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/suspend.h> 25 #include <linux/blkdev.h> 26 #include <linux/buffer_head.h> /* for try_to_release_page(), 27 buffer_heads_over_limit */ 28 #include <linux/mm_inline.h> 29 #include <linux/pagevec.h> 30 #include <linux/backing-dev.h> 31 #include <linux/rmap.h> 32 #include <linux/topology.h> 33 #include <linux/cpu.h> 34 #include <linux/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 unsigned int gfp_mask; 74 75 int may_writepage; 76 }; 77 78 /* 79 * The list of shrinker callbacks used by to apply pressure to 80 * ageable caches. 81 */ 82 struct shrinker { 83 shrinker_t shrinker; 84 struct list_head list; 85 int seeks; /* seeks to recreate an obj */ 86 long nr; /* objs pending delete */ 87 }; 88 89 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru)) 90 91 #ifdef ARCH_HAS_PREFETCH 92 #define prefetch_prev_lru_page(_page, _base, _field) \ 93 do { \ 94 if ((_page)->lru.prev != _base) { \ 95 struct page *prev; \ 96 \ 97 prev = lru_to_page(&(_page->lru)); \ 98 prefetch(&prev->_field); \ 99 } \ 100 } while (0) 101 #else 102 #define prefetch_prev_lru_page(_page, _base, _field) do { } while (0) 103 #endif 104 105 #ifdef ARCH_HAS_PREFETCHW 106 #define prefetchw_prev_lru_page(_page, _base, _field) \ 107 do { \ 108 if ((_page)->lru.prev != _base) { \ 109 struct page *prev; \ 110 \ 111 prev = lru_to_page(&(_page->lru)); \ 112 prefetchw(&prev->_field); \ 113 } \ 114 } while (0) 115 #else 116 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0) 117 #endif 118 119 /* 120 * From 0 .. 100. Higher means more swappy. 121 */ 122 int vm_swappiness = 60; 123 static long total_memory; 124 125 static LIST_HEAD(shrinker_list); 126 static DECLARE_RWSEM(shrinker_rwsem); 127 128 /* 129 * Add a shrinker callback to be called from the vm 130 */ 131 struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker) 132 { 133 struct shrinker *shrinker; 134 135 shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL); 136 if (shrinker) { 137 shrinker->shrinker = theshrinker; 138 shrinker->seeks = seeks; 139 shrinker->nr = 0; 140 down_write(&shrinker_rwsem); 141 list_add(&shrinker->list, &shrinker_list); 142 up_write(&shrinker_rwsem); 143 } 144 return shrinker; 145 } 146 EXPORT_SYMBOL(set_shrinker); 147 148 /* 149 * Remove one 150 */ 151 void remove_shrinker(struct shrinker *shrinker) 152 { 153 down_write(&shrinker_rwsem); 154 list_del(&shrinker->list); 155 up_write(&shrinker_rwsem); 156 kfree(shrinker); 157 } 158 EXPORT_SYMBOL(remove_shrinker); 159 160 #define SHRINK_BATCH 128 161 /* 162 * Call the shrink functions to age shrinkable caches 163 * 164 * Here we assume it costs one seek to replace a lru page and that it also 165 * takes a seek to recreate a cache object. With this in mind we age equal 166 * percentages of the lru and ageable caches. This should balance the seeks 167 * generated by these structures. 168 * 169 * If the vm encounted mapped pages on the LRU it increase the pressure on 170 * slab to avoid swapping. 171 * 172 * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits. 173 * 174 * `lru_pages' represents the number of on-LRU pages in all the zones which 175 * are eligible for the caller's allocation attempt. It is used for balancing 176 * slab reclaim versus page reclaim. 177 */ 178 static int shrink_slab(unsigned long scanned, unsigned int gfp_mask, 179 unsigned long lru_pages) 180 { 181 struct shrinker *shrinker; 182 183 if (scanned == 0) 184 scanned = SWAP_CLUSTER_MAX; 185 186 if (!down_read_trylock(&shrinker_rwsem)) 187 return 0; 188 189 list_for_each_entry(shrinker, &shrinker_list, list) { 190 unsigned long long delta; 191 unsigned long total_scan; 192 193 delta = (4 * scanned) / shrinker->seeks; 194 delta *= (*shrinker->shrinker)(0, gfp_mask); 195 do_div(delta, lru_pages + 1); 196 shrinker->nr += delta; 197 if (shrinker->nr < 0) 198 shrinker->nr = LONG_MAX; /* It wrapped! */ 199 200 total_scan = shrinker->nr; 201 shrinker->nr = 0; 202 203 while (total_scan >= SHRINK_BATCH) { 204 long this_scan = SHRINK_BATCH; 205 int shrink_ret; 206 207 shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask); 208 if (shrink_ret == -1) 209 break; 210 mod_page_state(slabs_scanned, this_scan); 211 total_scan -= this_scan; 212 213 cond_resched(); 214 } 215 216 shrinker->nr += total_scan; 217 } 218 up_read(&shrinker_rwsem); 219 return 0; 220 } 221 222 /* Must be called with page's rmap lock held. */ 223 static inline int page_mapping_inuse(struct page *page) 224 { 225 struct address_space *mapping; 226 227 /* Page is in somebody's page tables. */ 228 if (page_mapped(page)) 229 return 1; 230 231 /* Be more reluctant to reclaim swapcache than pagecache */ 232 if (PageSwapCache(page)) 233 return 1; 234 235 mapping = page_mapping(page); 236 if (!mapping) 237 return 0; 238 239 /* File is mmap'd by somebody? */ 240 return mapping_mapped(mapping); 241 } 242 243 static inline int is_page_cache_freeable(struct page *page) 244 { 245 return page_count(page) - !!PagePrivate(page) == 2; 246 } 247 248 static int may_write_to_queue(struct backing_dev_info *bdi) 249 { 250 if (current_is_kswapd()) 251 return 1; 252 if (current_is_pdflush()) /* This is unlikely, but why not... */ 253 return 1; 254 if (!bdi_write_congested(bdi)) 255 return 1; 256 if (bdi == current->backing_dev_info) 257 return 1; 258 return 0; 259 } 260 261 /* 262 * We detected a synchronous write error writing a page out. Probably 263 * -ENOSPC. We need to propagate that into the address_space for a subsequent 264 * fsync(), msync() or close(). 265 * 266 * The tricky part is that after writepage we cannot touch the mapping: nothing 267 * prevents it from being freed up. But we have a ref on the page and once 268 * that page is locked, the mapping is pinned. 269 * 270 * We're allowed to run sleeping lock_page() here because we know the caller has 271 * __GFP_FS. 272 */ 273 static void handle_write_error(struct address_space *mapping, 274 struct page *page, int error) 275 { 276 lock_page(page); 277 if (page_mapping(page) == mapping) { 278 if (error == -ENOSPC) 279 set_bit(AS_ENOSPC, &mapping->flags); 280 else 281 set_bit(AS_EIO, &mapping->flags); 282 } 283 unlock_page(page); 284 } 285 286 /* 287 * pageout is called by shrink_list() for each dirty page. Calls ->writepage(). 288 */ 289 static pageout_t pageout(struct page *page, struct address_space *mapping) 290 { 291 /* 292 * If the page is dirty, only perform writeback if that write 293 * will be non-blocking. To prevent this allocation from being 294 * stalled by pagecache activity. But note that there may be 295 * stalls if we need to run get_block(). We could test 296 * PagePrivate for that. 297 * 298 * If this process is currently in generic_file_write() against 299 * this page's queue, we can perform writeback even if that 300 * will block. 301 * 302 * If the page is swapcache, write it back even if that would 303 * block, for some throttling. This happens by accident, because 304 * swap_backing_dev_info is bust: it doesn't reflect the 305 * congestion state of the swapdevs. Easy to fix, if needed. 306 * See swapfile.c:page_queue_congested(). 307 */ 308 if (!is_page_cache_freeable(page)) 309 return PAGE_KEEP; 310 if (!mapping) 311 return PAGE_KEEP; 312 if (mapping->a_ops->writepage == NULL) 313 return PAGE_ACTIVATE; 314 if (!may_write_to_queue(mapping->backing_dev_info)) 315 return PAGE_KEEP; 316 317 if (clear_page_dirty_for_io(page)) { 318 int res; 319 struct writeback_control wbc = { 320 .sync_mode = WB_SYNC_NONE, 321 .nr_to_write = SWAP_CLUSTER_MAX, 322 .nonblocking = 1, 323 .for_reclaim = 1, 324 }; 325 326 SetPageReclaim(page); 327 res = mapping->a_ops->writepage(page, &wbc); 328 if (res < 0) 329 handle_write_error(mapping, page, res); 330 if (res == WRITEPAGE_ACTIVATE) { 331 ClearPageReclaim(page); 332 return PAGE_ACTIVATE; 333 } 334 if (!PageWriteback(page)) { 335 /* synchronous write or broken a_ops? */ 336 ClearPageReclaim(page); 337 } 338 339 return PAGE_SUCCESS; 340 } 341 342 return PAGE_CLEAN; 343 } 344 345 /* 346 * shrink_list adds the number of reclaimed pages to sc->nr_reclaimed 347 */ 348 static int shrink_list(struct list_head *page_list, struct scan_control *sc) 349 { 350 LIST_HEAD(ret_pages); 351 struct pagevec freed_pvec; 352 int pgactivate = 0; 353 int reclaimed = 0; 354 355 cond_resched(); 356 357 pagevec_init(&freed_pvec, 1); 358 while (!list_empty(page_list)) { 359 struct address_space *mapping; 360 struct page *page; 361 int may_enter_fs; 362 int referenced; 363 364 page = lru_to_page(page_list); 365 list_del(&page->lru); 366 367 if (TestSetPageLocked(page)) 368 goto keep; 369 370 BUG_ON(PageActive(page)); 371 372 if (PageWriteback(page)) 373 goto keep_locked; 374 375 sc->nr_scanned++; 376 /* Double the slab pressure for mapped and swapcache pages */ 377 if (page_mapped(page) || PageSwapCache(page)) 378 sc->nr_scanned++; 379 380 page_map_lock(page); 381 referenced = page_referenced(page); 382 if (referenced && page_mapping_inuse(page)) { 383 /* In active use or really unfreeable. Activate it. */ 384 page_map_unlock(page); 385 goto activate_locked; 386 } 387 388 #ifdef CONFIG_SWAP 389 /* 390 * Anonymous process memory has backing store? 391 * Try to allocate it some swap space here. 392 * 393 * XXX: implement swap clustering ? 394 */ 395 if (PageAnon(page) && !PageSwapCache(page)) { 396 page_map_unlock(page); 397 if (!add_to_swap(page)) 398 goto activate_locked; 399 page_map_lock(page); 400 } 401 #endif /* CONFIG_SWAP */ 402 403 mapping = page_mapping(page); 404 may_enter_fs = (sc->gfp_mask & __GFP_FS) || 405 (PageSwapCache(page) && (sc->gfp_mask & __GFP_IO)); 406 407 /* 408 * The page is mapped into the page tables of one or more 409 * processes. Try to unmap it here. 410 */ 411 if (page_mapped(page) && mapping) { 412 switch (try_to_unmap(page)) { 413 case SWAP_FAIL: 414 page_map_unlock(page); 415 goto activate_locked; 416 case SWAP_AGAIN: 417 page_map_unlock(page); 418 goto keep_locked; 419 case SWAP_SUCCESS: 420 ; /* try to free the page below */ 421 } 422 } 423 page_map_unlock(page); 424 425 if (PageDirty(page)) { 426 if (referenced) 427 goto keep_locked; 428 if (!may_enter_fs) 429 goto keep_locked; 430 if (laptop_mode && !sc->may_writepage) 431 goto keep_locked; 432 433 /* Page is dirty, try to write it out here */ 434 switch(pageout(page, mapping)) { 435 case PAGE_KEEP: 436 goto keep_locked; 437 case PAGE_ACTIVATE: 438 goto activate_locked; 439 case PAGE_SUCCESS: 440 if (PageWriteback(page) || PageDirty(page)) 441 goto keep; 442 /* 443 * A synchronous write - probably a ramdisk. Go 444 * ahead and try to reclaim the page. 445 */ 446 if (TestSetPageLocked(page)) 447 goto keep; 448 if (PageDirty(page) || PageWriteback(page)) 449 goto keep_locked; 450 mapping = page_mapping(page); 451 case PAGE_CLEAN: 452 ; /* try to free the page below */ 453 } 454 } 455 456 /* 457 * If the page has buffers, try to free the buffer mappings 458 * associated with this page. If we succeed we try to free 459 * the page as well. 460 * 461 * We do this even if the page is PageDirty(). 462 * try_to_release_page() does not perform I/O, but it is 463 * possible for a page to have PageDirty set, but it is actually 464 * clean (all its buffers are clean). This happens if the 465 * buffers were written out directly, with submit_bh(). ext3 466 * will do this, as well as the blockdev mapping. 467 * try_to_release_page() will discover that cleanness and will 468 * drop the buffers and mark the page clean - it can be freed. 469 * 470 * Rarely, pages can have buffers and no ->mapping. These are 471 * the pages which were not successfully invalidated in 472 * truncate_complete_page(). We try to drop those buffers here 473 * and if that worked, and the page is no longer mapped into 474 * process address space (page_count == 1) it can be freed. 475 * Otherwise, leave the page on the LRU so it is swappable. 476 */ 477 if (PagePrivate(page)) { 478 if (!try_to_release_page(page, sc->gfp_mask)) 479 goto activate_locked; 480 if (!mapping && page_count(page) == 1) 481 goto free_it; 482 } 483 484 if (!mapping) 485 goto keep_locked; /* truncate got there first */ 486 487 spin_lock_irq(&mapping->tree_lock); 488 489 /* 490 * The non-racy check for busy page. It is critical to check 491 * PageDirty _after_ making sure that the page is freeable and 492 * not in use by anybody. (pagecache + us == 2) 493 */ 494 if (page_count(page) != 2 || PageDirty(page)) { 495 spin_unlock_irq(&mapping->tree_lock); 496 goto keep_locked; 497 } 498 499 #ifdef CONFIG_SWAP 500 if (PageSwapCache(page)) { 501 swp_entry_t swap = { .val = page->private }; 502 __delete_from_swap_cache(page); 503 spin_unlock_irq(&mapping->tree_lock); 504 swap_free(swap); 505 __put_page(page); /* The pagecache ref */ 506 goto free_it; 507 } 508 #endif /* CONFIG_SWAP */ 509 510 __remove_from_page_cache(page); 511 spin_unlock_irq(&mapping->tree_lock); 512 __put_page(page); 513 514 free_it: 515 unlock_page(page); 516 reclaimed++; 517 if (!pagevec_add(&freed_pvec, page)) 518 __pagevec_release_nonlru(&freed_pvec); 519 continue; 520 521 activate_locked: 522 SetPageActive(page); 523 pgactivate++; 524 keep_locked: 525 unlock_page(page); 526 keep: 527 list_add(&page->lru, &ret_pages); 528 BUG_ON(PageLRU(page)); 529 } 530 list_splice(&ret_pages, page_list); 531 if (pagevec_count(&freed_pvec)) 532 __pagevec_release_nonlru(&freed_pvec); 533 mod_page_state(pgactivate, pgactivate); 534 sc->nr_reclaimed += reclaimed; 535 return reclaimed; 536 } 537 538 /* 539 * zone->lru_lock is heavily contented. We relieve it by quickly privatising 540 * a batch of pages and working on them outside the lock. Any pages which were 541 * not freed will be added back to the LRU. 542 * 543 * shrink_cache() adds the number of pages reclaimed to sc->nr_reclaimed 544 * 545 * For pagecache intensive workloads, the first loop here is the hottest spot 546 * in the kernel (apart from the copy_*_user functions). 547 */ 548 static void shrink_cache(struct zone *zone, struct scan_control *sc) 549 { 550 LIST_HEAD(page_list); 551 struct pagevec pvec; 552 int max_scan = sc->nr_to_scan; 553 554 pagevec_init(&pvec, 1); 555 556 lru_add_drain(); 557 spin_lock_irq(&zone->lru_lock); 558 while (max_scan > 0) { 559 struct page *page; 560 int nr_taken = 0; 561 int nr_scan = 0; 562 int nr_freed; 563 564 while (nr_scan++ < SWAP_CLUSTER_MAX && 565 !list_empty(&zone->inactive_list)) { 566 page = lru_to_page(&zone->inactive_list); 567 568 prefetchw_prev_lru_page(page, 569 &zone->inactive_list, flags); 570 571 if (!TestClearPageLRU(page)) 572 BUG(); 573 list_del(&page->lru); 574 if (get_page_testone(page)) { 575 /* 576 * It is being freed elsewhere 577 */ 578 __put_page(page); 579 SetPageLRU(page); 580 list_add(&page->lru, &zone->inactive_list); 581 continue; 582 } 583 list_add(&page->lru, &page_list); 584 nr_taken++; 585 } 586 zone->nr_inactive -= nr_taken; 587 spin_unlock_irq(&zone->lru_lock); 588 589 if (nr_taken == 0) 590 goto done; 591 592 max_scan -= nr_scan; 593 if (current_is_kswapd()) 594 mod_page_state_zone(zone, pgscan_kswapd, nr_scan); 595 else 596 mod_page_state_zone(zone, pgscan_direct, nr_scan); 597 nr_freed = shrink_list(&page_list, sc); 598 if (current_is_kswapd()) 599 mod_page_state(kswapd_steal, nr_freed); 600 mod_page_state_zone(zone, pgsteal, nr_freed); 601 sc->nr_to_reclaim -= nr_freed; 602 603 spin_lock_irq(&zone->lru_lock); 604 /* 605 * Put back any unfreeable pages. 606 */ 607 while (!list_empty(&page_list)) { 608 page = lru_to_page(&page_list); 609 if (TestSetPageLRU(page)) 610 BUG(); 611 list_del(&page->lru); 612 if (PageActive(page)) 613 add_page_to_active_list(zone, page); 614 else 615 add_page_to_inactive_list(zone, page); 616 if (!pagevec_add(&pvec, page)) { 617 spin_unlock_irq(&zone->lru_lock); 618 __pagevec_release(&pvec); 619 spin_lock_irq(&zone->lru_lock); 620 } 621 } 622 } 623 spin_unlock_irq(&zone->lru_lock); 624 done: 625 pagevec_release(&pvec); 626 } 627 628 /* 629 * This moves pages from the active list to the inactive list. 630 * 631 * We move them the other way if the page is referenced by one or more 632 * processes, from rmap. 633 * 634 * If the pages are mostly unmapped, the processing is fast and it is 635 * appropriate to hold zone->lru_lock across the whole operation. But if 636 * the pages are mapped, the processing is slow (page_referenced()) so we 637 * should drop zone->lru_lock around each page. It's impossible to balance 638 * this, so instead we remove the pages from the LRU while processing them. 639 * It is safe to rely on PG_active against the non-LRU pages in here because 640 * nobody will play with that bit on a non-LRU page. 641 * 642 * The downside is that we have to touch page->_count against each page. 643 * But we had to alter page->flags anyway. 644 */ 645 static void 646 refill_inactive_zone(struct zone *zone, struct scan_control *sc) 647 { 648 int pgmoved; 649 int pgdeactivate = 0; 650 int pgscanned = 0; 651 int nr_pages = sc->nr_to_scan; 652 LIST_HEAD(l_hold); /* The pages which were snipped off */ 653 LIST_HEAD(l_inactive); /* Pages to go onto the inactive_list */ 654 LIST_HEAD(l_active); /* Pages to go onto the active_list */ 655 struct page *page; 656 struct pagevec pvec; 657 int reclaim_mapped = 0; 658 long mapped_ratio; 659 long distress; 660 long swap_tendency; 661 662 lru_add_drain(); 663 pgmoved = 0; 664 spin_lock_irq(&zone->lru_lock); 665 while (pgscanned < nr_pages && !list_empty(&zone->active_list)) { 666 page = lru_to_page(&zone->active_list); 667 prefetchw_prev_lru_page(page, &zone->active_list, flags); 668 if (!TestClearPageLRU(page)) 669 BUG(); 670 list_del(&page->lru); 671 if (get_page_testone(page)) { 672 /* 673 * It was already free! release_pages() or put_page() 674 * are about to remove it from the LRU and free it. So 675 * put the refcount back and put the page back on the 676 * LRU 677 */ 678 __put_page(page); 679 SetPageLRU(page); 680 list_add(&page->lru, &zone->active_list); 681 } else { 682 list_add(&page->lru, &l_hold); 683 pgmoved++; 684 } 685 pgscanned++; 686 } 687 zone->pages_scanned += pgscanned; 688 zone->nr_active -= pgmoved; 689 spin_unlock_irq(&zone->lru_lock); 690 691 /* 692 * `distress' is a measure of how much trouble we're having reclaiming 693 * pages. 0 -> no problems. 100 -> great trouble. 694 */ 695 distress = 100 >> zone->prev_priority; 696 697 /* 698 * The point of this algorithm is to decide when to start reclaiming 699 * mapped memory instead of just pagecache. Work out how much memory 700 * is mapped. 701 */ 702 mapped_ratio = (sc->nr_mapped * 100) / total_memory; 703 704 /* 705 * Now decide how much we really want to unmap some pages. The mapped 706 * ratio is downgraded - just because there's a lot of mapped memory 707 * doesn't necessarily mean that page reclaim isn't succeeding. 708 * 709 * The distress ratio is important - we don't want to start going oom. 710 * 711 * A 100% value of vm_swappiness overrides this algorithm altogether. 712 */ 713 swap_tendency = mapped_ratio / 2 + distress + vm_swappiness; 714 715 /* 716 * Now use this metric to decide whether to start moving mapped memory 717 * onto the inactive list. 718 */ 719 if (swap_tendency >= 100) 720 reclaim_mapped = 1; 721 722 while (!list_empty(&l_hold)) { 723 page = lru_to_page(&l_hold); 724 list_del(&page->lru); 725 if (page_mapped(page)) { 726 if (!reclaim_mapped) { 727 list_add(&page->lru, &l_active); 728 continue; 729 } 730 page_map_lock(page); 731 if (page_referenced(page)) { 732 page_map_unlock(page); 733 list_add(&page->lru, &l_active); 734 continue; 735 } 736 page_map_unlock(page); 737 } 738 /* 739 * FIXME: need to consider page_count(page) here if/when we 740 * reap orphaned pages via the LRU (Daniel's locking stuff) 741 */ 742 if (total_swap_pages == 0 && PageAnon(page)) { 743 list_add(&page->lru, &l_active); 744 continue; 745 } 746 list_add(&page->lru, &l_inactive); 747 } 748 749 pagevec_init(&pvec, 1); 750 pgmoved = 0; 751 spin_lock_irq(&zone->lru_lock); 752 while (!list_empty(&l_inactive)) { 753 page = lru_to_page(&l_inactive); 754 prefetchw_prev_lru_page(page, &l_inactive, flags); 755 if (TestSetPageLRU(page)) 756 BUG(); 757 if (!TestClearPageActive(page)) 758 BUG(); 759 list_move(&page->lru, &zone->inactive_list); 760 pgmoved++; 761 if (!pagevec_add(&pvec, page)) { 762 zone->nr_inactive += pgmoved; 763 spin_unlock_irq(&zone->lru_lock); 764 pgdeactivate += pgmoved; 765 pgmoved = 0; 766 if (buffer_heads_over_limit) 767 pagevec_strip(&pvec); 768 __pagevec_release(&pvec); 769 spin_lock_irq(&zone->lru_lock); 770 } 771 } 772 zone->nr_inactive += pgmoved; 773 pgdeactivate += pgmoved; 774 if (buffer_heads_over_limit) { 775 spin_unlock_irq(&zone->lru_lock); 776 pagevec_strip(&pvec); 777 spin_lock_irq(&zone->lru_lock); 778 } 779 780 pgmoved = 0; 781 while (!list_empty(&l_active)) { 782 page = lru_to_page(&l_active); 783 prefetchw_prev_lru_page(page, &l_active, flags); 784 if (TestSetPageLRU(page)) 785 BUG(); 786 BUG_ON(!PageActive(page)); 787 list_move(&page->lru, &zone->active_list); 788 pgmoved++; 789 if (!pagevec_add(&pvec, page)) { 790 zone->nr_active += pgmoved; 791 pgmoved = 0; 792 spin_unlock_irq(&zone->lru_lock); 793 __pagevec_release(&pvec); 794 spin_lock_irq(&zone->lru_lock); 795 } 796 } 797 zone->nr_active += pgmoved; 798 spin_unlock_irq(&zone->lru_lock); 799 pagevec_release(&pvec); 800 801 mod_page_state_zone(zone, pgrefill, pgscanned); 802 mod_page_state(pgdeactivate, pgdeactivate); 803 } 804 805 /* 806 * This is a basic per-zone page freer. Used by both kswapd and direct reclaim. 807 */ 808 static void 809 shrink_zone(struct zone *zone, struct scan_control *sc) 810 { 811 unsigned long nr_active; 812 unsigned long nr_inactive; 813 814 /* 815 * Add one to `nr_to_scan' just to make sure that the kernel will 816 * slowly sift through the active list. 817 */ 818 zone->nr_scan_active += (zone->nr_active >> sc->priority) + 1; 819 nr_active = zone->nr_scan_active; 820 if (nr_active >= SWAP_CLUSTER_MAX) 821 zone->nr_scan_active = 0; 822 else 823 nr_active = 0; 824 825 zone->nr_scan_inactive += (zone->nr_inactive >> sc->priority) + 1; 826 nr_inactive = zone->nr_scan_inactive; 827 if (nr_inactive >= SWAP_CLUSTER_MAX) 828 zone->nr_scan_inactive = 0; 829 else 830 nr_inactive = 0; 831 832 sc->nr_to_reclaim = SWAP_CLUSTER_MAX; 833 834 while (nr_active || nr_inactive) { 835 if (nr_active) { 836 sc->nr_to_scan = min(nr_active, 837 (unsigned long)SWAP_CLUSTER_MAX); 838 nr_active -= sc->nr_to_scan; 839 refill_inactive_zone(zone, sc); 840 } 841 842 if (nr_inactive) { 843 sc->nr_to_scan = min(nr_inactive, 844 (unsigned long)SWAP_CLUSTER_MAX); 845 nr_inactive -= sc->nr_to_scan; 846 shrink_cache(zone, sc); 847 if (sc->nr_to_reclaim <= 0) 848 break; 849 } 850 } 851 } 852 853 /* 854 * This is the direct reclaim path, for page-allocating processes. We only 855 * try to reclaim pages from zones which will satisfy the caller's allocation 856 * request. 857 * 858 * We reclaim from a zone even if that zone is over pages_high. Because: 859 * a) The caller may be trying to free *extra* pages to satisfy a higher-order 860 * allocation or 861 * b) The zones may be over pages_high but they must go *over* pages_high to 862 * satisfy the `incremental min' zone defense algorithm. 863 * 864 * Returns the number of reclaimed pages. 865 * 866 * If a zone is deemed to be full of pinned pages then just give it a light 867 * scan then give up on it. 868 */ 869 static void 870 shrink_caches(struct zone **zones, struct scan_control *sc) 871 { 872 int i; 873 874 for (i = 0; zones[i] != NULL; i++) { 875 struct zone *zone = zones[i]; 876 877 if (zone->present_pages == 0) 878 continue; 879 880 zone->temp_priority = sc->priority; 881 if (zone->prev_priority > sc->priority) 882 zone->prev_priority = sc->priority; 883 884 if (zone->all_unreclaimable && sc->priority != DEF_PRIORITY) 885 continue; /* Let kswapd poll it */ 886 887 shrink_zone(zone, sc); 888 } 889 } 890 891 /* 892 * This is the main entry point to direct page reclaim. 893 * 894 * If a full scan of the inactive list fails to free enough memory then we 895 * are "out of memory" and something needs to be killed. 896 * 897 * If the caller is !__GFP_FS then the probability of a failure is reasonably 898 * high - the zone may be full of dirty or under-writeback pages, which this 899 * caller can't do much about. We kick pdflush and take explicit naps in the 900 * hope that some of these pages can be written. But if the allocating task 901 * holds filesystem locks which prevent writeout this might not work, and the 902 * allocation attempt will fail. 903 */ 904 int try_to_free_pages(struct zone **zones, 905 unsigned int gfp_mask, unsigned int order) 906 { 907 int priority; 908 int ret = 0; 909 int total_scanned = 0, total_reclaimed = 0; 910 struct reclaim_state *reclaim_state = current->reclaim_state; 911 struct scan_control sc; 912 unsigned long lru_pages = 0; 913 int i; 914 915 sc.gfp_mask = gfp_mask; 916 sc.may_writepage = 0; 917 918 inc_page_state(allocstall); 919 920 for (i = 0; zones[i] != NULL; i++) { 921 struct zone *zone = zones[i]; 922 923 zone->temp_priority = DEF_PRIORITY; 924 lru_pages += zone->nr_active + zone->nr_inactive; 925 } 926 927 for (priority = DEF_PRIORITY; priority >= 0; priority--) { 928 sc.nr_mapped = read_page_state(nr_mapped); 929 sc.nr_scanned = 0; 930 sc.nr_reclaimed = 0; 931 sc.priority = priority; 932 shrink_caches(zones, &sc); 933 shrink_slab(sc.nr_scanned, gfp_mask, lru_pages); 934 if (reclaim_state) { 935 sc.nr_reclaimed += reclaim_state->reclaimed_slab; 936 reclaim_state->reclaimed_slab = 0; 937 } 938 if (sc.nr_reclaimed >= SWAP_CLUSTER_MAX) { 939 ret = 1; 940 goto out; 941 } 942 total_scanned += sc.nr_scanned; 943 total_reclaimed += sc.nr_reclaimed; 944 945 /* 946 * Try to write back as many pages as we just scanned. This 947 * tends to cause slow streaming writers to write data to the 948 * disk smoothly, at the dirtying rate, which is nice. But 949 * that's undesirable in laptop mode, where we *want* lumpy 950 * writeout. So in laptop mode, write out the whole world. 951 */ 952 if (total_scanned > SWAP_CLUSTER_MAX + SWAP_CLUSTER_MAX/2) { 953 wakeup_bdflush(laptop_mode ? 0 : total_scanned); 954 sc.may_writepage = 1; 955 } 956 957 /* Take a nap, wait for some writeback to complete */ 958 if (sc.nr_scanned && priority < DEF_PRIORITY - 2) 959 blk_congestion_wait(WRITE, HZ/10); 960 } 961 if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)) 962 out_of_memory(gfp_mask); 963 out: 964 for (i = 0; zones[i] != 0; i++) 965 zones[i]->prev_priority = zones[i]->temp_priority; 966 return ret; 967 } 968 969 /* 970 * For kswapd, balance_pgdat() will work across all this node's zones until 971 * they are all at pages_high. 972 * 973 * If `nr_pages' is non-zero then it is the number of pages which are to be 974 * reclaimed, regardless of the zone occupancies. This is a software suspend 975 * special. 976 * 977 * Returns the number of pages which were actually freed. 978 * 979 * There is special handling here for zones which are full of pinned pages. 980 * This can happen if the pages are all mlocked, or if they are all used by 981 * device drivers (say, ZONE_DMA). Or if they are all in use by hugetlb. 982 * What we do is to detect the case where all pages in the zone have been 983 * scanned twice and there has been zero successful reclaim. Mark the zone as 984 * dead and from now on, only perform a short scan. Basically we're polling 985 * the zone for when the problem goes away. 986 * 987 * kswapd scans the zones in the highmem->normal->dma direction. It skips 988 * zones which have free_pages > pages_high, but once a zone is found to have 989 * free_pages <= pages_high, we scan that zone and the lower zones regardless 990 * of the number of free pages in the lower zones. This interoperates with 991 * the page allocator fallback scheme to ensure that aging of pages is balanced 992 * across the zones. 993 */ 994 static int balance_pgdat(pg_data_t *pgdat, int nr_pages) 995 { 996 int to_free = nr_pages; 997 int all_zones_ok; 998 int priority; 999 int i; 1000 int total_scanned, total_reclaimed; 1001 struct reclaim_state *reclaim_state = current->reclaim_state; 1002 struct scan_control sc; 1003 1004 loop_again: 1005 total_scanned = 0; 1006 total_reclaimed = 0; 1007 sc.gfp_mask = GFP_KERNEL; 1008 sc.may_writepage = 0; 1009 sc.nr_mapped = read_page_state(nr_mapped); 1010 1011 inc_page_state(pageoutrun); 1012 1013 for (i = 0; i < pgdat->nr_zones; i++) { 1014 struct zone *zone = pgdat->node_zones + i; 1015 1016 zone->temp_priority = DEF_PRIORITY; 1017 } 1018 1019 for (priority = DEF_PRIORITY; priority >= 0; priority--) { 1020 int end_zone = 0; /* Inclusive. 0 = ZONE_DMA */ 1021 unsigned long lru_pages = 0; 1022 1023 all_zones_ok = 1; 1024 1025 if (nr_pages == 0) { 1026 /* 1027 * Scan in the highmem->dma direction for the highest 1028 * zone which needs scanning 1029 */ 1030 for (i = pgdat->nr_zones - 1; i >= 0; i--) { 1031 struct zone *zone = pgdat->node_zones + i; 1032 1033 if (zone->present_pages == 0) 1034 continue; 1035 1036 if (zone->all_unreclaimable && 1037 priority != DEF_PRIORITY) 1038 continue; 1039 1040 if (zone->free_pages <= zone->pages_high) { 1041 end_zone = i; 1042 goto scan; 1043 } 1044 } 1045 goto out; 1046 } else { 1047 end_zone = pgdat->nr_zones - 1; 1048 } 1049 scan: 1050 for (i = 0; i <= end_zone; i++) { 1051 struct zone *zone = pgdat->node_zones + i; 1052 1053 lru_pages += zone->nr_active + zone->nr_inactive; 1054 } 1055 1056 /* 1057 * Now scan the zone in the dma->highmem direction, stopping 1058 * at the last zone which needs scanning. 1059 * 1060 * We do this because the page allocator works in the opposite 1061 * direction. This prevents the page allocator from allocating 1062 * pages behind kswapd's direction of progress, which would 1063 * cause too much scanning of the lower zones. 1064 */ 1065 for (i = 0; i <= end_zone; i++) { 1066 struct zone *zone = pgdat->node_zones + i; 1067 1068 if (zone->present_pages == 0) 1069 continue; 1070 1071 if (zone->all_unreclaimable && priority != DEF_PRIORITY) 1072 continue; 1073 1074 if (nr_pages == 0) { /* Not software suspend */ 1075 if (zone->free_pages <= zone->pages_high) 1076 all_zones_ok = 0; 1077 } 1078 zone->temp_priority = priority; 1079 if (zone->prev_priority > priority) 1080 zone->prev_priority = priority; 1081 sc.nr_scanned = 0; 1082 sc.nr_reclaimed = 0; 1083 sc.priority = priority; 1084 shrink_zone(zone, &sc); 1085 reclaim_state->reclaimed_slab = 0; 1086 shrink_slab(sc.nr_scanned, GFP_KERNEL, lru_pages); 1087 sc.nr_reclaimed += reclaim_state->reclaimed_slab; 1088 total_reclaimed += sc.nr_reclaimed; 1089 if (zone->all_unreclaimable) 1090 continue; 1091 if (zone->pages_scanned >= (zone->nr_active + 1092 zone->nr_inactive) * 4) 1093 zone->all_unreclaimable = 1; 1094 /* 1095 * If we've done a decent amount of scanning and 1096 * the reclaim ratio is low, start doing writepage 1097 * even in laptop mode 1098 */ 1099 if (total_scanned > SWAP_CLUSTER_MAX * 2 && 1100 total_scanned > total_reclaimed+total_reclaimed/2) 1101 sc.may_writepage = 1; 1102 } 1103 if (nr_pages && to_free > total_reclaimed) 1104 continue; /* swsusp: need to do more work */ 1105 if (all_zones_ok) 1106 break; /* kswapd: all done */ 1107 /* 1108 * OK, kswapd is getting into trouble. Take a nap, then take 1109 * another pass across the zones. 1110 */ 1111 if (total_scanned && priority < DEF_PRIORITY - 2) 1112 blk_congestion_wait(WRITE, HZ/10); 1113 1114 /* 1115 * We do this so kswapd doesn't build up large priorities for 1116 * example when it is freeing in parallel with allocators. It 1117 * matches the direct reclaim path behaviour in terms of impact 1118 * on zone->*_priority. 1119 */ 1120 if (total_reclaimed >= SWAP_CLUSTER_MAX) 1121 break; 1122 } 1123 out: 1124 for (i = 0; i < pgdat->nr_zones; i++) { 1125 struct zone *zone = pgdat->node_zones + i; 1126 1127 zone->prev_priority = zone->temp_priority; 1128 } 1129 if (!all_zones_ok) { 1130 cond_resched(); 1131 goto loop_again; 1132 } 1133 1134 return total_reclaimed; 1135 } 1136 1137 /* 1138 * The background pageout daemon, started as a kernel thread 1139 * from the init process. 1140 * 1141 * This basically trickles out pages so that we have _some_ 1142 * free memory available even if there is no other activity 1143 * that frees anything up. This is needed for things like routing 1144 * etc, where we otherwise might have all activity going on in 1145 * asynchronous contexts that cannot page things out. 1146 * 1147 * If there are applications that are active memory-allocators 1148 * (most normal use), this basically shouldn't matter. 1149 */ 1150 static int kswapd(void *p) 1151 { 1152 pg_data_t *pgdat = (pg_data_t*)p; 1153 struct task_struct *tsk = current; 1154 DEFINE_WAIT(wait); 1155 struct reclaim_state reclaim_state = { 1156 .reclaimed_slab = 0, 1157 }; 1158 cpumask_t cpumask; 1159 1160 daemonize("kswapd%d", pgdat->node_id); 1161 cpumask = node_to_cpumask(pgdat->node_id); 1162 if (!cpus_empty(cpumask)) 1163 set_cpus_allowed(tsk, cpumask); 1164 current->reclaim_state = &reclaim_state; 1165 1166 /* 1167 * Tell the memory management that we're a "memory allocator", 1168 * and that if we need more memory we should get access to it 1169 * regardless (see "__alloc_pages()"). "kswapd" should 1170 * never get caught in the normal page freeing logic. 1171 * 1172 * (Kswapd normally doesn't need memory anyway, but sometimes 1173 * you need a small amount of memory in order to be able to 1174 * page out something else, and this flag essentially protects 1175 * us from recursively trying to free more memory as we're 1176 * trying to free the first piece of memory in the first place). 1177 */ 1178 tsk->flags |= PF_MEMALLOC|PF_KSWAPD; 1179 1180 for ( ; ; ) { 1181 if (current->flags & PF_FREEZE) 1182 refrigerator(PF_FREEZE); 1183 prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE); 1184 schedule(); 1185 finish_wait(&pgdat->kswapd_wait, &wait); 1186 1187 balance_pgdat(pgdat, 0); 1188 } 1189 return 0; 1190 } 1191 1192 /* 1193 * A zone is low on free memory, so wake its kswapd task to service it. 1194 */ 1195 void wakeup_kswapd(struct zone *zone) 1196 { 1197 if (zone->present_pages == 0) 1198 return; 1199 if (zone->free_pages > zone->pages_low) 1200 return; 1201 if (!waitqueue_active(&zone->zone_pgdat->kswapd_wait)) 1202 return; 1203 wake_up_interruptible(&zone->zone_pgdat->kswapd_wait); 1204 } 1205 1206 #ifdef CONFIG_PM 1207 /* 1208 * Try to free `nr_pages' of memory, system-wide. Returns the number of freed 1209 * pages. 1210 */ 1211 int shrink_all_memory(int nr_pages) 1212 { 1213 pg_data_t *pgdat; 1214 int nr_to_free = nr_pages; 1215 int ret = 0; 1216 struct reclaim_state reclaim_state = { 1217 .reclaimed_slab = 0, 1218 }; 1219 1220 current->reclaim_state = &reclaim_state; 1221 for_each_pgdat(pgdat) { 1222 int freed; 1223 freed = balance_pgdat(pgdat, nr_to_free); 1224 ret += freed; 1225 nr_to_free -= freed; 1226 if (nr_to_free <= 0) 1227 break; 1228 } 1229 current->reclaim_state = NULL; 1230 return ret; 1231 } 1232 #endif 1233 1234 #ifdef CONFIG_HOTPLUG_CPU 1235 /* It's optimal to keep kswapds on the same CPUs as their memory, but 1236 not required for correctness. So if the last cpu in a node goes 1237 away, we get changed to run anywhere: as the first one comes back, 1238 restore their cpu bindings. */ 1239 static int __devinit cpu_callback(struct notifier_block *nfb, 1240 unsigned long action, 1241 void *hcpu) 1242 { 1243 pg_data_t *pgdat; 1244 cpumask_t mask; 1245 1246 if (action == CPU_ONLINE) { 1247 for_each_pgdat(pgdat) { 1248 mask = node_to_cpumask(pgdat->node_id); 1249 if (any_online_cpu(mask) != NR_CPUS) 1250 /* One of our CPUs online: restore mask */ 1251 set_cpus_allowed(pgdat->kswapd, mask); 1252 } 1253 } 1254 return NOTIFY_OK; 1255 } 1256 #endif /* CONFIG_HOTPLUG_CPU */ 1257 1258 static int __init kswapd_init(void) 1259 { 1260 pg_data_t *pgdat; 1261 swap_setup(); 1262 for_each_pgdat(pgdat) 1263 pgdat->kswapd 1264 = find_task_by_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL)); 1265 total_memory = nr_free_pagecache_pages(); 1266 hotcpu_notifier(cpu_callback, 0); 1267 return 0; 1268 } 1269 1270 module_init(kswapd_init) 1271
This page was automatically generated by LXR 0.3.1. • Linux is a registered trademark of Linus Torvalds