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;
 131unsigned long 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)) {
 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)) {
 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                                      enum ttu_flags ttu_flags,
 678                                      unsigned long *ret_nr_dirty,
 679                                      unsigned long *ret_nr_writeback,
 680                                      bool force_reclaim)
 681{
 682        LIST_HEAD(ret_pages);
 683        LIST_HEAD(free_pages);
 684        int pgactivate = 0;
 685        unsigned long nr_dirty = 0;
 686        unsigned long nr_congested = 0;
 687        unsigned long nr_reclaimed = 0;
 688        unsigned long nr_writeback = 0;
 689
 690        cond_resched();
 691
 692        mem_cgroup_uncharge_start();
 693        while (!list_empty(page_list)) {
 694                struct address_space *mapping;
 695                struct page *page;
 696                int may_enter_fs;
 697                enum page_references references = PAGEREF_RECLAIM_CLEAN;
 698
 699                cond_resched();
 700
 701                page = lru_to_page(page_list);
 702                list_del(&page->lru);
 703
 704                if (!trylock_page(page))
 705                        goto keep;
 706
 707                VM_BUG_ON(PageActive(page));
 708                VM_BUG_ON(page_zone(page) != zone);
 709
 710                sc->nr_scanned++;
 711
 712                if (unlikely(!page_evictable(page)))
 713                        goto cull_mlocked;
 714
 715                if (!sc->may_unmap && page_mapped(page))
 716                        goto keep_locked;
 717
 718                /* Double the slab pressure for mapped and swapcache pages */
 719                if (page_mapped(page) || PageSwapCache(page))
 720                        sc->nr_scanned++;
 721
 722                may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
 723                        (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 724
 725                if (PageWriteback(page)) {
 726                        /*
 727                         * memcg doesn't have any dirty pages throttling so we
 728                         * could easily OOM just because too many pages are in
 729                         * writeback and there is nothing else to reclaim.
 730                         *
 731                         * Check __GFP_IO, certainly because a loop driver
 732                         * thread might enter reclaim, and deadlock if it waits
 733                         * on a page for which it is needed to do the write
 734                         * (loop masks off __GFP_IO|__GFP_FS for this reason);
 735                         * but more thought would probably show more reasons.
 736                         *
 737                         * Don't require __GFP_FS, since we're not going into
 738                         * the FS, just waiting on its writeback completion.
 739                         * Worryingly, ext4 gfs2 and xfs allocate pages with
 740                         * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so
 741                         * testing may_enter_fs here is liable to OOM on them.
 742                         */
 743                        if (global_reclaim(sc) ||
 744                            !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) {
 745                                /*
 746                                 * This is slightly racy - end_page_writeback()
 747                                 * might have just cleared PageReclaim, then
 748                                 * setting PageReclaim here end up interpreted
 749                                 * as PageReadahead - but that does not matter
 750                                 * enough to care.  What we do want is for this
 751                                 * page to have PageReclaim set next time memcg
 752                                 * reclaim reaches the tests above, so it will
 753                                 * then wait_on_page_writeback() to avoid OOM;
 754                                 * and it's also appropriate in global reclaim.
 755                                 */
 756                                SetPageReclaim(page);
 757                                nr_writeback++;
 758                                goto keep_locked;
 759                        }
 760                        wait_on_page_writeback(page);
 761                }
 762
 763                if (!force_reclaim)
 764                        references = page_check_references(page, sc);
 765
 766                switch (references) {
 767                case PAGEREF_ACTIVATE:
 768                        goto activate_locked;
 769                case PAGEREF_KEEP:
 770                        goto keep_locked;
 771                case PAGEREF_RECLAIM:
 772                case PAGEREF_RECLAIM_CLEAN:
 773                        ; /* try to reclaim the page below */
 774                }
 775
 776                /*
 777                 * Anonymous process memory has backing store?
 778                 * Try to allocate it some swap space here.
 779                 */
 780                if (PageAnon(page) && !PageSwapCache(page)) {
 781                        if (!(sc->gfp_mask & __GFP_IO))
 782                                goto keep_locked;
 783                        if (!add_to_swap(page))
 784                                goto activate_locked;
 785                        may_enter_fs = 1;
 786                }
 787
 788                mapping = page_mapping(page);
 789
 790                /*
 791                 * The page is mapped into the page tables of one or more
 792                 * processes. Try to unmap it here.
 793                 */
 794                if (page_mapped(page) && mapping) {
 795                        switch (try_to_unmap(page, ttu_flags)) {
 796                        case SWAP_FAIL:
 797                                goto activate_locked;
 798                        case SWAP_AGAIN:
 799                                goto keep_locked;
 800                        case SWAP_MLOCK:
 801                                goto cull_mlocked;
 802                        case SWAP_SUCCESS:
 803                                ; /* try to free the page below */
 804                        }
 805                }
 806
 807                if (PageDirty(page)) {
 808                        nr_dirty++;
 809
 810                        /*
 811                         * Only kswapd can writeback filesystem pages to
 812                         * avoid risk of stack overflow but do not writeback
 813                         * unless under significant pressure.
 814                         */
 815                        if (page_is_file_cache(page) &&
 816                                        (!current_is_kswapd() ||
 817                                         sc->priority >= DEF_PRIORITY - 2)) {
 818                                /*
 819                                 * Immediately reclaim when written back.
 820                                 * Similar in principal to deactivate_page()
 821                                 * except we already have the page isolated
 822                                 * and know it's dirty
 823                                 */
 824                                inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE);
 825                                SetPageReclaim(page);
 826
 827                                goto keep_locked;
 828                        }
 829
 830                        if (references == PAGEREF_RECLAIM_CLEAN)
 831                                goto keep_locked;
 832                        if (!may_enter_fs)
 833                                goto keep_locked;
 834                        if (!sc->may_writepage)
 835                                goto keep_locked;
 836
 837                        /* Page is dirty, try to write it out here */
 838                        switch (pageout(page, mapping, sc)) {
 839                        case PAGE_KEEP:
 840                                nr_congested++;
 841                                goto keep_locked;
 842                        case PAGE_ACTIVATE:
 843                                goto activate_locked;
 844                        case PAGE_SUCCESS:
 845                                if (PageWriteback(page))
 846                                        goto keep;
 847                                if (PageDirty(page))
 848                                        goto keep;
 849
 850                                /*
 851                                 * A synchronous write - probably a ramdisk.  Go
 852                                 * ahead and try to reclaim the page.
 853                                 */
 854                                if (!trylock_page(page))
 855                                        goto keep;
 856                                if (PageDirty(page) || PageWriteback(page))
 857                                        goto keep_locked;
 858                                mapping = page_mapping(page);
 859                        case PAGE_CLEAN:
 860                                ; /* try to free the page below */
 861                        }
 862                }
 863
 864                /*
 865                 * If the page has buffers, try to free the buffer mappings
 866                 * associated with this page. If we succeed we try to free
 867                 * the page as well.
 868                 *
 869                 * We do this even if the page is PageDirty().
 870                 * try_to_release_page() does not perform I/O, but it is
 871                 * possible for a page to have PageDirty set, but it is actually
 872                 * clean (all its buffers are clean).  This happens if the
 873                 * buffers were written out directly, with submit_bh(). ext3
 874                 * will do this, as well as the blockdev mapping.
 875                 * try_to_release_page() will discover that cleanness and will
 876                 * drop the buffers and mark the page clean - it can be freed.
 877                 *
 878                 * Rarely, pages can have buffers and no ->mapping.  These are
 879                 * the pages which were not successfully invalidated in
 880                 * truncate_complete_page().  We try to drop those buffers here
 881                 * and if that worked, and the page is no longer mapped into
 882                 * process address space (page_count == 1) it can be freed.
 883                 * Otherwise, leave the page on the LRU so it is swappable.
 884                 */
 885                if (page_has_private(page)) {
 886                        if (!try_to_release_page(page, sc->gfp_mask))
 887                                goto activate_locked;
 888                        if (!mapping && page_count(page) == 1) {
 889                                unlock_page(page);
 890                                if (put_page_testzero(page))
 891                                        goto free_it;
 892                                else {
 893                                        /*
 894                                         * rare race with speculative reference.
 895                                         * the speculative reference will free
 896                                         * this page shortly, so we may
 897                                         * increment nr_reclaimed here (and
 898                                         * leave it off the LRU).
 899                                         */
 900                                        nr_reclaimed++;
 901                                        continue;
 902                                }
 903                        }
 904                }
 905
 906                if (!mapping || !__remove_mapping(mapping, page))
 907                        goto keep_locked;
 908
 909                /*
 910                 * At this point, we have no other references and there is
 911                 * no way to pick any more up (removed from LRU, removed
 912                 * from pagecache). Can use non-atomic bitops now (and
 913                 * we obviously don't have to worry about waking up a process
 914                 * waiting on the page lock, because there are no references.
 915                 */
 916                __clear_page_locked(page);
 917free_it:
 918                nr_reclaimed++;
 919
 920                /*
 921                 * Is there need to periodically free_page_list? It would
 922                 * appear not as the counts should be low
 923                 */
 924                list_add(&page->lru, &free_pages);
 925                continue;
 926
 927cull_mlocked:
 928                if (PageSwapCache(page))
 929                        try_to_free_swap(page);
 930                unlock_page(page);
 931                putback_lru_page(page);
 932                continue;
 933
 934activate_locked:
 935                /* Not a candidate for swapping, so reclaim swap space. */
 936                if (PageSwapCache(page) && vm_swap_full())
 937                        try_to_free_swap(page);
 938                VM_BUG_ON(PageActive(page));
 939                SetPageActive(page);
 940                pgactivate++;
 941keep_locked:
 942                unlock_page(page);
 943keep:
 944                list_add(&page->lru, &ret_pages);
 945                VM_BUG_ON(PageLRU(page) || PageUnevictable(page));
 946        }
 947
 948        /*
 949         * Tag a zone as congested if all the dirty pages encountered were
 950         * backed by a congested BDI. In this case, reclaimers should just
 951         * back off and wait for congestion to clear because further reclaim
 952         * will encounter the same problem
 953         */
 954        if (nr_dirty && nr_dirty == nr_congested && global_reclaim(sc))
 955                zone_set_flag(zone, ZONE_CONGESTED);
 956
 957        free_hot_cold_page_list(&free_pages, 1);
 958
 959        list_splice(&ret_pages, page_list);
 960        count_vm_events(PGACTIVATE, pgactivate);
 961        mem_cgroup_uncharge_end();
 962        *ret_nr_dirty += nr_dirty;
 963        *ret_nr_writeback += nr_writeback;
 964        return nr_reclaimed;
 965}
 966
 967unsigned long reclaim_clean_pages_from_list(struct zone *zone,
 968                                            struct list_head *page_list)
 969{
 970        struct scan_control sc = {
 971                .gfp_mask = GFP_KERNEL,
 972                .priority = DEF_PRIORITY,
 973                .may_unmap = 1,
 974        };
 975        unsigned long ret, dummy1, dummy2;
 976        struct page *page, *next;
 977        LIST_HEAD(clean_pages);
 978
 979        list_for_each_entry_safe(page, next, page_list, lru) {
 980                if (page_is_file_cache(page) && !PageDirty(page)) {
 981                        ClearPageActive(page);
 982                        list_move(&page->lru, &clean_pages);
 983                }
 984        }
 985
 986        ret = shrink_page_list(&clean_pages, zone, &sc,
 987                                TTU_UNMAP|TTU_IGNORE_ACCESS,
 988                                &dummy1, &dummy2, true);
 989        list_splice(&clean_pages, page_list);
 990        __mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret);
 991        return ret;
 992}
 993
 994/*
 995 * Attempt to remove the specified page from its LRU.  Only take this page
 996 * if it is of the appropriate PageActive status.  Pages which are being
 997 * freed elsewhere are also ignored.
 998 *
 999 * page:        page to consider
1000 * mode:        one of the LRU isolation modes defined above
1001 *
1002 * returns 0 on success, -ve errno on failure.
1003 */
1004int __isolate_lru_page(struct page *page, isolate_mode_t mode)
1005{
1006        int ret = -EINVAL;
1007
1008        /* Only take pages on the LRU. */
1009        if (!PageLRU(page))
1010                return ret;
1011
1012        /* Compaction should not handle unevictable pages but CMA can do so */
1013        if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE))
1014                return ret;
1015
1016        ret = -EBUSY;
1017
1018        /*
1019         * To minimise LRU disruption, the caller can indicate that it only
1020         * wants to isolate pages it will be able to operate on without
1021         * blocking - clean pages for the most part.
1022         *
1023         * ISOLATE_CLEAN means that only clean pages should be isolated. This
1024         * is used by reclaim when it is cannot write to backing storage
1025         *
1026         * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
1027         * that it is possible to migrate without blocking
1028         */
1029        if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
1030                /* All the caller can do on PageWriteback is block */
1031                if (PageWriteback(page))
1032                        return ret;
1033
1034                if (PageDirty(page)) {
1035                        struct address_space *mapping;
1036
1037                        /* ISOLATE_CLEAN means only clean pages */
1038                        if (mode & ISOLATE_CLEAN)
1039                                return ret;
1040
1041                        /*
1042                         * Only pages without mappings or that have a
1043                         * ->migratepage callback are possible to migrate
1044                         * without blocking
1045                         */
1046                        mapping = page_mapping(page);
1047                        if (mapping && !mapping->a_ops->migratepage)
1048                                return ret;
1049                }
1050        }
1051
1052        if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
1053                return ret;
1054
1055        if (likely(get_page_unless_zero(page))) {
1056                /*
1057                 * Be careful not to clear PageLRU until after we're
1058                 * sure the page is not being freed elsewhere -- the
1059                 * page release code relies on it.
1060                 */
1061                ClearPageLRU(page);
1062                ret = 0;
1063        }
1064
1065        return ret;
1066}
1067
1068/*
1069 * zone->lru_lock is heavily contended.  Some of the functions that
1070 * shrink the lists perform better by taking out a batch of pages
1071 * and working on them outside the LRU lock.
1072 *
1073 * For pagecache intensive workloads, this function is the hottest
1074 * spot in the kernel (apart from copy_*_user functions).
1075 *
1076 * Appropriate locks must be held before calling this function.
1077 *
1078 * @nr_to_scan: The number of pages to look through on the list.
1079 * @lruvec:     The LRU vector to pull pages from.
1080 * @dst:        The temp list to put pages on to.
1081 * @nr_scanned: The number of pages that were scanned.
1082 * @sc:         The scan_control struct for this reclaim session
1083 * @mode:       One of the LRU isolation modes
1084 * @lru:        LRU list id for isolating
1085 *
1086 * returns how many pages were moved onto *@dst.
1087 */
1088static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
1089                struct lruvec *lruvec, struct list_head *dst,
1090                unsigned long *nr_scanned, struct scan_control *sc,
1091                isolate_mode_t mode, enum lru_list lru)
1092{
1093        struct list_head *src = &lruvec->lists[lru];
1094        unsigned long nr_taken = 0;
1095        unsigned long scan;
1096
1097        for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
1098                struct page *page;
1099                int nr_pages;
1100
1101                page = lru_to_page(src);
1102                prefetchw_prev_lru_page(page, src, flags);
1103
1104                VM_BUG_ON(!PageLRU(page));
1105
1106                switch (__isolate_lru_page(page, mode)) {
1107                case 0:
1108                        nr_pages = hpage_nr_pages(page);
1109                        mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
1110                        list_move(&page->lru, dst);
1111                        nr_taken += nr_pages;
1112                        break;
1113
1114                case -EBUSY:
1115                        /* else it is being freed elsewhere */
1116                        list_move(&page->lru, src);
1117                        continue;
1118
1119                default:
1120                        BUG();
1121                }
1122        }
1123
1124        *nr_scanned = scan;
1125        trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
1126                                    nr_taken, mode, is_file_lru(lru));
1127        return nr_taken;
1128}
1129
1130/**
1131 * isolate_lru_page - tries to isolate a page from its LRU list
1132 * @page: page to isolate from its LRU list
1133 *
1134 * Isolates a @page from an LRU list, clears PageLRU and adjusts the
1135 * vmstat statistic corresponding to whatever LRU list the page was on.
1136 *
1137 * Returns 0 if the page was removed from an LRU list.
1138 * Returns -EBUSY if the page was not on an LRU list.
1139 *
1140 * The returned page will have PageLRU() cleared.  If it was found on
1141 * the active list, it will have PageActive set.  If it was found on
1142 * the unevictable list, it will have the PageUnevictable bit set. That flag
1143 * may need to be cleared by the caller before letting the page go.
1144 *
1145 * The vmstat statistic corresponding to the list on which the page was
1146 * found will be decremented.
1147 *
1148 * Restrictions:
1149 * (1) Must be called with an elevated refcount on the page. This is a
1150 *     fundamentnal difference from isolate_lru_pages (which is called
1151 *     without a stable reference).
1152 * (2) the lru_lock must not be held.
1153 * (3) interrupts must be enabled.
1154 */
1155int isolate_lru_page(struct page *page)
1156{
1157        int ret = -EBUSY;
1158
1159        VM_BUG_ON(!page_count(page));
1160
1161        if (PageLRU(page)) {
1162                struct zone *zone = page_zone(page);
1163                struct lruvec *lruvec;
1164
1165                spin_lock_irq(&zone->lru_lock);
1166                lruvec = mem_cgroup_page_lruvec(page, zone);
1167                if (PageLRU(page)) {
1168                        int lru = page_lru(page);
1169                        get_page(page);
1170                        ClearPageLRU(page);
1171                        del_page_from_lru_list(page, lruvec, lru);
1172                        ret = 0;
1173                }
1174                spin_unlock_irq(&zone->lru_lock);
1175        }
1176        return ret;
1177}
1178
1179/*
1180 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and
1181 * then get resheduled. When there are massive number of tasks doing page
1182 * allocation, such sleeping direct reclaimers may keep piling up on each CPU,
1183 * the LRU list will go small and be scanned faster than necessary, leading to
1184 * unnecessary swapping, thrashing and OOM.
1185 */
1186static int too_many_isolated(struct zone *zone, int file,
1187                struct scan_control *sc)
1188{
1189        unsigned long inactive, isolated;
1190
1191        if (current_is_kswapd())
1192                return 0;
1193
1194        if (!global_reclaim(sc))
1195                return 0;
1196
1197        if (file) {
1198                inactive = zone_page_state(zone, NR_INACTIVE_FILE);
1199                isolated = zone_page_state(zone, NR_ISOLATED_FILE);
1200        } else {
1201                inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1202                isolated = zone_page_state(zone, NR_ISOLATED_ANON);
1203        }
1204
1205        /*
1206         * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they
1207         * won't get blocked by normal direct-reclaimers, forming a circular
1208         * deadlock.
1209         */
1210        if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS)
1211                inactive >>= 3;
1212
1213        return isolated > inactive;
1214}
1215
1216static noinline_for_stack void
1217putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list)
1218{
1219        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1220        struct zone *zone = lruvec_zone(lruvec);
1221        LIST_HEAD(pages_to_free);
1222
1223        /*
1224         * Put back any unfreeable pages.
1225         */
1226        while (!list_empty(page_list)) {
1227                struct page *page = lru_to_page(page_list);
1228                int lru;
1229
1230                VM_BUG_ON(PageLRU(page));
1231                list_del(&page->lru);
1232                if (unlikely(!page_evictable(page))) {
1233                        spin_unlock_irq(&zone->lru_lock);
1234                        putback_lru_page(page);
1235                        spin_lock_irq(&zone->lru_lock);
1236                        continue;
1237                }
1238
1239                lruvec = mem_cgroup_page_lruvec(page, zone);
1240
1241                SetPageLRU(page);
1242                lru = page_lru(page);
1243                add_page_to_lru_list(page, lruvec, lru);
1244
1245                if (is_active_lru(lru)) {
1246                        int file = is_file_lru(lru);
1247                        int numpages = hpage_nr_pages(page);
1248                        reclaim_stat->recent_rotated[file] += numpages;
1249                }
1250                if (put_page_testzero(page)) {
1251                        __ClearPageLRU(page);
1252                        __ClearPageActive(page);
1253                        del_page_from_lru_list(page, lruvec, lru);
1254
1255                        if (unlikely(PageCompound(page))) {
1256                                spin_unlock_irq(&zone->lru_lock);
1257                                (*get_compound_page_dtor(page))(page);
1258                                spin_lock_irq(&zone->lru_lock);
1259                        } else
1260                                list_add(&page->lru, &pages_to_free);
1261                }
1262        }
1263
1264        /*
1265         * To save our caller's stack, now use input list for pages to free.
1266         */
1267        list_splice(&pages_to_free, page_list);
1268}
1269
1270/*
1271 * shrink_inactive_list() is a helper for shrink_zone().  It returns the number
1272 * of reclaimed pages
1273 */
1274static noinline_for_stack unsigned long
1275shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
1276                     struct scan_control *sc, enum lru_list lru)
1277{
1278        LIST_HEAD(page_list);
1279        unsigned long nr_scanned;
1280        unsigned long nr_reclaimed = 0;
1281        unsigned long nr_taken;
1282        unsigned long nr_dirty = 0;
1283        unsigned long nr_writeback = 0;
1284        isolate_mode_t isolate_mode = 0;
1285        int file = is_file_lru(lru);
1286        struct zone *zone = lruvec_zone(lruvec);
1287        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1288
1289        while (unlikely(too_many_isolated(zone, file, sc))) {
1290                congestion_wait(BLK_RW_ASYNC, HZ/10);
1291
1292                /* We are about to die and free our memory. Return now. */
1293                if (fatal_signal_pending(current))
1294                        return SWAP_CLUSTER_MAX;
1295        }
1296
1297        lru_add_drain();
1298
1299        if (!sc->may_unmap)
1300                isolate_mode |= ISOLATE_UNMAPPED;
1301        if (!sc->may_writepage)
1302                isolate_mode |= ISOLATE_CLEAN;
1303
1304        spin_lock_irq(&zone->lru_lock);
1305
1306        nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list,
1307                                     &nr_scanned, sc, isolate_mode, lru);
1308
1309        __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1310        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1311
1312        if (global_reclaim(sc)) {
1313                zone->pages_scanned += nr_scanned;
1314                if (current_is_kswapd())
1315                        __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);
1316                else
1317                        __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned);
1318        }
1319        spin_unlock_irq(&zone->lru_lock);
1320
1321        if (nr_taken == 0)
1322                return 0;
1323
1324        nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP,
1325                                        &nr_dirty, &nr_writeback, false);
1326
1327        spin_lock_irq(&zone->lru_lock);
1328
1329        reclaim_stat->recent_scanned[file] += nr_taken;
1330
1331        if (global_reclaim(sc)) {
1332                if (current_is_kswapd())
1333                        __count_zone_vm_events(PGSTEAL_KSWAPD, zone,
1334                                               nr_reclaimed);
1335                else
1336                        __count_zone_vm_events(PGSTEAL_DIRECT, zone,
1337                                               nr_reclaimed);
1338        }
1339
1340        putback_inactive_pages(lruvec, &page_list);
1341
1342        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1343
1344        spin_unlock_irq(&zone->lru_lock);
1345
1346        free_hot_cold_page_list(&page_list, 1);
1347
1348        /*
1349         * If reclaim is isolating dirty pages under writeback, it implies
1350         * that the long-lived page allocation rate is exceeding the page
1351         * laundering rate. Either the global limits are not being effective
1352         * at throttling processes due to the page distribution throughout
1353         * zones or there is heavy usage of a slow backing device. The
1354         * only option is to throttle from reclaim context which is not ideal
1355         * as there is no guarantee the dirtying process is throttled in the
1356         * same way balance_dirty_pages() manages.
1357         *
1358         * This scales the number of dirty pages that must be under writeback
1359         * before throttling depending on priority. It is a simple backoff
1360         * function that has the most effect in the range DEF_PRIORITY to
1361         * DEF_PRIORITY-2 which is the priority reclaim is considered to be
1362         * in trouble and reclaim is considered to be in trouble.
1363         *
1364         * DEF_PRIORITY   100% isolated pages must be PageWriteback to throttle
1365         * DEF_PRIORITY-1  50% must be PageWriteback
1366         * DEF_PRIORITY-2  25% must be PageWriteback, kswapd in trouble
1367         * ...
1368         * DEF_PRIORITY-6 For SWAP_CLUSTER_MAX isolated pages, throttle if any
1369         *                     isolated page is PageWriteback
1370         */
1371        if (nr_writeback && nr_writeback >=
1372                        (nr_taken >> (DEF_PRIORITY - sc->priority)))
1373                wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
1374
1375        trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id,
1376                zone_idx(zone),
1377                nr_scanned, nr_reclaimed,
1378                sc->priority,
1379                trace_shrink_flags(file));
1380        return nr_reclaimed;
1381}
1382
1383/*
1384 * This moves pages from the active list to the inactive list.
1385 *
1386 * We move them the other way if the page is referenced by one or more
1387 * processes, from rmap.
1388 *
1389 * If the pages are mostly unmapped, the processing is fast and it is
1390 * appropriate to hold zone->lru_lock across the whole operation.  But if
1391 * the pages are mapped, the processing is slow (page_referenced()) so we
1392 * should drop zone->lru_lock around each page.  It's impossible to balance
1393 * this, so instead we remove the pages from the LRU while processing them.
1394 * It is safe to rely on PG_active against the non-LRU pages in here because
1395 * nobody will play with that bit on a non-LRU page.
1396 *
1397 * The downside is that we have to touch page->_count against each page.
1398 * But we had to alter page->flags anyway.
1399 */
1400
1401static void move_active_pages_to_lru(struct lruvec *lruvec,
1402                                     struct list_head *list,
1403                                     struct list_head *pages_to_free,
1404                                     enum lru_list lru)
1405{
1406        struct zone *zone = lruvec_zone(lruvec);
1407        unsigned long pgmoved = 0;
1408        struct page *page;
1409        int nr_pages;
1410
1411        while (!list_empty(list)) {
1412                page = lru_to_page(list);
1413                lruvec = mem_cgroup_page_lruvec(page, zone);
1414
1415                VM_BUG_ON(PageLRU(page));
1416                SetPageLRU(page);
1417
1418                nr_pages = hpage_nr_pages(page);
1419                mem_cgroup_update_lru_size(lruvec, lru, nr_pages);
1420                list_move(&page->lru, &lruvec->lists[lru]);
1421                pgmoved += nr_pages;
1422
1423                if (put_page_testzero(page)) {
1424                        __ClearPageLRU(page);
1425                        __ClearPageActive(page);
1426                        del_page_from_lru_list(page, lruvec, lru);
1427
1428                        if (unlikely(PageCompound(page))) {
1429                                spin_unlock_irq(&zone->lru_lock);
1430                                (*get_compound_page_dtor(page))(page);
1431                                spin_lock_irq(&zone->lru_lock);
1432                        } else
1433                                list_add(&page->lru, pages_to_free);
1434                }
1435        }
1436        __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved);
1437        if (!is_active_lru(lru))
1438                __count_vm_events(PGDEACTIVATE, pgmoved);
1439}
1440
1441static void shrink_active_list(unsigned long nr_to_scan,
1442                               struct lruvec *lruvec,
1443                               struct scan_control *sc,
1444                               enum lru_list lru)
1445{
1446        unsigned long nr_taken;
1447        unsigned long nr_scanned;
1448        unsigned long vm_flags;
1449        LIST_HEAD(l_hold);      /* The pages which were snipped off */
1450        LIST_HEAD(l_active);
1451        LIST_HEAD(l_inactive);
1452        struct page *page;
1453        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1454        unsigned long nr_rotated = 0;
1455        isolate_mode_t isolate_mode = 0;
1456        int file = is_file_lru(lru);
1457        struct zone *zone = lruvec_zone(lruvec);
1458
1459        lru_add_drain();
1460
1461        if (!sc->may_unmap)
1462                isolate_mode |= ISOLATE_UNMAPPED;
1463        if (!sc->may_writepage)
1464                isolate_mode |= ISOLATE_CLEAN;
1465
1466        spin_lock_irq(&zone->lru_lock);
1467
1468        nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,
1469                                     &nr_scanned, sc, isolate_mode, lru);
1470        if (global_reclaim(sc))
1471                zone->pages_scanned += nr_scanned;
1472
1473        reclaim_stat->recent_scanned[file] += nr_taken;
1474
1475        __count_zone_vm_events(PGREFILL, zone, nr_scanned);
1476        __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken);
1477        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);
1478        spin_unlock_irq(&zone->lru_lock);
1479
1480        while (!list_empty(&l_hold)) {
1481                cond_resched();
1482                page = lru_to_page(&l_hold);
1483                list_del(&page->lru);
1484
1485                if (unlikely(!page_evictable(page))) {
1486                        putback_lru_page(page);
1487                        continue;
1488                }
1489
1490                if (unlikely(buffer_heads_over_limit)) {
1491                        if (page_has_private(page) && trylock_page(page)) {
1492                                if (page_has_private(page))
1493                                        try_to_release_page(page, 0);
1494                                unlock_page(page);
1495                        }
1496                }
1497
1498                if (page_referenced(page, 0, sc->target_mem_cgroup,
1499                                    &vm_flags)) {
1500                        nr_rotated += hpage_nr_pages(page);
1501                        /*
1502                         * Identify referenced, file-backed active pages and
1503                         * give them one more trip around the active list. So
1504                         * that executable code get better chances to stay in
1505                         * memory under moderate memory pressure.  Anon pages
1506                         * are not likely to be evicted by use-once streaming
1507                         * IO, plus JVM can create lots of anon VM_EXEC pages,
1508                         * so we ignore them here.
1509                         */
1510                        if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) {
1511                                list_add(&page->lru, &l_active);
1512                                continue;
1513                        }
1514                }
1515
1516                ClearPageActive(page);  /* we are de-activating */
1517                list_add(&page->lru, &l_inactive);
1518        }
1519
1520        /*
1521         * Move pages back to the lru list.
1522         */
1523        spin_lock_irq(&zone->lru_lock);
1524        /*
1525         * Count referenced pages from currently used mappings as rotated,
1526         * even though only some of them are actually re-activated.  This
1527         * helps balance scan pressure between file and anonymous pages in
1528         * get_scan_ratio.
1529         */
1530        reclaim_stat->recent_rotated[file] += nr_rotated;
1531
1532        move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru);
1533        move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE);
1534        __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken);
1535        spin_unlock_irq(&zone->lru_lock);
1536
1537        free_hot_cold_page_list(&l_hold, 1);
1538}
1539
1540#ifdef CONFIG_SWAP
1541static int inactive_anon_is_low_global(struct zone *zone)
1542{
1543        unsigned long active, inactive;
1544
1545        active = zone_page_state(zone, NR_ACTIVE_ANON);
1546        inactive = zone_page_state(zone, NR_INACTIVE_ANON);
1547
1548        if (inactive * zone->inactive_ratio < active)
1549                return 1;
1550
1551        return 0;
1552}
1553
1554/**
1555 * inactive_anon_is_low - check if anonymous pages need to be deactivated
1556 * @lruvec: LRU vector to check
1557 *
1558 * Returns true if the zone does not have enough inactive anon pages,
1559 * meaning some active anon pages need to be deactivated.
1560 */
1561static int inactive_anon_is_low(struct lruvec *lruvec)
1562{
1563        /*
1564         * If we don't have swap space, anonymous page deactivation
1565         * is pointless.
1566         */
1567        if (!total_swap_pages)
1568                return 0;
1569
1570        if (!mem_cgroup_disabled())
1571                return mem_cgroup_inactive_anon_is_low(lruvec);
1572
1573        return inactive_anon_is_low_global(lruvec_zone(lruvec));
1574}
1575#else
1576static inline int inactive_anon_is_low(struct lruvec *lruvec)
1577{
1578        return 0;
1579}
1580#endif
1581
1582/**
1583 * inactive_file_is_low - check if file pages need to be deactivated
1584 * @lruvec: LRU vector to check
1585 *
1586 * When the system is doing streaming IO, memory pressure here
1587 * ensures that active file pages get deactivated, until more
1588 * than half of the file pages are on the inactive list.
1589 *
1590 * Once we get to that situation, protect the system's working
1591 * set from being evicted by disabling active file page aging.
1592 *
1593 * This uses a different ratio than the anonymous pages, because
1594 * the page cache uses a use-once replacement algorithm.
1595 */
1596static int inactive_file_is_low(struct lruvec *lruvec)
1597{
1598        unsigned long inactive;
1599        unsigned long active;
1600
1601        inactive = get_lru_size(lruvec, LRU_INACTIVE_FILE);
1602        active = get_lru_size(lruvec, LRU_ACTIVE_FILE);
1603
1604        return active > inactive;
1605}
1606
1607static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru)
1608{
1609        if (is_file_lru(lru))
1610                return inactive_file_is_low(lruvec);
1611        else
1612                return inactive_anon_is_low(lruvec);
1613}
1614
1615static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan,
1616                                 struct lruvec *lruvec, struct scan_control *sc)
1617{
1618        if (is_active_lru(lru)) {
1619                if (inactive_list_is_low(lruvec, lru))
1620                        shrink_active_list(nr_to_scan, lruvec, sc, lru);
1621                return 0;
1622        }
1623
1624        return shrink_inactive_list(nr_to_scan, lruvec, sc, lru);
1625}
1626
1627static int vmscan_swappiness(struct scan_control *sc)
1628{
1629        if (global_reclaim(sc))
1630                return vm_swappiness;
1631        return mem_cgroup_swappiness(sc->target_mem_cgroup);
1632}
1633
1634enum scan_balance {
1635        SCAN_EQUAL,
1636        SCAN_FRACT,
1637        SCAN_ANON,
1638        SCAN_FILE,
1639};
1640
1641/*
1642 * Determine how aggressively the anon and file LRU lists should be
1643 * scanned.  The relative value of each set of LRU lists is determined
1644 * by looking at the fraction of the pages scanned we did rotate back
1645 * onto the active list instead of evict.
1646 *
1647 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan
1648 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan
1649 */
1650static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
1651                           unsigned long *nr)
1652{
1653        struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
1654        u64 fraction[2];
1655        u64 denominator = 0;    /* gcc */
1656        struct zone *zone = lruvec_zone(lruvec);
1657        unsigned long anon_prio, file_prio;
1658        enum scan_balance scan_balance;
1659        unsigned long anon, file, free;
1660        bool force_scan = false;
1661        unsigned long ap, fp;
1662        enum lru_list lru;
1663
1664        /*
1665         * If the zone or memcg is small, nr[l] can be 0.  This
1666         * results in no scanning on this priority and a potential
1667         * priority drop.  Global direct reclaim can go to the next
1668         * zone and tends to have no problems. Global kswapd is for
1669         * zone balancing and it needs to scan a minimum amount. When
1670         * reclaiming for a memcg, a priority drop can cause high
1671         * latencies, so it's better to scan a minimum amount there as
1672         * well.
1673         */
1674        if (current_is_kswapd() && zone->all_unreclaimable)
1675                force_scan = true;
1676        if (!global_reclaim(sc))
1677                force_scan = true;
1678
1679        /* If we have no swap space, do not bother scanning anon pages. */
1680        if (!sc->may_swap || (get_nr_swap_pages() <= 0)) {
1681                scan_balance = SCAN_FILE;
1682                goto out;
1683        }
1684
1685        /*
1686         * Global reclaim will swap to prevent OOM even with no
1687         * swappiness, but memcg users want to use this knob to
1688         * disable swapping for individual groups completely when
1689         * using the memory controller's swap limit feature would be
1690         * too expensive.
1691         */
1692        if (!global_reclaim(sc) && !vmscan_swappiness(sc)) {
1693                scan_balance = SCAN_FILE;
1694                goto out;
1695        }
1696
1697        /*
1698         * Do not apply any pressure balancing cleverness when the
1699         * system is close to OOM, scan both anon and file equally
1700         * (unless the swappiness setting disagrees with swapping).
1701         */
1702        if (!sc->priority && vmscan_swappiness(sc)) {
1703                scan_balance = SCAN_EQUAL;
1704                goto out;
1705        }
1706
1707        anon  = get_lru_size(lruvec, LRU_ACTIVE_ANON) +
1708                get_lru_size(lruvec, LRU_INACTIVE_ANON);
1709        file  = get_lru_size(lruvec, LRU_ACTIVE_FILE) +
1710                get_lru_size(lruvec, LRU_INACTIVE_FILE);
1711
1712        /*
1713         * If it's foreseeable that reclaiming the file cache won't be
1714         * enough to get the zone back into a desirable shape, we have
1715         * to swap.  Better start now and leave the - probably heavily
1716         * thrashing - remaining file pages alone.
1717         */
1718        if (global_reclaim(sc)) {
1719                free = zone_page_state(zone, NR_FREE_PAGES);
1720                if (unlikely(file + free <= high_wmark_pages(zone))) {
1721                        scan_balance = SCAN_ANON;
1722                        goto out;
1723                }
1724        }
1725
1726        /*
1727         * There is enough inactive page cache, do not reclaim
1728         * anything from the anonymous working set right now.
1729         */
1730        if (!inactive_file_is_low(lruvec)) {
1731                scan_balance = SCAN_FILE;
1732                goto out;
1733        }
1734
1735        scan_balance = SCAN_FRACT;
1736
1737        /*
1738         * With swappiness at 100, anonymous and file have the same priority.
1739         * This scanning priority is essentially the inverse of IO cost.
1740         */
1741        anon_prio = vmscan_swappiness(sc);
1742        file_prio = 200 - anon_prio;
1743
1744        /*
1745         * OK, so we have swap space and a fair amount of page cache
1746         * pages.  We use the recently rotated / recently scanned
1747         * ratios to determine how valuable each cache is.
1748         *
1749         * Because workloads change over time (and to avoid overflow)
1750         * we keep these statistics as a floating average, which ends
1751         * up weighing recent references more than old ones.
1752         *
1753         * anon in [0], file in [1]
1754         */
1755        spin_lock_irq(&zone->lru_lock);
1756        if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) {
1757                reclaim_stat->recent_scanned[0] /= 2;
1758                reclaim_stat->recent_rotated[0] /= 2;
1759        }
1760
1761        if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) {
1762                reclaim_stat->recent_scanned[1] /= 2;
1763                reclaim_stat->recent_rotated[1] /= 2;
1764        }
1765
1766        /*
1767         * The amount of pressure on anon vs file pages is inversely
1768         * proportional to the fraction of recently scanned pages on
1769         * each list that were recently referenced and in active use.
1770         */
1771        ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1);
1772        ap /= reclaim_stat->recent_rotated[0] + 1;
1773
1774        fp = file_prio * (reclaim_stat->recent_scanned[1] + 1);
1775        fp /= reclaim_stat->recent_rotated[1] + 1;
1776        spin_unlock_irq(&zone->lru_lock);
1777
1778        fraction[0] = ap;
1779        fraction[1] = fp;
1780        denominator = ap + fp + 1;
1781out:
1782        for_each_evictable_lru(lru) {
1783                int file = is_file_lru(lru);
1784                unsigned long size;
1785                unsigned long scan;
1786
1787                size = get_lru_size(lruvec, lru);
1788                scan = size >> sc->priority;
1789
1790                if (!scan && force_scan)
1791                        scan = min(size, SWAP_CLUSTER_MAX);
1792
1793                switch (scan_balance) {
1794                case SCAN_EQUAL:
1795                        /* Scan lists relative to size */
1796                        break;
1797                case SCAN_FRACT:
1798                        /*
1799                         * Scan types proportional to swappiness and
1800                         * their relative recent reclaim efficiency.
1801                         */
1802                        scan = div64_u64(scan * fraction[file], denominator);
1803                        break;
1804                case SCAN_FILE:
1805                case SCAN_ANON:
1806                        /* Scan one type exclusively */
1807                        if ((scan_balance == SCAN_FILE) != file)
1808                                scan = 0;
1809                        break;
1810                default:
1811                        /* Look ma, no brain */
1812                        BUG();
1813                }
1814                nr[lru] = scan;
1815        }
1816}
1817
1818/*
1819 * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
1820 */
1821static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
1822{
1823        unsigned long nr[NR_LRU_LISTS];
1824        unsigned long nr_to_scan;
1825        enum lru_list lru;
1826        unsigned long nr_reclaimed = 0;
1827        unsigned long nr_to_reclaim = sc->nr_to_reclaim;
1828        struct blk_plug plug;
1829
1830        get_scan_count(lruvec, sc, nr);
1831
1832        blk_start_plug(&plug);
1833        while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
1834                                        nr[LRU_INACTIVE_FILE]) {
1835                for_each_evictable_lru(lru) {
1836                        if (nr[lru]) {
1837                                nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX);
1838                                nr[lru] -= nr_to_scan;
1839
1840                                nr_reclaimed += shrink_list(lru, nr_to_scan,
1841                                                            lruvec, sc);
1842                        }
1843                }
1844                /*
1845                 * On large memory systems, scan >> priority can become
1846                 * really large. This is fine for the starting priority;
1847                 * we want to put equal scanning pressure on each zone.
1848                 * However, if the VM has a harder time of freeing pages,
1849                 * with multiple processes reclaiming pages, the total
1850                 * freeing target can get unreasonably large.
1851                 */
1852                if (nr_reclaimed >= nr_to_reclaim &&
1853                    sc->priority < DEF_PRIORITY)
1854                        break;
1855        }
1856        blk_finish_plug(&plug);
1857        sc->nr_reclaimed += nr_reclaimed;
1858
1859        /*
1860         * Even if we did not try to evict anon pages at all, we want to
1861         * rebalance the anon lru active/inactive ratio.
1862         */
1863        if (inactive_anon_is_low(lruvec))
1864                shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
1865                                   sc, LRU_ACTIVE_ANON);
1866
1867        throttle_vm_writeout(sc->gfp_mask);
1868}
1869
1870/* Use reclaim/compaction for costly allocs or under memory pressure */
1871static bool in_reclaim_compaction(struct scan_control *sc)
1872{
1873        if (IS_ENABLED(CONFIG_COMPACTION) && sc->order &&
1874                        (sc->order > PAGE_ALLOC_COSTLY_ORDER ||
1875                         sc->priority < DEF_PRIORITY - 2))
1876                return true;
1877
1878        return false;
1879}
1880
1881/*
1882 * Reclaim/compaction is used for high-order allocation requests. It reclaims
1883 * order-0 pages before compacting the zone. should_continue_reclaim() returns
1884 * true if more pages should be reclaimed such that when the page allocator
1885 * calls try_to_compact_zone() that it will have enough free pages to succeed.
1886 * It will give up earlier than that if there is difficulty reclaiming pages.
1887 */
1888static inline bool should_continue_reclaim(struct zone *zone,
1889                                        unsigned long nr_reclaimed,
1890                                        unsigned long nr_scanned,
1891                                        struct scan_control *sc)
1892{
1893        unsigned long pages_for_compaction;
1894        unsigned long inactive_lru_pages;
1895
1896        /* If not in reclaim/compaction mode, stop */
1897        if (!in_reclaim_compaction(sc))
1898                return false;
1899
1900        /* Consider stopping depending on scan and reclaim activity */
1901        if (sc->gfp_mask & __GFP_REPEAT) {
1902                /*
1903                 * For __GFP_REPEAT allocations, stop reclaiming if the
1904                 * full LRU list has been scanned and we are still failing
1905                 * to reclaim pages. This full LRU scan is potentially
1906                 * expensive but a __GFP_REPEAT caller really wants to succeed
1907                 */
1908                if (!nr_reclaimed && !nr_scanned)
1909                        return false;
1910        } else {
1911                /*
1912                 * For non-__GFP_REPEAT allocations which can presumably
1913                 * fail without consequence, stop if we failed to reclaim
1914                 * any pages from the last SWAP_CLUSTER_MAX number of
1915                 * pages that were scanned. This will return to the
1916                 * caller faster at the risk reclaim/compaction and
1917                 * the resulting allocation attempt fails
1918                 */
1919                if (!nr_reclaimed)
1920                        return false;
1921        }
1922
1923        /*
1924         * If we have not reclaimed enough pages for compaction and the
1925         * inactive lists are large enough, continue reclaiming
1926         */
1927        pages_for_compaction = (2UL << sc->order);
1928        inactive_lru_pages = zone_page_state(zone, NR_INACTIVE_FILE);
1929        if (get_nr_swap_pages() > 0)
1930                inactive_lru_pages += zone_page_state(zone, NR_INACTIVE_ANON);
1931        if (sc->nr_reclaimed < pages_for_compaction &&
1932                        inactive_lru_pages > pages_for_compaction)
1933                return true;
1934
1935        /* If compaction would go ahead or the allocation would succeed, stop */
1936        switch (compaction_suitable(zone, sc->order)) {
1937        case COMPACT_PARTIAL:
1938        case COMPACT_CONTINUE:
1939                return false;
1940        default:
1941                return true;
1942        }
1943}
1944
1945static void shrink_zone(struct zone *zone, struct scan_control *sc)
1946{
1947        unsigned long nr_reclaimed, nr_scanned;
1948
1949        do {
1950                struct mem_cgroup *root = sc->target_mem_cgroup;
1951                struct mem_cgroup_reclaim_cookie reclaim = {
1952                        .zone = zone,
1953                        .priority = sc->priority,
1954                };
1955                struct mem_cgroup *memcg;
1956
1957                nr_reclaimed = sc->nr_reclaimed;
1958                nr_scanned = sc->nr_scanned;
1959
1960                memcg = mem_cgroup_iter(root, NULL, &reclaim);
1961                do {
1962                        struct lruvec *lruvec;
1963
1964                        lruvec = mem_cgroup_zone_lruvec(zone, memcg);
1965
1966                        shrink_lruvec(lruvec, sc);
1967
1968                        /*
1969                         * Direct reclaim and kswapd have to scan all memory
1970                         * cgroups to fulfill the overall scan target for the
1971                         * zone.
1972                         *
1973                         * Limit reclaim, on the other hand, only cares about
1974                         * nr_to_reclaim pages to be reclaimed and it will
1975                         * retry with decreasing priority if one round over the
1976                         * whole hierarchy is not sufficient.
1977                         */
1978                        if (!global_reclaim(sc) &&
1979                                        sc->nr_reclaimed >= sc->nr_to_reclaim) {
1980                                mem_cgroup_iter_break(root, memcg);
1981                                break;
1982                        }
1983                        memcg = mem_cgroup_iter(root, memcg, &reclaim);
1984                } while (memcg);
1985        } while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed,
1986                                         sc->nr_scanned - nr_scanned, sc));
1987}
1988
1989/* Returns true if compaction should go ahead for a high-order request */
1990static inline bool compaction_ready(struct zone *zone, struct scan_control *sc)
1991{
1992        unsigned long balance_gap, watermark;
1993        bool watermark_ok;
1994
1995        /* Do not consider compaction for orders reclaim is meant to satisfy */
1996        if (sc->order <= PAGE_ALLOC_COSTLY_ORDER)
1997                return false;
1998
1999        /*
2000         * Compaction takes time to run and there are potentially other
2001         * callers using the pages just freed. Continue reclaiming until
2002         * there is a buffer of free pages available to give compaction
2003         * a reasonable chance of completing and allocating the page
2004         */
2005        balance_gap = min(low_wmark_pages(zone),
2006                (zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2007                        KSWAPD_ZONE_BALANCE_GAP_RATIO);
2008        watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order);
2009        watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0);
2010
2011        /*
2012         * If compaction is deferred, reclaim up to a point where
2013         * compaction will have a chance of success when re-enabled
2014         */
2015        if (compaction_deferred(zone, sc->order))
2016                return watermark_ok;
2017
2018        /* If compaction is not ready to start, keep reclaiming */
2019        if (!compaction_suitable(zone, sc->order))
2020                return false;
2021
2022        return watermark_ok;
2023}
2024
2025/*
2026 * This is the direct reclaim path, for page-allocating processes.  We only
2027 * try to reclaim pages from zones which will satisfy the caller's allocation
2028 * request.
2029 *
2030 * We reclaim from a zone even if that zone is over high_wmark_pages(zone).
2031 * Because:
2032 * a) The caller may be trying to free *extra* pages to satisfy a higher-order
2033 *    allocation or
2034 * b) The target zone may be at high_wmark_pages(zone) but the lower zones
2035 *    must go *over* high_wmark_pages(zone) to satisfy the `incremental min'
2036 *    zone defense algorithm.
2037 *
2038 * If a zone is deemed to be full of pinned pages then just give it a light
2039 * scan then give up on it.
2040 *
2041 * This function returns true if a zone is being reclaimed for a costly
2042 * high-order allocation and compaction is ready to begin. This indicates to
2043 * the caller that it should consider retrying the allocation instead of
2044 * further reclaim.
2045 */
2046static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
2047{
2048        struct zoneref *z;
2049        struct zone *zone;
2050        unsigned long nr_soft_reclaimed;
2051        unsigned long nr_soft_scanned;
2052        bool aborted_reclaim = false;
2053
2054        /*
2055         * If the number of buffer_heads in the machine exceeds the maximum
2056         * allowed level, force direct reclaim to scan the highmem zone as
2057         * highmem pages could be pinning lowmem pages storing buffer_heads
2058         */
2059        if (buffer_heads_over_limit)
2060                sc->gfp_mask |= __GFP_HIGHMEM;
2061
2062        for_each_zone_zonelist_nodemask(zone, z, zonelist,
2063                                        gfp_zone(sc->gfp_mask), sc->nodemask) {
2064                if (!populated_zone(zone))
2065                        continue;
2066                /*
2067                 * Take care memory controller reclaiming has small influence
2068                 * to global LRU.
2069                 */
2070                if (global_reclaim(sc)) {
2071                        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2072                                continue;
2073                        if (zone->all_unreclaimable &&
2074                                        sc->priority != DEF_PRIORITY)
2075                                continue;       /* Let kswapd poll it */
2076                        if (IS_ENABLED(CONFIG_COMPACTION)) {
2077                                /*
2078                                 * If we already have plenty of memory free for
2079                                 * compaction in this zone, don't free any more.
2080                                 * Even though compaction is invoked for any
2081                                 * non-zero order, only frequent costly order
2082                                 * reclamation is disruptive enough to become a
2083                                 * noticeable problem, like transparent huge
2084                                 * page allocations.
2085                                 */
2086                                if (compaction_ready(zone, sc)) {
2087                                        aborted_reclaim = true;
2088                                        continue;
2089                                }
2090                        }
2091                        /*
2092                         * This steals pages from memory cgroups over softlimit
2093                         * and returns the number of reclaimed pages and
2094                         * scanned pages. This works for global memory pressure
2095                         * and balancing, not for a memcg's limit.
2096                         */
2097                        nr_soft_scanned = 0;
2098                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2099                                                sc->order, sc->gfp_mask,
2100                                                &nr_soft_scanned);
2101                        sc->nr_reclaimed += nr_soft_reclaimed;
2102                        sc->nr_scanned += nr_soft_scanned;
2103                        /* need some check for avoid more shrink_zone() */
2104                }
2105
2106                shrink_zone(zone, sc);
2107        }
2108
2109        return aborted_reclaim;
2110}
2111
2112static bool zone_reclaimable(struct zone *zone)
2113{
2114        return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;
2115}
2116
2117/* All zones in zonelist are unreclaimable? */
2118static bool all_unreclaimable(struct zonelist *zonelist,
2119                struct scan_control *sc)
2120{
2121        struct zoneref *z;
2122        struct zone *zone;
2123
2124        for_each_zone_zonelist_nodemask(zone, z, zonelist,
2125                        gfp_zone(sc->gfp_mask), sc->nodemask) {
2126                if (!populated_zone(zone))
2127                        continue;
2128                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2129                        continue;
2130                if (!zone->all_unreclaimable)
2131                        return false;
2132        }
2133
2134        return true;
2135}
2136
2137/*
2138 * This is the main entry point to direct page reclaim.
2139 *
2140 * If a full scan of the inactive list fails to free enough memory then we
2141 * are "out of memory" and something needs to be killed.
2142 *
2143 * If the caller is !__GFP_FS then the probability of a failure is reasonably
2144 * high - the zone may be full of dirty or under-writeback pages, which this
2145 * caller can't do much about.  We kick the writeback threads and take explicit
2146 * naps in the hope that some of these pages can be written.  But if the
2147 * allocating task holds filesystem locks which prevent writeout this might not
2148 * work, and the allocation attempt will fail.
2149 *
2150 * returns:     0, if no pages reclaimed
2151 *              else, the number of pages reclaimed
2152 */
2153static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
2154                                        struct scan_control *sc,
2155                                        struct shrink_control *shrink)
2156{
2157        unsigned long total_scanned = 0;
2158        struct reclaim_state *reclaim_state = current->reclaim_state;
2159        struct zoneref *z;
2160        struct zone *zone;
2161        unsigned long writeback_threshold;
2162        bool aborted_reclaim;
2163
2164        delayacct_freepages_start();
2165
2166        if (global_reclaim(sc))
2167                count_vm_event(ALLOCSTALL);
2168
2169        do {
2170                sc->nr_scanned = 0;
2171                aborted_reclaim = shrink_zones(zonelist, sc);
2172
2173                /*
2174                 * Don't shrink slabs when reclaiming memory from
2175                 * over limit cgroups
2176                 */
2177                if (global_reclaim(sc)) {
2178                        unsigned long lru_pages = 0;
2179                        for_each_zone_zonelist(zone, z, zonelist,
2180                                        gfp_zone(sc->gfp_mask)) {
2181                                if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
2182                                        continue;
2183
2184                                lru_pages += zone_reclaimable_pages(zone);
2185                        }
2186
2187                        shrink_slab(shrink, sc->nr_scanned, lru_pages);
2188                        if (reclaim_state) {
2189                                sc->nr_reclaimed += reclaim_state->reclaimed_slab;
2190                                reclaim_state->reclaimed_slab = 0;
2191                        }
2192                }
2193                total_scanned += sc->nr_scanned;
2194                if (sc->nr_reclaimed >= sc->nr_to_reclaim)
2195                        goto out;
2196
2197                /*
2198                 * If we're getting trouble reclaiming, start doing
2199                 * writepage even in laptop mode.
2200                 */
2201                if (sc->priority < DEF_PRIORITY - 2)
2202                        sc->may_writepage = 1;
2203
2204                /*
2205                 * Try to write back as many pages as we just scanned.  This
2206                 * tends to cause slow streaming writers to write data to the
2207                 * disk smoothly, at the dirtying rate, which is nice.   But
2208                 * that's undesirable in laptop mode, where we *want* lumpy
2209                 * writeout.  So in laptop mode, write out the whole world.
2210                 */
2211                writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2;
2212                if (total_scanned > writeback_threshold) {
2213                        wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
2214                                                WB_REASON_TRY_TO_FREE_PAGES);
2215                        sc->may_writepage = 1;
2216                }
2217
2218                /* Take a nap, wait for some writeback to complete */
2219                if (!sc->hibernation_mode && sc->nr_scanned &&
2220                    sc->priority < DEF_PRIORITY - 2) {
2221                        struct zone *preferred_zone;
2222
2223                        first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
2224                                                &cpuset_current_mems_allowed,
2225                                                &preferred_zone);
2226                        wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
2227                }
2228        } while (--sc->priority >= 0);
2229
2230out:
2231        delayacct_freepages_end();
2232
2233        if (sc->nr_reclaimed)
2234                return sc->nr_reclaimed;
2235
2236        /*
2237         * As hibernation is going on, kswapd is freezed so that it can't mark
2238         * the zone into all_unreclaimable. Thus bypassing all_unreclaimable
2239         * check.
2240         */
2241        if (oom_killer_disabled)
2242                return 0;
2243
2244        /* Aborted reclaim to try compaction? don't OOM, then */
2245        if (aborted_reclaim)
2246                return 1;
2247
2248        /* top priority shrink_zones still had more to do? don't OOM, then */
2249        if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc))
2250                return 1;
2251
2252        return 0;
2253}
2254
2255static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
2256{
2257        struct zone *zone;
2258        unsigned long pfmemalloc_reserve = 0;
2259        unsigned long free_pages = 0;
2260        int i;
2261        bool wmark_ok;
2262
2263        for (i = 0; i <= ZONE_NORMAL; i++) {
2264                zone = &pgdat->node_zones[i];
2265                pfmemalloc_reserve += min_wmark_pages(zone);
2266                free_pages += zone_page_state(zone, NR_FREE_PAGES);
2267        }
2268
2269        wmark_ok = free_pages > pfmemalloc_reserve / 2;
2270
2271        /* kswapd must be awake if processes are being throttled */
2272        if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) {
2273                pgdat->classzone_idx = min(pgdat->classzone_idx,
2274                                                (enum zone_type)ZONE_NORMAL);
2275                wake_up_interruptible(&pgdat->kswapd_wait);
2276        }
2277
2278        return wmark_ok;
2279}
2280
2281/*
2282 * Throttle direct reclaimers if backing storage is backed by the network
2283 * and the PFMEMALLOC reserve for the preferred node is getting dangerously
2284 * depleted. kswapd will continue to make progress and wake the processes
2285 * when the low watermark is reached.
2286 *
2287 * Returns true if a fatal signal was delivered during throttling. If this
2288 * happens, the page allocator should not consider triggering the OOM killer.
2289 */
2290static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist,
2291                                        nodemask_t *nodemask)
2292{
2293        struct zone *zone;
2294        int high_zoneidx = gfp_zone(gfp_mask);
2295        pg_data_t *pgdat;
2296
2297        /*
2298         * Kernel threads should not be throttled as they may be indirectly
2299         * responsible for cleaning pages necessary for reclaim to make forward
2300         * progress. kjournald for example may enter direct reclaim while
2301         * committing a transaction where throttling it could forcing other
2302         * processes to block on log_wait_commit().
2303         */
2304        if (current->flags & PF_KTHREAD)
2305                goto out;
2306
2307        /*
2308         * If a fatal signal is pending, this process should not throttle.
2309         * It should return quickly so it can exit and free its memory
2310         */
2311        if (fatal_signal_pending(current))
2312                goto out;
2313
2314        /* Check if the pfmemalloc reserves are ok */
2315        first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone);
2316        pgdat = zone->zone_pgdat;
2317        if (pfmemalloc_watermark_ok(pgdat))
2318                goto out;
2319
2320        /* Account for the throttling */
2321        count_vm_event(PGSCAN_DIRECT_THROTTLE);
2322
2323        /*
2324         * If the caller cannot enter the filesystem, it's possible that it
2325         * is due to the caller holding an FS lock or performing a journal
2326         * transaction in the case of a filesystem like ext[3|4]. In this case,
2327         * it is not safe to block on pfmemalloc_wait as kswapd could be
2328         * blocked waiting on the same lock. Instead, throttle for up to a
2329         * second before continuing.
2330         */
2331        if (!(gfp_mask & __GFP_FS)) {
2332                wait_event_interruptible_timeout(pgdat->pfmemalloc_wait,
2333                        pfmemalloc_watermark_ok(pgdat), HZ);
2334
2335                goto check_pending;
2336        }
2337
2338        /* Throttle until kswapd wakes the process */
2339        wait_event_killable(zone->zone_pgdat->pfmemalloc_wait,
2340                pfmemalloc_watermark_ok(pgdat));
2341
2342check_pending:
2343        if (fatal_signal_pending(current))
2344                return true;
2345
2346out:
2347        return false;
2348}
2349
2350unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
2351                                gfp_t gfp_mask, nodemask_t *nodemask)
2352{
2353        unsigned long nr_reclaimed;
2354        struct scan_control sc = {
2355                .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
2356                .may_writepage = !laptop_mode,
2357                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2358                .may_unmap = 1,
2359                .may_swap = 1,
2360                .order = order,
2361                .priority = DEF_PRIORITY,
2362                .target_mem_cgroup = NULL,
2363                .nodemask = nodemask,
2364        };
2365        struct shrink_control shrink = {
2366                .gfp_mask = sc.gfp_mask,
2367        };
2368
2369        /*
2370         * Do not enter reclaim if fatal signal was delivered while throttled.
2371         * 1 is returned so that the page allocator does not OOM kill at this
2372         * point.
2373         */
2374        if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask))
2375                return 1;
2376
2377        trace_mm_vmscan_direct_reclaim_begin(order,
2378                                sc.may_writepage,
2379                                gfp_mask);
2380
2381        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2382
2383        trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
2384
2385        return nr_reclaimed;
2386}
2387
2388#ifdef CONFIG_MEMCG
2389
2390unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
2391                                                gfp_t gfp_mask, bool noswap,
2392                                                struct zone *zone,
2393                                                unsigned long *nr_scanned)
2394{
2395        struct scan_control sc = {
2396                .nr_scanned = 0,
2397                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2398                .may_writepage = !laptop_mode,
2399                .may_unmap = 1,
2400                .may_swap = !noswap,
2401                .order = 0,
2402                .priority = 0,
2403                .target_mem_cgroup = memcg,
2404        };
2405        struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2406
2407        sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2408                        (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
2409
2410        trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
2411                                                      sc.may_writepage,
2412                                                      sc.gfp_mask);
2413
2414        /*
2415         * NOTE: Although we can get the priority field, using it
2416         * here is not a good idea, since it limits the pages we can scan.
2417         * if we don't reclaim here, the shrink_zone from balance_pgdat
2418         * will pick up pages from other mem cgroup's as well. We hack
2419         * the priority and make it zero.
2420         */
2421        shrink_lruvec(lruvec, &sc);
2422
2423        trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed);
2424
2425        *nr_scanned = sc.nr_scanned;
2426        return sc.nr_reclaimed;
2427}
2428
2429unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
2430                                           gfp_t gfp_mask,
2431                                           bool noswap)
2432{
2433        struct zonelist *zonelist;
2434        unsigned long nr_reclaimed;
2435        int nid;
2436        struct scan_control sc = {
2437                .may_writepage = !laptop_mode,
2438                .may_unmap = 1,
2439                .may_swap = !noswap,
2440                .nr_to_reclaim = SWAP_CLUSTER_MAX,
2441                .order = 0,
2442                .priority = DEF_PRIORITY,
2443                .target_mem_cgroup = memcg,
2444                .nodemask = NULL, /* we don't care the placement */
2445                .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
2446                                (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
2447        };
2448        struct shrink_control shrink = {
2449                .gfp_mask = sc.gfp_mask,
2450        };
2451
2452        /*
2453         * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
2454         * take care of from where we get pages. So the node where we start the
2455         * scan does not need to be the current node.
2456         */
2457        nid = mem_cgroup_select_victim_node(memcg);
2458
2459        zonelist = NODE_DATA(nid)->node_zonelists;
2460
2461        trace_mm_vmscan_memcg_reclaim_begin(0,
2462                                            sc.may_writepage,
2463                                            sc.gfp_mask);
2464
2465        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
2466
2467        trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
2468
2469        return nr_reclaimed;
2470}
2471#endif
2472
2473static void age_active_anon(struct zone *zone, struct scan_control *sc)
2474{
2475        struct mem_cgroup *memcg;
2476
2477        if (!total_swap_pages)
2478                return;
2479
2480        memcg = mem_cgroup_iter(NULL, NULL, NULL);
2481        do {
2482                struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
2483
2484                if (inactive_anon_is_low(lruvec))
2485                        shrink_active_list(SWAP_CLUSTER_MAX, lruvec,
2486                                           sc, LRU_ACTIVE_ANON);
2487
2488                memcg = mem_cgroup_iter(NULL, memcg, NULL);
2489        } while (memcg);
2490}
2491
2492static bool zone_balanced(struct zone *zone, int order,
2493                          unsigned long balance_gap, int classzone_idx)
2494{
2495        if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) +
2496                                    balance_gap, classzone_idx, 0))
2497                return false;
2498
2499        if (IS_ENABLED(CONFIG_COMPACTION) && order &&
2500            !compaction_suitable(zone, order))
2501                return false;
2502
2503        return true;
2504}
2505
2506/*
2507 * pgdat_balanced() is used when checking if a node is balanced.
2508 *
2509 * For order-0, all zones must be balanced!
2510 *
2511 * For high-order allocations only zones that meet watermarks and are in a
2512 * zone allowed by the callers classzone_idx are added to balanced_pages. The
2513 * total of balanced pages must be at least 25% of the zones allowed by
2514 * classzone_idx for the node to be considered balanced. Forcing all zones to
2515 * be balanced for high orders can cause excessive reclaim when there are
2516 * imbalanced zones.
2517 * The choice of 25% is due to
2518 *   o a 16M DMA zone that is balanced will not balance a zone on any
2519 *     reasonable sized machine
2520 *   o On all other machines, the top zone must be at least a reasonable
2521 *     percentage of the middle zones. For example, on 32-bit x86, highmem
2522 *     would need to be at least 256M for it to be balance a whole node.
2523 *     Similarly, on x86-64 the Normal zone would need to be at least 1G
2524 *     to balance a node on its own. These seemed like reasonable ratios.
2525 */
2526static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx)
2527{
2528        unsigned long managed_pages = 0;
2529        unsigned long balanced_pages = 0;
2530        int i;
2531
2532        /* Check the watermark levels */
2533        for (i = 0; i <= classzone_idx; i++) {
2534                struct zone *zone = pgdat->node_zones + i;
2535
2536                if (!populated_zone(zone))
2537                        continue;
2538
2539                managed_pages += zone->managed_pages;
2540
2541                /*
2542                 * A special case here:
2543                 *
2544                 * balance_pgdat() skips over all_unreclaimable after
2545                 * DEF_PRIORITY. Effectively, it considers them balanced so
2546                 * they must be considered balanced here as well!
2547                 */
2548                if (zone->all_unreclaimable) {
2549                        balanced_pages += zone->managed_pages;
2550                        continue;
2551                }
2552
2553                if (zone_balanced(zone, order, 0, i))
2554                        balanced_pages += zone->managed_pages;
2555                else if (!order)
2556                        return false;
2557        }
2558
2559        if (order)
2560                return balanced_pages >= (managed_pages >> 2);
2561        else
2562                return true;
2563}
2564
2565/*
2566 * Prepare kswapd for sleeping. This verifies that there are no processes
2567 * waiting in throttle_direct_reclaim() and that watermarks have been met.
2568 *
2569 * Returns true if kswapd is ready to sleep
2570 */
2571static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining,
2572                                        int classzone_idx)
2573{
2574        /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
2575        if (remaining)
2576                return false;
2577
2578        /*
2579         * There is a potential race between when kswapd checks its watermarks
2580         * and a process gets throttled. There is also a potential race if
2581         * processes get throttled, kswapd wakes, a large process exits therby
2582         * balancing the zones that causes kswapd to miss a wakeup. If kswapd
2583         * is going to sleep, no process should be sleeping on pfmemalloc_wait
2584         * so wake them now if necessary. If necessary, processes will wake
2585         * kswapd and get throttled again
2586         */
2587        if (waitqueue_active(&pgdat->pfmemalloc_wait)) {
2588                wake_up(&pgdat->pfmemalloc_wait);
2589                return false;
2590        }
2591
2592        return pgdat_balanced(pgdat, order, classzone_idx);
2593}
2594
2595/*
2596 * For kswapd, balance_pgdat() will work across all this node's zones until
2597 * they are all at high_wmark_pages(zone).
2598 *
2599 * Returns the final order kswapd was reclaiming at
2600 *
2601 * There is special handling here for zones which are full of pinned pages.
2602 * This can happen if the pages are all mlocked, or if they are all used by
2603 * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
2604 * What we do is to detect the case where all pages in the zone have been
2605 * scanned twice and there has been zero successful reclaim.  Mark the zone as
2606 * dead and from now on, only perform a short scan.  Basically we're polling
2607 * the zone for when the problem goes away.
2608 *
2609 * kswapd scans the zones in the highmem->normal->dma direction.  It skips
2610 * zones which have free_pages > high_wmark_pages(zone), but once a zone is
2611 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the
2612 * lower zones regardless of the number of free pages in the lower zones. This
2613 * interoperates with the page allocator fallback scheme to ensure that aging
2614 * of pages is balanced across the zones.
2615 */
2616static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
2617                                                        int *classzone_idx)
2618{
2619        bool pgdat_is_balanced = false;
2620        int i;
2621        int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
2622        unsigned long total_scanned;
2623        struct reclaim_state *reclaim_state = current->reclaim_state;
2624        unsigned long nr_soft_reclaimed;
2625        unsigned long nr_soft_scanned;
2626        struct scan_control sc = {
2627                .gfp_mask = GFP_KERNEL,
2628                .may_unmap = 1,
2629                .may_swap = 1,
2630                /*
2631                 * kswapd doesn't want to be bailed out while reclaim. because
2632                 * we want to put equal scanning pressure on each zone.
2633                 */
2634                .nr_to_reclaim = ULONG_MAX,
2635                .order = order,
2636                .target_mem_cgroup = NULL,
2637        };
2638        struct shrink_control shrink = {
2639                .gfp_mask = sc.gfp_mask,
2640        };
2641loop_again:
2642        total_scanned = 0;
2643        sc.priority = DEF_PRIORITY;
2644        sc.nr_reclaimed = 0;
2645        sc.may_writepage = !laptop_mode;
2646        count_vm_event(PAGEOUTRUN);
2647
2648        do {
2649                unsigned long lru_pages = 0;
2650
2651                /*
2652                 * Scan in the highmem->dma direction for the highest
2653                 * zone which needs scanning
2654                 */
2655                for (i = pgdat->nr_zones - 1; i >= 0; i--) {
2656                        struct zone *zone = pgdat->node_zones + i;
2657
2658                        if (!populated_zone(zone))
2659                                continue;
2660
2661                        if (zone->all_unreclaimable &&
2662                            sc.priority != DEF_PRIORITY)
2663                                continue;
2664
2665                        /*
2666                         * Do some background aging of the anon list, to give
2667                         * pages a chance to be referenced before reclaiming.
2668                         */
2669                        age_active_anon(zone, &sc);
2670
2671                        /*
2672                         * If the number of buffer_heads in the machine
2673                         * exceeds the maximum allowed level and this node
2674                         * has a highmem zone, force kswapd to reclaim from
2675                         * it to relieve lowmem pressure.
2676                         */
2677                        if (buffer_heads_over_limit && is_highmem_idx(i)) {
2678                                end_zone = i;
2679                                break;
2680                        }
2681
2682                        if (!zone_balanced(zone, order, 0, 0)) {
2683                                end_zone = i;
2684                                break;
2685                        } else {
2686                                /* If balanced, clear the congested flag */
2687                                zone_clear_flag(zone, ZONE_CONGESTED);
2688                        }
2689                }
2690
2691                if (i < 0) {
2692                        pgdat_is_balanced = true;
2693                        goto out;
2694                }
2695
2696                for (i = 0; i <= end_zone; i++) {
2697                        struct zone *zone = pgdat->node_zones + i;
2698
2699                        lru_pages += zone_reclaimable_pages(zone);
2700                }
2701
2702                /*
2703                 * Now scan the zone in the dma->highmem direction, stopping
2704                 * at the last zone which needs scanning.
2705                 *
2706                 * We do this because the page allocator works in the opposite
2707                 * direction.  This prevents the page allocator from allocating
2708                 * pages behind kswapd's direction of progress, which would
2709                 * cause too much scanning of the lower zones.
2710                 */
2711                for (i = 0; i <= end_zone; i++) {
2712                        struct zone *zone = pgdat->node_zones + i;
2713                        int nr_slab, testorder;
2714                        unsigned long balance_gap;
2715
2716                        if (!populated_zone(zone))
2717                                continue;
2718
2719                        if (zone->all_unreclaimable &&
2720                            sc.priority != DEF_PRIORITY)
2721                                continue;
2722
2723                        sc.nr_scanned = 0;
2724
2725                        nr_soft_scanned = 0;
2726                        /*
2727                         * Call soft limit reclaim before calling shrink_zone.
2728                         */
2729                        nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
2730                                                        order, sc.gfp_mask,
2731                                                        &nr_soft_scanned);
2732                        sc.nr_reclaimed += nr_soft_reclaimed;
2733                        total_scanned += nr_soft_scanned;
2734
2735                        /*
2736                         * We put equal pressure on every zone, unless
2737                         * one zone has way too many pages free
2738                         * already. The "too many pages" is defined
2739                         * as the high wmark plus a "gap" where the
2740                         * gap is either the low watermark or 1%
2741                         * of the zone, whichever is smaller.
2742                         */
2743                        balance_gap = min(low_wmark_pages(zone),
2744                                (zone->managed_pages +
2745                                        KSWAPD_ZONE_BALANCE_GAP_RATIO-1) /
2746                                KSWAPD_ZONE_BALANCE_GAP_RATIO);
2747                        /*
2748                         * Kswapd reclaims only single pages with compaction
2749                         * enabled. Trying too hard to reclaim until contiguous
2750                         * free pages have become available can hurt performance
2751                         * by evicting too much useful data from memory.
2752                         * Do not reclaim more than needed for compaction.
2753                         */
2754                        testorder = order;
2755                        if (IS_ENABLED(CONFIG_COMPACTION) && order &&
2756                                        compaction_suitable(zone, order) !=
2757                                                COMPACT_SKIPPED)
2758                                testorder = 0;
2759
2760                        if ((buffer_heads_over_limit && is_highmem_idx(i)) ||
2761                            !zone_balanced(zone, testorder,
2762                                           balance_gap, end_zone)) {
2763                                shrink_zone(zone, &sc);
2764
2765                                reclaim_state->reclaimed_slab = 0;
2766                                nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages);
2767                                sc.nr_reclaimed += reclaim_state->reclaimed_slab;
2768                                total_scanned += sc.nr_scanned;
2769
2770                                if (nr_slab == 0 && !zone_reclaimable(zone))
2771                                        zone->all_unreclaimable = 1;
2772                        }
2773
2774                        /*
2775                         * If we're getting trouble reclaiming, start doing
2776                         * writepage even in laptop mode.
2777                         */
2778                        if (sc.priority < DEF_PRIORITY - 2)
2779                                sc.may_writepage = 1;
2780
2781                        if (zone->all_unreclaimable) {
2782                                if (end_zone && end_zone == i)
2783                                        end_zone--;
2784                                continue;
2785                        }
2786
2787                        if (zone_balanced(zone, testorder, 0, end_zone))
2788                                /*
2789                                 * If a zone reaches its high watermark,
2790                                 * consider it to be no longer congested. It's
2791                                 * possible there are dirty pages backed by
2792                                 * congested BDIs but as pressure is relieved,
2793                                 * speculatively avoid congestion waits
2794                                 */
2795                                zone_clear_flag(zone, ZONE_CONGESTED);
2796                }
2797
2798                /*
2799                 * If the low watermark is met there is no need for processes
2800                 * to be throttled on pfmemalloc_wait as they should not be
2801                 * able to safely make forward progress. Wake them
2802                 */
2803                if (waitqueue_active(&pgdat->pfmemalloc_wait) &&
2804                                pfmemalloc_watermark_ok(pgdat))
2805                        wake_up(&pgdat->pfmemalloc_wait);
2806
2807                if (pgdat_balanced(pgdat, order, *classzone_idx)) {
2808                        pgdat_is_balanced = true;
2809                        break;          /* kswapd: all done */
2810                }
2811
2812                /*
2813                 * We do this so kswapd doesn't build up large priorities for
2814                 * example when it is freeing in parallel with allocators. It
2815                 * matches the direct reclaim path behaviour in terms of impact
2816                 * on zone->*_priority.
2817                 */
2818                if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX)
2819                        break;
2820        } while (--sc.priority >= 0);
2821
2822out:
2823        if (!pgdat_is_balanced) {
2824                cond_resched();
2825
2826                try_to_freeze();
2827
2828                /*
2829                 * Fragmentation may mean that the system cannot be
2830                 * rebalanced for high-order allocations in all zones.
2831                 * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX,
2832                 * it means the zones have been fully scanned and are still
2833                 * not balanced. For high-order allocations, there is
2834                 * little point trying all over again as kswapd may
2835                 * infinite loop.
2836                 *
2837                 * Instead, recheck all watermarks at order-0 as they
2838                 * are the most important. If watermarks are ok, kswapd will go
2839                 * back to sleep. High-order users can still perform direct
2840                 * reclaim if they wish.
2841                 */
2842                if (sc.nr_reclaimed < SWAP_CLUSTER_MAX)
2843                        order = sc.order = 0;
2844
2845                goto loop_again;
2846        }
2847
2848        /*
2849         * If kswapd was reclaiming at a higher order, it has the option of
2850         * sleeping without all zones being balanced. Before it does, it must
2851         * ensure that the watermarks for order-0 on *all* zones are met and
2852         * that the congestion flags are cleared. The congestion flag must
2853         * be cleared as kswapd is the only mechanism that clears the flag
2854         * and it is potentially going to sleep here.
2855         */
2856        if (order) {
2857                int zones_need_compaction = 1;
2858
2859                for (i = 0; i <= end_zone; i++) {
2860                        struct zone *zone = pgdat->node_zones + i;
2861
2862                        if (!populated_zone(zone))
2863                                continue;
2864
2865                        /* Check if the memory needs to be defragmented. */
2866                        if (zone_watermark_ok(zone, order,
2867                                    low_wmark_pages(zone), *classzone_idx, 0))
2868                                zones_need_compaction = 0;
2869                }
2870
2871                if (zones_need_compaction)
2872                        compact_pgdat(pgdat, order);
2873        }
2874
2875        /*
2876         * Return the order we were reclaiming at so prepare_kswapd_sleep()
2877         * makes a decision on the order we were last reclaiming at. However,
2878         * if another caller entered the allocator slow path while kswapd
2879         * was awake, order will remain at the higher level
2880         */
2881        *classzone_idx = end_zone;
2882        return order;
2883}
2884
2885static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx)
2886{
2887        long remaining = 0;
2888        DEFINE_WAIT(wait);
2889
2890        if (freezing(current) || kthread_should_stop())
2891                return;
2892
2893        prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2894
2895        /* Try to sleep for a short interval */
2896        if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2897                remaining = schedule_timeout(HZ/10);
2898                finish_wait(&pgdat->kswapd_wait, &wait);
2899                prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
2900        }
2901
2902        /*
2903         * After a short sleep, check if it was a premature sleep. If not, then
2904         * go fully to sleep until explicitly woken up.
2905         */
2906        if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) {
2907                trace_mm_vmscan_kswapd_sleep(pgdat->node_id);
2908
2909                /*
2910                 * vmstat counters are not perfectly accurate and the estimated
2911                 * value for counters such as NR_FREE_PAGES can deviate from the
2912                 * true value by nr_online_cpus * threshold. To avoid the zone
2913                 * watermarks being breached while under pressure, we reduce the
2914                 * per-cpu vmstat threshold while kswapd is awake and restore
2915                 * them before going back to sleep.
2916                 */
2917                set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold);
2918
2919                /*
2920                 * Compaction records what page blocks it recently failed to
2921                 * isolate pages from and skips them in the future scanning.
2922                 * When kswapd is going to sleep, it is reasonable to assume
2923                 * that pages and compaction may succeed so reset the cache.
2924                 */
2925                reset_isolation_suitable(pgdat);
2926
2927                if (!kthread_should_stop())
2928                        schedule();
2929
2930                set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold);
2931        } else {
2932                if (remaining)
2933                        count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY);
2934                else
2935                        count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY);
2936        }
2937        finish_wait(&pgdat->kswapd_wait, &wait);
2938}
2939
2940/*
2941 * The background pageout daemon, started as a kernel thread
2942 * from the init process.
2943 *
2944 * This basically trickles out pages so that we have _some_
2945 * free memory available even if there is no other activity
2946 * that frees anything up. This is needed for things like routing
2947 * etc, where we otherwise might have all activity going on in
2948 * asynchronous contexts that cannot page things out.
2949 *
2950 * If there are applications that are active memory-allocators
2951 * (most normal use), this basically shouldn't matter.
2952 */
2953static int kswapd(void *p)
2954{
2955        unsigned long order, new_order;
2956        unsigned balanced_order;
2957        int classzone_idx, new_classzone_idx;
2958        int balanced_classzone_idx;
2959        pg_data_t *pgdat = (pg_data_t*)p;
2960        struct task_struct *tsk = current;
2961
2962        struct reclaim_state reclaim_state = {
2963                .reclaimed_slab = 0,
2964        };
2965        const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id);
2966
2967        lockdep_set_current_reclaim_state(GFP_KERNEL);
2968
2969        if (!cpumask_empty(cpumask))
2970                set_cpus_allowed_ptr(tsk, cpumask);
2971        current->reclaim_state = &reclaim_state;
2972
2973        /*
2974         * Tell the memory management that we're a "memory allocator",
2975         * and that if we need more memory we should get access to it
2976         * regardless (see "__alloc_pages()"). "kswapd" should
2977         * never get caught in the normal page freeing logic.
2978         *
2979         * (Kswapd normally doesn't need memory anyway, but sometimes
2980         * you need a small amount of memory in order to be able to
2981         * page out something else, and this flag essentially protects
2982         * us from recursively trying to free more memory as we're
2983         * trying to free the first piece of memory in the first place).
2984         */
2985        tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
2986        set_freezable();
2987
2988        order = new_order = 0;
2989        balanced_order = 0;
2990        classzone_idx = new_classzone_idx = pgdat->nr_zones - 1;
2991        balanced_classzone_idx = classzone_idx;
2992        for ( ; ; ) {
2993                bool ret;
2994
2995                /*
2996                 * If the last balance_pgdat was unsuccessful it's unlikely a
2997                 * new request of a similar or harder type will succeed soon
2998                 * so consider going to sleep on the basis we reclaimed at
2999                 */
3000                if (balanced_classzone_idx >= new_classzone_idx &&
3001                                        balanced_order == new_order) {
3002                        new_order = pgdat->kswapd_max_order;
3003                        new_classzone_idx = pgdat->classzone_idx;
3004                        pgdat->kswapd_max_order =  0;
3005                        pgdat->classzone_idx = pgdat->nr_zones - 1;
3006                }
3007
3008                if (order < new_order || classzone_idx > new_classzone_idx) {
3009                        /*
3010                         * Don't sleep if someone wants a larger 'order'
3011                         * allocation or has tigher zone constraints
3012                         */
3013                        order = new_order;
3014                        classzone_idx = new_classzone_idx;
3015                } else {
3016                        kswapd_try_to_sleep(pgdat, balanced_order,
3017                                                balanced_classzone_idx);
3018                        order = pgdat->kswapd_max_order;
3019                        classzone_idx = pgdat->classzone_idx;
3020                        new_order = order;
3021                        new_classzone_idx = classzone_idx;
3022                        pgdat->kswapd_max_order = 0;
3023                        pgdat->classzone_idx = pgdat->nr_zones - 1;
3024                }
3025
3026                ret = try_to_freeze();
3027                if (kthread_should_stop())
3028                        break;
3029
3030                /*
3031                 * We can speed up thawing tasks if we don't call balance_pgdat
3032                 * after returning from the refrigerator
3033                 */
3034                if (!ret) {
3035                        trace_mm_vmscan_kswapd_wake(pgdat->node_id, order);
3036                        balanced_classzone_idx = classzone_idx;
3037                        balanced_order = balance_pgdat(pgdat, order,
3038                                                &balanced_classzone_idx);
3039                }
3040        }
3041
3042        current->reclaim_state = NULL;
3043        return 0;
3044}
3045
3046/*
3047 * A zone is low on free memory, so wake its kswapd task to service it.
3048 */
3049void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
3050{
3051        pg_data_t *pgdat;
3052
3053        if (!populated_zone(zone))
3054                return;
3055
3056        if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
3057                return;
3058        pgdat = zone->zone_pgdat;
3059        if (pgdat->kswapd_max_order < order) {
3060                pgdat->kswapd_max_order = order;
3061                pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx);
3062        }
3063        if (!waitqueue_active(&pgdat->kswapd_wait))
3064                return;
3065        if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
3066                return;
3067
3068        trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
3069        wake_up_interruptible(&pgdat->kswapd_wait);
3070}
3071
3072/*
3073 * The reclaimable count would be mostly accurate.
3074 * The less reclaimable pages may be
3075 * - mlocked pages, which will be moved to unevictable list when encountered
3076 * - mapped pages, which may require several travels to be reclaimed
3077 * - dirty pages, which is not "instantly" reclaimable
3078 */
3079unsigned long global_reclaimable_pages(void)
3080{
3081        int nr;
3082
3083        nr = global_page_state(NR_ACTIVE_FILE) +
3084             global_page_state(NR_INACTIVE_FILE);
3085
3086        if (get_nr_swap_pages() > 0)
3087                nr += global_page_state(NR_ACTIVE_ANON) +
3088                      global_page_state(NR_INACTIVE_ANON);
3089
3090        return nr;
3091}
3092
3093unsigned long zone_reclaimable_pages(struct zone *zone)
3094{
3095        int nr;
3096
3097        nr = zone_page_state(zone, NR_ACTIVE_FILE) +
3098             zone_page_state(zone, NR_INACTIVE_FILE);
3099
3100        if (get_nr_swap_pages() > 0)
3101                nr += zone_page_state(zone, NR_ACTIVE_ANON) +
3102                      zone_page_state(zone, NR_INACTIVE_ANON);
3103
3104        return nr;
3105}
3106
3107#ifdef CONFIG_HIBERNATION
3108/*
3109 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of
3110 * freed pages.
3111 *
3112 * Rather than trying to age LRUs the aim is to preserve the overall
3113 * LRU order by reclaiming preferentially
3114 * inactive > active > active referenced > active mapped
3115 */
3116unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
3117{
3118        struct reclaim_state reclaim_state;
3119        struct scan_control sc = {
3120                .gfp_mask = GFP_HIGHUSER_MOVABLE,
3121                .may_swap = 1,
3122                .may_unmap = 1,
3123                .may_writepage = 1,
3124                .nr_to_reclaim = nr_to_reclaim,
3125                .hibernation_mode = 1,
3126                .order = 0,
3127                .priority = DEF_PRIORITY,
3128        };
3129        struct shrink_control shrink = {
3130                .gfp_mask = sc.gfp_mask,
3131        };
3132        struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
3133        struct task_struct *p = current;
3134        unsigned long nr_reclaimed;
3135
3136        p->flags |= PF_MEMALLOC;
3137        lockdep_set_current_reclaim_state(sc.gfp_mask);
3138        reclaim_state.reclaimed_slab = 0;
3139        p->reclaim_state = &reclaim_state;
3140
3141        nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
3142
3143        p->reclaim_state = NULL;
3144        lockdep_clear_current_reclaim_state();
3145        p->flags &= ~PF_MEMALLOC;
3146
3147        return nr_reclaimed;
3148}
3149#endif /* CONFIG_HIBERNATION */
3150
3151/* It's optimal to keep kswapds on the same CPUs as their memory, but
3152   not required for correctness.  So if the last cpu in a node goes
3153   away, we get changed to run anywhere: as the first one comes back,
3154   restore their cpu bindings. */
3155static int cpu_callback(struct notifier_block *nfb, unsigned long action,
3156                        void *hcpu)
3157{
3158        int nid;
3159
3160        if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) {
3161                for_each_node_state(nid, N_MEMORY) {
3162                        pg_data_t *pgdat = NODE_DATA(nid);
3163                        const struct cpumask *mask;
3164
3165                        mask = cpumask_of_node(pgdat->node_id);
3166
3167                        if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids)
3168                                /* One of our CPUs online: restore mask */
3169                                set_cpus_allowed_ptr(pgdat->kswapd, mask);
3170                }
3171        }
3172        return NOTIFY_OK;
3173}
3174
3175/*
3176 * This kswapd start function will be called by init and node-hot-add.
3177 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added.
3178 */
3179int kswapd_run(int nid)
3180{
3181        pg_data_t *pgdat = NODE_DATA(nid);
3182        int ret = 0;
3183
3184        if (pgdat->kswapd)
3185                return 0;
3186
3187        pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
3188        if (IS_ERR(pgdat->kswapd)) {
3189                /* failure at boot is fatal */
3190                BUG_ON(system_state == SYSTEM_BOOTING);
3191                pr_err("Failed to start kswapd on node %d\n", nid);
3192                ret = PTR_ERR(pgdat->kswapd);
3193                pgdat->kswapd = NULL;
3194        }
3195        return ret;
3196}
3197
3198/*
3199 * Called by memory hotplug when all memory in a node is offlined.  Caller must
3200 * hold lock_memory_hotplug().
3201 */
3202void kswapd_stop(int nid)
3203{
3204        struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
3205
3206        if (kswapd) {
3207                kthread_stop(kswapd);
3208                NODE_DATA(nid)->kswapd = NULL;
3209        }
3210}
3211
3212static int __init kswapd_init(void)
3213{
3214        int nid;
3215
3216        swap_setup();
3217        for_each_node_state(nid, N_MEMORY)
3218                kswapd_run(nid);
3219        hotcpu_notifier(cpu_callback, 0);
3220        return 0;
3221}
3222
3223module_init(kswapd_init)
3224
3225#ifdef CONFIG_NUMA
3226/*
3227 * Zone reclaim mode
3228 *
3229 * If non-zero call zone_reclaim when the number of free pages falls below
3230 * the watermarks.
3231 */
3232int zone_reclaim_mode __read_mostly;
3233
3234#define RECLAIM_OFF 0
3235#define RECLAIM_ZONE (1<<0)     /* Run shrink_inactive_list on the zone */
3236#define RECLAIM_WRITE (1<<1)    /* Writeout pages during reclaim */
3237#define RECLAIM_SWAP (1<<2)     /* Swap pages out during reclaim */
3238
3239/*
3240 * Priority for ZONE_RECLAIM. This determines the fraction of pages
3241 * of a node considered for each zone_reclaim. 4 scans 1/16th of
3242 * a zone.
3243 */
3244#define ZONE_RECLAIM_PRIORITY 4
3245
3246/*
3247 * Percentage of pages in a zone that must be unmapped for zone_reclaim to
3248 * occur.
3249 */
3250int sysctl_min_unmapped_ratio = 1;
3251
3252/*
3253 * If the number of slab pages in a zone grows beyond this percentage then
3254 * slab reclaim needs to occur.
3255 */
3256int sysctl_min_slab_ratio = 5;
3257
3258static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
3259{
3260        unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED);
3261        unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) +
3262                zone_page_state(zone, NR_ACTIVE_FILE);
3263
3264        /*
3265         * It's possible for there to be more file mapped pages than
3266         * accounted for by the pages on the file LRU lists because
3267         * tmpfs pages accounted for as ANON can also be FILE_MAPPED
3268         */
3269        return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0;
3270}
3271
3272/* Work out how many page cache pages we can reclaim in this reclaim_mode */
3273static long zone_pagecache_reclaimable(struct zone *zone)
3274{
3275        long nr_pagecache_reclaimable;
3276        long delta = 0;
3277
3278        /*
3279         * If RECLAIM_SWAP is set, then all file pages are considered
3280         * potentially reclaimable. Otherwise, we have to worry about
3281         * pages like swapcache and zone_unmapped_file_pages() provides
3282         * a better estimate
3283         */
3284        if (zone_reclaim_mode & RECLAIM_SWAP)
3285                nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
3286        else
3287                nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
3288
3289        /* If we can't clean pages, remove dirty pages from consideration */
3290        if (!(zone_reclaim_mode & RECLAIM_WRITE))
3291                delta += zone_page_state(zone, NR_FILE_DIRTY);
3292
3293        /* Watch for any possible underflows due to delta */
3294        if (unlikely(delta > nr_pagecache_reclaimable))
3295                delta = nr_pagecache_reclaimable;
3296
3297        return nr_pagecache_reclaimable - delta;
3298}
3299
3300/*
3301 * Try to free up some pages from this zone through reclaim.
3302 */
3303static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3304{
3305        /* Minimum pages needed in order to stay on node */
3306        const unsigned long nr_pages = 1 << order;
3307        struct task_struct *p = current;
3308        struct reclaim_state reclaim_state;
3309        struct scan_control sc = {
3310                .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
3311                .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
3312                .may_swap = 1,
3313                .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
3314                .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
3315                .order = order,
3316                .priority = ZONE_RECLAIM_PRIORITY,
3317        };
3318        struct shrink_control shrink = {
3319                .gfp_mask = sc.gfp_mask,
3320        };
3321        unsigned long nr_slab_pages0, nr_slab_pages1;
3322
3323        cond_resched();
3324        /*
3325         * We need to be able to allocate from the reserves for RECLAIM_SWAP
3326         * and we also need to be able to write out pages for RECLAIM_WRITE
3327         * and RECLAIM_SWAP.
3328         */
3329        p->flags |= PF_MEMALLOC | PF_SWAPWRITE;
3330        lockdep_set_current_reclaim_state(gfp_mask);
3331        reclaim_state.reclaimed_slab = 0;
3332        p->reclaim_state = &reclaim_state;
3333
3334        if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
3335                /*
3336                 * Free memory by calling shrink zone with increasing
3337                 * priorities until we have enough memory freed.
3338                 */
3339                do {
3340                        shrink_zone(zone, &sc);
3341                } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
3342        }
3343
3344        nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3345        if (nr_slab_pages0 > zone->min_slab_pages) {
3346                /*
3347                 * shrink_slab() does not currently allow us to determine how
3348                 * many pages were freed in this zone. So we take the current
3349                 * number of slab pages and shake the slab until it is reduced
3350                 * by the same nr_pages that we used for reclaiming unmapped
3351                 * pages.
3352                 *
3353                 * Note that shrink_slab will free memory on all zones and may
3354                 * take a long time.
3355                 */
3356                for (;;) {
3357                        unsigned long lru_pages = zone_reclaimable_pages(zone);
3358
3359                        /* No reclaimable slab or very low memory pressure */
3360                        if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages))
3361                                break;
3362
3363                        /* Freed enough memory */
3364                        nr_slab_pages1 = zone_page_state(zone,
3365                                                        NR_SLAB_RECLAIMABLE);
3366                        if (nr_slab_pages1 + nr_pages <= nr_slab_pages0)
3367                                break;
3368                }
3369
3370                /*
3371                 * Update nr_reclaimed by the number of slab pages we
3372                 * reclaimed from this zone.
3373                 */
3374                nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
3375                if (nr_slab_pages1 < nr_slab_pages0)
3376                        sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1;
3377        }
3378
3379        p->reclaim_state = NULL;
3380        current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE);
3381        lockdep_clear_current_reclaim_state();
3382        return sc.nr_reclaimed >= nr_pages;
3383}
3384
3385int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
3386{
3387        int node_id;
3388        int ret;
3389
3390        /*
3391         * Zone reclaim reclaims unmapped file backed pages and
3392         * slab pages if we are over the defined limits.
3393         *
3394         * A small portion of unmapped file backed pages is needed for
3395         * file I/O otherwise pages read by file I/O will be immediately
3396         * thrown out if the zone is overallocated. So we do not reclaim
3397         * if less than a specified percentage of the zone is used by
3398         * unmapped file backed pages.
3399         */
3400        if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
3401            zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
3402                return ZONE_RECLAIM_FULL;
3403
3404        if (zone->all_unreclaimable)
3405                return ZONE_RECLAIM_FULL;
3406
3407        /*
3408         * Do not scan if the allocation should not be delayed.
3409         */
3410        if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC))
3411                return ZONE_RECLAIM_NOSCAN;
3412
3413        /*
3414         * Only run zone reclaim on the local zone or on zones that do not
3415         * have associated processors. This will favor the local processor
3416         * over remote processors and spread off node memory allocations
3417         * as wide as possible.
3418         */
3419        node_id = zone_to_nid(zone);
3420        if (node_state(node_id, N_CPU) && node_id != numa_node_id())
3421                return ZONE_RECLAIM_NOSCAN;
3422
3423        if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED))
3424                return ZONE_RECLAIM_NOSCAN;
3425
3426        ret = __zone_reclaim(zone, gfp_mask, order);
3427        zone_clear_flag(zone, ZONE_RECLAIM_LOCKED);
3428
3429        if (!ret)
3430                count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED);
3431
3432        return ret;
3433}
3434#endif
3435
3436/*
3437 * page_evictable - test whether a page is evictable
3438 * @page: the page to test
3439 *
3440 * Test whether page is evictable--i.e., should be placed on active/inactive
3441 * lists vs unevictable list.
3442 *
3443 * Reasons page might not be evictable:
3444 * (1) page's mapping marked unevictable
3445 * (2) page is part of an mlocked VMA
3446 *
3447 */
3448int page_evictable(struct page *page)
3449{
3450        return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page);
3451}
3452
3453#ifdef CONFIG_SHMEM
3454/**
3455 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list
3456 * @pages:      array of pages to check
3457 * @nr_pages:   number of pages to check
3458 *
3459 * Checks pages for evictability and moves them to the appropriate lru list.
3460 *
3461 * This function is only used for SysV IPC SHM_UNLOCK.
3462 */
3463void check_move_unevictable_pages(struct page **pages, int nr_pages)
3464{
3465        struct lruvec *lruvec;
3466        struct zone *zone = NULL;
3467        int pgscanned = 0;
3468        int pgrescued = 0;
3469        int i;
3470
3471        for (i = 0; i < nr_pages; i++) {
3472                struct page *page = pages[i];
3473                struct zone *pagezone;
3474
3475                pgscanned++;
3476                pagezone = page_zone(page);
3477                if (pagezone != zone) {
3478                        if (zone)
3479                                spin_unlock_irq(&zone->lru_lock);
3480                        zone = pagezone;
3481                        spin_lock_irq(&zone->lru_lock);
3482                }
3483                lruvec = mem_cgroup_page_lruvec(page, zone);
3484
3485                if (!PageLRU(page) || !PageUnevictable(page))
3486                        continue;
3487
3488                if (page_evictable(page)) {
3489                        enum lru_list lru = page_lru_base_type(page);
3490
3491                        VM_BUG_ON(PageActive(page));
3492                        ClearPageUnevictable(page);
3493                        del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE);
3494                        add_page_to_lru_list(page, lruvec, lru);
3495                        pgrescued++;
3496                }
3497        }
3498
3499        if (zone) {
3500                __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued);
3501                __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned);
3502                spin_unlock_irq(&zone->lru_lock);
3503        }
3504}
3505#endif /* CONFIG_SHMEM */
3506
3507static void warn_scan_unevictable_pages(void)
3508{
3509        printk_once(KERN_WARNING
3510                    "%s: The scan_unevictable_pages sysctl/node-interface has been "
3511                    "disabled for lack of a legitimate use case.  If you have "
3512                    "one, please send an email to linux-mm@kvack.org.\n",
3513                    current->comm);
3514}
3515
3516/*
3517 * scan_unevictable_pages [vm] sysctl handler.  On demand re-scan of
3518 * all nodes' unevictable lists for evictable pages
3519 */
3520unsigned long scan_unevictable_pages;
3521
3522int scan_unevictable_handler(struct ctl_table *table, int write,
3523                           void __user *buffer,
3524                           size_t *length, loff_t *ppos)
3525{
3526        warn_scan_unevictable_pages();
3527        proc_doulongvec_minmax(table, write, buffer, length, ppos);
3528        scan_unevictable_pages = 0;
3529        return 0;
3530}
3531
3532#ifdef CONFIG_NUMA
3533/*
3534 * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
3535 * a specified node's per zone unevictable lists for evictable pages.
3536 */
3537
3538static ssize_t read_scan_unevictable_node(struct device *dev,
3539                                          struct device_attribute *attr,
3540                                          char *buf)
3541{
3542        warn_scan_unevictable_pages();
3543        return sprintf(buf, "0\n");     /* always zero; should fit... */
3544}
3545
3546static ssize_t write_scan_unevictable_node(struct device *dev,
3547                                           struct device_attribute *attr,
3548                                        const char *buf, size_t count)
3549{
3550        warn_scan_unevictable_pages();
3551        return 1;
3552}
3553
3554
3555static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR,
3556                        read_scan_unevictable_node,
3557                        write_scan_unevictable_node);
3558
3559int scan_unevictable_register_node(struct node *node)
3560{
3561        return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages);
3562}
3563
3564void scan_unevictable_unregister_node(struct node *node)
3565{
3566        device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages);
3567}
3568#endif
3569
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