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/vmpressure.h> 23 #include <linux/vmstat.h> 24 #include <linux/file.h> 25 #include <linux/writeback.h> 26 #include <linux/blkdev.h> 27 #include <linux/buffer_head.h> /* for try_to_release_page(), 28 buffer_heads_over_limit */ 29 #include <linux/mm_inline.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 struct scan_control { 58 /* Incremented by the number of inactive pages that were scanned */ 59 unsigned long nr_scanned; 60 61 /* Number of pages freed so far during a call to shrink_zones() */ 62 unsigned long nr_reclaimed; 63 64 /* How many pages shrink_list() should reclaim */ 65 unsigned long nr_to_reclaim; 66 67 unsigned long hibernation_mode; 68 69 /* This context's GFP mask */ 70 gfp_t gfp_mask; 71 72 int may_writepage; 73 74 /* Can mapped pages be reclaimed? */ 75 int may_unmap; 76 77 /* Can pages be swapped as part of reclaim? */ 78 int may_swap; 79 80 int order; 81 82 /* Scan (total_size >> priority) pages at once */ 83 int priority; 84 85 /* 86 * The memory cgroup that hit its limit and as a result is the 87 * primary target of this reclaim invocation. 88 */ 89 struct mem_cgroup *target_mem_cgroup; 90 91 /* 92 * Nodemask of nodes allowed by the caller. If NULL, all nodes 93 * are scanned. 94 */ 95 nodemask_t *nodemask; 96 }; 97 98 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru)) 99 100 #ifdef ARCH_HAS_PREFETCH 101 #define prefetch_prev_lru_page(_page, _base, _field) \ 102 do { \ 103 if ((_page)->lru.prev != _base) { \ 104 struct page *prev; \ 105 \ 106 prev = lru_to_page(&(_page->lru)); \ 107 prefetch(&prev->_field); \ 108 } \ 109 } while (0) 110 #else 111 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0) 112 #endif 113 114 #ifdef ARCH_HAS_PREFETCHW 115 #define prefetchw_prev_lru_page(_page, _base, _field) \ 116 do { \ 117 if ((_page)->lru.prev != _base) { \ 118 struct page *prev; \ 119 \ 120 prev = lru_to_page(&(_page->lru)); \ 121 prefetchw(&prev->_field); \ 122 } \ 123 } while (0) 124 #else 125 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0) 126 #endif 127 128 /* 129 * From 0 .. 100. Higher means more swappy. 130 */ 131 int vm_swappiness = 60; 132 unsigned long vm_total_pages; /* The total number of pages which the VM controls */ 133 134 static LIST_HEAD(shrinker_list); 135 static DECLARE_RWSEM(shrinker_rwsem); 136 137 #ifdef CONFIG_MEMCG 138 static bool global_reclaim(struct scan_control *sc) 139 { 140 return !sc->target_mem_cgroup; 141 } 142 #else 143 static bool global_reclaim(struct scan_control *sc) 144 { 145 return true; 146 } 147 #endif 148 149 static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru) 150 { 151 if (!mem_cgroup_disabled()) 152 return mem_cgroup_get_lru_size(lruvec, lru); 153 154 return zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru); 155 } 156 157 /* 158 * Add a shrinker callback to be called from the vm 159 */ 160 void register_shrinker(struct shrinker *shrinker) 161 { 162 atomic_long_set(&shrinker->nr_in_batch, 0); 163 down_write(&shrinker_rwsem); 164 list_add_tail(&shrinker->list, &shrinker_list); 165 up_write(&shrinker_rwsem); 166 } 167 EXPORT_SYMBOL(register_shrinker); 168 169 /* 170 * Remove one 171 */ 172 void unregister_shrinker(struct shrinker *shrinker) 173 { 174 down_write(&shrinker_rwsem); 175 list_del(&shrinker->list); 176 up_write(&shrinker_rwsem); 177 } 178 EXPORT_SYMBOL(unregister_shrinker); 179 180 static inline int do_shrinker_shrink(struct shrinker *shrinker, 181 struct shrink_control *sc, 182 unsigned long nr_to_scan) 183 { 184 sc->nr_to_scan = nr_to_scan; 185 return (*shrinker->shrink)(shrinker, sc); 186 } 187 188 #define SHRINK_BATCH 128 189 /* 190 * Call the shrink functions to age shrinkable caches 191 * 192 * Here we assume it costs one seek to replace a lru page and that it also 193 * takes a seek to recreate a cache object. With this in mind we age equal 194 * percentages of the lru and ageable caches. This should balance the seeks 195 * generated by these structures. 196 * 197 * If the vm encountered mapped pages on the LRU it increase the pressure on 198 * slab to avoid swapping. 199 * 200 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits. 201 * 202 * `lru_pages' represents the number of on-LRU pages in all the zones which 203 * are eligible for the caller's allocation attempt. It is used for balancing 204 * slab reclaim versus page reclaim. 205 * 206 * Returns the number of slab objects which we shrunk. 207 */ 208 unsigned long shrink_slab(struct shrink_control *shrink, 209 unsigned long nr_pages_scanned, 210 unsigned long lru_pages) 211 { 212 struct shrinker *shrinker; 213 unsigned long ret = 0; 214 215 if (nr_pages_scanned == 0) 216 nr_pages_scanned = SWAP_CLUSTER_MAX; 217 218 if (!down_read_trylock(&shrinker_rwsem)) { 219 /* Assume we'll be able to shrink next time */ 220 ret = 1; 221 goto out; 222 } 223 224 list_for_each_entry(shrinker, &shrinker_list, list) { 225 unsigned long long delta; 226 long total_scan; 227 long max_pass; 228 int shrink_ret = 0; 229 long nr; 230 long new_nr; 231 long batch_size = shrinker->batch ? shrinker->batch 232 : SHRINK_BATCH; 233 234 max_pass = do_shrinker_shrink(shrinker, shrink, 0); 235 if (max_pass <= 0) 236 continue; 237 238 /* 239 * copy the current shrinker scan count into a local variable 240 * and zero it so that other concurrent shrinker invocations 241 * don't also do this scanning work. 242 */ 243 nr = atomic_long_xchg(&shrinker->nr_in_batch, 0); 244 245 total_scan = nr; 246 delta = (4 * nr_pages_scanned) / shrinker->seeks; 247 delta *= max_pass; 248 do_div(delta, lru_pages + 1); 249 total_scan += delta; 250 if (total_scan < 0) { 251 printk(KERN_ERR "shrink_slab: %pF negative objects to " 252 "delete nr=%ld\n", 253 shrinker->shrink, total_scan); 254 total_scan = max_pass; 255 } 256 257 /* 258 * We need to avoid excessive windup on filesystem shrinkers 259 * due to large numbers of GFP_NOFS allocations causing the 260 * shrinkers to return -1 all the time. This results in a large 261 * nr being built up so when a shrink that can do some work 262 * comes along it empties the entire cache due to nr >>> 263 * max_pass. This is bad for sustaining a working set in 264 * memory. 265 * 266 * Hence only allow the shrinker to scan the entire cache when 267 * a large delta change is calculated directly. 268 */ 269 if (delta < max_pass / 4) 270 total_scan = min(total_scan, max_pass / 2); 271 272 /* 273 * Avoid risking looping forever due to too large nr value: 274 * never try to free more than twice the estimate number of 275 * freeable entries. 276 */ 277 if (total_scan > max_pass * 2) 278 total_scan = max_pass * 2; 279 280 trace_mm_shrink_slab_start(shrinker, shrink, nr, 281 nr_pages_scanned, lru_pages, 282 max_pass, delta, total_scan); 283 284 while (total_scan >= batch_size) { 285 int nr_before; 286 287 nr_before = do_shrinker_shrink(shrinker, shrink, 0); 288 shrink_ret = do_shrinker_shrink(shrinker, shrink, 289 batch_size); 290 if (shrink_ret == -1) 291 break; 292 if (shrink_ret < nr_before) 293 ret += nr_before - shrink_ret; 294 count_vm_events(SLABS_SCANNED, batch_size); 295 total_scan -= batch_size; 296 297 cond_resched(); 298 } 299 300 /* 301 * move the unused scan count back into the shrinker in a 302 * manner that handles concurrent updates. If we exhausted the 303 * scan, there is no need to do an update. 304 */ 305 if (total_scan > 0) 306 new_nr = atomic_long_add_return(total_scan, 307 &shrinker->nr_in_batch); 308 else 309 new_nr = atomic_long_read(&shrinker->nr_in_batch); 310 311 trace_mm_shrink_slab_end(shrinker, shrink_ret, nr, new_nr); 312 } 313 up_read(&shrinker_rwsem); 314 out: 315 cond_resched(); 316 return ret; 317 } 318 319 static inline int is_page_cache_freeable(struct page *page) 320 { 321 /* 322 * A freeable page cache page is referenced only by the caller 323 * that isolated the page, the page cache radix tree and 324 * optional buffer heads at page->private. 325 */ 326 return page_count(page) - page_has_private(page) == 2; 327 } 328 329 static int may_write_to_queue(struct backing_dev_info *bdi, 330 struct scan_control *sc) 331 { 332 if (current->flags & PF_SWAPWRITE) 333 return 1; 334 if (!bdi_write_congested(bdi)) 335 return 1; 336 if (bdi == current->backing_dev_info) 337 return 1; 338 return 0; 339 } 340 341 /* 342 * We detected a synchronous write error writing a page out. Probably 343 * -ENOSPC. We need to propagate that into the address_space for a subsequent 344 * fsync(), msync() or close(). 345 * 346 * The tricky part is that after writepage we cannot touch the mapping: nothing 347 * prevents it from being freed up. But we have a ref on the page and once 348 * that page is locked, the mapping is pinned. 349 * 350 * We're allowed to run sleeping lock_page() here because we know the caller has 351 * __GFP_FS. 352 */ 353 static void handle_write_error(struct address_space *mapping, 354 struct page *page, int error) 355 { 356 lock_page(page); 357 if (page_mapping(page) == mapping) 358 mapping_set_error(mapping, error); 359 unlock_page(page); 360 } 361 362 /* possible outcome of pageout() */ 363 typedef enum { 364 /* failed to write page out, page is locked */ 365 PAGE_KEEP, 366 /* move page to the active list, page is locked */ 367 PAGE_ACTIVATE, 368 /* page has been sent to the disk successfully, page is unlocked */ 369 PAGE_SUCCESS, 370 /* page is clean and locked */ 371 PAGE_CLEAN, 372 } pageout_t; 373 374 /* 375 * pageout is called by shrink_page_list() for each dirty page. 376 * Calls ->writepage(). 377 */ 378 static pageout_t pageout(struct page *page, struct address_space *mapping, 379 struct scan_control *sc) 380 { 381 /* 382 * If the page is dirty, only perform writeback if that write 383 * will be non-blocking. To prevent this allocation from being 384 * stalled by pagecache activity. But note that there may be 385 * stalls if we need to run get_block(). We could test 386 * PagePrivate for that. 387 * 388 * If this process is currently in __generic_file_aio_write() against 389 * this page's queue, we can perform writeback even if that 390 * will block. 391 * 392 * If the page is swapcache, write it back even if that would 393 * block, for some throttling. This happens by accident, because 394 * swap_backing_dev_info is bust: it doesn't reflect the 395 * congestion state of the swapdevs. Easy to fix, if needed. 396 */ 397 if (!is_page_cache_freeable(page)) 398 return PAGE_KEEP; 399 if (!mapping) { 400 /* 401 * Some data journaling orphaned pages can have 402 * page->mapping == NULL while being dirty with clean buffers. 403 */ 404 if (page_has_private(page)) { 405 if (try_to_free_buffers(page)) { 406 ClearPageDirty(page); 407 printk("%s: orphaned page\n", __func__); 408 return PAGE_CLEAN; 409 } 410 } 411 return PAGE_KEEP; 412 } 413 if (mapping->a_ops->writepage == NULL) 414 return PAGE_ACTIVATE; 415 if (!may_write_to_queue(mapping->backing_dev_info, sc)) 416 return PAGE_KEEP; 417 418 if (clear_page_dirty_for_io(page)) { 419 int res; 420 struct writeback_control wbc = { 421 .sync_mode = WB_SYNC_NONE, 422 .nr_to_write = SWAP_CLUSTER_MAX, 423 .range_start = 0, 424 .range_end = LLONG_MAX, 425 .for_reclaim = 1, 426 }; 427 428 SetPageReclaim(page); 429 res = mapping->a_ops->writepage(page, &wbc); 430 if (res < 0) 431 handle_write_error(mapping, page, res); 432 if (res == AOP_WRITEPAGE_ACTIVATE) { 433 ClearPageReclaim(page); 434 return PAGE_ACTIVATE; 435 } 436 437 if (!PageWriteback(page)) { 438 /* synchronous write or broken a_ops? */ 439 ClearPageReclaim(page); 440 } 441 trace_mm_vmscan_writepage(page, trace_reclaim_flags(page)); 442 inc_zone_page_state(page, NR_VMSCAN_WRITE); 443 return PAGE_SUCCESS; 444 } 445 446 return PAGE_CLEAN; 447 } 448 449 /* 450 * Same as remove_mapping, but if the page is removed from the mapping, it 451 * gets returned with a refcount of 0. 452 */ 453 static int __remove_mapping(struct address_space *mapping, struct page *page) 454 { 455 BUG_ON(!PageLocked(page)); 456 BUG_ON(mapping != page_mapping(page)); 457 458 spin_lock_irq(&mapping->tree_lock); 459 /* 460 * The non racy check for a busy page. 461 * 462 * Must be careful with the order of the tests. When someone has 463 * a ref to the page, it may be possible that they dirty it then 464 * drop the reference. So if PageDirty is tested before page_count 465 * here, then the following race may occur: 466 * 467 * get_user_pages(&page); 468 * [user mapping goes away] 469 * write_to(page); 470 * !PageDirty(page) [good] 471 * SetPageDirty(page); 472 * put_page(page); 473 * !page_count(page) [good, discard it] 474 * 475 * [oops, our write_to data is lost] 476 * 477 * Reversing the order of the tests ensures such a situation cannot 478 * escape unnoticed. The smp_rmb is needed to ensure the page->flags 479 * load is not satisfied before that of page->_count. 480 * 481 * Note that if SetPageDirty is always performed via set_page_dirty, 482 * and thus under tree_lock, then this ordering is not required. 483 */ 484 if (!page_freeze_refs(page, 2)) 485 goto cannot_free; 486 /* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */ 487 if (unlikely(PageDirty(page))) { 488 page_unfreeze_refs(page, 2); 489 goto cannot_free; 490 } 491 492 if (PageSwapCache(page)) { 493 swp_entry_t swap = { .val = page_private(page) }; 494 __delete_from_swap_cache(page); 495 spin_unlock_irq(&mapping->tree_lock); 496 swapcache_free(swap, page); 497 } else { 498 void (*freepage)(struct page *); 499 500 freepage = mapping->a_ops->freepage; 501 502 __delete_from_page_cache(page); 503 spin_unlock_irq(&mapping->tree_lock); 504 mem_cgroup_uncharge_cache_page(page); 505 506 if (freepage != NULL) 507 freepage(page); 508 } 509 510 return 1; 511 512 cannot_free: 513 spin_unlock_irq(&mapping->tree_lock); 514 return 0; 515 } 516 517 /* 518 * Attempt to detach a locked page from its ->mapping. If it is dirty or if 519 * someone else has a ref on the page, abort and return 0. If it was 520 * successfully detached, return 1. Assumes the caller has a single ref on 521 * this page. 522 */ 523 int remove_mapping(struct address_space *mapping, struct page *page) 524 { 525 if (__remove_mapping(mapping, page)) { 526 /* 527 * Unfreezing the refcount with 1 rather than 2 effectively 528 * drops the pagecache ref for us without requiring another 529 * atomic operation. 530 */ 531 page_unfreeze_refs(page, 1); 532 return 1; 533 } 534 return 0; 535 } 536 537 /** 538 * putback_lru_page - put previously isolated page onto appropriate LRU list 539 * @page: page to be put back to appropriate lru list 540 * 541 * Add previously isolated @page to appropriate LRU list. 542 * Page may still be unevictable for other reasons. 543 * 544 * lru_lock must not be held, interrupts must be enabled. 545 */ 546 void putback_lru_page(struct page *page) 547 { 548 int lru; 549 int active = !!TestClearPageActive(page); 550 int was_unevictable = PageUnevictable(page); 551 552 VM_BUG_ON(PageLRU(page)); 553 554 redo: 555 ClearPageUnevictable(page); 556 557 if (page_evictable(page)) { 558 /* 559 * For evictable pages, we can use the cache. 560 * In event of a race, worst case is we end up with an 561 * unevictable page on [in]active list. 562 * We know how to handle that. 563 */ 564 lru = active + page_lru_base_type(page); 565 lru_cache_add_lru(page, lru); 566 } else { 567 /* 568 * Put unevictable pages directly on zone's unevictable 569 * list. 570 */ 571 lru = LRU_UNEVICTABLE; 572 add_page_to_unevictable_list(page); 573 /* 574 * When racing with an mlock or AS_UNEVICTABLE clearing 575 * (page is unlocked) make sure that if the other thread 576 * does not observe our setting of PG_lru and fails 577 * isolation/check_move_unevictable_pages, 578 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move 579 * the page back to the evictable list. 580 * 581 * The other side is TestClearPageMlocked() or shmem_lock(). 582 */ 583 smp_mb(); 584 } 585 586 /* 587 * page's status can change while we move it among lru. If an evictable 588 * page is on unevictable list, it never be freed. To avoid that, 589 * check after we added it to the list, again. 590 */ 591 if (lru == LRU_UNEVICTABLE && page_evictable(page)) { 592 if (!isolate_lru_page(page)) { 593 put_page(page); 594 goto redo; 595 } 596 /* This means someone else dropped this page from LRU 597 * So, it will be freed or putback to LRU again. There is 598 * nothing to do here. 599 */ 600 } 601 602 if (was_unevictable && lru != LRU_UNEVICTABLE) 603 count_vm_event(UNEVICTABLE_PGRESCUED); 604 else if (!was_unevictable && lru == LRU_UNEVICTABLE) 605 count_vm_event(UNEVICTABLE_PGCULLED); 606 607 put_page(page); /* drop ref from isolate */ 608 } 609 610 enum page_references { 611 PAGEREF_RECLAIM, 612 PAGEREF_RECLAIM_CLEAN, 613 PAGEREF_KEEP, 614 PAGEREF_ACTIVATE, 615 }; 616 617 static enum page_references page_check_references(struct page *page, 618 struct scan_control *sc) 619 { 620 int referenced_ptes, referenced_page; 621 unsigned long vm_flags; 622 623 referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup, 624 &vm_flags); 625 referenced_page = TestClearPageReferenced(page); 626 627 /* 628 * Mlock lost the isolation race with us. Let try_to_unmap() 629 * move the page to the unevictable list. 630 */ 631 if (vm_flags & VM_LOCKED) 632 return PAGEREF_RECLAIM; 633 634 if (referenced_ptes) { 635 if (PageSwapBacked(page)) 636 return PAGEREF_ACTIVATE; 637 /* 638 * All mapped pages start out with page table 639 * references from the instantiating fault, so we need 640 * to look twice if a mapped file page is used more 641 * than once. 642 * 643 * Mark it and spare it for another trip around the 644 * inactive list. Another page table reference will 645 * lead to its activation. 646 * 647 * Note: the mark is set for activated pages as well 648 * so that recently deactivated but used pages are 649 * quickly recovered. 650 */ 651 SetPageReferenced(page); 652 653 if (referenced_page || referenced_ptes > 1) 654 return PAGEREF_ACTIVATE; 655 656 /* 657 * Activate file-backed executable pages after first usage. 658 */ 659 if (vm_flags & VM_EXEC) 660 return PAGEREF_ACTIVATE; 661 662 return PAGEREF_KEEP; 663 } 664 665 /* Reclaim if clean, defer dirty pages to writeback */ 666 if (referenced_page && !PageSwapBacked(page)) 667 return PAGEREF_RECLAIM_CLEAN; 668 669 return PAGEREF_RECLAIM; 670 } 671 672 /* 673 * shrink_page_list() returns the number of reclaimed pages 674 */ 675 static unsigned long shrink_page_list(struct list_head *page_list, 676 struct zone *zone, 677 struct scan_control *sc, 678 enum ttu_flags ttu_flags, 679 unsigned long *ret_nr_dirty, 680 unsigned long *ret_nr_writeback, 681 bool force_reclaim) 682 { 683 LIST_HEAD(ret_pages); 684 LIST_HEAD(free_pages); 685 int pgactivate = 0; 686 unsigned long nr_dirty = 0; 687 unsigned long nr_congested = 0; 688 unsigned long nr_reclaimed = 0; 689 unsigned long nr_writeback = 0; 690 691 cond_resched(); 692 693 mem_cgroup_uncharge_start(); 694 while (!list_empty(page_list)) { 695 struct address_space *mapping; 696 struct page *page; 697 int may_enter_fs; 698 enum page_references references = PAGEREF_RECLAIM_CLEAN; 699 700 cond_resched(); 701 702 page = lru_to_page(page_list); 703 list_del(&page->lru); 704 705 if (!trylock_page(page)) 706 goto keep; 707 708 VM_BUG_ON(PageActive(page)); 709 VM_BUG_ON(page_zone(page) != zone); 710 711 sc->nr_scanned++; 712 713 if (unlikely(!page_evictable(page))) 714 goto cull_mlocked; 715 716 if (!sc->may_unmap && page_mapped(page)) 717 goto keep_locked; 718 719 /* Double the slab pressure for mapped and swapcache pages */ 720 if (page_mapped(page) || PageSwapCache(page)) 721 sc->nr_scanned++; 722 723 may_enter_fs = (sc->gfp_mask & __GFP_FS) || 724 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); 725 726 if (PageWriteback(page)) { 727 /* 728 * memcg doesn't have any dirty pages throttling so we 729 * could easily OOM just because too many pages are in 730 * writeback and there is nothing else to reclaim. 731 * 732 * Check __GFP_IO, certainly because a loop driver 733 * thread might enter reclaim, and deadlock if it waits 734 * on a page for which it is needed to do the write 735 * (loop masks off __GFP_IO|__GFP_FS for this reason); 736 * but more thought would probably show more reasons. 737 * 738 * Don't require __GFP_FS, since we're not going into 739 * the FS, just waiting on its writeback completion. 740 * Worryingly, ext4 gfs2 and xfs allocate pages with 741 * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so 742 * testing may_enter_fs here is liable to OOM on them. 743 */ 744 if (global_reclaim(sc) || 745 !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) { 746 /* 747 * This is slightly racy - end_page_writeback() 748 * might have just cleared PageReclaim, then 749 * setting PageReclaim here end up interpreted 750 * as PageReadahead - but that does not matter 751 * enough to care. What we do want is for this 752 * page to have PageReclaim set next time memcg 753 * reclaim reaches the tests above, so it will 754 * then wait_on_page_writeback() to avoid OOM; 755 * and it's also appropriate in global reclaim. 756 */ 757 SetPageReclaim(page); 758 nr_writeback++; 759 goto keep_locked; 760 } 761 wait_on_page_writeback(page); 762 } 763 764 if (!force_reclaim) 765 references = page_check_references(page, sc); 766 767 switch (references) { 768 case PAGEREF_ACTIVATE: 769 goto activate_locked; 770 case PAGEREF_KEEP: 771 goto keep_locked; 772 case PAGEREF_RECLAIM: 773 case PAGEREF_RECLAIM_CLEAN: 774 ; /* try to reclaim the page below */ 775 } 776 777 /* 778 * Anonymous process memory has backing store? 779 * Try to allocate it some swap space here. 780 */ 781 if (PageAnon(page) && !PageSwapCache(page)) { 782 if (!(sc->gfp_mask & __GFP_IO)) 783 goto keep_locked; 784 if (!add_to_swap(page, page_list)) 785 goto activate_locked; 786 may_enter_fs = 1; 787 } 788 789 mapping = page_mapping(page); 790 791 /* 792 * The page is mapped into the page tables of one or more 793 * processes. Try to unmap it here. 794 */ 795 if (page_mapped(page) && mapping) { 796 switch (try_to_unmap(page, ttu_flags)) { 797 case SWAP_FAIL: 798 goto activate_locked; 799 case SWAP_AGAIN: 800 goto keep_locked; 801 case SWAP_MLOCK: 802 goto cull_mlocked; 803 case SWAP_SUCCESS: 804 ; /* try to free the page below */ 805 } 806 } 807 808 if (PageDirty(page)) { 809 nr_dirty++; 810 811 /* 812 * Only kswapd can writeback filesystem pages to 813 * avoid risk of stack overflow but do not writeback 814 * unless under significant pressure. 815 */ 816 if (page_is_file_cache(page) && 817 (!current_is_kswapd() || 818 sc->priority >= DEF_PRIORITY - 2)) { 819 /* 820 * Immediately reclaim when written back. 821 * Similar in principal to deactivate_page() 822 * except we already have the page isolated 823 * and know it's dirty 824 */ 825 inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE); 826 SetPageReclaim(page); 827 828 goto keep_locked; 829 } 830 831 if (references == PAGEREF_RECLAIM_CLEAN) 832 goto keep_locked; 833 if (!may_enter_fs) 834 goto keep_locked; 835 if (!sc->may_writepage) 836 goto keep_locked; 837 838 /* Page is dirty, try to write it out here */ 839 switch (pageout(page, mapping, sc)) { 840 case PAGE_KEEP: 841 nr_congested++; 842 goto keep_locked; 843 case PAGE_ACTIVATE: 844 goto activate_locked; 845 case PAGE_SUCCESS: 846 if (PageWriteback(page)) 847 goto keep; 848 if (PageDirty(page)) 849 goto keep; 850 851 /* 852 * A synchronous write - probably a ramdisk. Go 853 * ahead and try to reclaim the page. 854 */ 855 if (!trylock_page(page)) 856 goto keep; 857 if (PageDirty(page) || PageWriteback(page)) 858 goto keep_locked; 859 mapping = page_mapping(page); 860 case PAGE_CLEAN: 861 ; /* try to free the page below */ 862 } 863 } 864 865 /* 866 * If the page has buffers, try to free the buffer mappings 867 * associated with this page. If we succeed we try to free 868 * the page as well. 869 * 870 * We do this even if the page is PageDirty(). 871 * try_to_release_page() does not perform I/O, but it is 872 * possible for a page to have PageDirty set, but it is actually 873 * clean (all its buffers are clean). This happens if the 874 * buffers were written out directly, with submit_bh(). ext3 875 * will do this, as well as the blockdev mapping. 876 * try_to_release_page() will discover that cleanness and will 877 * drop the buffers and mark the page clean - it can be freed. 878 * 879 * Rarely, pages can have buffers and no ->mapping. These are 880 * the pages which were not successfully invalidated in 881 * truncate_complete_page(). We try to drop those buffers here 882 * and if that worked, and the page is no longer mapped into 883 * process address space (page_count == 1) it can be freed. 884 * Otherwise, leave the page on the LRU so it is swappable. 885 */ 886 if (page_has_private(page)) { 887 if (!try_to_release_page(page, sc->gfp_mask)) 888 goto activate_locked; 889 if (!mapping && page_count(page) == 1) { 890 unlock_page(page); 891 if (put_page_testzero(page)) 892 goto free_it; 893 else { 894 /* 895 * rare race with speculative reference. 896 * the speculative reference will free 897 * this page shortly, so we may 898 * increment nr_reclaimed here (and 899 * leave it off the LRU). 900 */ 901 nr_reclaimed++; 902 continue; 903 } 904 } 905 } 906 907 if (!mapping || !__remove_mapping(mapping, page)) 908 goto keep_locked; 909 910 /* 911 * At this point, we have no other references and there is 912 * no way to pick any more up (removed from LRU, removed 913 * from pagecache). Can use non-atomic bitops now (and 914 * we obviously don't have to worry about waking up a process 915 * waiting on the page lock, because there are no references. 916 */ 917 __clear_page_locked(page); 918 free_it: 919 nr_reclaimed++; 920 921 /* 922 * Is there need to periodically free_page_list? It would 923 * appear not as the counts should be low 924 */ 925 list_add(&page->lru, &free_pages); 926 continue; 927 928 cull_mlocked: 929 if (PageSwapCache(page)) 930 try_to_free_swap(page); 931 unlock_page(page); 932 putback_lru_page(page); 933 continue; 934 935 activate_locked: 936 /* Not a candidate for swapping, so reclaim swap space. */ 937 if (PageSwapCache(page) && vm_swap_full()) 938 try_to_free_swap(page); 939 VM_BUG_ON(PageActive(page)); 940 SetPageActive(page); 941 pgactivate++; 942 keep_locked: 943 unlock_page(page); 944 keep: 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 && global_reclaim(sc)) 956 zone_set_flag(zone, ZONE_CONGESTED); 957 958 free_hot_cold_page_list(&free_pages, 1); 959 960 list_splice(&ret_pages, page_list); 961 count_vm_events(PGACTIVATE, pgactivate); 962 mem_cgroup_uncharge_end(); 963 *ret_nr_dirty += nr_dirty; 964 *ret_nr_writeback += nr_writeback; 965 return nr_reclaimed; 966 } 967 968 unsigned long reclaim_clean_pages_from_list(struct zone *zone, 969 struct list_head *page_list) 970 { 971 struct scan_control sc = { 972 .gfp_mask = GFP_KERNEL, 973 .priority = DEF_PRIORITY, 974 .may_unmap = 1, 975 }; 976 unsigned long ret, dummy1, dummy2; 977 struct page *page, *next; 978 LIST_HEAD(clean_pages); 979 980 list_for_each_entry_safe(page, next, page_list, lru) { 981 if (page_is_file_cache(page) && !PageDirty(page)) { 982 ClearPageActive(page); 983 list_move(&page->lru, &clean_pages); 984 } 985 } 986 987 ret = shrink_page_list(&clean_pages, zone, &sc, 988 TTU_UNMAP|TTU_IGNORE_ACCESS, 989 &dummy1, &dummy2, true); 990 list_splice(&clean_pages, page_list); 991 __mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret); 992 return ret; 993 } 994 995 /* 996 * Attempt to remove the specified page from its LRU. Only take this page 997 * if it is of the appropriate PageActive status. Pages which are being 998 * freed elsewhere are also ignored. 999 * 1000 * page: page to consider 1001 * mode: one of the LRU isolation modes defined above 1002 * 1003 * returns 0 on success, -ve errno on failure. 1004 */ 1005 int __isolate_lru_page(struct page *page, isolate_mode_t mode) 1006 { 1007 int ret = -EINVAL; 1008 1009 /* Only take pages on the LRU. */ 1010 if (!PageLRU(page)) 1011 return ret; 1012 1013 /* Compaction should not handle unevictable pages but CMA can do so */ 1014 if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE)) 1015 return ret; 1016 1017 ret = -EBUSY; 1018 1019 /* 1020 * To minimise LRU disruption, the caller can indicate that it only 1021 * wants to isolate pages it will be able to operate on without 1022 * blocking - clean pages for the most part. 1023 * 1024 * ISOLATE_CLEAN means that only clean pages should be isolated. This 1025 * is used by reclaim when it is cannot write to backing storage 1026 * 1027 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages 1028 * that it is possible to migrate without blocking 1029 */ 1030 if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) { 1031 /* All the caller can do on PageWriteback is block */ 1032 if (PageWriteback(page)) 1033 return ret; 1034 1035 if (PageDirty(page)) { 1036 struct address_space *mapping; 1037 1038 /* ISOLATE_CLEAN means only clean pages */ 1039 if (mode & ISOLATE_CLEAN) 1040 return ret; 1041 1042 /* 1043 * Only pages without mappings or that have a 1044 * ->migratepage callback are possible to migrate 1045 * without blocking 1046 */ 1047 mapping = page_mapping(page); 1048 if (mapping && !mapping->a_ops->migratepage) 1049 return ret; 1050 } 1051 } 1052 1053 if ((mode & ISOLATE_UNMAPPED) && page_mapped(page)) 1054 return ret; 1055 1056 if (likely(get_page_unless_zero(page))) { 1057 /* 1058 * Be careful not to clear PageLRU until after we're 1059 * sure the page is not being freed elsewhere -- the 1060 * page release code relies on it. 1061 */ 1062 ClearPageLRU(page); 1063 ret = 0; 1064 } 1065 1066 return ret; 1067 } 1068 1069 /* 1070 * zone->lru_lock is heavily contended. Some of the functions that 1071 * shrink the lists perform better by taking out a batch of pages 1072 * and working on them outside the LRU lock. 1073 * 1074 * For pagecache intensive workloads, this function is the hottest 1075 * spot in the kernel (apart from copy_*_user functions). 1076 * 1077 * Appropriate locks must be held before calling this function. 1078 * 1079 * @nr_to_scan: The number of pages to look through on the list. 1080 * @lruvec: The LRU vector to pull pages from. 1081 * @dst: The temp list to put pages on to. 1082 * @nr_scanned: The number of pages that were scanned. 1083 * @sc: The scan_control struct for this reclaim session 1084 * @mode: One of the LRU isolation modes 1085 * @lru: LRU list id for isolating 1086 * 1087 * returns how many pages were moved onto *@dst. 1088 */ 1089 static unsigned long isolate_lru_pages(unsigned long nr_to_scan, 1090 struct lruvec *lruvec, struct list_head *dst, 1091 unsigned long *nr_scanned, struct scan_control *sc, 1092 isolate_mode_t mode, enum lru_list lru) 1093 { 1094 struct list_head *src = &lruvec->lists[lru]; 1095 unsigned long nr_taken = 0; 1096 unsigned long scan; 1097 1098 for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) { 1099 struct page *page; 1100 int nr_pages; 1101 1102 page = lru_to_page(src); 1103 prefetchw_prev_lru_page(page, src, flags); 1104 1105 VM_BUG_ON(!PageLRU(page)); 1106 1107 switch (__isolate_lru_page(page, mode)) { 1108 case 0: 1109 nr_pages = hpage_nr_pages(page); 1110 mem_cgroup_update_lru_size(lruvec, lru, -nr_pages); 1111 list_move(&page->lru, dst); 1112 nr_taken += nr_pages; 1113 break; 1114 1115 case -EBUSY: 1116 /* else it is being freed elsewhere */ 1117 list_move(&page->lru, src); 1118 continue; 1119 1120 default: 1121 BUG(); 1122 } 1123 } 1124 1125 *nr_scanned = scan; 1126 trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan, 1127 nr_taken, mode, is_file_lru(lru)); 1128 return nr_taken; 1129 } 1130 1131 /** 1132 * isolate_lru_page - tries to isolate a page from its LRU list 1133 * @page: page to isolate from its LRU list 1134 * 1135 * Isolates a @page from an LRU list, clears PageLRU and adjusts the 1136 * vmstat statistic corresponding to whatever LRU list the page was on. 1137 * 1138 * Returns 0 if the page was removed from an LRU list. 1139 * Returns -EBUSY if the page was not on an LRU list. 1140 * 1141 * The returned page will have PageLRU() cleared. If it was found on 1142 * the active list, it will have PageActive set. If it was found on 1143 * the unevictable list, it will have the PageUnevictable bit set. That flag 1144 * may need to be cleared by the caller before letting the page go. 1145 * 1146 * The vmstat statistic corresponding to the list on which the page was 1147 * found will be decremented. 1148 * 1149 * Restrictions: 1150 * (1) Must be called with an elevated refcount on the page. This is a 1151 * fundamentnal difference from isolate_lru_pages (which is called 1152 * without a stable reference). 1153 * (2) the lru_lock must not be held. 1154 * (3) interrupts must be enabled. 1155 */ 1156 int isolate_lru_page(struct page *page) 1157 { 1158 int ret = -EBUSY; 1159 1160 VM_BUG_ON(!page_count(page)); 1161 1162 if (PageLRU(page)) { 1163 struct zone *zone = page_zone(page); 1164 struct lruvec *lruvec; 1165 1166 spin_lock_irq(&zone->lru_lock); 1167 lruvec = mem_cgroup_page_lruvec(page, zone); 1168 if (PageLRU(page)) { 1169 int lru = page_lru(page); 1170 get_page(page); 1171 ClearPageLRU(page); 1172 del_page_from_lru_list(page, lruvec, lru); 1173 ret = 0; 1174 } 1175 spin_unlock_irq(&zone->lru_lock); 1176 } 1177 return ret; 1178 } 1179 1180 /* 1181 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and 1182 * then get resheduled. When there are massive number of tasks doing page 1183 * allocation, such sleeping direct reclaimers may keep piling up on each CPU, 1184 * the LRU list will go small and be scanned faster than necessary, leading to 1185 * unnecessary swapping, thrashing and OOM. 1186 */ 1187 static int too_many_isolated(struct zone *zone, int file, 1188 struct scan_control *sc) 1189 { 1190 unsigned long inactive, isolated; 1191 1192 if (current_is_kswapd()) 1193 return 0; 1194 1195 if (!global_reclaim(sc)) 1196 return 0; 1197 1198 if (file) { 1199 inactive = zone_page_state(zone, NR_INACTIVE_FILE); 1200 isolated = zone_page_state(zone, NR_ISOLATED_FILE); 1201 } else { 1202 inactive = zone_page_state(zone, NR_INACTIVE_ANON); 1203 isolated = zone_page_state(zone, NR_ISOLATED_ANON); 1204 } 1205 1206 /* 1207 * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they 1208 * won't get blocked by normal direct-reclaimers, forming a circular 1209 * deadlock. 1210 */ 1211 if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS) 1212 inactive >>= 3; 1213 1214 return isolated > inactive; 1215 } 1216 1217 static noinline_for_stack void 1218 putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list) 1219 { 1220 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; 1221 struct zone *zone = lruvec_zone(lruvec); 1222 LIST_HEAD(pages_to_free); 1223 1224 /* 1225 * Put back any unfreeable pages. 1226 */ 1227 while (!list_empty(page_list)) { 1228 struct page *page = lru_to_page(page_list); 1229 int lru; 1230 1231 VM_BUG_ON(PageLRU(page)); 1232 list_del(&page->lru); 1233 if (unlikely(!page_evictable(page))) { 1234 spin_unlock_irq(&zone->lru_lock); 1235 putback_lru_page(page); 1236 spin_lock_irq(&zone->lru_lock); 1237 continue; 1238 } 1239 1240 lruvec = mem_cgroup_page_lruvec(page, zone); 1241 1242 SetPageLRU(page); 1243 lru = page_lru(page); 1244 add_page_to_lru_list(page, lruvec, lru); 1245 1246 if (is_active_lru(lru)) { 1247 int file = is_file_lru(lru); 1248 int numpages = hpage_nr_pages(page); 1249 reclaim_stat->recent_rotated[file] += numpages; 1250 } 1251 if (put_page_testzero(page)) { 1252 __ClearPageLRU(page); 1253 __ClearPageActive(page); 1254 del_page_from_lru_list(page, lruvec, lru); 1255 1256 if (unlikely(PageCompound(page))) { 1257 spin_unlock_irq(&zone->lru_lock); 1258 (*get_compound_page_dtor(page))(page); 1259 spin_lock_irq(&zone->lru_lock); 1260 } else 1261 list_add(&page->lru, &pages_to_free); 1262 } 1263 } 1264 1265 /* 1266 * To save our caller's stack, now use input list for pages to free. 1267 */ 1268 list_splice(&pages_to_free, page_list); 1269 } 1270 1271 /* 1272 * shrink_inactive_list() is a helper for shrink_zone(). It returns the number 1273 * of reclaimed pages 1274 */ 1275 static noinline_for_stack unsigned long 1276 shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec, 1277 struct scan_control *sc, enum lru_list lru) 1278 { 1279 LIST_HEAD(page_list); 1280 unsigned long nr_scanned; 1281 unsigned long nr_reclaimed = 0; 1282 unsigned long nr_taken; 1283 unsigned long nr_dirty = 0; 1284 unsigned long nr_writeback = 0; 1285 isolate_mode_t isolate_mode = 0; 1286 int file = is_file_lru(lru); 1287 struct zone *zone = lruvec_zone(lruvec); 1288 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; 1289 1290 while (unlikely(too_many_isolated(zone, file, sc))) { 1291 congestion_wait(BLK_RW_ASYNC, HZ/10); 1292 1293 /* We are about to die and free our memory. Return now. */ 1294 if (fatal_signal_pending(current)) 1295 return SWAP_CLUSTER_MAX; 1296 } 1297 1298 lru_add_drain(); 1299 1300 if (!sc->may_unmap) 1301 isolate_mode |= ISOLATE_UNMAPPED; 1302 if (!sc->may_writepage) 1303 isolate_mode |= ISOLATE_CLEAN; 1304 1305 spin_lock_irq(&zone->lru_lock); 1306 1307 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list, 1308 &nr_scanned, sc, isolate_mode, lru); 1309 1310 __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken); 1311 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken); 1312 1313 if (global_reclaim(sc)) { 1314 zone->pages_scanned += nr_scanned; 1315 if (current_is_kswapd()) 1316 __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned); 1317 else 1318 __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned); 1319 } 1320 spin_unlock_irq(&zone->lru_lock); 1321 1322 if (nr_taken == 0) 1323 return 0; 1324 1325 nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP, 1326 &nr_dirty, &nr_writeback, false); 1327 1328 spin_lock_irq(&zone->lru_lock); 1329 1330 reclaim_stat->recent_scanned[file] += nr_taken; 1331 1332 if (global_reclaim(sc)) { 1333 if (current_is_kswapd()) 1334 __count_zone_vm_events(PGSTEAL_KSWAPD, zone, 1335 nr_reclaimed); 1336 else 1337 __count_zone_vm_events(PGSTEAL_DIRECT, zone, 1338 nr_reclaimed); 1339 } 1340 1341 putback_inactive_pages(lruvec, &page_list); 1342 1343 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken); 1344 1345 spin_unlock_irq(&zone->lru_lock); 1346 1347 free_hot_cold_page_list(&page_list, 1); 1348 1349 /* 1350 * If reclaim is isolating dirty pages under writeback, it implies 1351 * that the long-lived page allocation rate is exceeding the page 1352 * laundering rate. Either the global limits are not being effective 1353 * at throttling processes due to the page distribution throughout 1354 * zones or there is heavy usage of a slow backing device. The 1355 * only option is to throttle from reclaim context which is not ideal 1356 * as there is no guarantee the dirtying process is throttled in the 1357 * same way balance_dirty_pages() manages. 1358 * 1359 * This scales the number of dirty pages that must be under writeback 1360 * before throttling depending on priority. It is a simple backoff 1361 * function that has the most effect in the range DEF_PRIORITY to 1362 * DEF_PRIORITY-2 which is the priority reclaim is considered to be 1363 * in trouble and reclaim is considered to be in trouble. 1364 * 1365 * DEF_PRIORITY 100% isolated pages must be PageWriteback to throttle 1366 * DEF_PRIORITY-1 50% must be PageWriteback 1367 * DEF_PRIORITY-2 25% must be PageWriteback, kswapd in trouble 1368 * ... 1369 * DEF_PRIORITY-6 For SWAP_CLUSTER_MAX isolated pages, throttle if any 1370 * isolated page is PageWriteback 1371 */ 1372 if (nr_writeback && nr_writeback >= 1373 (nr_taken >> (DEF_PRIORITY - sc->priority))) 1374 wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10); 1375 1376 trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id, 1377 zone_idx(zone), 1378 nr_scanned, nr_reclaimed, 1379 sc->priority, 1380 trace_shrink_flags(file)); 1381 return nr_reclaimed; 1382 } 1383 1384 /* 1385 * This moves pages from the active list to the inactive list. 1386 * 1387 * We move them the other way if the page is referenced by one or more 1388 * processes, from rmap. 1389 * 1390 * If the pages are mostly unmapped, the processing is fast and it is 1391 * appropriate to hold zone->lru_lock across the whole operation. But if 1392 * the pages are mapped, the processing is slow (page_referenced()) so we 1393 * should drop zone->lru_lock around each page. It's impossible to balance 1394 * this, so instead we remove the pages from the LRU while processing them. 1395 * It is safe to rely on PG_active against the non-LRU pages in here because 1396 * nobody will play with that bit on a non-LRU page. 1397 * 1398 * The downside is that we have to touch page->_count against each page. 1399 * But we had to alter page->flags anyway. 1400 */ 1401 1402 static void move_active_pages_to_lru(struct lruvec *lruvec, 1403 struct list_head *list, 1404 struct list_head *pages_to_free, 1405 enum lru_list lru) 1406 { 1407 struct zone *zone = lruvec_zone(lruvec); 1408 unsigned long pgmoved = 0; 1409 struct page *page; 1410 int nr_pages; 1411 1412 while (!list_empty(list)) { 1413 page = lru_to_page(list); 1414 lruvec = mem_cgroup_page_lruvec(page, zone); 1415 1416 VM_BUG_ON(PageLRU(page)); 1417 SetPageLRU(page); 1418 1419 nr_pages = hpage_nr_pages(page); 1420 mem_cgroup_update_lru_size(lruvec, lru, nr_pages); 1421 list_move(&page->lru, &lruvec->lists[lru]); 1422 pgmoved += nr_pages; 1423 1424 if (put_page_testzero(page)) { 1425 __ClearPageLRU(page); 1426 __ClearPageActive(page); 1427 del_page_from_lru_list(page, lruvec, lru); 1428 1429 if (unlikely(PageCompound(page))) { 1430 spin_unlock_irq(&zone->lru_lock); 1431 (*get_compound_page_dtor(page))(page); 1432 spin_lock_irq(&zone->lru_lock); 1433 } else 1434 list_add(&page->lru, pages_to_free); 1435 } 1436 } 1437 __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved); 1438 if (!is_active_lru(lru)) 1439 __count_vm_events(PGDEACTIVATE, pgmoved); 1440 } 1441 1442 static void shrink_active_list(unsigned long nr_to_scan, 1443 struct lruvec *lruvec, 1444 struct scan_control *sc, 1445 enum lru_list lru) 1446 { 1447 unsigned long nr_taken; 1448 unsigned long nr_scanned; 1449 unsigned long vm_flags; 1450 LIST_HEAD(l_hold); /* The pages which were snipped off */ 1451 LIST_HEAD(l_active); 1452 LIST_HEAD(l_inactive); 1453 struct page *page; 1454 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; 1455 unsigned long nr_rotated = 0; 1456 isolate_mode_t isolate_mode = 0; 1457 int file = is_file_lru(lru); 1458 struct zone *zone = lruvec_zone(lruvec); 1459 1460 lru_add_drain(); 1461 1462 if (!sc->may_unmap) 1463 isolate_mode |= ISOLATE_UNMAPPED; 1464 if (!sc->may_writepage) 1465 isolate_mode |= ISOLATE_CLEAN; 1466 1467 spin_lock_irq(&zone->lru_lock); 1468 1469 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold, 1470 &nr_scanned, sc, isolate_mode, lru); 1471 if (global_reclaim(sc)) 1472 zone->pages_scanned += nr_scanned; 1473 1474 reclaim_stat->recent_scanned[file] += nr_taken; 1475 1476 __count_zone_vm_events(PGREFILL, zone, nr_scanned); 1477 __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken); 1478 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken); 1479 spin_unlock_irq(&zone->lru_lock); 1480 1481 while (!list_empty(&l_hold)) { 1482 cond_resched(); 1483 page = lru_to_page(&l_hold); 1484 list_del(&page->lru); 1485 1486 if (unlikely(!page_evictable(page))) { 1487 putback_lru_page(page); 1488 continue; 1489 } 1490 1491 if (unlikely(buffer_heads_over_limit)) { 1492 if (page_has_private(page) && trylock_page(page)) { 1493 if (page_has_private(page)) 1494 try_to_release_page(page, 0); 1495 unlock_page(page); 1496 } 1497 } 1498 1499 if (page_referenced(page, 0, sc->target_mem_cgroup, 1500 &vm_flags)) { 1501 nr_rotated += hpage_nr_pages(page); 1502 /* 1503 * Identify referenced, file-backed active pages and 1504 * give them one more trip around the active list. So 1505 * that executable code get better chances to stay in 1506 * memory under moderate memory pressure. Anon pages 1507 * are not likely to be evicted by use-once streaming 1508 * IO, plus JVM can create lots of anon VM_EXEC pages, 1509 * so we ignore them here. 1510 */ 1511 if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) { 1512 list_add(&page->lru, &l_active); 1513 continue; 1514 } 1515 } 1516 1517 ClearPageActive(page); /* we are de-activating */ 1518 list_add(&page->lru, &l_inactive); 1519 } 1520 1521 /* 1522 * Move pages back to the lru list. 1523 */ 1524 spin_lock_irq(&zone->lru_lock); 1525 /* 1526 * Count referenced pages from currently used mappings as rotated, 1527 * even though only some of them are actually re-activated. This 1528 * helps balance scan pressure between file and anonymous pages in 1529 * get_scan_ratio. 1530 */ 1531 reclaim_stat->recent_rotated[file] += nr_rotated; 1532 1533 move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru); 1534 move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE); 1535 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken); 1536 spin_unlock_irq(&zone->lru_lock); 1537 1538 free_hot_cold_page_list(&l_hold, 1); 1539 } 1540 1541 #ifdef CONFIG_SWAP 1542 static int inactive_anon_is_low_global(struct zone *zone) 1543 { 1544 unsigned long active, inactive; 1545 1546 active = zone_page_state(zone, NR_ACTIVE_ANON); 1547 inactive = zone_page_state(zone, NR_INACTIVE_ANON); 1548 1549 if (inactive * zone->inactive_ratio < active) 1550 return 1; 1551 1552 return 0; 1553 } 1554 1555 /** 1556 * inactive_anon_is_low - check if anonymous pages need to be deactivated 1557 * @lruvec: LRU vector to check 1558 * 1559 * Returns true if the zone does not have enough inactive anon pages, 1560 * meaning some active anon pages need to be deactivated. 1561 */ 1562 static int inactive_anon_is_low(struct lruvec *lruvec) 1563 { 1564 /* 1565 * If we don't have swap space, anonymous page deactivation 1566 * is pointless. 1567 */ 1568 if (!total_swap_pages) 1569 return 0; 1570 1571 if (!mem_cgroup_disabled()) 1572 return mem_cgroup_inactive_anon_is_low(lruvec); 1573 1574 return inactive_anon_is_low_global(lruvec_zone(lruvec)); 1575 } 1576 #else 1577 static inline int inactive_anon_is_low(struct lruvec *lruvec) 1578 { 1579 return 0; 1580 } 1581 #endif 1582 1583 /** 1584 * inactive_file_is_low - check if file pages need to be deactivated 1585 * @lruvec: LRU vector to check 1586 * 1587 * When the system is doing streaming IO, memory pressure here 1588 * ensures that active file pages get deactivated, until more 1589 * than half of the file pages are on the inactive list. 1590 * 1591 * Once we get to that situation, protect the system's working 1592 * set from being evicted by disabling active file page aging. 1593 * 1594 * This uses a different ratio than the anonymous pages, because 1595 * the page cache uses a use-once replacement algorithm. 1596 */ 1597 static int inactive_file_is_low(struct lruvec *lruvec) 1598 { 1599 unsigned long inactive; 1600 unsigned long active; 1601 1602 inactive = get_lru_size(lruvec, LRU_INACTIVE_FILE); 1603 active = get_lru_size(lruvec, LRU_ACTIVE_FILE); 1604 1605 return active > inactive; 1606 } 1607 1608 static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru) 1609 { 1610 if (is_file_lru(lru)) 1611 return inactive_file_is_low(lruvec); 1612 else 1613 return inactive_anon_is_low(lruvec); 1614 } 1615 1616 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan, 1617 struct lruvec *lruvec, struct scan_control *sc) 1618 { 1619 if (is_active_lru(lru)) { 1620 if (inactive_list_is_low(lruvec, lru)) 1621 shrink_active_list(nr_to_scan, lruvec, sc, lru); 1622 return 0; 1623 } 1624 1625 return shrink_inactive_list(nr_to_scan, lruvec, sc, lru); 1626 } 1627 1628 static int vmscan_swappiness(struct scan_control *sc) 1629 { 1630 if (global_reclaim(sc)) 1631 return vm_swappiness; 1632 return mem_cgroup_swappiness(sc->target_mem_cgroup); 1633 } 1634 1635 enum scan_balance { 1636 SCAN_EQUAL, 1637 SCAN_FRACT, 1638 SCAN_ANON, 1639 SCAN_FILE, 1640 }; 1641 1642 /* 1643 * Determine how aggressively the anon and file LRU lists should be 1644 * scanned. The relative value of each set of LRU lists is determined 1645 * by looking at the fraction of the pages scanned we did rotate back 1646 * onto the active list instead of evict. 1647 * 1648 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan 1649 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan 1650 */ 1651 static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, 1652 unsigned long *nr) 1653 { 1654 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; 1655 u64 fraction[2]; 1656 u64 denominator = 0; /* gcc */ 1657 struct zone *zone = lruvec_zone(lruvec); 1658 unsigned long anon_prio, file_prio; 1659 enum scan_balance scan_balance; 1660 unsigned long anon, file, free; 1661 bool force_scan = false; 1662 unsigned long ap, fp; 1663 enum lru_list lru; 1664 1665 /* 1666 * If the zone or memcg is small, nr[l] can be 0. This 1667 * results in no scanning on this priority and a potential 1668 * priority drop. Global direct reclaim can go to the next 1669 * zone and tends to have no problems. Global kswapd is for 1670 * zone balancing and it needs to scan a minimum amount. When 1671 * reclaiming for a memcg, a priority drop can cause high 1672 * latencies, so it's better to scan a minimum amount there as 1673 * well. 1674 */ 1675 if (current_is_kswapd() && zone->all_unreclaimable) 1676 force_scan = true; 1677 if (!global_reclaim(sc)) 1678 force_scan = true; 1679 1680 /* If we have no swap space, do not bother scanning anon pages. */ 1681 if (!sc->may_swap || (get_nr_swap_pages() <= 0)) { 1682 scan_balance = SCAN_FILE; 1683 goto out; 1684 } 1685 1686 /* 1687 * Global reclaim will swap to prevent OOM even with no 1688 * swappiness, but memcg users want to use this knob to 1689 * disable swapping for individual groups completely when 1690 * using the memory controller's swap limit feature would be 1691 * too expensive. 1692 */ 1693 if (!global_reclaim(sc) && !vmscan_swappiness(sc)) { 1694 scan_balance = SCAN_FILE; 1695 goto out; 1696 } 1697 1698 /* 1699 * Do not apply any pressure balancing cleverness when the 1700 * system is close to OOM, scan both anon and file equally 1701 * (unless the swappiness setting disagrees with swapping). 1702 */ 1703 if (!sc->priority && vmscan_swappiness(sc)) { 1704 scan_balance = SCAN_EQUAL; 1705 goto out; 1706 } 1707 1708 anon = get_lru_size(lruvec, LRU_ACTIVE_ANON) + 1709 get_lru_size(lruvec, LRU_INACTIVE_ANON); 1710 file = get_lru_size(lruvec, LRU_ACTIVE_FILE) + 1711 get_lru_size(lruvec, LRU_INACTIVE_FILE); 1712 1713 /* 1714 * If it's foreseeable that reclaiming the file cache won't be 1715 * enough to get the zone back into a desirable shape, we have 1716 * to swap. Better start now and leave the - probably heavily 1717 * thrashing - remaining file pages alone. 1718 */ 1719 if (global_reclaim(sc)) { 1720 free = zone_page_state(zone, NR_FREE_PAGES); 1721 if (unlikely(file + free <= high_wmark_pages(zone))) { 1722 scan_balance = SCAN_ANON; 1723 goto out; 1724 } 1725 } 1726 1727 /* 1728 * There is enough inactive page cache, do not reclaim 1729 * anything from the anonymous working set right now. 1730 */ 1731 if (!inactive_file_is_low(lruvec)) { 1732 scan_balance = SCAN_FILE; 1733 goto out; 1734 } 1735 1736 scan_balance = SCAN_FRACT; 1737 1738 /* 1739 * With swappiness at 100, anonymous and file have the same priority. 1740 * This scanning priority is essentially the inverse of IO cost. 1741 */ 1742 anon_prio = vmscan_swappiness(sc); 1743 file_prio = 200 - anon_prio; 1744 1745 /* 1746 * OK, so we have swap space and a fair amount of page cache 1747 * pages. We use the recently rotated / recently scanned 1748 * ratios to determine how valuable each cache is. 1749 * 1750 * Because workloads change over time (and to avoid overflow) 1751 * we keep these statistics as a floating average, which ends 1752 * up weighing recent references more than old ones. 1753 * 1754 * anon in [0], file in [1] 1755 */ 1756 spin_lock_irq(&zone->lru_lock); 1757 if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) { 1758 reclaim_stat->recent_scanned[0] /= 2; 1759 reclaim_stat->recent_rotated[0] /= 2; 1760 } 1761 1762 if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) { 1763 reclaim_stat->recent_scanned[1] /= 2; 1764 reclaim_stat->recent_rotated[1] /= 2; 1765 } 1766 1767 /* 1768 * The amount of pressure on anon vs file pages is inversely 1769 * proportional to the fraction of recently scanned pages on 1770 * each list that were recently referenced and in active use. 1771 */ 1772 ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1); 1773 ap /= reclaim_stat->recent_rotated[0] + 1; 1774 1775 fp = file_prio * (reclaim_stat->recent_scanned[1] + 1); 1776 fp /= reclaim_stat->recent_rotated[1] + 1; 1777 spin_unlock_irq(&zone->lru_lock); 1778 1779 fraction[0] = ap; 1780 fraction[1] = fp; 1781 denominator = ap + fp + 1; 1782 out: 1783 for_each_evictable_lru(lru) { 1784 int file = is_file_lru(lru); 1785 unsigned long size; 1786 unsigned long scan; 1787 1788 size = get_lru_size(lruvec, lru); 1789 scan = size >> sc->priority; 1790 1791 if (!scan && force_scan) 1792 scan = min(size, SWAP_CLUSTER_MAX); 1793 1794 switch (scan_balance) { 1795 case SCAN_EQUAL: 1796 /* Scan lists relative to size */ 1797 break; 1798 case SCAN_FRACT: 1799 /* 1800 * Scan types proportional to swappiness and 1801 * their relative recent reclaim efficiency. 1802 */ 1803 scan = div64_u64(scan * fraction[file], denominator); 1804 break; 1805 case SCAN_FILE: 1806 case SCAN_ANON: 1807 /* Scan one type exclusively */ 1808 if ((scan_balance == SCAN_FILE) != file) 1809 scan = 0; 1810 break; 1811 default: 1812 /* Look ma, no brain */ 1813 BUG(); 1814 } 1815 nr[lru] = scan; 1816 } 1817 } 1818 1819 /* 1820 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim. 1821 */ 1822 static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) 1823 { 1824 unsigned long nr[NR_LRU_LISTS]; 1825 unsigned long nr_to_scan; 1826 enum lru_list lru; 1827 unsigned long nr_reclaimed = 0; 1828 unsigned long nr_to_reclaim = sc->nr_to_reclaim; 1829 struct blk_plug plug; 1830 1831 get_scan_count(lruvec, sc, nr); 1832 1833 blk_start_plug(&plug); 1834 while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || 1835 nr[LRU_INACTIVE_FILE]) { 1836 for_each_evictable_lru(lru) { 1837 if (nr[lru]) { 1838 nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX); 1839 nr[lru] -= nr_to_scan; 1840 1841 nr_reclaimed += shrink_list(lru, nr_to_scan, 1842 lruvec, sc); 1843 } 1844 } 1845 /* 1846 * On large memory systems, scan >> priority can become 1847 * really large. This is fine for the starting priority; 1848 * we want to put equal scanning pressure on each zone. 1849 * However, if the VM has a harder time of freeing pages, 1850 * with multiple processes reclaiming pages, the total 1851 * freeing target can get unreasonably large. 1852 */ 1853 if (nr_reclaimed >= nr_to_reclaim && 1854 sc->priority < DEF_PRIORITY) 1855 break; 1856 } 1857 blk_finish_plug(&plug); 1858 sc->nr_reclaimed += nr_reclaimed; 1859 1860 /* 1861 * Even if we did not try to evict anon pages at all, we want to 1862 * rebalance the anon lru active/inactive ratio. 1863 */ 1864 if (inactive_anon_is_low(lruvec)) 1865 shrink_active_list(SWAP_CLUSTER_MAX, lruvec, 1866 sc, LRU_ACTIVE_ANON); 1867 1868 throttle_vm_writeout(sc->gfp_mask); 1869 } 1870 1871 /* Use reclaim/compaction for costly allocs or under memory pressure */ 1872 static bool in_reclaim_compaction(struct scan_control *sc) 1873 { 1874 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order && 1875 (sc->order > PAGE_ALLOC_COSTLY_ORDER || 1876 sc->priority < DEF_PRIORITY - 2)) 1877 return true; 1878 1879 return false; 1880 } 1881 1882 /* 1883 * Reclaim/compaction is used for high-order allocation requests. It reclaims 1884 * order-0 pages before compacting the zone. should_continue_reclaim() returns 1885 * true if more pages should be reclaimed such that when the page allocator 1886 * calls try_to_compact_zone() that it will have enough free pages to succeed. 1887 * It will give up earlier than that if there is difficulty reclaiming pages. 1888 */ 1889 static inline bool should_continue_reclaim(struct zone *zone, 1890 unsigned long nr_reclaimed, 1891 unsigned long nr_scanned, 1892 struct scan_control *sc) 1893 { 1894 unsigned long pages_for_compaction; 1895 unsigned long inactive_lru_pages; 1896 1897 /* If not in reclaim/compaction mode, stop */ 1898 if (!in_reclaim_compaction(sc)) 1899 return false; 1900 1901 /* Consider stopping depending on scan and reclaim activity */ 1902 if (sc->gfp_mask & __GFP_REPEAT) { 1903 /* 1904 * For __GFP_REPEAT allocations, stop reclaiming if the 1905 * full LRU list has been scanned and we are still failing 1906 * to reclaim pages. This full LRU scan is potentially 1907 * expensive but a __GFP_REPEAT caller really wants to succeed 1908 */ 1909 if (!nr_reclaimed && !nr_scanned) 1910 return false; 1911 } else { 1912 /* 1913 * For non-__GFP_REPEAT allocations which can presumably 1914 * fail without consequence, stop if we failed to reclaim 1915 * any pages from the last SWAP_CLUSTER_MAX number of 1916 * pages that were scanned. This will return to the 1917 * caller faster at the risk reclaim/compaction and 1918 * the resulting allocation attempt fails 1919 */ 1920 if (!nr_reclaimed) 1921 return false; 1922 } 1923 1924 /* 1925 * If we have not reclaimed enough pages for compaction and the 1926 * inactive lists are large enough, continue reclaiming 1927 */ 1928 pages_for_compaction = (2UL << sc->order); 1929 inactive_lru_pages = zone_page_state(zone, NR_INACTIVE_FILE); 1930 if (get_nr_swap_pages() > 0) 1931 inactive_lru_pages += zone_page_state(zone, NR_INACTIVE_ANON); 1932 if (sc->nr_reclaimed < pages_for_compaction && 1933 inactive_lru_pages > pages_for_compaction) 1934 return true; 1935 1936 /* If compaction would go ahead or the allocation would succeed, stop */ 1937 switch (compaction_suitable(zone, sc->order)) { 1938 case COMPACT_PARTIAL: 1939 case COMPACT_CONTINUE: 1940 return false; 1941 default: 1942 return true; 1943 } 1944 } 1945 1946 static void shrink_zone(struct zone *zone, struct scan_control *sc) 1947 { 1948 unsigned long nr_reclaimed, nr_scanned; 1949 1950 do { 1951 struct mem_cgroup *root = sc->target_mem_cgroup; 1952 struct mem_cgroup_reclaim_cookie reclaim = { 1953 .zone = zone, 1954 .priority = sc->priority, 1955 }; 1956 struct mem_cgroup *memcg; 1957 1958 nr_reclaimed = sc->nr_reclaimed; 1959 nr_scanned = sc->nr_scanned; 1960 1961 memcg = mem_cgroup_iter(root, NULL, &reclaim); 1962 do { 1963 struct lruvec *lruvec; 1964 1965 lruvec = mem_cgroup_zone_lruvec(zone, memcg); 1966 1967 shrink_lruvec(lruvec, sc); 1968 1969 /* 1970 * Direct reclaim and kswapd have to scan all memory 1971 * cgroups to fulfill the overall scan target for the 1972 * zone. 1973 * 1974 * Limit reclaim, on the other hand, only cares about 1975 * nr_to_reclaim pages to be reclaimed and it will 1976 * retry with decreasing priority if one round over the 1977 * whole hierarchy is not sufficient. 1978 */ 1979 if (!global_reclaim(sc) && 1980 sc->nr_reclaimed >= sc->nr_to_reclaim) { 1981 mem_cgroup_iter_break(root, memcg); 1982 break; 1983 } 1984 memcg = mem_cgroup_iter(root, memcg, &reclaim); 1985 } while (memcg); 1986 1987 vmpressure(sc->gfp_mask, sc->target_mem_cgroup, 1988 sc->nr_scanned - nr_scanned, 1989 sc->nr_reclaimed - nr_reclaimed); 1990 1991 } while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed, 1992 sc->nr_scanned - nr_scanned, sc)); 1993 } 1994 1995 /* Returns true if compaction should go ahead for a high-order request */ 1996 static inline bool compaction_ready(struct zone *zone, struct scan_control *sc) 1997 { 1998 unsigned long balance_gap, watermark; 1999 bool watermark_ok; 2000 2001 /* Do not consider compaction for orders reclaim is meant to satisfy */ 2002 if (sc->order <= PAGE_ALLOC_COSTLY_ORDER) 2003 return false; 2004 2005 /* 2006 * Compaction takes time to run and there are potentially other 2007 * callers using the pages just freed. Continue reclaiming until 2008 * there is a buffer of free pages available to give compaction 2009 * a reasonable chance of completing and allocating the page 2010 */ 2011 balance_gap = min(low_wmark_pages(zone), 2012 (zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) / 2013 KSWAPD_ZONE_BALANCE_GAP_RATIO); 2014 watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order); 2015 watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0); 2016 2017 /* 2018 * If compaction is deferred, reclaim up to a point where 2019 * compaction will have a chance of success when re-enabled 2020 */ 2021 if (compaction_deferred(zone, sc->order)) 2022 return watermark_ok; 2023 2024 /* If compaction is not ready to start, keep reclaiming */ 2025 if (!compaction_suitable(zone, sc->order)) 2026 return false; 2027 2028 return watermark_ok; 2029 } 2030 2031 /* 2032 * This is the direct reclaim path, for page-allocating processes. We only 2033 * try to reclaim pages from zones which will satisfy the caller's allocation 2034 * request. 2035 * 2036 * We reclaim from a zone even if that zone is over high_wmark_pages(zone). 2037 * Because: 2038 * a) The caller may be trying to free *extra* pages to satisfy a higher-order 2039 * allocation or 2040 * b) The target zone may be at high_wmark_pages(zone) but the lower zones 2041 * must go *over* high_wmark_pages(zone) to satisfy the `incremental min' 2042 * zone defense algorithm. 2043 * 2044 * If a zone is deemed to be full of pinned pages then just give it a light 2045 * scan then give up on it. 2046 * 2047 * This function returns true if a zone is being reclaimed for a costly 2048 * high-order allocation and compaction is ready to begin. This indicates to 2049 * the caller that it should consider retrying the allocation instead of 2050 * further reclaim. 2051 */ 2052 static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc) 2053 { 2054 struct zoneref *z; 2055 struct zone *zone; 2056 unsigned long nr_soft_reclaimed; 2057 unsigned long nr_soft_scanned; 2058 bool aborted_reclaim = false; 2059 2060 /* 2061 * If the number of buffer_heads in the machine exceeds the maximum 2062 * allowed level, force direct reclaim to scan the highmem zone as 2063 * highmem pages could be pinning lowmem pages storing buffer_heads 2064 */ 2065 if (buffer_heads_over_limit) 2066 sc->gfp_mask |= __GFP_HIGHMEM; 2067 2068 for_each_zone_zonelist_nodemask(zone, z, zonelist, 2069 gfp_zone(sc->gfp_mask), sc->nodemask) { 2070 if (!populated_zone(zone)) 2071 continue; 2072 /* 2073 * Take care memory controller reclaiming has small influence 2074 * to global LRU. 2075 */ 2076 if (global_reclaim(sc)) { 2077 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2078 continue; 2079 if (zone->all_unreclaimable && 2080 sc->priority != DEF_PRIORITY) 2081 continue; /* Let kswapd poll it */ 2082 if (IS_ENABLED(CONFIG_COMPACTION)) { 2083 /* 2084 * If we already have plenty of memory free for 2085 * compaction in this zone, don't free any more. 2086 * Even though compaction is invoked for any 2087 * non-zero order, only frequent costly order 2088 * reclamation is disruptive enough to become a 2089 * noticeable problem, like transparent huge 2090 * page allocations. 2091 */ 2092 if (compaction_ready(zone, sc)) { 2093 aborted_reclaim = true; 2094 continue; 2095 } 2096 } 2097 /* 2098 * This steals pages from memory cgroups over softlimit 2099 * and returns the number of reclaimed pages and 2100 * scanned pages. This works for global memory pressure 2101 * and balancing, not for a memcg's limit. 2102 */ 2103 nr_soft_scanned = 0; 2104 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone, 2105 sc->order, sc->gfp_mask, 2106 &nr_soft_scanned); 2107 sc->nr_reclaimed += nr_soft_reclaimed; 2108 sc->nr_scanned += nr_soft_scanned; 2109 /* need some check for avoid more shrink_zone() */ 2110 } 2111 2112 shrink_zone(zone, sc); 2113 } 2114 2115 return aborted_reclaim; 2116 } 2117 2118 static bool zone_reclaimable(struct zone *zone) 2119 { 2120 return zone->pages_scanned < zone_reclaimable_pages(zone) * 6; 2121 } 2122 2123 /* All zones in zonelist are unreclaimable? */ 2124 static bool all_unreclaimable(struct zonelist *zonelist, 2125 struct scan_control *sc) 2126 { 2127 struct zoneref *z; 2128 struct zone *zone; 2129 2130 for_each_zone_zonelist_nodemask(zone, z, zonelist, 2131 gfp_zone(sc->gfp_mask), sc->nodemask) { 2132 if (!populated_zone(zone)) 2133 continue; 2134 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2135 continue; 2136 if (!zone->all_unreclaimable) 2137 return false; 2138 } 2139 2140 return true; 2141 } 2142 2143 /* 2144 * This is the main entry point to direct page reclaim. 2145 * 2146 * If a full scan of the inactive list fails to free enough memory then we 2147 * are "out of memory" and something needs to be killed. 2148 * 2149 * If the caller is !__GFP_FS then the probability of a failure is reasonably 2150 * high - the zone may be full of dirty or under-writeback pages, which this 2151 * caller can't do much about. We kick the writeback threads and take explicit 2152 * naps in the hope that some of these pages can be written. But if the 2153 * allocating task holds filesystem locks which prevent writeout this might not 2154 * work, and the allocation attempt will fail. 2155 * 2156 * returns: 0, if no pages reclaimed 2157 * else, the number of pages reclaimed 2158 */ 2159 static unsigned long do_try_to_free_pages(struct zonelist *zonelist, 2160 struct scan_control *sc, 2161 struct shrink_control *shrink) 2162 { 2163 unsigned long total_scanned = 0; 2164 struct reclaim_state *reclaim_state = current->reclaim_state; 2165 struct zoneref *z; 2166 struct zone *zone; 2167 unsigned long writeback_threshold; 2168 bool aborted_reclaim; 2169 2170 delayacct_freepages_start(); 2171 2172 if (global_reclaim(sc)) 2173 count_vm_event(ALLOCSTALL); 2174 2175 do { 2176 vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup, 2177 sc->priority); 2178 sc->nr_scanned = 0; 2179 aborted_reclaim = shrink_zones(zonelist, sc); 2180 2181 /* 2182 * Don't shrink slabs when reclaiming memory from 2183 * over limit cgroups 2184 */ 2185 if (global_reclaim(sc)) { 2186 unsigned long lru_pages = 0; 2187 for_each_zone_zonelist(zone, z, zonelist, 2188 gfp_zone(sc->gfp_mask)) { 2189 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2190 continue; 2191 2192 lru_pages += zone_reclaimable_pages(zone); 2193 } 2194 2195 shrink_slab(shrink, sc->nr_scanned, lru_pages); 2196 if (reclaim_state) { 2197 sc->nr_reclaimed += reclaim_state->reclaimed_slab; 2198 reclaim_state->reclaimed_slab = 0; 2199 } 2200 } 2201 total_scanned += sc->nr_scanned; 2202 if (sc->nr_reclaimed >= sc->nr_to_reclaim) 2203 goto out; 2204 2205 /* 2206 * If we're getting trouble reclaiming, start doing 2207 * writepage even in laptop mode. 2208 */ 2209 if (sc->priority < DEF_PRIORITY - 2) 2210 sc->may_writepage = 1; 2211 2212 /* 2213 * Try to write back as many pages as we just scanned. This 2214 * tends to cause slow streaming writers to write data to the 2215 * disk smoothly, at the dirtying rate, which is nice. But 2216 * that's undesirable in laptop mode, where we *want* lumpy 2217 * writeout. So in laptop mode, write out the whole world. 2218 */ 2219 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2; 2220 if (total_scanned > writeback_threshold) { 2221 wakeup_flusher_threads(laptop_mode ? 0 : total_scanned, 2222 WB_REASON_TRY_TO_FREE_PAGES); 2223 sc->may_writepage = 1; 2224 } 2225 2226 /* Take a nap, wait for some writeback to complete */ 2227 if (!sc->hibernation_mode && sc->nr_scanned && 2228 sc->priority < DEF_PRIORITY - 2) { 2229 struct zone *preferred_zone; 2230 2231 first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask), 2232 &cpuset_current_mems_allowed, 2233 &preferred_zone); 2234 wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10); 2235 } 2236 } while (--sc->priority >= 0); 2237 2238 out: 2239 delayacct_freepages_end(); 2240 2241 if (sc->nr_reclaimed) 2242 return sc->nr_reclaimed; 2243 2244 /* 2245 * As hibernation is going on, kswapd is freezed so that it can't mark 2246 * the zone into all_unreclaimable. Thus bypassing all_unreclaimable 2247 * check. 2248 */ 2249 if (oom_killer_disabled) 2250 return 0; 2251 2252 /* Aborted reclaim to try compaction? don't OOM, then */ 2253 if (aborted_reclaim) 2254 return 1; 2255 2256 /* top priority shrink_zones still had more to do? don't OOM, then */ 2257 if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc)) 2258 return 1; 2259 2260 return 0; 2261 } 2262 2263 static bool pfmemalloc_watermark_ok(pg_data_t *pgdat) 2264 { 2265 struct zone *zone; 2266 unsigned long pfmemalloc_reserve = 0; 2267 unsigned long free_pages = 0; 2268 int i; 2269 bool wmark_ok; 2270 2271 for (i = 0; i <= ZONE_NORMAL; i++) { 2272 zone = &pgdat->node_zones[i]; 2273 pfmemalloc_reserve += min_wmark_pages(zone); 2274 free_pages += zone_page_state(zone, NR_FREE_PAGES); 2275 } 2276 2277 wmark_ok = free_pages > pfmemalloc_reserve / 2; 2278 2279 /* kswapd must be awake if processes are being throttled */ 2280 if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) { 2281 pgdat->classzone_idx = min(pgdat->classzone_idx, 2282 (enum zone_type)ZONE_NORMAL); 2283 wake_up_interruptible(&pgdat->kswapd_wait); 2284 } 2285 2286 return wmark_ok; 2287 } 2288 2289 /* 2290 * Throttle direct reclaimers if backing storage is backed by the network 2291 * and the PFMEMALLOC reserve for the preferred node is getting dangerously 2292 * depleted. kswapd will continue to make progress and wake the processes 2293 * when the low watermark is reached. 2294 * 2295 * Returns true if a fatal signal was delivered during throttling. If this 2296 * happens, the page allocator should not consider triggering the OOM killer. 2297 */ 2298 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist, 2299 nodemask_t *nodemask) 2300 { 2301 struct zone *zone; 2302 int high_zoneidx = gfp_zone(gfp_mask); 2303 pg_data_t *pgdat; 2304 2305 /* 2306 * Kernel threads should not be throttled as they may be indirectly 2307 * responsible for cleaning pages necessary for reclaim to make forward 2308 * progress. kjournald for example may enter direct reclaim while 2309 * committing a transaction where throttling it could forcing other 2310 * processes to block on log_wait_commit(). 2311 */ 2312 if (current->flags & PF_KTHREAD) 2313 goto out; 2314 2315 /* 2316 * If a fatal signal is pending, this process should not throttle. 2317 * It should return quickly so it can exit and free its memory 2318 */ 2319 if (fatal_signal_pending(current)) 2320 goto out; 2321 2322 /* Check if the pfmemalloc reserves are ok */ 2323 first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone); 2324 pgdat = zone->zone_pgdat; 2325 if (pfmemalloc_watermark_ok(pgdat)) 2326 goto out; 2327 2328 /* Account for the throttling */ 2329 count_vm_event(PGSCAN_DIRECT_THROTTLE); 2330 2331 /* 2332 * If the caller cannot enter the filesystem, it's possible that it 2333 * is due to the caller holding an FS lock or performing a journal 2334 * transaction in the case of a filesystem like ext[3|4]. In this case, 2335 * it is not safe to block on pfmemalloc_wait as kswapd could be 2336 * blocked waiting on the same lock. Instead, throttle for up to a 2337 * second before continuing. 2338 */ 2339 if (!(gfp_mask & __GFP_FS)) { 2340 wait_event_interruptible_timeout(pgdat->pfmemalloc_wait, 2341 pfmemalloc_watermark_ok(pgdat), HZ); 2342 2343 goto check_pending; 2344 } 2345 2346 /* Throttle until kswapd wakes the process */ 2347 wait_event_killable(zone->zone_pgdat->pfmemalloc_wait, 2348 pfmemalloc_watermark_ok(pgdat)); 2349 2350 check_pending: 2351 if (fatal_signal_pending(current)) 2352 return true; 2353 2354 out: 2355 return false; 2356 } 2357 2358 unsigned long try_to_free_pages(struct zonelist *zonelist, int order, 2359 gfp_t gfp_mask, nodemask_t *nodemask) 2360 { 2361 unsigned long nr_reclaimed; 2362 struct scan_control sc = { 2363 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)), 2364 .may_writepage = !laptop_mode, 2365 .nr_to_reclaim = SWAP_CLUSTER_MAX, 2366 .may_unmap = 1, 2367 .may_swap = 1, 2368 .order = order, 2369 .priority = DEF_PRIORITY, 2370 .target_mem_cgroup = NULL, 2371 .nodemask = nodemask, 2372 }; 2373 struct shrink_control shrink = { 2374 .gfp_mask = sc.gfp_mask, 2375 }; 2376 2377 /* 2378 * Do not enter reclaim if fatal signal was delivered while throttled. 2379 * 1 is returned so that the page allocator does not OOM kill at this 2380 * point. 2381 */ 2382 if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask)) 2383 return 1; 2384 2385 trace_mm_vmscan_direct_reclaim_begin(order, 2386 sc.may_writepage, 2387 gfp_mask); 2388 2389 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); 2390 2391 trace_mm_vmscan_direct_reclaim_end(nr_reclaimed); 2392 2393 return nr_reclaimed; 2394 } 2395 2396 #ifdef CONFIG_MEMCG 2397 2398 unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg, 2399 gfp_t gfp_mask, bool noswap, 2400 struct zone *zone, 2401 unsigned long *nr_scanned) 2402 { 2403 struct scan_control sc = { 2404 .nr_scanned = 0, 2405 .nr_to_reclaim = SWAP_CLUSTER_MAX, 2406 .may_writepage = !laptop_mode, 2407 .may_unmap = 1, 2408 .may_swap = !noswap, 2409 .order = 0, 2410 .priority = 0, 2411 .target_mem_cgroup = memcg, 2412 }; 2413 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg); 2414 2415 sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | 2416 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK); 2417 2418 trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order, 2419 sc.may_writepage, 2420 sc.gfp_mask); 2421 2422 /* 2423 * NOTE: Although we can get the priority field, using it 2424 * here is not a good idea, since it limits the pages we can scan. 2425 * if we don't reclaim here, the shrink_zone from balance_pgdat 2426 * will pick up pages from other mem cgroup's as well. We hack 2427 * the priority and make it zero. 2428 */ 2429 shrink_lruvec(lruvec, &sc); 2430 2431 trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed); 2432 2433 *nr_scanned = sc.nr_scanned; 2434 return sc.nr_reclaimed; 2435 } 2436 2437 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, 2438 gfp_t gfp_mask, 2439 bool noswap) 2440 { 2441 struct zonelist *zonelist; 2442 unsigned long nr_reclaimed; 2443 int nid; 2444 struct scan_control sc = { 2445 .may_writepage = !laptop_mode, 2446 .may_unmap = 1, 2447 .may_swap = !noswap, 2448 .nr_to_reclaim = SWAP_CLUSTER_MAX, 2449 .order = 0, 2450 .priority = DEF_PRIORITY, 2451 .target_mem_cgroup = memcg, 2452 .nodemask = NULL, /* we don't care the placement */ 2453 .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | 2454 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK), 2455 }; 2456 struct shrink_control shrink = { 2457 .gfp_mask = sc.gfp_mask, 2458 }; 2459 2460 /* 2461 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't 2462 * take care of from where we get pages. So the node where we start the 2463 * scan does not need to be the current node. 2464 */ 2465 nid = mem_cgroup_select_victim_node(memcg); 2466 2467 zonelist = NODE_DATA(nid)->node_zonelists; 2468 2469 trace_mm_vmscan_memcg_reclaim_begin(0, 2470 sc.may_writepage, 2471 sc.gfp_mask); 2472 2473 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); 2474 2475 trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed); 2476 2477 return nr_reclaimed; 2478 } 2479 #endif 2480 2481 static void age_active_anon(struct zone *zone, struct scan_control *sc) 2482 { 2483 struct mem_cgroup *memcg; 2484 2485 if (!total_swap_pages) 2486 return; 2487 2488 memcg = mem_cgroup_iter(NULL, NULL, NULL); 2489 do { 2490 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg); 2491 2492 if (inactive_anon_is_low(lruvec)) 2493 shrink_active_list(SWAP_CLUSTER_MAX, lruvec, 2494 sc, LRU_ACTIVE_ANON); 2495 2496 memcg = mem_cgroup_iter(NULL, memcg, NULL); 2497 } while (memcg); 2498 } 2499 2500 static bool zone_balanced(struct zone *zone, int order, 2501 unsigned long balance_gap, int classzone_idx) 2502 { 2503 if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) + 2504 balance_gap, classzone_idx, 0)) 2505 return false; 2506 2507 if (IS_ENABLED(CONFIG_COMPACTION) && order && 2508 !compaction_suitable(zone, order)) 2509 return false; 2510 2511 return true; 2512 } 2513 2514 /* 2515 * pgdat_balanced() is used when checking if a node is balanced. 2516 * 2517 * For order-0, all zones must be balanced! 2518 * 2519 * For high-order allocations only zones that meet watermarks and are in a 2520 * zone allowed by the callers classzone_idx are added to balanced_pages. The 2521 * total of balanced pages must be at least 25% of the zones allowed by 2522 * classzone_idx for the node to be considered balanced. Forcing all zones to 2523 * be balanced for high orders can cause excessive reclaim when there are 2524 * imbalanced zones. 2525 * The choice of 25% is due to 2526 * o a 16M DMA zone that is balanced will not balance a zone on any 2527 * reasonable sized machine 2528 * o On all other machines, the top zone must be at least a reasonable 2529 * percentage of the middle zones. For example, on 32-bit x86, highmem 2530 * would need to be at least 256M for it to be balance a whole node. 2531 * Similarly, on x86-64 the Normal zone would need to be at least 1G 2532 * to balance a node on its own. These seemed like reasonable ratios. 2533 */ 2534 static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx) 2535 { 2536 unsigned long managed_pages = 0; 2537 unsigned long balanced_pages = 0; 2538 int i; 2539 2540 /* Check the watermark levels */ 2541 for (i = 0; i <= classzone_idx; i++) { 2542 struct zone *zone = pgdat->node_zones + i; 2543 2544 if (!populated_zone(zone)) 2545 continue; 2546 2547 managed_pages += zone->managed_pages; 2548 2549 /* 2550 * A special case here: 2551 * 2552 * balance_pgdat() skips over all_unreclaimable after 2553 * DEF_PRIORITY. Effectively, it considers them balanced so 2554 * they must be considered balanced here as well! 2555 */ 2556 if (zone->all_unreclaimable) { 2557 balanced_pages += zone->managed_pages; 2558 continue; 2559 } 2560 2561 if (zone_balanced(zone, order, 0, i)) 2562 balanced_pages += zone->managed_pages; 2563 else if (!order) 2564 return false; 2565 } 2566 2567 if (order) 2568 return balanced_pages >= (managed_pages >> 2); 2569 else 2570 return true; 2571 } 2572 2573 /* 2574 * Prepare kswapd for sleeping. This verifies that there are no processes 2575 * waiting in throttle_direct_reclaim() and that watermarks have been met. 2576 * 2577 * Returns true if kswapd is ready to sleep 2578 */ 2579 static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining, 2580 int classzone_idx) 2581 { 2582 /* If a direct reclaimer woke kswapd within HZ/10, it's premature */ 2583 if (remaining) 2584 return false; 2585 2586 /* 2587 * There is a potential race between when kswapd checks its watermarks 2588 * and a process gets throttled. There is also a potential race if 2589 * processes get throttled, kswapd wakes, a large process exits therby 2590 * balancing the zones that causes kswapd to miss a wakeup. If kswapd 2591 * is going to sleep, no process should be sleeping on pfmemalloc_wait 2592 * so wake them now if necessary. If necessary, processes will wake 2593 * kswapd and get throttled again 2594 */ 2595 if (waitqueue_active(&pgdat->pfmemalloc_wait)) { 2596 wake_up(&pgdat->pfmemalloc_wait); 2597 return false; 2598 } 2599 2600 return pgdat_balanced(pgdat, order, classzone_idx); 2601 } 2602 2603 /* 2604 * For kswapd, balance_pgdat() will work across all this node's zones until 2605 * they are all at high_wmark_pages(zone). 2606 * 2607 * Returns the final order kswapd was reclaiming at 2608 * 2609 * There is special handling here for zones which are full of pinned pages. 2610 * This can happen if the pages are all mlocked, or if they are all used by 2611 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb. 2612 * What we do is to detect the case where all pages in the zone have been 2613 * scanned twice and there has been zero successful reclaim. Mark the zone as 2614 * dead and from now on, only perform a short scan. Basically we're polling 2615 * the zone for when the problem goes away. 2616 * 2617 * kswapd scans the zones in the highmem->normal->dma direction. It skips 2618 * zones which have free_pages > high_wmark_pages(zone), but once a zone is 2619 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the 2620 * lower zones regardless of the number of free pages in the lower zones. This 2621 * interoperates with the page allocator fallback scheme to ensure that aging 2622 * of pages is balanced across the zones. 2623 */ 2624 static unsigned long balance_pgdat(pg_data_t *pgdat, int order, 2625 int *classzone_idx) 2626 { 2627 bool pgdat_is_balanced = false; 2628 int i; 2629 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ 2630 struct reclaim_state *reclaim_state = current->reclaim_state; 2631 unsigned long nr_soft_reclaimed; 2632 unsigned long nr_soft_scanned; 2633 struct scan_control sc = { 2634 .gfp_mask = GFP_KERNEL, 2635 .may_unmap = 1, 2636 .may_swap = 1, 2637 /* 2638 * kswapd doesn't want to be bailed out while reclaim. because 2639 * we want to put equal scanning pressure on each zone. 2640 */ 2641 .nr_to_reclaim = ULONG_MAX, 2642 .order = order, 2643 .target_mem_cgroup = NULL, 2644 }; 2645 struct shrink_control shrink = { 2646 .gfp_mask = sc.gfp_mask, 2647 }; 2648 loop_again: 2649 sc.priority = DEF_PRIORITY; 2650 sc.nr_reclaimed = 0; 2651 sc.may_writepage = !laptop_mode; 2652 count_vm_event(PAGEOUTRUN); 2653 2654 do { 2655 unsigned long lru_pages = 0; 2656 2657 /* 2658 * Scan in the highmem->dma direction for the highest 2659 * zone which needs scanning 2660 */ 2661 for (i = pgdat->nr_zones - 1; i >= 0; i--) { 2662 struct zone *zone = pgdat->node_zones + i; 2663 2664 if (!populated_zone(zone)) 2665 continue; 2666 2667 if (zone->all_unreclaimable && 2668 sc.priority != DEF_PRIORITY) 2669 continue; 2670 2671 /* 2672 * Do some background aging of the anon list, to give 2673 * pages a chance to be referenced before reclaiming. 2674 */ 2675 age_active_anon(zone, &sc); 2676 2677 /* 2678 * If the number of buffer_heads in the machine 2679 * exceeds the maximum allowed level and this node 2680 * has a highmem zone, force kswapd to reclaim from 2681 * it to relieve lowmem pressure. 2682 */ 2683 if (buffer_heads_over_limit && is_highmem_idx(i)) { 2684 end_zone = i; 2685 break; 2686 } 2687 2688 if (!zone_balanced(zone, order, 0, 0)) { 2689 end_zone = i; 2690 break; 2691 } else { 2692 /* If balanced, clear the congested flag */ 2693 zone_clear_flag(zone, ZONE_CONGESTED); 2694 } 2695 } 2696 2697 if (i < 0) { 2698 pgdat_is_balanced = true; 2699 goto out; 2700 } 2701 2702 for (i = 0; i <= end_zone; i++) { 2703 struct zone *zone = pgdat->node_zones + i; 2704 2705 lru_pages += zone_reclaimable_pages(zone); 2706 } 2707 2708 /* 2709 * Now scan the zone in the dma->highmem direction, stopping 2710 * at the last zone which needs scanning. 2711 * 2712 * We do this because the page allocator works in the opposite 2713 * direction. This prevents the page allocator from allocating 2714 * pages behind kswapd's direction of progress, which would 2715 * cause too much scanning of the lower zones. 2716 */ 2717 for (i = 0; i <= end_zone; i++) { 2718 struct zone *zone = pgdat->node_zones + i; 2719 int nr_slab, testorder; 2720 unsigned long balance_gap; 2721 2722 if (!populated_zone(zone)) 2723 continue; 2724 2725 if (zone->all_unreclaimable && 2726 sc.priority != DEF_PRIORITY) 2727 continue; 2728 2729 sc.nr_scanned = 0; 2730 2731 nr_soft_scanned = 0; 2732 /* 2733 * Call soft limit reclaim before calling shrink_zone. 2734 */ 2735 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone, 2736 order, sc.gfp_mask, 2737 &nr_soft_scanned); 2738 sc.nr_reclaimed += nr_soft_reclaimed; 2739 2740 /* 2741 * We put equal pressure on every zone, unless 2742 * one zone has way too many pages free 2743 * already. The "too many pages" is defined 2744 * as the high wmark plus a "gap" where the 2745 * gap is either the low watermark or 1% 2746 * of the zone, whichever is smaller. 2747 */ 2748 balance_gap = min(low_wmark_pages(zone), 2749 (zone->managed_pages + 2750 KSWAPD_ZONE_BALANCE_GAP_RATIO-1) / 2751 KSWAPD_ZONE_BALANCE_GAP_RATIO); 2752 /* 2753 * Kswapd reclaims only single pages with compaction 2754 * enabled. Trying too hard to reclaim until contiguous 2755 * free pages have become available can hurt performance 2756 * by evicting too much useful data from memory. 2757 * Do not reclaim more than needed for compaction. 2758 */ 2759 testorder = order; 2760 if (IS_ENABLED(CONFIG_COMPACTION) && order && 2761 compaction_suitable(zone, order) != 2762 COMPACT_SKIPPED) 2763 testorder = 0; 2764 2765 if ((buffer_heads_over_limit && is_highmem_idx(i)) || 2766 !zone_balanced(zone, testorder, 2767 balance_gap, end_zone)) { 2768 shrink_zone(zone, &sc); 2769 2770 reclaim_state->reclaimed_slab = 0; 2771 nr_slab = shrink_slab(&shrink, sc.nr_scanned, lru_pages); 2772 sc.nr_reclaimed += reclaim_state->reclaimed_slab; 2773 2774 if (nr_slab == 0 && !zone_reclaimable(zone)) 2775 zone->all_unreclaimable = 1; 2776 } 2777 2778 /* 2779 * If we're getting trouble reclaiming, start doing 2780 * writepage even in laptop mode. 2781 */ 2782 if (sc.priority < DEF_PRIORITY - 2) 2783 sc.may_writepage = 1; 2784 2785 if (zone->all_unreclaimable) { 2786 if (end_zone && end_zone == i) 2787 end_zone--; 2788 continue; 2789 } 2790 2791 if (zone_balanced(zone, testorder, 0, end_zone)) 2792 /* 2793 * If a zone reaches its high watermark, 2794 * consider it to be no longer congested. It's 2795 * possible there are dirty pages backed by 2796 * congested BDIs but as pressure is relieved, 2797 * speculatively avoid congestion waits 2798 */ 2799 zone_clear_flag(zone, ZONE_CONGESTED); 2800 } 2801 2802 /* 2803 * If the low watermark is met there is no need for processes 2804 * to be throttled on pfmemalloc_wait as they should not be 2805 * able to safely make forward progress. Wake them 2806 */ 2807 if (waitqueue_active(&pgdat->pfmemalloc_wait) && 2808 pfmemalloc_watermark_ok(pgdat)) 2809 wake_up(&pgdat->pfmemalloc_wait); 2810 2811 if (pgdat_balanced(pgdat, order, *classzone_idx)) { 2812 pgdat_is_balanced = true; 2813 break; /* kswapd: all done */ 2814 } 2815 2816 /* 2817 * We do this so kswapd doesn't build up large priorities for 2818 * example when it is freeing in parallel with allocators. It 2819 * matches the direct reclaim path behaviour in terms of impact 2820 * on zone->*_priority. 2821 */ 2822 if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX) 2823 break; 2824 } while (--sc.priority >= 0); 2825 2826 out: 2827 if (!pgdat_is_balanced) { 2828 cond_resched(); 2829 2830 try_to_freeze(); 2831 2832 /* 2833 * Fragmentation may mean that the system cannot be 2834 * rebalanced for high-order allocations in all zones. 2835 * At this point, if nr_reclaimed < SWAP_CLUSTER_MAX, 2836 * it means the zones have been fully scanned and are still 2837 * not balanced. For high-order allocations, there is 2838 * little point trying all over again as kswapd may 2839 * infinite loop. 2840 * 2841 * Instead, recheck all watermarks at order-0 as they 2842 * are the most important. If watermarks are ok, kswapd will go 2843 * back to sleep. High-order users can still perform direct 2844 * reclaim if they wish. 2845 */ 2846 if (sc.nr_reclaimed < SWAP_CLUSTER_MAX) 2847 order = sc.order = 0; 2848 2849 goto loop_again; 2850 } 2851 2852 /* 2853 * If kswapd was reclaiming at a higher order, it has the option of 2854 * sleeping without all zones being balanced. Before it does, it must 2855 * ensure that the watermarks for order-0 on *all* zones are met and 2856 * that the congestion flags are cleared. The congestion flag must 2857 * be cleared as kswapd is the only mechanism that clears the flag 2858 * and it is potentially going to sleep here. 2859 */ 2860 if (order) { 2861 int zones_need_compaction = 1; 2862 2863 for (i = 0; i <= end_zone; i++) { 2864 struct zone *zone = pgdat->node_zones + i; 2865 2866 if (!populated_zone(zone)) 2867 continue; 2868 2869 /* Check if the memory needs to be defragmented. */ 2870 if (zone_watermark_ok(zone, order, 2871 low_wmark_pages(zone), *classzone_idx, 0)) 2872 zones_need_compaction = 0; 2873 } 2874 2875 if (zones_need_compaction) 2876 compact_pgdat(pgdat, order); 2877 } 2878 2879 /* 2880 * Return the order we were reclaiming at so prepare_kswapd_sleep() 2881 * makes a decision on the order we were last reclaiming at. However, 2882 * if another caller entered the allocator slow path while kswapd 2883 * was awake, order will remain at the higher level 2884 */ 2885 *classzone_idx = end_zone; 2886 return order; 2887 } 2888 2889 static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx) 2890 { 2891 long remaining = 0; 2892 DEFINE_WAIT(wait); 2893 2894 if (freezing(current) || kthread_should_stop()) 2895 return; 2896 2897 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); 2898 2899 /* Try to sleep for a short interval */ 2900 if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) { 2901 remaining = schedule_timeout(HZ/10); 2902 finish_wait(&pgdat->kswapd_wait, &wait); 2903 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); 2904 } 2905 2906 /* 2907 * After a short sleep, check if it was a premature sleep. If not, then 2908 * go fully to sleep until explicitly woken up. 2909 */ 2910 if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) { 2911 trace_mm_vmscan_kswapd_sleep(pgdat->node_id); 2912 2913 /* 2914 * vmstat counters are not perfectly accurate and the estimated 2915 * value for counters such as NR_FREE_PAGES can deviate from the 2916 * true value by nr_online_cpus * threshold. To avoid the zone 2917 * watermarks being breached while under pressure, we reduce the 2918 * per-cpu vmstat threshold while kswapd is awake and restore 2919 * them before going back to sleep. 2920 */ 2921 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold); 2922 2923 /* 2924 * Compaction records what page blocks it recently failed to 2925 * isolate pages from and skips them in the future scanning. 2926 * When kswapd is going to sleep, it is reasonable to assume 2927 * that pages and compaction may succeed so reset the cache. 2928 */ 2929 reset_isolation_suitable(pgdat); 2930 2931 if (!kthread_should_stop()) 2932 schedule(); 2933 2934 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold); 2935 } else { 2936 if (remaining) 2937 count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY); 2938 else 2939 count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY); 2940 } 2941 finish_wait(&pgdat->kswapd_wait, &wait); 2942 } 2943 2944 /* 2945 * The background pageout daemon, started as a kernel thread 2946 * from the init process. 2947 * 2948 * This basically trickles out pages so that we have _some_ 2949 * free memory available even if there is no other activity 2950 * that frees anything up. This is needed for things like routing 2951 * etc, where we otherwise might have all activity going on in 2952 * asynchronous contexts that cannot page things out. 2953 * 2954 * If there are applications that are active memory-allocators 2955 * (most normal use), this basically shouldn't matter. 2956 */ 2957 static int kswapd(void *p) 2958 { 2959 unsigned long order, new_order; 2960 unsigned balanced_order; 2961 int classzone_idx, new_classzone_idx; 2962 int balanced_classzone_idx; 2963 pg_data_t *pgdat = (pg_data_t*)p; 2964 struct task_struct *tsk = current; 2965 2966 struct reclaim_state reclaim_state = { 2967 .reclaimed_slab = 0, 2968 }; 2969 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id); 2970 2971 lockdep_set_current_reclaim_state(GFP_KERNEL); 2972 2973 if (!cpumask_empty(cpumask)) 2974 set_cpus_allowed_ptr(tsk, cpumask); 2975 current->reclaim_state = &reclaim_state; 2976 2977 /* 2978 * Tell the memory management that we're a "memory allocator", 2979 * and that if we need more memory we should get access to it 2980 * regardless (see "__alloc_pages()"). "kswapd" should 2981 * never get caught in the normal page freeing logic. 2982 * 2983 * (Kswapd normally doesn't need memory anyway, but sometimes 2984 * you need a small amount of memory in order to be able to 2985 * page out something else, and this flag essentially protects 2986 * us from recursively trying to free more memory as we're 2987 * trying to free the first piece of memory in the first place). 2988 */ 2989 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; 2990 set_freezable(); 2991 2992 order = new_order = 0; 2993 balanced_order = 0; 2994 classzone_idx = new_classzone_idx = pgdat->nr_zones - 1; 2995 balanced_classzone_idx = classzone_idx; 2996 for ( ; ; ) { 2997 bool ret; 2998 2999 /* 3000 * If the last balance_pgdat was unsuccessful it's unlikely a 3001 * new request of a similar or harder type will succeed soon 3002 * so consider going to sleep on the basis we reclaimed at 3003 */ 3004 if (balanced_classzone_idx >= new_classzone_idx && 3005 balanced_order == new_order) { 3006 new_order = pgdat->kswapd_max_order; 3007 new_classzone_idx = pgdat->classzone_idx; 3008 pgdat->kswapd_max_order = 0; 3009 pgdat->classzone_idx = pgdat->nr_zones - 1; 3010 } 3011 3012 if (order < new_order || classzone_idx > new_classzone_idx) { 3013 /* 3014 * Don't sleep if someone wants a larger 'order' 3015 * allocation or has tigher zone constraints 3016 */ 3017 order = new_order; 3018 classzone_idx = new_classzone_idx; 3019 } else { 3020 kswapd_try_to_sleep(pgdat, balanced_order, 3021 balanced_classzone_idx); 3022 order = pgdat->kswapd_max_order; 3023 classzone_idx = pgdat->classzone_idx; 3024 new_order = order; 3025 new_classzone_idx = classzone_idx; 3026 pgdat->kswapd_max_order = 0; 3027 pgdat->classzone_idx = pgdat->nr_zones - 1; 3028 } 3029 3030 ret = try_to_freeze(); 3031 if (kthread_should_stop()) 3032 break; 3033 3034 /* 3035 * We can speed up thawing tasks if we don't call balance_pgdat 3036 * after returning from the refrigerator 3037 */ 3038 if (!ret) { 3039 trace_mm_vmscan_kswapd_wake(pgdat->node_id, order); 3040 balanced_classzone_idx = classzone_idx; 3041 balanced_order = balance_pgdat(pgdat, order, 3042 &balanced_classzone_idx); 3043 } 3044 } 3045 3046 current->reclaim_state = NULL; 3047 return 0; 3048 } 3049 3050 /* 3051 * A zone is low on free memory, so wake its kswapd task to service it. 3052 */ 3053 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx) 3054 { 3055 pg_data_t *pgdat; 3056 3057 if (!populated_zone(zone)) 3058 return; 3059 3060 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 3061 return; 3062 pgdat = zone->zone_pgdat; 3063 if (pgdat->kswapd_max_order < order) { 3064 pgdat->kswapd_max_order = order; 3065 pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx); 3066 } 3067 if (!waitqueue_active(&pgdat->kswapd_wait)) 3068 return; 3069 if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0)) 3070 return; 3071 3072 trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order); 3073 wake_up_interruptible(&pgdat->kswapd_wait); 3074 } 3075 3076 /* 3077 * The reclaimable count would be mostly accurate. 3078 * The less reclaimable pages may be 3079 * - mlocked pages, which will be moved to unevictable list when encountered 3080 * - mapped pages, which may require several travels to be reclaimed 3081 * - dirty pages, which is not "instantly" reclaimable 3082 */ 3083 unsigned long global_reclaimable_pages(void) 3084 { 3085 int nr; 3086 3087 nr = global_page_state(NR_ACTIVE_FILE) + 3088 global_page_state(NR_INACTIVE_FILE); 3089 3090 if (get_nr_swap_pages() > 0) 3091 nr += global_page_state(NR_ACTIVE_ANON) + 3092 global_page_state(NR_INACTIVE_ANON); 3093 3094 return nr; 3095 } 3096 3097 unsigned long zone_reclaimable_pages(struct zone *zone) 3098 { 3099 int nr; 3100 3101 nr = zone_page_state(zone, NR_ACTIVE_FILE) + 3102 zone_page_state(zone, NR_INACTIVE_FILE); 3103 3104 if (get_nr_swap_pages() > 0) 3105 nr += zone_page_state(zone, NR_ACTIVE_ANON) + 3106 zone_page_state(zone, NR_INACTIVE_ANON); 3107 3108 return nr; 3109 } 3110 3111 #ifdef CONFIG_HIBERNATION 3112 /* 3113 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of 3114 * freed pages. 3115 * 3116 * Rather than trying to age LRUs the aim is to preserve the overall 3117 * LRU order by reclaiming preferentially 3118 * inactive > active > active referenced > active mapped 3119 */ 3120 unsigned long shrink_all_memory(unsigned long nr_to_reclaim) 3121 { 3122 struct reclaim_state reclaim_state; 3123 struct scan_control sc = { 3124 .gfp_mask = GFP_HIGHUSER_MOVABLE, 3125 .may_swap = 1, 3126 .may_unmap = 1, 3127 .may_writepage = 1, 3128 .nr_to_reclaim = nr_to_reclaim, 3129 .hibernation_mode = 1, 3130 .order = 0, 3131 .priority = DEF_PRIORITY, 3132 }; 3133 struct shrink_control shrink = { 3134 .gfp_mask = sc.gfp_mask, 3135 }; 3136 struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask); 3137 struct task_struct *p = current; 3138 unsigned long nr_reclaimed; 3139 3140 p->flags |= PF_MEMALLOC; 3141 lockdep_set_current_reclaim_state(sc.gfp_mask); 3142 reclaim_state.reclaimed_slab = 0; 3143 p->reclaim_state = &reclaim_state; 3144 3145 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); 3146 3147 p->reclaim_state = NULL; 3148 lockdep_clear_current_reclaim_state(); 3149 p->flags &= ~PF_MEMALLOC; 3150 3151 return nr_reclaimed; 3152 } 3153 #endif /* CONFIG_HIBERNATION */ 3154 3155 /* It's optimal to keep kswapds on the same CPUs as their memory, but 3156 not required for correctness. So if the last cpu in a node goes 3157 away, we get changed to run anywhere: as the first one comes back, 3158 restore their cpu bindings. */ 3159 static int cpu_callback(struct notifier_block *nfb, unsigned long action, 3160 void *hcpu) 3161 { 3162 int nid; 3163 3164 if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) { 3165 for_each_node_state(nid, N_MEMORY) { 3166 pg_data_t *pgdat = NODE_DATA(nid); 3167 const struct cpumask *mask; 3168 3169 mask = cpumask_of_node(pgdat->node_id); 3170 3171 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids) 3172 /* One of our CPUs online: restore mask */ 3173 set_cpus_allowed_ptr(pgdat->kswapd, mask); 3174 } 3175 } 3176 return NOTIFY_OK; 3177 } 3178 3179 /* 3180 * This kswapd start function will be called by init and node-hot-add. 3181 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added. 3182 */ 3183 int kswapd_run(int nid) 3184 { 3185 pg_data_t *pgdat = NODE_DATA(nid); 3186 int ret = 0; 3187 3188 if (pgdat->kswapd) 3189 return 0; 3190 3191 pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid); 3192 if (IS_ERR(pgdat->kswapd)) { 3193 /* failure at boot is fatal */ 3194 BUG_ON(system_state == SYSTEM_BOOTING); 3195 pr_err("Failed to start kswapd on node %d\n", nid); 3196 ret = PTR_ERR(pgdat->kswapd); 3197 pgdat->kswapd = NULL; 3198 } 3199 return ret; 3200 } 3201 3202 /* 3203 * Called by memory hotplug when all memory in a node is offlined. Caller must 3204 * hold lock_memory_hotplug(). 3205 */ 3206 void kswapd_stop(int nid) 3207 { 3208 struct task_struct *kswapd = NODE_DATA(nid)->kswapd; 3209 3210 if (kswapd) { 3211 kthread_stop(kswapd); 3212 NODE_DATA(nid)->kswapd = NULL; 3213 } 3214 } 3215 3216 static int __init kswapd_init(void) 3217 { 3218 int nid; 3219 3220 swap_setup(); 3221 for_each_node_state(nid, N_MEMORY) 3222 kswapd_run(nid); 3223 hotcpu_notifier(cpu_callback, 0); 3224 return 0; 3225 } 3226 3227 module_init(kswapd_init) 3228 3229 #ifdef CONFIG_NUMA 3230 /* 3231 * Zone reclaim mode 3232 * 3233 * If non-zero call zone_reclaim when the number of free pages falls below 3234 * the watermarks. 3235 */ 3236 int zone_reclaim_mode __read_mostly; 3237 3238 #define RECLAIM_OFF 0 3239 #define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */ 3240 #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ 3241 #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */ 3242 3243 /* 3244 * Priority for ZONE_RECLAIM. This determines the fraction of pages 3245 * of a node considered for each zone_reclaim. 4 scans 1/16th of 3246 * a zone. 3247 */ 3248 #define ZONE_RECLAIM_PRIORITY 4 3249 3250 /* 3251 * Percentage of pages in a zone that must be unmapped for zone_reclaim to 3252 * occur. 3253 */ 3254 int sysctl_min_unmapped_ratio = 1; 3255 3256 /* 3257 * If the number of slab pages in a zone grows beyond this percentage then 3258 * slab reclaim needs to occur. 3259 */ 3260 int sysctl_min_slab_ratio = 5; 3261 3262 static inline unsigned long zone_unmapped_file_pages(struct zone *zone) 3263 { 3264 unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED); 3265 unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) + 3266 zone_page_state(zone, NR_ACTIVE_FILE); 3267 3268 /* 3269 * It's possible for there to be more file mapped pages than 3270 * accounted for by the pages on the file LRU lists because 3271 * tmpfs pages accounted for as ANON can also be FILE_MAPPED 3272 */ 3273 return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0; 3274 } 3275 3276 /* Work out how many page cache pages we can reclaim in this reclaim_mode */ 3277 static long zone_pagecache_reclaimable(struct zone *zone) 3278 { 3279 long nr_pagecache_reclaimable; 3280 long delta = 0; 3281 3282 /* 3283 * If RECLAIM_SWAP is set, then all file pages are considered 3284 * potentially reclaimable. Otherwise, we have to worry about 3285 * pages like swapcache and zone_unmapped_file_pages() provides 3286 * a better estimate 3287 */ 3288 if (zone_reclaim_mode & RECLAIM_SWAP) 3289 nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES); 3290 else 3291 nr_pagecache_reclaimable = zone_unmapped_file_pages(zone); 3292 3293 /* If we can't clean pages, remove dirty pages from consideration */ 3294 if (!(zone_reclaim_mode & RECLAIM_WRITE)) 3295 delta += zone_page_state(zone, NR_FILE_DIRTY); 3296 3297 /* Watch for any possible underflows due to delta */ 3298 if (unlikely(delta > nr_pagecache_reclaimable)) 3299 delta = nr_pagecache_reclaimable; 3300 3301 return nr_pagecache_reclaimable - delta; 3302 } 3303 3304 /* 3305 * Try to free up some pages from this zone through reclaim. 3306 */ 3307 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) 3308 { 3309 /* Minimum pages needed in order to stay on node */ 3310 const unsigned long nr_pages = 1 << order; 3311 struct task_struct *p = current; 3312 struct reclaim_state reclaim_state; 3313 struct scan_control sc = { 3314 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE), 3315 .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP), 3316 .may_swap = 1, 3317 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX), 3318 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)), 3319 .order = order, 3320 .priority = ZONE_RECLAIM_PRIORITY, 3321 }; 3322 struct shrink_control shrink = { 3323 .gfp_mask = sc.gfp_mask, 3324 }; 3325 unsigned long nr_slab_pages0, nr_slab_pages1; 3326 3327 cond_resched(); 3328 /* 3329 * We need to be able to allocate from the reserves for RECLAIM_SWAP 3330 * and we also need to be able to write out pages for RECLAIM_WRITE 3331 * and RECLAIM_SWAP. 3332 */ 3333 p->flags |= PF_MEMALLOC | PF_SWAPWRITE; 3334 lockdep_set_current_reclaim_state(gfp_mask); 3335 reclaim_state.reclaimed_slab = 0; 3336 p->reclaim_state = &reclaim_state; 3337 3338 if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) { 3339 /* 3340 * Free memory by calling shrink zone with increasing 3341 * priorities until we have enough memory freed. 3342 */ 3343 do { 3344 shrink_zone(zone, &sc); 3345 } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0); 3346 } 3347 3348 nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE); 3349 if (nr_slab_pages0 > zone->min_slab_pages) { 3350 /* 3351 * shrink_slab() does not currently allow us to determine how 3352 * many pages were freed in this zone. So we take the current 3353 * number of slab pages and shake the slab until it is reduced 3354 * by the same nr_pages that we used for reclaiming unmapped 3355 * pages. 3356 * 3357 * Note that shrink_slab will free memory on all zones and may 3358 * take a long time. 3359 */ 3360 for (;;) { 3361 unsigned long lru_pages = zone_reclaimable_pages(zone); 3362 3363 /* No reclaimable slab or very low memory pressure */ 3364 if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages)) 3365 break; 3366 3367 /* Freed enough memory */ 3368 nr_slab_pages1 = zone_page_state(zone, 3369 NR_SLAB_RECLAIMABLE); 3370 if (nr_slab_pages1 + nr_pages <= nr_slab_pages0) 3371 break; 3372 } 3373 3374 /* 3375 * Update nr_reclaimed by the number of slab pages we 3376 * reclaimed from this zone. 3377 */ 3378 nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE); 3379 if (nr_slab_pages1 < nr_slab_pages0) 3380 sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1; 3381 } 3382 3383 p->reclaim_state = NULL; 3384 current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE); 3385 lockdep_clear_current_reclaim_state(); 3386 return sc.nr_reclaimed >= nr_pages; 3387 } 3388 3389 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) 3390 { 3391 int node_id; 3392 int ret; 3393 3394 /* 3395 * Zone reclaim reclaims unmapped file backed pages and 3396 * slab pages if we are over the defined limits. 3397 * 3398 * A small portion of unmapped file backed pages is needed for 3399 * file I/O otherwise pages read by file I/O will be immediately 3400 * thrown out if the zone is overallocated. So we do not reclaim 3401 * if less than a specified percentage of the zone is used by 3402 * unmapped file backed pages. 3403 */ 3404 if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages && 3405 zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages) 3406 return ZONE_RECLAIM_FULL; 3407 3408 if (zone->all_unreclaimable) 3409 return ZONE_RECLAIM_FULL; 3410 3411 /* 3412 * Do not scan if the allocation should not be delayed. 3413 */ 3414 if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC)) 3415 return ZONE_RECLAIM_NOSCAN; 3416 3417 /* 3418 * Only run zone reclaim on the local zone or on zones that do not 3419 * have associated processors. This will favor the local processor 3420 * over remote processors and spread off node memory allocations 3421 * as wide as possible. 3422 */ 3423 node_id = zone_to_nid(zone); 3424 if (node_state(node_id, N_CPU) && node_id != numa_node_id()) 3425 return ZONE_RECLAIM_NOSCAN; 3426 3427 if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED)) 3428 return ZONE_RECLAIM_NOSCAN; 3429 3430 ret = __zone_reclaim(zone, gfp_mask, order); 3431 zone_clear_flag(zone, ZONE_RECLAIM_LOCKED); 3432 3433 if (!ret) 3434 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED); 3435 3436 return ret; 3437 } 3438 #endif 3439 3440 /* 3441 * page_evictable - test whether a page is evictable 3442 * @page: the page to test 3443 * 3444 * Test whether page is evictable--i.e., should be placed on active/inactive 3445 * lists vs unevictable list. 3446 * 3447 * Reasons page might not be evictable: 3448 * (1) page's mapping marked unevictable 3449 * (2) page is part of an mlocked VMA 3450 * 3451 */ 3452 int page_evictable(struct page *page) 3453 { 3454 return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page); 3455 } 3456 3457 #ifdef CONFIG_SHMEM 3458 /** 3459 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list 3460 * @pages: array of pages to check 3461 * @nr_pages: number of pages to check 3462 * 3463 * Checks pages for evictability and moves them to the appropriate lru list. 3464 * 3465 * This function is only used for SysV IPC SHM_UNLOCK. 3466 */ 3467 void check_move_unevictable_pages(struct page **pages, int nr_pages) 3468 { 3469 struct lruvec *lruvec; 3470 struct zone *zone = NULL; 3471 int pgscanned = 0; 3472 int pgrescued = 0; 3473 int i; 3474 3475 for (i = 0; i < nr_pages; i++) { 3476 struct page *page = pages[i]; 3477 struct zone *pagezone; 3478 3479 pgscanned++; 3480 pagezone = page_zone(page); 3481 if (pagezone != zone) { 3482 if (zone) 3483 spin_unlock_irq(&zone->lru_lock); 3484 zone = pagezone; 3485 spin_lock_irq(&zone->lru_lock); 3486 } 3487 lruvec = mem_cgroup_page_lruvec(page, zone); 3488 3489 if (!PageLRU(page) || !PageUnevictable(page)) 3490 continue; 3491 3492 if (page_evictable(page)) { 3493 enum lru_list lru = page_lru_base_type(page); 3494 3495 VM_BUG_ON(PageActive(page)); 3496 ClearPageUnevictable(page); 3497 del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE); 3498 add_page_to_lru_list(page, lruvec, lru); 3499 pgrescued++; 3500 } 3501 } 3502 3503 if (zone) { 3504 __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued); 3505 __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned); 3506 spin_unlock_irq(&zone->lru_lock); 3507 } 3508 } 3509 #endif /* CONFIG_SHMEM */ 3510 3511 static void warn_scan_unevictable_pages(void) 3512 { 3513 printk_once(KERN_WARNING 3514 "%s: The scan_unevictable_pages sysctl/node-interface has been " 3515 "disabled for lack of a legitimate use case. If you have " 3516 "one, please send an email to linux-mm@kvack.org.\n", 3517 current->comm); 3518 } 3519 3520 /* 3521 * scan_unevictable_pages [vm] sysctl handler. On demand re-scan of 3522 * all nodes' unevictable lists for evictable pages 3523 */ 3524 unsigned long scan_unevictable_pages; 3525 3526 int scan_unevictable_handler(struct ctl_table *table, int write, 3527 void __user *buffer, 3528 size_t *length, loff_t *ppos) 3529 { 3530 warn_scan_unevictable_pages(); 3531 proc_doulongvec_minmax(table, write, buffer, length, ppos); 3532 scan_unevictable_pages = 0; 3533 return 0; 3534 } 3535 3536 #ifdef CONFIG_NUMA 3537 /* 3538 * per node 'scan_unevictable_pages' attribute. On demand re-scan of 3539 * a specified node's per zone unevictable lists for evictable pages. 3540 */ 3541 3542 static ssize_t read_scan_unevictable_node(struct device *dev, 3543 struct device_attribute *attr, 3544 char *buf) 3545 { 3546 warn_scan_unevictable_pages(); 3547 return sprintf(buf, "0\n"); /* always zero; should fit... */ 3548 } 3549 3550 static ssize_t write_scan_unevictable_node(struct device *dev, 3551 struct device_attribute *attr, 3552 const char *buf, size_t count) 3553 { 3554 warn_scan_unevictable_pages(); 3555 return 1; 3556 } 3557 3558 3559 static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR, 3560 read_scan_unevictable_node, 3561 write_scan_unevictable_node); 3562 3563 int scan_unevictable_register_node(struct node *node) 3564 { 3565 return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages); 3566 } 3567 3568 void scan_unevictable_unregister_node(struct node *node) 3569 { 3570 device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages); 3571 } 3572 #endif 3573