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_MEMCG
 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        mem_cgroup_uncharge_start();
 691        while (!list_empty(page_list)) {
 692                enum page_references references;
 693                struct address_space *mapping;
 694                struct page *page;
 695                int may_enter_fs;
 696
 697                cond_resched();
 698
 699                page = lru_to_page(page_list);
 700                list_del(&page->lru);
 701
 702                if (!trylock_page(page))
 703                        goto keep;
 704
 705                VM_BUG_ON(PageActive(page));
 706                VM_BUG_ON(page_zone(page) != zone);
 707
 708                sc->nr_scanned++;
 709
 710                if (unlikely(!page_evictable(page, NULL)))
 711                        goto cull_mlocked;
 712
 713                if (!sc->may_unmap && page_mapped(page))
 714                        goto keep_locked;
 715
 716                /* Double the slab pressure for mapped and swapcache pages */
 717                if (page_mapped(page) || PageSwapCache(page))
 718                        sc->nr_scanned++;
 719
 720                may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
 721                        (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 722
 723                if (PageWriteback(page)) {
 724                        /*
 725                         * memcg doesn't have any dirty pages throttling so we
 726                         * could easily OOM just because too many pages are in
 727                         * writeback and there is nothing else to reclaim.
 728                         *
 729                         * Check __GFP_IO, certainly because a loop driver
 730                         * thread might enter reclaim, and deadlock if it waits
 731                         * on a page for which it is needed to do the write
 732                         * (loop masks off __GFP_IO|__GFP_FS for this reason);
 733                         * but more thought would probably show more reasons.
 734                         *
 735                         * Don't require __GFP_FS, since we're not going into
 736                         * the FS, just waiting on its writeback completion.
 737                         * Worryingly, ext4 gfs2 and xfs allocate pages with
 738                         * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so
 739                         * testing may_enter_fs here is liable to OOM on them.
 740                         */
 741                        if (global_reclaim(sc) ||
 742                            !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
 743                                /*
 744                                 * This is slightly racy - end_page_writeback()
 745                                 * might have just cleared PageReclaim, then
 746                                 * setting PageReclaim here end up interpreted
 747                                 * as PageReadahead - but that does not matter
 748                                 * enough to care.  What we do want is for this
 749                                 * page to have PageReclaim set next time memcg
 750                                 * reclaim reaches the tests above, so it will
 751                                 * then wait_on_page_writeback() to avoid OOM;
 752                                 * and it's also appropriate in global reclaim.
 753                                 */
 754                                SetPageReclaim(page);
 755                                nr_writeback++;
 756                                goto keep_locked;
 757                        }
 758                        wait_on_page_writeback(page);
 759                }
 760
 761                references = page_check_references(page, sc);
 762                switch (references) {
 763                case PAGEREF_ACTIVATE:
 764                        goto activate_locked;
 765                case PAGEREF_KEEP:
 766                        goto keep_locked;
 767                case PAGEREF_RECLAIM:
 768                case PAGEREF_RECLAIM_CLEAN:
 769                        ; /* try to reclaim the page below */
 770                }
 771
 772                /*
 773                 * Anonymous process memory has backing store?
 774                 * Try to allocate it some swap space here.
 775                 */
 776                if (PageAnon(page) && !PageSwapCache(page)) {
 777                        if (!(sc->gfp_mask & __GFP_IO))
 778                                goto keep_locked;
 779                        if (!add_to_swap(page))
 780                                goto activate_locked;
 781                        may_enter_fs = 1;
 782                }
 783
 784                mapping = page_mapping(page);
 785
 786                /*
 787                 * The page is mapped into the page tables of one or more
 788                 * processes. Try to unmap it here.
 789                 */
 790                if (page_mapped(page) && mapping) {
 791                        switch (try_to_unmap(page, TTU_UNMAP)) {
 792                        case SWAP_FAIL:
 793                                goto activate_locked;
 794                        case SWAP_AGAIN:
 795                                goto keep_locked;
 796                        case SWAP_MLOCK:
 797                                goto cull_mlocked;
 798                        case SWAP_SUCCESS:
 799                                ; /* try to free the page below */
 800                        }
 801                }
 802
 803                if (PageDirty(page)) {
 804                        nr_dirty++;
 805
 806                        /*
 807                         * Only kswapd can writeback filesystem pages to
 808                         * avoid risk of stack overflow but do not writeback
 809                         * unless under significant pressure.
 810                         */
 811                        if (page_is_file_cache(page) &&
 812                                        (!current_is_kswapd() ||
 813                                         sc->priority >= DEF_PRIORITY - 2)) {
 814                                /*
 815                                 * Immediately reclaim when written back.
 816                                 * Similar in principal to deactivate_page()
 817                                 * except we already have the page isolated
 818                                 * and know it's dirty
 819                                 */
 820                                inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
 821                                SetPageReclaim(page);
 822
 823                                goto keep_locked;
 824                        }
 825
 826                        if (references == PAGEREF_RECLAIM_CLEAN)
 827                                goto keep_locked;
 828                        if (!may_enter_fs)
 829                                goto keep_locked;
 830                        if (!sc->may_writepage)
 831                                goto keep_locked;
 832
 833                        /* Page is dirty, try to write it out here */
 834                        switch (pageout(page, mapping, sc)) {
 835                        case PAGE_KEEP:
 836                                nr_congested++;
 837                                goto keep_locked;
 838                        case PAGE_ACTIVATE:
 839                                goto activate_locked;
 840                        case PAGE_SUCCESS:
 841                                if (PageWriteback(page))
 842                                        goto keep;
 843                                if (PageDirty(page))
 844                                        goto keep;
 845
 846                                /*
 847                                 * A synchronous write - probably a ramdisk.  Go
 848                                 * ahead and try to reclaim the page.
 849                                 */
 850                                if (!trylock_page(page))
 851                                        goto keep;
 852                                if (PageDirty(page) || PageWriteback(page))
 853                                        goto keep_locked;
 854                                mapping = page_mapping(page);
 855                        case PAGE_CLEAN:
 856                                ; /* try to free the page below */
 857                        }
 858                }
 859
 860                /*
 861                 * If the page has buffers, try to free the buffer mappings
 862                 * associated with this page. If we succeed we try to free
 863                 * the page as well.
 864                 *
 865                 * We do this even if the page is PageDirty().
 866                 * try_to_release_page() does not perform I/O, but it is
 867                 * possible for a page to have PageDirty set, but it is actually
 868                 * clean (all its buffers are clean).  This happens if the
 869                 * buffers were written out directly, with submit_bh(). ext3
 870                 * will do this, as well as the blockdev mapping.
 871                 * try_to_release_page() will discover that cleanness and will
 872                 * drop the buffers and mark the page clean - it can be freed.
 873                 *
 874                 * Rarely, pages can have buffers and no ->mapping.  These are
 875                 * the pages which were not successfully invalidated in
 876                 * truncate_complete_page().  We try to drop those buffers here
 877                 * and if that worked, and the page is no longer mapped into
 878                 * process address space (page_count == 1) it can be freed.
 879                 * Otherwise, leave the page on the LRU so it is swappable.
 880                 */
 881                if (page_has_private(page)) {
 882                        if (!try_to_release_page(page, sc->gfp_mask))
 883                                goto activate_locked;
 884                        if (!mapping && page_count(page) == 1) {
 885                                unlock_page(page);
 886                                if (put_page_testzero(page))
 887                                        goto free_it;
 888                                else {
 889                                        /*
 890                                         * rare race with speculative reference.
 891                                         * the speculative reference will free
 892                                         * this page shortly, so we may
 893                                         * increment nr_reclaimed here (and
 894                                         * leave it off the LRU).
 895                                         */
 896                                        nr_reclaimed++;
 897                                        continue;
 898                                }
 899                        }
 900                }
 901
 902                if (!mapping || !__remove_mapping(mapping, page))
 903                        goto keep_locked;
 904
 905                /*
 906                 * At this point, we have no other references and there is
 907                 * no way to pick any more up (removed from LRU, removed
 908                 * from pagecache). Can use non-atomic bitops now (and
 909                 * we obviously don't have to worry about waking up a process
 910                 * waiting on the page lock, because there are no references.
 911                 */
 912                __clear_page_locked(page);
 913free_it:
 914                nr_reclaimed++;
 915
 916                /*
 917                 * Is there need to periodically free_page_list? It would
 918                 * appear not as the counts should be low
 919                 */
 920                list_add(&page->lru, &free_pages);
 921                continue;
 922
 923cull_mlocked:
 924                if (PageSwapCache(page))
 925                        try_to_free_swap(page);
 926                unlock_page(page);
 927                putback_lru_page(page);
 928                continue;
 929
 930activate_locked:
 931                /* Not a candidate for swapping, so reclaim swap space. */
 932                if (PageSwapCache(page) && vm_swap_full())
 933                        try_to_free_swap(page);
 934                VM_BUG_ON(PageActive(page));
 935                SetPageActive(page);
 936                pgactivate++;
 937keep_locked:
 938                unlock_page(page);
 939keep:
 940                list_add(&page->lru, &ret_pages);
 941                VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
 942        }
 943
 944        /*
 945         * Tag a zone as congested if all the dirty pages encountered were
 946         * backed by a congested BDI. In this case, reclaimers should just
 947         * back off and wait for congestion to clear because further reclaim
 948         * will encounter the same problem
 949         */
 950        if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
 951                zone_set_flag(zone, ZONE_CONGESTED);
 952
 953        free_hot_cold_page_list(&free_pages, 1);
 954
 955        list_splice(&ret_pages, page_list);
 956        count_vm_events(PGACTIVATE, pgactivate);
 957        mem_cgroup_uncharge_end();
 958        *ret_nr_dirty += nr_dirty;
 959        *ret_nr_writeback += nr_writeback;
 960        return nr_reclaimed;
 961}
 962
 963/*
 964 * Attempt to remove the specified page from its LRU.  Only take this page
 965 * if it is of the appropriate PageActive status.  Pages which are being
 966 * freed elsewhere are also ignored.
 967 *
 968 * page:        page to consider
 969 * mode:        one of the LRU isolation modes defined above
 970 *
 971 * returns 0 on success, -ve errno on failure.
 972 */
 973int __isolate_lru_page(struct page *page, isolate_mode_t mode)
 974{
 975        int ret = -EINVAL;
 976
 977        /* Only take pages on the LRU. */
 978        if (!PageLRU(page))
 979                return ret;
 980
 981        /* Do not give back unevictable pages for compaction */
 982        if (PageUnevictable(page))
 983                return ret;
 984
 985        ret = -EBUSY;
 986
 987        /*
 988         * To minimise LRU disruption, the caller can indicate that it only
 989         * wants to isolate pages it will be able to operate on without
 990         * blocking - clean pages for the most part.
 991         *
 992         * ISOLATE_CLEAN means that only clean pages should be isolated. This
 993         * is used by reclaim when it is cannot write to backing storage
 994         *
 995         * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
 996         * that it is possible to migrate without blocking
 997         */
 998        if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
 999                /* All the caller can do on PageWriteback is block */
1000                if (PageWriteback(page))
1001                        return ret;
1002
1003                if (PageDirty(page)) {
1004                        struct address_space *mapping;
1005
1006                        /* ISOLATE_CLEAN means only clean pages */
1007                        if (mode & ISOLATE_CLEAN)
1008                                return ret;
1009
1010                        /*
1011                         * Only pages without mappings or that have a
1012                         * ->migratepage callback are possible to migrate
1013                         * without blocking
1014                         */
1015                        mapping = page_mapping(page);
1016                        if (mapping && !mapping->a_ops->migratepage)
1017                                return ret;
1018                }
1019        }
1020
1021        if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1022                return ret;
1023
1024        if (likely(get_page_unless_zero(page))) {
1025                /*
1026                 * Be careful not to clear PageLRU until after we're
1027                 * sure the page is not being freed elsewhere -- the
1028                 * page release code relies on it.
1029                 */
1030                ClearPageLRU(page);
1031                ret = 0;
1032        }
1033
1034        return ret;
1035}
1036
1037/*
1038 * zone->lru_lock is heavily contended.  Some of the functions that
1039 * shrink the lists perform better by taking out a batch of pages
1040 * and working on them outside the LRU lock.
1041 *
1042 * For pagecache intensive workloads, this function is the hottest
1043 * spot in the kernel (apart from copy_*_user functions).
1044 *
1045 * Appropriate locks must be held before calling this function.
1046 *
1047 * @nr_to_scan: The number of pages to look through on the list.
1048 * @lruvec:     The LRU vector to pull pages from.
1049 * @dst:        The temp list to put pages on to.
1050 * @nr_scanned: The number of pages that were scanned.
1051 * @sc:         The scan_control struct for this reclaim session
1052 * @mode:       One of the LRU isolation modes
1053 * @lru:        LRU list id for isolating
1054 *
1055 * returns how many pages were moved onto *@dst.
1056 */
1057static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1058                struct lruvec *lruvec, struct list_head *dst,
1059                unsigned long *nr_scanned, struct scan_control *sc,
1060                isolate_mode_t mode, enum lru_list lru)
1061{
1062        struct list_head *src = &lruvec->lists[lru];
1063        unsigned long nr_taken = 0;
1064        unsigned long scan;
1065
1066        for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1067                struct page *page;
1068                int nr_pages;
1069
1070                page = lru_to_page(src);
1071                prefetchw_prev_lru_page(page, src, flags);
1072
1073                VM_BUG_ON(!PageLRU(page));
1074
1075                switch (__isolate_lru_page(page, mode)) {
1076                case 0:
1077                        nr_pages = hpage_nr_pages(page);
1078                        mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
1079                        list_move(&page->lru, dst);
1080                        nr_taken += nr_pages;
1081                        break;
1082
1083                case -EBUSY:
1084                        /* else it is being freed elsewhere */
1085                        list_move(&page->lru, src);
1086                        continue;
1087
1088                default:
1089                        BUG();
1090                }
1091        }
1092
1093        *nr_scanned = scan;
1094        trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
1095                                    nr_taken, mode, is_file_lru(lru));
1096        return nr_taken;
1097}
1098
1099/**
1100 * isolate_lru_page - tries to isolate a page from its LRU list
1101 * @page: page to isolate from its LRU list
1102 *
1103 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1104 * vmstat statistic corresponding to whatever LRU list the page was on.
1105 *
1106 * Returns 0 if the page was removed from an LRU list.
1107 * Returns -EBUSY if the page was not on an LRU list.
1108 *
1109 * The returned page will have PageLRU() cleared.  If it was found on
1110 * the active list, it will have PageActive set.  If it was found on
1111 * the unevictable list, it will have the PageUnevictable bit set. That flag
1112 * may need to be cleared by the caller before letting the page go.
1113 *
1114 * The vmstat statistic corresponding to the list on which the page was
1115 * found will be decremented.
1116 *
1117 * Restrictions:
1118 * (1) Must be called with an elevated refcount on the page. This is a
1119 *     fundamentnal difference from isolate_lru_pages (which is called
1120 *     without a stable reference).
1121 * (2) the lru_lock must not be held.
1122 * (3) interrupts must be enabled.
1123 */
1124int isolate_lru_page(struct page *page)
1125{
1126        int ret = -EBUSY;
1127
1128        VM_BUG_ON(!page_count(page));
1129
1130        if (PageLRU(page)) {
1131                struct zone *zone = page_zone(page);
1132                struct lruvec *lruvec;
1133
1134                spin_lock_irq(&zone->lru_lock);
1135                lruvec = mem_cgroup_page_lruvec(page, zone);
1136                if (PageLRU(page)) {
1137                        int lru = page_lru(page);
1138                        get_page(page);
1139                        ClearPageLRU(page);
1140                        del_page_from_lru_list(page, lruvec, lru);
1141                        ret = 0;
1142                }
1143                spin_unlock_irq(&zone->lru_lock);
1144        }
1145        return ret;
1146}
1147
1148/*
1149 * Are there way too many processes in the direct reclaim path already?
1150 */
1151static int too_many_isolated(struct zone *zone, int file,
1152                struct scan_control *sc)
1153{
1154        unsigned long inactive, isolated;
1155
1156        if (current_is_kswapd())
1157                return 0;
1158
1159        if (!global_reclaim(sc))
1160                return 0;
1161
1162        if (file) {
1163                inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1164                isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1165        } else {
1166                inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1167                isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1168        }
1169
1170        return isolated > inactive;
1171}
1172
1173static noinline_for_stack void
1174putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1175{
1176        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1177        struct zone *zone = lruvec_zone(lruvec);
1178        LIST_HEAD(pages_to_free);
1179
1180        /*
1181         * Put back any unfreeable pages.
1182         */
1183        while (!list_empty(page_list)) {
1184                struct page *page = lru_to_page(page_list);
1185                int lru;
1186
1187                VM_BUG_ON(PageLRU(page));
1188                list_del(&page->lru);
1189                if (unlikely(!page_evictable(page, NULL))) {
1190                        spin_unlock_irq(&zone->lru_lock);
1191                        putback_lru_page(page);
1192                        spin_lock_irq(&zone->lru_lock);
1193                        continue;
1194                }
1195
1196                lruvec = mem_cgroup_page_lruvec(page, zone);
1197
1198                SetPageLRU(page);
1199                lru = page_lru(page);
1200                add_page_to_lru_list(page, lruvec, lru);
1201
1202                if (is_active_lru(lru)) {
1203                        int file = is_file_lru(lru);
1204                        int numpages = hpage_nr_pages(page);
1205                        reclaim_stat->recent_rotated[file] += numpages;
1206                }
1207                if (put_page_testzero(page)) {
1208                        __ClearPageLRU(page);
1209                        __ClearPageActive(page);
1210                        del_page_from_lru_list(page, lruvec, lru);
1211
1212                        if (unlikely(PageCompound(page))) {
1213                                spin_unlock_irq(&zone->lru_lock);
1214                                (*get_compound_page_dtor(page))(page);
1215                                spin_lock_irq(&zone->lru_lock);
1216                        } else
1217                                list_add(&page->lru, &pages_to_free);
1218                }
1219        }
1220
1221        /*
1222         * To save our caller's stack, now use input list for pages to free.
1223         */
1224        list_splice(&pages_to_free, page_list);
1225}
1226
1227/*
1228 * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
1229 * of reclaimed pages
1230 */
1231static noinline_for_stack unsigned long
1232shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1233                     struct scan_control *sc, enum lru_list lru)
1234{
1235        LIST_HEAD(page_list);
1236        unsigned long nr_scanned;
1237        unsigned long nr_reclaimed = 0;
1238        unsigned long nr_taken;
1239        unsigned long nr_dirty = 0;
1240        unsigned long nr_writeback = 0;
1241        isolate_mode_t isolate_mode = 0;
1242        int file = is_file_lru(lru);
1243        struct zone *zone = lruvec_zone(lruvec);
1244        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1245
1246        while (unlikely(too_many_isolated(zone, file, sc))) {
1247                congestion_wait(BLK_RW_ASYNC, HZ/10);
1248
1249                /* We are about to die and free our memory. Return now. */
1250                if (fatal_signal_pending(current))
1251                        return SWAP_CLUSTER_MAX;
1252        }
1253
1254        lru_add_drain();
1255
1256        if (!sc->may_unmap)
1257                isolate_mode |= ISOLATE_UNMAPPED;
1258        if (!sc->may_writepage)
1259                isolate_mode |= ISOLATE_CLEAN;
1260
1261        spin_lock_irq(&zone->lru_lock);
1262
1263        nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1264                                     &nr_scanned, sc, isolate_mode, lru);
1265
1266        __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1267        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1268
1269        if (global_reclaim(sc)) {
1270                zone->pages_scanned += nr_scanned;
1271                if (current_is_kswapd())
1272                        __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1273                else
1274                        __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1275        }
1276        spin_unlock_irq(&zone->lru_lock);
1277
1278        if (nr_taken == 0)
1279                return 0;
1280
1281        nr_reclaimed = shrink_page_list(&page_list, zone, sc,
1282                                                &nr_dirty, &nr_writeback);
1283
1284        spin_lock_irq(&zone->lru_lock);
1285
1286        reclaim_stat->recent_scanned[file] += nr_taken;
1287
1288        if (global_reclaim(sc)) {
1289                if (current_is_kswapd())
1290                        __count_zone_vm_events(PGSTEAL_KSWAPD, zone,
1291                                               nr_reclaimed);
1292                else
1293                        __count_zone_vm_events(PGSTEAL_DIRECT, zone,
1294                                               nr_reclaimed);
1295        }
1296
1297        putback_inactive_pages(lruvec, &page_list);
1298
1299        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1300
1301        spin_unlock_irq(&zone->lru_lock);
1302
1303        free_hot_cold_page_list(&page_list, 1);
1304
1305        /*
1306         * If reclaim is isolating dirty pages under writeback, it implies
1307         * that the long-lived page allocation rate is exceeding the page
1308         * laundering rate. Either the global limits are not being effective
1309         * at throttling processes due to the page distribution throughout
1310         * zones or there is heavy usage of a slow backing device. The
1311         * only option is to throttle from reclaim context which is not ideal
1312         * as there is no guarantee the dirtying process is throttled in the
1313         * same way balance_dirty_pages() manages.
1314         *
1315         * This scales the number of dirty pages that must be under writeback
1316         * before throttling depending on priority. It is a simple backoff
1317         * function that has the most effect in the range DEF_PRIORITY to
1318         * DEF_PRIORITY-2 which is the priority reclaim is considered to be
1319         * in trouble and reclaim is considered to be in trouble.
1320         *
1321         * DEF_PRIORITY   100% isolated pages must be PageWriteback to throttle
1322         * DEF_PRIORITY-1  50% must be PageWriteback
1323         * DEF_PRIORITY-2  25% must be PageWriteback, kswapd in trouble
1324         * ...
1325         * DEF_PRIORITY-6 For SWAP_CLUSTER_MAX isolated pages, throttle if any
1326         *                     isolated page is PageWriteback
1327         */
1328        if (nr_writeback && nr_writeback >=
1329                        (nr_taken >> (DEF_PRIORITY - sc->priority)))
1330                wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
1331
1332        trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1333                zone_idx(zone),
1334                nr_scanned, nr_reclaimed,
1335                sc->priority,
1336                trace_shrink_flags(file));
1337        return nr_reclaimed;
1338}
1339
1340/*
1341 * This moves pages from the active list to the inactive list.
1342 *
1343 * We move them the other way if the page is referenced by one or more
1344 * processes, from rmap.
1345 *
1346 * If the pages are mostly unmapped, the processing is fast and it is
1347 * appropriate to hold zone->lru_lock across the whole operation.  But if
1348 * the pages are mapped, the processing is slow (page_referenced()) so we
1349 * should drop zone->lru_lock around each page.  It's impossible to balance
1350 * this, so instead we remove the pages from the LRU while processing them.
1351 * It is safe to rely on PG_active against the non-LRU pages in here because
1352 * nobody will play with that bit on a non-LRU page.
1353 *
1354 * The downside is that we have to touch page->_count against each page.
1355 * But we had to alter page->flags anyway.
1356 */
1357
1358static void move_active_pages_to_lru(struct lruvec *lruvec,
1359                                     struct list_head *list,
1360                                     struct list_head *pages_to_free,
1361                                     enum lru_list lru)
1362{
1363        struct zone *zone = lruvec_zone(lruvec);
1364        unsigned long pgmoved = 0;
1365        struct page *page;
1366        int nr_pages;
1367
1368        while (!list_empty(list)) {
1369                page = lru_to_page(list);
1370                lruvec = mem_cgroup_page_lruvec(page, zone);
1371
1372                VM_BUG_ON(PageLRU(page));
1373                SetPageLRU(page);
1374
1375                nr_pages = hpage_nr_pages(page);
1376                mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1377                list_move(&page->lru, &lruvec->lists[lru]);
1378                pgmoved += nr_pages;
1379
1380                if (put_page_testzero(page)) {
1381                        __ClearPageLRU(page);
1382                        __ClearPageActive(page);
1383                        del_page_from_lru_list(page, lruvec, lru);
1384
1385                        if (unlikely(PageCompound(page))) {
1386                                spin_unlock_irq(&zone->lru_lock);
1387                                (*get_compound_page_dtor(page))(page);
1388                                spin_lock_irq(&zone->lru_lock);
1389                        } else
1390                                list_add(&page->lru, pages_to_free);
1391                }
1392        }
1393        __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1394        if (!is_active_lru(lru))
1395                __count_vm_events(PGDEACTIVATE, pgmoved);
1396}
1397
1398static void shrink_active_list(unsigned long nr_to_scan,
1399                               struct lruvec *lruvec,
1400                               struct scan_control *sc,
1401                               enum lru_list lru)
1402{
1403        unsigned long nr_taken;
1404        unsigned long nr_scanned;
1405        unsigned long vm_flags;
1406        LIST_HEAD(l_hold);      /* The pages which were snipped off */
1407        LIST_HEAD(l_active);
1408        LIST_HEAD(l_inactive);
1409        struct page *page;
1410        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1411        unsigned long nr_rotated = 0;
1412        isolate_mode_t isolate_mode = 0;
1413        int file = is_file_lru(lru);
1414        struct zone *zone = lruvec_zone(lruvec);
1415
1416        lru_add_drain();
1417
1418        if (!sc->may_unmap)
1419                isolate_mode |= ISOLATE_UNMAPPED;
1420        if (!sc->may_writepage)
1421                isolate_mode |= ISOLATE_CLEAN;
1422
1423        spin_lock_irq(&zone->lru_lock);
1424
1425        nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1426                                     &nr_scanned, sc, isolate_mode, lru);
1427        if (global_reclaim(sc))
1428                zone->pages_scanned += nr_scanned;
1429
1430        reclaim_stat->recent_scanned[file] += nr_taken;
1431
1432        __count_zone_vm_events(PGREFILL, zone, nr_scanned);
1433        __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1434        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1435        spin_unlock_irq(&zone->lru_lock);
1436
1437        while (!list_empty(&l_hold)) {
1438                cond_resched();
1439                page = lru_to_page(&l_hold);
1440                list_del(&page->lru);
1441
1442                if (unlikely(!page_evictable(page, NULL))) {
1443                        putback_lru_page(page);
1444                        continue;
1445                }
1446
1447                if (unlikely(buffer_heads_over_limit)) {
1448                        if (page_has_private(page) && trylock_page(page)) {
1449                                if (page_has_private(page))
1450                                        try_to_release_page(page, 0);
1451                                unlock_page(page);
1452                        }
1453                }
1454
1455                if (page_referenced(page, 0, sc->target_mem_cgroup,
1456                                    &vm_flags)) {
1457                        nr_rotated += hpage_nr_pages(page);
1458                        /*
1459                         * Identify referenced, file-backed active pages and
1460                         * give them one more trip around the active list. So
1461                         * that executable code get better chances to stay in
1462                         * memory under moderate memory pressure.  Anon pages
1463                         * are not likely to be evicted by use-once streaming
1464                         * IO, plus JVM can create lots of anon VM_EXEC pages,
1465                         * so we ignore them here.
1466                         */
1467                        if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1468                                list_add(&page->lru, &l_active);
1469                                continue;
1470                        }
1471                }
1472
1473                ClearPageActive(page);  /* we are de-activating */
1474                list_add(&page->lru, &l_inactive);
1475        }
1476
1477        /*
1478         * Move pages back to the lru list.
1479         */
1480        spin_lock_irq(&zone->lru_lock);
1481        /*
1482         * Count referenced pages from currently used mappings as rotated,
1483         * even though only some of them are actually re-activated.  This
1484         * helps balance scan pressure between file and anonymous pages in
1485         * get_scan_ratio.
1486         */
1487        reclaim_stat->recent_rotated[file] += nr_rotated;
1488
1489        move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1490        move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1491        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1492        spin_unlock_irq(&zone->lru_lock);
1493
1494        free_hot_cold_page_list(&l_hold, 1);
1495}
1496
1497#ifdef CONFIG_SWAP
1498static int inactive_anon_is_low_global(struct zone *zone)
1499{
1500        unsigned long active, inactive;
1501
1502        active = zone_page_state(zone, NR_ACTIVE_ANON);
1503        inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1504
1505        if (inactive * zone->inactive_ratio < active)
1506                return 1;
1507
1508        return 0;
1509}
1510
1511/**
1512 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1513 * @lruvec: LRU vector to check
1514 *
1515 * Returns true if the zone does not have enough inactive anon pages,
1516 * meaning some active anon pages need to be deactivated.
1517 */
1518static int inactive_anon_is_low(struct lruvec *lruvec)
1519{
1520        /*
1521         * If we don't have swap space, anonymous page deactivation
1522         * is pointless.
1523         */
1524        if (!total_swap_pages)
1525                return 0;
1526
1527        if (!mem_cgroup_disabled())
1528                return mem_cgroup_inactive_anon_is_low(lruvec);
1529
1530        return inactive_anon_is_low_global(lruvec_zone(lruvec));
1531}
1532#else
1533static inline int inactive_anon_is_low(struct lruvec *lruvec)
1534{
1535        return 0;
1536}
1537#endif
1538
1539static int inactive_file_is_low_global(struct zone *zone)
1540{
1541        unsigned long active, inactive;
1542
1543        active = zone_page_state(zone, NR_ACTIVE_FILE);
1544        inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1545
1546        return (active > inactive);
1547}
1548
1549/**
1550 * inactive_file_is_low - check if file pages need to be deactivated
1551 * @lruvec: LRU vector to check
1552 *
1553 * When the system is doing streaming IO, memory pressure here
1554 * ensures that active file pages get deactivated, until more
1555 * than half of the file pages are on the inactive list.
1556 *
1557 * Once we get to that situation, protect the system's working
1558 * set from being evicted by disabling active file page aging.
1559 *
1560 * This uses a different ratio than the anonymous pages, because
1561 * the page cache uses a use-once replacement algorithm.
1562 */
1563static int inactive_file_is_low(struct lruvec *lruvec)
1564{
1565        if (!mem_cgroup_disabled())
1566                return mem_cgroup_inactive_file_is_low(lruvec);
1567
1568        return inactive_file_is_low_global(lruvec_zone(lruvec));
1569}
1570
1571static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1572{
1573        if (is_file_lru(lru))
1574                return inactive_file_is_low(lruvec);
1575        else
1576                return inactive_anon_is_low(lruvec);
1577}
1578
1579static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1580                                 struct lruvec *lruvec, struct scan_control *sc)
1581{
1582        if (is_active_lru(lru)) {
1583                if (inactive_list_is_low(lruvec, lru))
1584                        shrink_active_list(nr_to_scan, lruvec, sc, lru);
1585                return 0;
1586        }
1587
1588        return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1589}
1590
1591static int vmscan_swappiness(struct scan_control *sc)
1592{
1593        if (global_reclaim(sc))
1594                return vm_swappiness;
1595        return mem_cgroup_swappiness(sc->target_mem_cgroup);
1596}
1597
1598/*
1599 * Determine how aggressively the anon and file LRU lists should be
1600 * scanned.  The relative value of each set of LRU lists is determined
1601 * by looking at the fraction of the pages scanned we did rotate back
1602 * onto the active list instead of evict.
1603 *
1604 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
1605 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
1606 */
1607static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
1608                           unsigned long *nr)
1609{
1610        unsigned long anon, file, free;
1611        unsigned long anon_prio, file_prio;
1612        unsigned long ap, fp;
1613        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1614        u64 fraction[2], denominator;
1615        enum lru_list lru;
1616        int noswap = 0;
1617        bool force_scan = false;
1618        struct zone *zone = lruvec_zone(lruvec);
1619
1620        /*
1621         * If the zone or memcg is small, nr[l] can be 0.  This
1622         * results in no scanning on this priority and a potential
1623         * priority drop.  Global direct reclaim can go to the next
1624         * zone and tends to have no problems. Global kswapd is for
1625         * zone balancing and it needs to scan a minimum amount. When
1626         * reclaiming for a memcg, a priority drop can cause high
1627         * latencies, so it's better to scan a minimum amount there as
1628         * well.
1629         */
1630        if (current_is_kswapd() && zone->all_unreclaimable)
1631                force_scan = true;
1632        if (!global_reclaim(sc))
1633                force_scan = true;
1634
1635        /* If we have no swap space, do not bother scanning anon pages. */
1636        if (!sc->may_swap || (nr_swap_pages <= 0)) {
1637                noswap = 1;
1638                fraction[0] = 0;
1639                fraction[1] = 1;
1640                denominator = 1;
1641                goto out;
1642        }
1643
1644        anon  = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
1645                get_lru_size(lruvec, LRU_INACTIVE_ANON);
1646        file  = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
1647                get_lru_size(lruvec, LRU_INACTIVE_FILE);
1648
1649        if (global_reclaim(sc)) {
1650                free  = zone_page_state(zone, NR_FREE_PAGES);
1651                /* If we have very few page cache pages,
1652                   force-scan anon pages. */
1653                if (unlikely(file + free <= high_wmark_pages(zone))) {
1654                        fraction[0] = 1;
1655                        fraction[1] = 0;
1656                        denominator = 1;
1657                        goto out;
1658                }
1659        }
1660
1661        /*
1662         * With swappiness at 100, anonymous and file have the same priority.
1663         * This scanning priority is essentially the inverse of IO cost.
1664         */
1665        anon_prio = vmscan_swappiness(sc);
1666        file_prio = 200 - anon_prio;
1667
1668        /*
1669         * OK, so we have swap space and a fair amount of page cache
1670         * pages.  We use the recently rotated / recently scanned
1671         * ratios to determine how valuable each cache is.
1672         *
1673         * Because workloads change over time (and to avoid overflow)
1674         * we keep these statistics as a floating average, which ends
1675         * up weighing recent references more than old ones.
1676         *
1677         * anon in [0], file in [1]
1678         */
1679        spin_lock_irq(&zone->lru_lock);
1680        if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1681                reclaim_stat->recent_scanned[0] /= 2;
1682                reclaim_stat->recent_rotated[0] /= 2;
1683        }
1684
1685        if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1686                reclaim_stat->recent_scanned[1] /= 2;
1687                reclaim_stat->recent_rotated[1] /= 2;
1688        }
1689
1690        /*
1691         * The amount of pressure on anon vs file pages is inversely
1692         * proportional to the fraction of recently scanned pages on
1693         * each list that were recently referenced and in active use.
1694         */
1695        ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1696        ap /= reclaim_stat->recent_rotated[0] + 1;
1697
1698        fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
1699        fp /= reclaim_stat->recent_rotated[1] + 1;
1700        spin_unlock_irq(&zone->lru_lock);
1701
1702        fraction[0] = ap;
1703        fraction[1] = fp;
1704        denominator = ap + fp + 1;
1705out:
1706        for_each_evictable_lru(lru) {
1707                int file = is_file_lru(lru);
1708                unsigned long scan;
1709
1710                scan = get_lru_size(lruvec, lru);
1711                if (sc->priority || noswap || !vmscan_swappiness(sc)) {
1712                        scan >>= sc->priority;
1713                        if (!scan && force_scan)
1714                                scan = SWAP_CLUSTER_MAX;
1715                        scan = div64_u64(scan * fraction[file], denominator);
1716                }
1717                nr[lru] = scan;
1718        }
1719}
1720
1721/* Use reclaim/compaction for costly allocs or under memory pressure */
1722static bool in_reclaim_compaction(struct scan_control *sc)
1723{
1724        if (COMPACTION_BUILD && sc->order &&
1725                        (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
1726                         sc->priority < DEF_PRIORITY - 2))
1727                return true;
1728
1729        return false;
1730}
1731
1732/*
1733 * Reclaim/compaction is used for high-order allocation requests. It reclaims
1734 * order-0 pages before compacting the zone. should_continue_reclaim() returns
1735 * true if more pages should be reclaimed such that when the page allocator
1736 * calls try_to_compact_zone() that it will have enough free pages to succeed.
1737 * It will give up earlier than that if there is difficulty reclaiming pages.
1738 */
1739static inline bool should_continue_reclaim(struct lruvec *lruvec,
1740                                        unsigned long nr_reclaimed,
1741                                        unsigned long nr_scanned,
1742                                        struct scan_control *sc)
1743{
1744        unsigned long pages_for_compaction;
1745        unsigned long inactive_lru_pages;
1746
1747        /* If not in reclaim/compaction mode, stop */
1748        if (!in_reclaim_compaction(sc))
1749                return false;
1750
1751        /* Consider stopping depending on scan and reclaim activity */
1752        if (sc->gfp_mask & __GFP_REPEAT) {
1753                /*
1754                 * For __GFP_REPEAT allocations, stop reclaiming if the
1755                 * full LRU list has been scanned and we are still failing
1756                 * to reclaim pages. This full LRU scan is potentially
1757                 * expensive but a __GFP_REPEAT caller really wants to succeed
1758                 */
1759                if (!nr_reclaimed && !nr_scanned)
1760                        return false;
1761        } else {
1762                /*
1763                 * For non-__GFP_REPEAT allocations which can presumably
1764                 * fail without consequence, stop if we failed to reclaim
1765                 * any pages from the last SWAP_CLUSTER_MAX number of
1766                 * pages that were scanned. This will return to the
1767                 * caller faster at the risk reclaim/compaction and
1768                 * the resulting allocation attempt fails
1769                 */
1770                if (!nr_reclaimed)
1771                        return false;
1772        }
1773
1774        /*
1775         * If we have not reclaimed enough pages for compaction and the
1776         * inactive lists are large enough, continue reclaiming
1777         */
1778        pages_for_compaction = (2UL << sc->order);
1779        inactive_lru_pages = get_lru_size(lruvec, LRU_INACTIVE_FILE);
1780        if (nr_swap_pages > 0)
1781                inactive_lru_pages += get_lru_size(lruvec, LRU_INACTIVE_ANON);
1782        if (sc->nr_reclaimed < pages_for_compaction &&
1783                        inactive_lru_pages > pages_for_compaction)
1784                return true;
1785
1786        /* If compaction would go ahead or the allocation would succeed, stop */
1787        switch (compaction_suitable(lruvec_zone(lruvec), sc->order)) {
1788        case COMPACT_PARTIAL:
1789        case COMPACT_CONTINUE:
1790                return false;
1791        default:
1792                return true;
1793        }
1794}
1795
1796/*
1797 * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1798 */
1799static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
1800{
1801        unsigned long nr[NR_LRU_LISTS];
1802        unsigned long nr_to_scan;
1803        enum lru_list lru;
1804        unsigned long nr_reclaimed, nr_scanned;
1805        unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1806        struct blk_plug plug;
1807
1808restart:
1809        nr_reclaimed = 0;
1810        nr_scanned = sc->nr_scanned;
1811        get_scan_count(lruvec, sc, nr);
1812
1813        blk_start_plug(&plug);
1814        while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1815                                        nr[LRU_INACTIVE_FILE]) {
1816                for_each_evictable_lru(lru) {
1817                        if (nr[lru]) {
1818                                nr_to_scan = min_t(unsigned long,
1819                                                   nr[lru], SWAP_CLUSTER_MAX);
1820                                nr[lru] -= nr_to_scan;
1821
1822                                nr_reclaimed += shrink_list(lru, nr_to_scan,
1823                                                            lruvec, sc);
1824                        }
1825                }
1826                /*
1827                 * On large memory systems, scan >> priority can become
1828                 * really large. This is fine for the starting priority;
1829                 * we want to put equal scanning pressure on each zone.
1830                 * However, if the VM has a harder time of freeing pages,
1831                 * with multiple processes reclaiming pages, the total
1832                 * freeing target can get unreasonably large.
1833                 */
1834                if (nr_reclaimed >= nr_to_reclaim &&
1835                    sc->priority < DEF_PRIORITY)
1836                        break;
1837        }
1838        blk_finish_plug(&plug);
1839        sc->nr_reclaimed += nr_reclaimed;
1840
1841        /*
1842         * Even if we did not try to evict anon pages at all, we want to
1843         * rebalance the anon lru active/inactive ratio.
1844         */
1845        if (inactive_anon_is_low(lruvec))
1846                shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
1847                                   sc, LRU_ACTIVE_ANON);
1848
1849        /* reclaim/compaction might need reclaim to continue */
1850        if (should_continue_reclaim(lruvec, nr_reclaimed,
1851                                    sc->nr_scanned - nr_scanned, sc))
1852                goto restart;
1853
1854        throttle_vm_writeout(sc->gfp_mask);
1855}
1856
1857static void shrink_zone(struct zone *zone, struct scan_control *sc)
1858{
1859        struct mem_cgroup *root = sc->target_mem_cgroup;
1860        struct mem_cgroup_reclaim_cookie reclaim = {
1861                .zone = zone,
1862                .priority = sc->priority,
1863        };
1864        struct mem_cgroup *memcg;
1865
1866        memcg = mem_cgroup_iter(root, NULL, &reclaim);
1867        do {
1868                struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
1869
1870                shrink_lruvec(lruvec, sc);
1871
1872                /*
1873                 * Limit reclaim has historically picked one memcg and
1874                 * scanned it with decreasing priority levels until
1875                 * nr_to_reclaim had been reclaimed.  This priority
1876                 * cycle is thus over after a single memcg.
1877                 *
1878                 * Direct reclaim and kswapd, on the other hand, have
1879                 * to scan all memory cgroups to fulfill the overall
1880                 * scan target for the zone.
1881                 */
1882                if (!global_reclaim(sc)) {
1883                        mem_cgroup_iter_break(root, memcg);
1884                        break;
1885                }
1886                memcg = mem_cgroup_iter(root, memcg, &reclaim);
1887        } while (memcg);
1888}
1889
1890/* Returns true if compaction should go ahead for a high-order request */
1891static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
1892{
1893        unsigned long balance_gap, watermark;
1894        bool watermark_ok;
1895
1896        /* Do not consider compaction for orders reclaim is meant to satisfy */
1897        if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
1898                return false;
1899
1900        /*
1901         * Compaction takes time to run and there are potentially other
1902         * callers using the pages just freed. Continue reclaiming until
1903         * there is a buffer of free pages available to give compaction
1904         * a reasonable chance of completing and allocating the page
1905         */
1906        balance_gap = min(low_wmark_pages(zone),
1907                (zone->present_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
1908                        KSWAPD_ZONE_BALANCE_GAP_RATIO);
1909        watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
1910        watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
1911
1912        /*
1913         * If compaction is deferred, reclaim up to a point where
1914         * compaction will have a chance of success when re-enabled
1915         */
1916        if (compaction_deferred(zone, sc->order))
1917                return watermark_ok;
1918
1919        /* If compaction is not ready to start, keep reclaiming */
1920        if (!compaction_suitable(zone, sc->order))
1921                return false;
1922
1923        return watermark_ok;
1924}
1925
1926/*
1927 * This is the direct reclaim path, for page-allocating processes.  We only
1928 * try to reclaim pages from zones which will satisfy the caller's allocation
1929 * request.
1930 *
1931 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
1932 * Because:
1933 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
1934 *    allocation or
1935 * b) The target zone may be at high_wmark_pages(zone) but the lower zones
1936 *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
1937 *    zone defense algorithm.
1938 *
1939 * If a zone is deemed to be full of pinned pages then just give it a light
1940 * scan then give up on it.
1941 *
1942 * This function returns true if a zone is being reclaimed for a costly
1943 * high-order allocation and compaction is ready to begin. This indicates to
1944 * the caller that it should consider retrying the allocation instead of
1945 * further reclaim.
1946 */
1947static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
1948{
1949        struct zoneref *z;
1950        struct zone *zone;
1951        unsigned long nr_soft_reclaimed;
1952        unsigned long nr_soft_scanned;
1953        bool aborted_reclaim = false;
1954
1955        /*
1956         * If the number of buffer_heads in the machine exceeds the maximum
1957         * allowed level, force direct reclaim to scan the highmem zone as
1958         * highmem pages could be pinning lowmem pages storing buffer_heads
1959         */
1960        if (buffer_heads_over_limit)
1961                sc->gfp_mask |= __GFP_HIGHMEM;
1962
1963        for_each_zone_zonelist_nodemask(zone, z, zonelist,
1964                                        gfp_zone(sc->gfp_mask), sc->nodemask) {
1965                if (!populated_zone(zone))
1966                        continue;
1967                /*
1968                 * Take care memory controller reclaiming has small influence
1969                 * to global LRU.
1970                 */
1971                if (global_reclaim(sc)) {
1972                        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
1973                                continue;
1974                        if (zone->all_unreclaimable &&
1975                                        sc->priority != DEF_PRIORITY)
1976                                continue;       /* Let kswapd poll it */
1977                        if (COMPACTION_BUILD) {
1978                                /*
1979                                 * If we already have plenty of memory free for
1980                                 * compaction in this zone, don't free any more.
1981                                 * Even though compaction is invoked for any
1982                                 * non-zero order, only frequent costly order
1983                                 * reclamation is disruptive enough to become a
1984                                 * noticeable problem, like transparent huge
1985                                 * page allocations.
1986                                 */
1987                                if (compaction_ready(zone, sc)) {
1988                                        aborted_reclaim = true;
1989                                        continue;
1990                                }
1991                        }
1992                        /*
1993                         * This steals pages from memory cgroups over softlimit
1994                         * and returns the number of reclaimed pages and
1995                         * scanned pages. This works for global memory pressure
1996                         * and balancing, not for a memcg's limit.
1997                         */
1998                        nr_soft_scanned = 0;
1999                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2000                                                sc->order, sc->gfp_mask,
2001                                                &nr_soft_scanned);
2002                        sc->nr_reclaimed += nr_soft_reclaimed;
2003                        sc->nr_scanned += nr_soft_scanned;
2004                        /* need some check for avoid more shrink_zone() */
2005                }
2006
2007                shrink_zone(zone, sc);
2008        }
2009
2010        return aborted_reclaim;
2011}
2012
2013static bool zone_reclaimable(struct zone *zone)
2014{
2015        return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
2016}
2017
2018/* All zones in zonelist are unreclaimable? */
2019static bool all_unreclaimable(struct zonelist *zonelist,
2020                struct scan_control *sc)
2021{
2022        struct zoneref *z;
2023        struct zone *zone;
2024
2025        for_each_zone_zonelist_nodemask(zone, z, zonelist,
2026                        gfp_zone(sc->gfp_mask), sc->nodemask) {
2027                if (!populated_zone(zone))
2028                        continue;
2029                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2030                        continue;
2031                if (!zone->all_unreclaimable)
2032                        return false;
2033        }
2034
2035        return true;
2036}
2037
2038/*
2039 * This is the main entry point to direct page reclaim.
2040 *
2041 * If a full scan of the inactive list fails to free enough memory then we
2042 * are "out of memory" and something needs to be killed.
2043 *
2044 * If the caller is !__GFP_FS then the probability of a failure is reasonably
2045 * high - the zone may be full of dirty or under-writeback pages, which this
2046 * caller can't do much about.  We kick the writeback threads and take explicit
2047 * naps in the hope that some of these pages can be written.  But if the
2048 * allocating task holds filesystem locks which prevent writeout this might not
2049 * work, and the allocation attempt will fail.
2050 *
2051 * returns:     0, if no pages reclaimed
2052 *              else, the number of pages reclaimed
2053 */
2054static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2055                                        struct scan_control *sc,
2056                                        struct shrink_control *shrink)
2057{
2058        unsigned long total_scanned = 0;
2059        struct reclaim_state *reclaim_state = current->reclaim_state;
2060        struct zoneref *z;
2061        struct zone *zone;
2062        unsigned long writeback_threshold;
2063        bool aborted_reclaim;
2064
2065        delayacct_freepages_start();
2066
2067        if (global_reclaim(sc))
2068                count_vm_event(ALLOCSTALL);
2069
2070        do {
2071                sc->nr_scanned = 0;
2072                aborted_reclaim = shrink_zones(zonelist, sc);
2073
2074                /*
2075                 * Don't shrink slabs when reclaiming memory from
2076                 * over limit cgroups
2077                 */
2078                if (global_reclaim(sc)) {
2079                        unsigned long lru_pages = 0;
2080                        for_each_zone_zonelist(zone, z, zonelist,
2081                                        gfp_zone(sc->gfp_mask)) {
2082                                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2083                                        continue;
2084
2085                                lru_pages += zone_reclaimable_pages(zone);
2086                        }
2087
2088                        shrink_slab(shrink, sc->nr_scanned, lru_pages);
2089                        if (reclaim_state) {
2090                                sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2091                                reclaim_state->reclaimed_slab = 0;
2092                        }
2093                }
2094                total_scanned += sc->nr_scanned;
2095                if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2096                        goto out;
2097
2098                /*
2099                 * Try to write back as many pages as we just scanned.  This
2100                 * tends to cause slow streaming writers to write data to the
2101                 * disk smoothly, at the dirtying rate, which is nice.   But
2102                 * that's undesirable in laptop mode, where we *want* lumpy
2103                 * writeout.  So in laptop mode, write out the whole world.
2104                 */
2105                writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2106                if (total_scanned > writeback_threshold) {
2107                        wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2108                                                WB_REASON_TRY_TO_FREE_PAGES);
2109                        sc->may_writepage = 1;
2110                }
2111
2112                /* Take a nap, wait for some writeback to complete */
2113                if (!sc->hibernation_mode && sc->nr_scanned &&
2114                    sc->priority < DEF_PRIORITY - 2) {
2115                        struct zone *preferred_zone;
2116
2117                        first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
2118                                                &cpuset_current_mems_allowed,
2119                                                &preferred_zone);
2120                        wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
2121                }
2122        } while (--sc->priority >= 0);
2123
2124out:
2125        delayacct_freepages_end();
2126
2127        if (sc->nr_reclaimed)
2128                return sc->nr_reclaimed;
2129
2130        /*
2131         * As hibernation is going on, kswapd is freezed so that it can't mark
2132         * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2133         * check.
2134         */
2135        if (oom_killer_disabled)
2136                return 0;
2137
2138        /* Aborted reclaim to try compaction? don't OOM, then */
2139        if (aborted_reclaim)
2140                return 1;
2141
2142        /* top priority shrink_zones still had more to do? don't OOM, then */
2143        if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2144                return 1;
2145
2146        return 0;
2147}
2148
2149static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2150{
2151        struct zone *zone;
2152        unsigned long pfmemalloc_reserve = 0;
2153        unsigned long free_pages = 0;
2154        int i;
2155        bool wmark_ok;
2156
2157        for (i = 0; i <= ZONE_NORMAL; i++) {
2158                zone = &pgdat->node_zones[i];
2159                pfmemalloc_reserve += min_wmark_pages(zone);
2160                free_pages += zone_page_state(zone, NR_FREE_PAGES);
2161        }
2162
2163        wmark_ok = free_pages > pfmemalloc_reserve / 2;
2164
2165        /* kswapd must be awake if processes are being throttled */
2166        if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2167                pgdat->classzone_idx = min(pgdat->classzone_idx,
2168                                                (enum zone_type)ZONE_NORMAL);
2169                wake_up_interruptible(&pgdat->kswapd_wait);
2170        }
2171
2172        return wmark_ok;
2173}
2174
2175/*
2176 * Throttle direct reclaimers if backing storage is backed by the network
2177 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
2178 * depleted. kswapd will continue to make progress and wake the processes
2179 * when the low watermark is reached.
2180 *
2181 * Returns true if a fatal signal was delivered during throttling. If this
2182 * happens, the page allocator should not consider triggering the OOM killer.
2183 */
2184static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2185                                        nodemask_t *nodemask)
2186{
2187        struct zone *zone;
2188        int high_zoneidx = gfp_zone(gfp_mask);
2189        pg_data_t *pgdat;
2190
2191        /*
2192         * Kernel threads should not be throttled as they may be indirectly
2193         * responsible for cleaning pages necessary for reclaim to make forward
2194         * progress. kjournald for example may enter direct reclaim while
2195         * committing a transaction where throttling it could forcing other
2196         * processes to block on log_wait_commit().
2197         */
2198        if (current->flags & PF_KTHREAD)
2199                goto out;
2200
2201        /*
2202         * If a fatal signal is pending, this process should not throttle.
2203         * It should return quickly so it can exit and free its memory
2204         */
2205        if (fatal_signal_pending(current))
2206                goto out;
2207
2208        /* Check if the pfmemalloc reserves are ok */
2209        first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
2210        pgdat = zone->zone_pgdat;
2211        if (pfmemalloc_watermark_ok(pgdat))
2212                goto out;
2213
2214        /* Account for the throttling */
2215        count_vm_event(PGSCAN_DIRECT_THROTTLE);
2216
2217        /*
2218         * If the caller cannot enter the filesystem, it's possible that it
2219         * is due to the caller holding an FS lock or performing a journal
2220         * transaction in the case of a filesystem like ext[3|4]. In this case,
2221         * it is not safe to block on pfmemalloc_wait as kswapd could be
2222         * blocked waiting on the same lock. Instead, throttle for up to a
2223         * second before continuing.
2224         */
2225        if (!(gfp_mask & __GFP_FS)) {
2226                wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2227                        pfmemalloc_watermark_ok(pgdat), HZ);
2228
2229                goto check_pending;
2230        }
2231
2232        /* Throttle until kswapd wakes the process */
2233        wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2234                pfmemalloc_watermark_ok(pgdat));
2235
2236check_pending:
2237        if (fatal_signal_pending(current))
2238                return true;
2239
2240out:
2241        return false;
2242}
2243
2244unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2245                                gfp_t gfp_mask, nodemask_t *nodemask)
2246{
2247        unsigned long nr_reclaimed;
2248        struct scan_control sc = {
2249                .gfp_mask = gfp_mask,
2250                .may_writepage = !laptop_mode,
2251                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2252                .may_unmap = 1,
2253                .may_swap = 1,
2254                .order = order,
2255                .priority = DEF_PRIORITY,
2256                .target_mem_cgroup = NULL,
2257                .nodemask = nodemask,
2258        };
2259        struct shrink_control shrink = {
2260                .gfp_mask = sc.gfp_mask,
2261        };
2262
2263        /*
2264         * Do not enter reclaim if fatal signal was delivered while throttled.
2265         * 1 is returned so that the page allocator does not OOM kill at this
2266         * point.
2267         */
2268        if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2269                return 1;
2270
2271        trace_mm_vmscan_direct_reclaim_begin(order,
2272                                sc.may_writepage,
2273                                gfp_mask);
2274
2275        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2276
2277        trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2278
2279        return nr_reclaimed;
2280}
2281
2282#ifdef CONFIG_MEMCG
2283
2284unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2285                                                gfp_t gfp_mask, bool noswap,
2286                                                struct zone *zone,
2287                                                unsigned long *nr_scanned)
2288{
2289        struct scan_control sc = {
2290                .nr_scanned = 0,
2291                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2292                .may_writepage = !laptop_mode,
2293                .may_unmap = 1,
2294                .may_swap = !noswap,
2295                .order = 0,
2296                .priority = 0,
2297                .target_mem_cgroup = memcg,
2298        };
2299        struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2300
2301        sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2302                        (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2303
2304        trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2305                                                      sc.may_writepage,
2306                                                      sc.gfp_mask);
2307
2308        /*
2309         * NOTE: Although we can get the priority field, using it
2310         * here is not a good idea, since it limits the pages we can scan.
2311         * if we don't reclaim here, the shrink_zone from balance_pgdat
2312         * will pick up pages from other mem cgroup's as well. We hack
2313         * the priority and make it zero.
2314         */
2315        shrink_lruvec(lruvec, &sc);
2316
2317        trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2318
2319        *nr_scanned = sc.nr_scanned;
2320        return sc.nr_reclaimed;
2321}
2322
2323unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
2324                                           gfp_t gfp_mask,
2325                                           bool noswap)
2326{
2327        struct zonelist *zonelist;
2328        unsigned long nr_reclaimed;
2329        int nid;
2330        struct scan_control sc = {
2331                .may_writepage = !laptop_mode,
2332                .may_unmap = 1,
2333                .may_swap = !noswap,
2334                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2335                .order = 0,
2336                .priority = DEF_PRIORITY,
2337                .target_mem_cgroup = memcg,
2338                .nodemask = NULL, /* we don't care the placement */
2339                .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2340                                (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2341        };
2342        struct shrink_control shrink = {
2343                .gfp_mask = sc.gfp_mask,
2344        };
2345
2346        /*
2347         * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2348         * take care of from where we get pages. So the node where we start the
2349         * scan does not need to be the current node.
2350         */
2351        nid = mem_cgroup_select_victim_node(memcg);
2352
2353        zonelist = NODE_DATA(nid)->node_zonelists;
2354
2355        trace_mm_vmscan_memcg_reclaim_begin(0,
2356                                            sc.may_writepage,
2357                                            sc.gfp_mask);
2358
2359        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2360
2361        trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2362
2363        return nr_reclaimed;
2364}
2365#endif
2366
2367static void age_active_anon(struct zone *zone, struct scan_control *sc)
2368{
2369        struct mem_cgroup *memcg;
2370
2371        if (!total_swap_pages)
2372                return;
2373
2374        memcg = mem_cgroup_iter(NULL, NULL, NULL);
2375        do {
2376                struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2377
2378                if (inactive_anon_is_low(lruvec))
2379                        shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2380                                           sc, LRU_ACTIVE_ANON);
2381
2382                memcg = mem_cgroup_iter(NULL, memcg, NULL);
2383        } while (memcg);
2384}
2385
2386/*
2387 * pgdat_balanced is used when checking if a node is balanced for high-order
2388 * allocations. Only zones that meet watermarks and are in a zone allowed
2389 * by the callers classzone_idx are added to balanced_pages. The total of
2390 * balanced pages must be at least 25% of the zones allowed by classzone_idx
2391 * for the node to be considered balanced. Forcing all zones to be balanced
2392 * for high orders can cause excessive reclaim when there are imbalanced zones.
2393 * The choice of 25% is due to
2394 *   o a 16M DMA zone that is balanced will not balance a zone on any
2395 *     reasonable sized machine
2396 *   o On all other machines, the top zone must be at least a reasonable
2397 *     percentage of the middle zones. For example, on 32-bit x86, highmem
2398 *     would need to be at least 256M for it to be balance a whole node.
2399 *     Similarly, on x86-64 the Normal zone would need to be at least 1G
2400 *     to balance a node on its own. These seemed like reasonable ratios.
2401 */
2402static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
2403                                                int classzone_idx)
2404{
2405        unsigned long present_pages = 0;
2406        int i;
2407
2408        for (i = 0; i <= classzone_idx; i++)
2409                present_pages += pgdat->node_zones[i].present_pages;
2410
2411        /* A special case here: if zone has no page, we think it's balanced */
2412        return balanced_pages >= (present_pages >> 2);
2413}
2414
2415/*
2416 * Prepare kswapd for sleeping. This verifies that there are no processes
2417 * waiting in throttle_direct_reclaim() and that watermarks have been met.
2418 *
2419 * Returns true if kswapd is ready to sleep
2420 */
2421static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
2422                                        int classzone_idx)
2423{
2424        int i;
2425        unsigned long balanced = 0;
2426        bool all_zones_ok = true;
2427
2428        /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2429        if (remaining)
2430                return false;
2431
2432        /*
2433         * There is a potential race between when kswapd checks its watermarks
2434         * and a process gets throttled. There is also a potential race if
2435         * processes get throttled, kswapd wakes, a large process exits therby
2436         * balancing the zones that causes kswapd to miss a wakeup. If kswapd
2437         * is going to sleep, no process should be sleeping on pfmemalloc_wait
2438         * so wake them now if necessary. If necessary, processes will wake
2439         * kswapd and get throttled again
2440         */
2441        if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
2442                wake_up(&pgdat->pfmemalloc_wait);
2443                return false;
2444        }
2445
2446        /* Check the watermark levels */
2447        for (i = 0; i <= classzone_idx; i++) {
2448                struct zone *zone = pgdat->node_zones + i;
2449
2450                if (!populated_zone(zone))
2451                        continue;
2452
2453                /*
2454                 * balance_pgdat() skips over all_unreclaimable after
2455                 * DEF_PRIORITY. Effectively, it considers them balanced so
2456                 * they must be considered balanced here as well if kswapd
2457                 * is to sleep
2458                 */
2459                if (zone->all_unreclaimable) {
2460                        balanced += zone->present_pages;
2461                        continue;
2462                }
2463
2464                if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
2465                                                        i, 0))
2466                        all_zones_ok = false;
2467                else
2468                        balanced += zone->present_pages;
2469        }
2470
2471        /*
2472         * For high-order requests, the balanced zones must contain at least
2473         * 25% of the nodes pages for kswapd to sleep. For order-0, all zones
2474         * must be balanced
2475         */
2476        if (order)
2477                return pgdat_balanced(pgdat, balanced, classzone_idx);
2478        else
2479                return all_zones_ok;
2480}
2481
2482/*
2483 * For kswapd, balance_pgdat() will work across all this node's zones until
2484 * they are all at high_wmark_pages(zone).
2485 *
2486 * Returns the final order kswapd was reclaiming at
2487 *
2488 * There is special handling here for zones which are full of pinned pages.
2489 * This can happen if the pages are all mlocked, or if they are all used by
2490 * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
2491 * What we do is to detect the case where all pages in the zone have been
2492 * scanned twice and there has been zero successful reclaim.  Mark the zone as
2493 * dead and from now on, only perform a short scan.  Basically we're polling
2494 * the zone for when the problem goes away.
2495 *
2496 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
2497 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2498 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2499 * lower zones regardless of the number of free pages in the lower zones. This
2500 * interoperates with the page allocator fallback scheme to ensure that aging
2501 * of pages is balanced across the zones.
2502 */
2503static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2504                                                        int *classzone_idx)
2505{
2506        int all_zones_ok;
2507        unsigned long balanced;
2508        int i;
2509        int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
2510        unsigned long total_scanned;
2511        struct reclaim_state *reclaim_state = current->reclaim_state;
2512        unsigned long nr_soft_reclaimed;
2513        unsigned long nr_soft_scanned;
2514        struct scan_control sc = {
2515                .gfp_mask = GFP_KERNEL,
2516                .may_unmap = 1,
2517                .may_swap = 1,
2518                /*
2519                 * kswapd doesn't want to be bailed out while reclaim. because
2520                 * we want to put equal scanning pressure on each zone.
2521                 */
2522                .nr_to_reclaim = ULONG_MAX,
2523                .order = order,
2524                .target_mem_cgroup = NULL,
2525        };
2526        struct shrink_control shrink = {
2527                .gfp_mask = sc.gfp_mask,
2528        };
2529loop_again:
2530        total_scanned = 0;
2531        sc.priority = DEF_PRIORITY;
2532        sc.nr_reclaimed = 0;
2533        sc.may_writepage = !laptop_mode;
2534        count_vm_event(PAGEOUTRUN);
2535
2536        do {
2537                unsigned long lru_pages = 0;
2538                int has_under_min_watermark_zone = 0;
2539
2540                all_zones_ok = 1;
2541                balanced = 0;
2542
2543                /*
2544                 * Scan in the highmem->dma direction for the highest
2545                 * zone which needs scanning
2546                 */
2547                for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2548                        struct zone *zone = pgdat->node_zones + i;
2549
2550                        if (!populated_zone(zone))
2551                                continue;
2552
2553                        if (zone->all_unreclaimable &&
2554                            sc.priority != DEF_PRIORITY)
2555                                continue;
2556
2557                        /*
2558                         * Do some background aging of the anon list, to give
2559                         * pages a chance to be referenced before reclaiming.
2560                         */
2561                        age_active_anon(zone, &sc);
2562
2563                        /*
2564                         * If the number of buffer_heads in the machine
2565                         * exceeds the maximum allowed level and this node
2566                         * has a highmem zone, force kswapd to reclaim from
2567                         * it to relieve lowmem pressure.
2568                         */
2569                        if (buffer_heads_over_limit && is_highmem_idx(i)) {
2570                                end_zone = i;
2571                                break;
2572                        }
2573
2574                        if (!zone_watermark_ok_safe(zone, order,
2575                                        high_wmark_pages(zone), 0, 0)) {
2576                                end_zone = i;
2577                                break;
2578                        } else {
2579                                /* If balanced, clear the congested flag */
2580                                zone_clear_flag(zone, ZONE_CONGESTED);
2581                        }
2582                }
2583                if (i < 0)
2584                        goto out;
2585
2586                for (i = 0; i <= end_zone; i++) {
2587                        struct zone *zone = pgdat->node_zones + i;
2588
2589                        lru_pages += zone_reclaimable_pages(zone);
2590                }
2591
2592                /*
2593                 * Now scan the zone in the dma->highmem direction, stopping
2594                 * at the last zone which needs scanning.
2595                 *
2596                 * We do this because the page allocator works in the opposite
2597                 * direction.  This prevents the page allocator from allocating
2598                 * pages behind kswapd's direction of progress, which would
2599                 * cause too much scanning of the lower zones.
2600                 */
2601                for (i = 0; i <= end_zone; i++) {
2602                        struct zone *zone = pgdat->node_zones + i;
2603                        int nr_slab, testorder;
2604                        unsigned long balance_gap;
2605
2606                        if (!populated_zone(zone))
2607                                continue;
2608
2609                        if (zone->all_unreclaimable &&
2610                            sc.priority != DEF_PRIORITY)
2611                                continue;
2612
2613                        sc.nr_scanned = 0;
2614
2615                        nr_soft_scanned = 0;
2616                        /*
2617                         * Call soft limit reclaim before calling shrink_zone.
2618                         */
2619                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2620                                                        order, sc.gfp_mask,
2621                                                        &nr_soft_scanned);
2622                        sc.nr_reclaimed += nr_soft_reclaimed;
2623                        total_scanned += nr_soft_scanned;
2624
2625                        /*
2626                         * We put equal pressure on every zone, unless
2627                         * one zone has way too many pages free
2628                         * already. The "too many pages" is defined
2629                         * as the high wmark plus a "gap" where the
2630                         * gap is either the low watermark or 1%
2631                         * of the zone, whichever is smaller.
2632                         */
2633                        balance_gap = min(low_wmark_pages(zone),
2634                                (zone->present_pages +
2635                                        KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2636                                KSWAPD_ZONE_BALANCE_GAP_RATIO);
2637                        /*
2638                         * Kswapd reclaims only single pages with compaction
2639                         * enabled. Trying too hard to reclaim until contiguous
2640                         * free pages have become available can hurt performance
2641                         * by evicting too much useful data from memory.
2642                         * Do not reclaim more than needed for compaction.
2643                         */
2644                        testorder = order;
2645                        if (COMPACTION_BUILD && order &&
2646                                        compaction_suitable(zone, order) !=
2647                                                COMPACT_SKIPPED)
2648                                testorder = 0;
2649
2650                        if ((buffer_heads_over_limit && is_highmem_idx(i)) ||
2651                                    !zone_watermark_ok_safe(zone, testorder,
2652                                        high_wmark_pages(zone) + balance_gap,
2653                                        end_zone, 0)) {
2654                                shrink_zone(zone, &sc);
2655
2656                                reclaim_state->reclaimed_slab = 0;
2657                                nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages);
2658                                sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2659                                total_scanned += sc.nr_scanned;
2660
2661                                if (nr_slab == 0 && !zone_reclaimable(zone))
2662                                        zone->all_unreclaimable = 1;
2663                        }
2664
2665                        /*
2666                         * If we've done a decent amount of scanning and
2667                         * the reclaim ratio is low, start doing writepage
2668                         * even in laptop mode
2669                         */
2670                        if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
2671                            total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2)
2672                                sc.may_writepage = 1;
2673
2674                        if (zone->all_unreclaimable) {
2675                                if (end_zone && end_zone == i)
2676                                        end_zone--;
2677                                continue;
2678                        }
2679
2680                        if (!zone_watermark_ok_safe(zone, testorder,
2681                                        high_wmark_pages(zone), end_zone, 0)) {
2682                                all_zones_ok = 0;
2683                                /*
2684                                 * We are still under min water mark.  This
2685                                 * means that we have a GFP_ATOMIC allocation
2686                                 * failure risk. Hurry up!
2687                                 */
2688                                if (!zone_watermark_ok_safe(zone, order,
2689                                            min_wmark_pages(zone), end_zone, 0))
2690                                        has_under_min_watermark_zone = 1;
2691                        } else {
2692                                /*
2693                                 * If a zone reaches its high watermark,
2694                                 * consider it to be no longer congested. It's
2695                                 * possible there are dirty pages backed by
2696                                 * congested BDIs but as pressure is relieved,
2697                                 * speculatively avoid congestion waits
2698                                 */
2699                                zone_clear_flag(zone, ZONE_CONGESTED);
2700                                if (i <= *classzone_idx)
2701                                        balanced += zone->present_pages;
2702                        }
2703
2704                }
2705
2706                /*
2707                 * If the low watermark is met there is no need for processes
2708                 * to be throttled on pfmemalloc_wait as they should not be
2709                 * able to safely make forward progress. Wake them
2710                 */
2711                if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
2712                                pfmemalloc_watermark_ok(pgdat))
2713                        wake_up(&pgdat->pfmemalloc_wait);
2714
2715                if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))
2716                        break;          /* kswapd: all done */
2717                /*
2718                 * OK, kswapd is getting into trouble.  Take a nap, then take
2719                 * another pass across the zones.
2720                 */
2721                if (total_scanned && (sc.priority < DEF_PRIORITY - 2)) {
2722                        if (has_under_min_watermark_zone)
2723                                count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT);
2724                        else
2725                                congestion_wait(BLK_RW_ASYNC, HZ/10);
2726                }
2727
2728                /*
2729                 * We do this so kswapd doesn't build up large priorities for
2730                 * example when it is freeing in parallel with allocators. It
2731                 * matches the direct reclaim path behaviour in terms of impact
2732                 * on zone->*_priority.
2733                 */
2734                if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2735                        break;
2736        } while (--sc.priority >= 0);
2737out:
2738
2739        /*
2740         * order-0: All zones must meet high watermark for a balanced node
2741         * high-order: Balanced zones must make up at least 25% of the node
2742         *             for the node to be balanced
2743         */
2744        if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) {
2745                cond_resched();
2746
2747                try_to_freeze();
2748
2749                /*
2750                 * Fragmentation may mean that the system cannot be
2751                 * rebalanced for high-order allocations in all zones.
2752                 * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2753                 * it means the zones have been fully scanned and are still
2754                 * not balanced. For high-order allocations, there is
2755                 * little point trying all over again as kswapd may
2756                 * infinite loop.
2757                 *
2758                 * Instead, recheck all watermarks at order-0 as they
2759                 * are the most important. If watermarks are ok, kswapd will go
2760                 * back to sleep. High-order users can still perform direct
2761                 * reclaim if they wish.
2762                 */
2763                if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2764                        order = sc.order = 0;
2765
2766                goto loop_again;
2767        }
2768
2769        /*
2770         * If kswapd was reclaiming at a higher order, it has the option of
2771         * sleeping without all zones being balanced. Before it does, it must
2772         * ensure that the watermarks for order-0 on *all* zones are met and
2773         * that the congestion flags are cleared. The congestion flag must
2774         * be cleared as kswapd is the only mechanism that clears the flag
2775         * and it is potentially going to sleep here.
2776         */
2777        if (order) {
2778                int zones_need_compaction = 1;
2779
2780                for (i = 0; i <= end_zone; i++) {
2781                        struct zone *zone = pgdat->node_zones + i;
2782
2783                        if (!populated_zone(zone))
2784                                continue;
2785
2786                        if (zone->all_unreclaimable &&
2787                            sc.priority != DEF_PRIORITY)
2788                                continue;
2789
2790                        /* Would compaction fail due to lack of free memory? */
2791                        if (COMPACTION_BUILD &&
2792                            compaction_suitable(zone, order) == COMPACT_SKIPPED)
2793                                goto loop_again;
2794
2795                        /* Confirm the zone is balanced for order-0 */
2796                        if (!zone_watermark_ok(zone, 0,
2797                                        high_wmark_pages(zone), 0, 0)) {
2798                                order = sc.order = 0;
2799                                goto loop_again;
2800                        }
2801
2802                        /* Check if the memory needs to be defragmented. */
2803                        if (zone_watermark_ok(zone, order,
2804                                    low_wmark_pages(zone), *classzone_idx, 0))
2805                                zones_need_compaction = 0;
2806
2807                        /* If balanced, clear the congested flag */
2808                        zone_clear_flag(zone, ZONE_CONGESTED);
2809                }
2810
2811                if (zones_need_compaction)
2812                        compact_pgdat(pgdat, order);
2813        }
2814
2815        /*
2816         * Return the order we were reclaiming at so prepare_kswapd_sleep()
2817         * makes a decision on the order we were last reclaiming at. However,
2818         * if another caller entered the allocator slow path while kswapd
2819         * was awake, order will remain at the higher level
2820         */
2821        *classzone_idx = end_zone;
2822        return order;
2823}
2824
2825static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
2826{
2827        long remaining = 0;
2828        DEFINE_WAIT(wait);
2829
2830        if (freezing(current) || kthread_should_stop())
2831                return;
2832
2833        prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2834
2835        /* Try to sleep for a short interval */
2836        if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2837                remaining = schedule_timeout(HZ/10);
2838                finish_wait(&pgdat->kswapd_wait, &wait);
2839                prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2840        }
2841
2842        /*
2843         * After a short sleep, check if it was a premature sleep. If not, then
2844         * go fully to sleep until explicitly woken up.
2845         */
2846        if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2847                trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
2848
2849                /*
2850                 * vmstat counters are not perfectly accurate and the estimated
2851                 * value for counters such as NR_FREE_PAGES can deviate from the
2852                 * true value by nr_online_cpus * threshold. To avoid the zone
2853                 * watermarks being breached while under pressure, we reduce the
2854                 * per-cpu vmstat threshold while kswapd is awake and restore
2855                 * them before going back to sleep.
2856                 */
2857                set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
2858
2859                if (!kthread_should_stop())
2860                        schedule();
2861
2862                set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
2863        } else {
2864                if (remaining)
2865                        count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2866                else
2867                        count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2868        }
2869        finish_wait(&pgdat->kswapd_wait, &wait);
2870}
2871
2872/*
2873 * The background pageout daemon, started as a kernel thread
2874 * from the init process.
2875 *
2876 * This basically trickles out pages so that we have _some_
2877 * free memory available even if there is no other activity
2878 * that frees anything up. This is needed for things like routing
2879 * etc, where we otherwise might have all activity going on in
2880 * asynchronous contexts that cannot page things out.
2881 *
2882 * If there are applications that are active memory-allocators
2883 * (most normal use), this basically shouldn't matter.
2884 */
2885static int kswapd(void *p)
2886{
2887        unsigned long order, new_order;
2888        unsigned balanced_order;
2889        int classzone_idx, new_classzone_idx;
2890        int balanced_classzone_idx;
2891        pg_data_t *pgdat = (pg_data_t*)p;
2892        struct task_struct *tsk = current;
2893
2894        struct reclaim_state reclaim_state = {
2895                .reclaimed_slab = 0,
2896        };
2897        const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2898
2899        lockdep_set_current_reclaim_state(GFP_KERNEL);
2900
2901        if (!cpumask_empty(cpumask))
2902                set_cpus_allowed_ptr(tsk, cpumask);
2903        current->reclaim_state = &reclaim_state;
2904
2905        /*
2906         * Tell the memory management that we're a "memory allocator",
2907         * and that if we need more memory we should get access to it
2908         * regardless (see "__alloc_pages()"). "kswapd" should
2909         * never get caught in the normal page freeing logic.
2910         *
2911         * (Kswapd normally doesn't need memory anyway, but sometimes
2912         * you need a small amount of memory in order to be able to
2913         * page out something else, and this flag essentially protects
2914         * us from recursively trying to free more memory as we're
2915         * trying to free the first piece of memory in the first place).
2916         */
2917        tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2918        set_freezable();
2919
2920        order = new_order = 0;
2921        balanced_order = 0;
2922        classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
2923        balanced_classzone_idx = classzone_idx;
2924        for ( ; ; ) {
2925                int ret;
2926
2927                /*
2928                 * If the last balance_pgdat was unsuccessful it's unlikely a
2929                 * new request of a similar or harder type will succeed soon
2930                 * so consider going to sleep on the basis we reclaimed at
2931                 */
2932                if (balanced_classzone_idx >= new_classzone_idx &&
2933                                        balanced_order == new_order) {
2934                        new_order = pgdat->kswapd_max_order;
2935                        new_classzone_idx = pgdat->classzone_idx;
2936                        pgdat->kswapd_max_order =  0;
2937                        pgdat->classzone_idx = pgdat->nr_zones - 1;
2938                }
2939
2940                if (order < new_order || classzone_idx > new_classzone_idx) {
2941                        /*
2942                         * Don't sleep if someone wants a larger 'order'
2943                         * allocation or has tigher zone constraints
2944                         */
2945                        order = new_order;
2946                        classzone_idx = new_classzone_idx;
2947                } else {
2948                        kswapd_try_to_sleep(pgdat, balanced_order,
2949                                                balanced_classzone_idx);
2950                        order = pgdat->kswapd_max_order;
2951                        classzone_idx = pgdat->classzone_idx;
2952                        new_order = order;
2953                        new_classzone_idx = classzone_idx;
2954                        pgdat->kswapd_max_order = 0;
2955                        pgdat->classzone_idx = pgdat->nr_zones - 1;
2956                }
2957
2958                ret = try_to_freeze();
2959                if (kthread_should_stop())
2960                        break;
2961
2962                /*
2963                 * We can speed up thawing tasks if we don't call balance_pgdat
2964                 * after returning from the refrigerator
2965                 */
2966                if (!ret) {
2967                        trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
2968                        balanced_classzone_idx = classzone_idx;
2969                        balanced_order = balance_pgdat(pgdat, order,
2970                                                &balanced_classzone_idx);
2971                }
2972        }
2973
2974        current->reclaim_state = NULL;
2975        return 0;
2976}
2977
2978/*
2979 * A zone is low on free memory, so wake its kswapd task to service it.
2980 */
2981void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
2982{
2983        pg_data_t *pgdat;
2984
2985        if (!populated_zone(zone))
2986                return;
2987
2988        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2989                return;
2990        pgdat = zone->zone_pgdat;
2991        if (pgdat->kswapd_max_order < order) {
2992                pgdat->kswapd_max_order = order;
2993                pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
2994        }
2995        if (!waitqueue_active(&pgdat->kswapd_wait))
2996                return;
2997        if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
2998                return;
2999
3000        trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3001        wake_up_interruptible(&pgdat->kswapd_wait);
3002}
3003
3004/*
3005 * The reclaimable count would be mostly accurate.
3006 * The less reclaimable pages may be
3007 * - mlocked pages, which will be moved to unevictable list when encountered
3008 * - mapped pages, which may require several travels to be reclaimed
3009 * - dirty pages, which is not "instantly" reclaimable
3010 */
3011unsigned long global_reclaimable_pages(void)
3012{
3013        int nr;
3014
3015        nr = global_page_state(NR_ACTIVE_FILE) +
3016             global_page_state(NR_INACTIVE_FILE);
3017
3018        if (nr_swap_pages > 0)
3019                nr += global_page_state(NR_ACTIVE_ANON) +
3020                      global_page_state(NR_INACTIVE_ANON);
3021
3022        return nr;
3023}
3024
3025unsigned long zone_reclaimable_pages(struct zone *zone)
3026{
3027        int nr;
3028
3029        nr = zone_page_state(zone, NR_ACTIVE_FILE) +
3030             zone_page_state(zone, NR_INACTIVE_FILE);
3031
3032        if (nr_swap_pages > 0)
3033                nr += zone_page_state(zone, NR_ACTIVE_ANON) +
3034                      zone_page_state(zone, NR_INACTIVE_ANON);
3035
3036        return nr;
3037}
3038
3039#ifdef CONFIG_HIBERNATION
3040/*
3041 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3042 * freed pages.
3043 *
3044 * Rather than trying to age LRUs the aim is to preserve the overall
3045 * LRU order by reclaiming preferentially
3046 * inactive > active > active referenced > active mapped
3047 */
3048unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3049{
3050        struct reclaim_state reclaim_state;
3051        struct scan_control sc = {
3052                .gfp_mask = GFP_HIGHUSER_MOVABLE,
3053                .may_swap = 1,
3054                .may_unmap = 1,
3055                .may_writepage = 1,
3056                .nr_to_reclaim = nr_to_reclaim,
3057                .hibernation_mode = 1,
3058                .order = 0,
3059                .priority = DEF_PRIORITY,
3060        };
3061        struct shrink_control shrink = {
3062                .gfp_mask = sc.gfp_mask,
3063        };
3064        struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3065        struct task_struct *p = current;
3066        unsigned long nr_reclaimed;
3067
3068        p->flags |= PF_MEMALLOC;
3069        lockdep_set_current_reclaim_state(sc.gfp_mask);
3070        reclaim_state.reclaimed_slab = 0;
3071        p->reclaim_state = &reclaim_state;
3072
3073        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
3074
3075        p->reclaim_state = NULL;
3076        lockdep_clear_current_reclaim_state();
3077        p->flags &= ~PF_MEMALLOC;
3078
3079        return nr_reclaimed;
3080}
3081#endif /* CONFIG_HIBERNATION */
3082
3083/* It's optimal to keep kswapds on the same CPUs as their memory, but
3084   not required for correctness.  So if the last cpu in a node goes
3085   away, we get changed to run anywhere: as the first one comes back,
3086   restore their cpu bindings. */
3087static int __devinit cpu_callback(struct notifier_block *nfb,
3088                                  unsigned long action, void *hcpu)
3089{
3090        int nid;
3091
3092        if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
3093                for_each_node_state(nid, N_HIGH_MEMORY) {
3094                        pg_data_t *pgdat = NODE_DATA(nid);
3095                        const struct cpumask *mask;
3096
3097                        mask = cpumask_of_node(pgdat->node_id);
3098
3099                        if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3100                                /* One of our CPUs online: restore mask */
3101                                set_cpus_allowed_ptr(pgdat->kswapd, mask);
3102                }
3103        }
3104        return NOTIFY_OK;
3105}
3106
3107/*
3108 * This kswapd start function will be called by init and node-hot-add.
3109 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3110 */
3111int kswapd_run(int nid)
3112{
3113        pg_data_t *pgdat = NODE_DATA(nid);
3114        int ret = 0;
3115
3116        if (pgdat->kswapd)
3117                return 0;
3118
3119        pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3120        if (IS_ERR(pgdat->kswapd)) {
3121                /* failure at boot is fatal */
3122                BUG_ON(system_state == SYSTEM_BOOTING);
3123                printk("Failed to start kswapd on node %d\n",nid);
3124                pgdat->kswapd = NULL;
3125                ret = -1;
3126        }
3127        return ret;
3128}
3129
3130/*
3131 * Called by memory hotplug when all memory in a node is offlined.  Caller must
3132 * hold lock_memory_hotplug().
3133 */
3134void kswapd_stop(int nid)
3135{
3136        struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3137
3138        if (kswapd) {
3139                kthread_stop(kswapd);
3140                NODE_DATA(nid)->kswapd = NULL;
3141        }
3142}
3143
3144static int __init kswapd_init(void)
3145{
3146        int nid;
3147
3148        swap_setup();
3149        for_each_node_state(nid, N_HIGH_MEMORY)
3150                kswapd_run(nid);
3151        hotcpu_notifier(cpu_callback, 0);
3152        return 0;
3153}
3154
3155module_init(kswapd_init)
3156
3157#ifdef CONFIG_NUMA
3158/*
3159 * Zone reclaim mode
3160 *
3161 * If non-zero call zone_reclaim when the number of free pages falls below
3162 * the watermarks.
3163 */
3164int zone_reclaim_mode __read_mostly;
3165
3166#define RECLAIM_OFF 0
3167#define RECLAIM_ZONE (1<<0)     /* Run shrink_inactive_list on the zone */
3168#define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
3169#define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
3170
3171/*
3172 * Priority for ZONE_RECLAIM. This determines the fraction of pages
3173 * of a node considered for each zone_reclaim. 4 scans 1/16th of
3174 * a zone.
3175 */
3176#define ZONE_RECLAIM_PRIORITY 4
3177
3178/*
3179 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
3180 * occur.
3181 */
3182int sysctl_min_unmapped_ratio = 1;
3183
3184/*
3185 * If the number of slab pages in a zone grows beyond this percentage then
3186 * slab reclaim needs to occur.
3187 */
3188int sysctl_min_slab_ratio = 5;
3189
3190static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3191{
3192        unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3193        unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3194                zone_page_state(zone, NR_ACTIVE_FILE);
3195
3196        /*
3197         * It's possible for there to be more file mapped pages than
3198         * accounted for by the pages on the file LRU lists because
3199         * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3200         */
3201        return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3202}
3203
3204/* Work out how many page cache pages we can reclaim in this reclaim_mode */
3205static long zone_pagecache_reclaimable(struct zone *zone)
3206{
3207        long nr_pagecache_reclaimable;
3208        long delta = 0;
3209
3210        /*
3211         * If RECLAIM_SWAP is set, then all file pages are considered
3212         * potentially reclaimable. Otherwise, we have to worry about
3213         * pages like swapcache and zone_unmapped_file_pages() provides
3214         * a better estimate
3215         */
3216        if (zone_reclaim_mode & RECLAIM_SWAP)
3217                nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3218        else
3219                nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3220
3221        /* If we can't clean pages, remove dirty pages from consideration */
3222        if (!(zone_reclaim_mode & RECLAIM_WRITE))
3223                delta += zone_page_state(zone, NR_FILE_DIRTY);
3224
3225        /* Watch for any possible underflows due to delta */
3226        if (unlikely(delta > nr_pagecache_reclaimable))
3227                delta = nr_pagecache_reclaimable;
3228
3229        return nr_pagecache_reclaimable - delta;
3230}
3231
3232/*
3233 * Try to free up some pages from this zone through reclaim.
3234 */
3235static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3236{
3237        /* Minimum pages needed in order to stay on node */
3238        const unsigned long nr_pages = 1 << order;
3239        struct task_struct *p = current;
3240        struct reclaim_state reclaim_state;
3241        struct scan_control sc = {
3242                .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3243                .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3244                .may_swap = 1,
3245                .nr_to_reclaim = max_t(unsigned long, nr_pages,
3246                                       SWAP_CLUSTER_MAX),
3247                .gfp_mask = gfp_mask,
3248                .order = order,
3249                .priority = ZONE_RECLAIM_PRIORITY,
3250        };
3251        struct shrink_control shrink = {
3252                .gfp_mask = sc.gfp_mask,
3253        };
3254        unsigned long nr_slab_pages0, nr_slab_pages1;
3255
3256        cond_resched();
3257        /*
3258         * We need to be able to allocate from the reserves for RECLAIM_SWAP
3259         * and we also need to be able to write out pages for RECLAIM_WRITE
3260         * and RECLAIM_SWAP.
3261         */
3262        p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3263        lockdep_set_current_reclaim_state(gfp_mask);
3264        reclaim_state.reclaimed_slab = 0;
3265        p->reclaim_state = &reclaim_state;
3266
3267        if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3268                /*
3269                 * Free memory by calling shrink zone with increasing
3270                 * priorities until we have enough memory freed.
3271                 */
3272                do {
3273                        shrink_zone(zone, &sc);
3274                } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3275        }
3276
3277        nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3278        if (nr_slab_pages0 > zone->min_slab_pages) {
3279                /*
3280                 * shrink_slab() does not currently allow us to determine how
3281                 * many pages were freed in this zone. So we take the current
3282                 * number of slab pages and shake the slab until it is reduced
3283                 * by the same nr_pages that we used for reclaiming unmapped
3284                 * pages.
3285                 *
3286                 * Note that shrink_slab will free memory on all zones and may
3287                 * take a long time.
3288                 */
3289                for (;;) {
3290                        unsigned long lru_pages = zone_reclaimable_pages(zone);
3291
3292                        /* No reclaimable slab or very low memory pressure */
3293                        if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3294                                break;
3295
3296                        /* Freed enough memory */
3297                        nr_slab_pages1 = zone_page_state(zone,
3298                                                        NR_SLAB_RECLAIMABLE);
3299                        if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3300                                break;
3301                }
3302
3303                /*
3304                 * Update nr_reclaimed by the number of slab pages we
3305                 * reclaimed from this zone.
3306                 */
3307                nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3308                if (nr_slab_pages1 < nr_slab_pages0)
3309                        sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3310        }
3311
3312        p->reclaim_state = NULL;
3313        current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3314        lockdep_clear_current_reclaim_state();
3315        return sc.nr_reclaimed >= nr_pages;
3316}
3317
3318int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3319{
3320        int node_id;
3321        int ret;
3322
3323        /*
3324         * Zone reclaim reclaims unmapped file backed pages and
3325         * slab pages if we are over the defined limits.
3326         *
3327         * A small portion of unmapped file backed pages is needed for
3328         * file I/O otherwise pages read by file I/O will be immediately
3329         * thrown out if the zone is overallocated. So we do not reclaim
3330         * if less than a specified percentage of the zone is used by
3331         * unmapped file backed pages.
3332         */
3333        if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3334            zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3335                return ZONE_RECLAIM_FULL;
3336
3337        if (zone->all_unreclaimable)
3338                return ZONE_RECLAIM_FULL;
3339
3340        /*
3341         * Do not scan if the allocation should not be delayed.
3342         */
3343        if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3344                return ZONE_RECLAIM_NOSCAN;
3345
3346        /*
3347         * Only run zone reclaim on the local zone or on zones that do not
3348         * have associated processors. This will favor the local processor
3349         * over remote processors and spread off node memory allocations
3350         * as wide as possible.
3351         */
3352        node_id = zone_to_nid(zone);
3353        if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3354                return ZONE_RECLAIM_NOSCAN;
3355
3356        if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3357                return ZONE_RECLAIM_NOSCAN;
3358
3359        ret = __zone_reclaim(zone, gfp_mask, order);
3360        zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3361
3362        if (!ret)
3363                count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3364
3365        return ret;
3366}
3367#endif
3368
3369/*
3370 * page_evictable - test whether a page is evictable
3371 * @page: the page to test
3372 * @vma: the VMA in which the page is or will be mapped, may be NULL
3373 *
3374 * Test whether page is evictable--i.e., should be placed on active/inactive
3375 * lists vs unevictable list.  The vma argument is !NULL when called from the
3376 * fault path to determine how to instantate a new page.
3377 *
3378 * Reasons page might not be evictable:
3379 * (1) page's mapping marked unevictable
3380 * (2) page is part of an mlocked VMA
3381 *
3382 */
3383int page_evictable(struct page *page, struct vm_area_struct *vma)
3384{
3385
3386        if (mapping_unevictable(page_mapping(page)))
3387                return 0;
3388
3389        if (PageMlocked(page) || (vma && mlocked_vma_newpage(vma, page)))
3390                return 0;
3391
3392        return 1;
3393}
3394
3395#ifdef CONFIG_SHMEM
3396/**
3397 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3398 * @pages:      array of pages to check
3399 * @nr_pages:   number of pages to check
3400 *
3401 * Checks pages for evictability and moves them to the appropriate lru list.
3402 *
3403 * This function is only used for SysV IPC SHM_UNLOCK.
3404 */
3405void check_move_unevictable_pages(struct page **pages, int nr_pages)
3406{
3407        struct lruvec *lruvec;
3408        struct zone *zone = NULL;
3409        int pgscanned = 0;
3410        int pgrescued = 0;
3411        int i;
3412
3413        for (i = 0; i < nr_pages; i++) {
3414                struct page *page = pages[i];
3415                struct zone *pagezone;
3416
3417                pgscanned++;
3418                pagezone = page_zone(page);
3419                if (pagezone != zone) {
3420                        if (zone)
3421                                spin_unlock_irq(&zone->lru_lock);
3422                        zone = pagezone;
3423                        spin_lock_irq(&zone->lru_lock);
3424                }
3425                lruvec = mem_cgroup_page_lruvec(page, zone);
3426
3427                if (!PageLRU(page) || !PageUnevictable(page))
3428                        continue;
3429
3430                if (page_evictable(page, NULL)) {
3431                        enum lru_list lru = page_lru_base_type(page);
3432
3433                        VM_BUG_ON(PageActive(page));
3434                        ClearPageUnevictable(page);
3435                        del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3436                        add_page_to_lru_list(page, lruvec, lru);
3437                        pgrescued++;
3438                }
3439        }
3440
3441        if (zone) {
3442                __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3443                __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3444                spin_unlock_irq(&zone->lru_lock);
3445        }
3446}
3447#endif /* CONFIG_SHMEM */
3448
3449static void warn_scan_unevictable_pages(void)
3450{
3451        printk_once(KERN_WARNING
3452                    "%s: The scan_unevictable_pages sysctl/node-interface has been "
3453                    "disabled for lack of a legitimate use case.  If you have "
3454                    "one, please send an email to linux-mm@kvack.org.\n",
3455                    current->comm);
3456}
3457
3458/*
3459 * scan_unevictable_pages [vm] sysctl handler.  On demand re-scan of
3460 * all nodes' unevictable lists for evictable pages
3461 */
3462unsigned long scan_unevictable_pages;
3463
3464int scan_unevictable_handler(struct ctl_table *table, int write,
3465                           void __user *buffer,
3466                           size_t *length, loff_t *ppos)
3467{
3468        warn_scan_unevictable_pages();
3469        proc_doulongvec_minmax(table, write, buffer, length, ppos);
3470        scan_unevictable_pages = 0;
3471        return 0;
3472}
3473
3474#ifdef CONFIG_NUMA
3475/*
3476 * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
3477 * a specified node's per zone unevictable lists for evictable pages.
3478 */
3479
3480static ssize_t read_scan_unevictable_node(struct device *dev,
3481                                          struct device_attribute *attr,
3482                                          char *buf)
3483{
3484        warn_scan_unevictable_pages();
3485        return sprintf(buf, "0\n");     /* always zero; should fit... */
3486}
3487
3488static ssize_t write_scan_unevictable_node(struct device *dev,
3489                                           struct device_attribute *attr,
3490                                        const char *buf, size_t count)
3491{
3492        warn_scan_unevictable_pages();
3493        return 1;
3494}
3495
3496
3497static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3498                        read_scan_unevictable_node,
3499                        write_scan_unevictable_node);
3500
3501int scan_unevictable_register_node(struct node *node)
3502{
3503        return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages);
3504}
3505
3506void scan_unevictable_unregister_node(struct node *node)
3507{
3508        device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages);
3509}
3510#endif
3511
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