage = !laptop_mode;
2409        count_vm_event(PAGEOUTRUN);
2410
2411        do {
2412                unsigned long lru_pages = 0;
2413                int has_under_min_watermark_zone = 0;
2414
2415                all_zones_ok = 1;
2416                balanced = 0;
2417
2418                /*
2419                 * Scan in the highmem->dma direction for the highest
2420                 * zone which needs scanning
2421                 */
2422                for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2423                        struct zone *zone = pgdat->node_zones + i;
2424
2425                        if (!populated_zone(zone))
2426                                continue;
2427
2428                        if (zone->all_unreclaimable &&
2429                            sc.priority != DEF_PRIORITY)
2430                                continue;
2431
2432                        /*
2433                         * Do some background aging of the anon list, to give
2434                         * pages a chance to be referenced before reclaiming.
2435                         */
2436                        age_active_anon(zone, &sc);
2437
2438                        /*
2439                         * If the number of buffer_heads in the machine
2440                         * exceeds the maximum allowed level and this node
2441                         * has a highmem zone, force kswapd to reclaim from
2442                         * it to relieve lowmem pressure.
2443                         */
2444                        if (buffer_heads_over_limit && is_highmem_idx(i)) {
2445                                end_zone = i;
2446                                break;
2447                        }
2448
2449                        if (!zone_watermark_ok_safe(zone, order,
2450                                        high_wmark_pages(zone), 0, 0)) {
2451                                end_zone = i;
2452                                break;
2453                        } else {
2454                                /* If balanced, clear the congested flag */
2455                                zone_clear_flag(zone, ZONE_CONGESTED);
2456                        }
2457                }
2458                if (i < 0)
2459                        goto out;
2460
2461                for (i = 0; i <= end_zone; i++) {
2462                        struct zone *zone = pgdat->node_zones + i;
2463
2464                        lru_pages += zone_reclaimable_pages(zone);
2465                }
2466
2467                /*
2468                 * Now scan the zone in the dma->highmem direction, stopping
2469                 * at the last zone which needs scanning.
2470                 *
2471                 * We do this because the page allocator works in the opposite
2472                 * direction.  This prevents the page allocator from allocating
2473                 * pages behind kswapd's direction of progress, which would
2474                 * cause too much scanning of the lower zones.
2475                 */
2476                for (i = 0; i <= end_zone; i++) {
2477                        struct zone *zone = pgdat->node_zones + i;
2478                        int nr_slab, testorder;
2479                        unsigned long balance_gap;
2480
2481                        if (!populated_zone(zone))
2482                                continue;
2483
2484                        if (zone->all_unreclaimable &&
2485                            sc.priority != DEF_PRIORITY)
2486                                continue;
2487
2488                        sc.nr_scanned = 0;
2489
2490                        nr_soft_scanned = 0;
2491                        /*
2492                         * Call soft limit reclaim before calling shrink_zone.
2493                         */
2494                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2495                                                        order, sc.gfp_mask,
2496                                                        &nr_soft_scanned);
2497                        sc.nr_reclaimed += nr_soft_reclaimed;
2498                        total_scanned += nr_soft_scanned;
2499
2500                        /*
2501                         * We put equal pressure on every zone, unless
2502                         * one zone has way too many pages free
2503                         * already. The "too many pages" is defined
2504                         * as the high wmark plus a "gap" where the
2505                         * gap is either the low watermark or 1%
2506                         * of the zone, whichever is smaller.
2507                         */
2508                        balance_gap = min(low_wmark_pages(zone),
2509                                (zone->present_pages +
2510                                        KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2511                                KSWAPD_ZONE_BALANCE_GAP_RATIO);
2512                        /*
2513                         * Kswapd reclaims only single pages with compaction
2514                         * enabled. Trying too hard to reclaim until contiguous
2515                         * free pages have become available can hurt performance
2516                         * by evicting too much useful data from memory.
2517                         * Do not reclaim more than needed for compaction.
2518                         */
2519                        testorder = order;
2520                        if (COMPACTION_BUILD && order &&
2521                                        compaction_suitable(zone, order) !=
2522                                                COMPACT_SKIPPED)
2523                                testorder = 0;
2524
2525                        if ((buffer_heads_over_limit && is_highmem_idx(i)) ||
2526                                    !zone_watermark_ok_safe(zone, testorder,
2527                                        high_wmark_pages(zone) + balance_gap,
2528                                        end_zone, 0)) {
2529                                shrink_zone(zone, &sc);
2530
2531                                reclaim_state->reclaimed_slab = 0;
2532                                nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages);
2533                                sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2534                                total_scanned += sc.nr_scanned;
2535
2536                                if (nr_slab == 0 && !zone_reclaimable(zone))
2537                                        zone->all_unreclaimable = 1;
2538                        }
2539
2540                        /*
2541                         * If we've done a decent amount of scanning and
2542                         * the reclaim ratio is low, start doing writepage
2543                         * even in laptop mode
2544                         */
2545                        if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2546                            total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
2547                                sc.may_writepage = 1;
2548
2549                        if (zone->all_unreclaimable) {
2550                                if (end_zone && end_zone == i)
2551                                        end_zone--;
2552                                continue;
2553                        }
2554
2555                        if (!zone_watermark_ok_safe(zone, testorder,
2556                                        high_wmark_pages(zone), end_zone, 0)) {
2557                                all_zones_ok = 0;
2558                                /*
2559                                 * We are still under min water mark.  This
2560                                 * means that we have a GFP_ATOMIC allocation
2561                                 * failure risk. Hurry up!
2562                                 */
2563                                if (!zone_watermark_ok_safe(zone, order,
2564                                            min_wmark_pages(zone), end_zone, 0))
2565                                        has_under_min_watermark_zone = 1;
2566                        } else {
2567                                /*
2568                                 * If a zone reaches its high watermark,
2569                                 * consider it to be no longer congested. It's
2570                                 * possible there are dirty pages backed by
2571                                 * congested BDIs but as pressure is relieved,
2572                                 * spectulatively avoid congestion waits
2573                                 */
2574                                zone_clear_flag(zone, ZONE_CONGESTED);
2575                                if (i <= *classzone_idx)
2576                                        balanced += zone->present_pages;
2577                        }
2578
2579                }
2580                if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
2581                        break;          /* kswapd: all done */
2582                /*
2583                 * OK, kswapd is getting into trouble.  Take a nap, then take
2584                 * another pass across the zones.
2585                 */
2586                if (total_scanned && (sc.priority < DEF_PRIORITY - 2)) {
2587                        if (has_under_min_watermark_zone)
2588                                count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
2589                        else
2590                                congestion_wait(BLK_RW_ASYNC, HZ/10);
2591                }
2592
2593                /*
2594                 * We do this so kswapd doesn't build up large priorities for
2595                 * example when it is freeing in parallel with allocators. It
2596                 * matches the direct reclaim path behaviour in terms of impact
2597                 * on zone->*_priority.
2598                 */
2599                if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2600                        break;
2601        } while (--sc.priority >= 0);
2602out:
2603
2604        /*
2605         * order-0: All zones must meet high watermark for a balanced node
2606         * high-order: Balanced zones must make up at least 25% of the node
2607         *             for the node to be balanced
2608         */
2609        if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) {
2610                cond_resched();
2611
2612                try_to_freeze();
2613
2614                /*
2615                 * Fragmentation may mean that the system cannot be
2616                 * rebalanced for high-order allocations in all zones.
2617                 * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2618                 * it means the zones have been fully scanned and are still
2619                 * not balanced. For high-order allocations, there is
2620                 * little point trying all over again as kswapd may
2621                 * infinite loop.
2622                 *
2623                 * Instead, recheck all watermarks at order-0 as they
2624                 * are the most important. If watermarks are ok, kswapd will go
2625                 * back to sleep. High-order users can still perform direct
2626                 * reclaim if they wish.
2627                 */
2628                if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2629                        order = sc.order = 0;
2630
2631                goto loop_again;
2632        }
2633
2634        /*
2635         * If kswapd was reclaiming at a higher order, it has the option of
2636         * sleeping without all zones being balanced. Before it does, it must
2637         * ensure that the watermarks for order-0 on *all* zones are met and
2638         * that the congestion flags are cleared. The congestion flag must
2639         * be cleared as kswapd is the only mechanism that clears the flag
2640         * and it is potentially going to sleep here.
2641         */
2642        if (order) {
2643                int zones_need_compaction = 1;
2644
2645                for (i = 0; i <= end_zone; i++) {
2646                        struct zone *zone = pgdat->node_zones + i;
2647
2648                        if (!populated_zone(zone))
2649                                continue;
2650
2651                        if (zone->all_unreclaimable &&
2652                            sc.priority != DEF_PRIORITY)
2653                                continue;
2654
2655                        /* Would compaction fail due to lack of free memory? */
2656                        if (COMPACTION_BUILD &&
2657                            compaction_suitable(zone, order) == COMPACT_SKIPPED)
2658                                goto loop_again;
2659
2660                        /* Confirm the zone is balanced for order-0 */
2661                        if (!zone_watermark_ok(zone, 0,
2662                                        high_wmark_pages(zone), 0, 0)) {
2663                                order = sc.order = 0;
2664                                goto loop_again;
2665                        }
2666
2667                        /* Check if the memory needs to be defragmented. */
2668                        if (zone_watermark_ok(zone, order,
2669                                    low_wmark_pages(zone), *classzone_idx, 0))
2670                                zones_need_compaction = 0;
2671
2672                        /* If balanced, clear the congested flag */
2673                        zone_clear_flag(zone, ZONE_CONGESTED);
2674                }
2675
2676                if (zones_need_compaction)
2677                        compact_pgdat(pgdat, order);
2678        }
2679
2680        /*
2681         * Return the order we were reclaiming at so sleeping_prematurely()
2682         * makes a decision on the order we were last reclaiming at. However,
2683         * if another caller entered the allocator slow path while kswapd
2684         * was awake, order will remain at the higher level
2685         */
2686        *classzone_idx = end_zone;
2687        return order;
2688}
2689
2690static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
2691{
2692        long remaining = 0;
2693        DEFINE_WAIT(wait);
2694
2695        if (freezing(current) || kthread_should_stop())
2696                return;
2697
2698        prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2699
2700        /* Try to sleep for a short interval */
2701        if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
2702                remaining = schedule_timeout(HZ/10);
2703                finish_wait(&pgdat->kswapd_wait, &wait);
2704                prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2705        }
2706
2707        /*
2708         * After a short sleep, check if it was a premature sleep. If not, then
2709         * go fully to sleep until explicitly woken up.
2710         */
2711        if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) {
2712                trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
2713
2714                /*
2715                 * vmstat counters are not perfectly accurate and the estimated
2716                 * value for counters such as NR_FREE_PAGES can deviate from the
2717                 * true value by nr_online_cpus * threshold. To avoid the zone
2718                 * watermarks being breached while under pressure, we reduce the
2719                 * per-cpu vmstat threshold while kswapd is awake and restore
2720                 * them before going back to sleep.
2721                 */
2722                set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
2723
2724                if (!kthread_should_stop())
2725                        schedule();
2726
2727                set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
2728        } else {
2729                if (remaining)
2730                        count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2731                else
2732                        count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2733        }
2734        finish_wait(&pgdat->kswapd_wait, &wait);
2735}
2736
2737/*
2738 * The background pageout daemon, started as a kernel thread
2739 * from the init process.
2740 *
2741 * This basically trickles out pages so that we have _some_
2742 * free memory available even if there is no other activity
2743 * that frees anything up. This is needed for things like routing
2744 * etc, where we otherwise might have all activity going on in
2745 * asynchronous contexts that cannot page things out.
2746 *
2747 * If there are applications that are active memory-allocators
2748 * (most normal use), this basically shouldn't matter.
2749 */
2750static int kswapd(void *p)
2751{
2752        unsigned long order, new_order;
2753        unsigned balanced_order;
2754        int classzone_idx, new_classzone_idx;
2755        int balanced_classzone_idx;
2756        pg_data_t *pgdat = (pg_data_t*)p;
2757        struct task_struct *tsk = current;
2758
2759        struct reclaim_state reclaim_state = {
2760                .reclaimed_slab = 0,
2761        };
2762        const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2763
2764        lockdep_set_current_reclaim_state(GFP_KERNEL);
2765
2766        if (!cpumask_empty(cpumask))
2767                set_cpus_allowed_ptr(tsk, cpumask);
2768        current->reclaim_state = &reclaim_state;
2769
2770        /*
2771         * Tell the memory management that we're a "memory allocator",
2772         * and that if we need more memory we should get access to it
2773         * regardless (see "__alloc_pages()"). "kswapd" should
2774         * never get caught in the normal page freeing logic.
2775         *
2776         * (Kswapd normally doesn't need memory anyway, but sometimes
2777         * you need a small amount of memory in order to be able to
2778         * page out something else, and this flag essentially protects
2779         * us from recursively trying to free more memory as we're
2780         * trying to free the first piece of memory in the first place).
2781         */
2782        tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2783        set_freezable();
2784
2785        order = new_order = 0;
2786        balanced_order = 0;
2787        classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
2788        balanced_classzone_idx = classzone_idx;
2789        for ( ; ; ) {
2790                int ret;
2791
2792                /*
2793                 * If the last balance_pgdat was unsuccessful it's unlikely a
2794                 * new request of a similar or harder type will succeed soon
2795                 * so consider going to sleep on the basis we reclaimed at
2796                 */
2797                if (balanced_classzone_idx >= new_classzone_idx &&
2798                                        balanced_order == new_order) {
2799                        new_order = pgdat->kswapd_max_order;
2800                        new_classzone_idx = pgdat->classzone_idx;
2801                        pgdat->kswapd_max_order =  0;
2802                        pgdat->classzone_idx = pgdat->nr_zones - 1;
2803                }
2804
2805                if (order < new_order || classzone_idx > new_classzone_idx) {
2806                        /*
2807                         * Don't sleep if someone wants a larger 'order'
2808                         * allocation or has tigher zone constraints
2809                         */
2810                        order = new_order;
2811                        classzone_idx = new_classzone_idx;
2812                } else {
2813                        kswapd_try_to_sleep(pgdat, balanced_order,
2814                                                balanced_classzone_idx);
2815                        order = pgdat->kswapd_max_order;
2816                        classzone_idx = pgdat->classzone_idx;
2817                        new_order = order;
2818                        new_classzone_idx = classzone_idx;
2819                        pgdat->kswapd_max_order = 0;
2820                        pgdat->classzone_idx = pgdat->nr_zones - 1;
2821                }
2822
2823                ret = try_to_freeze();
2824                if (kthread_should_stop())
2825                        break;
2826
2827                /*
2828                 * We can speed up thawing tasks if we don't call balance_pgdat
2829                 * after returning from the refrigerator
2830                 */
2831                if (!ret) {
2832                        trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
2833                        balanced_classzone_idx = classzone_idx;
2834                        balanced_order = balance_pgdat(pgdat, order,
2835                                                &balanced_classzone_idx);
2836                }
2837        }
2838        return 0;
2839}
2840
2841/*
2842 * A zone is low on free memory, so wake its kswapd task to service it.
2843 */
2844void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
2845{
2846        pg_data_t *pgdat;
2847
2848        if (!populated_zone(zone))
2849                return;
2850
2851        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2852                return;
2853        pgdat = zone->zone_pgdat;
2854        if (pgdat->kswapd_max_order < order) {
2855                pgdat->kswapd_max_order = order;
2856                pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
2857        }
2858        if (!waitqueue_active(&pgdat->kswapd_wait))
2859                return;
2860        if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
2861                return;
2862
2863        trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
2864        wake_up_interruptible(&pgdat->kswapd_wait);
2865}
2866
2867/*
2868 * The reclaimable count would be mostly accurate.
2869 * The less reclaimable pages may be
2870 * - mlocked pages, which will be moved to unevictable list when encountered
2871 * - mapped pages, which may require several travels to be reclaimed
2872 * - dirty pages, which is not "instantly" reclaimable
2873 */
2874unsigned long global_reclaimable_pages(void)
2875{
2876        int nr;
2877
2878        nr = global_page_state(NR_ACTIVE_FILE) +
2879             global_page_state(NR_INACTIVE_FILE);
2880
2881        if (nr_swap_pages > 0)
2882                nr += global_page_state(NR_ACTIVE_ANON) +
2883                      global_page_state(NR_INACTIVE_ANON);
2884
2885        return nr;
2886}
2887
2888unsigned long zone_reclaimable_pages(struct zone *zone)
2889{
2890        int nr;
2891
2892        nr = zone_page_state(zone, NR_ACTIVE_FILE) +
2893             zone_page_state(zone, NR_INACTIVE_FILE);
2894
2895        if (nr_swap_pages > 0)
2896                nr += zone_page_state(zone, NR_ACTIVE_ANON) +
2897                      zone_page_state(zone, NR_INACTIVE_ANON);
2898
2899        return nr;
2900}
2901
2902#ifdef CONFIG_HIBERNATION
2903/*
2904 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
2905 * freed pages.
2906 *
2907 * Rather than trying to age LRUs the aim is to preserve the overall
2908 * LRU order by reclaiming preferentially
2909 * inactive > active > active referenced > active mapped
2910 */
2911unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
2912{
2913        struct reclaim_state reclaim_state;
2914        struct scan_control sc = {
2915                .gfp_mask = GFP_HIGHUSER_MOVABLE,
2916                .may_swap = 1,
2917                .may_unmap = 1,
2918                .may_writepage = 1,
2919                .nr_to_reclaim = nr_to_reclaim,
2920                .hibernation_mode = 1,
2921                .order = 0,
2922                .priority = DEF_PRIORITY,
2923        };
2924        struct shrink_control shrink = {
2925                .gfp_mask = sc.gfp_mask,
2926        };
2927        struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
2928        struct task_struct *p = current;
2929        unsigned long nr_reclaimed;
2930
2931        p->flags |= PF_MEMALLOC;
2932        lockdep_set_current_reclaim_state(sc.gfp_mask);
2933        reclaim_state.reclaimed_slab = 0;
2934        p->reclaim_state = &reclaim_state;
2935
2936        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2937
2938        p->reclaim_state = NULL;
2939        lockdep_clear_current_reclaim_state();
2940        p->flags &= ~PF_MEMALLOC;
2941
2942        return nr_reclaimed;
2943}
2944#endif /* CONFIG_HIBERNATION */
2945
2946/* It's optimal to keep kswapds on the same CPUs as their memory, but
2947   not required for correctness.  So if the last cpu in a node goes
2948   away, we get changed to run anywhere: as the first one comes back,
2949   restore their cpu bindings. */
2950static int __devinit cpu_callback(struct notifier_block *nfb,
2951                                  unsigned long action, void *hcpu)
2952{
2953        int nid;
2954
2955        if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
2956                for_each_node_state(nid, N_HIGH_MEMORY) {
2957                        pg_data_t *pgdat = NODE_DATA(nid);
2958                        const struct cpumask *mask;
2959
2960                        mask = cpumask_of_node(pgdat->node_id);
2961
2962                        if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
2963                                /* One of our CPUs online: restore mask */
2964                                set_cpus_allowed_ptr(pgdat->kswapd, mask);
2965                }
2966        }
2967        return NOTIFY_OK;
2968}
2969
2970/*
2971 * This kswapd start function will be called by init and node-hot-add.
2972 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
2973 */
2974int kswapd_run(int nid)
2975{
2976        pg_data_t *pgdat = NODE_DATA(nid);
2977        int ret = 0;
2978
2979        if (pgdat->kswapd)
2980                return 0;
2981
2982        pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
2983        if (IS_ERR(pgdat->kswapd)) {
2984                /* failure at boot is fatal */
2985                BUG_ON(system_state == SYSTEM_BOOTING);
2986                printk("Failed to start kswapd on node %d\n",nid);
2987                ret = -1;
2988        }
2989        return ret;
2990}
2991
2992/*
2993 * Called by memory hotplug when all memory in a node is offlined.  Caller must
2994 * hold lock_memory_hotplug().
2995 */
2996void kswapd_stop(int nid)
2997{
2998        struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
2999
3000        if (kswapd) {
3001                kthread_stop(kswapd);
3002                NODE_DATA(nid)->kswapd = NULL;
3003        }
3004}
3005
3006static int __init kswapd_init(void)
3007{
3008        int nid;
3009
3010        swap_setup();
3011        for_each_node_state(nid, N_HIGH_MEMORY)
3012                kswapd_run(nid);
3013        hotcpu_notifier(cpu_callback, 0);
3014        return 0;
3015}
3016
3017module_init(kswapd_init)
3018
3019#ifdef CONFIG_NUMA
3020/*
3021 * Zone reclaim mode
3022 *
3023 * If non-zero call zone_reclaim when the number of free pages falls below
3024 * the watermarks.
3025 */
3026int zone_reclaim_mode __read_mostly;
3027
3028#define RECLAIM_OFF 0
3029#define RECLAIM_ZONE (1<<0)     /* Run shrink_inactive_list on the zone */
3030#define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
3031#define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
3032
3033/*
3034 * Priority for ZONE_RECLAIM. This determines the fraction of pages
3035 * of a node considered for each zone_reclaim. 4 scans 1/16th of
3036 * a zone.
3037 */
3038#define ZONE_RECLAIM_PRIORITY 4
3039
3040/*
3041 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
3042 * occur.
3043 */
3044int sysctl_min_unmapped_ratio = 1;
3045
3046/*
3047 * If the number of slab pages in a zone grows beyond this percentage then
3048 * slab reclaim needs to occur.
3049 */
3050int sysctl_min_slab_ratio = 5;
3051
3052static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3053{
3054        unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3055        unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3056                zone_page_state(zone, NR_ACTIVE_FILE);
3057
3058        /*
3059         * It's possible for there to be more file mapped pages than
3060         * accounted for by the pages on the file LRU lists because
3061         * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3062         */
3063        return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3064}
3065
3066/* Work out how many page cache pages we can reclaim in this reclaim_mode */
3067static long zone_pagecache_reclaimable(struct zone *zone)
3068{
3069        long nr_pagecache_reclaimable;
3070        long delta = 0;
3071
3072        /*
3073         * If RECLAIM_SWAP is set, then all file pages are considered
3074         * potentially reclaimable. Otherwise, we have to worry about
3075         * pages like swapcache and zone_unmapped_file_pages() provides
3076         * a better estimate
3077         */
3078        if (zone_reclaim_mode & RECLAIM_SWAP)
3079                nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3080        else
3081                nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3082
3083        /* If we can't clean pages, remove dirty pages from consideration */
3084        if (!(zone_reclaim_mode & RECLAIM_WRITE))
3085                delta += zone_page_state(zone, NR_FILE_DIRTY);
3086
3087        /* Watch for any possible underflows due to delta */
3088        if (unlikely(delta > nr_pagecache_reclaimable))
3089                delta = nr_pagecache_reclaimable;
3090
3091        return nr_pagecache_reclaimable - delta;
3092}
3093
3094/*
3095 * Try to free up some pages from this zone through reclaim.
3096 */
3097static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3098{
3099        /* Minimum pages needed in order to stay on node */
3100        const unsigned long nr_pages = 1 << order;
3101        struct task_struct *p = current;
3102        struct reclaim_state reclaim_state;
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                .priority = ZONE_RECLAIM_PRIORITY,
3112        };
3113        struct shrink_control shrink = {
3114                .gfp_mask = sc.gfp_mask,
3115        };
3116        unsigned long nr_slab_pages0, nr_slab_pages1;
3117
3118        cond_resched();
3119        /*
3120         * We need to be able to allocate from the reserves for RECLAIM_SWAP
3121         * and we also need to be able to write out pages for RECLAIM_WRITE
3122         * and RECLAIM_SWAP.
3123         */
3124        p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3125        lockdep_set_current_reclaim_state(gfp_mask);
3126        reclaim_state.reclaimed_slab = 0;
3127        p->reclaim_state = &reclaim_state;
3128
3129        if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3130                /*
3131                 * Free memory by calling shrink zone with increasing
3132                 * priorities until we have enough memory freed.
3133                 */
3134                do {
3135                        shrink_zone(zone, &sc);
3136                } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3137        }
3138
3139        nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3140        if (nr_slab_pages0 > zone->min_slab_pages) {
3141                /*
3142                 * shrink_slab() does not currently allow us to determine how
3143                 * many pages were freed in this zone. So we take the current
3144                 * number of slab pages and shake the slab until it is reduced
3145                 * by the same nr_pages that we used for reclaiming unmapped
3146                 * pages.
3147                 *
3148                 * Note that shrink_slab will free memory on all zones and may
3149                 * take a long time.
3150                 */
3151                for (;;) {
3152                        unsigned long lru_pages = zone_reclaimable_pages(zone);
3153
3154                        /* No reclaimable slab or very low memory pressure */
3155                        if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3156                                break;
3157
3158                        /* Freed enough memory */
3159                        nr_slab_pages1 = zone_page_state(zone,
3160                                                        NR_SLAB_RECLAIMABLE);
3161                        if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3162                                break;
3163                }
3164
3165                /*
3166                 * Update nr_reclaimed by the number of slab pages we
3167                 * reclaimed from this zone.
3168                 */
3169                nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3170                if (nr_slab_pages1 < nr_slab_pages0)
3171                        sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3172        }
3173
3174        p->reclaim_state = NULL;
3175        current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3176        lockdep_clear_current_reclaim_state();
3177        return sc.nr_reclaimed >= nr_pages;
3178}
3179
3180int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3181{
3182        int node_id;
3183        int ret;
3184
3185        /*
3186         * Zone reclaim reclaims unmapped file backed pages and
3187         * slab pages if we are over the defined limits.
3188         *
3189         * A small portion of unmapped file backed pages is needed for
3190         * file I/O otherwise pages read by file I/O will be immediately
3191         * thrown out if the zone is overallocated. So we do not reclaim
3192         * if less than a specified percentage of the zone is used by
3193         * unmapped file backed pages.
3194         */
3195        if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3196            zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3197                return ZONE_RECLAIM_FULL;
3198
3199        if (zone->all_unreclaimable)
3200                return ZONE_RECLAIM_FULL;
3201
3202        /*
3203         * Do not scan if the allocation should not be delayed.
3204         */
3205        if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3206                return ZONE_RECLAIM_NOSCAN;
3207
3208        /*
3209         * Only run zone reclaim on the local zone or on zones that do not
3210         * have associated processors. This will favor the local processor
3211         * over remote processors and spread off node memory allocations
3212         * as wide as possible.
3213         */
3214        node_id = zone_to_nid(zone);
3215        if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3216                return ZONE_RECLAIM_NOSCAN;
3217
3218        if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3219                return ZONE_RECLAIM_NOSCAN;
3220
3221        ret = __zone_reclaim(zone, gfp_mask, order);
3222        zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3223
3224        if (!ret)
3225                count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3226
3227        return ret;
3228}
3229#endif
3230
3231/*
3232 * page_evictable - test whether a page is evictable
3233 * @page: the page to test
3234 * @vma: the VMA in which the page is or will be mapped, may be NULL
3235 *
3236 * Test whether page is evictable--i.e., should be placed on active/inactive
3237 * lists vs unevictable list.  The vma argument is !NULL when called from the
3238 * fault path to determine how to instantate a new page.
3239 *
3240 * Reasons page might not be evictable:
3241 * (1) page's mapping marked unevictable
3242 * (2) page is part of an mlocked VMA
3243 *
3244 */
3245int page_evictable(struct page *page, struct vm_area_struct *vma)
3246{
3247
3248        if (mapping_unevictable(page_mapping(page)))
3249                return 0;
3250
3251        if (PageMlocked(page) || (vma && mlocked_vma_newpage(vma, page)))
3252                return 0;
3253
3254        return 1;
3255}
3256
3257#ifdef CONFIG_SHMEM
3258/**
3259 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3260 * @pages:      array of pages to check
3261 * @nr_pages:   number of pages to check
3262 *
3263 * Checks pages for evictability and moves them to the appropriate lru list.
3264 *
3265 * This function is only used for SysV IPC SHM_UNLOCK.
3266 */
3267void check_move_unevictable_pages(struct page **pages, int nr_pages)
3268{
3269        struct lruvec *lruvec;
3270        struct zone *zone = NULL;
3271        int pgscanned = 0;
3272        int pgrescued = 0;
3273        int i;
3274
3275        for (i = 0; i < nr_pages; i++) {
3276                struct page *page = pages[i];
3277                struct zone *pagezone;
3278
3279                pgscanned++;
3280                pagezone = page_zone(page);
3281                if (pagezone != zone) {
3282                        if (zone)
3283                                spin_unlock_irq(&zone->lru_lock);
3284                        zone = pagezone;
3285                        spin_lock_irq(&zone->lru_lock);
3286                }
3287                lruvec = mem_cgroup_page_lruvec(page, zone);
3288
3289                if (!PageLRU(page) || !PageUnevictable(page))
3290                        continue;
3291
3292                if (page_evictable(page, NULL)) {
3293                        enum lru_list lru = page_lru_base_type(page);
3294
3295                        VM_BUG_ON(PageActive(page));
3296                        ClearPageUnevictable(page);
3297                        del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3298                        add_page_to_lru_list(page, lruvec, lru);
3299                        pgrescued++;
3300                }
3301        }
3302
3303        if (zone) {
3304                __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3305                __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3306                spin_unlock_irq(&zone->lru_lock);
3307        }
3308}
3309#endif /* CONFIG_SHMEM */
3310
3311static void warn_scan_unevictable_pages(void)
3312{
3313        printk_once(KERN_WARNING
3314                    "%s: The scan_unevictable_pages sysctl/node-interface has been "
3315                    "disabled for lack of a legitimate use case.  If you have "
3316                    "one, please send an email to linux-mm@kvack.org.\n",
3317                    current->comm);
3318}
3319
3320/*
3321 * scan_unevictable_pages [vm] sysctl handler.  On demand re-scan of
3322 * all nodes' unevictable lists for evictable pages
3323 */
3324unsigned long scan_unevictable_pages;
3325
3326int scan_unevictable_handler(struct ctl_table *table, int write,
3327                           void __user *buffer,
3328                           size_t *length, loff_t *ppos)
3329{
3330        warn_scan_unevictable_pages();
3331        proc_doulongvec_minmax(table, write, buffer, length, ppos);
3332        scan_unevictable_pages = 0;
3333        return 0;
3334}
3335
3336#ifdef CONFIG_NUMA
3337/*
3338 * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
3339 * a specified node's per zone unevictable lists for evictable pages.
3340 */
3341
3342static ssize_t read_scan_unevictable_node(struct device *dev,
3343                                          struct device_attribute *attr,
3344                                          char *buf)
3345{
3346        warn_scan_unevictable_pages();
3347        return sprintf(buf, "0\n");     /* always zero; should fit... */
3348}
3349
3350static ssize_t write_scan_unevictable_node(struct device *dev,
3351                                           struct device_attribute *attr,
3352                                        const char *buf, size_t count)
3353{
3354        warn_scan_unevictable_pages();
3355        return 1;
3356}
3357
3358
3359static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3360                        read_scan_unevictable_node,
3361                        write_scan_unevictable_node);
3362
3363int scan_unevictable_register_node(struct node *node)
3364{
3365        return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages);
3366}
3367
3368void scan_unevictable_unregister_node(struct node *node)
3369{
3370        device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages);
3371}
3372#endif
3373
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