rmap.c revision bf89c8c867322338f3f2b1255f280a3236b61a69
1/* 2 * mm/rmap.c - physical to virtual reverse mappings 3 * 4 * Copyright 2001, Rik van Riel <riel@conectiva.com.br> 5 * Released under the General Public License (GPL). 6 * 7 * Simple, low overhead reverse mapping scheme. 8 * Please try to keep this thing as modular as possible. 9 * 10 * Provides methods for unmapping each kind of mapped page: 11 * the anon methods track anonymous pages, and 12 * the file methods track pages belonging to an inode. 13 * 14 * Original design by Rik van Riel <riel@conectiva.com.br> 2001 15 * File methods by Dave McCracken <dmccr@us.ibm.com> 2003, 2004 16 * Anonymous methods by Andrea Arcangeli <andrea@suse.de> 2004 17 * Contributions by Hugh Dickins 2003, 2004 18 */ 19 20/* 21 * Lock ordering in mm: 22 * 23 * inode->i_mutex (while writing or truncating, not reading or faulting) 24 * inode->i_alloc_sem (vmtruncate_range) 25 * mm->mmap_sem 26 * page->flags PG_locked (lock_page) 27 * mapping->i_mmap_lock 28 * anon_vma->lock 29 * mm->page_table_lock or pte_lock 30 * zone->lru_lock (in mark_page_accessed, isolate_lru_page) 31 * swap_lock (in swap_duplicate, swap_info_get) 32 * mmlist_lock (in mmput, drain_mmlist and others) 33 * mapping->private_lock (in __set_page_dirty_buffers) 34 * inode_lock (in set_page_dirty's __mark_inode_dirty) 35 * sb_lock (within inode_lock in fs/fs-writeback.c) 36 * mapping->tree_lock (widely used, in set_page_dirty, 37 * in arch-dependent flush_dcache_mmap_lock, 38 * within inode_lock in __sync_single_inode) 39 * 40 * (code doesn't rely on that order so it could be switched around) 41 * ->tasklist_lock 42 * anon_vma->lock (memory_failure, collect_procs_anon) 43 * pte map lock 44 */ 45 46#include <linux/mm.h> 47#include <linux/pagemap.h> 48#include <linux/swap.h> 49#include <linux/swapops.h> 50#include <linux/slab.h> 51#include <linux/init.h> 52#include <linux/rmap.h> 53#include <linux/rcupdate.h> 54#include <linux/module.h> 55#include <linux/memcontrol.h> 56#include <linux/mmu_notifier.h> 57#include <linux/migrate.h> 58 59#include <asm/tlbflush.h> 60 61#include "internal.h" 62 63static struct kmem_cache *anon_vma_cachep; 64 65static inline struct anon_vma *anon_vma_alloc(void) 66{ 67 return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL); 68} 69 70static inline void anon_vma_free(struct anon_vma *anon_vma) 71{ 72 kmem_cache_free(anon_vma_cachep, anon_vma); 73} 74 75/** 76 * anon_vma_prepare - attach an anon_vma to a memory region 77 * @vma: the memory region in question 78 * 79 * This makes sure the memory mapping described by 'vma' has 80 * an 'anon_vma' attached to it, so that we can associate the 81 * anonymous pages mapped into it with that anon_vma. 82 * 83 * The common case will be that we already have one, but if 84 * if not we either need to find an adjacent mapping that we 85 * can re-use the anon_vma from (very common when the only 86 * reason for splitting a vma has been mprotect()), or we 87 * allocate a new one. 88 * 89 * Anon-vma allocations are very subtle, because we may have 90 * optimistically looked up an anon_vma in page_lock_anon_vma() 91 * and that may actually touch the spinlock even in the newly 92 * allocated vma (it depends on RCU to make sure that the 93 * anon_vma isn't actually destroyed). 94 * 95 * As a result, we need to do proper anon_vma locking even 96 * for the new allocation. At the same time, we do not want 97 * to do any locking for the common case of already having 98 * an anon_vma. 99 * 100 * This must be called with the mmap_sem held for reading. 101 */ 102int anon_vma_prepare(struct vm_area_struct *vma) 103{ 104 struct anon_vma *anon_vma = vma->anon_vma; 105 106 might_sleep(); 107 if (unlikely(!anon_vma)) { 108 struct mm_struct *mm = vma->vm_mm; 109 struct anon_vma *allocated; 110 111 anon_vma = find_mergeable_anon_vma(vma); 112 allocated = NULL; 113 if (!anon_vma) { 114 anon_vma = anon_vma_alloc(); 115 if (unlikely(!anon_vma)) 116 return -ENOMEM; 117 allocated = anon_vma; 118 } 119 spin_lock(&anon_vma->lock); 120 121 /* page_table_lock to protect against threads */ 122 spin_lock(&mm->page_table_lock); 123 if (likely(!vma->anon_vma)) { 124 vma->anon_vma = anon_vma; 125 list_add_tail(&vma->anon_vma_node, &anon_vma->head); 126 allocated = NULL; 127 } 128 spin_unlock(&mm->page_table_lock); 129 130 spin_unlock(&anon_vma->lock); 131 if (unlikely(allocated)) 132 anon_vma_free(allocated); 133 } 134 return 0; 135} 136 137void __anon_vma_merge(struct vm_area_struct *vma, struct vm_area_struct *next) 138{ 139 BUG_ON(vma->anon_vma != next->anon_vma); 140 list_del(&next->anon_vma_node); 141} 142 143void __anon_vma_link(struct vm_area_struct *vma) 144{ 145 struct anon_vma *anon_vma = vma->anon_vma; 146 147 if (anon_vma) 148 list_add_tail(&vma->anon_vma_node, &anon_vma->head); 149} 150 151void anon_vma_link(struct vm_area_struct *vma) 152{ 153 struct anon_vma *anon_vma = vma->anon_vma; 154 155 if (anon_vma) { 156 spin_lock(&anon_vma->lock); 157 list_add_tail(&vma->anon_vma_node, &anon_vma->head); 158 spin_unlock(&anon_vma->lock); 159 } 160} 161 162void anon_vma_unlink(struct vm_area_struct *vma) 163{ 164 struct anon_vma *anon_vma = vma->anon_vma; 165 int empty; 166 167 if (!anon_vma) 168 return; 169 170 spin_lock(&anon_vma->lock); 171 list_del(&vma->anon_vma_node); 172 173 /* We must garbage collect the anon_vma if it's empty */ 174 empty = list_empty(&anon_vma->head); 175 spin_unlock(&anon_vma->lock); 176 177 if (empty) 178 anon_vma_free(anon_vma); 179} 180 181static void anon_vma_ctor(void *data) 182{ 183 struct anon_vma *anon_vma = data; 184 185 spin_lock_init(&anon_vma->lock); 186 INIT_LIST_HEAD(&anon_vma->head); 187} 188 189void __init anon_vma_init(void) 190{ 191 anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma), 192 0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor); 193} 194 195/* 196 * Getting a lock on a stable anon_vma from a page off the LRU is 197 * tricky: page_lock_anon_vma rely on RCU to guard against the races. 198 */ 199struct anon_vma *page_lock_anon_vma(struct page *page) 200{ 201 struct anon_vma *anon_vma; 202 unsigned long anon_mapping; 203 204 rcu_read_lock(); 205 anon_mapping = (unsigned long) page->mapping; 206 if (!(anon_mapping & PAGE_MAPPING_ANON)) 207 goto out; 208 if (!page_mapped(page)) 209 goto out; 210 211 anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON); 212 spin_lock(&anon_vma->lock); 213 return anon_vma; 214out: 215 rcu_read_unlock(); 216 return NULL; 217} 218 219void page_unlock_anon_vma(struct anon_vma *anon_vma) 220{ 221 spin_unlock(&anon_vma->lock); 222 rcu_read_unlock(); 223} 224 225/* 226 * At what user virtual address is page expected in @vma? 227 * Returns virtual address or -EFAULT if page's index/offset is not 228 * within the range mapped the @vma. 229 */ 230static inline unsigned long 231vma_address(struct page *page, struct vm_area_struct *vma) 232{ 233 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 234 unsigned long address; 235 236 address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT); 237 if (unlikely(address < vma->vm_start || address >= vma->vm_end)) { 238 /* page should be within @vma mapping range */ 239 return -EFAULT; 240 } 241 return address; 242} 243 244/* 245 * At what user virtual address is page expected in vma? 246 * checking that the page matches the vma. 247 */ 248unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma) 249{ 250 if (PageAnon(page)) { 251 if ((void *)vma->anon_vma != 252 (void *)page->mapping - PAGE_MAPPING_ANON) 253 return -EFAULT; 254 } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) { 255 if (!vma->vm_file || 256 vma->vm_file->f_mapping != page->mapping) 257 return -EFAULT; 258 } else 259 return -EFAULT; 260 return vma_address(page, vma); 261} 262 263/* 264 * Check that @page is mapped at @address into @mm. 265 * 266 * If @sync is false, page_check_address may perform a racy check to avoid 267 * the page table lock when the pte is not present (helpful when reclaiming 268 * highly shared pages). 269 * 270 * On success returns with pte mapped and locked. 271 */ 272pte_t *page_check_address(struct page *page, struct mm_struct *mm, 273 unsigned long address, spinlock_t **ptlp, int sync) 274{ 275 pgd_t *pgd; 276 pud_t *pud; 277 pmd_t *pmd; 278 pte_t *pte; 279 spinlock_t *ptl; 280 281 pgd = pgd_offset(mm, address); 282 if (!pgd_present(*pgd)) 283 return NULL; 284 285 pud = pud_offset(pgd, address); 286 if (!pud_present(*pud)) 287 return NULL; 288 289 pmd = pmd_offset(pud, address); 290 if (!pmd_present(*pmd)) 291 return NULL; 292 293 pte = pte_offset_map(pmd, address); 294 /* Make a quick check before getting the lock */ 295 if (!sync && !pte_present(*pte)) { 296 pte_unmap(pte); 297 return NULL; 298 } 299 300 ptl = pte_lockptr(mm, pmd); 301 spin_lock(ptl); 302 if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) { 303 *ptlp = ptl; 304 return pte; 305 } 306 pte_unmap_unlock(pte, ptl); 307 return NULL; 308} 309 310/** 311 * page_mapped_in_vma - check whether a page is really mapped in a VMA 312 * @page: the page to test 313 * @vma: the VMA to test 314 * 315 * Returns 1 if the page is mapped into the page tables of the VMA, 0 316 * if the page is not mapped into the page tables of this VMA. Only 317 * valid for normal file or anonymous VMAs. 318 */ 319int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma) 320{ 321 unsigned long address; 322 pte_t *pte; 323 spinlock_t *ptl; 324 325 address = vma_address(page, vma); 326 if (address == -EFAULT) /* out of vma range */ 327 return 0; 328 pte = page_check_address(page, vma->vm_mm, address, &ptl, 1); 329 if (!pte) /* the page is not in this mm */ 330 return 0; 331 pte_unmap_unlock(pte, ptl); 332 333 return 1; 334} 335 336/* 337 * Subfunctions of page_referenced: page_referenced_one called 338 * repeatedly from either page_referenced_anon or page_referenced_file. 339 */ 340static int page_referenced_one(struct page *page, 341 struct vm_area_struct *vma, 342 unsigned int *mapcount, 343 unsigned long *vm_flags) 344{ 345 struct mm_struct *mm = vma->vm_mm; 346 unsigned long address; 347 pte_t *pte; 348 spinlock_t *ptl; 349 int referenced = 0; 350 351 address = vma_address(page, vma); 352 if (address == -EFAULT) 353 goto out; 354 355 pte = page_check_address(page, mm, address, &ptl, 0); 356 if (!pte) 357 goto out; 358 359 /* 360 * Don't want to elevate referenced for mlocked page that gets this far, 361 * in order that it progresses to try_to_unmap and is moved to the 362 * unevictable list. 363 */ 364 if (vma->vm_flags & VM_LOCKED) { 365 *mapcount = 1; /* break early from loop */ 366 *vm_flags |= VM_LOCKED; 367 goto out_unmap; 368 } 369 370 if (ptep_clear_flush_young_notify(vma, address, pte)) { 371 /* 372 * Don't treat a reference through a sequentially read 373 * mapping as such. If the page has been used in 374 * another mapping, we will catch it; if this other 375 * mapping is already gone, the unmap path will have 376 * set PG_referenced or activated the page. 377 */ 378 if (likely(!VM_SequentialReadHint(vma))) 379 referenced++; 380 } 381 382 /* Pretend the page is referenced if the task has the 383 swap token and is in the middle of a page fault. */ 384 if (mm != current->mm && has_swap_token(mm) && 385 rwsem_is_locked(&mm->mmap_sem)) 386 referenced++; 387 388out_unmap: 389 (*mapcount)--; 390 pte_unmap_unlock(pte, ptl); 391out: 392 if (referenced) 393 *vm_flags |= vma->vm_flags; 394 return referenced; 395} 396 397static int page_referenced_anon(struct page *page, 398 struct mem_cgroup *mem_cont, 399 unsigned long *vm_flags) 400{ 401 unsigned int mapcount; 402 struct anon_vma *anon_vma; 403 struct vm_area_struct *vma; 404 int referenced = 0; 405 406 anon_vma = page_lock_anon_vma(page); 407 if (!anon_vma) 408 return referenced; 409 410 mapcount = page_mapcount(page); 411 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) { 412 /* 413 * If we are reclaiming on behalf of a cgroup, skip 414 * counting on behalf of references from different 415 * cgroups 416 */ 417 if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont)) 418 continue; 419 referenced += page_referenced_one(page, vma, 420 &mapcount, vm_flags); 421 if (!mapcount) 422 break; 423 } 424 425 page_unlock_anon_vma(anon_vma); 426 return referenced; 427} 428 429/** 430 * page_referenced_file - referenced check for object-based rmap 431 * @page: the page we're checking references on. 432 * @mem_cont: target memory controller 433 * @vm_flags: collect encountered vma->vm_flags who actually referenced the page 434 * 435 * For an object-based mapped page, find all the places it is mapped and 436 * check/clear the referenced flag. This is done by following the page->mapping 437 * pointer, then walking the chain of vmas it holds. It returns the number 438 * of references it found. 439 * 440 * This function is only called from page_referenced for object-based pages. 441 */ 442static int page_referenced_file(struct page *page, 443 struct mem_cgroup *mem_cont, 444 unsigned long *vm_flags) 445{ 446 unsigned int mapcount; 447 struct address_space *mapping = page->mapping; 448 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 449 struct vm_area_struct *vma; 450 struct prio_tree_iter iter; 451 int referenced = 0; 452 453 /* 454 * The caller's checks on page->mapping and !PageAnon have made 455 * sure that this is a file page: the check for page->mapping 456 * excludes the case just before it gets set on an anon page. 457 */ 458 BUG_ON(PageAnon(page)); 459 460 /* 461 * The page lock not only makes sure that page->mapping cannot 462 * suddenly be NULLified by truncation, it makes sure that the 463 * structure at mapping cannot be freed and reused yet, 464 * so we can safely take mapping->i_mmap_lock. 465 */ 466 BUG_ON(!PageLocked(page)); 467 468 spin_lock(&mapping->i_mmap_lock); 469 470 /* 471 * i_mmap_lock does not stabilize mapcount at all, but mapcount 472 * is more likely to be accurate if we note it after spinning. 473 */ 474 mapcount = page_mapcount(page); 475 476 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { 477 /* 478 * If we are reclaiming on behalf of a cgroup, skip 479 * counting on behalf of references from different 480 * cgroups 481 */ 482 if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont)) 483 continue; 484 referenced += page_referenced_one(page, vma, 485 &mapcount, vm_flags); 486 if (!mapcount) 487 break; 488 } 489 490 spin_unlock(&mapping->i_mmap_lock); 491 return referenced; 492} 493 494/** 495 * page_referenced - test if the page was referenced 496 * @page: the page to test 497 * @is_locked: caller holds lock on the page 498 * @mem_cont: target memory controller 499 * @vm_flags: collect encountered vma->vm_flags who actually referenced the page 500 * 501 * Quick test_and_clear_referenced for all mappings to a page, 502 * returns the number of ptes which referenced the page. 503 */ 504int page_referenced(struct page *page, 505 int is_locked, 506 struct mem_cgroup *mem_cont, 507 unsigned long *vm_flags) 508{ 509 int referenced = 0; 510 511 if (TestClearPageReferenced(page)) 512 referenced++; 513 514 *vm_flags = 0; 515 if (page_mapped(page) && page->mapping) { 516 if (PageAnon(page)) 517 referenced += page_referenced_anon(page, mem_cont, 518 vm_flags); 519 else if (is_locked) 520 referenced += page_referenced_file(page, mem_cont, 521 vm_flags); 522 else if (!trylock_page(page)) 523 referenced++; 524 else { 525 if (page->mapping) 526 referenced += page_referenced_file(page, 527 mem_cont, vm_flags); 528 unlock_page(page); 529 } 530 } 531 532 if (page_test_and_clear_young(page)) 533 referenced++; 534 535 return referenced; 536} 537 538static int page_mkclean_one(struct page *page, struct vm_area_struct *vma) 539{ 540 struct mm_struct *mm = vma->vm_mm; 541 unsigned long address; 542 pte_t *pte; 543 spinlock_t *ptl; 544 int ret = 0; 545 546 address = vma_address(page, vma); 547 if (address == -EFAULT) 548 goto out; 549 550 pte = page_check_address(page, mm, address, &ptl, 1); 551 if (!pte) 552 goto out; 553 554 if (pte_dirty(*pte) || pte_write(*pte)) { 555 pte_t entry; 556 557 flush_cache_page(vma, address, pte_pfn(*pte)); 558 entry = ptep_clear_flush_notify(vma, address, pte); 559 entry = pte_wrprotect(entry); 560 entry = pte_mkclean(entry); 561 set_pte_at(mm, address, pte, entry); 562 ret = 1; 563 } 564 565 pte_unmap_unlock(pte, ptl); 566out: 567 return ret; 568} 569 570static int page_mkclean_file(struct address_space *mapping, struct page *page) 571{ 572 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 573 struct vm_area_struct *vma; 574 struct prio_tree_iter iter; 575 int ret = 0; 576 577 BUG_ON(PageAnon(page)); 578 579 spin_lock(&mapping->i_mmap_lock); 580 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { 581 if (vma->vm_flags & VM_SHARED) 582 ret += page_mkclean_one(page, vma); 583 } 584 spin_unlock(&mapping->i_mmap_lock); 585 return ret; 586} 587 588int page_mkclean(struct page *page) 589{ 590 int ret = 0; 591 592 BUG_ON(!PageLocked(page)); 593 594 if (page_mapped(page)) { 595 struct address_space *mapping = page_mapping(page); 596 if (mapping) { 597 ret = page_mkclean_file(mapping, page); 598 if (page_test_dirty(page)) { 599 page_clear_dirty(page); 600 ret = 1; 601 } 602 } 603 } 604 605 return ret; 606} 607EXPORT_SYMBOL_GPL(page_mkclean); 608 609/** 610 * __page_set_anon_rmap - setup new anonymous rmap 611 * @page: the page to add the mapping to 612 * @vma: the vm area in which the mapping is added 613 * @address: the user virtual address mapped 614 */ 615static void __page_set_anon_rmap(struct page *page, 616 struct vm_area_struct *vma, unsigned long address) 617{ 618 struct anon_vma *anon_vma = vma->anon_vma; 619 620 BUG_ON(!anon_vma); 621 anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; 622 page->mapping = (struct address_space *) anon_vma; 623 624 page->index = linear_page_index(vma, address); 625 626 /* 627 * nr_mapped state can be updated without turning off 628 * interrupts because it is not modified via interrupt. 629 */ 630 __inc_zone_page_state(page, NR_ANON_PAGES); 631} 632 633/** 634 * __page_check_anon_rmap - sanity check anonymous rmap addition 635 * @page: the page to add the mapping to 636 * @vma: the vm area in which the mapping is added 637 * @address: the user virtual address mapped 638 */ 639static void __page_check_anon_rmap(struct page *page, 640 struct vm_area_struct *vma, unsigned long address) 641{ 642#ifdef CONFIG_DEBUG_VM 643 /* 644 * The page's anon-rmap details (mapping and index) are guaranteed to 645 * be set up correctly at this point. 646 * 647 * We have exclusion against page_add_anon_rmap because the caller 648 * always holds the page locked, except if called from page_dup_rmap, 649 * in which case the page is already known to be setup. 650 * 651 * We have exclusion against page_add_new_anon_rmap because those pages 652 * are initially only visible via the pagetables, and the pte is locked 653 * over the call to page_add_new_anon_rmap. 654 */ 655 struct anon_vma *anon_vma = vma->anon_vma; 656 anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; 657 BUG_ON(page->mapping != (struct address_space *)anon_vma); 658 BUG_ON(page->index != linear_page_index(vma, address)); 659#endif 660} 661 662/** 663 * page_add_anon_rmap - add pte mapping to an anonymous page 664 * @page: the page to add the mapping to 665 * @vma: the vm area in which the mapping is added 666 * @address: the user virtual address mapped 667 * 668 * The caller needs to hold the pte lock and the page must be locked. 669 */ 670void page_add_anon_rmap(struct page *page, 671 struct vm_area_struct *vma, unsigned long address) 672{ 673 VM_BUG_ON(!PageLocked(page)); 674 VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end); 675 if (atomic_inc_and_test(&page->_mapcount)) 676 __page_set_anon_rmap(page, vma, address); 677 else 678 __page_check_anon_rmap(page, vma, address); 679} 680 681/** 682 * page_add_new_anon_rmap - add pte mapping to a new anonymous page 683 * @page: the page to add the mapping to 684 * @vma: the vm area in which the mapping is added 685 * @address: the user virtual address mapped 686 * 687 * Same as page_add_anon_rmap but must only be called on *new* pages. 688 * This means the inc-and-test can be bypassed. 689 * Page does not have to be locked. 690 */ 691void page_add_new_anon_rmap(struct page *page, 692 struct vm_area_struct *vma, unsigned long address) 693{ 694 VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end); 695 SetPageSwapBacked(page); 696 atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */ 697 __page_set_anon_rmap(page, vma, address); 698 if (page_evictable(page, vma)) 699 lru_cache_add_lru(page, LRU_ACTIVE_ANON); 700 else 701 add_page_to_unevictable_list(page); 702} 703 704/** 705 * page_add_file_rmap - add pte mapping to a file page 706 * @page: the page to add the mapping to 707 * 708 * The caller needs to hold the pte lock. 709 */ 710void page_add_file_rmap(struct page *page) 711{ 712 if (atomic_inc_and_test(&page->_mapcount)) { 713 __inc_zone_page_state(page, NR_FILE_MAPPED); 714 mem_cgroup_update_mapped_file_stat(page, 1); 715 } 716} 717 718/** 719 * page_remove_rmap - take down pte mapping from a page 720 * @page: page to remove mapping from 721 * 722 * The caller needs to hold the pte lock. 723 */ 724void page_remove_rmap(struct page *page) 725{ 726 /* page still mapped by someone else? */ 727 if (!atomic_add_negative(-1, &page->_mapcount)) 728 return; 729 730 /* 731 * Now that the last pte has gone, s390 must transfer dirty 732 * flag from storage key to struct page. We can usually skip 733 * this if the page is anon, so about to be freed; but perhaps 734 * not if it's in swapcache - there might be another pte slot 735 * containing the swap entry, but page not yet written to swap. 736 */ 737 if ((!PageAnon(page) || PageSwapCache(page)) && page_test_dirty(page)) { 738 page_clear_dirty(page); 739 set_page_dirty(page); 740 } 741 if (PageAnon(page)) { 742 mem_cgroup_uncharge_page(page); 743 __dec_zone_page_state(page, NR_ANON_PAGES); 744 } else { 745 __dec_zone_page_state(page, NR_FILE_MAPPED); 746 } 747 mem_cgroup_update_mapped_file_stat(page, -1); 748 /* 749 * It would be tidy to reset the PageAnon mapping here, 750 * but that might overwrite a racing page_add_anon_rmap 751 * which increments mapcount after us but sets mapping 752 * before us: so leave the reset to free_hot_cold_page, 753 * and remember that it's only reliable while mapped. 754 * Leaving it set also helps swapoff to reinstate ptes 755 * faster for those pages still in swapcache. 756 */ 757} 758 759/* 760 * Subfunctions of try_to_unmap: try_to_unmap_one called 761 * repeatedly from either try_to_unmap_anon or try_to_unmap_file. 762 */ 763static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, 764 enum ttu_flags flags) 765{ 766 struct mm_struct *mm = vma->vm_mm; 767 unsigned long address; 768 pte_t *pte; 769 pte_t pteval; 770 spinlock_t *ptl; 771 int ret = SWAP_AGAIN; 772 773 address = vma_address(page, vma); 774 if (address == -EFAULT) 775 goto out; 776 777 pte = page_check_address(page, mm, address, &ptl, 0); 778 if (!pte) 779 goto out; 780 781 /* 782 * If the page is mlock()d, we cannot swap it out. 783 * If it's recently referenced (perhaps page_referenced 784 * skipped over this mm) then we should reactivate it. 785 */ 786 if (!(flags & TTU_IGNORE_MLOCK)) { 787 if (vma->vm_flags & VM_LOCKED) { 788 ret = SWAP_MLOCK; 789 goto out_unmap; 790 } 791 } 792 if (!(flags & TTU_IGNORE_ACCESS)) { 793 if (ptep_clear_flush_young_notify(vma, address, pte)) { 794 ret = SWAP_FAIL; 795 goto out_unmap; 796 } 797 } 798 799 /* Nuke the page table entry. */ 800 flush_cache_page(vma, address, page_to_pfn(page)); 801 pteval = ptep_clear_flush_notify(vma, address, pte); 802 803 /* Move the dirty bit to the physical page now the pte is gone. */ 804 if (pte_dirty(pteval)) 805 set_page_dirty(page); 806 807 /* Update high watermark before we lower rss */ 808 update_hiwater_rss(mm); 809 810 if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) { 811 if (PageAnon(page)) 812 dec_mm_counter(mm, anon_rss); 813 else 814 dec_mm_counter(mm, file_rss); 815 set_pte_at(mm, address, pte, 816 swp_entry_to_pte(make_hwpoison_entry(page))); 817 } else if (PageAnon(page)) { 818 swp_entry_t entry = { .val = page_private(page) }; 819 820 if (PageSwapCache(page)) { 821 /* 822 * Store the swap location in the pte. 823 * See handle_pte_fault() ... 824 */ 825 swap_duplicate(entry); 826 if (list_empty(&mm->mmlist)) { 827 spin_lock(&mmlist_lock); 828 if (list_empty(&mm->mmlist)) 829 list_add(&mm->mmlist, &init_mm.mmlist); 830 spin_unlock(&mmlist_lock); 831 } 832 dec_mm_counter(mm, anon_rss); 833 } else if (PAGE_MIGRATION) { 834 /* 835 * Store the pfn of the page in a special migration 836 * pte. do_swap_page() will wait until the migration 837 * pte is removed and then restart fault handling. 838 */ 839 BUG_ON(TTU_ACTION(flags) != TTU_MIGRATION); 840 entry = make_migration_entry(page, pte_write(pteval)); 841 } 842 set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); 843 BUG_ON(pte_file(*pte)); 844 } else if (PAGE_MIGRATION && (TTU_ACTION(flags) == TTU_MIGRATION)) { 845 /* Establish migration entry for a file page */ 846 swp_entry_t entry; 847 entry = make_migration_entry(page, pte_write(pteval)); 848 set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); 849 } else 850 dec_mm_counter(mm, file_rss); 851 852 853 page_remove_rmap(page); 854 page_cache_release(page); 855 856out_unmap: 857 pte_unmap_unlock(pte, ptl); 858out: 859 return ret; 860} 861 862/* 863 * objrmap doesn't work for nonlinear VMAs because the assumption that 864 * offset-into-file correlates with offset-into-virtual-addresses does not hold. 865 * Consequently, given a particular page and its ->index, we cannot locate the 866 * ptes which are mapping that page without an exhaustive linear search. 867 * 868 * So what this code does is a mini "virtual scan" of each nonlinear VMA which 869 * maps the file to which the target page belongs. The ->vm_private_data field 870 * holds the current cursor into that scan. Successive searches will circulate 871 * around the vma's virtual address space. 872 * 873 * So as more replacement pressure is applied to the pages in a nonlinear VMA, 874 * more scanning pressure is placed against them as well. Eventually pages 875 * will become fully unmapped and are eligible for eviction. 876 * 877 * For very sparsely populated VMAs this is a little inefficient - chances are 878 * there there won't be many ptes located within the scan cluster. In this case 879 * maybe we could scan further - to the end of the pte page, perhaps. 880 * 881 * Mlocked pages: check VM_LOCKED under mmap_sem held for read, if we can 882 * acquire it without blocking. If vma locked, mlock the pages in the cluster, 883 * rather than unmapping them. If we encounter the "check_page" that vmscan is 884 * trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN. 885 */ 886#define CLUSTER_SIZE min(32*PAGE_SIZE, PMD_SIZE) 887#define CLUSTER_MASK (~(CLUSTER_SIZE - 1)) 888 889static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount, 890 struct vm_area_struct *vma, struct page *check_page) 891{ 892 struct mm_struct *mm = vma->vm_mm; 893 pgd_t *pgd; 894 pud_t *pud; 895 pmd_t *pmd; 896 pte_t *pte; 897 pte_t pteval; 898 spinlock_t *ptl; 899 struct page *page; 900 unsigned long address; 901 unsigned long end; 902 int ret = SWAP_AGAIN; 903 int locked_vma = 0; 904 905 address = (vma->vm_start + cursor) & CLUSTER_MASK; 906 end = address + CLUSTER_SIZE; 907 if (address < vma->vm_start) 908 address = vma->vm_start; 909 if (end > vma->vm_end) 910 end = vma->vm_end; 911 912 pgd = pgd_offset(mm, address); 913 if (!pgd_present(*pgd)) 914 return ret; 915 916 pud = pud_offset(pgd, address); 917 if (!pud_present(*pud)) 918 return ret; 919 920 pmd = pmd_offset(pud, address); 921 if (!pmd_present(*pmd)) 922 return ret; 923 924 /* 925 * MLOCK_PAGES => feature is configured. 926 * if we can acquire the mmap_sem for read, and vma is VM_LOCKED, 927 * keep the sem while scanning the cluster for mlocking pages. 928 */ 929 if (MLOCK_PAGES && down_read_trylock(&vma->vm_mm->mmap_sem)) { 930 locked_vma = (vma->vm_flags & VM_LOCKED); 931 if (!locked_vma) 932 up_read(&vma->vm_mm->mmap_sem); /* don't need it */ 933 } 934 935 pte = pte_offset_map_lock(mm, pmd, address, &ptl); 936 937 /* Update high watermark before we lower rss */ 938 update_hiwater_rss(mm); 939 940 for (; address < end; pte++, address += PAGE_SIZE) { 941 if (!pte_present(*pte)) 942 continue; 943 page = vm_normal_page(vma, address, *pte); 944 BUG_ON(!page || PageAnon(page)); 945 946 if (locked_vma) { 947 mlock_vma_page(page); /* no-op if already mlocked */ 948 if (page == check_page) 949 ret = SWAP_MLOCK; 950 continue; /* don't unmap */ 951 } 952 953 if (ptep_clear_flush_young_notify(vma, address, pte)) 954 continue; 955 956 /* Nuke the page table entry. */ 957 flush_cache_page(vma, address, pte_pfn(*pte)); 958 pteval = ptep_clear_flush_notify(vma, address, pte); 959 960 /* If nonlinear, store the file page offset in the pte. */ 961 if (page->index != linear_page_index(vma, address)) 962 set_pte_at(mm, address, pte, pgoff_to_pte(page->index)); 963 964 /* Move the dirty bit to the physical page now the pte is gone. */ 965 if (pte_dirty(pteval)) 966 set_page_dirty(page); 967 968 page_remove_rmap(page); 969 page_cache_release(page); 970 dec_mm_counter(mm, file_rss); 971 (*mapcount)--; 972 } 973 pte_unmap_unlock(pte - 1, ptl); 974 if (locked_vma) 975 up_read(&vma->vm_mm->mmap_sem); 976 return ret; 977} 978 979/* 980 * common handling for pages mapped in VM_LOCKED vmas 981 */ 982static int try_to_mlock_page(struct page *page, struct vm_area_struct *vma) 983{ 984 int mlocked = 0; 985 986 if (down_read_trylock(&vma->vm_mm->mmap_sem)) { 987 if (vma->vm_flags & VM_LOCKED) { 988 mlock_vma_page(page); 989 mlocked++; /* really mlocked the page */ 990 } 991 up_read(&vma->vm_mm->mmap_sem); 992 } 993 return mlocked; 994} 995 996/** 997 * try_to_unmap_anon - unmap or unlock anonymous page using the object-based 998 * rmap method 999 * @page: the page to unmap/unlock 1000 * @unlock: request for unlock rather than unmap [unlikely] 1001 * @migration: unmapping for migration - ignored if @unlock 1002 * 1003 * Find all the mappings of a page using the mapping pointer and the vma chains 1004 * contained in the anon_vma struct it points to. 1005 * 1006 * This function is only called from try_to_unmap/try_to_munlock for 1007 * anonymous pages. 1008 * When called from try_to_munlock(), the mmap_sem of the mm containing the vma 1009 * where the page was found will be held for write. So, we won't recheck 1010 * vm_flags for that VMA. That should be OK, because that vma shouldn't be 1011 * 'LOCKED. 1012 */ 1013static int try_to_unmap_anon(struct page *page, enum ttu_flags flags) 1014{ 1015 struct anon_vma *anon_vma; 1016 struct vm_area_struct *vma; 1017 unsigned int mlocked = 0; 1018 int ret = SWAP_AGAIN; 1019 int unlock = TTU_ACTION(flags) == TTU_MUNLOCK; 1020 1021 if (MLOCK_PAGES && unlikely(unlock)) 1022 ret = SWAP_SUCCESS; /* default for try_to_munlock() */ 1023 1024 anon_vma = page_lock_anon_vma(page); 1025 if (!anon_vma) 1026 return ret; 1027 1028 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) { 1029 if (MLOCK_PAGES && unlikely(unlock)) { 1030 if (!((vma->vm_flags & VM_LOCKED) && 1031 page_mapped_in_vma(page, vma))) 1032 continue; /* must visit all unlocked vmas */ 1033 ret = SWAP_MLOCK; /* saw at least one mlocked vma */ 1034 } else { 1035 ret = try_to_unmap_one(page, vma, flags); 1036 if (ret == SWAP_FAIL || !page_mapped(page)) 1037 break; 1038 } 1039 if (ret == SWAP_MLOCK) { 1040 mlocked = try_to_mlock_page(page, vma); 1041 if (mlocked) 1042 break; /* stop if actually mlocked page */ 1043 } 1044 } 1045 1046 page_unlock_anon_vma(anon_vma); 1047 1048 if (mlocked) 1049 ret = SWAP_MLOCK; /* actually mlocked the page */ 1050 else if (ret == SWAP_MLOCK) 1051 ret = SWAP_AGAIN; /* saw VM_LOCKED vma */ 1052 1053 return ret; 1054} 1055 1056/** 1057 * try_to_unmap_file - unmap/unlock file page using the object-based rmap method 1058 * @page: the page to unmap/unlock 1059 * @flags: action and flags 1060 * 1061 * Find all the mappings of a page using the mapping pointer and the vma chains 1062 * contained in the address_space struct it points to. 1063 * 1064 * This function is only called from try_to_unmap/try_to_munlock for 1065 * object-based pages. 1066 * When called from try_to_munlock(), the mmap_sem of the mm containing the vma 1067 * where the page was found will be held for write. So, we won't recheck 1068 * vm_flags for that VMA. That should be OK, because that vma shouldn't be 1069 * 'LOCKED. 1070 */ 1071static int try_to_unmap_file(struct page *page, enum ttu_flags flags) 1072{ 1073 struct address_space *mapping = page->mapping; 1074 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 1075 struct vm_area_struct *vma; 1076 struct prio_tree_iter iter; 1077 int ret = SWAP_AGAIN; 1078 unsigned long cursor; 1079 unsigned long max_nl_cursor = 0; 1080 unsigned long max_nl_size = 0; 1081 unsigned int mapcount; 1082 unsigned int mlocked = 0; 1083 int unlock = TTU_ACTION(flags) == TTU_MUNLOCK; 1084 1085 if (MLOCK_PAGES && unlikely(unlock)) 1086 ret = SWAP_SUCCESS; /* default for try_to_munlock() */ 1087 1088 spin_lock(&mapping->i_mmap_lock); 1089 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { 1090 if (MLOCK_PAGES && unlikely(unlock)) { 1091 if (!((vma->vm_flags & VM_LOCKED) && 1092 page_mapped_in_vma(page, vma))) 1093 continue; /* must visit all vmas */ 1094 ret = SWAP_MLOCK; 1095 } else { 1096 ret = try_to_unmap_one(page, vma, flags); 1097 if (ret == SWAP_FAIL || !page_mapped(page)) 1098 goto out; 1099 } 1100 if (ret == SWAP_MLOCK) { 1101 mlocked = try_to_mlock_page(page, vma); 1102 if (mlocked) 1103 break; /* stop if actually mlocked page */ 1104 } 1105 } 1106 1107 if (mlocked) 1108 goto out; 1109 1110 if (list_empty(&mapping->i_mmap_nonlinear)) 1111 goto out; 1112 1113 list_for_each_entry(vma, &mapping->i_mmap_nonlinear, 1114 shared.vm_set.list) { 1115 if (MLOCK_PAGES && unlikely(unlock)) { 1116 if (!(vma->vm_flags & VM_LOCKED)) 1117 continue; /* must visit all vmas */ 1118 ret = SWAP_MLOCK; /* leave mlocked == 0 */ 1119 goto out; /* no need to look further */ 1120 } 1121 if (!MLOCK_PAGES && !(flags & TTU_IGNORE_MLOCK) && 1122 (vma->vm_flags & VM_LOCKED)) 1123 continue; 1124 cursor = (unsigned long) vma->vm_private_data; 1125 if (cursor > max_nl_cursor) 1126 max_nl_cursor = cursor; 1127 cursor = vma->vm_end - vma->vm_start; 1128 if (cursor > max_nl_size) 1129 max_nl_size = cursor; 1130 } 1131 1132 if (max_nl_size == 0) { /* all nonlinears locked or reserved ? */ 1133 ret = SWAP_FAIL; 1134 goto out; 1135 } 1136 1137 /* 1138 * We don't try to search for this page in the nonlinear vmas, 1139 * and page_referenced wouldn't have found it anyway. Instead 1140 * just walk the nonlinear vmas trying to age and unmap some. 1141 * The mapcount of the page we came in with is irrelevant, 1142 * but even so use it as a guide to how hard we should try? 1143 */ 1144 mapcount = page_mapcount(page); 1145 if (!mapcount) 1146 goto out; 1147 cond_resched_lock(&mapping->i_mmap_lock); 1148 1149 max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK; 1150 if (max_nl_cursor == 0) 1151 max_nl_cursor = CLUSTER_SIZE; 1152 1153 do { 1154 list_for_each_entry(vma, &mapping->i_mmap_nonlinear, 1155 shared.vm_set.list) { 1156 if (!MLOCK_PAGES && !(flags & TTU_IGNORE_MLOCK) && 1157 (vma->vm_flags & VM_LOCKED)) 1158 continue; 1159 cursor = (unsigned long) vma->vm_private_data; 1160 while ( cursor < max_nl_cursor && 1161 cursor < vma->vm_end - vma->vm_start) { 1162 ret = try_to_unmap_cluster(cursor, &mapcount, 1163 vma, page); 1164 if (ret == SWAP_MLOCK) 1165 mlocked = 2; /* to return below */ 1166 cursor += CLUSTER_SIZE; 1167 vma->vm_private_data = (void *) cursor; 1168 if ((int)mapcount <= 0) 1169 goto out; 1170 } 1171 vma->vm_private_data = (void *) max_nl_cursor; 1172 } 1173 cond_resched_lock(&mapping->i_mmap_lock); 1174 max_nl_cursor += CLUSTER_SIZE; 1175 } while (max_nl_cursor <= max_nl_size); 1176 1177 /* 1178 * Don't loop forever (perhaps all the remaining pages are 1179 * in locked vmas). Reset cursor on all unreserved nonlinear 1180 * vmas, now forgetting on which ones it had fallen behind. 1181 */ 1182 list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list) 1183 vma->vm_private_data = NULL; 1184out: 1185 spin_unlock(&mapping->i_mmap_lock); 1186 if (mlocked) 1187 ret = SWAP_MLOCK; /* actually mlocked the page */ 1188 else if (ret == SWAP_MLOCK) 1189 ret = SWAP_AGAIN; /* saw VM_LOCKED vma */ 1190 return ret; 1191} 1192 1193/** 1194 * try_to_unmap - try to remove all page table mappings to a page 1195 * @page: the page to get unmapped 1196 * @flags: action and flags 1197 * 1198 * Tries to remove all the page table entries which are mapping this 1199 * page, used in the pageout path. Caller must hold the page lock. 1200 * Return values are: 1201 * 1202 * SWAP_SUCCESS - we succeeded in removing all mappings 1203 * SWAP_AGAIN - we missed a mapping, try again later 1204 * SWAP_FAIL - the page is unswappable 1205 * SWAP_MLOCK - page is mlocked. 1206 */ 1207int try_to_unmap(struct page *page, enum ttu_flags flags) 1208{ 1209 int ret; 1210 1211 BUG_ON(!PageLocked(page)); 1212 1213 if (PageAnon(page)) 1214 ret = try_to_unmap_anon(page, flags); 1215 else 1216 ret = try_to_unmap_file(page, flags); 1217 if (ret != SWAP_MLOCK && !page_mapped(page)) 1218 ret = SWAP_SUCCESS; 1219 return ret; 1220} 1221 1222/** 1223 * try_to_munlock - try to munlock a page 1224 * @page: the page to be munlocked 1225 * 1226 * Called from munlock code. Checks all of the VMAs mapping the page 1227 * to make sure nobody else has this page mlocked. The page will be 1228 * returned with PG_mlocked cleared if no other vmas have it mlocked. 1229 * 1230 * Return values are: 1231 * 1232 * SWAP_SUCCESS - no vma's holding page mlocked. 1233 * SWAP_AGAIN - page mapped in mlocked vma -- couldn't acquire mmap sem 1234 * SWAP_MLOCK - page is now mlocked. 1235 */ 1236int try_to_munlock(struct page *page) 1237{ 1238 VM_BUG_ON(!PageLocked(page) || PageLRU(page)); 1239 1240 if (PageAnon(page)) 1241 return try_to_unmap_anon(page, TTU_MUNLOCK); 1242 else 1243 return try_to_unmap_file(page, TTU_MUNLOCK); 1244} 1245 1246