vmscan.c revision 08951e545918c1594434d000d88a7793e2452a9b
1/* 2 * linux/mm/vmscan.c 3 * 4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds 5 * 6 * Swap reorganised 29.12.95, Stephen Tweedie. 7 * kswapd added: 7.1.96 sct 8 * Removed kswapd_ctl limits, and swap out as many pages as needed 9 * to bring the system back to freepages.high: 2.4.97, Rik van Riel. 10 * Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com). 11 * Multiqueue VM started 5.8.00, Rik van Riel. 12 */ 13 14#include <linux/mm.h> 15#include <linux/module.h> 16#include <linux/gfp.h> 17#include <linux/kernel_stat.h> 18#include <linux/swap.h> 19#include <linux/pagemap.h> 20#include <linux/init.h> 21#include <linux/highmem.h> 22#include <linux/vmstat.h> 23#include <linux/file.h> 24#include <linux/writeback.h> 25#include <linux/blkdev.h> 26#include <linux/buffer_head.h> /* for try_to_release_page(), 27 buffer_heads_over_limit */ 28#include <linux/mm_inline.h> 29#include <linux/pagevec.h> 30#include <linux/backing-dev.h> 31#include <linux/rmap.h> 32#include <linux/topology.h> 33#include <linux/cpu.h> 34#include <linux/cpuset.h> 35#include <linux/compaction.h> 36#include <linux/notifier.h> 37#include <linux/rwsem.h> 38#include <linux/delay.h> 39#include <linux/kthread.h> 40#include <linux/freezer.h> 41#include <linux/memcontrol.h> 42#include <linux/delayacct.h> 43#include <linux/sysctl.h> 44#include <linux/oom.h> 45#include <linux/prefetch.h> 46 47#include <asm/tlbflush.h> 48#include <asm/div64.h> 49 50#include <linux/swapops.h> 51 52#include "internal.h" 53 54#define CREATE_TRACE_POINTS 55#include <trace/events/vmscan.h> 56 57/* 58 * reclaim_mode determines how the inactive list is shrunk 59 * RECLAIM_MODE_SINGLE: Reclaim only order-0 pages 60 * RECLAIM_MODE_ASYNC: Do not block 61 * RECLAIM_MODE_SYNC: Allow blocking e.g. call wait_on_page_writeback 62 * RECLAIM_MODE_LUMPYRECLAIM: For high-order allocations, take a reference 63 * page from the LRU and reclaim all pages within a 64 * naturally aligned range 65 * RECLAIM_MODE_COMPACTION: For high-order allocations, reclaim a number of 66 * order-0 pages and then compact the zone 67 */ 68typedef unsigned __bitwise__ reclaim_mode_t; 69#define RECLAIM_MODE_SINGLE ((__force reclaim_mode_t)0x01u) 70#define RECLAIM_MODE_ASYNC ((__force reclaim_mode_t)0x02u) 71#define RECLAIM_MODE_SYNC ((__force reclaim_mode_t)0x04u) 72#define RECLAIM_MODE_LUMPYRECLAIM ((__force reclaim_mode_t)0x08u) 73#define RECLAIM_MODE_COMPACTION ((__force reclaim_mode_t)0x10u) 74 75struct scan_control { 76 /* Incremented by the number of inactive pages that were scanned */ 77 unsigned long nr_scanned; 78 79 /* Number of pages freed so far during a call to shrink_zones() */ 80 unsigned long nr_reclaimed; 81 82 /* How many pages shrink_list() should reclaim */ 83 unsigned long nr_to_reclaim; 84 85 unsigned long hibernation_mode; 86 87 /* This context's GFP mask */ 88 gfp_t gfp_mask; 89 90 int may_writepage; 91 92 /* Can mapped pages be reclaimed? */ 93 int may_unmap; 94 95 /* Can pages be swapped as part of reclaim? */ 96 int may_swap; 97 98 int swappiness; 99 100 int order; 101 102 /* 103 * Intend to reclaim enough continuous memory rather than reclaim 104 * enough amount of memory. i.e, mode for high order allocation. 105 */ 106 reclaim_mode_t reclaim_mode; 107 108 /* Which cgroup do we reclaim from */ 109 struct mem_cgroup *mem_cgroup; 110 111 /* 112 * Nodemask of nodes allowed by the caller. If NULL, all nodes 113 * are scanned. 114 */ 115 nodemask_t *nodemask; 116}; 117 118#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru)) 119 120#ifdef ARCH_HAS_PREFETCH 121#define prefetch_prev_lru_page(_page, _base, _field) \ 122 do { \ 123 if ((_page)->lru.prev != _base) { \ 124 struct page *prev; \ 125 \ 126 prev = lru_to_page(&(_page->lru)); \ 127 prefetch(&prev->_field); \ 128 } \ 129 } while (0) 130#else 131#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0) 132#endif 133 134#ifdef ARCH_HAS_PREFETCHW 135#define prefetchw_prev_lru_page(_page, _base, _field) \ 136 do { \ 137 if ((_page)->lru.prev != _base) { \ 138 struct page *prev; \ 139 \ 140 prev = lru_to_page(&(_page->lru)); \ 141 prefetchw(&prev->_field); \ 142 } \ 143 } while (0) 144#else 145#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0) 146#endif 147 148/* 149 * From 0 .. 100. Higher means more swappy. 150 */ 151int vm_swappiness = 60; 152long vm_total_pages; /* The total number of pages which the VM controls */ 153 154static LIST_HEAD(shrinker_list); 155static DECLARE_RWSEM(shrinker_rwsem); 156 157#ifdef CONFIG_CGROUP_MEM_RES_CTLR 158#define scanning_global_lru(sc) (!(sc)->mem_cgroup) 159#else 160#define scanning_global_lru(sc) (1) 161#endif 162 163static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone, 164 struct scan_control *sc) 165{ 166 if (!scanning_global_lru(sc)) 167 return mem_cgroup_get_reclaim_stat(sc->mem_cgroup, zone); 168 169 return &zone->reclaim_stat; 170} 171 172static unsigned long zone_nr_lru_pages(struct zone *zone, 173 struct scan_control *sc, enum lru_list lru) 174{ 175 if (!scanning_global_lru(sc)) 176 return mem_cgroup_zone_nr_lru_pages(sc->mem_cgroup, zone, lru); 177 178 return zone_page_state(zone, NR_LRU_BASE + lru); 179} 180 181 182/* 183 * Add a shrinker callback to be called from the vm 184 */ 185void register_shrinker(struct shrinker *shrinker) 186{ 187 shrinker->nr = 0; 188 down_write(&shrinker_rwsem); 189 list_add_tail(&shrinker->list, &shrinker_list); 190 up_write(&shrinker_rwsem); 191} 192EXPORT_SYMBOL(register_shrinker); 193 194/* 195 * Remove one 196 */ 197void unregister_shrinker(struct shrinker *shrinker) 198{ 199 down_write(&shrinker_rwsem); 200 list_del(&shrinker->list); 201 up_write(&shrinker_rwsem); 202} 203EXPORT_SYMBOL(unregister_shrinker); 204 205static inline int do_shrinker_shrink(struct shrinker *shrinker, 206 struct shrink_control *sc, 207 unsigned long nr_to_scan) 208{ 209 sc->nr_to_scan = nr_to_scan; 210 return (*shrinker->shrink)(shrinker, sc); 211} 212 213#define SHRINK_BATCH 128 214/* 215 * Call the shrink functions to age shrinkable caches 216 * 217 * Here we assume it costs one seek to replace a lru page and that it also 218 * takes a seek to recreate a cache object. With this in mind we age equal 219 * percentages of the lru and ageable caches. This should balance the seeks 220 * generated by these structures. 221 * 222 * If the vm encountered mapped pages on the LRU it increase the pressure on 223 * slab to avoid swapping. 224 * 225 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits. 226 * 227 * `lru_pages' represents the number of on-LRU pages in all the zones which 228 * are eligible for the caller's allocation attempt. It is used for balancing 229 * slab reclaim versus page reclaim. 230 * 231 * Returns the number of slab objects which we shrunk. 232 */ 233unsigned long shrink_slab(struct shrink_control *shrink, 234 unsigned long nr_pages_scanned, 235 unsigned long lru_pages) 236{ 237 struct shrinker *shrinker; 238 unsigned long ret = 0; 239 240 if (nr_pages_scanned == 0) 241 nr_pages_scanned = SWAP_CLUSTER_MAX; 242 243 if (!down_read_trylock(&shrinker_rwsem)) { 244 /* Assume we'll be able to shrink next time */ 245 ret = 1; 246 goto out; 247 } 248 249 list_for_each_entry(shrinker, &shrinker_list, list) { 250 unsigned long long delta; 251 unsigned long total_scan; 252 unsigned long max_pass; 253 254 max_pass = do_shrinker_shrink(shrinker, shrink, 0); 255 delta = (4 * nr_pages_scanned) / shrinker->seeks; 256 delta *= max_pass; 257 do_div(delta, lru_pages + 1); 258 shrinker->nr += delta; 259 if (shrinker->nr < 0) { 260 printk(KERN_ERR "shrink_slab: %pF negative objects to " 261 "delete nr=%ld\n", 262 shrinker->shrink, shrinker->nr); 263 shrinker->nr = max_pass; 264 } 265 266 /* 267 * Avoid risking looping forever due to too large nr value: 268 * never try to free more than twice the estimate number of 269 * freeable entries. 270 */ 271 if (shrinker->nr > max_pass * 2) 272 shrinker->nr = max_pass * 2; 273 274 total_scan = shrinker->nr; 275 shrinker->nr = 0; 276 277 while (total_scan >= SHRINK_BATCH) { 278 long this_scan = SHRINK_BATCH; 279 int shrink_ret; 280 int nr_before; 281 282 nr_before = do_shrinker_shrink(shrinker, shrink, 0); 283 shrink_ret = do_shrinker_shrink(shrinker, shrink, 284 this_scan); 285 if (shrink_ret == -1) 286 break; 287 if (shrink_ret < nr_before) 288 ret += nr_before - shrink_ret; 289 count_vm_events(SLABS_SCANNED, this_scan); 290 total_scan -= this_scan; 291 292 cond_resched(); 293 } 294 295 shrinker->nr += total_scan; 296 } 297 up_read(&shrinker_rwsem); 298out: 299 cond_resched(); 300 return ret; 301} 302 303static void set_reclaim_mode(int priority, struct scan_control *sc, 304 bool sync) 305{ 306 reclaim_mode_t syncmode = sync ? RECLAIM_MODE_SYNC : RECLAIM_MODE_ASYNC; 307 308 /* 309 * Initially assume we are entering either lumpy reclaim or 310 * reclaim/compaction.Depending on the order, we will either set the 311 * sync mode or just reclaim order-0 pages later. 312 */ 313 if (COMPACTION_BUILD) 314 sc->reclaim_mode = RECLAIM_MODE_COMPACTION; 315 else 316 sc->reclaim_mode = RECLAIM_MODE_LUMPYRECLAIM; 317 318 /* 319 * Avoid using lumpy reclaim or reclaim/compaction if possible by 320 * restricting when its set to either costly allocations or when 321 * under memory pressure 322 */ 323 if (sc->order > PAGE_ALLOC_COSTLY_ORDER) 324 sc->reclaim_mode |= syncmode; 325 else if (sc->order && priority < DEF_PRIORITY - 2) 326 sc->reclaim_mode |= syncmode; 327 else 328 sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC; 329} 330 331static void reset_reclaim_mode(struct scan_control *sc) 332{ 333 sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC; 334} 335 336static inline int is_page_cache_freeable(struct page *page) 337{ 338 /* 339 * A freeable page cache page is referenced only by the caller 340 * that isolated the page, the page cache radix tree and 341 * optional buffer heads at page->private. 342 */ 343 return page_count(page) - page_has_private(page) == 2; 344} 345 346static int may_write_to_queue(struct backing_dev_info *bdi, 347 struct scan_control *sc) 348{ 349 if (current->flags & PF_SWAPWRITE) 350 return 1; 351 if (!bdi_write_congested(bdi)) 352 return 1; 353 if (bdi == current->backing_dev_info) 354 return 1; 355 356 /* lumpy reclaim for hugepage often need a lot of write */ 357 if (sc->order > PAGE_ALLOC_COSTLY_ORDER) 358 return 1; 359 return 0; 360} 361 362/* 363 * We detected a synchronous write error writing a page out. Probably 364 * -ENOSPC. We need to propagate that into the address_space for a subsequent 365 * fsync(), msync() or close(). 366 * 367 * The tricky part is that after writepage we cannot touch the mapping: nothing 368 * prevents it from being freed up. But we have a ref on the page and once 369 * that page is locked, the mapping is pinned. 370 * 371 * We're allowed to run sleeping lock_page() here because we know the caller has 372 * __GFP_FS. 373 */ 374static void handle_write_error(struct address_space *mapping, 375 struct page *page, int error) 376{ 377 lock_page(page); 378 if (page_mapping(page) == mapping) 379 mapping_set_error(mapping, error); 380 unlock_page(page); 381} 382 383/* possible outcome of pageout() */ 384typedef enum { 385 /* failed to write page out, page is locked */ 386 PAGE_KEEP, 387 /* move page to the active list, page is locked */ 388 PAGE_ACTIVATE, 389 /* page has been sent to the disk successfully, page is unlocked */ 390 PAGE_SUCCESS, 391 /* page is clean and locked */ 392 PAGE_CLEAN, 393} pageout_t; 394 395/* 396 * pageout is called by shrink_page_list() for each dirty page. 397 * Calls ->writepage(). 398 */ 399static pageout_t pageout(struct page *page, struct address_space *mapping, 400 struct scan_control *sc) 401{ 402 /* 403 * If the page is dirty, only perform writeback if that write 404 * will be non-blocking. To prevent this allocation from being 405 * stalled by pagecache activity. But note that there may be 406 * stalls if we need to run get_block(). We could test 407 * PagePrivate for that. 408 * 409 * If this process is currently in __generic_file_aio_write() against 410 * this page's queue, we can perform writeback even if that 411 * will block. 412 * 413 * If the page is swapcache, write it back even if that would 414 * block, for some throttling. This happens by accident, because 415 * swap_backing_dev_info is bust: it doesn't reflect the 416 * congestion state of the swapdevs. Easy to fix, if needed. 417 */ 418 if (!is_page_cache_freeable(page)) 419 return PAGE_KEEP; 420 if (!mapping) { 421 /* 422 * Some data journaling orphaned pages can have 423 * page->mapping == NULL while being dirty with clean buffers. 424 */ 425 if (page_has_private(page)) { 426 if (try_to_free_buffers(page)) { 427 ClearPageDirty(page); 428 printk("%s: orphaned page\n", __func__); 429 return PAGE_CLEAN; 430 } 431 } 432 return PAGE_KEEP; 433 } 434 if (mapping->a_ops->writepage == NULL) 435 return PAGE_ACTIVATE; 436 if (!may_write_to_queue(mapping->backing_dev_info, sc)) 437 return PAGE_KEEP; 438 439 if (clear_page_dirty_for_io(page)) { 440 int res; 441 struct writeback_control wbc = { 442 .sync_mode = WB_SYNC_NONE, 443 .nr_to_write = SWAP_CLUSTER_MAX, 444 .range_start = 0, 445 .range_end = LLONG_MAX, 446 .for_reclaim = 1, 447 }; 448 449 SetPageReclaim(page); 450 res = mapping->a_ops->writepage(page, &wbc); 451 if (res < 0) 452 handle_write_error(mapping, page, res); 453 if (res == AOP_WRITEPAGE_ACTIVATE) { 454 ClearPageReclaim(page); 455 return PAGE_ACTIVATE; 456 } 457 458 /* 459 * Wait on writeback if requested to. This happens when 460 * direct reclaiming a large contiguous area and the 461 * first attempt to free a range of pages fails. 462 */ 463 if (PageWriteback(page) && 464 (sc->reclaim_mode & RECLAIM_MODE_SYNC)) 465 wait_on_page_writeback(page); 466 467 if (!PageWriteback(page)) { 468 /* synchronous write or broken a_ops? */ 469 ClearPageReclaim(page); 470 } 471 trace_mm_vmscan_writepage(page, 472 trace_reclaim_flags(page, sc->reclaim_mode)); 473 inc_zone_page_state(page, NR_VMSCAN_WRITE); 474 return PAGE_SUCCESS; 475 } 476 477 return PAGE_CLEAN; 478} 479 480/* 481 * Same as remove_mapping, but if the page is removed from the mapping, it 482 * gets returned with a refcount of 0. 483 */ 484static int __remove_mapping(struct address_space *mapping, struct page *page) 485{ 486 BUG_ON(!PageLocked(page)); 487 BUG_ON(mapping != page_mapping(page)); 488 489 spin_lock_irq(&mapping->tree_lock); 490 /* 491 * The non racy check for a busy page. 492 * 493 * Must be careful with the order of the tests. When someone has 494 * a ref to the page, it may be possible that they dirty it then 495 * drop the reference. So if PageDirty is tested before page_count 496 * here, then the following race may occur: 497 * 498 * get_user_pages(&page); 499 * [user mapping goes away] 500 * write_to(page); 501 * !PageDirty(page) [good] 502 * SetPageDirty(page); 503 * put_page(page); 504 * !page_count(page) [good, discard it] 505 * 506 * [oops, our write_to data is lost] 507 * 508 * Reversing the order of the tests ensures such a situation cannot 509 * escape unnoticed. The smp_rmb is needed to ensure the page->flags 510 * load is not satisfied before that of page->_count. 511 * 512 * Note that if SetPageDirty is always performed via set_page_dirty, 513 * and thus under tree_lock, then this ordering is not required. 514 */ 515 if (!page_freeze_refs(page, 2)) 516 goto cannot_free; 517 /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */ 518 if (unlikely(PageDirty(page))) { 519 page_unfreeze_refs(page, 2); 520 goto cannot_free; 521 } 522 523 if (PageSwapCache(page)) { 524 swp_entry_t swap = { .val = page_private(page) }; 525 __delete_from_swap_cache(page); 526 spin_unlock_irq(&mapping->tree_lock); 527 swapcache_free(swap, page); 528 } else { 529 void (*freepage)(struct page *); 530 531 freepage = mapping->a_ops->freepage; 532 533 __delete_from_page_cache(page); 534 spin_unlock_irq(&mapping->tree_lock); 535 mem_cgroup_uncharge_cache_page(page); 536 537 if (freepage != NULL) 538 freepage(page); 539 } 540 541 return 1; 542 543cannot_free: 544 spin_unlock_irq(&mapping->tree_lock); 545 return 0; 546} 547 548/* 549 * Attempt to detach a locked page from its ->mapping. If it is dirty or if 550 * someone else has a ref on the page, abort and return 0. If it was 551 * successfully detached, return 1. Assumes the caller has a single ref on 552 * this page. 553 */ 554int remove_mapping(struct address_space *mapping, struct page *page) 555{ 556 if (__remove_mapping(mapping, page)) { 557 /* 558 * Unfreezing the refcount with 1 rather than 2 effectively 559 * drops the pagecache ref for us without requiring another 560 * atomic operation. 561 */ 562 page_unfreeze_refs(page, 1); 563 return 1; 564 } 565 return 0; 566} 567 568/** 569 * putback_lru_page - put previously isolated page onto appropriate LRU list 570 * @page: page to be put back to appropriate lru list 571 * 572 * Add previously isolated @page to appropriate LRU list. 573 * Page may still be unevictable for other reasons. 574 * 575 * lru_lock must not be held, interrupts must be enabled. 576 */ 577void putback_lru_page(struct page *page) 578{ 579 int lru; 580 int active = !!TestClearPageActive(page); 581 int was_unevictable = PageUnevictable(page); 582 583 VM_BUG_ON(PageLRU(page)); 584 585redo: 586 ClearPageUnevictable(page); 587 588 if (page_evictable(page, NULL)) { 589 /* 590 * For evictable pages, we can use the cache. 591 * In event of a race, worst case is we end up with an 592 * unevictable page on [in]active list. 593 * We know how to handle that. 594 */ 595 lru = active + page_lru_base_type(page); 596 lru_cache_add_lru(page, lru); 597 } else { 598 /* 599 * Put unevictable pages directly on zone's unevictable 600 * list. 601 */ 602 lru = LRU_UNEVICTABLE; 603 add_page_to_unevictable_list(page); 604 /* 605 * When racing with an mlock clearing (page is 606 * unlocked), make sure that if the other thread does 607 * not observe our setting of PG_lru and fails 608 * isolation, we see PG_mlocked cleared below and move 609 * the page back to the evictable list. 610 * 611 * The other side is TestClearPageMlocked(). 612 */ 613 smp_mb(); 614 } 615 616 /* 617 * page's status can change while we move it among lru. If an evictable 618 * page is on unevictable list, it never be freed. To avoid that, 619 * check after we added it to the list, again. 620 */ 621 if (lru == LRU_UNEVICTABLE && page_evictable(page, NULL)) { 622 if (!isolate_lru_page(page)) { 623 put_page(page); 624 goto redo; 625 } 626 /* This means someone else dropped this page from LRU 627 * So, it will be freed or putback to LRU again. There is 628 * nothing to do here. 629 */ 630 } 631 632 if (was_unevictable && lru != LRU_UNEVICTABLE) 633 count_vm_event(UNEVICTABLE_PGRESCUED); 634 else if (!was_unevictable && lru == LRU_UNEVICTABLE) 635 count_vm_event(UNEVICTABLE_PGCULLED); 636 637 put_page(page); /* drop ref from isolate */ 638} 639 640enum page_references { 641 PAGEREF_RECLAIM, 642 PAGEREF_RECLAIM_CLEAN, 643 PAGEREF_KEEP, 644 PAGEREF_ACTIVATE, 645}; 646 647static enum page_references page_check_references(struct page *page, 648 struct scan_control *sc) 649{ 650 int referenced_ptes, referenced_page; 651 unsigned long vm_flags; 652 653 referenced_ptes = page_referenced(page, 1, sc->mem_cgroup, &vm_flags); 654 referenced_page = TestClearPageReferenced(page); 655 656 /* Lumpy reclaim - ignore references */ 657 if (sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM) 658 return PAGEREF_RECLAIM; 659 660 /* 661 * Mlock lost the isolation race with us. Let try_to_unmap() 662 * move the page to the unevictable list. 663 */ 664 if (vm_flags & VM_LOCKED) 665 return PAGEREF_RECLAIM; 666 667 if (referenced_ptes) { 668 if (PageAnon(page)) 669 return PAGEREF_ACTIVATE; 670 /* 671 * All mapped pages start out with page table 672 * references from the instantiating fault, so we need 673 * to look twice if a mapped file page is used more 674 * than once. 675 * 676 * Mark it and spare it for another trip around the 677 * inactive list. Another page table reference will 678 * lead to its activation. 679 * 680 * Note: the mark is set for activated pages as well 681 * so that recently deactivated but used pages are 682 * quickly recovered. 683 */ 684 SetPageReferenced(page); 685 686 if (referenced_page) 687 return PAGEREF_ACTIVATE; 688 689 return PAGEREF_KEEP; 690 } 691 692 /* Reclaim if clean, defer dirty pages to writeback */ 693 if (referenced_page && !PageSwapBacked(page)) 694 return PAGEREF_RECLAIM_CLEAN; 695 696 return PAGEREF_RECLAIM; 697} 698 699static noinline_for_stack void free_page_list(struct list_head *free_pages) 700{ 701 struct pagevec freed_pvec; 702 struct page *page, *tmp; 703 704 pagevec_init(&freed_pvec, 1); 705 706 list_for_each_entry_safe(page, tmp, free_pages, lru) { 707 list_del(&page->lru); 708 if (!pagevec_add(&freed_pvec, page)) { 709 __pagevec_free(&freed_pvec); 710 pagevec_reinit(&freed_pvec); 711 } 712 } 713 714 pagevec_free(&freed_pvec); 715} 716 717/* 718 * shrink_page_list() returns the number of reclaimed pages 719 */ 720static unsigned long shrink_page_list(struct list_head *page_list, 721 struct zone *zone, 722 struct scan_control *sc) 723{ 724 LIST_HEAD(ret_pages); 725 LIST_HEAD(free_pages); 726 int pgactivate = 0; 727 unsigned long nr_dirty = 0; 728 unsigned long nr_congested = 0; 729 unsigned long nr_reclaimed = 0; 730 731 cond_resched(); 732 733 while (!list_empty(page_list)) { 734 enum page_references references; 735 struct address_space *mapping; 736 struct page *page; 737 int may_enter_fs; 738 739 cond_resched(); 740 741 page = lru_to_page(page_list); 742 list_del(&page->lru); 743 744 if (!trylock_page(page)) 745 goto keep; 746 747 VM_BUG_ON(PageActive(page)); 748 VM_BUG_ON(page_zone(page) != zone); 749 750 sc->nr_scanned++; 751 752 if (unlikely(!page_evictable(page, NULL))) 753 goto cull_mlocked; 754 755 if (!sc->may_unmap && page_mapped(page)) 756 goto keep_locked; 757 758 /* Double the slab pressure for mapped and swapcache pages */ 759 if (page_mapped(page) || PageSwapCache(page)) 760 sc->nr_scanned++; 761 762 may_enter_fs = (sc->gfp_mask & __GFP_FS) || 763 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); 764 765 if (PageWriteback(page)) { 766 /* 767 * Synchronous reclaim is performed in two passes, 768 * first an asynchronous pass over the list to 769 * start parallel writeback, and a second synchronous 770 * pass to wait for the IO to complete. Wait here 771 * for any page for which writeback has already 772 * started. 773 */ 774 if ((sc->reclaim_mode & RECLAIM_MODE_SYNC) && 775 may_enter_fs) 776 wait_on_page_writeback(page); 777 else { 778 unlock_page(page); 779 goto keep_lumpy; 780 } 781 } 782 783 references = page_check_references(page, sc); 784 switch (references) { 785 case PAGEREF_ACTIVATE: 786 goto activate_locked; 787 case PAGEREF_KEEP: 788 goto keep_locked; 789 case PAGEREF_RECLAIM: 790 case PAGEREF_RECLAIM_CLEAN: 791 ; /* try to reclaim the page below */ 792 } 793 794 /* 795 * Anonymous process memory has backing store? 796 * Try to allocate it some swap space here. 797 */ 798 if (PageAnon(page) && !PageSwapCache(page)) { 799 if (!(sc->gfp_mask & __GFP_IO)) 800 goto keep_locked; 801 if (!add_to_swap(page)) 802 goto activate_locked; 803 may_enter_fs = 1; 804 } 805 806 mapping = page_mapping(page); 807 808 /* 809 * The page is mapped into the page tables of one or more 810 * processes. Try to unmap it here. 811 */ 812 if (page_mapped(page) && mapping) { 813 switch (try_to_unmap(page, TTU_UNMAP)) { 814 case SWAP_FAIL: 815 goto activate_locked; 816 case SWAP_AGAIN: 817 goto keep_locked; 818 case SWAP_MLOCK: 819 goto cull_mlocked; 820 case SWAP_SUCCESS: 821 ; /* try to free the page below */ 822 } 823 } 824 825 if (PageDirty(page)) { 826 nr_dirty++; 827 828 if (references == PAGEREF_RECLAIM_CLEAN) 829 goto keep_locked; 830 if (!may_enter_fs) 831 goto keep_locked; 832 if (!sc->may_writepage) 833 goto keep_locked; 834 835 /* Page is dirty, try to write it out here */ 836 switch (pageout(page, mapping, sc)) { 837 case PAGE_KEEP: 838 nr_congested++; 839 goto keep_locked; 840 case PAGE_ACTIVATE: 841 goto activate_locked; 842 case PAGE_SUCCESS: 843 if (PageWriteback(page)) 844 goto keep_lumpy; 845 if (PageDirty(page)) 846 goto keep; 847 848 /* 849 * A synchronous write - probably a ramdisk. Go 850 * ahead and try to reclaim the page. 851 */ 852 if (!trylock_page(page)) 853 goto keep; 854 if (PageDirty(page) || PageWriteback(page)) 855 goto keep_locked; 856 mapping = page_mapping(page); 857 case PAGE_CLEAN: 858 ; /* try to free the page below */ 859 } 860 } 861 862 /* 863 * If the page has buffers, try to free the buffer mappings 864 * associated with this page. If we succeed we try to free 865 * the page as well. 866 * 867 * We do this even if the page is PageDirty(). 868 * try_to_release_page() does not perform I/O, but it is 869 * possible for a page to have PageDirty set, but it is actually 870 * clean (all its buffers are clean). This happens if the 871 * buffers were written out directly, with submit_bh(). ext3 872 * will do this, as well as the blockdev mapping. 873 * try_to_release_page() will discover that cleanness and will 874 * drop the buffers and mark the page clean - it can be freed. 875 * 876 * Rarely, pages can have buffers and no ->mapping. These are 877 * the pages which were not successfully invalidated in 878 * truncate_complete_page(). We try to drop those buffers here 879 * and if that worked, and the page is no longer mapped into 880 * process address space (page_count == 1) it can be freed. 881 * Otherwise, leave the page on the LRU so it is swappable. 882 */ 883 if (page_has_private(page)) { 884 if (!try_to_release_page(page, sc->gfp_mask)) 885 goto activate_locked; 886 if (!mapping && page_count(page) == 1) { 887 unlock_page(page); 888 if (put_page_testzero(page)) 889 goto free_it; 890 else { 891 /* 892 * rare race with speculative reference. 893 * the speculative reference will free 894 * this page shortly, so we may 895 * increment nr_reclaimed here (and 896 * leave it off the LRU). 897 */ 898 nr_reclaimed++; 899 continue; 900 } 901 } 902 } 903 904 if (!mapping || !__remove_mapping(mapping, page)) 905 goto keep_locked; 906 907 /* 908 * At this point, we have no other references and there is 909 * no way to pick any more up (removed from LRU, removed 910 * from pagecache). Can use non-atomic bitops now (and 911 * we obviously don't have to worry about waking up a process 912 * waiting on the page lock, because there are no references. 913 */ 914 __clear_page_locked(page); 915free_it: 916 nr_reclaimed++; 917 918 /* 919 * Is there need to periodically free_page_list? It would 920 * appear not as the counts should be low 921 */ 922 list_add(&page->lru, &free_pages); 923 continue; 924 925cull_mlocked: 926 if (PageSwapCache(page)) 927 try_to_free_swap(page); 928 unlock_page(page); 929 putback_lru_page(page); 930 reset_reclaim_mode(sc); 931 continue; 932 933activate_locked: 934 /* Not a candidate for swapping, so reclaim swap space. */ 935 if (PageSwapCache(page) && vm_swap_full()) 936 try_to_free_swap(page); 937 VM_BUG_ON(PageActive(page)); 938 SetPageActive(page); 939 pgactivate++; 940keep_locked: 941 unlock_page(page); 942keep: 943 reset_reclaim_mode(sc); 944keep_lumpy: 945 list_add(&page->lru, &ret_pages); 946 VM_BUG_ON(PageLRU(page) || PageUnevictable(page)); 947 } 948 949 /* 950 * Tag a zone as congested if all the dirty pages encountered were 951 * backed by a congested BDI. In this case, reclaimers should just 952 * back off and wait for congestion to clear because further reclaim 953 * will encounter the same problem 954 */ 955 if (nr_dirty && nr_dirty == nr_congested && scanning_global_lru(sc)) 956 zone_set_flag(zone, ZONE_CONGESTED); 957 958 free_page_list(&free_pages); 959 960 list_splice(&ret_pages, page_list); 961 count_vm_events(PGACTIVATE, pgactivate); 962 return nr_reclaimed; 963} 964 965/* 966 * Attempt to remove the specified page from its LRU. Only take this page 967 * if it is of the appropriate PageActive status. Pages which are being 968 * freed elsewhere are also ignored. 969 * 970 * page: page to consider 971 * mode: one of the LRU isolation modes defined above 972 * 973 * returns 0 on success, -ve errno on failure. 974 */ 975int __isolate_lru_page(struct page *page, int mode, int file) 976{ 977 int ret = -EINVAL; 978 979 /* Only take pages on the LRU. */ 980 if (!PageLRU(page)) 981 return ret; 982 983 /* 984 * When checking the active state, we need to be sure we are 985 * dealing with comparible boolean values. Take the logical not 986 * of each. 987 */ 988 if (mode != ISOLATE_BOTH && (!PageActive(page) != !mode)) 989 return ret; 990 991 if (mode != ISOLATE_BOTH && page_is_file_cache(page) != file) 992 return ret; 993 994 /* 995 * When this function is being called for lumpy reclaim, we 996 * initially look into all LRU pages, active, inactive and 997 * unevictable; only give shrink_page_list evictable pages. 998 */ 999 if (PageUnevictable(page)) 1000 return ret; 1001 1002 ret = -EBUSY; 1003 1004 if (likely(get_page_unless_zero(page))) { 1005 /* 1006 * Be careful not to clear PageLRU until after we're 1007 * sure the page is not being freed elsewhere -- the 1008 * page release code relies on it. 1009 */ 1010 ClearPageLRU(page); 1011 ret = 0; 1012 } 1013 1014 return ret; 1015} 1016 1017/* 1018 * zone->lru_lock is heavily contended. Some of the functions that 1019 * shrink the lists perform better by taking out a batch of pages 1020 * and working on them outside the LRU lock. 1021 * 1022 * For pagecache intensive workloads, this function is the hottest 1023 * spot in the kernel (apart from copy_*_user functions). 1024 * 1025 * Appropriate locks must be held before calling this function. 1026 * 1027 * @nr_to_scan: The number of pages to look through on the list. 1028 * @src: The LRU list to pull pages off. 1029 * @dst: The temp list to put pages on to. 1030 * @scanned: The number of pages that were scanned. 1031 * @order: The caller's attempted allocation order 1032 * @mode: One of the LRU isolation modes 1033 * @file: True [1] if isolating file [!anon] pages 1034 * 1035 * returns how many pages were moved onto *@dst. 1036 */ 1037static unsigned long isolate_lru_pages(unsigned long nr_to_scan, 1038 struct list_head *src, struct list_head *dst, 1039 unsigned long *scanned, int order, int mode, int file) 1040{ 1041 unsigned long nr_taken = 0; 1042 unsigned long nr_lumpy_taken = 0; 1043 unsigned long nr_lumpy_dirty = 0; 1044 unsigned long nr_lumpy_failed = 0; 1045 unsigned long scan; 1046 1047 for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) { 1048 struct page *page; 1049 unsigned long pfn; 1050 unsigned long end_pfn; 1051 unsigned long page_pfn; 1052 int zone_id; 1053 1054 page = lru_to_page(src); 1055 prefetchw_prev_lru_page(page, src, flags); 1056 1057 VM_BUG_ON(!PageLRU(page)); 1058 1059 switch (__isolate_lru_page(page, mode, file)) { 1060 case 0: 1061 list_move(&page->lru, dst); 1062 mem_cgroup_del_lru(page); 1063 nr_taken += hpage_nr_pages(page); 1064 break; 1065 1066 case -EBUSY: 1067 /* else it is being freed elsewhere */ 1068 list_move(&page->lru, src); 1069 mem_cgroup_rotate_lru_list(page, page_lru(page)); 1070 continue; 1071 1072 default: 1073 BUG(); 1074 } 1075 1076 if (!order) 1077 continue; 1078 1079 /* 1080 * Attempt to take all pages in the order aligned region 1081 * surrounding the tag page. Only take those pages of 1082 * the same active state as that tag page. We may safely 1083 * round the target page pfn down to the requested order 1084 * as the mem_map is guaranteed valid out to MAX_ORDER, 1085 * where that page is in a different zone we will detect 1086 * it from its zone id and abort this block scan. 1087 */ 1088 zone_id = page_zone_id(page); 1089 page_pfn = page_to_pfn(page); 1090 pfn = page_pfn & ~((1 << order) - 1); 1091 end_pfn = pfn + (1 << order); 1092 for (; pfn < end_pfn; pfn++) { 1093 struct page *cursor_page; 1094 1095 /* The target page is in the block, ignore it. */ 1096 if (unlikely(pfn == page_pfn)) 1097 continue; 1098 1099 /* Avoid holes within the zone. */ 1100 if (unlikely(!pfn_valid_within(pfn))) 1101 break; 1102 1103 cursor_page = pfn_to_page(pfn); 1104 1105 /* Check that we have not crossed a zone boundary. */ 1106 if (unlikely(page_zone_id(cursor_page) != zone_id)) 1107 break; 1108 1109 /* 1110 * If we don't have enough swap space, reclaiming of 1111 * anon page which don't already have a swap slot is 1112 * pointless. 1113 */ 1114 if (nr_swap_pages <= 0 && PageAnon(cursor_page) && 1115 !PageSwapCache(cursor_page)) 1116 break; 1117 1118 if (__isolate_lru_page(cursor_page, mode, file) == 0) { 1119 list_move(&cursor_page->lru, dst); 1120 mem_cgroup_del_lru(cursor_page); 1121 nr_taken += hpage_nr_pages(page); 1122 nr_lumpy_taken++; 1123 if (PageDirty(cursor_page)) 1124 nr_lumpy_dirty++; 1125 scan++; 1126 } else { 1127 /* 1128 * Check if the page is freed already. 1129 * 1130 * We can't use page_count() as that 1131 * requires compound_head and we don't 1132 * have a pin on the page here. If a 1133 * page is tail, we may or may not 1134 * have isolated the head, so assume 1135 * it's not free, it'd be tricky to 1136 * track the head status without a 1137 * page pin. 1138 */ 1139 if (!PageTail(cursor_page) && 1140 !atomic_read(&cursor_page->_count)) 1141 continue; 1142 break; 1143 } 1144 } 1145 1146 /* If we break out of the loop above, lumpy reclaim failed */ 1147 if (pfn < end_pfn) 1148 nr_lumpy_failed++; 1149 } 1150 1151 *scanned = scan; 1152 1153 trace_mm_vmscan_lru_isolate(order, 1154 nr_to_scan, scan, 1155 nr_taken, 1156 nr_lumpy_taken, nr_lumpy_dirty, nr_lumpy_failed, 1157 mode); 1158 return nr_taken; 1159} 1160 1161static unsigned long isolate_pages_global(unsigned long nr, 1162 struct list_head *dst, 1163 unsigned long *scanned, int order, 1164 int mode, struct zone *z, 1165 int active, int file) 1166{ 1167 int lru = LRU_BASE; 1168 if (active) 1169 lru += LRU_ACTIVE; 1170 if (file) 1171 lru += LRU_FILE; 1172 return isolate_lru_pages(nr, &z->lru[lru].list, dst, scanned, order, 1173 mode, file); 1174} 1175 1176/* 1177 * clear_active_flags() is a helper for shrink_active_list(), clearing 1178 * any active bits from the pages in the list. 1179 */ 1180static unsigned long clear_active_flags(struct list_head *page_list, 1181 unsigned int *count) 1182{ 1183 int nr_active = 0; 1184 int lru; 1185 struct page *page; 1186 1187 list_for_each_entry(page, page_list, lru) { 1188 int numpages = hpage_nr_pages(page); 1189 lru = page_lru_base_type(page); 1190 if (PageActive(page)) { 1191 lru += LRU_ACTIVE; 1192 ClearPageActive(page); 1193 nr_active += numpages; 1194 } 1195 if (count) 1196 count[lru] += numpages; 1197 } 1198 1199 return nr_active; 1200} 1201 1202/** 1203 * isolate_lru_page - tries to isolate a page from its LRU list 1204 * @page: page to isolate from its LRU list 1205 * 1206 * Isolates a @page from an LRU list, clears PageLRU and adjusts the 1207 * vmstat statistic corresponding to whatever LRU list the page was on. 1208 * 1209 * Returns 0 if the page was removed from an LRU list. 1210 * Returns -EBUSY if the page was not on an LRU list. 1211 * 1212 * The returned page will have PageLRU() cleared. If it was found on 1213 * the active list, it will have PageActive set. If it was found on 1214 * the unevictable list, it will have the PageUnevictable bit set. That flag 1215 * may need to be cleared by the caller before letting the page go. 1216 * 1217 * The vmstat statistic corresponding to the list on which the page was 1218 * found will be decremented. 1219 * 1220 * Restrictions: 1221 * (1) Must be called with an elevated refcount on the page. This is a 1222 * fundamentnal difference from isolate_lru_pages (which is called 1223 * without a stable reference). 1224 * (2) the lru_lock must not be held. 1225 * (3) interrupts must be enabled. 1226 */ 1227int isolate_lru_page(struct page *page) 1228{ 1229 int ret = -EBUSY; 1230 1231 VM_BUG_ON(!page_count(page)); 1232 1233 if (PageLRU(page)) { 1234 struct zone *zone = page_zone(page); 1235 1236 spin_lock_irq(&zone->lru_lock); 1237 if (PageLRU(page)) { 1238 int lru = page_lru(page); 1239 ret = 0; 1240 get_page(page); 1241 ClearPageLRU(page); 1242 1243 del_page_from_lru_list(zone, page, lru); 1244 } 1245 spin_unlock_irq(&zone->lru_lock); 1246 } 1247 return ret; 1248} 1249 1250/* 1251 * Are there way too many processes in the direct reclaim path already? 1252 */ 1253static int too_many_isolated(struct zone *zone, int file, 1254 struct scan_control *sc) 1255{ 1256 unsigned long inactive, isolated; 1257 1258 if (current_is_kswapd()) 1259 return 0; 1260 1261 if (!scanning_global_lru(sc)) 1262 return 0; 1263 1264 if (file) { 1265 inactive = zone_page_state(zone, NR_INACTIVE_FILE); 1266 isolated = zone_page_state(zone, NR_ISOLATED_FILE); 1267 } else { 1268 inactive = zone_page_state(zone, NR_INACTIVE_ANON); 1269 isolated = zone_page_state(zone, NR_ISOLATED_ANON); 1270 } 1271 1272 return isolated > inactive; 1273} 1274 1275/* 1276 * TODO: Try merging with migrations version of putback_lru_pages 1277 */ 1278static noinline_for_stack void 1279putback_lru_pages(struct zone *zone, struct scan_control *sc, 1280 unsigned long nr_anon, unsigned long nr_file, 1281 struct list_head *page_list) 1282{ 1283 struct page *page; 1284 struct pagevec pvec; 1285 struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); 1286 1287 pagevec_init(&pvec, 1); 1288 1289 /* 1290 * Put back any unfreeable pages. 1291 */ 1292 spin_lock(&zone->lru_lock); 1293 while (!list_empty(page_list)) { 1294 int lru; 1295 page = lru_to_page(page_list); 1296 VM_BUG_ON(PageLRU(page)); 1297 list_del(&page->lru); 1298 if (unlikely(!page_evictable(page, NULL))) { 1299 spin_unlock_irq(&zone->lru_lock); 1300 putback_lru_page(page); 1301 spin_lock_irq(&zone->lru_lock); 1302 continue; 1303 } 1304 SetPageLRU(page); 1305 lru = page_lru(page); 1306 add_page_to_lru_list(zone, page, lru); 1307 if (is_active_lru(lru)) { 1308 int file = is_file_lru(lru); 1309 int numpages = hpage_nr_pages(page); 1310 reclaim_stat->recent_rotated[file] += numpages; 1311 } 1312 if (!pagevec_add(&pvec, page)) { 1313 spin_unlock_irq(&zone->lru_lock); 1314 __pagevec_release(&pvec); 1315 spin_lock_irq(&zone->lru_lock); 1316 } 1317 } 1318 __mod_zone_page_state(zone, NR_ISOLATED_ANON, -nr_anon); 1319 __mod_zone_page_state(zone, NR_ISOLATED_FILE, -nr_file); 1320 1321 spin_unlock_irq(&zone->lru_lock); 1322 pagevec_release(&pvec); 1323} 1324 1325static noinline_for_stack void update_isolated_counts(struct zone *zone, 1326 struct scan_control *sc, 1327 unsigned long *nr_anon, 1328 unsigned long *nr_file, 1329 struct list_head *isolated_list) 1330{ 1331 unsigned long nr_active; 1332 unsigned int count[NR_LRU_LISTS] = { 0, }; 1333 struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); 1334 1335 nr_active = clear_active_flags(isolated_list, count); 1336 __count_vm_events(PGDEACTIVATE, nr_active); 1337 1338 __mod_zone_page_state(zone, NR_ACTIVE_FILE, 1339 -count[LRU_ACTIVE_FILE]); 1340 __mod_zone_page_state(zone, NR_INACTIVE_FILE, 1341 -count[LRU_INACTIVE_FILE]); 1342 __mod_zone_page_state(zone, NR_ACTIVE_ANON, 1343 -count[LRU_ACTIVE_ANON]); 1344 __mod_zone_page_state(zone, NR_INACTIVE_ANON, 1345 -count[LRU_INACTIVE_ANON]); 1346 1347 *nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON]; 1348 *nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE]; 1349 __mod_zone_page_state(zone, NR_ISOLATED_ANON, *nr_anon); 1350 __mod_zone_page_state(zone, NR_ISOLATED_FILE, *nr_file); 1351 1352 reclaim_stat->recent_scanned[0] += *nr_anon; 1353 reclaim_stat->recent_scanned[1] += *nr_file; 1354} 1355 1356/* 1357 * Returns true if the caller should wait to clean dirty/writeback pages. 1358 * 1359 * If we are direct reclaiming for contiguous pages and we do not reclaim 1360 * everything in the list, try again and wait for writeback IO to complete. 1361 * This will stall high-order allocations noticeably. Only do that when really 1362 * need to free the pages under high memory pressure. 1363 */ 1364static inline bool should_reclaim_stall(unsigned long nr_taken, 1365 unsigned long nr_freed, 1366 int priority, 1367 struct scan_control *sc) 1368{ 1369 int lumpy_stall_priority; 1370 1371 /* kswapd should not stall on sync IO */ 1372 if (current_is_kswapd()) 1373 return false; 1374 1375 /* Only stall on lumpy reclaim */ 1376 if (sc->reclaim_mode & RECLAIM_MODE_SINGLE) 1377 return false; 1378 1379 /* If we have relaimed everything on the isolated list, no stall */ 1380 if (nr_freed == nr_taken) 1381 return false; 1382 1383 /* 1384 * For high-order allocations, there are two stall thresholds. 1385 * High-cost allocations stall immediately where as lower 1386 * order allocations such as stacks require the scanning 1387 * priority to be much higher before stalling. 1388 */ 1389 if (sc->order > PAGE_ALLOC_COSTLY_ORDER) 1390 lumpy_stall_priority = DEF_PRIORITY; 1391 else 1392 lumpy_stall_priority = DEF_PRIORITY / 3; 1393 1394 return priority <= lumpy_stall_priority; 1395} 1396 1397/* 1398 * shrink_inactive_list() is a helper for shrink_zone(). It returns the number 1399 * of reclaimed pages 1400 */ 1401static noinline_for_stack unsigned long 1402shrink_inactive_list(unsigned long nr_to_scan, struct zone *zone, 1403 struct scan_control *sc, int priority, int file) 1404{ 1405 LIST_HEAD(page_list); 1406 unsigned long nr_scanned; 1407 unsigned long nr_reclaimed = 0; 1408 unsigned long nr_taken; 1409 unsigned long nr_anon; 1410 unsigned long nr_file; 1411 1412 while (unlikely(too_many_isolated(zone, file, sc))) { 1413 congestion_wait(BLK_RW_ASYNC, HZ/10); 1414 1415 /* We are about to die and free our memory. Return now. */ 1416 if (fatal_signal_pending(current)) 1417 return SWAP_CLUSTER_MAX; 1418 } 1419 1420 set_reclaim_mode(priority, sc, false); 1421 lru_add_drain(); 1422 spin_lock_irq(&zone->lru_lock); 1423 1424 if (scanning_global_lru(sc)) { 1425 nr_taken = isolate_pages_global(nr_to_scan, 1426 &page_list, &nr_scanned, sc->order, 1427 sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ? 1428 ISOLATE_BOTH : ISOLATE_INACTIVE, 1429 zone, 0, file); 1430 zone->pages_scanned += nr_scanned; 1431 if (current_is_kswapd()) 1432 __count_zone_vm_events(PGSCAN_KSWAPD, zone, 1433 nr_scanned); 1434 else 1435 __count_zone_vm_events(PGSCAN_DIRECT, zone, 1436 nr_scanned); 1437 } else { 1438 nr_taken = mem_cgroup_isolate_pages(nr_to_scan, 1439 &page_list, &nr_scanned, sc->order, 1440 sc->reclaim_mode & RECLAIM_MODE_LUMPYRECLAIM ? 1441 ISOLATE_BOTH : ISOLATE_INACTIVE, 1442 zone, sc->mem_cgroup, 1443 0, file); 1444 /* 1445 * mem_cgroup_isolate_pages() keeps track of 1446 * scanned pages on its own. 1447 */ 1448 } 1449 1450 if (nr_taken == 0) { 1451 spin_unlock_irq(&zone->lru_lock); 1452 return 0; 1453 } 1454 1455 update_isolated_counts(zone, sc, &nr_anon, &nr_file, &page_list); 1456 1457 spin_unlock_irq(&zone->lru_lock); 1458 1459 nr_reclaimed = shrink_page_list(&page_list, zone, sc); 1460 1461 /* Check if we should syncronously wait for writeback */ 1462 if (should_reclaim_stall(nr_taken, nr_reclaimed, priority, sc)) { 1463 set_reclaim_mode(priority, sc, true); 1464 nr_reclaimed += shrink_page_list(&page_list, zone, sc); 1465 } 1466 1467 local_irq_disable(); 1468 if (current_is_kswapd()) 1469 __count_vm_events(KSWAPD_STEAL, nr_reclaimed); 1470 __count_zone_vm_events(PGSTEAL, zone, nr_reclaimed); 1471 1472 putback_lru_pages(zone, sc, nr_anon, nr_file, &page_list); 1473 1474 trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id, 1475 zone_idx(zone), 1476 nr_scanned, nr_reclaimed, 1477 priority, 1478 trace_shrink_flags(file, sc->reclaim_mode)); 1479 return nr_reclaimed; 1480} 1481 1482/* 1483 * This moves pages from the active list to the inactive list. 1484 * 1485 * We move them the other way if the page is referenced by one or more 1486 * processes, from rmap. 1487 * 1488 * If the pages are mostly unmapped, the processing is fast and it is 1489 * appropriate to hold zone->lru_lock across the whole operation. But if 1490 * the pages are mapped, the processing is slow (page_referenced()) so we 1491 * should drop zone->lru_lock around each page. It's impossible to balance 1492 * this, so instead we remove the pages from the LRU while processing them. 1493 * It is safe to rely on PG_active against the non-LRU pages in here because 1494 * nobody will play with that bit on a non-LRU page. 1495 * 1496 * The downside is that we have to touch page->_count against each page. 1497 * But we had to alter page->flags anyway. 1498 */ 1499 1500static void move_active_pages_to_lru(struct zone *zone, 1501 struct list_head *list, 1502 enum lru_list lru) 1503{ 1504 unsigned long pgmoved = 0; 1505 struct pagevec pvec; 1506 struct page *page; 1507 1508 pagevec_init(&pvec, 1); 1509 1510 while (!list_empty(list)) { 1511 page = lru_to_page(list); 1512 1513 VM_BUG_ON(PageLRU(page)); 1514 SetPageLRU(page); 1515 1516 list_move(&page->lru, &zone->lru[lru].list); 1517 mem_cgroup_add_lru_list(page, lru); 1518 pgmoved += hpage_nr_pages(page); 1519 1520 if (!pagevec_add(&pvec, page) || list_empty(list)) { 1521 spin_unlock_irq(&zone->lru_lock); 1522 if (buffer_heads_over_limit) 1523 pagevec_strip(&pvec); 1524 __pagevec_release(&pvec); 1525 spin_lock_irq(&zone->lru_lock); 1526 } 1527 } 1528 __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved); 1529 if (!is_active_lru(lru)) 1530 __count_vm_events(PGDEACTIVATE, pgmoved); 1531} 1532 1533static void shrink_active_list(unsigned long nr_pages, struct zone *zone, 1534 struct scan_control *sc, int priority, int file) 1535{ 1536 unsigned long nr_taken; 1537 unsigned long pgscanned; 1538 unsigned long vm_flags; 1539 LIST_HEAD(l_hold); /* The pages which were snipped off */ 1540 LIST_HEAD(l_active); 1541 LIST_HEAD(l_inactive); 1542 struct page *page; 1543 struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); 1544 unsigned long nr_rotated = 0; 1545 1546 lru_add_drain(); 1547 spin_lock_irq(&zone->lru_lock); 1548 if (scanning_global_lru(sc)) { 1549 nr_taken = isolate_pages_global(nr_pages, &l_hold, 1550 &pgscanned, sc->order, 1551 ISOLATE_ACTIVE, zone, 1552 1, file); 1553 zone->pages_scanned += pgscanned; 1554 } else { 1555 nr_taken = mem_cgroup_isolate_pages(nr_pages, &l_hold, 1556 &pgscanned, sc->order, 1557 ISOLATE_ACTIVE, zone, 1558 sc->mem_cgroup, 1, file); 1559 /* 1560 * mem_cgroup_isolate_pages() keeps track of 1561 * scanned pages on its own. 1562 */ 1563 } 1564 1565 reclaim_stat->recent_scanned[file] += nr_taken; 1566 1567 __count_zone_vm_events(PGREFILL, zone, pgscanned); 1568 if (file) 1569 __mod_zone_page_state(zone, NR_ACTIVE_FILE, -nr_taken); 1570 else 1571 __mod_zone_page_state(zone, NR_ACTIVE_ANON, -nr_taken); 1572 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken); 1573 spin_unlock_irq(&zone->lru_lock); 1574 1575 while (!list_empty(&l_hold)) { 1576 cond_resched(); 1577 page = lru_to_page(&l_hold); 1578 list_del(&page->lru); 1579 1580 if (unlikely(!page_evictable(page, NULL))) { 1581 putback_lru_page(page); 1582 continue; 1583 } 1584 1585 if (page_referenced(page, 0, sc->mem_cgroup, &vm_flags)) { 1586 nr_rotated += hpage_nr_pages(page); 1587 /* 1588 * Identify referenced, file-backed active pages and 1589 * give them one more trip around the active list. So 1590 * that executable code get better chances to stay in 1591 * memory under moderate memory pressure. Anon pages 1592 * are not likely to be evicted by use-once streaming 1593 * IO, plus JVM can create lots of anon VM_EXEC pages, 1594 * so we ignore them here. 1595 */ 1596 if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) { 1597 list_add(&page->lru, &l_active); 1598 continue; 1599 } 1600 } 1601 1602 ClearPageActive(page); /* we are de-activating */ 1603 list_add(&page->lru, &l_inactive); 1604 } 1605 1606 /* 1607 * Move pages back to the lru list. 1608 */ 1609 spin_lock_irq(&zone->lru_lock); 1610 /* 1611 * Count referenced pages from currently used mappings as rotated, 1612 * even though only some of them are actually re-activated. This 1613 * helps balance scan pressure between file and anonymous pages in 1614 * get_scan_ratio. 1615 */ 1616 reclaim_stat->recent_rotated[file] += nr_rotated; 1617 1618 move_active_pages_to_lru(zone, &l_active, 1619 LRU_ACTIVE + file * LRU_FILE); 1620 move_active_pages_to_lru(zone, &l_inactive, 1621 LRU_BASE + file * LRU_FILE); 1622 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken); 1623 spin_unlock_irq(&zone->lru_lock); 1624} 1625 1626#ifdef CONFIG_SWAP 1627static int inactive_anon_is_low_global(struct zone *zone) 1628{ 1629 unsigned long active, inactive; 1630 1631 active = zone_page_state(zone, NR_ACTIVE_ANON); 1632 inactive = zone_page_state(zone, NR_INACTIVE_ANON); 1633 1634 if (inactive * zone->inactive_ratio < active) 1635 return 1; 1636 1637 return 0; 1638} 1639 1640/** 1641 * inactive_anon_is_low - check if anonymous pages need to be deactivated 1642 * @zone: zone to check 1643 * @sc: scan control of this context 1644 * 1645 * Returns true if the zone does not have enough inactive anon pages, 1646 * meaning some active anon pages need to be deactivated. 1647 */ 1648static int inactive_anon_is_low(struct zone *zone, struct scan_control *sc) 1649{ 1650 int low; 1651 1652 /* 1653 * If we don't have swap space, anonymous page deactivation 1654 * is pointless. 1655 */ 1656 if (!total_swap_pages) 1657 return 0; 1658 1659 if (scanning_global_lru(sc)) 1660 low = inactive_anon_is_low_global(zone); 1661 else 1662 low = mem_cgroup_inactive_anon_is_low(sc->mem_cgroup); 1663 return low; 1664} 1665#else 1666static inline int inactive_anon_is_low(struct zone *zone, 1667 struct scan_control *sc) 1668{ 1669 return 0; 1670} 1671#endif 1672 1673static int inactive_file_is_low_global(struct zone *zone) 1674{ 1675 unsigned long active, inactive; 1676 1677 active = zone_page_state(zone, NR_ACTIVE_FILE); 1678 inactive = zone_page_state(zone, NR_INACTIVE_FILE); 1679 1680 return (active > inactive); 1681} 1682 1683/** 1684 * inactive_file_is_low - check if file pages need to be deactivated 1685 * @zone: zone to check 1686 * @sc: scan control of this context 1687 * 1688 * When the system is doing streaming IO, memory pressure here 1689 * ensures that active file pages get deactivated, until more 1690 * than half of the file pages are on the inactive list. 1691 * 1692 * Once we get to that situation, protect the system's working 1693 * set from being evicted by disabling active file page aging. 1694 * 1695 * This uses a different ratio than the anonymous pages, because 1696 * the page cache uses a use-once replacement algorithm. 1697 */ 1698static int inactive_file_is_low(struct zone *zone, struct scan_control *sc) 1699{ 1700 int low; 1701 1702 if (scanning_global_lru(sc)) 1703 low = inactive_file_is_low_global(zone); 1704 else 1705 low = mem_cgroup_inactive_file_is_low(sc->mem_cgroup); 1706 return low; 1707} 1708 1709static int inactive_list_is_low(struct zone *zone, struct scan_control *sc, 1710 int file) 1711{ 1712 if (file) 1713 return inactive_file_is_low(zone, sc); 1714 else 1715 return inactive_anon_is_low(zone, sc); 1716} 1717 1718static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan, 1719 struct zone *zone, struct scan_control *sc, int priority) 1720{ 1721 int file = is_file_lru(lru); 1722 1723 if (is_active_lru(lru)) { 1724 if (inactive_list_is_low(zone, sc, file)) 1725 shrink_active_list(nr_to_scan, zone, sc, priority, file); 1726 return 0; 1727 } 1728 1729 return shrink_inactive_list(nr_to_scan, zone, sc, priority, file); 1730} 1731 1732/* 1733 * Determine how aggressively the anon and file LRU lists should be 1734 * scanned. The relative value of each set of LRU lists is determined 1735 * by looking at the fraction of the pages scanned we did rotate back 1736 * onto the active list instead of evict. 1737 * 1738 * nr[0] = anon pages to scan; nr[1] = file pages to scan 1739 */ 1740static void get_scan_count(struct zone *zone, struct scan_control *sc, 1741 unsigned long *nr, int priority) 1742{ 1743 unsigned long anon, file, free; 1744 unsigned long anon_prio, file_prio; 1745 unsigned long ap, fp; 1746 struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc); 1747 u64 fraction[2], denominator; 1748 enum lru_list l; 1749 int noswap = 0; 1750 int force_scan = 0; 1751 1752 1753 anon = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) + 1754 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON); 1755 file = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) + 1756 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE); 1757 1758 if (((anon + file) >> priority) < SWAP_CLUSTER_MAX) { 1759 /* kswapd does zone balancing and need to scan this zone */ 1760 if (scanning_global_lru(sc) && current_is_kswapd()) 1761 force_scan = 1; 1762 /* memcg may have small limit and need to avoid priority drop */ 1763 if (!scanning_global_lru(sc)) 1764 force_scan = 1; 1765 } 1766 1767 /* If we have no swap space, do not bother scanning anon pages. */ 1768 if (!sc->may_swap || (nr_swap_pages <= 0)) { 1769 noswap = 1; 1770 fraction[0] = 0; 1771 fraction[1] = 1; 1772 denominator = 1; 1773 goto out; 1774 } 1775 1776 if (scanning_global_lru(sc)) { 1777 free = zone_page_state(zone, NR_FREE_PAGES); 1778 /* If we have very few page cache pages, 1779 force-scan anon pages. */ 1780 if (unlikely(file + free <= high_wmark_pages(zone))) { 1781 fraction[0] = 1; 1782 fraction[1] = 0; 1783 denominator = 1; 1784 goto out; 1785 } 1786 } 1787 1788 /* 1789 * With swappiness at 100, anonymous and file have the same priority. 1790 * This scanning priority is essentially the inverse of IO cost. 1791 */ 1792 anon_prio = sc->swappiness; 1793 file_prio = 200 - sc->swappiness; 1794 1795 /* 1796 * OK, so we have swap space and a fair amount of page cache 1797 * pages. We use the recently rotated / recently scanned 1798 * ratios to determine how valuable each cache is. 1799 * 1800 * Because workloads change over time (and to avoid overflow) 1801 * we keep these statistics as a floating average, which ends 1802 * up weighing recent references more than old ones. 1803 * 1804 * anon in [0], file in [1] 1805 */ 1806 spin_lock_irq(&zone->lru_lock); 1807 if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) { 1808 reclaim_stat->recent_scanned[0] /= 2; 1809 reclaim_stat->recent_rotated[0] /= 2; 1810 } 1811 1812 if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) { 1813 reclaim_stat->recent_scanned[1] /= 2; 1814 reclaim_stat->recent_rotated[1] /= 2; 1815 } 1816 1817 /* 1818 * The amount of pressure on anon vs file pages is inversely 1819 * proportional to the fraction of recently scanned pages on 1820 * each list that were recently referenced and in active use. 1821 */ 1822 ap = (anon_prio + 1) * (reclaim_stat->recent_scanned[0] + 1); 1823 ap /= reclaim_stat->recent_rotated[0] + 1; 1824 1825 fp = (file_prio + 1) * (reclaim_stat->recent_scanned[1] + 1); 1826 fp /= reclaim_stat->recent_rotated[1] + 1; 1827 spin_unlock_irq(&zone->lru_lock); 1828 1829 fraction[0] = ap; 1830 fraction[1] = fp; 1831 denominator = ap + fp + 1; 1832out: 1833 for_each_evictable_lru(l) { 1834 int file = is_file_lru(l); 1835 unsigned long scan; 1836 1837 scan = zone_nr_lru_pages(zone, sc, l); 1838 if (priority || noswap) { 1839 scan >>= priority; 1840 scan = div64_u64(scan * fraction[file], denominator); 1841 } 1842 1843 /* 1844 * If zone is small or memcg is small, nr[l] can be 0. 1845 * This results no-scan on this priority and priority drop down. 1846 * For global direct reclaim, it can visit next zone and tend 1847 * not to have problems. For global kswapd, it's for zone 1848 * balancing and it need to scan a small amounts. When using 1849 * memcg, priority drop can cause big latency. So, it's better 1850 * to scan small amount. See may_noscan above. 1851 */ 1852 if (!scan && force_scan) { 1853 if (file) 1854 scan = SWAP_CLUSTER_MAX; 1855 else if (!noswap) 1856 scan = SWAP_CLUSTER_MAX; 1857 } 1858 nr[l] = scan; 1859 } 1860} 1861 1862/* 1863 * Reclaim/compaction depends on a number of pages being freed. To avoid 1864 * disruption to the system, a small number of order-0 pages continue to be 1865 * rotated and reclaimed in the normal fashion. However, by the time we get 1866 * back to the allocator and call try_to_compact_zone(), we ensure that 1867 * there are enough free pages for it to be likely successful 1868 */ 1869static inline bool should_continue_reclaim(struct zone *zone, 1870 unsigned long nr_reclaimed, 1871 unsigned long nr_scanned, 1872 struct scan_control *sc) 1873{ 1874 unsigned long pages_for_compaction; 1875 unsigned long inactive_lru_pages; 1876 1877 /* If not in reclaim/compaction mode, stop */ 1878 if (!(sc->reclaim_mode & RECLAIM_MODE_COMPACTION)) 1879 return false; 1880 1881 /* Consider stopping depending on scan and reclaim activity */ 1882 if (sc->gfp_mask & __GFP_REPEAT) { 1883 /* 1884 * For __GFP_REPEAT allocations, stop reclaiming if the 1885 * full LRU list has been scanned and we are still failing 1886 * to reclaim pages. This full LRU scan is potentially 1887 * expensive but a __GFP_REPEAT caller really wants to succeed 1888 */ 1889 if (!nr_reclaimed && !nr_scanned) 1890 return false; 1891 } else { 1892 /* 1893 * For non-__GFP_REPEAT allocations which can presumably 1894 * fail without consequence, stop if we failed to reclaim 1895 * any pages from the last SWAP_CLUSTER_MAX number of 1896 * pages that were scanned. This will return to the 1897 * caller faster at the risk reclaim/compaction and 1898 * the resulting allocation attempt fails 1899 */ 1900 if (!nr_reclaimed) 1901 return false; 1902 } 1903 1904 /* 1905 * If we have not reclaimed enough pages for compaction and the 1906 * inactive lists are large enough, continue reclaiming 1907 */ 1908 pages_for_compaction = (2UL << sc->order); 1909 inactive_lru_pages = zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON) + 1910 zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE); 1911 if (sc->nr_reclaimed < pages_for_compaction && 1912 inactive_lru_pages > pages_for_compaction) 1913 return true; 1914 1915 /* If compaction would go ahead or the allocation would succeed, stop */ 1916 switch (compaction_suitable(zone, sc->order)) { 1917 case COMPACT_PARTIAL: 1918 case COMPACT_CONTINUE: 1919 return false; 1920 default: 1921 return true; 1922 } 1923} 1924 1925/* 1926 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim. 1927 */ 1928static void shrink_zone(int priority, struct zone *zone, 1929 struct scan_control *sc) 1930{ 1931 unsigned long nr[NR_LRU_LISTS]; 1932 unsigned long nr_to_scan; 1933 enum lru_list l; 1934 unsigned long nr_reclaimed, nr_scanned; 1935 unsigned long nr_to_reclaim = sc->nr_to_reclaim; 1936 1937restart: 1938 nr_reclaimed = 0; 1939 nr_scanned = sc->nr_scanned; 1940 get_scan_count(zone, sc, nr, priority); 1941 1942 while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || 1943 nr[LRU_INACTIVE_FILE]) { 1944 for_each_evictable_lru(l) { 1945 if (nr[l]) { 1946 nr_to_scan = min_t(unsigned long, 1947 nr[l], SWAP_CLUSTER_MAX); 1948 nr[l] -= nr_to_scan; 1949 1950 nr_reclaimed += shrink_list(l, nr_to_scan, 1951 zone, sc, priority); 1952 } 1953 } 1954 /* 1955 * On large memory systems, scan >> priority can become 1956 * really large. This is fine for the starting priority; 1957 * we want to put equal scanning pressure on each zone. 1958 * However, if the VM has a harder time of freeing pages, 1959 * with multiple processes reclaiming pages, the total 1960 * freeing target can get unreasonably large. 1961 */ 1962 if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY) 1963 break; 1964 } 1965 sc->nr_reclaimed += nr_reclaimed; 1966 1967 /* 1968 * Even if we did not try to evict anon pages at all, we want to 1969 * rebalance the anon lru active/inactive ratio. 1970 */ 1971 if (inactive_anon_is_low(zone, sc)) 1972 shrink_active_list(SWAP_CLUSTER_MAX, zone, sc, priority, 0); 1973 1974 /* reclaim/compaction might need reclaim to continue */ 1975 if (should_continue_reclaim(zone, nr_reclaimed, 1976 sc->nr_scanned - nr_scanned, sc)) 1977 goto restart; 1978 1979 throttle_vm_writeout(sc->gfp_mask); 1980} 1981 1982/* 1983 * This is the direct reclaim path, for page-allocating processes. We only 1984 * try to reclaim pages from zones which will satisfy the caller's allocation 1985 * request. 1986 * 1987 * We reclaim from a zone even if that zone is over high_wmark_pages(zone). 1988 * Because: 1989 * a) The caller may be trying to free *extra* pages to satisfy a higher-order 1990 * allocation or 1991 * b) The target zone may be at high_wmark_pages(zone) but the lower zones 1992 * must go *over* high_wmark_pages(zone) to satisfy the `incremental min' 1993 * zone defense algorithm. 1994 * 1995 * If a zone is deemed to be full of pinned pages then just give it a light 1996 * scan then give up on it. 1997 */ 1998static void shrink_zones(int priority, struct zonelist *zonelist, 1999 struct scan_control *sc) 2000{ 2001 struct zoneref *z; 2002 struct zone *zone; 2003 unsigned long nr_soft_reclaimed; 2004 unsigned long nr_soft_scanned; 2005 2006 for_each_zone_zonelist_nodemask(zone, z, zonelist, 2007 gfp_zone(sc->gfp_mask), sc->nodemask) { 2008 if (!populated_zone(zone)) 2009 continue; 2010 /* 2011 * Take care memory controller reclaiming has small influence 2012 * to global LRU. 2013 */ 2014 if (scanning_global_lru(sc)) { 2015 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2016 continue; 2017 if (zone->all_unreclaimable && priority != DEF_PRIORITY) 2018 continue; /* Let kswapd poll it */ 2019 /* 2020 * This steals pages from memory cgroups over softlimit 2021 * and returns the number of reclaimed pages and 2022 * scanned pages. This works for global memory pressure 2023 * and balancing, not for a memcg's limit. 2024 */ 2025 nr_soft_scanned = 0; 2026 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone, 2027 sc->order, sc->gfp_mask, 2028 &nr_soft_scanned); 2029 sc->nr_reclaimed += nr_soft_reclaimed; 2030 sc->nr_scanned += nr_soft_scanned; 2031 /* need some check for avoid more shrink_zone() */ 2032 } 2033 2034 shrink_zone(priority, zone, sc); 2035 } 2036} 2037 2038static bool zone_reclaimable(struct zone *zone) 2039{ 2040 return zone->pages_scanned < zone_reclaimable_pages(zone) * 6; 2041} 2042 2043/* All zones in zonelist are unreclaimable? */ 2044static bool all_unreclaimable(struct zonelist *zonelist, 2045 struct scan_control *sc) 2046{ 2047 struct zoneref *z; 2048 struct zone *zone; 2049 2050 for_each_zone_zonelist_nodemask(zone, z, zonelist, 2051 gfp_zone(sc->gfp_mask), sc->nodemask) { 2052 if (!populated_zone(zone)) 2053 continue; 2054 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2055 continue; 2056 if (!zone->all_unreclaimable) 2057 return false; 2058 } 2059 2060 return true; 2061} 2062 2063/* 2064 * This is the main entry point to direct page reclaim. 2065 * 2066 * If a full scan of the inactive list fails to free enough memory then we 2067 * are "out of memory" and something needs to be killed. 2068 * 2069 * If the caller is !__GFP_FS then the probability of a failure is reasonably 2070 * high - the zone may be full of dirty or under-writeback pages, which this 2071 * caller can't do much about. We kick the writeback threads and take explicit 2072 * naps in the hope that some of these pages can be written. But if the 2073 * allocating task holds filesystem locks which prevent writeout this might not 2074 * work, and the allocation attempt will fail. 2075 * 2076 * returns: 0, if no pages reclaimed 2077 * else, the number of pages reclaimed 2078 */ 2079static unsigned long do_try_to_free_pages(struct zonelist *zonelist, 2080 struct scan_control *sc, 2081 struct shrink_control *shrink) 2082{ 2083 int priority; 2084 unsigned long total_scanned = 0; 2085 struct reclaim_state *reclaim_state = current->reclaim_state; 2086 struct zoneref *z; 2087 struct zone *zone; 2088 unsigned long writeback_threshold; 2089 2090 get_mems_allowed(); 2091 delayacct_freepages_start(); 2092 2093 if (scanning_global_lru(sc)) 2094 count_vm_event(ALLOCSTALL); 2095 2096 for (priority = DEF_PRIORITY; priority >= 0; priority--) { 2097 sc->nr_scanned = 0; 2098 if (!priority) 2099 disable_swap_token(sc->mem_cgroup); 2100 shrink_zones(priority, zonelist, sc); 2101 /* 2102 * Don't shrink slabs when reclaiming memory from 2103 * over limit cgroups 2104 */ 2105 if (scanning_global_lru(sc)) { 2106 unsigned long lru_pages = 0; 2107 for_each_zone_zonelist(zone, z, zonelist, 2108 gfp_zone(sc->gfp_mask)) { 2109 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2110 continue; 2111 2112 lru_pages += zone_reclaimable_pages(zone); 2113 } 2114 2115 shrink_slab(shrink, sc->nr_scanned, lru_pages); 2116 if (reclaim_state) { 2117 sc->nr_reclaimed += reclaim_state->reclaimed_slab; 2118 reclaim_state->reclaimed_slab = 0; 2119 } 2120 } 2121 total_scanned += sc->nr_scanned; 2122 if (sc->nr_reclaimed >= sc->nr_to_reclaim) 2123 goto out; 2124 2125 /* 2126 * Try to write back as many pages as we just scanned. This 2127 * tends to cause slow streaming writers to write data to the 2128 * disk smoothly, at the dirtying rate, which is nice. But 2129 * that's undesirable in laptop mode, where we *want* lumpy 2130 * writeout. So in laptop mode, write out the whole world. 2131 */ 2132 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2; 2133 if (total_scanned > writeback_threshold) { 2134 wakeup_flusher_threads(laptop_mode ? 0 : total_scanned); 2135 sc->may_writepage = 1; 2136 } 2137 2138 /* Take a nap, wait for some writeback to complete */ 2139 if (!sc->hibernation_mode && sc->nr_scanned && 2140 priority < DEF_PRIORITY - 2) { 2141 struct zone *preferred_zone; 2142 2143 first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask), 2144 &cpuset_current_mems_allowed, 2145 &preferred_zone); 2146 wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10); 2147 } 2148 } 2149 2150out: 2151 delayacct_freepages_end(); 2152 put_mems_allowed(); 2153 2154 if (sc->nr_reclaimed) 2155 return sc->nr_reclaimed; 2156 2157 /* 2158 * As hibernation is going on, kswapd is freezed so that it can't mark 2159 * the zone into all_unreclaimable. Thus bypassing all_unreclaimable 2160 * check. 2161 */ 2162 if (oom_killer_disabled) 2163 return 0; 2164 2165 /* top priority shrink_zones still had more to do? don't OOM, then */ 2166 if (scanning_global_lru(sc) && !all_unreclaimable(zonelist, sc)) 2167 return 1; 2168 2169 return 0; 2170} 2171 2172unsigned long try_to_free_pages(struct zonelist *zonelist, int order, 2173 gfp_t gfp_mask, nodemask_t *nodemask) 2174{ 2175 unsigned long nr_reclaimed; 2176 struct scan_control sc = { 2177 .gfp_mask = gfp_mask, 2178 .may_writepage = !laptop_mode, 2179 .nr_to_reclaim = SWAP_CLUSTER_MAX, 2180 .may_unmap = 1, 2181 .may_swap = 1, 2182 .swappiness = vm_swappiness, 2183 .order = order, 2184 .mem_cgroup = NULL, 2185 .nodemask = nodemask, 2186 }; 2187 struct shrink_control shrink = { 2188 .gfp_mask = sc.gfp_mask, 2189 }; 2190 2191 trace_mm_vmscan_direct_reclaim_begin(order, 2192 sc.may_writepage, 2193 gfp_mask); 2194 2195 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); 2196 2197 trace_mm_vmscan_direct_reclaim_end(nr_reclaimed); 2198 2199 return nr_reclaimed; 2200} 2201 2202#ifdef CONFIG_CGROUP_MEM_RES_CTLR 2203 2204unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *mem, 2205 gfp_t gfp_mask, bool noswap, 2206 unsigned int swappiness, 2207 struct zone *zone, 2208 unsigned long *nr_scanned) 2209{ 2210 struct scan_control sc = { 2211 .nr_scanned = 0, 2212 .nr_to_reclaim = SWAP_CLUSTER_MAX, 2213 .may_writepage = !laptop_mode, 2214 .may_unmap = 1, 2215 .may_swap = !noswap, 2216 .swappiness = swappiness, 2217 .order = 0, 2218 .mem_cgroup = mem, 2219 }; 2220 2221 sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | 2222 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK); 2223 2224 trace_mm_vmscan_memcg_softlimit_reclaim_begin(0, 2225 sc.may_writepage, 2226 sc.gfp_mask); 2227 2228 /* 2229 * NOTE: Although we can get the priority field, using it 2230 * here is not a good idea, since it limits the pages we can scan. 2231 * if we don't reclaim here, the shrink_zone from balance_pgdat 2232 * will pick up pages from other mem cgroup's as well. We hack 2233 * the priority and make it zero. 2234 */ 2235 shrink_zone(0, zone, &sc); 2236 2237 trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed); 2238 2239 *nr_scanned = sc.nr_scanned; 2240 return sc.nr_reclaimed; 2241} 2242 2243unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont, 2244 gfp_t gfp_mask, 2245 bool noswap, 2246 unsigned int swappiness) 2247{ 2248 struct zonelist *zonelist; 2249 unsigned long nr_reclaimed; 2250 int nid; 2251 struct scan_control sc = { 2252 .may_writepage = !laptop_mode, 2253 .may_unmap = 1, 2254 .may_swap = !noswap, 2255 .nr_to_reclaim = SWAP_CLUSTER_MAX, 2256 .swappiness = swappiness, 2257 .order = 0, 2258 .mem_cgroup = mem_cont, 2259 .nodemask = NULL, /* we don't care the placement */ 2260 .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | 2261 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK), 2262 }; 2263 struct shrink_control shrink = { 2264 .gfp_mask = sc.gfp_mask, 2265 }; 2266 2267 /* 2268 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't 2269 * take care of from where we get pages. So the node where we start the 2270 * scan does not need to be the current node. 2271 */ 2272 nid = mem_cgroup_select_victim_node(mem_cont); 2273 2274 zonelist = NODE_DATA(nid)->node_zonelists; 2275 2276 trace_mm_vmscan_memcg_reclaim_begin(0, 2277 sc.may_writepage, 2278 sc.gfp_mask); 2279 2280 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); 2281 2282 trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed); 2283 2284 return nr_reclaimed; 2285} 2286#endif 2287 2288/* 2289 * pgdat_balanced is used when checking if a node is balanced for high-order 2290 * allocations. Only zones that meet watermarks and are in a zone allowed 2291 * by the callers classzone_idx are added to balanced_pages. The total of 2292 * balanced pages must be at least 25% of the zones allowed by classzone_idx 2293 * for the node to be considered balanced. Forcing all zones to be balanced 2294 * for high orders can cause excessive reclaim when there are imbalanced zones. 2295 * The choice of 25% is due to 2296 * o a 16M DMA zone that is balanced will not balance a zone on any 2297 * reasonable sized machine 2298 * o On all other machines, the top zone must be at least a reasonable 2299 * percentage of the middle zones. For example, on 32-bit x86, highmem 2300 * would need to be at least 256M for it to be balance a whole node. 2301 * Similarly, on x86-64 the Normal zone would need to be at least 1G 2302 * to balance a node on its own. These seemed like reasonable ratios. 2303 */ 2304static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages, 2305 int classzone_idx) 2306{ 2307 unsigned long present_pages = 0; 2308 int i; 2309 2310 for (i = 0; i <= classzone_idx; i++) 2311 present_pages += pgdat->node_zones[i].present_pages; 2312 2313 return balanced_pages > (present_pages >> 2); 2314} 2315 2316/* is kswapd sleeping prematurely? */ 2317static bool sleeping_prematurely(pg_data_t *pgdat, int order, long remaining, 2318 int classzone_idx) 2319{ 2320 int i; 2321 unsigned long balanced = 0; 2322 bool all_zones_ok = true; 2323 2324 /* If a direct reclaimer woke kswapd within HZ/10, it's premature */ 2325 if (remaining) 2326 return true; 2327 2328 /* Check the watermark levels */ 2329 for (i = 0; i <= classzone_idx; i++) { 2330 struct zone *zone = pgdat->node_zones + i; 2331 2332 if (!populated_zone(zone)) 2333 continue; 2334 2335 /* 2336 * balance_pgdat() skips over all_unreclaimable after 2337 * DEF_PRIORITY. Effectively, it considers them balanced so 2338 * they must be considered balanced here as well if kswapd 2339 * is to sleep 2340 */ 2341 if (zone->all_unreclaimable) { 2342 balanced += zone->present_pages; 2343 continue; 2344 } 2345 2346 if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone), 2347 classzone_idx, 0)) 2348 all_zones_ok = false; 2349 else 2350 balanced += zone->present_pages; 2351 } 2352 2353 /* 2354 * For high-order requests, the balanced zones must contain at least 2355 * 25% of the nodes pages for kswapd to sleep. For order-0, all zones 2356 * must be balanced 2357 */ 2358 if (order) 2359 return !pgdat_balanced(pgdat, balanced, classzone_idx); 2360 else 2361 return !all_zones_ok; 2362} 2363 2364/* 2365 * For kswapd, balance_pgdat() will work across all this node's zones until 2366 * they are all at high_wmark_pages(zone). 2367 * 2368 * Returns the final order kswapd was reclaiming at 2369 * 2370 * There is special handling here for zones which are full of pinned pages. 2371 * This can happen if the pages are all mlocked, or if they are all used by 2372 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb. 2373 * What we do is to detect the case where all pages in the zone have been 2374 * scanned twice and there has been zero successful reclaim. Mark the zone as 2375 * dead and from now on, only perform a short scan. Basically we're polling 2376 * the zone for when the problem goes away. 2377 * 2378 * kswapd scans the zones in the highmem->normal->dma direction. It skips 2379 * zones which have free_pages > high_wmark_pages(zone), but once a zone is 2380 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the 2381 * lower zones regardless of the number of free pages in the lower zones. This 2382 * interoperates with the page allocator fallback scheme to ensure that aging 2383 * of pages is balanced across the zones. 2384 */ 2385static unsigned long balance_pgdat(pg_data_t *pgdat, int order, 2386 int *classzone_idx) 2387{ 2388 int all_zones_ok; 2389 unsigned long balanced; 2390 int priority; 2391 int i; 2392 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ 2393 unsigned long total_scanned; 2394 struct reclaim_state *reclaim_state = current->reclaim_state; 2395 unsigned long nr_soft_reclaimed; 2396 unsigned long nr_soft_scanned; 2397 struct scan_control sc = { 2398 .gfp_mask = GFP_KERNEL, 2399 .may_unmap = 1, 2400 .may_swap = 1, 2401 /* 2402 * kswapd doesn't want to be bailed out while reclaim. because 2403 * we want to put equal scanning pressure on each zone. 2404 */ 2405 .nr_to_reclaim = ULONG_MAX, 2406 .swappiness = vm_swappiness, 2407 .order = order, 2408 .mem_cgroup = NULL, 2409 }; 2410 struct shrink_control shrink = { 2411 .gfp_mask = sc.gfp_mask, 2412 }; 2413loop_again: 2414 total_scanned = 0; 2415 sc.nr_reclaimed = 0; 2416 sc.may_writepage = !laptop_mode; 2417 count_vm_event(PAGEOUTRUN); 2418 2419 for (priority = DEF_PRIORITY; priority >= 0; priority--) { 2420 unsigned long lru_pages = 0; 2421 int has_under_min_watermark_zone = 0; 2422 2423 /* The swap token gets in the way of swapout... */ 2424 if (!priority) 2425 disable_swap_token(NULL); 2426 2427 all_zones_ok = 1; 2428 balanced = 0; 2429 2430 /* 2431 * Scan in the highmem->dma direction for the highest 2432 * zone which needs scanning 2433 */ 2434 for (i = pgdat->nr_zones - 1; i >= 0; i--) { 2435 struct zone *zone = pgdat->node_zones + i; 2436 2437 if (!populated_zone(zone)) 2438 continue; 2439 2440 if (zone->all_unreclaimable && priority != DEF_PRIORITY) 2441 continue; 2442 2443 /* 2444 * Do some background aging of the anon list, to give 2445 * pages a chance to be referenced before reclaiming. 2446 */ 2447 if (inactive_anon_is_low(zone, &sc)) 2448 shrink_active_list(SWAP_CLUSTER_MAX, zone, 2449 &sc, priority, 0); 2450 2451 if (!zone_watermark_ok_safe(zone, order, 2452 high_wmark_pages(zone), 0, 0)) { 2453 end_zone = i; 2454 *classzone_idx = i; 2455 break; 2456 } 2457 } 2458 if (i < 0) 2459 goto out; 2460 2461 for (i = 0; i <= end_zone; i++) { 2462 struct zone *zone = pgdat->node_zones + i; 2463 2464 lru_pages += zone_reclaimable_pages(zone); 2465 } 2466 2467 /* 2468 * Now scan the zone in the dma->highmem direction, stopping 2469 * at the last zone which needs scanning. 2470 * 2471 * We do this because the page allocator works in the opposite 2472 * direction. This prevents the page allocator from allocating 2473 * pages behind kswapd's direction of progress, which would 2474 * cause too much scanning of the lower zones. 2475 */ 2476 for (i = 0; i <= end_zone; i++) { 2477 struct zone *zone = pgdat->node_zones + i; 2478 int nr_slab; 2479 unsigned long balance_gap; 2480 2481 if (!populated_zone(zone)) 2482 continue; 2483 2484 if (zone->all_unreclaimable && priority != DEF_PRIORITY) 2485 continue; 2486 2487 sc.nr_scanned = 0; 2488 2489 nr_soft_scanned = 0; 2490 /* 2491 * Call soft limit reclaim before calling shrink_zone. 2492 */ 2493 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone, 2494 order, sc.gfp_mask, 2495 &nr_soft_scanned); 2496 sc.nr_reclaimed += nr_soft_reclaimed; 2497 total_scanned += nr_soft_scanned; 2498 2499 /* 2500 * We put equal pressure on every zone, unless 2501 * one zone has way too many pages free 2502 * already. The "too many pages" is defined 2503 * as the high wmark plus a "gap" where the 2504 * gap is either the low watermark or 1% 2505 * of the zone, whichever is smaller. 2506 */ 2507 balance_gap = min(low_wmark_pages(zone), 2508 (zone->present_pages + 2509 KSWAPD_ZONE_BALANCE_GAP_RATIO-1) / 2510 KSWAPD_ZONE_BALANCE_GAP_RATIO); 2511 if (!zone_watermark_ok_safe(zone, order, 2512 high_wmark_pages(zone) + balance_gap, 2513 end_zone, 0)) 2514 shrink_zone(priority, zone, &sc); 2515 reclaim_state->reclaimed_slab = 0; 2516 nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages); 2517 sc.nr_reclaimed += reclaim_state->reclaimed_slab; 2518 total_scanned += sc.nr_scanned; 2519 2520 if (zone->all_unreclaimable) 2521 continue; 2522 if (nr_slab == 0 && 2523 !zone_reclaimable(zone)) 2524 zone->all_unreclaimable = 1; 2525 /* 2526 * If we've done a decent amount of scanning and 2527 * the reclaim ratio is low, start doing writepage 2528 * even in laptop mode 2529 */ 2530 if (total_scanned > SWAP_CLUSTER_MAX * 2 && 2531 total_scanned > sc.nr_reclaimed + sc.nr_reclaimed / 2) 2532 sc.may_writepage = 1; 2533 2534 if (!zone_watermark_ok_safe(zone, order, 2535 high_wmark_pages(zone), end_zone, 0)) { 2536 all_zones_ok = 0; 2537 /* 2538 * We are still under min water mark. This 2539 * means that we have a GFP_ATOMIC allocation 2540 * failure risk. Hurry up! 2541 */ 2542 if (!zone_watermark_ok_safe(zone, order, 2543 min_wmark_pages(zone), end_zone, 0)) 2544 has_under_min_watermark_zone = 1; 2545 } else { 2546 /* 2547 * If a zone reaches its high watermark, 2548 * consider it to be no longer congested. It's 2549 * possible there are dirty pages backed by 2550 * congested BDIs but as pressure is relieved, 2551 * spectulatively avoid congestion waits 2552 */ 2553 zone_clear_flag(zone, ZONE_CONGESTED); 2554 if (i <= *classzone_idx) 2555 balanced += zone->present_pages; 2556 } 2557 2558 } 2559 if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx))) 2560 break; /* kswapd: all done */ 2561 /* 2562 * OK, kswapd is getting into trouble. Take a nap, then take 2563 * another pass across the zones. 2564 */ 2565 if (total_scanned && (priority < DEF_PRIORITY - 2)) { 2566 if (has_under_min_watermark_zone) 2567 count_vm_event(KSWAPD_SKIP_CONGESTION_WAIT); 2568 else 2569 congestion_wait(BLK_RW_ASYNC, HZ/10); 2570 } 2571 2572 /* 2573 * We do this so kswapd doesn't build up large priorities for 2574 * example when it is freeing in parallel with allocators. It 2575 * matches the direct reclaim path behaviour in terms of impact 2576 * on zone->*_priority. 2577 */ 2578 if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX) 2579 break; 2580 } 2581out: 2582 2583 /* 2584 * order-0: All zones must meet high watermark for a balanced node 2585 * high-order: Balanced zones must make up at least 25% of the node 2586 * for the node to be balanced 2587 */ 2588 if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, *classzone_idx)))) { 2589 cond_resched(); 2590 2591 try_to_freeze(); 2592 2593 /* 2594 * Fragmentation may mean that the system cannot be 2595 * rebalanced for high-order allocations in all zones. 2596 * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX, 2597 * it means the zones have been fully scanned and are still 2598 * not balanced. For high-order allocations, there is 2599 * little point trying all over again as kswapd may 2600 * infinite loop. 2601 * 2602 * Instead, recheck all watermarks at order-0 as they 2603 * are the most important. If watermarks are ok, kswapd will go 2604 * back to sleep. High-order users can still perform direct 2605 * reclaim if they wish. 2606 */ 2607 if (sc.nr_reclaimed < SWAP_CLUSTER_MAX) 2608 order = sc.order = 0; 2609 2610 goto loop_again; 2611 } 2612 2613 /* 2614 * If kswapd was reclaiming at a higher order, it has the option of 2615 * sleeping without all zones being balanced. Before it does, it must 2616 * ensure that the watermarks for order-0 on *all* zones are met and 2617 * that the congestion flags are cleared. The congestion flag must 2618 * be cleared as kswapd is the only mechanism that clears the flag 2619 * and it is potentially going to sleep here. 2620 */ 2621 if (order) { 2622 for (i = 0; i <= end_zone; i++) { 2623 struct zone *zone = pgdat->node_zones + i; 2624 2625 if (!populated_zone(zone)) 2626 continue; 2627 2628 if (zone->all_unreclaimable && priority != DEF_PRIORITY) 2629 continue; 2630 2631 /* Confirm the zone is balanced for order-0 */ 2632 if (!zone_watermark_ok(zone, 0, 2633 high_wmark_pages(zone), 0, 0)) { 2634 order = sc.order = 0; 2635 goto loop_again; 2636 } 2637 2638 /* If balanced, clear the congested flag */ 2639 zone_clear_flag(zone, ZONE_CONGESTED); 2640 } 2641 } 2642 2643 /* 2644 * Return the order we were reclaiming at so sleeping_prematurely() 2645 * makes a decision on the order we were last reclaiming at. However, 2646 * if another caller entered the allocator slow path while kswapd 2647 * was awake, order will remain at the higher level 2648 */ 2649 *classzone_idx = end_zone; 2650 return order; 2651} 2652 2653static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx) 2654{ 2655 long remaining = 0; 2656 DEFINE_WAIT(wait); 2657 2658 if (freezing(current) || kthread_should_stop()) 2659 return; 2660 2661 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); 2662 2663 /* Try to sleep for a short interval */ 2664 if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) { 2665 remaining = schedule_timeout(HZ/10); 2666 finish_wait(&pgdat->kswapd_wait, &wait); 2667 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); 2668 } 2669 2670 /* 2671 * After a short sleep, check if it was a premature sleep. If not, then 2672 * go fully to sleep until explicitly woken up. 2673 */ 2674 if (!sleeping_prematurely(pgdat, order, remaining, classzone_idx)) { 2675 trace_mm_vmscan_kswapd_sleep(pgdat->node_id); 2676 2677 /* 2678 * vmstat counters are not perfectly accurate and the estimated 2679 * value for counters such as NR_FREE_PAGES can deviate from the 2680 * true value by nr_online_cpus * threshold. To avoid the zone 2681 * watermarks being breached while under pressure, we reduce the 2682 * per-cpu vmstat threshold while kswapd is awake and restore 2683 * them before going back to sleep. 2684 */ 2685 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold); 2686 schedule(); 2687 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold); 2688 } else { 2689 if (remaining) 2690 count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY); 2691 else 2692 count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY); 2693 } 2694 finish_wait(&pgdat->kswapd_wait, &wait); 2695} 2696 2697/* 2698 * The background pageout daemon, started as a kernel thread 2699 * from the init process. 2700 * 2701 * This basically trickles out pages so that we have _some_ 2702 * free memory available even if there is no other activity 2703 * that frees anything up. This is needed for things like routing 2704 * etc, where we otherwise might have all activity going on in 2705 * asynchronous contexts that cannot page things out. 2706 * 2707 * If there are applications that are active memory-allocators 2708 * (most normal use), this basically shouldn't matter. 2709 */ 2710static int kswapd(void *p) 2711{ 2712 unsigned long order; 2713 int classzone_idx; 2714 pg_data_t *pgdat = (pg_data_t*)p; 2715 struct task_struct *tsk = current; 2716 2717 struct reclaim_state reclaim_state = { 2718 .reclaimed_slab = 0, 2719 }; 2720 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id); 2721 2722 lockdep_set_current_reclaim_state(GFP_KERNEL); 2723 2724 if (!cpumask_empty(cpumask)) 2725 set_cpus_allowed_ptr(tsk, cpumask); 2726 current->reclaim_state = &reclaim_state; 2727 2728 /* 2729 * Tell the memory management that we're a "memory allocator", 2730 * and that if we need more memory we should get access to it 2731 * regardless (see "__alloc_pages()"). "kswapd" should 2732 * never get caught in the normal page freeing logic. 2733 * 2734 * (Kswapd normally doesn't need memory anyway, but sometimes 2735 * you need a small amount of memory in order to be able to 2736 * page out something else, and this flag essentially protects 2737 * us from recursively trying to free more memory as we're 2738 * trying to free the first piece of memory in the first place). 2739 */ 2740 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; 2741 set_freezable(); 2742 2743 order = 0; 2744 classzone_idx = MAX_NR_ZONES - 1; 2745 for ( ; ; ) { 2746 unsigned long new_order; 2747 int new_classzone_idx; 2748 int ret; 2749 2750 new_order = pgdat->kswapd_max_order; 2751 new_classzone_idx = pgdat->classzone_idx; 2752 pgdat->kswapd_max_order = 0; 2753 pgdat->classzone_idx = MAX_NR_ZONES - 1; 2754 if (order < new_order || classzone_idx > new_classzone_idx) { 2755 /* 2756 * Don't sleep if someone wants a larger 'order' 2757 * allocation or has tigher zone constraints 2758 */ 2759 order = new_order; 2760 classzone_idx = new_classzone_idx; 2761 } else { 2762 kswapd_try_to_sleep(pgdat, order, classzone_idx); 2763 order = pgdat->kswapd_max_order; 2764 classzone_idx = pgdat->classzone_idx; 2765 pgdat->kswapd_max_order = 0; 2766 pgdat->classzone_idx = MAX_NR_ZONES - 1; 2767 } 2768 2769 ret = try_to_freeze(); 2770 if (kthread_should_stop()) 2771 break; 2772 2773 /* 2774 * We can speed up thawing tasks if we don't call balance_pgdat 2775 * after returning from the refrigerator 2776 */ 2777 if (!ret) { 2778 trace_mm_vmscan_kswapd_wake(pgdat->node_id, order); 2779 order = balance_pgdat(pgdat, order, &classzone_idx); 2780 } 2781 } 2782 return 0; 2783} 2784 2785/* 2786 * A zone is low on free memory, so wake its kswapd task to service it. 2787 */ 2788void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx) 2789{ 2790 pg_data_t *pgdat; 2791 2792 if (!populated_zone(zone)) 2793 return; 2794 2795 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2796 return; 2797 pgdat = zone->zone_pgdat; 2798 if (pgdat->kswapd_max_order < order) { 2799 pgdat->kswapd_max_order = order; 2800 pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx); 2801 } 2802 if (!waitqueue_active(&pgdat->kswapd_wait)) 2803 return; 2804 if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0)) 2805 return; 2806 2807 trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order); 2808 wake_up_interruptible(&pgdat->kswapd_wait); 2809} 2810 2811/* 2812 * The reclaimable count would be mostly accurate. 2813 * The less reclaimable pages may be 2814 * - mlocked pages, which will be moved to unevictable list when encountered 2815 * - mapped pages, which may require several travels to be reclaimed 2816 * - dirty pages, which is not "instantly" reclaimable 2817 */ 2818unsigned long global_reclaimable_pages(void) 2819{ 2820 int nr; 2821 2822 nr = global_page_state(NR_ACTIVE_FILE) + 2823 global_page_state(NR_INACTIVE_FILE); 2824 2825 if (nr_swap_pages > 0) 2826 nr += global_page_state(NR_ACTIVE_ANON) + 2827 global_page_state(NR_INACTIVE_ANON); 2828 2829 return nr; 2830} 2831 2832unsigned long zone_reclaimable_pages(struct zone *zone) 2833{ 2834 int nr; 2835 2836 nr = zone_page_state(zone, NR_ACTIVE_FILE) + 2837 zone_page_state(zone, NR_INACTIVE_FILE); 2838 2839 if (nr_swap_pages > 0) 2840 nr += zone_page_state(zone, NR_ACTIVE_ANON) + 2841 zone_page_state(zone, NR_INACTIVE_ANON); 2842 2843 return nr; 2844} 2845 2846#ifdef CONFIG_HIBERNATION 2847/* 2848 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of 2849 * freed pages. 2850 * 2851 * Rather than trying to age LRUs the aim is to preserve the overall 2852 * LRU order by reclaiming preferentially 2853 * inactive > active > active referenced > active mapped 2854 */ 2855unsigned long shrink_all_memory(unsigned long nr_to_reclaim) 2856{ 2857 struct reclaim_state reclaim_state; 2858 struct scan_control sc = { 2859 .gfp_mask = GFP_HIGHUSER_MOVABLE, 2860 .may_swap = 1, 2861 .may_unmap = 1, 2862 .may_writepage = 1, 2863 .nr_to_reclaim = nr_to_reclaim, 2864 .hibernation_mode = 1, 2865 .swappiness = vm_swappiness, 2866 .order = 0, 2867 }; 2868 struct shrink_control shrink = { 2869 .gfp_mask = sc.gfp_mask, 2870 }; 2871 struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask); 2872 struct task_struct *p = current; 2873 unsigned long nr_reclaimed; 2874 2875 p->flags |= PF_MEMALLOC; 2876 lockdep_set_current_reclaim_state(sc.gfp_mask); 2877 reclaim_state.reclaimed_slab = 0; 2878 p->reclaim_state = &reclaim_state; 2879 2880 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); 2881 2882 p->reclaim_state = NULL; 2883 lockdep_clear_current_reclaim_state(); 2884 p->flags &= ~PF_MEMALLOC; 2885 2886 return nr_reclaimed; 2887} 2888#endif /* CONFIG_HIBERNATION */ 2889 2890/* It's optimal to keep kswapds on the same CPUs as their memory, but 2891 not required for correctness. So if the last cpu in a node goes 2892 away, we get changed to run anywhere: as the first one comes back, 2893 restore their cpu bindings. */ 2894static int __devinit cpu_callback(struct notifier_block *nfb, 2895 unsigned long action, void *hcpu) 2896{ 2897 int nid; 2898 2899 if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) { 2900 for_each_node_state(nid, N_HIGH_MEMORY) { 2901 pg_data_t *pgdat = NODE_DATA(nid); 2902 const struct cpumask *mask; 2903 2904 mask = cpumask_of_node(pgdat->node_id); 2905 2906 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids) 2907 /* One of our CPUs online: restore mask */ 2908 set_cpus_allowed_ptr(pgdat->kswapd, mask); 2909 } 2910 } 2911 return NOTIFY_OK; 2912} 2913 2914/* 2915 * This kswapd start function will be called by init and node-hot-add. 2916 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added. 2917 */ 2918int kswapd_run(int nid) 2919{ 2920 pg_data_t *pgdat = NODE_DATA(nid); 2921 int ret = 0; 2922 2923 if (pgdat->kswapd) 2924 return 0; 2925 2926 pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid); 2927 if (IS_ERR(pgdat->kswapd)) { 2928 /* failure at boot is fatal */ 2929 BUG_ON(system_state == SYSTEM_BOOTING); 2930 printk("Failed to start kswapd on node %d\n",nid); 2931 ret = -1; 2932 } 2933 return ret; 2934} 2935 2936/* 2937 * Called by memory hotplug when all memory in a node is offlined. 2938 */ 2939void kswapd_stop(int nid) 2940{ 2941 struct task_struct *kswapd = NODE_DATA(nid)->kswapd; 2942 2943 if (kswapd) 2944 kthread_stop(kswapd); 2945} 2946 2947static int __init kswapd_init(void) 2948{ 2949 int nid; 2950 2951 swap_setup(); 2952 for_each_node_state(nid, N_HIGH_MEMORY) 2953 kswapd_run(nid); 2954 hotcpu_notifier(cpu_callback, 0); 2955 return 0; 2956} 2957 2958module_init(kswapd_init) 2959 2960#ifdef CONFIG_NUMA 2961/* 2962 * Zone reclaim mode 2963 * 2964 * If non-zero call zone_reclaim when the number of free pages falls below 2965 * the watermarks. 2966 */ 2967int zone_reclaim_mode __read_mostly; 2968 2969#define RECLAIM_OFF 0 2970#define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */ 2971#define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ 2972#define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */ 2973 2974/* 2975 * Priority for ZONE_RECLAIM. This determines the fraction of pages 2976 * of a node considered for each zone_reclaim. 4 scans 1/16th of 2977 * a zone. 2978 */ 2979#define ZONE_RECLAIM_PRIORITY 4 2980 2981/* 2982 * Percentage of pages in a zone that must be unmapped for zone_reclaim to 2983 * occur. 2984 */ 2985int sysctl_min_unmapped_ratio = 1; 2986 2987/* 2988 * If the number of slab pages in a zone grows beyond this percentage then 2989 * slab reclaim needs to occur. 2990 */ 2991int sysctl_min_slab_ratio = 5; 2992 2993static inline unsigned long zone_unmapped_file_pages(struct zone *zone) 2994{ 2995 unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED); 2996 unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) + 2997 zone_page_state(zone, NR_ACTIVE_FILE); 2998 2999 /* 3000 * It's possible for there to be more file mapped pages than 3001 * accounted for by the pages on the file LRU lists because 3002 * tmpfs pages accounted for as ANON can also be FILE_MAPPED 3003 */ 3004 return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0; 3005} 3006 3007/* Work out how many page cache pages we can reclaim in this reclaim_mode */ 3008static long zone_pagecache_reclaimable(struct zone *zone) 3009{ 3010 long nr_pagecache_reclaimable; 3011 long delta = 0; 3012 3013 /* 3014 * If RECLAIM_SWAP is set, then all file pages are considered 3015 * potentially reclaimable. Otherwise, we have to worry about 3016 * pages like swapcache and zone_unmapped_file_pages() provides 3017 * a better estimate 3018 */ 3019 if (zone_reclaim_mode & RECLAIM_SWAP) 3020 nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES); 3021 else 3022 nr_pagecache_reclaimable = zone_unmapped_file_pages(zone); 3023 3024 /* If we can't clean pages, remove dirty pages from consideration */ 3025 if (!(zone_reclaim_mode & RECLAIM_WRITE)) 3026 delta += zone_page_state(zone, NR_FILE_DIRTY); 3027 3028 /* Watch for any possible underflows due to delta */ 3029 if (unlikely(delta > nr_pagecache_reclaimable)) 3030 delta = nr_pagecache_reclaimable; 3031 3032 return nr_pagecache_reclaimable - delta; 3033} 3034 3035/* 3036 * Try to free up some pages from this zone through reclaim. 3037 */ 3038static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) 3039{ 3040 /* Minimum pages needed in order to stay on node */ 3041 const unsigned long nr_pages = 1 << order; 3042 struct task_struct *p = current; 3043 struct reclaim_state reclaim_state; 3044 int priority; 3045 struct scan_control sc = { 3046 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE), 3047 .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP), 3048 .may_swap = 1, 3049 .nr_to_reclaim = max_t(unsigned long, nr_pages, 3050 SWAP_CLUSTER_MAX), 3051 .gfp_mask = gfp_mask, 3052 .swappiness = vm_swappiness, 3053 .order = order, 3054 }; 3055 struct shrink_control shrink = { 3056 .gfp_mask = sc.gfp_mask, 3057 }; 3058 unsigned long nr_slab_pages0, nr_slab_pages1; 3059 3060 cond_resched(); 3061 /* 3062 * We need to be able to allocate from the reserves for RECLAIM_SWAP 3063 * and we also need to be able to write out pages for RECLAIM_WRITE 3064 * and RECLAIM_SWAP. 3065 */ 3066 p->flags |= PF_MEMALLOC | PF_SWAPWRITE; 3067 lockdep_set_current_reclaim_state(gfp_mask); 3068 reclaim_state.reclaimed_slab = 0; 3069 p->reclaim_state = &reclaim_state; 3070 3071 if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) { 3072 /* 3073 * Free memory by calling shrink zone with increasing 3074 * priorities until we have enough memory freed. 3075 */ 3076 priority = ZONE_RECLAIM_PRIORITY; 3077 do { 3078 shrink_zone(priority, zone, &sc); 3079 priority--; 3080 } while (priority >= 0 && sc.nr_reclaimed < nr_pages); 3081 } 3082 3083 nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE); 3084 if (nr_slab_pages0 > zone->min_slab_pages) { 3085 /* 3086 * shrink_slab() does not currently allow us to determine how 3087 * many pages were freed in this zone. So we take the current 3088 * number of slab pages and shake the slab until it is reduced 3089 * by the same nr_pages that we used for reclaiming unmapped 3090 * pages. 3091 * 3092 * Note that shrink_slab will free memory on all zones and may 3093 * take a long time. 3094 */ 3095 for (;;) { 3096 unsigned long lru_pages = zone_reclaimable_pages(zone); 3097 3098 /* No reclaimable slab or very low memory pressure */ 3099 if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages)) 3100 break; 3101 3102 /* Freed enough memory */ 3103 nr_slab_pages1 = zone_page_state(zone, 3104 NR_SLAB_RECLAIMABLE); 3105 if (nr_slab_pages1 + nr_pages <= nr_slab_pages0) 3106 break; 3107 } 3108 3109 /* 3110 * Update nr_reclaimed by the number of slab pages we 3111 * reclaimed from this zone. 3112 */ 3113 nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE); 3114 if (nr_slab_pages1 < nr_slab_pages0) 3115 sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1; 3116 } 3117 3118 p->reclaim_state = NULL; 3119 current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE); 3120 lockdep_clear_current_reclaim_state(); 3121 return sc.nr_reclaimed >= nr_pages; 3122} 3123 3124int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) 3125{ 3126 int node_id; 3127 int ret; 3128 3129 /* 3130 * Zone reclaim reclaims unmapped file backed pages and 3131 * slab pages if we are over the defined limits. 3132 * 3133 * A small portion of unmapped file backed pages is needed for 3134 * file I/O otherwise pages read by file I/O will be immediately 3135 * thrown out if the zone is overallocated. So we do not reclaim 3136 * if less than a specified percentage of the zone is used by 3137 * unmapped file backed pages. 3138 */ 3139 if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages && 3140 zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages) 3141 return ZONE_RECLAIM_FULL; 3142 3143 if (zone->all_unreclaimable) 3144 return ZONE_RECLAIM_FULL; 3145 3146 /* 3147 * Do not scan if the allocation should not be delayed. 3148 */ 3149 if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC)) 3150 return ZONE_RECLAIM_NOSCAN; 3151 3152 /* 3153 * Only run zone reclaim on the local zone or on zones that do not 3154 * have associated processors. This will favor the local processor 3155 * over remote processors and spread off node memory allocations 3156 * as wide as possible. 3157 */ 3158 node_id = zone_to_nid(zone); 3159 if (node_state(node_id, N_CPU) && node_id != numa_node_id()) 3160 return ZONE_RECLAIM_NOSCAN; 3161 3162 if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED)) 3163 return ZONE_RECLAIM_NOSCAN; 3164 3165 ret = __zone_reclaim(zone, gfp_mask, order); 3166 zone_clear_flag(zone, ZONE_RECLAIM_LOCKED); 3167 3168 if (!ret) 3169 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED); 3170 3171 return ret; 3172} 3173#endif 3174 3175/* 3176 * page_evictable - test whether a page is evictable 3177 * @page: the page to test 3178 * @vma: the VMA in which the page is or will be mapped, may be NULL 3179 * 3180 * Test whether page is evictable--i.e., should be placed on active/inactive 3181 * lists vs unevictable list. The vma argument is !NULL when called from the 3182 * fault path to determine how to instantate a new page. 3183 * 3184 * Reasons page might not be evictable: 3185 * (1) page's mapping marked unevictable 3186 * (2) page is part of an mlocked VMA 3187 * 3188 */ 3189int page_evictable(struct page *page, struct vm_area_struct *vma) 3190{ 3191 3192 if (mapping_unevictable(page_mapping(page))) 3193 return 0; 3194 3195 if (PageMlocked(page) || (vma && is_mlocked_vma(vma, page))) 3196 return 0; 3197 3198 return 1; 3199} 3200 3201/** 3202 * check_move_unevictable_page - check page for evictability and move to appropriate zone lru list 3203 * @page: page to check evictability and move to appropriate lru list 3204 * @zone: zone page is in 3205 * 3206 * Checks a page for evictability and moves the page to the appropriate 3207 * zone lru list. 3208 * 3209 * Restrictions: zone->lru_lock must be held, page must be on LRU and must 3210 * have PageUnevictable set. 3211 */ 3212static void check_move_unevictable_page(struct page *page, struct zone *zone) 3213{ 3214 VM_BUG_ON(PageActive(page)); 3215 3216retry: 3217 ClearPageUnevictable(page); 3218 if (page_evictable(page, NULL)) { 3219 enum lru_list l = page_lru_base_type(page); 3220 3221 __dec_zone_state(zone, NR_UNEVICTABLE); 3222 list_move(&page->lru, &zone->lru[l].list); 3223 mem_cgroup_move_lists(page, LRU_UNEVICTABLE, l); 3224 __inc_zone_state(zone, NR_INACTIVE_ANON + l); 3225 __count_vm_event(UNEVICTABLE_PGRESCUED); 3226 } else { 3227 /* 3228 * rotate unevictable list 3229 */ 3230 SetPageUnevictable(page); 3231 list_move(&page->lru, &zone->lru[LRU_UNEVICTABLE].list); 3232 mem_cgroup_rotate_lru_list(page, LRU_UNEVICTABLE); 3233 if (page_evictable(page, NULL)) 3234 goto retry; 3235 } 3236} 3237 3238/** 3239 * scan_mapping_unevictable_pages - scan an address space for evictable pages 3240 * @mapping: struct address_space to scan for evictable pages 3241 * 3242 * Scan all pages in mapping. Check unevictable pages for 3243 * evictability and move them to the appropriate zone lru list. 3244 */ 3245void scan_mapping_unevictable_pages(struct address_space *mapping) 3246{ 3247 pgoff_t next = 0; 3248 pgoff_t end = (i_size_read(mapping->host) + PAGE_CACHE_SIZE - 1) >> 3249 PAGE_CACHE_SHIFT; 3250 struct zone *zone; 3251 struct pagevec pvec; 3252 3253 if (mapping->nrpages == 0) 3254 return; 3255 3256 pagevec_init(&pvec, 0); 3257 while (next < end && 3258 pagevec_lookup(&pvec, mapping, next, PAGEVEC_SIZE)) { 3259 int i; 3260 int pg_scanned = 0; 3261 3262 zone = NULL; 3263 3264 for (i = 0; i < pagevec_count(&pvec); i++) { 3265 struct page *page = pvec.pages[i]; 3266 pgoff_t page_index = page->index; 3267 struct zone *pagezone = page_zone(page); 3268 3269 pg_scanned++; 3270 if (page_index > next) 3271 next = page_index; 3272 next++; 3273 3274 if (pagezone != zone) { 3275 if (zone) 3276 spin_unlock_irq(&zone->lru_lock); 3277 zone = pagezone; 3278 spin_lock_irq(&zone->lru_lock); 3279 } 3280 3281 if (PageLRU(page) && PageUnevictable(page)) 3282 check_move_unevictable_page(page, zone); 3283 } 3284 if (zone) 3285 spin_unlock_irq(&zone->lru_lock); 3286 pagevec_release(&pvec); 3287 3288 count_vm_events(UNEVICTABLE_PGSCANNED, pg_scanned); 3289 } 3290 3291} 3292 3293/** 3294 * scan_zone_unevictable_pages - check unevictable list for evictable pages 3295 * @zone - zone of which to scan the unevictable list 3296 * 3297 * Scan @zone's unevictable LRU lists to check for pages that have become 3298 * evictable. Move those that have to @zone's inactive list where they 3299 * become candidates for reclaim, unless shrink_inactive_zone() decides 3300 * to reactivate them. Pages that are still unevictable are rotated 3301 * back onto @zone's unevictable list. 3302 */ 3303#define SCAN_UNEVICTABLE_BATCH_SIZE 16UL /* arbitrary lock hold batch size */ 3304static void scan_zone_unevictable_pages(struct zone *zone) 3305{ 3306 struct list_head *l_unevictable = &zone->lru[LRU_UNEVICTABLE].list; 3307 unsigned long scan; 3308 unsigned long nr_to_scan = zone_page_state(zone, NR_UNEVICTABLE); 3309 3310 while (nr_to_scan > 0) { 3311 unsigned long batch_size = min(nr_to_scan, 3312 SCAN_UNEVICTABLE_BATCH_SIZE); 3313 3314 spin_lock_irq(&zone->lru_lock); 3315 for (scan = 0; scan < batch_size; scan++) { 3316 struct page *page = lru_to_page(l_unevictable); 3317 3318 if (!trylock_page(page)) 3319 continue; 3320 3321 prefetchw_prev_lru_page(page, l_unevictable, flags); 3322 3323 if (likely(PageLRU(page) && PageUnevictable(page))) 3324 check_move_unevictable_page(page, zone); 3325 3326 unlock_page(page); 3327 } 3328 spin_unlock_irq(&zone->lru_lock); 3329 3330 nr_to_scan -= batch_size; 3331 } 3332} 3333 3334 3335/** 3336 * scan_all_zones_unevictable_pages - scan all unevictable lists for evictable pages 3337 * 3338 * A really big hammer: scan all zones' unevictable LRU lists to check for 3339 * pages that have become evictable. Move those back to the zones' 3340 * inactive list where they become candidates for reclaim. 3341 * This occurs when, e.g., we have unswappable pages on the unevictable lists, 3342 * and we add swap to the system. As such, it runs in the context of a task 3343 * that has possibly/probably made some previously unevictable pages 3344 * evictable. 3345 */ 3346static void scan_all_zones_unevictable_pages(void) 3347{ 3348 struct zone *zone; 3349 3350 for_each_zone(zone) { 3351 scan_zone_unevictable_pages(zone); 3352 } 3353} 3354 3355/* 3356 * scan_unevictable_pages [vm] sysctl handler. On demand re-scan of 3357 * all nodes' unevictable lists for evictable pages 3358 */ 3359unsigned long scan_unevictable_pages; 3360 3361int scan_unevictable_handler(struct ctl_table *table, int write, 3362 void __user *buffer, 3363 size_t *length, loff_t *ppos) 3364{ 3365 proc_doulongvec_minmax(table, write, buffer, length, ppos); 3366 3367 if (write && *(unsigned long *)table->data) 3368 scan_all_zones_unevictable_pages(); 3369 3370 scan_unevictable_pages = 0; 3371 return 0; 3372} 3373 3374#ifdef CONFIG_NUMA 3375/* 3376 * per node 'scan_unevictable_pages' attribute. On demand re-scan of 3377 * a specified node's per zone unevictable lists for evictable pages. 3378 */ 3379 3380static ssize_t read_scan_unevictable_node(struct sys_device *dev, 3381 struct sysdev_attribute *attr, 3382 char *buf) 3383{ 3384 return sprintf(buf, "0\n"); /* always zero; should fit... */ 3385} 3386 3387static ssize_t write_scan_unevictable_node(struct sys_device *dev, 3388 struct sysdev_attribute *attr, 3389 const char *buf, size_t count) 3390{ 3391 struct zone *node_zones = NODE_DATA(dev->id)->node_zones; 3392 struct zone *zone; 3393 unsigned long res; 3394 unsigned long req = strict_strtoul(buf, 10, &res); 3395 3396 if (!req) 3397 return 1; /* zero is no-op */ 3398 3399 for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) { 3400 if (!populated_zone(zone)) 3401 continue; 3402 scan_zone_unevictable_pages(zone); 3403 } 3404 return 1; 3405} 3406 3407 3408static SYSDEV_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR, 3409 read_scan_unevictable_node, 3410 write_scan_unevictable_node); 3411 3412int scan_unevictable_register_node(struct node *node) 3413{ 3414 return sysdev_create_file(&node->sysdev, &attr_scan_unevictable_pages); 3415} 3416 3417void scan_unevictable_unregister_node(struct node *node) 3418{ 3419 sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages); 3420} 3421#endif 3422