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 was_unevictable = PageUnevictable(page); 550 551 VM_BUG_ON(PageLRU(page)); 552 553 redo: 554 ClearPageUnevictable(page); 555 556 if (page_evictable(page)) { 557 /* 558 * For evictable pages, we can use the cache. 559 * In event of a race, worst case is we end up with an 560 * unevictable page on [in]active list. 561 * We know how to handle that. 562 */ 563 lru = page_lru_base_type(page); 564 lru_cache_add(page); 565 } else { 566 /* 567 * Put unevictable pages directly on zone's unevictable 568 * list. 569 */ 570 lru = LRU_UNEVICTABLE; 571 add_page_to_unevictable_list(page); 572 /* 573 * When racing with an mlock or AS_UNEVICTABLE clearing 574 * (page is unlocked) make sure that if the other thread 575 * does not observe our setting of PG_lru and fails 576 * isolation/check_move_unevictable_pages, 577 * we see PG_mlocked/AS_UNEVICTABLE cleared below and move 578 * the page back to the evictable list. 579 * 580 * The other side is TestClearPageMlocked() or shmem_lock(). 581 */ 582 smp_mb(); 583 } 584 585 /* 586 * page's status can change while we move it among lru. If an evictable 587 * page is on unevictable list, it never be freed. To avoid that, 588 * check after we added it to the list, again. 589 */ 590 if (lru == LRU_UNEVICTABLE && page_evictable(page)) { 591 if (!isolate_lru_page(page)) { 592 put_page(page); 593 goto redo; 594 } 595 /* This means someone else dropped this page from LRU 596 * So, it will be freed or putback to LRU again. There is 597 * nothing to do here. 598 */ 599 } 600 601 if (was_unevictable && lru != LRU_UNEVICTABLE) 602 count_vm_event(UNEVICTABLE_PGRESCUED); 603 else if (!was_unevictable && lru == LRU_UNEVICTABLE) 604 count_vm_event(UNEVICTABLE_PGCULLED); 605 606 put_page(page); /* drop ref from isolate */ 607 } 608 609 enum page_references { 610 PAGEREF_RECLAIM, 611 PAGEREF_RECLAIM_CLEAN, 612 PAGEREF_KEEP, 613 PAGEREF_ACTIVATE, 614 }; 615 616 static enum page_references page_check_references(struct page *page, 617 struct scan_control *sc) 618 { 619 int referenced_ptes, referenced_page; 620 unsigned long vm_flags; 621 622 referenced_ptes = page_referenced(page, 1, sc->target_mem_cgroup, 623 &vm_flags); 624 referenced_page = TestClearPageReferenced(page); 625 626 /* 627 * Mlock lost the isolation race with us. Let try_to_unmap() 628 * move the page to the unevictable list. 629 */ 630 if (vm_flags & VM_LOCKED) 631 return PAGEREF_RECLAIM; 632 633 if (referenced_ptes) { 634 if (PageSwapBacked(page)) 635 return PAGEREF_ACTIVATE; 636 /* 637 * All mapped pages start out with page table 638 * references from the instantiating fault, so we need 639 * to look twice if a mapped file page is used more 640 * than once. 641 * 642 * Mark it and spare it for another trip around the 643 * inactive list. Another page table reference will 644 * lead to its activation. 645 * 646 * Note: the mark is set for activated pages as well 647 * so that recently deactivated but used pages are 648 * quickly recovered. 649 */ 650 SetPageReferenced(page); 651 652 if (referenced_page || referenced_ptes > 1) 653 return PAGEREF_ACTIVATE; 654 655 /* 656 * Activate file-backed executable pages after first usage. 657 */ 658 if (vm_flags & VM_EXEC) 659 return PAGEREF_ACTIVATE; 660 661 return PAGEREF_KEEP; 662 } 663 664 /* Reclaim if clean, defer dirty pages to writeback */ 665 if (referenced_page && !PageSwapBacked(page)) 666 return PAGEREF_RECLAIM_CLEAN; 667 668 return PAGEREF_RECLAIM; 669 } 670 671 /* Check if a page is dirty or under writeback */ 672 static void page_check_dirty_writeback(struct page *page, 673 bool *dirty, bool *writeback) 674 { 675 struct address_space *mapping; 676 677 /* 678 * Anonymous pages are not handled by flushers and must be written 679 * from reclaim context. Do not stall reclaim based on them 680 */ 681 if (!page_is_file_cache(page)) { 682 *dirty = false; 683 *writeback = false; 684 return; 685 } 686 687 /* By default assume that the page flags are accurate */ 688 *dirty = PageDirty(page); 689 *writeback = PageWriteback(page); 690 691 /* Verify dirty/writeback state if the filesystem supports it */ 692 if (!page_has_private(page)) 693 return; 694 695 mapping = page_mapping(page); 696 if (mapping && mapping->a_ops->is_dirty_writeback) 697 mapping->a_ops->is_dirty_writeback(page, dirty, writeback); 698 } 699 700 /* 701 * shrink_page_list() returns the number of reclaimed pages 702 */ 703 static unsigned long shrink_page_list(struct list_head *page_list, 704 struct zone *zone, 705 struct scan_control *sc, 706 enum ttu_flags ttu_flags, 707 unsigned long *ret_nr_dirty, 708 unsigned long *ret_nr_unqueued_dirty, 709 unsigned long *ret_nr_congested, 710 unsigned long *ret_nr_writeback, 711 unsigned long *ret_nr_immediate, 712 bool force_reclaim) 713 { 714 LIST_HEAD(ret_pages); 715 LIST_HEAD(free_pages); 716 int pgactivate = 0; 717 unsigned long nr_unqueued_dirty = 0; 718 unsigned long nr_dirty = 0; 719 unsigned long nr_congested = 0; 720 unsigned long nr_reclaimed = 0; 721 unsigned long nr_writeback = 0; 722 unsigned long nr_immediate = 0; 723 724 cond_resched(); 725 726 mem_cgroup_uncharge_start(); 727 while (!list_empty(page_list)) { 728 struct address_space *mapping; 729 struct page *page; 730 int may_enter_fs; 731 enum page_references references = PAGEREF_RECLAIM_CLEAN; 732 bool dirty, writeback; 733 734 cond_resched(); 735 736 page = lru_to_page(page_list); 737 list_del(&page->lru); 738 739 if (!trylock_page(page)) 740 goto keep; 741 742 VM_BUG_ON(PageActive(page)); 743 VM_BUG_ON(page_zone(page) != zone); 744 745 sc->nr_scanned++; 746 747 if (unlikely(!page_evictable(page))) 748 goto cull_mlocked; 749 750 if (!sc->may_unmap && page_mapped(page)) 751 goto keep_locked; 752 753 /* Double the slab pressure for mapped and swapcache pages */ 754 if (page_mapped(page) || PageSwapCache(page)) 755 sc->nr_scanned++; 756 757 may_enter_fs = (sc->gfp_mask & __GFP_FS) || 758 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); 759 760 /* 761 * The number of dirty pages determines if a zone is marked 762 * reclaim_congested which affects wait_iff_congested. kswapd 763 * will stall and start writing pages if the tail of the LRU 764 * is all dirty unqueued pages. 765 */ 766 page_check_dirty_writeback(page, &dirty, &writeback); 767 if (dirty || writeback) 768 nr_dirty++; 769 770 if (dirty && !writeback) 771 nr_unqueued_dirty++; 772 773 /* 774 * Treat this page as congested if the underlying BDI is or if 775 * pages are cycling through the LRU so quickly that the 776 * pages marked for immediate reclaim are making it to the 777 * end of the LRU a second time. 778 */ 779 mapping = page_mapping(page); 780 if ((mapping && bdi_write_congested(mapping->backing_dev_info)) || 781 (writeback && PageReclaim(page))) 782 nr_congested++; 783 784 /* 785 * If a page at the tail of the LRU is under writeback, there 786 * are three cases to consider. 787 * 788 * 1) If reclaim is encountering an excessive number of pages 789 * under writeback and this page is both under writeback and 790 * PageReclaim then it indicates that pages are being queued 791 * for IO but are being recycled through the LRU before the 792 * IO can complete. Waiting on the page itself risks an 793 * indefinite stall if it is impossible to writeback the 794 * page due to IO error or disconnected storage so instead 795 * note that the LRU is being scanned too quickly and the 796 * caller can stall after page list has been processed. 797 * 798 * 2) Global reclaim encounters a page, memcg encounters a 799 * page that is not marked for immediate reclaim or 800 * the caller does not have __GFP_IO. In this case mark 801 * the page for immediate reclaim and continue scanning. 802 * 803 * __GFP_IO is checked because a loop driver thread might 804 * enter reclaim, and deadlock if it waits on a page for 805 * which it is needed to do the write (loop masks off 806 * __GFP_IO|__GFP_FS for this reason); but more thought 807 * would probably show more reasons. 808 * 809 * Don't require __GFP_FS, since we're not going into the 810 * FS, just waiting on its writeback completion. Worryingly, 811 * ext4 gfs2 and xfs allocate pages with 812 * grab_cache_page_write_begin(,,AOP_FLAG_NOFS), so testing 813 * may_enter_fs here is liable to OOM on them. 814 * 815 * 3) memcg encounters a page that is not already marked 816 * PageReclaim. memcg does not have any dirty pages 817 * throttling so we could easily OOM just because too many 818 * pages are in writeback and there is nothing else to 819 * reclaim. Wait for the writeback to complete. 820 */ 821 if (PageWriteback(page)) { 822 /* Case 1 above */ 823 if (current_is_kswapd() && 824 PageReclaim(page) && 825 zone_is_reclaim_writeback(zone)) { 826 nr_immediate++; 827 goto keep_locked; 828 829 /* Case 2 above */ 830 } else if (global_reclaim(sc) || 831 !PageReclaim(page) || !(sc->gfp_mask & __GFP_IO)) { 832 /* 833 * This is slightly racy - end_page_writeback() 834 * might have just cleared PageReclaim, then 835 * setting PageReclaim here end up interpreted 836 * as PageReadahead - but that does not matter 837 * enough to care. What we do want is for this 838 * page to have PageReclaim set next time memcg 839 * reclaim reaches the tests above, so it will 840 * then wait_on_page_writeback() to avoid OOM; 841 * and it's also appropriate in global reclaim. 842 */ 843 SetPageReclaim(page); 844 nr_writeback++; 845 846 goto keep_locked; 847 848 /* Case 3 above */ 849 } else { 850 wait_on_page_writeback(page); 851 } 852 } 853 854 if (!force_reclaim) 855 references = page_check_references(page, sc); 856 857 switch (references) { 858 case PAGEREF_ACTIVATE: 859 goto activate_locked; 860 case PAGEREF_KEEP: 861 goto keep_locked; 862 case PAGEREF_RECLAIM: 863 case PAGEREF_RECLAIM_CLEAN: 864 ; /* try to reclaim the page below */ 865 } 866 867 /* 868 * Anonymous process memory has backing store? 869 * Try to allocate it some swap space here. 870 */ 871 if (PageAnon(page) && !PageSwapCache(page)) { 872 if (!(sc->gfp_mask & __GFP_IO)) 873 goto keep_locked; 874 if (!add_to_swap(page, page_list)) 875 goto activate_locked; 876 may_enter_fs = 1; 877 878 /* Adding to swap updated mapping */ 879 mapping = page_mapping(page); 880 } 881 882 /* 883 * The page is mapped into the page tables of one or more 884 * processes. Try to unmap it here. 885 */ 886 if (page_mapped(page) && mapping) { 887 switch (try_to_unmap(page, ttu_flags)) { 888 case SWAP_FAIL: 889 goto activate_locked; 890 case SWAP_AGAIN: 891 goto keep_locked; 892 case SWAP_MLOCK: 893 goto cull_mlocked; 894 case SWAP_SUCCESS: 895 ; /* try to free the page below */ 896 } 897 } 898 899 if (PageDirty(page)) { 900 /* 901 * Only kswapd can writeback filesystem pages to 902 * avoid risk of stack overflow but only writeback 903 * if many dirty pages have been encountered. 904 */ 905 if (page_is_file_cache(page) && 906 (!current_is_kswapd() || 907 !zone_is_reclaim_dirty(zone))) { 908 /* 909 * Immediately reclaim when written back. 910 * Similar in principal to deactivate_page() 911 * except we already have the page isolated 912 * and know it's dirty 913 */ 914 inc_zone_page_state(page, NR_VMSCAN_IMMEDIATE); 915 SetPageReclaim(page); 916 917 goto keep_locked; 918 } 919 920 if (references == PAGEREF_RECLAIM_CLEAN) 921 goto keep_locked; 922 if (!may_enter_fs) 923 goto keep_locked; 924 if (!sc->may_writepage) 925 goto keep_locked; 926 927 /* Page is dirty, try to write it out here */ 928 switch (pageout(page, mapping, sc)) { 929 case PAGE_KEEP: 930 goto keep_locked; 931 case PAGE_ACTIVATE: 932 goto activate_locked; 933 case PAGE_SUCCESS: 934 if (PageWriteback(page)) 935 goto keep; 936 if (PageDirty(page)) 937 goto keep; 938 939 /* 940 * A synchronous write - probably a ramdisk. Go 941 * ahead and try to reclaim the page. 942 */ 943 if (!trylock_page(page)) 944 goto keep; 945 if (PageDirty(page) || PageWriteback(page)) 946 goto keep_locked; 947 mapping = page_mapping(page); 948 case PAGE_CLEAN: 949 ; /* try to free the page below */ 950 } 951 } 952 953 /* 954 * If the page has buffers, try to free the buffer mappings 955 * associated with this page. If we succeed we try to free 956 * the page as well. 957 * 958 * We do this even if the page is PageDirty(). 959 * try_to_release_page() does not perform I/O, but it is 960 * possible for a page to have PageDirty set, but it is actually 961 * clean (all its buffers are clean). This happens if the 962 * buffers were written out directly, with submit_bh(). ext3 963 * will do this, as well as the blockdev mapping. 964 * try_to_release_page() will discover that cleanness and will 965 * drop the buffers and mark the page clean - it can be freed. 966 * 967 * Rarely, pages can have buffers and no ->mapping. These are 968 * the pages which were not successfully invalidated in 969 * truncate_complete_page(). We try to drop those buffers here 970 * and if that worked, and the page is no longer mapped into 971 * process address space (page_count == 1) it can be freed. 972 * Otherwise, leave the page on the LRU so it is swappable. 973 */ 974 if (page_has_private(page)) { 975 if (!try_to_release_page(page, sc->gfp_mask)) 976 goto activate_locked; 977 if (!mapping && page_count(page) == 1) { 978 unlock_page(page); 979 if (put_page_testzero(page)) 980 goto free_it; 981 else { 982 /* 983 * rare race with speculative reference. 984 * the speculative reference will free 985 * this page shortly, so we may 986 * increment nr_reclaimed here (and 987 * leave it off the LRU). 988 */ 989 nr_reclaimed++; 990 continue; 991 } 992 } 993 } 994 995 if (!mapping || !__remove_mapping(mapping, page)) 996 goto keep_locked; 997 998 /* 999 * At this point, we have no other references and there is 1000 * no way to pick any more up (removed from LRU, removed 1001 * from pagecache). Can use non-atomic bitops now (and 1002 * we obviously don't have to worry about waking up a process 1003 * waiting on the page lock, because there are no references. 1004 */ 1005 __clear_page_locked(page); 1006 free_it: 1007 nr_reclaimed++; 1008 1009 /* 1010 * Is there need to periodically free_page_list? It would 1011 * appear not as the counts should be low 1012 */ 1013 list_add(&page->lru, &free_pages); 1014 continue; 1015 1016 cull_mlocked: 1017 if (PageSwapCache(page)) 1018 try_to_free_swap(page); 1019 unlock_page(page); 1020 putback_lru_page(page); 1021 continue; 1022 1023 activate_locked: 1024 /* Not a candidate for swapping, so reclaim swap space. */ 1025 if (PageSwapCache(page) && vm_swap_full()) 1026 try_to_free_swap(page); 1027 VM_BUG_ON(PageActive(page)); 1028 SetPageActive(page); 1029 pgactivate++; 1030 keep_locked: 1031 unlock_page(page); 1032 keep: 1033 list_add(&page->lru, &ret_pages); 1034 VM_BUG_ON(PageLRU(page) || PageUnevictable(page)); 1035 } 1036 1037 free_hot_cold_page_list(&free_pages, 1); 1038 1039 list_splice(&ret_pages, page_list); 1040 count_vm_events(PGACTIVATE, pgactivate); 1041 mem_cgroup_uncharge_end(); 1042 *ret_nr_dirty += nr_dirty; 1043 *ret_nr_congested += nr_congested; 1044 *ret_nr_unqueued_dirty += nr_unqueued_dirty; 1045 *ret_nr_writeback += nr_writeback; 1046 *ret_nr_immediate += nr_immediate; 1047 return nr_reclaimed; 1048 } 1049 1050 unsigned long reclaim_clean_pages_from_list(struct zone *zone, 1051 struct list_head *page_list) 1052 { 1053 struct scan_control sc = { 1054 .gfp_mask = GFP_KERNEL, 1055 .priority = DEF_PRIORITY, 1056 .may_unmap = 1, 1057 }; 1058 unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5; 1059 struct page *page, *next; 1060 LIST_HEAD(clean_pages); 1061 1062 list_for_each_entry_safe(page, next, page_list, lru) { 1063 if (page_is_file_cache(page) && !PageDirty(page)) { 1064 ClearPageActive(page); 1065 list_move(&page->lru, &clean_pages); 1066 } 1067 } 1068 1069 ret = shrink_page_list(&clean_pages, zone, &sc, 1070 TTU_UNMAP|TTU_IGNORE_ACCESS, 1071 &dummy1, &dummy2, &dummy3, &dummy4, &dummy5, true); 1072 list_splice(&clean_pages, page_list); 1073 __mod_zone_page_state(zone, NR_ISOLATED_FILE, -ret); 1074 return ret; 1075 } 1076 1077 /* 1078 * Attempt to remove the specified page from its LRU. Only take this page 1079 * if it is of the appropriate PageActive status. Pages which are being 1080 * freed elsewhere are also ignored. 1081 * 1082 * page: page to consider 1083 * mode: one of the LRU isolation modes defined above 1084 * 1085 * returns 0 on success, -ve errno on failure. 1086 */ 1087 int __isolate_lru_page(struct page *page, isolate_mode_t mode) 1088 { 1089 int ret = -EINVAL; 1090 1091 /* Only take pages on the LRU. */ 1092 if (!PageLRU(page)) 1093 return ret; 1094 1095 /* Compaction should not handle unevictable pages but CMA can do so */ 1096 if (PageUnevictable(page) && !(mode & ISOLATE_UNEVICTABLE)) 1097 return ret; 1098 1099 ret = -EBUSY; 1100 1101 /* 1102 * To minimise LRU disruption, the caller can indicate that it only 1103 * wants to isolate pages it will be able to operate on without 1104 * blocking - clean pages for the most part. 1105 * 1106 * ISOLATE_CLEAN means that only clean pages should be isolated. This 1107 * is used by reclaim when it is cannot write to backing storage 1108 * 1109 * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages 1110 * that it is possible to migrate without blocking 1111 */ 1112 if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) { 1113 /* All the caller can do on PageWriteback is block */ 1114 if (PageWriteback(page)) 1115 return ret; 1116 1117 if (PageDirty(page)) { 1118 struct address_space *mapping; 1119 1120 /* ISOLATE_CLEAN means only clean pages */ 1121 if (mode & ISOLATE_CLEAN) 1122 return ret; 1123 1124 /* 1125 * Only pages without mappings or that have a 1126 * ->migratepage callback are possible to migrate 1127 * without blocking 1128 */ 1129 mapping = page_mapping(page); 1130 if (mapping && !mapping->a_ops->migratepage) 1131 return ret; 1132 } 1133 } 1134 1135 if ((mode & ISOLATE_UNMAPPED) && page_mapped(page)) 1136 return ret; 1137 1138 if (likely(get_page_unless_zero(page))) { 1139 /* 1140 * Be careful not to clear PageLRU until after we're 1141 * sure the page is not being freed elsewhere -- the 1142 * page release code relies on it. 1143 */ 1144 ClearPageLRU(page); 1145 ret = 0; 1146 } 1147 1148 return ret; 1149 } 1150 1151 /* 1152 * zone->lru_lock is heavily contended. Some of the functions that 1153 * shrink the lists perform better by taking out a batch of pages 1154 * and working on them outside the LRU lock. 1155 * 1156 * For pagecache intensive workloads, this function is the hottest 1157 * spot in the kernel (apart from copy_*_user functions). 1158 * 1159 * Appropriate locks must be held before calling this function. 1160 * 1161 * @nr_to_scan: The number of pages to look through on the list. 1162 * @lruvec: The LRU vector to pull pages from. 1163 * @dst: The temp list to put pages on to. 1164 * @nr_scanned: The number of pages that were scanned. 1165 * @sc: The scan_control struct for this reclaim session 1166 * @mode: One of the LRU isolation modes 1167 * @lru: LRU list id for isolating 1168 * 1169 * returns how many pages were moved onto *@dst. 1170 */ 1171 static unsigned long isolate_lru_pages(unsigned long nr_to_scan, 1172 struct lruvec *lruvec, struct list_head *dst, 1173 unsigned long *nr_scanned, struct scan_control *sc, 1174 isolate_mode_t mode, enum lru_list lru) 1175 { 1176 struct list_head *src = &lruvec->lists[lru]; 1177 unsigned long nr_taken = 0; 1178 unsigned long scan; 1179 1180 for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) { 1181 struct page *page; 1182 int nr_pages; 1183 1184 page = lru_to_page(src); 1185 prefetchw_prev_lru_page(page, src, flags); 1186 1187 VM_BUG_ON(!PageLRU(page)); 1188 1189 switch (__isolate_lru_page(page, mode)) { 1190 case 0: 1191 nr_pages = hpage_nr_pages(page); 1192 mem_cgroup_update_lru_size(lruvec, lru, -nr_pages); 1193 list_move(&page->lru, dst); 1194 nr_taken += nr_pages; 1195 break; 1196 1197 case -EBUSY: 1198 /* else it is being freed elsewhere */ 1199 list_move(&page->lru, src); 1200 continue; 1201 1202 default: 1203 BUG(); 1204 } 1205 } 1206 1207 *nr_scanned = scan; 1208 trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan, 1209 nr_taken, mode, is_file_lru(lru)); 1210 return nr_taken; 1211 } 1212 1213 /** 1214 * isolate_lru_page - tries to isolate a page from its LRU list 1215 * @page: page to isolate from its LRU list 1216 * 1217 * Isolates a @page from an LRU list, clears PageLRU and adjusts the 1218 * vmstat statistic corresponding to whatever LRU list the page was on. 1219 * 1220 * Returns 0 if the page was removed from an LRU list. 1221 * Returns -EBUSY if the page was not on an LRU list. 1222 * 1223 * The returned page will have PageLRU() cleared. If it was found on 1224 * the active list, it will have PageActive set. If it was found on 1225 * the unevictable list, it will have the PageUnevictable bit set. That flag 1226 * may need to be cleared by the caller before letting the page go. 1227 * 1228 * The vmstat statistic corresponding to the list on which the page was 1229 * found will be decremented. 1230 * 1231 * Restrictions: 1232 * (1) Must be called with an elevated refcount on the page. This is a 1233 * fundamentnal difference from isolate_lru_pages (which is called 1234 * without a stable reference). 1235 * (2) the lru_lock must not be held. 1236 * (3) interrupts must be enabled. 1237 */ 1238 int isolate_lru_page(struct page *page) 1239 { 1240 int ret = -EBUSY; 1241 1242 VM_BUG_ON(!page_count(page)); 1243 1244 if (PageLRU(page)) { 1245 struct zone *zone = page_zone(page); 1246 struct lruvec *lruvec; 1247 1248 spin_lock_irq(&zone->lru_lock); 1249 lruvec = mem_cgroup_page_lruvec(page, zone); 1250 if (PageLRU(page)) { 1251 int lru = page_lru(page); 1252 get_page(page); 1253 ClearPageLRU(page); 1254 del_page_from_lru_list(page, lruvec, lru); 1255 ret = 0; 1256 } 1257 spin_unlock_irq(&zone->lru_lock); 1258 } 1259 return ret; 1260 } 1261 1262 /* 1263 * A direct reclaimer may isolate SWAP_CLUSTER_MAX pages from the LRU list and 1264 * then get resheduled. When there are massive number of tasks doing page 1265 * allocation, such sleeping direct reclaimers may keep piling up on each CPU, 1266 * the LRU list will go small and be scanned faster than necessary, leading to 1267 * unnecessary swapping, thrashing and OOM. 1268 */ 1269 static int too_many_isolated(struct zone *zone, int file, 1270 struct scan_control *sc) 1271 { 1272 unsigned long inactive, isolated; 1273 1274 if (current_is_kswapd()) 1275 return 0; 1276 1277 if (!global_reclaim(sc)) 1278 return 0; 1279 1280 if (file) { 1281 inactive = zone_page_state(zone, NR_INACTIVE_FILE); 1282 isolated = zone_page_state(zone, NR_ISOLATED_FILE); 1283 } else { 1284 inactive = zone_page_state(zone, NR_INACTIVE_ANON); 1285 isolated = zone_page_state(zone, NR_ISOLATED_ANON); 1286 } 1287 1288 /* 1289 * GFP_NOIO/GFP_NOFS callers are allowed to isolate more pages, so they 1290 * won't get blocked by normal direct-reclaimers, forming a circular 1291 * deadlock. 1292 */ 1293 if ((sc->gfp_mask & GFP_IOFS) == GFP_IOFS) 1294 inactive >>= 3; 1295 1296 return isolated > inactive; 1297 } 1298 1299 static noinline_for_stack void 1300 putback_inactive_pages(struct lruvec *lruvec, struct list_head *page_list) 1301 { 1302 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; 1303 struct zone *zone = lruvec_zone(lruvec); 1304 LIST_HEAD(pages_to_free); 1305 1306 /* 1307 * Put back any unfreeable pages. 1308 */ 1309 while (!list_empty(page_list)) { 1310 struct page *page = lru_to_page(page_list); 1311 int lru; 1312 1313 VM_BUG_ON(PageLRU(page)); 1314 list_del(&page->lru); 1315 if (unlikely(!page_evictable(page))) { 1316 spin_unlock_irq(&zone->lru_lock); 1317 putback_lru_page(page); 1318 spin_lock_irq(&zone->lru_lock); 1319 continue; 1320 } 1321 1322 lruvec = mem_cgroup_page_lruvec(page, zone); 1323 1324 SetPageLRU(page); 1325 lru = page_lru(page); 1326 add_page_to_lru_list(page, lruvec, lru); 1327 1328 if (is_active_lru(lru)) { 1329 int file = is_file_lru(lru); 1330 int numpages = hpage_nr_pages(page); 1331 reclaim_stat->recent_rotated[file] += numpages; 1332 } 1333 if (put_page_testzero(page)) { 1334 __ClearPageLRU(page); 1335 __ClearPageActive(page); 1336 del_page_from_lru_list(page, lruvec, lru); 1337 1338 if (unlikely(PageCompound(page))) { 1339 spin_unlock_irq(&zone->lru_lock); 1340 (*get_compound_page_dtor(page))(page); 1341 spin_lock_irq(&zone->lru_lock); 1342 } else 1343 list_add(&page->lru, &pages_to_free); 1344 } 1345 } 1346 1347 /* 1348 * To save our caller's stack, now use input list for pages to free. 1349 */ 1350 list_splice(&pages_to_free, page_list); 1351 } 1352 1353 /* 1354 * shrink_inactive_list() is a helper for shrink_zone(). It returns the number 1355 * of reclaimed pages 1356 */ 1357 static noinline_for_stack unsigned long 1358 shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec, 1359 struct scan_control *sc, enum lru_list lru) 1360 { 1361 LIST_HEAD(page_list); 1362 unsigned long nr_scanned; 1363 unsigned long nr_reclaimed = 0; 1364 unsigned long nr_taken; 1365 unsigned long nr_dirty = 0; 1366 unsigned long nr_congested = 0; 1367 unsigned long nr_unqueued_dirty = 0; 1368 unsigned long nr_writeback = 0; 1369 unsigned long nr_immediate = 0; 1370 isolate_mode_t isolate_mode = 0; 1371 int file = is_file_lru(lru); 1372 struct zone *zone = lruvec_zone(lruvec); 1373 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; 1374 1375 while (unlikely(too_many_isolated(zone, file, sc))) { 1376 congestion_wait(BLK_RW_ASYNC, HZ/10); 1377 1378 /* We are about to die and free our memory. Return now. */ 1379 if (fatal_signal_pending(current)) 1380 return SWAP_CLUSTER_MAX; 1381 } 1382 1383 lru_add_drain(); 1384 1385 if (!sc->may_unmap) 1386 isolate_mode |= ISOLATE_UNMAPPED; 1387 if (!sc->may_writepage) 1388 isolate_mode |= ISOLATE_CLEAN; 1389 1390 spin_lock_irq(&zone->lru_lock); 1391 1392 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &page_list, 1393 &nr_scanned, sc, isolate_mode, lru); 1394 1395 __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken); 1396 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken); 1397 1398 if (global_reclaim(sc)) { 1399 zone->pages_scanned += nr_scanned; 1400 if (current_is_kswapd()) 1401 __count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned); 1402 else 1403 __count_zone_vm_events(PGSCAN_DIRECT, zone, nr_scanned); 1404 } 1405 spin_unlock_irq(&zone->lru_lock); 1406 1407 if (nr_taken == 0) 1408 return 0; 1409 1410 nr_reclaimed = shrink_page_list(&page_list, zone, sc, TTU_UNMAP, 1411 &nr_dirty, &nr_unqueued_dirty, &nr_congested, 1412 &nr_writeback, &nr_immediate, 1413 false); 1414 1415 spin_lock_irq(&zone->lru_lock); 1416 1417 reclaim_stat->recent_scanned[file] += nr_taken; 1418 1419 if (global_reclaim(sc)) { 1420 if (current_is_kswapd()) 1421 __count_zone_vm_events(PGSTEAL_KSWAPD, zone, 1422 nr_reclaimed); 1423 else 1424 __count_zone_vm_events(PGSTEAL_DIRECT, zone, 1425 nr_reclaimed); 1426 } 1427 1428 putback_inactive_pages(lruvec, &page_list); 1429 1430 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken); 1431 1432 spin_unlock_irq(&zone->lru_lock); 1433 1434 free_hot_cold_page_list(&page_list, 1); 1435 1436 /* 1437 * If reclaim is isolating dirty pages under writeback, it implies 1438 * that the long-lived page allocation rate is exceeding the page 1439 * laundering rate. Either the global limits are not being effective 1440 * at throttling processes due to the page distribution throughout 1441 * zones or there is heavy usage of a slow backing device. The 1442 * only option is to throttle from reclaim context which is not ideal 1443 * as there is no guarantee the dirtying process is throttled in the 1444 * same way balance_dirty_pages() manages. 1445 * 1446 * Once a zone is flagged ZONE_WRITEBACK, kswapd will count the number 1447 * of pages under pages flagged for immediate reclaim and stall if any 1448 * are encountered in the nr_immediate check below. 1449 */ 1450 if (nr_writeback && nr_writeback == nr_taken) 1451 zone_set_flag(zone, ZONE_WRITEBACK); 1452 1453 /* 1454 * memcg will stall in page writeback so only consider forcibly 1455 * stalling for global reclaim 1456 */ 1457 if (global_reclaim(sc)) { 1458 /* 1459 * Tag a zone as congested if all the dirty pages scanned were 1460 * backed by a congested BDI and wait_iff_congested will stall. 1461 */ 1462 if (nr_dirty && nr_dirty == nr_congested) 1463 zone_set_flag(zone, ZONE_CONGESTED); 1464 1465 /* 1466 * If dirty pages are scanned that are not queued for IO, it 1467 * implies that flushers are not keeping up. In this case, flag 1468 * the zone ZONE_TAIL_LRU_DIRTY and kswapd will start writing 1469 * pages from reclaim context. It will forcibly stall in the 1470 * next check. 1471 */ 1472 if (nr_unqueued_dirty == nr_taken) 1473 zone_set_flag(zone, ZONE_TAIL_LRU_DIRTY); 1474 1475 /* 1476 * In addition, if kswapd scans pages marked marked for 1477 * immediate reclaim and under writeback (nr_immediate), it 1478 * implies that pages are cycling through the LRU faster than 1479 * they are written so also forcibly stall. 1480 */ 1481 if (nr_unqueued_dirty == nr_taken || nr_immediate) 1482 congestion_wait(BLK_RW_ASYNC, HZ/10); 1483 } 1484 1485 /* 1486 * Stall direct reclaim for IO completions if underlying BDIs or zone 1487 * is congested. Allow kswapd to continue until it starts encountering 1488 * unqueued dirty pages or cycling through the LRU too quickly. 1489 */ 1490 if (!sc->hibernation_mode && !current_is_kswapd()) 1491 wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10); 1492 1493 trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id, 1494 zone_idx(zone), 1495 nr_scanned, nr_reclaimed, 1496 sc->priority, 1497 trace_shrink_flags(file)); 1498 return nr_reclaimed; 1499 } 1500 1501 /* 1502 * This moves pages from the active list to the inactive list. 1503 * 1504 * We move them the other way if the page is referenced by one or more 1505 * processes, from rmap. 1506 * 1507 * If the pages are mostly unmapped, the processing is fast and it is 1508 * appropriate to hold zone->lru_lock across the whole operation. But if 1509 * the pages are mapped, the processing is slow (page_referenced()) so we 1510 * should drop zone->lru_lock around each page. It's impossible to balance 1511 * this, so instead we remove the pages from the LRU while processing them. 1512 * It is safe to rely on PG_active against the non-LRU pages in here because 1513 * nobody will play with that bit on a non-LRU page. 1514 * 1515 * The downside is that we have to touch page->_count against each page. 1516 * But we had to alter page->flags anyway. 1517 */ 1518 1519 static void move_active_pages_to_lru(struct lruvec *lruvec, 1520 struct list_head *list, 1521 struct list_head *pages_to_free, 1522 enum lru_list lru) 1523 { 1524 struct zone *zone = lruvec_zone(lruvec); 1525 unsigned long pgmoved = 0; 1526 struct page *page; 1527 int nr_pages; 1528 1529 while (!list_empty(list)) { 1530 page = lru_to_page(list); 1531 lruvec = mem_cgroup_page_lruvec(page, zone); 1532 1533 VM_BUG_ON(PageLRU(page)); 1534 SetPageLRU(page); 1535 1536 nr_pages = hpage_nr_pages(page); 1537 mem_cgroup_update_lru_size(lruvec, lru, nr_pages); 1538 list_move(&page->lru, &lruvec->lists[lru]); 1539 pgmoved += nr_pages; 1540 1541 if (put_page_testzero(page)) { 1542 __ClearPageLRU(page); 1543 __ClearPageActive(page); 1544 del_page_from_lru_list(page, lruvec, lru); 1545 1546 if (unlikely(PageCompound(page))) { 1547 spin_unlock_irq(&zone->lru_lock); 1548 (*get_compound_page_dtor(page))(page); 1549 spin_lock_irq(&zone->lru_lock); 1550 } else 1551 list_add(&page->lru, pages_to_free); 1552 } 1553 } 1554 __mod_zone_page_state(zone, NR_LRU_BASE + lru, pgmoved); 1555 if (!is_active_lru(lru)) 1556 __count_vm_events(PGDEACTIVATE, pgmoved); 1557 } 1558 1559 static void shrink_active_list(unsigned long nr_to_scan, 1560 struct lruvec *lruvec, 1561 struct scan_control *sc, 1562 enum lru_list lru) 1563 { 1564 unsigned long nr_taken; 1565 unsigned long nr_scanned; 1566 unsigned long vm_flags; 1567 LIST_HEAD(l_hold); /* The pages which were snipped off */ 1568 LIST_HEAD(l_active); 1569 LIST_HEAD(l_inactive); 1570 struct page *page; 1571 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; 1572 unsigned long nr_rotated = 0; 1573 isolate_mode_t isolate_mode = 0; 1574 int file = is_file_lru(lru); 1575 struct zone *zone = lruvec_zone(lruvec); 1576 1577 lru_add_drain(); 1578 1579 if (!sc->may_unmap) 1580 isolate_mode |= ISOLATE_UNMAPPED; 1581 if (!sc->may_writepage) 1582 isolate_mode |= ISOLATE_CLEAN; 1583 1584 spin_lock_irq(&zone->lru_lock); 1585 1586 nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold, 1587 &nr_scanned, sc, isolate_mode, lru); 1588 if (global_reclaim(sc)) 1589 zone->pages_scanned += nr_scanned; 1590 1591 reclaim_stat->recent_scanned[file] += nr_taken; 1592 1593 __count_zone_vm_events(PGREFILL, zone, nr_scanned); 1594 __mod_zone_page_state(zone, NR_LRU_BASE + lru, -nr_taken); 1595 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken); 1596 spin_unlock_irq(&zone->lru_lock); 1597 1598 while (!list_empty(&l_hold)) { 1599 cond_resched(); 1600 page = lru_to_page(&l_hold); 1601 list_del(&page->lru); 1602 1603 if (unlikely(!page_evictable(page))) { 1604 putback_lru_page(page); 1605 continue; 1606 } 1607 1608 if (unlikely(buffer_heads_over_limit)) { 1609 if (page_has_private(page) && trylock_page(page)) { 1610 if (page_has_private(page)) 1611 try_to_release_page(page, 0); 1612 unlock_page(page); 1613 } 1614 } 1615 1616 if (page_referenced(page, 0, sc->target_mem_cgroup, 1617 &vm_flags)) { 1618 nr_rotated += hpage_nr_pages(page); 1619 /* 1620 * Identify referenced, file-backed active pages and 1621 * give them one more trip around the active list. So 1622 * that executable code get better chances to stay in 1623 * memory under moderate memory pressure. Anon pages 1624 * are not likely to be evicted by use-once streaming 1625 * IO, plus JVM can create lots of anon VM_EXEC pages, 1626 * so we ignore them here. 1627 */ 1628 if ((vm_flags & VM_EXEC) && page_is_file_cache(page)) { 1629 list_add(&page->lru, &l_active); 1630 continue; 1631 } 1632 } 1633 1634 ClearPageActive(page); /* we are de-activating */ 1635 list_add(&page->lru, &l_inactive); 1636 } 1637 1638 /* 1639 * Move pages back to the lru list. 1640 */ 1641 spin_lock_irq(&zone->lru_lock); 1642 /* 1643 * Count referenced pages from currently used mappings as rotated, 1644 * even though only some of them are actually re-activated. This 1645 * helps balance scan pressure between file and anonymous pages in 1646 * get_scan_ratio. 1647 */ 1648 reclaim_stat->recent_rotated[file] += nr_rotated; 1649 1650 move_active_pages_to_lru(lruvec, &l_active, &l_hold, lru); 1651 move_active_pages_to_lru(lruvec, &l_inactive, &l_hold, lru - LRU_ACTIVE); 1652 __mod_zone_page_state(zone, NR_ISOLATED_ANON + file, -nr_taken); 1653 spin_unlock_irq(&zone->lru_lock); 1654 1655 free_hot_cold_page_list(&l_hold, 1); 1656 } 1657 1658 #ifdef CONFIG_SWAP 1659 static int inactive_anon_is_low_global(struct zone *zone) 1660 { 1661 unsigned long active, inactive; 1662 1663 active = zone_page_state(zone, NR_ACTIVE_ANON); 1664 inactive = zone_page_state(zone, NR_INACTIVE_ANON); 1665 1666 if (inactive * zone->inactive_ratio < active) 1667 return 1; 1668 1669 return 0; 1670 } 1671 1672 /** 1673 * inactive_anon_is_low - check if anonymous pages need to be deactivated 1674 * @lruvec: LRU vector to check 1675 * 1676 * Returns true if the zone does not have enough inactive anon pages, 1677 * meaning some active anon pages need to be deactivated. 1678 */ 1679 static int inactive_anon_is_low(struct lruvec *lruvec) 1680 { 1681 /* 1682 * If we don't have swap space, anonymous page deactivation 1683 * is pointless. 1684 */ 1685 if (!total_swap_pages) 1686 return 0; 1687 1688 if (!mem_cgroup_disabled()) 1689 return mem_cgroup_inactive_anon_is_low(lruvec); 1690 1691 return inactive_anon_is_low_global(lruvec_zone(lruvec)); 1692 } 1693 #else 1694 static inline int inactive_anon_is_low(struct lruvec *lruvec) 1695 { 1696 return 0; 1697 } 1698 #endif 1699 1700 /** 1701 * inactive_file_is_low - check if file pages need to be deactivated 1702 * @lruvec: LRU vector to check 1703 * 1704 * When the system is doing streaming IO, memory pressure here 1705 * ensures that active file pages get deactivated, until more 1706 * than half of the file pages are on the inactive list. 1707 * 1708 * Once we get to that situation, protect the system's working 1709 * set from being evicted by disabling active file page aging. 1710 * 1711 * This uses a different ratio than the anonymous pages, because 1712 * the page cache uses a use-once replacement algorithm. 1713 */ 1714 static int inactive_file_is_low(struct lruvec *lruvec) 1715 { 1716 unsigned long inactive; 1717 unsigned long active; 1718 1719 inactive = get_lru_size(lruvec, LRU_INACTIVE_FILE); 1720 active = get_lru_size(lruvec, LRU_ACTIVE_FILE); 1721 1722 return active > inactive; 1723 } 1724 1725 static int inactive_list_is_low(struct lruvec *lruvec, enum lru_list lru) 1726 { 1727 if (is_file_lru(lru)) 1728 return inactive_file_is_low(lruvec); 1729 else 1730 return inactive_anon_is_low(lruvec); 1731 } 1732 1733 static unsigned long shrink_list(enum lru_list lru, unsigned long nr_to_scan, 1734 struct lruvec *lruvec, struct scan_control *sc) 1735 { 1736 if (is_active_lru(lru)) { 1737 if (inactive_list_is_low(lruvec, lru)) 1738 shrink_active_list(nr_to_scan, lruvec, sc, lru); 1739 return 0; 1740 } 1741 1742 return shrink_inactive_list(nr_to_scan, lruvec, sc, lru); 1743 } 1744 1745 static int vmscan_swappiness(struct scan_control *sc) 1746 { 1747 if (global_reclaim(sc)) 1748 return vm_swappiness; 1749 return mem_cgroup_swappiness(sc->target_mem_cgroup); 1750 } 1751 1752 enum scan_balance { 1753 SCAN_EQUAL, 1754 SCAN_FRACT, 1755 SCAN_ANON, 1756 SCAN_FILE, 1757 }; 1758 1759 /* 1760 * Determine how aggressively the anon and file LRU lists should be 1761 * scanned. The relative value of each set of LRU lists is determined 1762 * by looking at the fraction of the pages scanned we did rotate back 1763 * onto the active list instead of evict. 1764 * 1765 * nr[0] = anon inactive pages to scan; nr[1] = anon active pages to scan 1766 * nr[2] = file inactive pages to scan; nr[3] = file active pages to scan 1767 */ 1768 static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc, 1769 unsigned long *nr) 1770 { 1771 struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat; 1772 u64 fraction[2]; 1773 u64 denominator = 0; /* gcc */ 1774 struct zone *zone = lruvec_zone(lruvec); 1775 unsigned long anon_prio, file_prio; 1776 enum scan_balance scan_balance; 1777 unsigned long anon, file, free; 1778 bool force_scan = false; 1779 unsigned long ap, fp; 1780 enum lru_list lru; 1781 1782 /* 1783 * If the zone or memcg is small, nr[l] can be 0. This 1784 * results in no scanning on this priority and a potential 1785 * priority drop. Global direct reclaim can go to the next 1786 * zone and tends to have no problems. Global kswapd is for 1787 * zone balancing and it needs to scan a minimum amount. When 1788 * reclaiming for a memcg, a priority drop can cause high 1789 * latencies, so it's better to scan a minimum amount there as 1790 * well. 1791 */ 1792 if (current_is_kswapd() && zone->all_unreclaimable) 1793 force_scan = true; 1794 if (!global_reclaim(sc)) 1795 force_scan = true; 1796 1797 /* If we have no swap space, do not bother scanning anon pages. */ 1798 if (!sc->may_swap || (get_nr_swap_pages() <= 0)) { 1799 scan_balance = SCAN_FILE; 1800 goto out; 1801 } 1802 1803 /* 1804 * Global reclaim will swap to prevent OOM even with no 1805 * swappiness, but memcg users want to use this knob to 1806 * disable swapping for individual groups completely when 1807 * using the memory controller's swap limit feature would be 1808 * too expensive. 1809 */ 1810 if (!global_reclaim(sc) && !vmscan_swappiness(sc)) { 1811 scan_balance = SCAN_FILE; 1812 goto out; 1813 } 1814 1815 /* 1816 * Do not apply any pressure balancing cleverness when the 1817 * system is close to OOM, scan both anon and file equally 1818 * (unless the swappiness setting disagrees with swapping). 1819 */ 1820 if (!sc->priority && vmscan_swappiness(sc)) { 1821 scan_balance = SCAN_EQUAL; 1822 goto out; 1823 } 1824 1825 anon = get_lru_size(lruvec, LRU_ACTIVE_ANON) + 1826 get_lru_size(lruvec, LRU_INACTIVE_ANON); 1827 file = get_lru_size(lruvec, LRU_ACTIVE_FILE) + 1828 get_lru_size(lruvec, LRU_INACTIVE_FILE); 1829 1830 /* 1831 * If it's foreseeable that reclaiming the file cache won't be 1832 * enough to get the zone back into a desirable shape, we have 1833 * to swap. Better start now and leave the - probably heavily 1834 * thrashing - remaining file pages alone. 1835 */ 1836 if (global_reclaim(sc)) { 1837 free = zone_page_state(zone, NR_FREE_PAGES); 1838 if (unlikely(file + free <= high_wmark_pages(zone))) { 1839 scan_balance = SCAN_ANON; 1840 goto out; 1841 } 1842 } 1843 1844 /* 1845 * There is enough inactive page cache, do not reclaim 1846 * anything from the anonymous working set right now. 1847 */ 1848 if (!inactive_file_is_low(lruvec)) { 1849 scan_balance = SCAN_FILE; 1850 goto out; 1851 } 1852 1853 scan_balance = SCAN_FRACT; 1854 1855 /* 1856 * With swappiness at 100, anonymous and file have the same priority. 1857 * This scanning priority is essentially the inverse of IO cost. 1858 */ 1859 anon_prio = vmscan_swappiness(sc); 1860 file_prio = 200 - anon_prio; 1861 1862 /* 1863 * OK, so we have swap space and a fair amount of page cache 1864 * pages. We use the recently rotated / recently scanned 1865 * ratios to determine how valuable each cache is. 1866 * 1867 * Because workloads change over time (and to avoid overflow) 1868 * we keep these statistics as a floating average, which ends 1869 * up weighing recent references more than old ones. 1870 * 1871 * anon in [0], file in [1] 1872 */ 1873 spin_lock_irq(&zone->lru_lock); 1874 if (unlikely(reclaim_stat->recent_scanned[0] > anon / 4)) { 1875 reclaim_stat->recent_scanned[0] /= 2; 1876 reclaim_stat->recent_rotated[0] /= 2; 1877 } 1878 1879 if (unlikely(reclaim_stat->recent_scanned[1] > file / 4)) { 1880 reclaim_stat->recent_scanned[1] /= 2; 1881 reclaim_stat->recent_rotated[1] /= 2; 1882 } 1883 1884 /* 1885 * The amount of pressure on anon vs file pages is inversely 1886 * proportional to the fraction of recently scanned pages on 1887 * each list that were recently referenced and in active use. 1888 */ 1889 ap = anon_prio * (reclaim_stat->recent_scanned[0] + 1); 1890 ap /= reclaim_stat->recent_rotated[0] + 1; 1891 1892 fp = file_prio * (reclaim_stat->recent_scanned[1] + 1); 1893 fp /= reclaim_stat->recent_rotated[1] + 1; 1894 spin_unlock_irq(&zone->lru_lock); 1895 1896 fraction[0] = ap; 1897 fraction[1] = fp; 1898 denominator = ap + fp + 1; 1899 out: 1900 for_each_evictable_lru(lru) { 1901 int file = is_file_lru(lru); 1902 unsigned long size; 1903 unsigned long scan; 1904 1905 size = get_lru_size(lruvec, lru); 1906 scan = size >> sc->priority; 1907 1908 if (!scan && force_scan) 1909 scan = min(size, SWAP_CLUSTER_MAX); 1910 1911 switch (scan_balance) { 1912 case SCAN_EQUAL: 1913 /* Scan lists relative to size */ 1914 break; 1915 case SCAN_FRACT: 1916 /* 1917 * Scan types proportional to swappiness and 1918 * their relative recent reclaim efficiency. 1919 */ 1920 scan = div64_u64(scan * fraction[file], denominator); 1921 break; 1922 case SCAN_FILE: 1923 case SCAN_ANON: 1924 /* Scan one type exclusively */ 1925 if ((scan_balance == SCAN_FILE) != file) 1926 scan = 0; 1927 break; 1928 default: 1929 /* Look ma, no brain */ 1930 BUG(); 1931 } 1932 nr[lru] = scan; 1933 } 1934 } 1935 1936 /* 1937 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim. 1938 */ 1939 static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) 1940 { 1941 unsigned long nr[NR_LRU_LISTS]; 1942 unsigned long targets[NR_LRU_LISTS]; 1943 unsigned long nr_to_scan; 1944 enum lru_list lru; 1945 unsigned long nr_reclaimed = 0; 1946 unsigned long nr_to_reclaim = sc->nr_to_reclaim; 1947 struct blk_plug plug; 1948 bool scan_adjusted = false; 1949 1950 get_scan_count(lruvec, sc, nr); 1951 1952 /* Record the original scan target for proportional adjustments later */ 1953 memcpy(targets, nr, sizeof(nr)); 1954 1955 blk_start_plug(&plug); 1956 while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || 1957 nr[LRU_INACTIVE_FILE]) { 1958 unsigned long nr_anon, nr_file, percentage; 1959 unsigned long nr_scanned; 1960 1961 for_each_evictable_lru(lru) { 1962 if (nr[lru]) { 1963 nr_to_scan = min(nr[lru], SWAP_CLUSTER_MAX); 1964 nr[lru] -= nr_to_scan; 1965 1966 nr_reclaimed += shrink_list(lru, nr_to_scan, 1967 lruvec, sc); 1968 } 1969 } 1970 1971 if (nr_reclaimed < nr_to_reclaim || scan_adjusted) 1972 continue; 1973 1974 /* 1975 * For global direct reclaim, reclaim only the number of pages 1976 * requested. Less care is taken to scan proportionally as it 1977 * is more important to minimise direct reclaim stall latency 1978 * than it is to properly age the LRU lists. 1979 */ 1980 if (global_reclaim(sc) && !current_is_kswapd()) 1981 break; 1982 1983 /* 1984 * For kswapd and memcg, reclaim at least the number of pages 1985 * requested. Ensure that the anon and file LRUs shrink 1986 * proportionally what was requested by get_scan_count(). We 1987 * stop reclaiming one LRU and reduce the amount scanning 1988 * proportional to the original scan target. 1989 */ 1990 nr_file = nr[LRU_INACTIVE_FILE] + nr[LRU_ACTIVE_FILE]; 1991 nr_anon = nr[LRU_INACTIVE_ANON] + nr[LRU_ACTIVE_ANON]; 1992 1993 if (nr_file > nr_anon) { 1994 unsigned long scan_target = targets[LRU_INACTIVE_ANON] + 1995 targets[LRU_ACTIVE_ANON] + 1; 1996 lru = LRU_BASE; 1997 percentage = nr_anon * 100 / scan_target; 1998 } else { 1999 unsigned long scan_target = targets[LRU_INACTIVE_FILE] + 2000 targets[LRU_ACTIVE_FILE] + 1; 2001 lru = LRU_FILE; 2002 percentage = nr_file * 100 / scan_target; 2003 } 2004 2005 /* Stop scanning the smaller of the LRU */ 2006 nr[lru] = 0; 2007 nr[lru + LRU_ACTIVE] = 0; 2008 2009 /* 2010 * Recalculate the other LRU scan count based on its original 2011 * scan target and the percentage scanning already complete 2012 */ 2013 lru = (lru == LRU_FILE) ? LRU_BASE : LRU_FILE; 2014 nr_scanned = targets[lru] - nr[lru]; 2015 nr[lru] = targets[lru] * (100 - percentage) / 100; 2016 nr[lru] -= min(nr[lru], nr_scanned); 2017 2018 lru += LRU_ACTIVE; 2019 nr_scanned = targets[lru] - nr[lru]; 2020 nr[lru] = targets[lru] * (100 - percentage) / 100; 2021 nr[lru] -= min(nr[lru], nr_scanned); 2022 2023 scan_adjusted = true; 2024 } 2025 blk_finish_plug(&plug); 2026 sc->nr_reclaimed += nr_reclaimed; 2027 2028 /* 2029 * Even if we did not try to evict anon pages at all, we want to 2030 * rebalance the anon lru active/inactive ratio. 2031 */ 2032 if (inactive_anon_is_low(lruvec)) 2033 shrink_active_list(SWAP_CLUSTER_MAX, lruvec, 2034 sc, LRU_ACTIVE_ANON); 2035 2036 throttle_vm_writeout(sc->gfp_mask); 2037 } 2038 2039 /* Use reclaim/compaction for costly allocs or under memory pressure */ 2040 static bool in_reclaim_compaction(struct scan_control *sc) 2041 { 2042 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order && 2043 (sc->order > PAGE_ALLOC_COSTLY_ORDER || 2044 sc->priority < DEF_PRIORITY - 2)) 2045 return true; 2046 2047 return false; 2048 } 2049 2050 /* 2051 * Reclaim/compaction is used for high-order allocation requests. It reclaims 2052 * order-0 pages before compacting the zone. should_continue_reclaim() returns 2053 * true if more pages should be reclaimed such that when the page allocator 2054 * calls try_to_compact_zone() that it will have enough free pages to succeed. 2055 * It will give up earlier than that if there is difficulty reclaiming pages. 2056 */ 2057 static inline bool should_continue_reclaim(struct zone *zone, 2058 unsigned long nr_reclaimed, 2059 unsigned long nr_scanned, 2060 struct scan_control *sc) 2061 { 2062 unsigned long pages_for_compaction; 2063 unsigned long inactive_lru_pages; 2064 2065 /* If not in reclaim/compaction mode, stop */ 2066 if (!in_reclaim_compaction(sc)) 2067 return false; 2068 2069 /* Consider stopping depending on scan and reclaim activity */ 2070 if (sc->gfp_mask & __GFP_REPEAT) { 2071 /* 2072 * For __GFP_REPEAT allocations, stop reclaiming if the 2073 * full LRU list has been scanned and we are still failing 2074 * to reclaim pages. This full LRU scan is potentially 2075 * expensive but a __GFP_REPEAT caller really wants to succeed 2076 */ 2077 if (!nr_reclaimed && !nr_scanned) 2078 return false; 2079 } else { 2080 /* 2081 * For non-__GFP_REPEAT allocations which can presumably 2082 * fail without consequence, stop if we failed to reclaim 2083 * any pages from the last SWAP_CLUSTER_MAX number of 2084 * pages that were scanned. This will return to the 2085 * caller faster at the risk reclaim/compaction and 2086 * the resulting allocation attempt fails 2087 */ 2088 if (!nr_reclaimed) 2089 return false; 2090 } 2091 2092 /* 2093 * If we have not reclaimed enough pages for compaction and the 2094 * inactive lists are large enough, continue reclaiming 2095 */ 2096 pages_for_compaction = (2UL << sc->order); 2097 inactive_lru_pages = zone_page_state(zone, NR_INACTIVE_FILE); 2098 if (get_nr_swap_pages() > 0) 2099 inactive_lru_pages += zone_page_state(zone, NR_INACTIVE_ANON); 2100 if (sc->nr_reclaimed < pages_for_compaction && 2101 inactive_lru_pages > pages_for_compaction) 2102 return true; 2103 2104 /* If compaction would go ahead or the allocation would succeed, stop */ 2105 switch (compaction_suitable(zone, sc->order)) { 2106 case COMPACT_PARTIAL: 2107 case COMPACT_CONTINUE: 2108 return false; 2109 default: 2110 return true; 2111 } 2112 } 2113 2114 static void shrink_zone(struct zone *zone, struct scan_control *sc) 2115 { 2116 unsigned long nr_reclaimed, nr_scanned; 2117 2118 do { 2119 struct mem_cgroup *root = sc->target_mem_cgroup; 2120 struct mem_cgroup_reclaim_cookie reclaim = { 2121 .zone = zone, 2122 .priority = sc->priority, 2123 }; 2124 struct mem_cgroup *memcg; 2125 2126 nr_reclaimed = sc->nr_reclaimed; 2127 nr_scanned = sc->nr_scanned; 2128 2129 memcg = mem_cgroup_iter(root, NULL, &reclaim); 2130 do { 2131 struct lruvec *lruvec; 2132 2133 lruvec = mem_cgroup_zone_lruvec(zone, memcg); 2134 2135 shrink_lruvec(lruvec, sc); 2136 2137 /* 2138 * Direct reclaim and kswapd have to scan all memory 2139 * cgroups to fulfill the overall scan target for the 2140 * zone. 2141 * 2142 * Limit reclaim, on the other hand, only cares about 2143 * nr_to_reclaim pages to be reclaimed and it will 2144 * retry with decreasing priority if one round over the 2145 * whole hierarchy is not sufficient. 2146 */ 2147 if (!global_reclaim(sc) && 2148 sc->nr_reclaimed >= sc->nr_to_reclaim) { 2149 mem_cgroup_iter_break(root, memcg); 2150 break; 2151 } 2152 memcg = mem_cgroup_iter(root, memcg, &reclaim); 2153 } while (memcg); 2154 2155 vmpressure(sc->gfp_mask, sc->target_mem_cgroup, 2156 sc->nr_scanned - nr_scanned, 2157 sc->nr_reclaimed - nr_reclaimed); 2158 2159 } while (should_continue_reclaim(zone, sc->nr_reclaimed - nr_reclaimed, 2160 sc->nr_scanned - nr_scanned, sc)); 2161 } 2162 2163 /* Returns true if compaction should go ahead for a high-order request */ 2164 static inline bool compaction_ready(struct zone *zone, struct scan_control *sc) 2165 { 2166 unsigned long balance_gap, watermark; 2167 bool watermark_ok; 2168 2169 /* Do not consider compaction for orders reclaim is meant to satisfy */ 2170 if (sc->order <= PAGE_ALLOC_COSTLY_ORDER) 2171 return false; 2172 2173 /* 2174 * Compaction takes time to run and there are potentially other 2175 * callers using the pages just freed. Continue reclaiming until 2176 * there is a buffer of free pages available to give compaction 2177 * a reasonable chance of completing and allocating the page 2178 */ 2179 balance_gap = min(low_wmark_pages(zone), 2180 (zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) / 2181 KSWAPD_ZONE_BALANCE_GAP_RATIO); 2182 watermark = high_wmark_pages(zone) + balance_gap + (2UL << sc->order); 2183 watermark_ok = zone_watermark_ok_safe(zone, 0, watermark, 0, 0); 2184 2185 /* 2186 * If compaction is deferred, reclaim up to a point where 2187 * compaction will have a chance of success when re-enabled 2188 */ 2189 if (compaction_deferred(zone, sc->order)) 2190 return watermark_ok; 2191 2192 /* If compaction is not ready to start, keep reclaiming */ 2193 if (!compaction_suitable(zone, sc->order)) 2194 return false; 2195 2196 return watermark_ok; 2197 } 2198 2199 /* 2200 * This is the direct reclaim path, for page-allocating processes. We only 2201 * try to reclaim pages from zones which will satisfy the caller's allocation 2202 * request. 2203 * 2204 * We reclaim from a zone even if that zone is over high_wmark_pages(zone). 2205 * Because: 2206 * a) The caller may be trying to free *extra* pages to satisfy a higher-order 2207 * allocation or 2208 * b) The target zone may be at high_wmark_pages(zone) but the lower zones 2209 * must go *over* high_wmark_pages(zone) to satisfy the `incremental min' 2210 * zone defense algorithm. 2211 * 2212 * If a zone is deemed to be full of pinned pages then just give it a light 2213 * scan then give up on it. 2214 * 2215 * This function returns true if a zone is being reclaimed for a costly 2216 * high-order allocation and compaction is ready to begin. This indicates to 2217 * the caller that it should consider retrying the allocation instead of 2218 * further reclaim. 2219 */ 2220 static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc) 2221 { 2222 struct zoneref *z; 2223 struct zone *zone; 2224 unsigned long nr_soft_reclaimed; 2225 unsigned long nr_soft_scanned; 2226 bool aborted_reclaim = false; 2227 2228 /* 2229 * If the number of buffer_heads in the machine exceeds the maximum 2230 * allowed level, force direct reclaim to scan the highmem zone as 2231 * highmem pages could be pinning lowmem pages storing buffer_heads 2232 */ 2233 if (buffer_heads_over_limit) 2234 sc->gfp_mask |= __GFP_HIGHMEM; 2235 2236 for_each_zone_zonelist_nodemask(zone, z, zonelist, 2237 gfp_zone(sc->gfp_mask), sc->nodemask) { 2238 if (!populated_zone(zone)) 2239 continue; 2240 /* 2241 * Take care memory controller reclaiming has small influence 2242 * to global LRU. 2243 */ 2244 if (global_reclaim(sc)) { 2245 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2246 continue; 2247 if (zone->all_unreclaimable && 2248 sc->priority != DEF_PRIORITY) 2249 continue; /* Let kswapd poll it */ 2250 if (IS_ENABLED(CONFIG_COMPACTION)) { 2251 /* 2252 * If we already have plenty of memory free for 2253 * compaction in this zone, don't free any more. 2254 * Even though compaction is invoked for any 2255 * non-zero order, only frequent costly order 2256 * reclamation is disruptive enough to become a 2257 * noticeable problem, like transparent huge 2258 * page allocations. 2259 */ 2260 if (compaction_ready(zone, sc)) { 2261 aborted_reclaim = true; 2262 continue; 2263 } 2264 } 2265 /* 2266 * This steals pages from memory cgroups over softlimit 2267 * and returns the number of reclaimed pages and 2268 * scanned pages. This works for global memory pressure 2269 * and balancing, not for a memcg's limit. 2270 */ 2271 nr_soft_scanned = 0; 2272 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone, 2273 sc->order, sc->gfp_mask, 2274 &nr_soft_scanned); 2275 sc->nr_reclaimed += nr_soft_reclaimed; 2276 sc->nr_scanned += nr_soft_scanned; 2277 /* need some check for avoid more shrink_zone() */ 2278 } 2279 2280 shrink_zone(zone, sc); 2281 } 2282 2283 return aborted_reclaim; 2284 } 2285 2286 static bool zone_reclaimable(struct zone *zone) 2287 { 2288 return zone->pages_scanned < zone_reclaimable_pages(zone) * 6; 2289 } 2290 2291 /* All zones in zonelist are unreclaimable? */ 2292 static bool all_unreclaimable(struct zonelist *zonelist, 2293 struct scan_control *sc) 2294 { 2295 struct zoneref *z; 2296 struct zone *zone; 2297 2298 for_each_zone_zonelist_nodemask(zone, z, zonelist, 2299 gfp_zone(sc->gfp_mask), sc->nodemask) { 2300 if (!populated_zone(zone)) 2301 continue; 2302 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2303 continue; 2304 if (!zone->all_unreclaimable) 2305 return false; 2306 } 2307 2308 return true; 2309 } 2310 2311 /* 2312 * This is the main entry point to direct page reclaim. 2313 * 2314 * If a full scan of the inactive list fails to free enough memory then we 2315 * are "out of memory" and something needs to be killed. 2316 * 2317 * If the caller is !__GFP_FS then the probability of a failure is reasonably 2318 * high - the zone may be full of dirty or under-writeback pages, which this 2319 * caller can't do much about. We kick the writeback threads and take explicit 2320 * naps in the hope that some of these pages can be written. But if the 2321 * allocating task holds filesystem locks which prevent writeout this might not 2322 * work, and the allocation attempt will fail. 2323 * 2324 * returns: 0, if no pages reclaimed 2325 * else, the number of pages reclaimed 2326 */ 2327 static unsigned long do_try_to_free_pages(struct zonelist *zonelist, 2328 struct scan_control *sc, 2329 struct shrink_control *shrink) 2330 { 2331 unsigned long total_scanned = 0; 2332 struct reclaim_state *reclaim_state = current->reclaim_state; 2333 struct zoneref *z; 2334 struct zone *zone; 2335 unsigned long writeback_threshold; 2336 bool aborted_reclaim; 2337 2338 delayacct_freepages_start(); 2339 2340 if (global_reclaim(sc)) 2341 count_vm_event(ALLOCSTALL); 2342 2343 do { 2344 vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup, 2345 sc->priority); 2346 sc->nr_scanned = 0; 2347 aborted_reclaim = shrink_zones(zonelist, sc); 2348 2349 /* 2350 * Don't shrink slabs when reclaiming memory from over limit 2351 * cgroups but do shrink slab at least once when aborting 2352 * reclaim for compaction to avoid unevenly scanning file/anon 2353 * LRU pages over slab pages. 2354 */ 2355 if (global_reclaim(sc)) { 2356 unsigned long lru_pages = 0; 2357 for_each_zone_zonelist(zone, z, zonelist, 2358 gfp_zone(sc->gfp_mask)) { 2359 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 2360 continue; 2361 2362 lru_pages += zone_reclaimable_pages(zone); 2363 } 2364 2365 shrink_slab(shrink, sc->nr_scanned, lru_pages); 2366 if (reclaim_state) { 2367 sc->nr_reclaimed += reclaim_state->reclaimed_slab; 2368 reclaim_state->reclaimed_slab = 0; 2369 } 2370 } 2371 total_scanned += sc->nr_scanned; 2372 if (sc->nr_reclaimed >= sc->nr_to_reclaim) 2373 goto out; 2374 2375 /* 2376 * If we're getting trouble reclaiming, start doing 2377 * writepage even in laptop mode. 2378 */ 2379 if (sc->priority < DEF_PRIORITY - 2) 2380 sc->may_writepage = 1; 2381 2382 /* 2383 * Try to write back as many pages as we just scanned. This 2384 * tends to cause slow streaming writers to write data to the 2385 * disk smoothly, at the dirtying rate, which is nice. But 2386 * that's undesirable in laptop mode, where we *want* lumpy 2387 * writeout. So in laptop mode, write out the whole world. 2388 */ 2389 writeback_threshold = sc->nr_to_reclaim + sc->nr_to_reclaim / 2; 2390 if (total_scanned > writeback_threshold) { 2391 wakeup_flusher_threads(laptop_mode ? 0 : total_scanned, 2392 WB_REASON_TRY_TO_FREE_PAGES); 2393 sc->may_writepage = 1; 2394 } 2395 } while (--sc->priority >= 0 && !aborted_reclaim); 2396 2397 out: 2398 delayacct_freepages_end(); 2399 2400 if (sc->nr_reclaimed) 2401 return sc->nr_reclaimed; 2402 2403 /* 2404 * As hibernation is going on, kswapd is freezed so that it can't mark 2405 * the zone into all_unreclaimable. Thus bypassing all_unreclaimable 2406 * check. 2407 */ 2408 if (oom_killer_disabled) 2409 return 0; 2410 2411 /* Aborted reclaim to try compaction? don't OOM, then */ 2412 if (aborted_reclaim) 2413 return 1; 2414 2415 /* top priority shrink_zones still had more to do? don't OOM, then */ 2416 if (global_reclaim(sc) && !all_unreclaimable(zonelist, sc)) 2417 return 1; 2418 2419 return 0; 2420 } 2421 2422 static bool pfmemalloc_watermark_ok(pg_data_t *pgdat) 2423 { 2424 struct zone *zone; 2425 unsigned long pfmemalloc_reserve = 0; 2426 unsigned long free_pages = 0; 2427 int i; 2428 bool wmark_ok; 2429 2430 for (i = 0; i <= ZONE_NORMAL; i++) { 2431 zone = &pgdat->node_zones[i]; 2432 pfmemalloc_reserve += min_wmark_pages(zone); 2433 free_pages += zone_page_state(zone, NR_FREE_PAGES); 2434 } 2435 2436 wmark_ok = free_pages > pfmemalloc_reserve / 2; 2437 2438 /* kswapd must be awake if processes are being throttled */ 2439 if (!wmark_ok && waitqueue_active(&pgdat->kswapd_wait)) { 2440 pgdat->classzone_idx = min(pgdat->classzone_idx, 2441 (enum zone_type)ZONE_NORMAL); 2442 wake_up_interruptible(&pgdat->kswapd_wait); 2443 } 2444 2445 return wmark_ok; 2446 } 2447 2448 /* 2449 * Throttle direct reclaimers if backing storage is backed by the network 2450 * and the PFMEMALLOC reserve for the preferred node is getting dangerously 2451 * depleted. kswapd will continue to make progress and wake the processes 2452 * when the low watermark is reached. 2453 * 2454 * Returns true if a fatal signal was delivered during throttling. If this 2455 * happens, the page allocator should not consider triggering the OOM killer. 2456 */ 2457 static bool throttle_direct_reclaim(gfp_t gfp_mask, struct zonelist *zonelist, 2458 nodemask_t *nodemask) 2459 { 2460 struct zone *zone; 2461 int high_zoneidx = gfp_zone(gfp_mask); 2462 pg_data_t *pgdat; 2463 2464 /* 2465 * Kernel threads should not be throttled as they may be indirectly 2466 * responsible for cleaning pages necessary for reclaim to make forward 2467 * progress. kjournald for example may enter direct reclaim while 2468 * committing a transaction where throttling it could forcing other 2469 * processes to block on log_wait_commit(). 2470 */ 2471 if (current->flags & PF_KTHREAD) 2472 goto out; 2473 2474 /* 2475 * If a fatal signal is pending, this process should not throttle. 2476 * It should return quickly so it can exit and free its memory 2477 */ 2478 if (fatal_signal_pending(current)) 2479 goto out; 2480 2481 /* Check if the pfmemalloc reserves are ok */ 2482 first_zones_zonelist(zonelist, high_zoneidx, NULL, &zone); 2483 pgdat = zone->zone_pgdat; 2484 if (pfmemalloc_watermark_ok(pgdat)) 2485 goto out; 2486 2487 /* Account for the throttling */ 2488 count_vm_event(PGSCAN_DIRECT_THROTTLE); 2489 2490 /* 2491 * If the caller cannot enter the filesystem, it's possible that it 2492 * is due to the caller holding an FS lock or performing a journal 2493 * transaction in the case of a filesystem like ext[3|4]. In this case, 2494 * it is not safe to block on pfmemalloc_wait as kswapd could be 2495 * blocked waiting on the same lock. Instead, throttle for up to a 2496 * second before continuing. 2497 */ 2498 if (!(gfp_mask & __GFP_FS)) { 2499 wait_event_interruptible_timeout(pgdat->pfmemalloc_wait, 2500 pfmemalloc_watermark_ok(pgdat), HZ); 2501 2502 goto check_pending; 2503 } 2504 2505 /* Throttle until kswapd wakes the process */ 2506 wait_event_killable(zone->zone_pgdat->pfmemalloc_wait, 2507 pfmemalloc_watermark_ok(pgdat)); 2508 2509 check_pending: 2510 if (fatal_signal_pending(current)) 2511 return true; 2512 2513 out: 2514 return false; 2515 } 2516 2517 unsigned long try_to_free_pages(struct zonelist *zonelist, int order, 2518 gfp_t gfp_mask, nodemask_t *nodemask) 2519 { 2520 unsigned long nr_reclaimed; 2521 struct scan_control sc = { 2522 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)), 2523 .may_writepage = !laptop_mode, 2524 .nr_to_reclaim = SWAP_CLUSTER_MAX, 2525 .may_unmap = 1, 2526 .may_swap = 1, 2527 .order = order, 2528 .priority = DEF_PRIORITY, 2529 .target_mem_cgroup = NULL, 2530 .nodemask = nodemask, 2531 }; 2532 struct shrink_control shrink = { 2533 .gfp_mask = sc.gfp_mask, 2534 }; 2535 2536 /* 2537 * Do not enter reclaim if fatal signal was delivered while throttled. 2538 * 1 is returned so that the page allocator does not OOM kill at this 2539 * point. 2540 */ 2541 if (throttle_direct_reclaim(gfp_mask, zonelist, nodemask)) 2542 return 1; 2543 2544 trace_mm_vmscan_direct_reclaim_begin(order, 2545 sc.may_writepage, 2546 gfp_mask); 2547 2548 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); 2549 2550 trace_mm_vmscan_direct_reclaim_end(nr_reclaimed); 2551 2552 return nr_reclaimed; 2553 } 2554 2555 #ifdef CONFIG_MEMCG 2556 2557 unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg, 2558 gfp_t gfp_mask, bool noswap, 2559 struct zone *zone, 2560 unsigned long *nr_scanned) 2561 { 2562 struct scan_control sc = { 2563 .nr_scanned = 0, 2564 .nr_to_reclaim = SWAP_CLUSTER_MAX, 2565 .may_writepage = !laptop_mode, 2566 .may_unmap = 1, 2567 .may_swap = !noswap, 2568 .order = 0, 2569 .priority = 0, 2570 .target_mem_cgroup = memcg, 2571 }; 2572 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg); 2573 2574 sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | 2575 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK); 2576 2577 trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order, 2578 sc.may_writepage, 2579 sc.gfp_mask); 2580 2581 /* 2582 * NOTE: Although we can get the priority field, using it 2583 * here is not a good idea, since it limits the pages we can scan. 2584 * if we don't reclaim here, the shrink_zone from balance_pgdat 2585 * will pick up pages from other mem cgroup's as well. We hack 2586 * the priority and make it zero. 2587 */ 2588 shrink_lruvec(lruvec, &sc); 2589 2590 trace_mm_vmscan_memcg_softlimit_reclaim_end(sc.nr_reclaimed); 2591 2592 *nr_scanned = sc.nr_scanned; 2593 return sc.nr_reclaimed; 2594 } 2595 2596 unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg, 2597 gfp_t gfp_mask, 2598 bool noswap) 2599 { 2600 struct zonelist *zonelist; 2601 unsigned long nr_reclaimed; 2602 int nid; 2603 struct scan_control sc = { 2604 .may_writepage = !laptop_mode, 2605 .may_unmap = 1, 2606 .may_swap = !noswap, 2607 .nr_to_reclaim = SWAP_CLUSTER_MAX, 2608 .order = 0, 2609 .priority = DEF_PRIORITY, 2610 .target_mem_cgroup = memcg, 2611 .nodemask = NULL, /* we don't care the placement */ 2612 .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) | 2613 (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK), 2614 }; 2615 struct shrink_control shrink = { 2616 .gfp_mask = sc.gfp_mask, 2617 }; 2618 2619 /* 2620 * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't 2621 * take care of from where we get pages. So the node where we start the 2622 * scan does not need to be the current node. 2623 */ 2624 nid = mem_cgroup_select_victim_node(memcg); 2625 2626 zonelist = NODE_DATA(nid)->node_zonelists; 2627 2628 trace_mm_vmscan_memcg_reclaim_begin(0, 2629 sc.may_writepage, 2630 sc.gfp_mask); 2631 2632 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); 2633 2634 trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed); 2635 2636 return nr_reclaimed; 2637 } 2638 #endif 2639 2640 static void age_active_anon(struct zone *zone, struct scan_control *sc) 2641 { 2642 struct mem_cgroup *memcg; 2643 2644 if (!total_swap_pages) 2645 return; 2646 2647 memcg = mem_cgroup_iter(NULL, NULL, NULL); 2648 do { 2649 struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg); 2650 2651 if (inactive_anon_is_low(lruvec)) 2652 shrink_active_list(SWAP_CLUSTER_MAX, lruvec, 2653 sc, LRU_ACTIVE_ANON); 2654 2655 memcg = mem_cgroup_iter(NULL, memcg, NULL); 2656 } while (memcg); 2657 } 2658 2659 static bool zone_balanced(struct zone *zone, int order, 2660 unsigned long balance_gap, int classzone_idx) 2661 { 2662 if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone) + 2663 balance_gap, classzone_idx, 0)) 2664 return false; 2665 2666 if (IS_ENABLED(CONFIG_COMPACTION) && order && 2667 !compaction_suitable(zone, order)) 2668 return false; 2669 2670 return true; 2671 } 2672 2673 /* 2674 * pgdat_balanced() is used when checking if a node is balanced. 2675 * 2676 * For order-0, all zones must be balanced! 2677 * 2678 * For high-order allocations only zones that meet watermarks and are in a 2679 * zone allowed by the callers classzone_idx are added to balanced_pages. The 2680 * total of balanced pages must be at least 25% of the zones allowed by 2681 * classzone_idx for the node to be considered balanced. Forcing all zones to 2682 * be balanced for high orders can cause excessive reclaim when there are 2683 * imbalanced zones. 2684 * The choice of 25% is due to 2685 * o a 16M DMA zone that is balanced will not balance a zone on any 2686 * reasonable sized machine 2687 * o On all other machines, the top zone must be at least a reasonable 2688 * percentage of the middle zones. For example, on 32-bit x86, highmem 2689 * would need to be at least 256M for it to be balance a whole node. 2690 * Similarly, on x86-64 the Normal zone would need to be at least 1G 2691 * to balance a node on its own. These seemed like reasonable ratios. 2692 */ 2693 static bool pgdat_balanced(pg_data_t *pgdat, int order, int classzone_idx) 2694 { 2695 unsigned long managed_pages = 0; 2696 unsigned long balanced_pages = 0; 2697 int i; 2698 2699 /* Check the watermark levels */ 2700 for (i = 0; i <= classzone_idx; i++) { 2701 struct zone *zone = pgdat->node_zones + i; 2702 2703 if (!populated_zone(zone)) 2704 continue; 2705 2706 managed_pages += zone->managed_pages; 2707 2708 /* 2709 * A special case here: 2710 * 2711 * balance_pgdat() skips over all_unreclaimable after 2712 * DEF_PRIORITY. Effectively, it considers them balanced so 2713 * they must be considered balanced here as well! 2714 */ 2715 if (zone->all_unreclaimable) { 2716 balanced_pages += zone->managed_pages; 2717 continue; 2718 } 2719 2720 if (zone_balanced(zone, order, 0, i)) 2721 balanced_pages += zone->managed_pages; 2722 else if (!order) 2723 return false; 2724 } 2725 2726 if (order) 2727 return balanced_pages >= (managed_pages >> 2); 2728 else 2729 return true; 2730 } 2731 2732 /* 2733 * Prepare kswapd for sleeping. This verifies that there are no processes 2734 * waiting in throttle_direct_reclaim() and that watermarks have been met. 2735 * 2736 * Returns true if kswapd is ready to sleep 2737 */ 2738 static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, long remaining, 2739 int classzone_idx) 2740 { 2741 /* If a direct reclaimer woke kswapd within HZ/10, it's premature */ 2742 if (remaining) 2743 return false; 2744 2745 /* 2746 * There is a potential race between when kswapd checks its watermarks 2747 * and a process gets throttled. There is also a potential race if 2748 * processes get throttled, kswapd wakes, a large process exits therby 2749 * balancing the zones that causes kswapd to miss a wakeup. If kswapd 2750 * is going to sleep, no process should be sleeping on pfmemalloc_wait 2751 * so wake them now if necessary. If necessary, processes will wake 2752 * kswapd and get throttled again 2753 */ 2754 if (waitqueue_active(&pgdat->pfmemalloc_wait)) { 2755 wake_up(&pgdat->pfmemalloc_wait); 2756 return false; 2757 } 2758 2759 return pgdat_balanced(pgdat, order, classzone_idx); 2760 } 2761 2762 /* 2763 * kswapd shrinks the zone by the number of pages required to reach 2764 * the high watermark. 2765 * 2766 * Returns true if kswapd scanned at least the requested number of pages to 2767 * reclaim or if the lack of progress was due to pages under writeback. 2768 * This is used to determine if the scanning priority needs to be raised. 2769 */ 2770 static bool kswapd_shrink_zone(struct zone *zone, 2771 int classzone_idx, 2772 struct scan_control *sc, 2773 unsigned long lru_pages, 2774 unsigned long *nr_attempted) 2775 { 2776 unsigned long nr_slab; 2777 int testorder = sc->order; 2778 unsigned long balance_gap; 2779 struct reclaim_state *reclaim_state = current->reclaim_state; 2780 struct shrink_control shrink = { 2781 .gfp_mask = sc->gfp_mask, 2782 }; 2783 bool lowmem_pressure; 2784 2785 /* Reclaim above the high watermark. */ 2786 sc->nr_to_reclaim = max(SWAP_CLUSTER_MAX, high_wmark_pages(zone)); 2787 2788 /* 2789 * Kswapd reclaims only single pages with compaction enabled. Trying 2790 * too hard to reclaim until contiguous free pages have become 2791 * available can hurt performance by evicting too much useful data 2792 * from memory. Do not reclaim more than needed for compaction. 2793 */ 2794 if (IS_ENABLED(CONFIG_COMPACTION) && sc->order && 2795 compaction_suitable(zone, sc->order) != 2796 COMPACT_SKIPPED) 2797 testorder = 0; 2798 2799 /* 2800 * We put equal pressure on every zone, unless one zone has way too 2801 * many pages free already. The "too many pages" is defined as the 2802 * high wmark plus a "gap" where the gap is either the low 2803 * watermark or 1% of the zone, whichever is smaller. 2804 */ 2805 balance_gap = min(low_wmark_pages(zone), 2806 (zone->managed_pages + KSWAPD_ZONE_BALANCE_GAP_RATIO-1) / 2807 KSWAPD_ZONE_BALANCE_GAP_RATIO); 2808 2809 /* 2810 * If there is no low memory pressure or the zone is balanced then no 2811 * reclaim is necessary 2812 */ 2813 lowmem_pressure = (buffer_heads_over_limit && is_highmem(zone)); 2814 if (!lowmem_pressure && zone_balanced(zone, testorder, 2815 balance_gap, classzone_idx)) 2816 return true; 2817 2818 shrink_zone(zone, sc); 2819 2820 reclaim_state->reclaimed_slab = 0; 2821 nr_slab = shrink_slab(&shrink, sc->nr_scanned, lru_pages); 2822 sc->nr_reclaimed += reclaim_state->reclaimed_slab; 2823 2824 /* Account for the number of pages attempted to reclaim */ 2825 *nr_attempted += sc->nr_to_reclaim; 2826 2827 if (nr_slab == 0 && !zone_reclaimable(zone)) 2828 zone->all_unreclaimable = 1; 2829 2830 zone_clear_flag(zone, ZONE_WRITEBACK); 2831 2832 /* 2833 * If a zone reaches its high watermark, consider it to be no longer 2834 * congested. It's possible there are dirty pages backed by congested 2835 * BDIs but as pressure is relieved, speculatively avoid congestion 2836 * waits. 2837 */ 2838 if (!zone->all_unreclaimable && 2839 zone_balanced(zone, testorder, 0, classzone_idx)) { 2840 zone_clear_flag(zone, ZONE_CONGESTED); 2841 zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY); 2842 } 2843 2844 return sc->nr_scanned >= sc->nr_to_reclaim; 2845 } 2846 2847 /* 2848 * For kswapd, balance_pgdat() will work across all this node's zones until 2849 * they are all at high_wmark_pages(zone). 2850 * 2851 * Returns the final order kswapd was reclaiming at 2852 * 2853 * There is special handling here for zones which are full of pinned pages. 2854 * This can happen if the pages are all mlocked, or if they are all used by 2855 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb. 2856 * What we do is to detect the case where all pages in the zone have been 2857 * scanned twice and there has been zero successful reclaim. Mark the zone as 2858 * dead and from now on, only perform a short scan. Basically we're polling 2859 * the zone for when the problem goes away. 2860 * 2861 * kswapd scans the zones in the highmem->normal->dma direction. It skips 2862 * zones which have free_pages > high_wmark_pages(zone), but once a zone is 2863 * found to have free_pages <= high_wmark_pages(zone), we scan that zone and the 2864 * lower zones regardless of the number of free pages in the lower zones. This 2865 * interoperates with the page allocator fallback scheme to ensure that aging 2866 * of pages is balanced across the zones. 2867 */ 2868 static unsigned long balance_pgdat(pg_data_t *pgdat, int order, 2869 int *classzone_idx) 2870 { 2871 int i; 2872 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ 2873 unsigned long nr_soft_reclaimed; 2874 unsigned long nr_soft_scanned; 2875 struct scan_control sc = { 2876 .gfp_mask = GFP_KERNEL, 2877 .priority = DEF_PRIORITY, 2878 .may_unmap = 1, 2879 .may_swap = 1, 2880 .may_writepage = !laptop_mode, 2881 .order = order, 2882 .target_mem_cgroup = NULL, 2883 }; 2884 count_vm_event(PAGEOUTRUN); 2885 2886 do { 2887 unsigned long lru_pages = 0; 2888 unsigned long nr_attempted = 0; 2889 bool raise_priority = true; 2890 bool pgdat_needs_compaction = (order > 0); 2891 2892 sc.nr_reclaimed = 0; 2893 2894 /* 2895 * Scan in the highmem->dma direction for the highest 2896 * zone which needs scanning 2897 */ 2898 for (i = pgdat->nr_zones - 1; i >= 0; i--) { 2899 struct zone *zone = pgdat->node_zones + i; 2900 2901 if (!populated_zone(zone)) 2902 continue; 2903 2904 if (zone->all_unreclaimable && 2905 sc.priority != DEF_PRIORITY) 2906 continue; 2907 2908 /* 2909 * Do some background aging of the anon list, to give 2910 * pages a chance to be referenced before reclaiming. 2911 */ 2912 age_active_anon(zone, &sc); 2913 2914 /* 2915 * If the number of buffer_heads in the machine 2916 * exceeds the maximum allowed level and this node 2917 * has a highmem zone, force kswapd to reclaim from 2918 * it to relieve lowmem pressure. 2919 */ 2920 if (buffer_heads_over_limit && is_highmem_idx(i)) { 2921 end_zone = i; 2922 break; 2923 } 2924 2925 if (!zone_balanced(zone, order, 0, 0)) { 2926 end_zone = i; 2927 break; 2928 } else { 2929 /* 2930 * If balanced, clear the dirty and congested 2931 * flags 2932 */ 2933 zone_clear_flag(zone, ZONE_CONGESTED); 2934 zone_clear_flag(zone, ZONE_TAIL_LRU_DIRTY); 2935 } 2936 } 2937 2938 if (i < 0) 2939 goto out; 2940 2941 for (i = 0; i <= end_zone; i++) { 2942 struct zone *zone = pgdat->node_zones + i; 2943 2944 if (!populated_zone(zone)) 2945 continue; 2946 2947 lru_pages += zone_reclaimable_pages(zone); 2948 2949 /* 2950 * If any zone is currently balanced then kswapd will 2951 * not call compaction as it is expected that the 2952 * necessary pages are already available. 2953 */ 2954 if (pgdat_needs_compaction && 2955 zone_watermark_ok(zone, order, 2956 low_wmark_pages(zone), 2957 *classzone_idx, 0)) 2958 pgdat_needs_compaction = false; 2959 } 2960 2961 /* 2962 * If we're getting trouble reclaiming, start doing writepage 2963 * even in laptop mode. 2964 */ 2965 if (sc.priority < DEF_PRIORITY - 2) 2966 sc.may_writepage = 1; 2967 2968 /* 2969 * Now scan the zone in the dma->highmem direction, stopping 2970 * at the last zone which needs scanning. 2971 * 2972 * We do this because the page allocator works in the opposite 2973 * direction. This prevents the page allocator from allocating 2974 * pages behind kswapd's direction of progress, which would 2975 * cause too much scanning of the lower zones. 2976 */ 2977 for (i = 0; i <= end_zone; i++) { 2978 struct zone *zone = pgdat->node_zones + i; 2979 2980 if (!populated_zone(zone)) 2981 continue; 2982 2983 if (zone->all_unreclaimable && 2984 sc.priority != DEF_PRIORITY) 2985 continue; 2986 2987 sc.nr_scanned = 0; 2988 2989 nr_soft_scanned = 0; 2990 /* 2991 * Call soft limit reclaim before calling shrink_zone. 2992 */ 2993 nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone, 2994 order, sc.gfp_mask, 2995 &nr_soft_scanned); 2996 sc.nr_reclaimed += nr_soft_reclaimed; 2997 2998 /* 2999 * There should be no need to raise the scanning 3000 * priority if enough pages are already being scanned 3001 * that that high watermark would be met at 100% 3002 * efficiency. 3003 */ 3004 if (kswapd_shrink_zone(zone, end_zone, &sc, 3005 lru_pages, &nr_attempted)) 3006 raise_priority = false; 3007 } 3008 3009 /* 3010 * If the low watermark is met there is no need for processes 3011 * to be throttled on pfmemalloc_wait as they should not be 3012 * able to safely make forward progress. Wake them 3013 */ 3014 if (waitqueue_active(&pgdat->pfmemalloc_wait) && 3015 pfmemalloc_watermark_ok(pgdat)) 3016 wake_up(&pgdat->pfmemalloc_wait); 3017 3018 /* 3019 * Fragmentation may mean that the system cannot be rebalanced 3020 * for high-order allocations in all zones. If twice the 3021 * allocation size has been reclaimed and the zones are still 3022 * not balanced then recheck the watermarks at order-0 to 3023 * prevent kswapd reclaiming excessively. Assume that a 3024 * process requested a high-order can direct reclaim/compact. 3025 */ 3026 if (order && sc.nr_reclaimed >= 2UL << order) 3027 order = sc.order = 0; 3028 3029 /* Check if kswapd should be suspending */ 3030 if (try_to_freeze() || kthread_should_stop()) 3031 break; 3032 3033 /* 3034 * Compact if necessary and kswapd is reclaiming at least the 3035 * high watermark number of pages as requsted 3036 */ 3037 if (pgdat_needs_compaction && sc.nr_reclaimed > nr_attempted) 3038 compact_pgdat(pgdat, order); 3039 3040 /* 3041 * Raise priority if scanning rate is too low or there was no 3042 * progress in reclaiming pages 3043 */ 3044 if (raise_priority || !sc.nr_reclaimed) 3045 sc.priority--; 3046 } while (sc.priority >= 1 && 3047 !pgdat_balanced(pgdat, order, *classzone_idx)); 3048 3049 out: 3050 /* 3051 * Return the order we were reclaiming at so prepare_kswapd_sleep() 3052 * makes a decision on the order we were last reclaiming at. However, 3053 * if another caller entered the allocator slow path while kswapd 3054 * was awake, order will remain at the higher level 3055 */ 3056 *classzone_idx = end_zone; 3057 return order; 3058 } 3059 3060 static void kswapd_try_to_sleep(pg_data_t *pgdat, int order, int classzone_idx) 3061 { 3062 long remaining = 0; 3063 DEFINE_WAIT(wait); 3064 3065 if (freezing(current) || kthread_should_stop()) 3066 return; 3067 3068 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); 3069 3070 /* Try to sleep for a short interval */ 3071 if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) { 3072 remaining = schedule_timeout(HZ/10); 3073 finish_wait(&pgdat->kswapd_wait, &wait); 3074 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); 3075 } 3076 3077 /* 3078 * After a short sleep, check if it was a premature sleep. If not, then 3079 * go fully to sleep until explicitly woken up. 3080 */ 3081 if (prepare_kswapd_sleep(pgdat, order, remaining, classzone_idx)) { 3082 trace_mm_vmscan_kswapd_sleep(pgdat->node_id); 3083 3084 /* 3085 * vmstat counters are not perfectly accurate and the estimated 3086 * value for counters such as NR_FREE_PAGES can deviate from the 3087 * true value by nr_online_cpus * threshold. To avoid the zone 3088 * watermarks being breached while under pressure, we reduce the 3089 * per-cpu vmstat threshold while kswapd is awake and restore 3090 * them before going back to sleep. 3091 */ 3092 set_pgdat_percpu_threshold(pgdat, calculate_normal_threshold); 3093 3094 /* 3095 * Compaction records what page blocks it recently failed to 3096 * isolate pages from and skips them in the future scanning. 3097 * When kswapd is going to sleep, it is reasonable to assume 3098 * that pages and compaction may succeed so reset the cache. 3099 */ 3100 reset_isolation_suitable(pgdat); 3101 3102 if (!kthread_should_stop()) 3103 schedule(); 3104 3105 set_pgdat_percpu_threshold(pgdat, calculate_pressure_threshold); 3106 } else { 3107 if (remaining) 3108 count_vm_event(KSWAPD_LOW_WMARK_HIT_QUICKLY); 3109 else 3110 count_vm_event(KSWAPD_HIGH_WMARK_HIT_QUICKLY); 3111 } 3112 finish_wait(&pgdat->kswapd_wait, &wait); 3113 } 3114 3115 /* 3116 * The background pageout daemon, started as a kernel thread 3117 * from the init process. 3118 * 3119 * This basically trickles out pages so that we have _some_ 3120 * free memory available even if there is no other activity 3121 * that frees anything up. This is needed for things like routing 3122 * etc, where we otherwise might have all activity going on in 3123 * asynchronous contexts that cannot page things out. 3124 * 3125 * If there are applications that are active memory-allocators 3126 * (most normal use), this basically shouldn't matter. 3127 */ 3128 static int kswapd(void *p) 3129 { 3130 unsigned long order, new_order; 3131 unsigned balanced_order; 3132 int classzone_idx, new_classzone_idx; 3133 int balanced_classzone_idx; 3134 pg_data_t *pgdat = (pg_data_t*)p; 3135 struct task_struct *tsk = current; 3136 3137 struct reclaim_state reclaim_state = { 3138 .reclaimed_slab = 0, 3139 }; 3140 const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id); 3141 3142 lockdep_set_current_reclaim_state(GFP_KERNEL); 3143 3144 if (!cpumask_empty(cpumask)) 3145 set_cpus_allowed_ptr(tsk, cpumask); 3146 current->reclaim_state = &reclaim_state; 3147 3148 /* 3149 * Tell the memory management that we're a "memory allocator", 3150 * and that if we need more memory we should get access to it 3151 * regardless (see "__alloc_pages()"). "kswapd" should 3152 * never get caught in the normal page freeing logic. 3153 * 3154 * (Kswapd normally doesn't need memory anyway, but sometimes 3155 * you need a small amount of memory in order to be able to 3156 * page out something else, and this flag essentially protects 3157 * us from recursively trying to free more memory as we're 3158 * trying to free the first piece of memory in the first place). 3159 */ 3160 tsk->flags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD; 3161 set_freezable(); 3162 3163 order = new_order = 0; 3164 balanced_order = 0; 3165 classzone_idx = new_classzone_idx = pgdat->nr_zones - 1; 3166 balanced_classzone_idx = classzone_idx; 3167 for ( ; ; ) { 3168 bool ret; 3169 3170 /* 3171 * If the last balance_pgdat was unsuccessful it's unlikely a 3172 * new request of a similar or harder type will succeed soon 3173 * so consider going to sleep on the basis we reclaimed at 3174 */ 3175 if (balanced_classzone_idx >= new_classzone_idx && 3176 balanced_order == new_order) { 3177 new_order = pgdat->kswapd_max_order; 3178 new_classzone_idx = pgdat->classzone_idx; 3179 pgdat->kswapd_max_order = 0; 3180 pgdat->classzone_idx = pgdat->nr_zones - 1; 3181 } 3182 3183 if (order < new_order || classzone_idx > new_classzone_idx) { 3184 /* 3185 * Don't sleep if someone wants a larger 'order' 3186 * allocation or has tigher zone constraints 3187 */ 3188 order = new_order; 3189 classzone_idx = new_classzone_idx; 3190 } else { 3191 kswapd_try_to_sleep(pgdat, balanced_order, 3192 balanced_classzone_idx); 3193 order = pgdat->kswapd_max_order; 3194 classzone_idx = pgdat->classzone_idx; 3195 new_order = order; 3196 new_classzone_idx = classzone_idx; 3197 pgdat->kswapd_max_order = 0; 3198 pgdat->classzone_idx = pgdat->nr_zones - 1; 3199 } 3200 3201 ret = try_to_freeze(); 3202 if (kthread_should_stop()) 3203 break; 3204 3205 /* 3206 * We can speed up thawing tasks if we don't call balance_pgdat 3207 * after returning from the refrigerator 3208 */ 3209 if (!ret) { 3210 trace_mm_vmscan_kswapd_wake(pgdat->node_id, order); 3211 balanced_classzone_idx = classzone_idx; 3212 balanced_order = balance_pgdat(pgdat, order, 3213 &balanced_classzone_idx); 3214 } 3215 } 3216 3217 current->reclaim_state = NULL; 3218 return 0; 3219 } 3220 3221 /* 3222 * A zone is low on free memory, so wake its kswapd task to service it. 3223 */ 3224 void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx) 3225 { 3226 pg_data_t *pgdat; 3227 3228 if (!populated_zone(zone)) 3229 return; 3230 3231 if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL)) 3232 return; 3233 pgdat = zone->zone_pgdat; 3234 if (pgdat->kswapd_max_order < order) { 3235 pgdat->kswapd_max_order = order; 3236 pgdat->classzone_idx = min(pgdat->classzone_idx, classzone_idx); 3237 } 3238 if (!waitqueue_active(&pgdat->kswapd_wait)) 3239 return; 3240 if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0)) 3241 return; 3242 3243 trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order); 3244 wake_up_interruptible(&pgdat->kswapd_wait); 3245 } 3246 3247 /* 3248 * The reclaimable count would be mostly accurate. 3249 * The less reclaimable pages may be 3250 * - mlocked pages, which will be moved to unevictable list when encountered 3251 * - mapped pages, which may require several travels to be reclaimed 3252 * - dirty pages, which is not "instantly" reclaimable 3253 */ 3254 unsigned long global_reclaimable_pages(void) 3255 { 3256 int nr; 3257 3258 nr = global_page_state(NR_ACTIVE_FILE) + 3259 global_page_state(NR_INACTIVE_FILE); 3260 3261 if (get_nr_swap_pages() > 0) 3262 nr += global_page_state(NR_ACTIVE_ANON) + 3263 global_page_state(NR_INACTIVE_ANON); 3264 3265 return nr; 3266 } 3267 3268 unsigned long zone_reclaimable_pages(struct zone *zone) 3269 { 3270 int nr; 3271 3272 nr = zone_page_state(zone, NR_ACTIVE_FILE) + 3273 zone_page_state(zone, NR_INACTIVE_FILE); 3274 3275 if (get_nr_swap_pages() > 0) 3276 nr += zone_page_state(zone, NR_ACTIVE_ANON) + 3277 zone_page_state(zone, NR_INACTIVE_ANON); 3278 3279 return nr; 3280 } 3281 3282 #ifdef CONFIG_HIBERNATION 3283 /* 3284 * Try to free `nr_to_reclaim' of memory, system-wide, and return the number of 3285 * freed pages. 3286 * 3287 * Rather than trying to age LRUs the aim is to preserve the overall 3288 * LRU order by reclaiming preferentially 3289 * inactive > active > active referenced > active mapped 3290 */ 3291 unsigned long shrink_all_memory(unsigned long nr_to_reclaim) 3292 { 3293 struct reclaim_state reclaim_state; 3294 struct scan_control sc = { 3295 .gfp_mask = GFP_HIGHUSER_MOVABLE, 3296 .may_swap = 1, 3297 .may_unmap = 1, 3298 .may_writepage = 1, 3299 .nr_to_reclaim = nr_to_reclaim, 3300 .hibernation_mode = 1, 3301 .order = 0, 3302 .priority = DEF_PRIORITY, 3303 }; 3304 struct shrink_control shrink = { 3305 .gfp_mask = sc.gfp_mask, 3306 }; 3307 struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask); 3308 struct task_struct *p = current; 3309 unsigned long nr_reclaimed; 3310 3311 p->flags |= PF_MEMALLOC; 3312 lockdep_set_current_reclaim_state(sc.gfp_mask); 3313 reclaim_state.reclaimed_slab = 0; 3314 p->reclaim_state = &reclaim_state; 3315 3316 nr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink); 3317 3318 p->reclaim_state = NULL; 3319 lockdep_clear_current_reclaim_state(); 3320 p->flags &= ~PF_MEMALLOC; 3321 3322 return nr_reclaimed; 3323 } 3324 #endif /* CONFIG_HIBERNATION */ 3325 3326 /* It's optimal to keep kswapds on the same CPUs as their memory, but 3327 not required for correctness. So if the last cpu in a node goes 3328 away, we get changed to run anywhere: as the first one comes back, 3329 restore their cpu bindings. */ 3330 static int cpu_callback(struct notifier_block *nfb, unsigned long action, 3331 void *hcpu) 3332 { 3333 int nid; 3334 3335 if (action == CPU_ONLINE || action == CPU_ONLINE_FROZEN) { 3336 for_each_node_state(nid, N_MEMORY) { 3337 pg_data_t *pgdat = NODE_DATA(nid); 3338 const struct cpumask *mask; 3339 3340 mask = cpumask_of_node(pgdat->node_id); 3341 3342 if (cpumask_any_and(cpu_online_mask, mask) < nr_cpu_ids) 3343 /* One of our CPUs online: restore mask */ 3344 set_cpus_allowed_ptr(pgdat->kswapd, mask); 3345 } 3346 } 3347 return NOTIFY_OK; 3348 } 3349 3350 /* 3351 * This kswapd start function will be called by init and node-hot-add. 3352 * On node-hot-add, kswapd will moved to proper cpus if cpus are hot-added. 3353 */ 3354 int kswapd_run(int nid) 3355 { 3356 pg_data_t *pgdat = NODE_DATA(nid); 3357 int ret = 0; 3358 3359 if (pgdat->kswapd) 3360 return 0; 3361 3362 pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid); 3363 if (IS_ERR(pgdat->kswapd)) { 3364 /* failure at boot is fatal */ 3365 BUG_ON(system_state == SYSTEM_BOOTING); 3366 pr_err("Failed to start kswapd on node %d\n", nid); 3367 ret = PTR_ERR(pgdat->kswapd); 3368 pgdat->kswapd = NULL; 3369 } 3370 return ret; 3371 } 3372 3373 /* 3374 * Called by memory hotplug when all memory in a node is offlined. Caller must 3375 * hold lock_memory_hotplug(). 3376 */ 3377 void kswapd_stop(int nid) 3378 { 3379 struct task_struct *kswapd = NODE_DATA(nid)->kswapd; 3380 3381 if (kswapd) { 3382 kthread_stop(kswapd); 3383 NODE_DATA(nid)->kswapd = NULL; 3384 } 3385 } 3386 3387 static int __init kswapd_init(void) 3388 { 3389 int nid; 3390 3391 swap_setup(); 3392 for_each_node_state(nid, N_MEMORY) 3393 kswapd_run(nid); 3394 hotcpu_notifier(cpu_callback, 0); 3395 return 0; 3396 } 3397 3398 module_init(kswapd_init) 3399 3400 #ifdef CONFIG_NUMA 3401 /* 3402 * Zone reclaim mode 3403 * 3404 * If non-zero call zone_reclaim when the number of free pages falls below 3405 * the watermarks. 3406 */ 3407 int zone_reclaim_mode __read_mostly; 3408 3409 #define RECLAIM_OFF 0 3410 #define RECLAIM_ZONE (1<<0) /* Run shrink_inactive_list on the zone */ 3411 #define RECLAIM_WRITE (1<<1) /* Writeout pages during reclaim */ 3412 #define RECLAIM_SWAP (1<<2) /* Swap pages out during reclaim */ 3413 3414 /* 3415 * Priority for ZONE_RECLAIM. This determines the fraction of pages 3416 * of a node considered for each zone_reclaim. 4 scans 1/16th of 3417 * a zone. 3418 */ 3419 #define ZONE_RECLAIM_PRIORITY 4 3420 3421 /* 3422 * Percentage of pages in a zone that must be unmapped for zone_reclaim to 3423 * occur. 3424 */ 3425 int sysctl_min_unmapped_ratio = 1; 3426 3427 /* 3428 * If the number of slab pages in a zone grows beyond this percentage then 3429 * slab reclaim needs to occur. 3430 */ 3431 int sysctl_min_slab_ratio = 5; 3432 3433 static inline unsigned long zone_unmapped_file_pages(struct zone *zone) 3434 { 3435 unsigned long file_mapped = zone_page_state(zone, NR_FILE_MAPPED); 3436 unsigned long file_lru = zone_page_state(zone, NR_INACTIVE_FILE) + 3437 zone_page_state(zone, NR_ACTIVE_FILE); 3438 3439 /* 3440 * It's possible for there to be more file mapped pages than 3441 * accounted for by the pages on the file LRU lists because 3442 * tmpfs pages accounted for as ANON can also be FILE_MAPPED 3443 */ 3444 return (file_lru > file_mapped) ? (file_lru - file_mapped) : 0; 3445 } 3446 3447 /* Work out how many page cache pages we can reclaim in this reclaim_mode */ 3448 static long zone_pagecache_reclaimable(struct zone *zone) 3449 { 3450 long nr_pagecache_reclaimable; 3451 long delta = 0; 3452 3453 /* 3454 * If RECLAIM_SWAP is set, then all file pages are considered 3455 * potentially reclaimable. Otherwise, we have to worry about 3456 * pages like swapcache and zone_unmapped_file_pages() provides 3457 * a better estimate 3458 */ 3459 if (zone_reclaim_mode & RECLAIM_SWAP) 3460 nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES); 3461 else 3462 nr_pagecache_reclaimable = zone_unmapped_file_pages(zone); 3463 3464 /* If we can't clean pages, remove dirty pages from consideration */ 3465 if (!(zone_reclaim_mode & RECLAIM_WRITE)) 3466 delta += zone_page_state(zone, NR_FILE_DIRTY); 3467 3468 /* Watch for any possible underflows due to delta */ 3469 if (unlikely(delta > nr_pagecache_reclaimable)) 3470 delta = nr_pagecache_reclaimable; 3471 3472 return nr_pagecache_reclaimable - delta; 3473 } 3474 3475 /* 3476 * Try to free up some pages from this zone through reclaim. 3477 */ 3478 static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) 3479 { 3480 /* Minimum pages needed in order to stay on node */ 3481 const unsigned long nr_pages = 1 << order; 3482 struct task_struct *p = current; 3483 struct reclaim_state reclaim_state; 3484 struct scan_control sc = { 3485 .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE), 3486 .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP), 3487 .may_swap = 1, 3488 .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX), 3489 .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)), 3490 .order = order, 3491 .priority = ZONE_RECLAIM_PRIORITY, 3492 }; 3493 struct shrink_control shrink = { 3494 .gfp_mask = sc.gfp_mask, 3495 }; 3496 unsigned long nr_slab_pages0, nr_slab_pages1; 3497 3498 cond_resched(); 3499 /* 3500 * We need to be able to allocate from the reserves for RECLAIM_SWAP 3501 * and we also need to be able to write out pages for RECLAIM_WRITE 3502 * and RECLAIM_SWAP. 3503 */ 3504 p->flags |= PF_MEMALLOC | PF_SWAPWRITE; 3505 lockdep_set_current_reclaim_state(gfp_mask); 3506 reclaim_state.reclaimed_slab = 0; 3507 p->reclaim_state = &reclaim_state; 3508 3509 if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) { 3510 /* 3511 * Free memory by calling shrink zone with increasing 3512 * priorities until we have enough memory freed. 3513 */ 3514 do { 3515 shrink_zone(zone, &sc); 3516 } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0); 3517 } 3518 3519 nr_slab_pages0 = zone_page_state(zone, NR_SLAB_RECLAIMABLE); 3520 if (nr_slab_pages0 > zone->min_slab_pages) { 3521 /* 3522 * shrink_slab() does not currently allow us to determine how 3523 * many pages were freed in this zone. So we take the current 3524 * number of slab pages and shake the slab until it is reduced 3525 * by the same nr_pages that we used for reclaiming unmapped 3526 * pages. 3527 * 3528 * Note that shrink_slab will free memory on all zones and may 3529 * take a long time. 3530 */ 3531 for (;;) { 3532 unsigned long lru_pages = zone_reclaimable_pages(zone); 3533 3534 /* No reclaimable slab or very low memory pressure */ 3535 if (!shrink_slab(&shrink, sc.nr_scanned, lru_pages)) 3536 break; 3537 3538 /* Freed enough memory */ 3539 nr_slab_pages1 = zone_page_state(zone, 3540 NR_SLAB_RECLAIMABLE); 3541 if (nr_slab_pages1 + nr_pages <= nr_slab_pages0) 3542 break; 3543 } 3544 3545 /* 3546 * Update nr_reclaimed by the number of slab pages we 3547 * reclaimed from this zone. 3548 */ 3549 nr_slab_pages1 = zone_page_state(zone, NR_SLAB_RECLAIMABLE); 3550 if (nr_slab_pages1 < nr_slab_pages0) 3551 sc.nr_reclaimed += nr_slab_pages0 - nr_slab_pages1; 3552 } 3553 3554 p->reclaim_state = NULL; 3555 current->flags &= ~(PF_MEMALLOC | PF_SWAPWRITE); 3556 lockdep_clear_current_reclaim_state(); 3557 return sc.nr_reclaimed >= nr_pages; 3558 } 3559 3560 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) 3561 { 3562 int node_id; 3563 int ret; 3564 3565 /* 3566 * Zone reclaim reclaims unmapped file backed pages and 3567 * slab pages if we are over the defined limits. 3568 * 3569 * A small portion of unmapped file backed pages is needed for 3570 * file I/O otherwise pages read by file I/O will be immediately 3571 * thrown out if the zone is overallocated. So we do not reclaim 3572 * if less than a specified percentage of the zone is used by 3573 * unmapped file backed pages. 3574 */ 3575 if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages && 3576 zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages) 3577 return ZONE_RECLAIM_FULL; 3578 3579 if (zone->all_unreclaimable) 3580 return ZONE_RECLAIM_FULL; 3581 3582 /* 3583 * Do not scan if the allocation should not be delayed. 3584 */ 3585 if (!(gfp_mask & __GFP_WAIT) || (current->flags & PF_MEMALLOC)) 3586 return ZONE_RECLAIM_NOSCAN; 3587 3588 /* 3589 * Only run zone reclaim on the local zone or on zones that do not 3590 * have associated processors. This will favor the local processor 3591 * over remote processors and spread off node memory allocations 3592 * as wide as possible. 3593 */ 3594 node_id = zone_to_nid(zone); 3595 if (node_state(node_id, N_CPU) && node_id != numa_node_id()) 3596 return ZONE_RECLAIM_NOSCAN; 3597 3598 if (zone_test_and_set_flag(zone, ZONE_RECLAIM_LOCKED)) 3599 return ZONE_RECLAIM_NOSCAN; 3600 3601 ret = __zone_reclaim(zone, gfp_mask, order); 3602 zone_clear_flag(zone, ZONE_RECLAIM_LOCKED); 3603 3604 if (!ret) 3605 count_vm_event(PGSCAN_ZONE_RECLAIM_FAILED); 3606 3607 return ret; 3608 } 3609 #endif 3610 3611 /* 3612 * page_evictable - test whether a page is evictable 3613 * @page: the page to test 3614 * 3615 * Test whether page is evictable--i.e., should be placed on active/inactive 3616 * lists vs unevictable list. 3617 * 3618 * Reasons page might not be evictable: 3619 * (1) page's mapping marked unevictable 3620 * (2) page is part of an mlocked VMA 3621 * 3622 */ 3623 int page_evictable(struct page *page) 3624 { 3625 return !mapping_unevictable(page_mapping(page)) && !PageMlocked(page); 3626 } 3627 3628 #ifdef CONFIG_SHMEM 3629 /** 3630 * check_move_unevictable_pages - check pages for evictability and move to appropriate zone lru list 3631 * @pages: array of pages to check 3632 * @nr_pages: number of pages to check 3633 * 3634 * Checks pages for evictability and moves them to the appropriate lru list. 3635 * 3636 * This function is only used for SysV IPC SHM_UNLOCK. 3637 */ 3638 void check_move_unevictable_pages(struct page **pages, int nr_pages) 3639 { 3640 struct lruvec *lruvec; 3641 struct zone *zone = NULL; 3642 int pgscanned = 0; 3643 int pgrescued = 0; 3644 int i; 3645 3646 for (i = 0; i < nr_pages; i++) { 3647 struct page *page = pages[i]; 3648 struct zone *pagezone; 3649 3650 pgscanned++; 3651 pagezone = page_zone(page); 3652 if (pagezone != zone) { 3653 if (zone) 3654 spin_unlock_irq(&zone->lru_lock); 3655 zone = pagezone; 3656 spin_lock_irq(&zone->lru_lock); 3657 } 3658 lruvec = mem_cgroup_page_lruvec(page, zone); 3659 3660 if (!PageLRU(page) || !PageUnevictable(page)) 3661 continue; 3662 3663 if (page_evictable(page)) { 3664 enum lru_list lru = page_lru_base_type(page); 3665 3666 VM_BUG_ON(PageActive(page)); 3667 ClearPageUnevictable(page); 3668 del_page_from_lru_list(page, lruvec, LRU_UNEVICTABLE); 3669 add_page_to_lru_list(page, lruvec, lru); 3670 pgrescued++; 3671 } 3672 } 3673 3674 if (zone) { 3675 __count_vm_events(UNEVICTABLE_PGRESCUED, pgrescued); 3676 __count_vm_events(UNEVICTABLE_PGSCANNED, pgscanned); 3677 spin_unlock_irq(&zone->lru_lock); 3678 } 3679 } 3680 #endif /* CONFIG_SHMEM */ 3681 3682 static void warn_scan_unevictable_pages(void) 3683 { 3684 printk_once(KERN_WARNING 3685 "%s: The scan_unevictable_pages sysctl/node-interface has been " 3686 "disabled for lack of a legitimate use case. If you have " 3687 "one, please send an email to linux-mm@kvack.org.\n", 3688 current->comm); 3689 } 3690 3691 /* 3692 * scan_unevictable_pages [vm] sysctl handler. On demand re-scan of 3693 * all nodes' unevictable lists for evictable pages 3694 */ 3695 unsigned long scan_unevictable_pages; 3696 3697 int scan_unevictable_handler(struct ctl_table *table, int write, 3698 void __user *buffer, 3699 size_t *length, loff_t *ppos) 3700 { 3701 warn_scan_unevictable_pages(); 3702 proc_doulongvec_minmax(table, write, buffer, length, ppos); 3703 scan_unevictable_pages = 0; 3704 return 0; 3705 } 3706 3707 #ifdef CONFIG_NUMA 3708 /* 3709 * per node 'scan_unevictable_pages' attribute. On demand re-scan of 3710 * a specified node's per zone unevictable lists for evictable pages. 3711 */ 3712 3713 static ssize_t read_scan_unevictable_node(struct device *dev, 3714 struct device_attribute *attr, 3715 char *buf) 3716 { 3717 warn_scan_unevictable_pages(); 3718 return sprintf(buf, "0\n"); /* always zero; should fit... */ 3719 } 3720 3721 static ssize_t write_scan_unevictable_node(struct device *dev, 3722 struct device_attribute *attr, 3723 const char *buf, size_t count) 3724 { 3725 warn_scan_unevictable_pages(); 3726 return 1; 3727 } 3728 3729 3730 static DEVICE_ATTR(scan_unevictable_pages, S_IRUGO | S_IWUSR, 3731 read_scan_unevictable_node, 3732 write_scan_unevictable_node); 3733 3734 int scan_unevictable_register_node(struct node *node) 3735 { 3736 return device_create_file(&node->dev, &dev_attr_scan_unevictable_pages); 3737 } 3738 3739 void scan_unevictable_unregister_node(struct node *node) 3740 { 3741 device_remove_file(&node->dev, &dev_attr_scan_unevictable_pages); 3742 } 3743 #endif 3744