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/slab.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/file.h> 23 #include <linux/writeback.h> 24 #include <linux/blkdev.h> 25 #include <linux/buffer_head.h> /* for try_to_release_page(), 26 buffer_heads_over_limit */ 27 #include <linux/mm_inline.h> 28 #include <linux/pagevec.h> 29 #include <linux/backing-dev.h> 30 #include <linux/rmap.h> 31 #include <linux/topology.h> 32 #include <linux/cpu.h> 33 #include <linux/cpuset.h> 34 #include <linux/notifier.h> 35 #include <linux/rwsem.h> 36 37 #include <asm/tlbflush.h> 38 #include <asm/div64.h> 39 40 #include <linux/swapops.h> 41 42 /* possible outcome of pageout() */ 43 typedef enum { 44 /* failed to write page out, page is locked */ 45 PAGE_KEEP, 46 /* move page to the active list, page is locked */ 47 PAGE_ACTIVATE, 48 /* page has been sent to the disk successfully, page is unlocked */ 49 PAGE_SUCCESS, 50 /* page is clean and locked */ 51 PAGE_CLEAN, 52 } pageout_t; 53 54 struct scan_control { 55 /* Ask refill_inactive_zone, or shrink_cache to scan this many pages */ 56 unsigned long nr_to_scan; 57 58 /* Incremented by the number of inactive pages that were scanned */ 59 unsigned long nr_scanned; 60 61 /* Incremented by the number of pages reclaimed */ 62 unsigned long nr_reclaimed; 63 64 unsigned long nr_mapped; /* From page_state */ 65 66 /* How many pages shrink_cache() should reclaim */ 67 int nr_to_reclaim; 68 69 /* Ask shrink_caches, or shrink_zone to scan at this priority */ 70 unsigned int priority; 71 72 /* This context's GFP mask */ 73 gfp_t gfp_mask; 74 75 int may_writepage; 76 77 /* Can pages be swapped as part of reclaim? */ 78 int may_swap; 79 80 /* This context's SWAP_CLUSTER_MAX. If freeing memory for 81 * suspend, we effectively ignore SWAP_CLUSTER_MAX. 82 * In this context, it doesn't matter that we scan the 83 * whole list at once. */ 84 int swap_cluster_max; 85 }; 86 87 /* 88 * The list of shrinker callbacks used by to apply pressure to 89 * ageable caches. 90 */ 91 struct shrinker { 92 shrinker_t shrinker; 93 struct list_head list; 94 int seeks; /* seeks to recreate an obj */ 95 long nr; /* objs pending delete */ 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 static long total_memory; 133 134 static LIST_HEAD(shrinker_list); 135 static DECLARE_RWSEM(shrinker_rwsem); 136 137 /* 138 * Add a shrinker callback to be called from the vm 139 */ 140 struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker) 141 { 142 struct shrinker *shrinker; 143 144 shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL); 145 if (shrinker) { 146 shrinker->shrinker = theshrinker; 147 shrinker->seeks = seeks; 148 shrinker->nr = 0; 149 down_write(&shrinker_rwsem); 150 list_add_tail(&shrinker->list, &shrinker_list); 151 up_write(&shrinker_rwsem); 152 } 153 return shrinker; 154 } 155 EXPORT_SYMBOL(set_shrinker); 156 157 /* 158 * Remove one 159 */ 160 void remove_shrinker(struct shrinker *shrinker) 161 { 162 down_write(&shrinker_rwsem); 163 list_del(&shrinker->list); 164 up_write(&shrinker_rwsem); 165 kfree(shrinker); 166 } 167 EXPORT_SYMBOL(remove_shrinker); 168 169 #define SHRINK_BATCH 128 170 /* 171 * Call the shrink functions to age shrinkable caches 172 * 173 * Here we assume it costs one seek to replace a lru page and that it also 174 * takes a seek to recreate a cache object. With this in mind we age equal 175 * percentages of the lru and ageable caches. This should balance the seeks 176 * generated by these structures. 177 * 178 * If the vm encounted mapped pages on the LRU it increase the pressure on 179 * slab to avoid swapping. 180 * 181 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits. 182 * 183 * `lru_pages' represents the number of on-LRU pages in all the zones which 184 * are eligible for the caller's allocation attempt. It is used for balancing 185 * slab reclaim versus page reclaim. 186 * 187 * Returns the number of slab objects which we shrunk. 188 */ 189 static int shrink_slab(unsigned long scanned, gfp_t gfp_mask, 190 unsigned long lru_pages) 191 { 192 struct shrinker *shrinker; 193 int ret = 0; 194 195 if (scanned == 0) 196 scanned = SWAP_CLUSTER_MAX; 197 198 if (!down_read_trylock(&shrinker_rwsem)) 199 return 1; /* Assume we'll be able to shrink next time */ 200 201 list_for_each_entry(shrinker, &shrinker_list, list) { 202 unsigned long long delta; 203 unsigned long total_scan; 204 205 delta = (4 * scanned) / shrinker->seeks; 206 delta *= (*shrinker->shrinker)(0, gfp_mask); 207 do_div(delta, lru_pages + 1); 208 shrinker->nr += delta; 209 if (shrinker->nr < 0) 210 shrinker->nr = LONG_MAX; /* It wrapped! */ 211 212 total_scan = shrinker->nr; 213 shrinker->nr = 0; 214 215 while (total_scan >= SHRINK_BATCH) { 216 long this_scan = SHRINK_BATCH; 217 int shrink_ret; 218 int nr_before; 219 220 nr_before = (*shrinker->shrinker)(0, gfp_mask); 221 shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask); 222 if (shrink_ret == -1) 223 break; 224 if (shrink_ret < nr_before) 225 ret += nr_before - shrink_ret; 226 mod_page_state(slabs_scanned, this_scan); 227 total_scan -= this_scan; 228 229 cond_resched(); 230 } 231 232 shrinker->nr += total_scan; 233 } 234 up_read(&shrinker_rwsem); 235 return ret; 236 } 237 238 /* Called without lock on whether page is mapped, so answer is unstable */ 239 static inline int page_mapping_inuse(struct page *page) 240 { 241 struct address_space *mapping; 242 243 /* Page is in somebody's page tables. */ 244 if (page_mapped(page)) 245 return 1; 246 247 /* Be more reluctant to reclaim swapcache than pagecache */ 248 if (PageSwapCache(page)) 249 return 1; 250 251 mapping = page_mapping(page); 252 if (!mapping) 253 return 0; 254 255 /* File is mmap'd by somebody? */ 256 return mapping_mapped(mapping); 257 } 258 259 static inline int is_page_cache_freeable(struct page *page) 260 { 261 return page_count(page) - !!PagePrivate(page) == 2; 262 } 263 264 static int may_write_to_queue(struct backing_dev_info *bdi) 265 { 266 if (current_is_kswapd()) 267 return 1; 268 if (current_is_pdflush()) /* This is unlikely, but why not... */ 269 return 1; 270 if (!bdi_write_congested(bdi)) 271 return 1; 272 if (bdi == current->backing_dev_info) 273 return 1; 274 return 0; 275 } 276 277 /* 278 * We detected a synchronous write error writing a page out. Probably 279 * -ENOSPC. We need to propagate that into the address_space for a subsequent 280 * fsync(), msync() or close(). 281 * 282 * The tricky part is that after writepage we cannot touch the mapping: nothing 283 * prevents it from being freed up. But we have a ref on the page and once 284 * that page is locked, the mapping is pinned. 285 * 286 * We're allowed to run sleeping lock_page() here because we know the caller has 287 * __GFP_FS. 288 */ 289 static void handle_write_error(struct address_space *mapping, 290 struct page *page, int error) 291 { 292 lock_page(page); 293 if (page_mapping(page) == mapping) { 294 if (error == -ENOSPC) 295 set_bit(AS_ENOSPC, &mapping->flags); 296 else 297 set_bit(AS_EIO, &mapping->flags); 298 } 299 unlock_page(page); 300 } 301 302 /* 303 * pageout is called by shrink_list() for each dirty page. Calls ->writepage(). 304 */ 305 static pageout_t pageout(struct page *page, struct address_space *mapping) 306 { 307 /* 308 * If the page is dirty, only perform writeback if that write 309 * will be non-blocking. To prevent this allocation from being 310 * stalled by pagecache activity. But note that there may be 311 * stalls if we need to run get_block(). We could test 312 * PagePrivate for that. 313 * 314 * If this process is currently in generic_file_write() against 315 * this page's queue, we can perform writeback even if that 316 * will block. 317 * 318 * If the page is swapcache, write it back even if that would 319 * block, for some throttling. This happens by accident, because 320 * swap_backing_dev_info is bust: it doesn't reflect the 321 * congestion state of the swapdevs. Easy to fix, if needed. 322 * See swapfile.c:page_queue_congested(). 323 */ 324 if (!is_page_cache_freeable(page)) 325 return PAGE_KEEP; 326 if (!mapping) { 327 /* 328 * Some data journaling orphaned pages can have 329 * page->mapping == NULL while being dirty with clean buffers. 330 */ 331 if (PagePrivate(page)) { 332 if (try_to_free_buffers(page)) { 333 ClearPageDirty(page); 334 printk("%s: orphaned page\n", __FUNCTION__); 335 return PAGE_CLEAN; 336 } 337 } 338 return PAGE_KEEP; 339 } 340 if (mapping->a_ops->writepage == NULL) 341 return PAGE_ACTIVATE; 342 if (!may_write_to_queue(mapping->backing_dev_info)) 343 return PAGE_KEEP; 344 345 if (clear_page_dirty_for_io(page)) { 346 int res; 347 struct writeback_control wbc = { 348 .sync_mode = WB_SYNC_NONE, 349 .nr_to_write = SWAP_CLUSTER_MAX, 350 .nonblocking = 1, 351 .for_reclaim = 1, 352 }; 353 354 SetPageReclaim(page); 355 res = mapping->a_ops->writepage(page, &wbc); 356 if (res < 0) 357 handle_write_error(mapping, page, res); 358 if (res == WRITEPAGE_ACTIVATE) { 359 ClearPageReclaim(page); 360 return PAGE_ACTIVATE; 361 } 362 if (!PageWriteback(page)) { 363 /* synchronous write or broken a_ops? */ 364 ClearPageReclaim(page); 365 } 366 367 return PAGE_SUCCESS; 368 } 369 370 return PAGE_CLEAN; 371 } 372 373 /* 374 * shrink_list adds the number of reclaimed pages to sc->nr_reclaimed 375 */ 376 static int shrink_list(struct list_head *page_list, struct scan_control *sc) 377 { 378 LIST_HEAD(ret_pages); 379 struct pagevec freed_pvec; 380 int pgactivate = 0; 381 int reclaimed = 0; 382 383 cond_resched(); 384 385 pagevec_init(&freed_pvec, 1); 386 while (!list_empty(page_list)) { 387 struct address_space *mapping; 388 struct page *page; 389 int may_enter_fs; 390 int referenced; 391 392 cond_resched(); 393 394 page = lru_to_page(page_list); 395 list_del(&page->lru); 396 397 if (TestSetPageLocked(page)) 398 goto keep; 399 400 BUG_ON(PageActive(page)); 401 402 sc->nr_scanned++; 403 /* Double the slab pressure for mapped and swapcache pages */ 404 if (page_mapped(page) || PageSwapCache(page)) 405 sc->nr_scanned++; 406 407 if (PageWriteback(page)) 408 goto keep_locked; 409 410 referenced = page_referenced(page, 1, sc->priority <= 0); 411 /* In active use or really unfreeable? Activate it. */ 412 if (referenced && page_mapping_inuse(page)) 413 goto activate_locked; 414 415 #ifdef CONFIG_SWAP 416 /* 417 * Anonymous process memory has backing store? 418 * Try to allocate it some swap space here. 419 */ 420 if (PageAnon(page) && !PageSwapCache(page)) { 421 if (!sc->may_swap) 422 goto keep_locked; 423 if (!add_to_swap(page)) 424 goto activate_locked; 425 } 426 #endif /* CONFIG_SWAP */ 427 428 mapping = page_mapping(page); 429 may_enter_fs = (sc->gfp_mask & __GFP_FS) || 430 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); 431 432 /* 433 * The page is mapped into the page tables of one or more 434 * processes. Try to unmap it here. 435 */ 436 if (page_mapped(page) && mapping) { 437 switch (try_to_unmap(page)) { 438 case SWAP_FAIL: 439 goto activate_locked; 440 case SWAP_AGAIN: 441 goto keep_locked; 442 case SWAP_SUCCESS: 443 ; /* try to free the page below */ 444 } 445 } 446 447 if (PageDirty(page)) { 448 if (referenced) 449 goto keep_locked; 450 if (!may_enter_fs) 451 goto keep_locked; 452 if (laptop_mode && !sc->may_writepage) 453 goto keep_locked; 454 455 /* Page is dirty, try to write it out here */ 456 switch(pageout(page, mapping)) { 457 case PAGE_KEEP: 458 goto keep_locked; 459 case PAGE_ACTIVATE: 460 goto activate_locked; 461 case PAGE_SUCCESS: 462 if (PageWriteback(page) || PageDirty(page)) 463 goto keep; 464 /* 465 * A synchronous write - probably a ramdisk. Go 466 * ahead and try to reclaim the page. 467 */ 468 if (TestSetPageLocked(page)) 469 goto keep; 470 if (PageDirty(page) || PageWriteback(page)) 471 goto keep_locked; 472 mapping = page_mapping(page); 473 case PAGE_CLEAN: 474 ; /* try to free the page below */ 475 } 476 } 477 478 /* 479 * If the page has buffers, try to free the buffer mappings 480 * associated with this page. If we succeed we try to free 481 * the page as well. 482 * 483 * We do this even if the page is PageDirty(). 484 * try_to_release_page() does not perform I/O, but it is 485 * possible for a page to have PageDirty set, but it is actually 486 * clean (all its buffers are clean). This happens if the 487 * buffers were written out directly, with submit_bh(). ext3 488 * will do this, as well as the blockdev mapping. 489 * try_to_release_page() will discover that cleanness and will 490 * drop the buffers and mark the page clean - it can be freed. 491 * 492 * Rarely, pages can have buffers and no ->mapping. These are 493 * the pages which were not successfully invalidated in 494 * truncate_complete_page(). We try to drop those buffers here 495 * and if that worked, and the page is no longer mapped into 496 * process address space (page_count == 1) it can be freed. 497 * Otherwise, leave the page on the LRU so it is swappable. 498 */ 499 if (PagePrivate(page)) { 500 if (!try_to_release_page(page, sc->gfp_mask)) 501 goto activate_locked; 502 if (!mapping && page_count(page) == 1) 503 goto free_it; 504 } 505 506 if (!mapping) 507 goto keep_locked; /* truncate got there first */ 508 509 write_lock_irq(&mapping->tree_lock); 510 511 /* 512 * The non-racy check for busy page. It is critical to check 513 * PageDirty _after_ making sure that the page is freeable and 514 * not in use by anybody. (pagecache + us == 2) 515 */ 516 if (unlikely(page_count(page) != 2)) 517 goto cannot_free; 518 smp_rmb(); 519 if (unlikely(PageDirty(page))) 520 goto cannot_free; 521 522 #ifdef CONFIG_SWAP 523 if (PageSwapCache(page)) { 524 swp_entry_t swap = { .val = page_private(page) }; 525 __delete_from_swap_cache(page); 526 write_unlock_irq(&mapping->tree_lock); 527 swap_free(swap); 528 __put_page(page); /* The pagecache ref */ 529 goto free_it; 530 } 531 #endif /* CONFIG_SWAP */ 532 533 __remove_from_page_cache(page); 534 write_unlock_irq(&mapping->tree_lock); 535 __put_page(page); 536 537 free_it: 538 unlock_page(page); 539 reclaimed++; 540 if (!pagevec_add(&freed_pvec, page)) 541 __pagevec_release_nonlru(&freed_pvec); 542 continue; 543 544 cannot_free: 545 write_unlock_irq(&mapping->tree_lock); 546 goto keep_locked; 547 548 activate_locked: 549 SetPageActive(page); 550 pgactivate++; 551 keep_locked: 552 unlock_page(page); 553 keep: 554 list_add(&page->lru, &ret_pages); 555 BUG_ON(PageLRU(page)); 556 } 557 list_splice(&ret_pages, page_list); 558 if (pagevec_count(&freed_pvec)) 559 __pagevec_release_nonlru(&freed_pvec); 560 mod_page_state(pgactivate, pgactivate); 561 sc->nr_reclaimed += reclaimed; 562 return reclaimed; 563 } 564 565 /* 566 * zone->lru_lock is heavily contended. Some of the functions that 567 * shrink the lists perform better by taking out a batch of pages 568 * and working on them outside the LRU lock. 569 * 570 * For pagecache intensive workloads, this function is the hottest 571 * spot in the kernel (apart from copy_*_user functions). 572 * 573 * Appropriate locks must be held before calling this function. 574 * 575 * @nr_to_scan: The number of pages to look through on the list. 576 * @src: The LRU list to pull pages off. 577 * @dst: The temp list to put pages on to. 578 * @scanned: The number of pages that were scanned. 579 * 580 * returns how many pages were moved onto *@dst. 581 */ 582 static int isolate_lru_pages(int nr_to_scan, struct list_head *src, 583 struct list_head *dst, int *scanned) 584 { 585 int nr_taken = 0; 586 struct page *page; 587 int scan = 0; 588 589 while (scan++ < nr_to_scan && !list_empty(src)) { 590 page = lru_to_page(src); 591 prefetchw_prev_lru_page(page, src, flags); 592 593 if (!TestClearPageLRU(page)) 594 BUG(); 595 list_del(&page->lru); 596 if (get_page_testone(page)) { 597 /* 598 * It is being freed elsewhere 599 */ 600 __put_page(page); 601 SetPageLRU(page); 602 list_add(&page->lru, src); 603 continue; 604 } else { 605 list_add(&page->lru, dst); 606 nr_taken++; 607 } 608 } 609 610 *scanned = scan; 611 return nr_taken; 612 } 613 614 /* 615 * shrink_cache() adds the number of pages reclaimed to sc->nr_reclaimed 616 */ 617 static void shrink_cache(struct zone *zone, struct scan_control *sc) 618 { 619 LIST_HEAD(page_list); 620 struct pagevec pvec; 621 int max_scan = sc->nr_to_scan; 622 623 pagevec_init(&pvec, 1); 624 625 lru_add_drain(); 626 spin_lock_irq(&zone->lru_lock); 627 while (max_scan > 0) { 628 struct page *page; 629 int nr_taken; 630 int nr_scan; 631 int nr_freed; 632 633 nr_taken = isolate_lru_pages(sc->swap_cluster_max, 634 &zone->inactive_list, 635 &page_list, &nr_scan); 636 zone->nr_inactive -= nr_taken; 637 zone->pages_scanned += nr_scan; 638 spin_unlock_irq(&zone->lru_lock); 639 640 if (nr_taken == 0) 641 goto done; 642 643 max_scan -= nr_scan; 644 if (current_is_kswapd()) 645 mod_page_state_zone(zone, pgscan_kswapd, nr_scan); 646 else 647 mod_page_state_zone(zone, pgscan_direct, nr_scan); 648 nr_freed = shrink_list(&page_list, sc); 649 if (current_is_kswapd()) 650 mod_page_state(kswapd_steal, nr_freed); 651 mod_page_state_zone(zone, pgsteal, nr_freed); 652 sc->nr_to_reclaim -= nr_freed; 653 654 spin_lock_irq(&zone->lru_lock); 655 /* 656 * Put back any unfreeable pages. 657 */ 658 while (!list_empty(&page_list)) { 659 page = lru_to_page(&page_list); 660 if (TestSetPageLRU(page)) 661 BUG(); 662 list_del(&page->lru); 663 if (PageActive(page)) 664 add_page_to_active_list(zone, page); 665 else 666 add_page_to_inactive_list(zone, page); 667 if (!pagevec_add(&pvec, page)) { 668 spin_unlock_irq(&zone->lru_lock); 669 __pagevec_release(&pvec); 670 spin_lock_irq(&zone->lru_lock); 671 } 672 } 673 } 674 spin_unlock_irq(&zone->lru_lock); 675 done: 676 pagevec_release(&pvec); 677 } 678 679 /* 680 * This moves pages from the active list to the inactive list. 681 * 682 * We move them the other way if the page is referenced by one or more 683 * processes, from rmap. 684 * 685 * If the pages are mostly unmapped, the processing is fast and it is 686 * appropriate to hold zone->lru_lock across the whole operation. But if 687 * the pages are mapped, the processing is slow (page_referenced()) so we 688 * should drop zone->lru_lock around each page. It's impossible to balance 689 * this, so instead we remove the pages from the LRU while processing them. 690 * It is safe to rely on PG_active against the non-LRU pages in here because 691 * nobody will play with that bit on a non-LRU page. 692 * 693 * The downside is that we have to touch page->_count against each page. 694 * But we had to alter page->flags anyway. 695 */ 696 static void 697 refill_inactive_zone(struct zone *zone, struct scan_control *sc) 698 { 699 int pgmoved; 700 int pgdeactivate = 0; 701 int pgscanned; 702 int nr_pages = sc->nr_to_scan; 703 LIST_HEAD(l_hold); /* The pages which were snipped off */ 704 LIST_HEAD(l_inactive); /* Pages to go onto the inactive_list */ 705 LIST_HEAD(l_active); /* Pages to go onto the active_list */ 706 struct page *page; 707 struct pagevec pvec; 708 int reclaim_mapped = 0; 709 long mapped_ratio; 710 long distress; 711 long swap_tendency; 712 713 lru_add_drain(); 714 spin_lock_irq(&zone->lru_lock); 715 pgmoved = isolate_lru_pages(nr_pages, &zone->active_list, 716 &l_hold, &pgscanned); 717 zone->pages_scanned += pgscanned; 718 zone->nr_active -= pgmoved; 719 spin_unlock_irq(&zone->lru_lock); 720 721 /* 722 * `distress' is a measure of how much trouble we're having reclaiming 723 * pages. 0 -> no problems. 100 -> great trouble. 724 */ 725 distress = 100 >> zone->prev_priority; 726 727 /* 728 * The point of this algorithm is to decide when to start reclaiming 729 * mapped memory instead of just pagecache. Work out how much memory 730 * is mapped. 731 */ 732 mapped_ratio = (sc->nr_mapped * 100) / total_memory; 733 734 /* 735 * Now decide how much we really want to unmap some pages. The mapped 736 * ratio is downgraded - just because there's a lot of mapped memory 737 * doesn't necessarily mean that page reclaim isn't succeeding. 738 * 739 * The distress ratio is important - we don't want to start going oom. 740 * 741 * A 100% value of vm_swappiness overrides this algorithm altogether. 742 */ 743 swap_tendency = mapped_ratio / 2 + distress + vm_swappiness; 744 745 /* 746 * Now use this metric to decide whether to start moving mapped memory 747 * onto the inactive list. 748 */ 749 if (swap_tendency >= 100) 750 reclaim_mapped = 1; 751 752 while (!list_empty(&l_hold)) { 753 cond_resched(); 754 page = lru_to_page(&l_hold); 755 list_del(&page->lru); 756 if (page_mapped(page)) { 757 if (!reclaim_mapped || 758 (total_swap_pages == 0 && PageAnon(page)) || 759 page_referenced(page, 0, sc->priority <= 0)) { 760 list_add(&page->lru, &l_active); 761 continue; 762 } 763 } 764 list_add(&page->lru, &l_inactive); 765 } 766 767 pagevec_init(&pvec, 1); 768 pgmoved = 0; 769 spin_lock_irq(&zone->lru_lock); 770 while (!list_empty(&l_inactive)) { 771 page = lru_to_page(&l_inactive); 772 prefetchw_prev_lru_page(page, &l_inactive, flags); 773 if (TestSetPageLRU(page)) 774 BUG(); 775 if (!TestClearPageActive(page)) 776 BUG(); 777 list_move(&page->lru, &zone->inactive_list); 778 pgmoved++; 779 if (!pagevec_add(&pvec, page)) { 780 zone->nr_inactive += pgmoved; 781 spin_unlock_irq(&zone->lru_lock); 782 pgdeactivate += pgmoved; 783 pgmoved = 0; 784 if (buffer_heads_over_limit) 785 pagevec_strip(&pvec); 786 __pagevec_release(&pvec); 787 spin_lock_irq(&zone->lru_lock); 788 } 789 } 790 zone->nr_inactive += pgmoved; 791 pgdeactivate += pgmoved; 792 if (buffer_heads_over_limit) { 793 spin_unlock_irq(&zone->lru_lock); 794 pagevec_strip(&pvec); 795 spin_lock_irq(&zone->lru_lock); 796 } 797 798 pgmoved = 0; 799 while (!list_empty(&l_active)) { 800 page = lru_to_page(&l_active); 801 prefetchw_prev_lru_page(page, &l_active, flags); 802 if (TestSetPageLRU(page)) 803 BUG(); 804 BUG_ON(!PageActive(page)); 805 list_move(&page->lru, &zone->active_list); 806 pgmoved++; 807 if (!pagevec_add(&pvec, page)) { 808 zone->nr_active += pgmoved; 809 pgmoved = 0; 810 spin_unlock_irq(&zone->lru_lock); 811 __pagevec_release(&pvec); 812 spin_lock_irq(&zone->lru_lock); 813 } 814 } 815 zone->nr_active += pgmoved; 816 spin_unlock_irq(&zone->lru_lock); 817 pagevec_release(&pvec); 818 819 mod_page_state_zone(zone, pgrefill, pgscanned); 820 mod_page_state(pgdeactivate, pgdeactivate); 821 } 822 823 /* 824 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim. 825 */ 826 static void 827 shrink_zone(struct zone *zone, struct scan_control *sc) 828 { 829 unsigned long nr_active; 830 unsigned long nr_inactive; 831 832 atomic_inc(&zone->reclaim_in_progress); 833 834 /* 835 * Add one to `nr_to_scan' just to make sure that the kernel will 836 * slowly sift through the active list. 837 */ 838 zone->nr_scan_active += (zone->nr_active >> sc->priority) + 1; 839 nr_active = zone->nr_scan_active; 840 if (nr_active >= sc->swap_cluster_max) 841 zone->nr_scan_active = 0; 842 else 843 nr_active = 0; 844 845 zone->nr_scan_inactive += (zone->nr_inactive >> sc->priority) + 1; 846 nr_inactive = zone->nr_scan_inactive; 847 if (nr_inactive >= sc->swap_cluster_max) 848 zone->nr_scan_inactive = 0; 849 else 850 nr_inactive = 0; 851 852 sc->nr_to_reclaim = sc->swap_cluster_max; 853 854 while (nr_active || nr_inactive) { 855 if (nr_active) { 856 sc->nr_to_scan = min(nr_active, 857 (unsigned long)sc->swap_cluster_max); 858 nr_active -= sc->nr_to_scan; 859 refill_inactive_zone(zone, sc); 860 } 861 862 if (nr_inactive) { 863 sc->nr_to_scan = min(nr_inactive, 864 (unsigned long)sc->swap_cluster_max); 865 nr_inactive -= sc->nr_to_scan; 866 shrink_cache(zone, sc); 867 if (sc->nr_to_reclaim <= 0) 868 break; 869 } 870 } 871 872 throttle_vm_writeout(); 873 874 atomic_dec(&zone->reclaim_in_progress); 875 } 876 877 /* 878 * This is the direct reclaim path, for page-allocating processes. We only 879 * try to reclaim pages from zones which will satisfy the caller's allocation 880 * request. 881 * 882 * We reclaim from a zone even if that zone is over pages_high. Because: 883 * a) The caller may be trying to free *extra* pages to satisfy a higher-order 884 * allocation or 885 * b) The zones may be over pages_high but they must go *over* pages_high to 886 * satisfy the `incremental min' zone defense algorithm. 887 * 888 * Returns the number of reclaimed pages. 889 * 890 * If a zone is deemed to be full of pinned pages then just give it a light 891 * scan then give up on it. 892 */ 893 static void 894 shrink_caches(struct zone **zones, struct scan_control *sc) 895 { 896 int i; 897 898 for (i = 0; zones[i] != NULL; i++) { 899 struct zone *zone = zones[i]; 900 901 if (zone->present_pages == 0) 902 continue; 903 904 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL)) 905 continue; 906 907 zone->temp_priority = sc->priority; 908 if (zone->prev_priority > sc->priority) 909 zone->prev_priority = sc->priority; 910 911 if (zone->all_unreclaimable && sc->priority != DEF_PRIORITY) 912 continue; /* Let kswapd poll it */ 913 914 shrink_zone(zone, sc); 915 } 916 } 917 918 /* 919 * This is the main entry point to direct page reclaim. 920 * 921 * If a full scan of the inactive list fails to free enough memory then we 922 * are "out of memory" and something needs to be killed. 923 * 924 * If the caller is !__GFP_FS then the probability of a failure is reasonably 925 * high - the zone may be full of dirty or under-writeback pages, which this 926 * caller can't do much about. We kick pdflush and take explicit naps in the 927 * hope that some of these pages can be written. But if the allocating task 928 * holds filesystem locks which prevent writeout this might not work, and the 929 * allocation attempt will fail. 930 */ 931 int try_to_free_pages(struct zone **zones, gfp_t gfp_mask) 932 { 933 int priority; 934 int ret = 0; 935 int total_scanned = 0, total_reclaimed = 0; 936 struct reclaim_state *reclaim_state = current->reclaim_state; 937 struct scan_control sc; 938 unsigned long lru_pages = 0; 939 int i; 940 941 sc.gfp_mask = gfp_mask; 942 sc.may_writepage = 0; 943 sc.may_swap = 1; 944 945 inc_page_state(allocstall); 946 947 for (i = 0; zones[i] != NULL; i++) { 948 struct zone *zone = zones[i]; 949 950 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL)) 951 continue; 952 953 zone->temp_priority = DEF_PRIORITY; 954 lru_pages += zone->nr_active + zone->nr_inactive; 955 } 956 957 for (priority = DEF_PRIORITY; priority >= 0; priority--) { 958 sc.nr_mapped = read_page_state(nr_mapped); 959 sc.nr_scanned = 0; 960 sc.nr_reclaimed = 0; 961 sc.priority = priority; 962 sc.swap_cluster_max = SWAP_CLUSTER_MAX; 963 shrink_caches(zones, &sc); 964 shrink_slab(sc.nr_scanned, gfp_mask, lru_pages); 965 if (reclaim_state) { 966 sc.nr_reclaimed += reclaim_state->reclaimed_slab; 967 reclaim_state->reclaimed_slab = 0; 968 } 969 total_scanned += sc.nr_scanned; 970 total_reclaimed += sc.nr_reclaimed; 971 if (total_reclaimed >= sc.swap_cluster_max) { 972 ret = 1; 973 goto out; 974 } 975 976 /* 977 * Try to write back as many pages as we just scanned. This 978 * tends to cause slow streaming writers to write data to the 979 * disk smoothly, at the dirtying rate, which is nice. But 980 * that's undesirable in laptop mode, where we *want* lumpy 981 * writeout. So in laptop mode, write out the whole world. 982 */ 983 if (total_scanned > sc.swap_cluster_max + sc.swap_cluster_max/2) { 984 wakeup_pdflush(laptop_mode ? 0 : total_scanned); 985 sc.may_writepage = 1; 986 } 987 988 /* Take a nap, wait for some writeback to complete */ 989 if (sc.nr_scanned && priority < DEF_PRIORITY - 2) 990 blk_congestion_wait(WRITE, HZ/10); 991 } 992 out: 993 for (i = 0; zones[i] != 0; i++) { 994 struct zone *zone = zones[i]; 995 996 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL)) 997 continue; 998 999 zone->prev_priority = zone->temp_priority; 1000 } 1001 return ret; 1002 } 1003 1004 /* 1005 * For kswapd, balance_pgdat() will work across all this node's zones until 1006 * they are all at pages_high. 1007 * 1008 * If `nr_pages' is non-zero then it is the number of pages which are to be 1009 * reclaimed, regardless of the zone occupancies. This is a software suspend 1010 * special. 1011 * 1012 * Returns the number of pages which were actually freed. 1013 * 1014 * There is special handling here for zones which are full of pinned pages. 1015 * This can happen if the pages are all mlocked, or if they are all used by 1016 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb. 1017 * What we do is to detect the case where all pages in the zone have been 1018 * scanned twice and there has been zero successful reclaim. Mark the zone as 1019 * dead and from now on, only perform a short scan. Basically we're polling 1020 * the zone for when the problem goes away. 1021 * 1022 * kswapd scans the zones in the highmem->normal->dma direction. It skips 1023 * zones which have free_pages > pages_high, but once a zone is found to have 1024 * free_pages <= pages_high, we scan that zone and the lower zones regardless 1025 * of the number of free pages in the lower zones. This interoperates with 1026 * the page allocator fallback scheme to ensure that aging of pages is balanced 1027 * across the zones. 1028 */ 1029 static int balance_pgdat(pg_data_t *pgdat, int nr_pages, int order) 1030 { 1031 int to_free = nr_pages; 1032 int all_zones_ok; 1033 int priority; 1034 int i; 1035 int total_scanned, total_reclaimed; 1036 struct reclaim_state *reclaim_state = current->reclaim_state; 1037 struct scan_control sc; 1038 1039 loop_again: 1040 total_scanned = 0; 1041 total_reclaimed = 0; 1042 sc.gfp_mask = GFP_KERNEL; 1043 sc.may_writepage = 0; 1044 sc.may_swap = 1; 1045 sc.nr_mapped = read_page_state(nr_mapped); 1046 1047 inc_page_state(pageoutrun); 1048 1049 for (i = 0; i < pgdat->nr_zones; i++) { 1050 struct zone *zone = pgdat->node_zones + i; 1051 1052 zone->temp_priority = DEF_PRIORITY; 1053 } 1054 1055 for (priority = DEF_PRIORITY; priority >= 0; priority--) { 1056 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ 1057 unsigned long lru_pages = 0; 1058 1059 all_zones_ok = 1; 1060 1061 if (nr_pages == 0) { 1062 /* 1063 * Scan in the highmem->dma direction for the highest 1064 * zone which needs scanning 1065 */ 1066 for (i = pgdat->nr_zones - 1; i >= 0; i--) { 1067 struct zone *zone = pgdat->node_zones + i; 1068 1069 if (zone->present_pages == 0) 1070 continue; 1071 1072 if (zone->all_unreclaimable && 1073 priority != DEF_PRIORITY) 1074 continue; 1075 1076 if (!zone_watermark_ok(zone, order, 1077 zone->pages_high, 0, 0, 0)) { 1078 end_zone = i; 1079 goto scan; 1080 } 1081 } 1082 goto out; 1083 } else { 1084 end_zone = pgdat->nr_zones - 1; 1085 } 1086 scan: 1087 for (i = 0; i <= end_zone; i++) { 1088 struct zone *zone = pgdat->node_zones + i; 1089 1090 lru_pages += zone->nr_active + zone->nr_inactive; 1091 } 1092 1093 /* 1094 * Now scan the zone in the dma->highmem direction, stopping 1095 * at the last zone which needs scanning. 1096 * 1097 * We do this because the page allocator works in the opposite 1098 * direction. This prevents the page allocator from allocating 1099 * pages behind kswapd's direction of progress, which would 1100 * cause too much scanning of the lower zones. 1101 */ 1102 for (i = 0; i <= end_zone; i++) { 1103 struct zone *zone = pgdat->node_zones + i; 1104 int nr_slab; 1105 1106 if (zone->present_pages == 0) 1107 continue; 1108 1109 if (zone->all_unreclaimable && priority != DEF_PRIORITY) 1110 continue; 1111 1112 if (nr_pages == 0) { /* Not software suspend */ 1113 if (!zone_watermark_ok(zone, order, 1114 zone->pages_high, end_zone, 0, 0)) 1115 all_zones_ok = 0; 1116 } 1117 zone->temp_priority = priority; 1118 if (zone->prev_priority > priority) 1119 zone->prev_priority = priority; 1120 sc.nr_scanned = 0; 1121 sc.nr_reclaimed = 0; 1122 sc.priority = priority; 1123 sc.swap_cluster_max = nr_pages? nr_pages : SWAP_CLUSTER_MAX; 1124 atomic_inc(&zone->reclaim_in_progress); 1125 shrink_zone(zone, &sc); 1126 atomic_dec(&zone->reclaim_in_progress); 1127 reclaim_state->reclaimed_slab = 0; 1128 nr_slab = shrink_slab(sc.nr_scanned, GFP_KERNEL, 1129 lru_pages); 1130 sc.nr_reclaimed += reclaim_state->reclaimed_slab; 1131 total_reclaimed += sc.nr_reclaimed; 1132 total_scanned += sc.nr_scanned; 1133 if (zone->all_unreclaimable) 1134 continue; 1135 if (nr_slab == 0 && zone->pages_scanned >= 1136 (zone->nr_active + zone->nr_inactive) * 4) 1137 zone->all_unreclaimable = 1; 1138 /* 1139 * If we've done a decent amount of scanning and 1140 * the reclaim ratio is low, start doing writepage 1141 * even in laptop mode 1142 */ 1143 if (total_scanned > SWAP_CLUSTER_MAX * 2 && 1144 total_scanned > total_reclaimed+total_reclaimed/2) 1145 sc.may_writepage = 1; 1146 } 1147 if (nr_pages && to_free > total_reclaimed) 1148 continue; /* swsusp: need to do more work */ 1149 if (all_zones_ok) 1150 break; /* kswapd: all done */ 1151 /* 1152 * OK, kswapd is getting into trouble. Take a nap, then take 1153 * another pass across the zones. 1154 */ 1155 if (total_scanned && priority < DEF_PRIORITY - 2) 1156 blk_congestion_wait(WRITE, HZ/10); 1157 1158 /* 1159 * We do this so kswapd doesn't build up large priorities for 1160 * example when it is freeing in parallel with allocators. It 1161 * matches the direct reclaim path behaviour in terms of impact 1162 * on zone->*_priority. 1163 */ 1164 if ((total_reclaimed >= SWAP_CLUSTER_MAX) && (!nr_pages)) 1165 break; 1166 } 1167 out: 1168 for (i = 0; i < pgdat->nr_zones; i++) { 1169 struct zone *zone = pgdat->node_zones + i; 1170 1171 zone->prev_priority = zone->temp_priority; 1172 } 1173 if (!all_zones_ok) { 1174 cond_resched(); 1175 goto loop_again; 1176 } 1177 1178 return total_reclaimed; 1179 } 1180 1181 /* 1182 * The background pageout daemon, started as a kernel thread 1183 * from the init process. 1184 * 1185 * This basically trickles out pages so that we have _some_ 1186 * free memory available even if there is no other activity 1187 * that frees anything up. This is needed for things like routing 1188 * etc, where we otherwise might have all activity going on in 1189 * asynchronous contexts that cannot page things out. 1190 * 1191 * If there are applications that are active memory-allocators 1192 * (most normal use), this basically shouldn't matter. 1193 */ 1194 static int kswapd(void *p) 1195 { 1196 unsigned long order; 1197 pg_data_t *pgdat = (pg_data_t*)p; 1198 struct task_struct *tsk = current; 1199 DEFINE_WAIT(wait); 1200 struct reclaim_state reclaim_state = { 1201 .reclaimed_slab = 0, 1202 }; 1203 cpumask_t cpumask; 1204 1205 daemonize("kswapd%d", pgdat->node_id); 1206 cpumask = node_to_cpumask(pgdat->node_id); 1207 if (!cpus_empty(cpumask)) 1208 set_cpus_allowed(tsk, cpumask); 1209 current->reclaim_state = &reclaim_state; 1210 1211 /* 1212 * Tell the memory management that we're a "memory allocator", 1213 * and that if we need more memory we should get access to it 1214 * regardless (see "__alloc_pages()"). "kswapd" should 1215 * never get caught in the normal page freeing logic. 1216 * 1217 * (Kswapd normally doesn't need memory anyway, but sometimes 1218 * you need a small amount of memory in order to be able to 1219 * page out something else, and this flag essentially protects 1220 * us from recursively trying to free more memory as we're 1221 * trying to free the first piece of memory in the first place). 1222 */ 1223 tsk->flags |= PF_MEMALLOC|PF_KSWAPD; 1224 1225 order = 0; 1226 for ( ; ; ) { 1227 unsigned long new_order; 1228 1229 try_to_freeze(); 1230 1231 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); 1232 new_order = pgdat->kswapd_max_order; 1233 pgdat->kswapd_max_order = 0; 1234 if (order < new_order) { 1235 /* 1236 * Don't sleep if someone wants a larger 'order' 1237 * allocation 1238 */ 1239 order = new_order; 1240 } else { 1241 schedule(); 1242 order = pgdat->kswapd_max_order; 1243 } 1244 finish_wait(&pgdat->kswapd_wait, &wait); 1245 1246 balance_pgdat(pgdat, 0, order); 1247 } 1248 return 0; 1249 } 1250 1251 /* 1252 * A zone is low on free memory, so wake its kswapd task to service it. 1253 */ 1254 void wakeup_kswapd(struct zone *zone, int order) 1255 { 1256 pg_data_t *pgdat; 1257 1258 if (zone->present_pages == 0) 1259 return; 1260 1261 pgdat = zone->zone_pgdat; 1262 if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0, 0)) 1263 return; 1264 if (pgdat->kswapd_max_order < order) 1265 pgdat->kswapd_max_order = order; 1266 if (!cpuset_zone_allowed(zone, __GFP_HARDWALL)) 1267 return; 1268 if (!waitqueue_active(&pgdat->kswapd_wait)) 1269 return; 1270 wake_up_interruptible(&pgdat->kswapd_wait); 1271 } 1272 1273 #ifdef CONFIG_PM 1274 /* 1275 * Try to free `nr_pages' of memory, system-wide. Returns the number of freed 1276 * pages. 1277 */ 1278 int shrink_all_memory(int nr_pages) 1279 { 1280 pg_data_t *pgdat; 1281 int nr_to_free = nr_pages; 1282 int ret = 0; 1283 struct reclaim_state reclaim_state = { 1284 .reclaimed_slab = 0, 1285 }; 1286 1287 current->reclaim_state = &reclaim_state; 1288 for_each_pgdat(pgdat) { 1289 int freed; 1290 freed = balance_pgdat(pgdat, nr_to_free, 0); 1291 ret += freed; 1292 nr_to_free -= freed; 1293 if (nr_to_free <= 0) 1294 break; 1295 } 1296 current->reclaim_state = NULL; 1297 return ret; 1298 } 1299 #endif 1300 1301 #ifdef CONFIG_HOTPLUG_CPU 1302 /* It's optimal to keep kswapds on the same CPUs as their memory, but 1303 not required for correctness. So if the last cpu in a node goes 1304 away, we get changed to run anywhere: as the first one comes back, 1305 restore their cpu bindings. */ 1306 static int __devinit cpu_callback(struct notifier_block *nfb, 1307 unsigned long action, 1308 void *hcpu) 1309 { 1310 pg_data_t *pgdat; 1311 cpumask_t mask; 1312 1313 if (action == CPU_ONLINE) { 1314 for_each_pgdat(pgdat) { 1315 mask = node_to_cpumask(pgdat->node_id); 1316 if (any_online_cpu(mask) != NR_CPUS) 1317 /* One of our CPUs online: restore mask */ 1318 set_cpus_allowed(pgdat->kswapd, mask); 1319 } 1320 } 1321 return NOTIFY_OK; 1322 } 1323 #endif /* CONFIG_HOTPLUG_CPU */ 1324 1325 static int __init kswapd_init(void) 1326 { 1327 pg_data_t *pgdat; 1328 swap_setup(); 1329 for_each_pgdat(pgdat) 1330 pgdat->kswapd 1331 = find_task_by_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL)); 1332 total_memory = nr_free_pagecache_pages(); 1333 hotcpu_notifier(cpu_callback, 0); 1334 return 0; 1335 } 1336 1337 module_init(kswapd_init) 1338 1339 1340 /* 1341 * Try to free up some pages from this zone through reclaim. 1342 */ 1343 int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order) 1344 { 1345 struct scan_control sc; 1346 int nr_pages = 1 << order; 1347 int total_reclaimed = 0; 1348 1349 /* The reclaim may sleep, so don't do it if sleep isn't allowed */ 1350 if (!(gfp_mask & __GFP_WAIT)) 1351 return 0; 1352 if (zone->all_unreclaimable) 1353 return 0; 1354 1355 sc.gfp_mask = gfp_mask; 1356 sc.may_writepage = 0; 1357 sc.may_swap = 0; 1358 sc.nr_mapped = read_page_state(nr_mapped); 1359 sc.nr_scanned = 0; 1360 sc.nr_reclaimed = 0; 1361 /* scan at the highest priority */ 1362 sc.priority = 0; 1363 1364 if (nr_pages > SWAP_CLUSTER_MAX) 1365 sc.swap_cluster_max = nr_pages; 1366 else 1367 sc.swap_cluster_max = SWAP_CLUSTER_MAX; 1368 1369 /* Don't reclaim the zone if there are other reclaimers active */ 1370 if (atomic_read(&zone->reclaim_in_progress) > 0) 1371 goto out; 1372 1373 shrink_zone(zone, &sc); 1374 total_reclaimed = sc.nr_reclaimed; 1375 1376 out: 1377 return total_reclaimed; 1378 } 1379 1380 asmlinkage long sys_set_zone_reclaim(unsigned int node, unsigned int zone, 1381 unsigned int state) 1382 { 1383 struct zone *z; 1384 int i; 1385 1386 if (!capable(CAP_SYS_ADMIN)) 1387 return -EACCES; 1388 1389 if (node >= MAX_NUMNODES || !node_online(node)) 1390 return -EINVAL; 1391 1392 /* This will break if we ever add more zones */ 1393 if (!(zone & (1<<ZONE_DMA|1<<ZONE_NORMAL|1<<ZONE_HIGHMEM))) 1394 return -EINVAL; 1395 1396 for (i = 0; i < MAX_NR_ZONES; i++) { 1397 if (!(zone & 1<<i)) 1398 continue; 1399 1400 z = &NODE_DATA(node)->node_zones[i]; 1401 1402 if (state) 1403 z->reclaim_pages = 1; 1404 else 1405 z->reclaim_pages = 0; 1406 } 1407 1408 return 0; 1409 } 1410