swap.c revision cc59850ef940e4ee6a765d28b439b9bafe07cf63
1/* 2 * linux/mm/swap.c 3 * 4 * Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds 5 */ 6 7/* 8 * This file contains the default values for the operation of the 9 * Linux VM subsystem. Fine-tuning documentation can be found in 10 * Documentation/sysctl/vm.txt. 11 * Started 18.12.91 12 * Swap aging added 23.2.95, Stephen Tweedie. 13 * Buffermem limits added 12.3.98, Rik van Riel. 14 */ 15 16#include <linux/mm.h> 17#include <linux/sched.h> 18#include <linux/kernel_stat.h> 19#include <linux/swap.h> 20#include <linux/mman.h> 21#include <linux/pagemap.h> 22#include <linux/pagevec.h> 23#include <linux/init.h> 24#include <linux/export.h> 25#include <linux/mm_inline.h> 26#include <linux/buffer_head.h> /* for try_to_release_page() */ 27#include <linux/percpu_counter.h> 28#include <linux/percpu.h> 29#include <linux/cpu.h> 30#include <linux/notifier.h> 31#include <linux/backing-dev.h> 32#include <linux/memcontrol.h> 33#include <linux/gfp.h> 34 35#include "internal.h" 36 37/* How many pages do we try to swap or page in/out together? */ 38int page_cluster; 39 40static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs); 41static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs); 42static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs); 43 44/* 45 * This path almost never happens for VM activity - pages are normally 46 * freed via pagevecs. But it gets used by networking. 47 */ 48static void __page_cache_release(struct page *page) 49{ 50 if (PageLRU(page)) { 51 unsigned long flags; 52 struct zone *zone = page_zone(page); 53 54 spin_lock_irqsave(&zone->lru_lock, flags); 55 VM_BUG_ON(!PageLRU(page)); 56 __ClearPageLRU(page); 57 del_page_from_lru(zone, page); 58 spin_unlock_irqrestore(&zone->lru_lock, flags); 59 } 60} 61 62static void __put_single_page(struct page *page) 63{ 64 __page_cache_release(page); 65 free_hot_cold_page(page, 0); 66} 67 68static void __put_compound_page(struct page *page) 69{ 70 compound_page_dtor *dtor; 71 72 __page_cache_release(page); 73 dtor = get_compound_page_dtor(page); 74 (*dtor)(page); 75} 76 77static void put_compound_page(struct page *page) 78{ 79 if (unlikely(PageTail(page))) { 80 /* __split_huge_page_refcount can run under us */ 81 struct page *page_head = compound_trans_head(page); 82 83 if (likely(page != page_head && 84 get_page_unless_zero(page_head))) { 85 unsigned long flags; 86 /* 87 * page_head wasn't a dangling pointer but it 88 * may not be a head page anymore by the time 89 * we obtain the lock. That is ok as long as it 90 * can't be freed from under us. 91 */ 92 flags = compound_lock_irqsave(page_head); 93 if (unlikely(!PageTail(page))) { 94 /* __split_huge_page_refcount run before us */ 95 compound_unlock_irqrestore(page_head, flags); 96 VM_BUG_ON(PageHead(page_head)); 97 if (put_page_testzero(page_head)) 98 __put_single_page(page_head); 99 out_put_single: 100 if (put_page_testzero(page)) 101 __put_single_page(page); 102 return; 103 } 104 VM_BUG_ON(page_head != page->first_page); 105 /* 106 * We can release the refcount taken by 107 * get_page_unless_zero() now that 108 * __split_huge_page_refcount() is blocked on 109 * the compound_lock. 110 */ 111 if (put_page_testzero(page_head)) 112 VM_BUG_ON(1); 113 /* __split_huge_page_refcount will wait now */ 114 VM_BUG_ON(page_mapcount(page) <= 0); 115 atomic_dec(&page->_mapcount); 116 VM_BUG_ON(atomic_read(&page_head->_count) <= 0); 117 VM_BUG_ON(atomic_read(&page->_count) != 0); 118 compound_unlock_irqrestore(page_head, flags); 119 if (put_page_testzero(page_head)) { 120 if (PageHead(page_head)) 121 __put_compound_page(page_head); 122 else 123 __put_single_page(page_head); 124 } 125 } else { 126 /* page_head is a dangling pointer */ 127 VM_BUG_ON(PageTail(page)); 128 goto out_put_single; 129 } 130 } else if (put_page_testzero(page)) { 131 if (PageHead(page)) 132 __put_compound_page(page); 133 else 134 __put_single_page(page); 135 } 136} 137 138void put_page(struct page *page) 139{ 140 if (unlikely(PageCompound(page))) 141 put_compound_page(page); 142 else if (put_page_testzero(page)) 143 __put_single_page(page); 144} 145EXPORT_SYMBOL(put_page); 146 147/* 148 * This function is exported but must not be called by anything other 149 * than get_page(). It implements the slow path of get_page(). 150 */ 151bool __get_page_tail(struct page *page) 152{ 153 /* 154 * This takes care of get_page() if run on a tail page 155 * returned by one of the get_user_pages/follow_page variants. 156 * get_user_pages/follow_page itself doesn't need the compound 157 * lock because it runs __get_page_tail_foll() under the 158 * proper PT lock that already serializes against 159 * split_huge_page(). 160 */ 161 unsigned long flags; 162 bool got = false; 163 struct page *page_head = compound_trans_head(page); 164 165 if (likely(page != page_head && get_page_unless_zero(page_head))) { 166 /* 167 * page_head wasn't a dangling pointer but it 168 * may not be a head page anymore by the time 169 * we obtain the lock. That is ok as long as it 170 * can't be freed from under us. 171 */ 172 flags = compound_lock_irqsave(page_head); 173 /* here __split_huge_page_refcount won't run anymore */ 174 if (likely(PageTail(page))) { 175 __get_page_tail_foll(page, false); 176 got = true; 177 } 178 compound_unlock_irqrestore(page_head, flags); 179 if (unlikely(!got)) 180 put_page(page_head); 181 } 182 return got; 183} 184EXPORT_SYMBOL(__get_page_tail); 185 186/** 187 * put_pages_list() - release a list of pages 188 * @pages: list of pages threaded on page->lru 189 * 190 * Release a list of pages which are strung together on page.lru. Currently 191 * used by read_cache_pages() and related error recovery code. 192 */ 193void put_pages_list(struct list_head *pages) 194{ 195 while (!list_empty(pages)) { 196 struct page *victim; 197 198 victim = list_entry(pages->prev, struct page, lru); 199 list_del(&victim->lru); 200 page_cache_release(victim); 201 } 202} 203EXPORT_SYMBOL(put_pages_list); 204 205static void pagevec_lru_move_fn(struct pagevec *pvec, 206 void (*move_fn)(struct page *page, void *arg), 207 void *arg) 208{ 209 int i; 210 struct zone *zone = NULL; 211 unsigned long flags = 0; 212 213 for (i = 0; i < pagevec_count(pvec); i++) { 214 struct page *page = pvec->pages[i]; 215 struct zone *pagezone = page_zone(page); 216 217 if (pagezone != zone) { 218 if (zone) 219 spin_unlock_irqrestore(&zone->lru_lock, flags); 220 zone = pagezone; 221 spin_lock_irqsave(&zone->lru_lock, flags); 222 } 223 224 (*move_fn)(page, arg); 225 } 226 if (zone) 227 spin_unlock_irqrestore(&zone->lru_lock, flags); 228 release_pages(pvec->pages, pvec->nr, pvec->cold); 229 pagevec_reinit(pvec); 230} 231 232static void pagevec_move_tail_fn(struct page *page, void *arg) 233{ 234 int *pgmoved = arg; 235 struct zone *zone = page_zone(page); 236 237 if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) { 238 enum lru_list lru = page_lru_base_type(page); 239 list_move_tail(&page->lru, &zone->lru[lru].list); 240 mem_cgroup_rotate_reclaimable_page(page); 241 (*pgmoved)++; 242 } 243} 244 245/* 246 * pagevec_move_tail() must be called with IRQ disabled. 247 * Otherwise this may cause nasty races. 248 */ 249static void pagevec_move_tail(struct pagevec *pvec) 250{ 251 int pgmoved = 0; 252 253 pagevec_lru_move_fn(pvec, pagevec_move_tail_fn, &pgmoved); 254 __count_vm_events(PGROTATED, pgmoved); 255} 256 257/* 258 * Writeback is about to end against a page which has been marked for immediate 259 * reclaim. If it still appears to be reclaimable, move it to the tail of the 260 * inactive list. 261 */ 262void rotate_reclaimable_page(struct page *page) 263{ 264 if (!PageLocked(page) && !PageDirty(page) && !PageActive(page) && 265 !PageUnevictable(page) && PageLRU(page)) { 266 struct pagevec *pvec; 267 unsigned long flags; 268 269 page_cache_get(page); 270 local_irq_save(flags); 271 pvec = &__get_cpu_var(lru_rotate_pvecs); 272 if (!pagevec_add(pvec, page)) 273 pagevec_move_tail(pvec); 274 local_irq_restore(flags); 275 } 276} 277 278static void update_page_reclaim_stat(struct zone *zone, struct page *page, 279 int file, int rotated) 280{ 281 struct zone_reclaim_stat *reclaim_stat = &zone->reclaim_stat; 282 struct zone_reclaim_stat *memcg_reclaim_stat; 283 284 memcg_reclaim_stat = mem_cgroup_get_reclaim_stat_from_page(page); 285 286 reclaim_stat->recent_scanned[file]++; 287 if (rotated) 288 reclaim_stat->recent_rotated[file]++; 289 290 if (!memcg_reclaim_stat) 291 return; 292 293 memcg_reclaim_stat->recent_scanned[file]++; 294 if (rotated) 295 memcg_reclaim_stat->recent_rotated[file]++; 296} 297 298static void __activate_page(struct page *page, void *arg) 299{ 300 struct zone *zone = page_zone(page); 301 302 if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) { 303 int file = page_is_file_cache(page); 304 int lru = page_lru_base_type(page); 305 del_page_from_lru_list(zone, page, lru); 306 307 SetPageActive(page); 308 lru += LRU_ACTIVE; 309 add_page_to_lru_list(zone, page, lru); 310 __count_vm_event(PGACTIVATE); 311 312 update_page_reclaim_stat(zone, page, file, 1); 313 } 314} 315 316#ifdef CONFIG_SMP 317static DEFINE_PER_CPU(struct pagevec, activate_page_pvecs); 318 319static void activate_page_drain(int cpu) 320{ 321 struct pagevec *pvec = &per_cpu(activate_page_pvecs, cpu); 322 323 if (pagevec_count(pvec)) 324 pagevec_lru_move_fn(pvec, __activate_page, NULL); 325} 326 327void activate_page(struct page *page) 328{ 329 if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) { 330 struct pagevec *pvec = &get_cpu_var(activate_page_pvecs); 331 332 page_cache_get(page); 333 if (!pagevec_add(pvec, page)) 334 pagevec_lru_move_fn(pvec, __activate_page, NULL); 335 put_cpu_var(activate_page_pvecs); 336 } 337} 338 339#else 340static inline void activate_page_drain(int cpu) 341{ 342} 343 344void activate_page(struct page *page) 345{ 346 struct zone *zone = page_zone(page); 347 348 spin_lock_irq(&zone->lru_lock); 349 __activate_page(page, NULL); 350 spin_unlock_irq(&zone->lru_lock); 351} 352#endif 353 354/* 355 * Mark a page as having seen activity. 356 * 357 * inactive,unreferenced -> inactive,referenced 358 * inactive,referenced -> active,unreferenced 359 * active,unreferenced -> active,referenced 360 */ 361void mark_page_accessed(struct page *page) 362{ 363 if (!PageActive(page) && !PageUnevictable(page) && 364 PageReferenced(page) && PageLRU(page)) { 365 activate_page(page); 366 ClearPageReferenced(page); 367 } else if (!PageReferenced(page)) { 368 SetPageReferenced(page); 369 } 370} 371 372EXPORT_SYMBOL(mark_page_accessed); 373 374void __lru_cache_add(struct page *page, enum lru_list lru) 375{ 376 struct pagevec *pvec = &get_cpu_var(lru_add_pvecs)[lru]; 377 378 page_cache_get(page); 379 if (!pagevec_add(pvec, page)) 380 ____pagevec_lru_add(pvec, lru); 381 put_cpu_var(lru_add_pvecs); 382} 383EXPORT_SYMBOL(__lru_cache_add); 384 385/** 386 * lru_cache_add_lru - add a page to a page list 387 * @page: the page to be added to the LRU. 388 * @lru: the LRU list to which the page is added. 389 */ 390void lru_cache_add_lru(struct page *page, enum lru_list lru) 391{ 392 if (PageActive(page)) { 393 VM_BUG_ON(PageUnevictable(page)); 394 ClearPageActive(page); 395 } else if (PageUnevictable(page)) { 396 VM_BUG_ON(PageActive(page)); 397 ClearPageUnevictable(page); 398 } 399 400 VM_BUG_ON(PageLRU(page) || PageActive(page) || PageUnevictable(page)); 401 __lru_cache_add(page, lru); 402} 403 404/** 405 * add_page_to_unevictable_list - add a page to the unevictable list 406 * @page: the page to be added to the unevictable list 407 * 408 * Add page directly to its zone's unevictable list. To avoid races with 409 * tasks that might be making the page evictable, through eg. munlock, 410 * munmap or exit, while it's not on the lru, we want to add the page 411 * while it's locked or otherwise "invisible" to other tasks. This is 412 * difficult to do when using the pagevec cache, so bypass that. 413 */ 414void add_page_to_unevictable_list(struct page *page) 415{ 416 struct zone *zone = page_zone(page); 417 418 spin_lock_irq(&zone->lru_lock); 419 SetPageUnevictable(page); 420 SetPageLRU(page); 421 add_page_to_lru_list(zone, page, LRU_UNEVICTABLE); 422 spin_unlock_irq(&zone->lru_lock); 423} 424 425/* 426 * If the page can not be invalidated, it is moved to the 427 * inactive list to speed up its reclaim. It is moved to the 428 * head of the list, rather than the tail, to give the flusher 429 * threads some time to write it out, as this is much more 430 * effective than the single-page writeout from reclaim. 431 * 432 * If the page isn't page_mapped and dirty/writeback, the page 433 * could reclaim asap using PG_reclaim. 434 * 435 * 1. active, mapped page -> none 436 * 2. active, dirty/writeback page -> inactive, head, PG_reclaim 437 * 3. inactive, mapped page -> none 438 * 4. inactive, dirty/writeback page -> inactive, head, PG_reclaim 439 * 5. inactive, clean -> inactive, tail 440 * 6. Others -> none 441 * 442 * In 4, why it moves inactive's head, the VM expects the page would 443 * be write it out by flusher threads as this is much more effective 444 * than the single-page writeout from reclaim. 445 */ 446static void lru_deactivate_fn(struct page *page, void *arg) 447{ 448 int lru, file; 449 bool active; 450 struct zone *zone = page_zone(page); 451 452 if (!PageLRU(page)) 453 return; 454 455 if (PageUnevictable(page)) 456 return; 457 458 /* Some processes are using the page */ 459 if (page_mapped(page)) 460 return; 461 462 active = PageActive(page); 463 464 file = page_is_file_cache(page); 465 lru = page_lru_base_type(page); 466 del_page_from_lru_list(zone, page, lru + active); 467 ClearPageActive(page); 468 ClearPageReferenced(page); 469 add_page_to_lru_list(zone, page, lru); 470 471 if (PageWriteback(page) || PageDirty(page)) { 472 /* 473 * PG_reclaim could be raced with end_page_writeback 474 * It can make readahead confusing. But race window 475 * is _really_ small and it's non-critical problem. 476 */ 477 SetPageReclaim(page); 478 } else { 479 /* 480 * The page's writeback ends up during pagevec 481 * We moves tha page into tail of inactive. 482 */ 483 list_move_tail(&page->lru, &zone->lru[lru].list); 484 mem_cgroup_rotate_reclaimable_page(page); 485 __count_vm_event(PGROTATED); 486 } 487 488 if (active) 489 __count_vm_event(PGDEACTIVATE); 490 update_page_reclaim_stat(zone, page, file, 0); 491} 492 493/* 494 * Drain pages out of the cpu's pagevecs. 495 * Either "cpu" is the current CPU, and preemption has already been 496 * disabled; or "cpu" is being hot-unplugged, and is already dead. 497 */ 498static void drain_cpu_pagevecs(int cpu) 499{ 500 struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu); 501 struct pagevec *pvec; 502 int lru; 503 504 for_each_lru(lru) { 505 pvec = &pvecs[lru - LRU_BASE]; 506 if (pagevec_count(pvec)) 507 ____pagevec_lru_add(pvec, lru); 508 } 509 510 pvec = &per_cpu(lru_rotate_pvecs, cpu); 511 if (pagevec_count(pvec)) { 512 unsigned long flags; 513 514 /* No harm done if a racing interrupt already did this */ 515 local_irq_save(flags); 516 pagevec_move_tail(pvec); 517 local_irq_restore(flags); 518 } 519 520 pvec = &per_cpu(lru_deactivate_pvecs, cpu); 521 if (pagevec_count(pvec)) 522 pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL); 523 524 activate_page_drain(cpu); 525} 526 527/** 528 * deactivate_page - forcefully deactivate a page 529 * @page: page to deactivate 530 * 531 * This function hints the VM that @page is a good reclaim candidate, 532 * for example if its invalidation fails due to the page being dirty 533 * or under writeback. 534 */ 535void deactivate_page(struct page *page) 536{ 537 /* 538 * In a workload with many unevictable page such as mprotect, unevictable 539 * page deactivation for accelerating reclaim is pointless. 540 */ 541 if (PageUnevictable(page)) 542 return; 543 544 if (likely(get_page_unless_zero(page))) { 545 struct pagevec *pvec = &get_cpu_var(lru_deactivate_pvecs); 546 547 if (!pagevec_add(pvec, page)) 548 pagevec_lru_move_fn(pvec, lru_deactivate_fn, NULL); 549 put_cpu_var(lru_deactivate_pvecs); 550 } 551} 552 553void lru_add_drain(void) 554{ 555 drain_cpu_pagevecs(get_cpu()); 556 put_cpu(); 557} 558 559static void lru_add_drain_per_cpu(struct work_struct *dummy) 560{ 561 lru_add_drain(); 562} 563 564/* 565 * Returns 0 for success 566 */ 567int lru_add_drain_all(void) 568{ 569 return schedule_on_each_cpu(lru_add_drain_per_cpu); 570} 571 572/* 573 * Batched page_cache_release(). Decrement the reference count on all the 574 * passed pages. If it fell to zero then remove the page from the LRU and 575 * free it. 576 * 577 * Avoid taking zone->lru_lock if possible, but if it is taken, retain it 578 * for the remainder of the operation. 579 * 580 * The locking in this function is against shrink_inactive_list(): we recheck 581 * the page count inside the lock to see whether shrink_inactive_list() 582 * grabbed the page via the LRU. If it did, give up: shrink_inactive_list() 583 * will free it. 584 */ 585void release_pages(struct page **pages, int nr, int cold) 586{ 587 int i; 588 LIST_HEAD(pages_to_free); 589 struct zone *zone = NULL; 590 unsigned long uninitialized_var(flags); 591 592 for (i = 0; i < nr; i++) { 593 struct page *page = pages[i]; 594 595 if (unlikely(PageCompound(page))) { 596 if (zone) { 597 spin_unlock_irqrestore(&zone->lru_lock, flags); 598 zone = NULL; 599 } 600 put_compound_page(page); 601 continue; 602 } 603 604 if (!put_page_testzero(page)) 605 continue; 606 607 if (PageLRU(page)) { 608 struct zone *pagezone = page_zone(page); 609 610 if (pagezone != zone) { 611 if (zone) 612 spin_unlock_irqrestore(&zone->lru_lock, 613 flags); 614 zone = pagezone; 615 spin_lock_irqsave(&zone->lru_lock, flags); 616 } 617 VM_BUG_ON(!PageLRU(page)); 618 __ClearPageLRU(page); 619 del_page_from_lru(zone, page); 620 } 621 622 list_add(&page->lru, &pages_to_free); 623 } 624 if (zone) 625 spin_unlock_irqrestore(&zone->lru_lock, flags); 626 627 free_hot_cold_page_list(&pages_to_free, cold); 628} 629EXPORT_SYMBOL(release_pages); 630 631/* 632 * The pages which we're about to release may be in the deferred lru-addition 633 * queues. That would prevent them from really being freed right now. That's 634 * OK from a correctness point of view but is inefficient - those pages may be 635 * cache-warm and we want to give them back to the page allocator ASAP. 636 * 637 * So __pagevec_release() will drain those queues here. __pagevec_lru_add() 638 * and __pagevec_lru_add_active() call release_pages() directly to avoid 639 * mutual recursion. 640 */ 641void __pagevec_release(struct pagevec *pvec) 642{ 643 lru_add_drain(); 644 release_pages(pvec->pages, pagevec_count(pvec), pvec->cold); 645 pagevec_reinit(pvec); 646} 647 648EXPORT_SYMBOL(__pagevec_release); 649 650/* used by __split_huge_page_refcount() */ 651void lru_add_page_tail(struct zone* zone, 652 struct page *page, struct page *page_tail) 653{ 654 int active; 655 enum lru_list lru; 656 const int file = 0; 657 struct list_head *head; 658 659 VM_BUG_ON(!PageHead(page)); 660 VM_BUG_ON(PageCompound(page_tail)); 661 VM_BUG_ON(PageLRU(page_tail)); 662 VM_BUG_ON(!spin_is_locked(&zone->lru_lock)); 663 664 SetPageLRU(page_tail); 665 666 if (page_evictable(page_tail, NULL)) { 667 if (PageActive(page)) { 668 SetPageActive(page_tail); 669 active = 1; 670 lru = LRU_ACTIVE_ANON; 671 } else { 672 active = 0; 673 lru = LRU_INACTIVE_ANON; 674 } 675 update_page_reclaim_stat(zone, page_tail, file, active); 676 if (likely(PageLRU(page))) 677 head = page->lru.prev; 678 else 679 head = &zone->lru[lru].list; 680 __add_page_to_lru_list(zone, page_tail, lru, head); 681 } else { 682 SetPageUnevictable(page_tail); 683 add_page_to_lru_list(zone, page_tail, LRU_UNEVICTABLE); 684 } 685} 686 687static void ____pagevec_lru_add_fn(struct page *page, void *arg) 688{ 689 enum lru_list lru = (enum lru_list)arg; 690 struct zone *zone = page_zone(page); 691 int file = is_file_lru(lru); 692 int active = is_active_lru(lru); 693 694 VM_BUG_ON(PageActive(page)); 695 VM_BUG_ON(PageUnevictable(page)); 696 VM_BUG_ON(PageLRU(page)); 697 698 SetPageLRU(page); 699 if (active) 700 SetPageActive(page); 701 update_page_reclaim_stat(zone, page, file, active); 702 add_page_to_lru_list(zone, page, lru); 703} 704 705/* 706 * Add the passed pages to the LRU, then drop the caller's refcount 707 * on them. Reinitialises the caller's pagevec. 708 */ 709void ____pagevec_lru_add(struct pagevec *pvec, enum lru_list lru) 710{ 711 VM_BUG_ON(is_unevictable_lru(lru)); 712 713 pagevec_lru_move_fn(pvec, ____pagevec_lru_add_fn, (void *)lru); 714} 715 716EXPORT_SYMBOL(____pagevec_lru_add); 717 718/* 719 * Try to drop buffers from the pages in a pagevec 720 */ 721void pagevec_strip(struct pagevec *pvec) 722{ 723 int i; 724 725 for (i = 0; i < pagevec_count(pvec); i++) { 726 struct page *page = pvec->pages[i]; 727 728 if (page_has_private(page) && trylock_page(page)) { 729 if (page_has_private(page)) 730 try_to_release_page(page, 0); 731 unlock_page(page); 732 } 733 } 734} 735 736/** 737 * pagevec_lookup - gang pagecache lookup 738 * @pvec: Where the resulting pages are placed 739 * @mapping: The address_space to search 740 * @start: The starting page index 741 * @nr_pages: The maximum number of pages 742 * 743 * pagevec_lookup() will search for and return a group of up to @nr_pages pages 744 * in the mapping. The pages are placed in @pvec. pagevec_lookup() takes a 745 * reference against the pages in @pvec. 746 * 747 * The search returns a group of mapping-contiguous pages with ascending 748 * indexes. There may be holes in the indices due to not-present pages. 749 * 750 * pagevec_lookup() returns the number of pages which were found. 751 */ 752unsigned pagevec_lookup(struct pagevec *pvec, struct address_space *mapping, 753 pgoff_t start, unsigned nr_pages) 754{ 755 pvec->nr = find_get_pages(mapping, start, nr_pages, pvec->pages); 756 return pagevec_count(pvec); 757} 758 759EXPORT_SYMBOL(pagevec_lookup); 760 761unsigned pagevec_lookup_tag(struct pagevec *pvec, struct address_space *mapping, 762 pgoff_t *index, int tag, unsigned nr_pages) 763{ 764 pvec->nr = find_get_pages_tag(mapping, index, tag, 765 nr_pages, pvec->pages); 766 return pagevec_count(pvec); 767} 768 769EXPORT_SYMBOL(pagevec_lookup_tag); 770 771/* 772 * Perform any setup for the swap system 773 */ 774void __init swap_setup(void) 775{ 776 unsigned long megs = totalram_pages >> (20 - PAGE_SHIFT); 777 778#ifdef CONFIG_SWAP 779 bdi_init(swapper_space.backing_dev_info); 780#endif 781 782 /* Use a smaller cluster for small-memory machines */ 783 if (megs < 16) 784 page_cluster = 2; 785 else 786 page_cluster = 3; 787 /* 788 * Right now other parts of the system means that we 789 * _really_ don't want to cluster much more 790 */ 791} 792