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 41 #include <linux/mm.h> 42 #include <linux/pagemap.h> 43 #include <linux/swap.h> 44 #include <linux/swapops.h> 45 #include <linux/slab.h> 46 #include <linux/init.h> 47 #include <linux/rmap.h> 48 #include <linux/rcupdate.h> 49 #include <linux/module.h> 50 #include <linux/memcontrol.h> 51 #include <linux/mmu_notifier.h> 52 #include <linux/migrate.h> 53 54 #include <asm/tlbflush.h> 55 56 #include "internal.h" 57 58 static struct kmem_cache *anon_vma_cachep; 59 60 static inline struct anon_vma *anon_vma_alloc(void) 61 { 62 return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL); 63 } 64 65 static inline void anon_vma_free(struct anon_vma *anon_vma) 66 { 67 kmem_cache_free(anon_vma_cachep, anon_vma); 68 } 69 70 /** 71 * anon_vma_prepare - attach an anon_vma to a memory region 72 * @vma: the memory region in question 73 * 74 * This makes sure the memory mapping described by 'vma' has 75 * an 'anon_vma' attached to it, so that we can associate the 76 * anonymous pages mapped into it with that anon_vma. 77 * 78 * The common case will be that we already have one, but if 79 * if not we either need to find an adjacent mapping that we 80 * can re-use the anon_vma from (very common when the only 81 * reason for splitting a vma has been mprotect()), or we 82 * allocate a new one. 83 * 84 * Anon-vma allocations are very subtle, because we may have 85 * optimistically looked up an anon_vma in page_lock_anon_vma() 86 * and that may actually touch the spinlock even in the newly 87 * allocated vma (it depends on RCU to make sure that the 88 * anon_vma isn't actually destroyed). 89 * 90 * As a result, we need to do proper anon_vma locking even 91 * for the new allocation. At the same time, we do not want 92 * to do any locking for the common case of already having 93 * an anon_vma. 94 * 95 * This must be called with the mmap_sem held for reading. 96 */ 97 int anon_vma_prepare(struct vm_area_struct *vma) 98 { 99 struct anon_vma *anon_vma = vma->anon_vma; 100 101 might_sleep(); 102 if (unlikely(!anon_vma)) { 103 struct mm_struct *mm = vma->vm_mm; 104 struct anon_vma *allocated; 105 106 anon_vma = find_mergeable_anon_vma(vma); 107 allocated = NULL; 108 if (!anon_vma) { 109 anon_vma = anon_vma_alloc(); 110 if (unlikely(!anon_vma)) 111 return -ENOMEM; 112 allocated = anon_vma; 113 } 114 spin_lock(&anon_vma->lock); 115 116 /* page_table_lock to protect against threads */ 117 spin_lock(&mm->page_table_lock); 118 if (likely(!vma->anon_vma)) { 119 vma->anon_vma = anon_vma; 120 list_add_tail(&vma->anon_vma_node, &anon_vma->head); 121 allocated = NULL; 122 } 123 spin_unlock(&mm->page_table_lock); 124 125 spin_unlock(&anon_vma->lock); 126 if (unlikely(allocated)) 127 anon_vma_free(allocated); 128 } 129 return 0; 130 } 131 132 void __anon_vma_merge(struct vm_area_struct *vma, struct vm_area_struct *next) 133 { 134 BUG_ON(vma->anon_vma != next->anon_vma); 135 list_del(&next->anon_vma_node); 136 } 137 138 void __anon_vma_link(struct vm_area_struct *vma) 139 { 140 struct anon_vma *anon_vma = vma->anon_vma; 141 142 if (anon_vma) 143 list_add_tail(&vma->anon_vma_node, &anon_vma->head); 144 } 145 146 void anon_vma_link(struct vm_area_struct *vma) 147 { 148 struct anon_vma *anon_vma = vma->anon_vma; 149 150 if (anon_vma) { 151 spin_lock(&anon_vma->lock); 152 list_add_tail(&vma->anon_vma_node, &anon_vma->head); 153 spin_unlock(&anon_vma->lock); 154 } 155 } 156 157 void anon_vma_unlink(struct vm_area_struct *vma) 158 { 159 struct anon_vma *anon_vma = vma->anon_vma; 160 int empty; 161 162 if (!anon_vma) 163 return; 164 165 spin_lock(&anon_vma->lock); 166 list_del(&vma->anon_vma_node); 167 168 /* We must garbage collect the anon_vma if it's empty */ 169 empty = list_empty(&anon_vma->head); 170 spin_unlock(&anon_vma->lock); 171 172 if (empty) 173 anon_vma_free(anon_vma); 174 } 175 176 static void anon_vma_ctor(void *data) 177 { 178 struct anon_vma *anon_vma = data; 179 180 spin_lock_init(&anon_vma->lock); 181 INIT_LIST_HEAD(&anon_vma->head); 182 } 183 184 void __init anon_vma_init(void) 185 { 186 anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma), 187 0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor); 188 } 189 190 /* 191 * Getting a lock on a stable anon_vma from a page off the LRU is 192 * tricky: page_lock_anon_vma rely on RCU to guard against the races. 193 */ 194 static struct anon_vma *page_lock_anon_vma(struct page *page) 195 { 196 struct anon_vma *anon_vma; 197 unsigned long anon_mapping; 198 199 rcu_read_lock(); 200 anon_mapping = (unsigned long) page->mapping; 201 if (!(anon_mapping & PAGE_MAPPING_ANON)) 202 goto out; 203 if (!page_mapped(page)) 204 goto out; 205 206 anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON); 207 spin_lock(&anon_vma->lock); 208 return anon_vma; 209 out: 210 rcu_read_unlock(); 211 return NULL; 212 } 213 214 static void page_unlock_anon_vma(struct anon_vma *anon_vma) 215 { 216 spin_unlock(&anon_vma->lock); 217 rcu_read_unlock(); 218 } 219 220 /* 221 * At what user virtual address is page expected in @vma? 222 * Returns virtual address or -EFAULT if page's index/offset is not 223 * within the range mapped the @vma. 224 */ 225 static inline unsigned long 226 vma_address(struct page *page, struct vm_area_struct *vma) 227 { 228 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 229 unsigned long address; 230 231 address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT); 232 if (unlikely(address < vma->vm_start || address >= vma->vm_end)) { 233 /* page should be within @vma mapping range */ 234 return -EFAULT; 235 } 236 return address; 237 } 238 239 /* 240 * At what user virtual address is page expected in vma? checking that the 241 * page matches the vma: currently only used on anon pages, by unuse_vma; 242 */ 243 unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma) 244 { 245 if (PageAnon(page)) { 246 if ((void *)vma->anon_vma != 247 (void *)page->mapping - PAGE_MAPPING_ANON) 248 return -EFAULT; 249 } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) { 250 if (!vma->vm_file || 251 vma->vm_file->f_mapping != page->mapping) 252 return -EFAULT; 253 } else 254 return -EFAULT; 255 return vma_address(page, vma); 256 } 257 258 /* 259 * Check that @page is mapped at @address into @mm. 260 * 261 * If @sync is false, page_check_address may perform a racy check to avoid 262 * the page table lock when the pte is not present (helpful when reclaiming 263 * highly shared pages). 264 * 265 * On success returns with pte mapped and locked. 266 */ 267 pte_t *page_check_address(struct page *page, struct mm_struct *mm, 268 unsigned long address, spinlock_t **ptlp, int sync) 269 { 270 pgd_t *pgd; 271 pud_t *pud; 272 pmd_t *pmd; 273 pte_t *pte; 274 spinlock_t *ptl; 275 276 pgd = pgd_offset(mm, address); 277 if (!pgd_present(*pgd)) 278 return NULL; 279 280 pud = pud_offset(pgd, address); 281 if (!pud_present(*pud)) 282 return NULL; 283 284 pmd = pmd_offset(pud, address); 285 if (!pmd_present(*pmd)) 286 return NULL; 287 288 pte = pte_offset_map(pmd, address); 289 /* Make a quick check before getting the lock */ 290 if (!sync && !pte_present(*pte)) { 291 pte_unmap(pte); 292 return NULL; 293 } 294 295 ptl = pte_lockptr(mm, pmd); 296 spin_lock(ptl); 297 if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) { 298 *ptlp = ptl; 299 return pte; 300 } 301 pte_unmap_unlock(pte, ptl); 302 return NULL; 303 } 304 305 /** 306 * page_mapped_in_vma - check whether a page is really mapped in a VMA 307 * @page: the page to test 308 * @vma: the VMA to test 309 * 310 * Returns 1 if the page is mapped into the page tables of the VMA, 0 311 * if the page is not mapped into the page tables of this VMA. Only 312 * valid for normal file or anonymous VMAs. 313 */ 314 static int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma) 315 { 316 unsigned long address; 317 pte_t *pte; 318 spinlock_t *ptl; 319 320 address = vma_address(page, vma); 321 if (address == -EFAULT) /* out of vma range */ 322 return 0; 323 pte = page_check_address(page, vma->vm_mm, address, &ptl, 1); 324 if (!pte) /* the page is not in this mm */ 325 return 0; 326 pte_unmap_unlock(pte, ptl); 327 328 return 1; 329 } 330 331 /* 332 * Subfunctions of page_referenced: page_referenced_one called 333 * repeatedly from either page_referenced_anon or page_referenced_file. 334 */ 335 static int page_referenced_one(struct page *page, 336 struct vm_area_struct *vma, 337 unsigned int *mapcount, 338 unsigned long *vm_flags) 339 { 340 struct mm_struct *mm = vma->vm_mm; 341 unsigned long address; 342 pte_t *pte; 343 spinlock_t *ptl; 344 int referenced = 0; 345 346 address = vma_address(page, vma); 347 if (address == -EFAULT) 348 goto out; 349 350 pte = page_check_address(page, mm, address, &ptl, 0); 351 if (!pte) 352 goto out; 353 354 /* 355 * Don't want to elevate referenced for mlocked page that gets this far, 356 * in order that it progresses to try_to_unmap and is moved to the 357 * unevictable list. 358 */ 359 if (vma->vm_flags & VM_LOCKED) { 360 *mapcount = 1; /* break early from loop */ 361 *vm_flags |= VM_LOCKED; 362 goto out_unmap; 363 } 364 365 if (ptep_clear_flush_young_notify(vma, address, pte)) { 366 /* 367 * Don't treat a reference through a sequentially read 368 * mapping as such. If the page has been used in 369 * another mapping, we will catch it; if this other 370 * mapping is already gone, the unmap path will have 371 * set PG_referenced or activated the page. 372 */ 373 if (likely(!VM_SequentialReadHint(vma))) 374 referenced++; 375 } 376 377 /* Pretend the page is referenced if the task has the 378 swap token and is in the middle of a page fault. */ 379 if (mm != current->mm && has_swap_token(mm) && 380 rwsem_is_locked(&mm->mmap_sem)) 381 referenced++; 382 383 out_unmap: 384 (*mapcount)--; 385 pte_unmap_unlock(pte, ptl); 386 out: 387 if (referenced) 388 *vm_flags |= vma->vm_flags; 389 return referenced; 390 } 391 392 static int page_referenced_anon(struct page *page, 393 struct mem_cgroup *mem_cont, 394 unsigned long *vm_flags) 395 { 396 unsigned int mapcount; 397 struct anon_vma *anon_vma; 398 struct vm_area_struct *vma; 399 int referenced = 0; 400 401 anon_vma = page_lock_anon_vma(page); 402 if (!anon_vma) 403 return referenced; 404 405 mapcount = page_mapcount(page); 406 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) { 407 /* 408 * If we are reclaiming on behalf of a cgroup, skip 409 * counting on behalf of references from different 410 * cgroups 411 */ 412 if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont)) 413 continue; 414 referenced += page_referenced_one(page, vma, 415 &mapcount, vm_flags); 416 if (!mapcount) 417 break; 418 } 419 420 page_unlock_anon_vma(anon_vma); 421 return referenced; 422 } 423 424 /** 425 * page_referenced_file - referenced check for object-based rmap 426 * @page: the page we're checking references on. 427 * @mem_cont: target memory controller 428 * @vm_flags: collect encountered vma->vm_flags who actually referenced the page 429 * 430 * For an object-based mapped page, find all the places it is mapped and 431 * check/clear the referenced flag. This is done by following the page->mapping 432 * pointer, then walking the chain of vmas it holds. It returns the number 433 * of references it found. 434 * 435 * This function is only called from page_referenced for object-based pages. 436 */ 437 static int page_referenced_file(struct page *page, 438 struct mem_cgroup *mem_cont, 439 unsigned long *vm_flags) 440 { 441 unsigned int mapcount; 442 struct address_space *mapping = page->mapping; 443 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 444 struct vm_area_struct *vma; 445 struct prio_tree_iter iter; 446 int referenced = 0; 447 448 /* 449 * The caller's checks on page->mapping and !PageAnon have made 450 * sure that this is a file page: the check for page->mapping 451 * excludes the case just before it gets set on an anon page. 452 */ 453 BUG_ON(PageAnon(page)); 454 455 /* 456 * The page lock not only makes sure that page->mapping cannot 457 * suddenly be NULLified by truncation, it makes sure that the 458 * structure at mapping cannot be freed and reused yet, 459 * so we can safely take mapping->i_mmap_lock. 460 */ 461 BUG_ON(!PageLocked(page)); 462 463 spin_lock(&mapping->i_mmap_lock); 464 465 /* 466 * i_mmap_lock does not stabilize mapcount at all, but mapcount 467 * is more likely to be accurate if we note it after spinning. 468 */ 469 mapcount = page_mapcount(page); 470 471 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { 472 /* 473 * If we are reclaiming on behalf of a cgroup, skip 474 * counting on behalf of references from different 475 * cgroups 476 */ 477 if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont)) 478 continue; 479 referenced += page_referenced_one(page, vma, 480 &mapcount, vm_flags); 481 if (!mapcount) 482 break; 483 } 484 485 spin_unlock(&mapping->i_mmap_lock); 486 return referenced; 487 } 488 489 /** 490 * page_referenced - test if the page was referenced 491 * @page: the page to test 492 * @is_locked: caller holds lock on the page 493 * @mem_cont: target memory controller 494 * @vm_flags: collect encountered vma->vm_flags who actually referenced the page 495 * 496 * Quick test_and_clear_referenced for all mappings to a page, 497 * returns the number of ptes which referenced the page. 498 */ 499 int page_referenced(struct page *page, 500 int is_locked, 501 struct mem_cgroup *mem_cont, 502 unsigned long *vm_flags) 503 { 504 int referenced = 0; 505 506 if (TestClearPageReferenced(page)) 507 referenced++; 508 509 *vm_flags = 0; 510 if (page_mapped(page) && page->mapping) { 511 if (PageAnon(page)) 512 referenced += page_referenced_anon(page, mem_cont, 513 vm_flags); 514 else if (is_locked) 515 referenced += page_referenced_file(page, mem_cont, 516 vm_flags); 517 else if (!trylock_page(page)) 518 referenced++; 519 else { 520 if (page->mapping) 521 referenced += page_referenced_file(page, 522 mem_cont, vm_flags); 523 unlock_page(page); 524 } 525 } 526 527 if (page_test_and_clear_young(page)) 528 referenced++; 529 530 return referenced; 531 } 532 533 static int page_mkclean_one(struct page *page, struct vm_area_struct *vma) 534 { 535 struct mm_struct *mm = vma->vm_mm; 536 unsigned long address; 537 pte_t *pte; 538 spinlock_t *ptl; 539 int ret = 0; 540 541 address = vma_address(page, vma); 542 if (address == -EFAULT) 543 goto out; 544 545 pte = page_check_address(page, mm, address, &ptl, 1); 546 if (!pte) 547 goto out; 548 549 if (pte_dirty(*pte) || pte_write(*pte)) { 550 pte_t entry; 551 552 flush_cache_page(vma, address, pte_pfn(*pte)); 553 entry = ptep_clear_flush_notify(vma, address, pte); 554 entry = pte_wrprotect(entry); 555 entry = pte_mkclean(entry); 556 set_pte_at(mm, address, pte, entry); 557 ret = 1; 558 } 559 560 pte_unmap_unlock(pte, ptl); 561 out: 562 return ret; 563 } 564 565 static int page_mkclean_file(struct address_space *mapping, struct page *page) 566 { 567 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 568 struct vm_area_struct *vma; 569 struct prio_tree_iter iter; 570 int ret = 0; 571 572 BUG_ON(PageAnon(page)); 573 574 spin_lock(&mapping->i_mmap_lock); 575 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { 576 if (vma->vm_flags & VM_SHARED) 577 ret += page_mkclean_one(page, vma); 578 } 579 spin_unlock(&mapping->i_mmap_lock); 580 return ret; 581 } 582 583 int page_mkclean(struct page *page) 584 { 585 int ret = 0; 586 587 BUG_ON(!PageLocked(page)); 588 589 if (page_mapped(page)) { 590 struct address_space *mapping = page_mapping(page); 591 if (mapping) { 592 ret = page_mkclean_file(mapping, page); 593 if (page_test_dirty(page)) { 594 page_clear_dirty(page); 595 ret = 1; 596 } 597 } 598 } 599 600 return ret; 601 } 602 EXPORT_SYMBOL_GPL(page_mkclean); 603 604 /** 605 * __page_set_anon_rmap - setup new anonymous rmap 606 * @page: the page to add the mapping to 607 * @vma: the vm area in which the mapping is added 608 * @address: the user virtual address mapped 609 */ 610 static void __page_set_anon_rmap(struct page *page, 611 struct vm_area_struct *vma, unsigned long address) 612 { 613 struct anon_vma *anon_vma = vma->anon_vma; 614 615 BUG_ON(!anon_vma); 616 anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; 617 page->mapping = (struct address_space *) anon_vma; 618 619 page->index = linear_page_index(vma, address); 620 621 /* 622 * nr_mapped state can be updated without turning off 623 * interrupts because it is not modified via interrupt. 624 */ 625 __inc_zone_page_state(page, NR_ANON_PAGES); 626 } 627 628 /** 629 * __page_check_anon_rmap - sanity check anonymous rmap addition 630 * @page: the page to add the mapping to 631 * @vma: the vm area in which the mapping is added 632 * @address: the user virtual address mapped 633 */ 634 static void __page_check_anon_rmap(struct page *page, 635 struct vm_area_struct *vma, unsigned long address) 636 { 637 #ifdef CONFIG_DEBUG_VM 638 /* 639 * The page's anon-rmap details (mapping and index) are guaranteed to 640 * be set up correctly at this point. 641 * 642 * We have exclusion against page_add_anon_rmap because the caller 643 * always holds the page locked, except if called from page_dup_rmap, 644 * in which case the page is already known to be setup. 645 * 646 * We have exclusion against page_add_new_anon_rmap because those pages 647 * are initially only visible via the pagetables, and the pte is locked 648 * over the call to page_add_new_anon_rmap. 649 */ 650 struct anon_vma *anon_vma = vma->anon_vma; 651 anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; 652 BUG_ON(page->mapping != (struct address_space *)anon_vma); 653 BUG_ON(page->index != linear_page_index(vma, address)); 654 #endif 655 } 656 657 /** 658 * page_add_anon_rmap - add pte mapping to an anonymous page 659 * @page: the page to add the mapping to 660 * @vma: the vm area in which the mapping is added 661 * @address: the user virtual address mapped 662 * 663 * The caller needs to hold the pte lock and the page must be locked. 664 */ 665 void page_add_anon_rmap(struct page *page, 666 struct vm_area_struct *vma, unsigned long address) 667 { 668 VM_BUG_ON(!PageLocked(page)); 669 VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end); 670 if (atomic_inc_and_test(&page->_mapcount)) 671 __page_set_anon_rmap(page, vma, address); 672 else 673 __page_check_anon_rmap(page, vma, address); 674 } 675 676 /** 677 * page_add_new_anon_rmap - add pte mapping to a new anonymous page 678 * @page: the page to add the mapping to 679 * @vma: the vm area in which the mapping is added 680 * @address: the user virtual address mapped 681 * 682 * Same as page_add_anon_rmap but must only be called on *new* pages. 683 * This means the inc-and-test can be bypassed. 684 * Page does not have to be locked. 685 */ 686 void page_add_new_anon_rmap(struct page *page, 687 struct vm_area_struct *vma, unsigned long address) 688 { 689 VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end); 690 SetPageSwapBacked(page); 691 atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */ 692 __page_set_anon_rmap(page, vma, address); 693 if (page_evictable(page, vma)) 694 lru_cache_add_lru(page, LRU_ACTIVE_ANON); 695 else 696 add_page_to_unevictable_list(page); 697 } 698 699 /** 700 * page_add_file_rmap - add pte mapping to a file page 701 * @page: the page to add the mapping to 702 * 703 * The caller needs to hold the pte lock. 704 */ 705 void page_add_file_rmap(struct page *page) 706 { 707 if (atomic_inc_and_test(&page->_mapcount)) { 708 __inc_zone_page_state(page, NR_FILE_MAPPED); 709 mem_cgroup_update_mapped_file_stat(page, 1); 710 } 711 } 712 713 #ifdef CONFIG_DEBUG_VM 714 /** 715 * page_dup_rmap - duplicate pte mapping to a page 716 * @page: the page to add the mapping to 717 * @vma: the vm area being duplicated 718 * @address: the user virtual address mapped 719 * 720 * For copy_page_range only: minimal extract from page_add_file_rmap / 721 * page_add_anon_rmap, avoiding unnecessary tests (already checked) so it's 722 * quicker. 723 * 724 * The caller needs to hold the pte lock. 725 */ 726 void page_dup_rmap(struct page *page, struct vm_area_struct *vma, unsigned long address) 727 { 728 if (PageAnon(page)) 729 __page_check_anon_rmap(page, vma, address); 730 atomic_inc(&page->_mapcount); 731 } 732 #endif 733 734 /** 735 * page_remove_rmap - take down pte mapping from a page 736 * @page: page to remove mapping from 737 * 738 * The caller needs to hold the pte lock. 739 */ 740 void page_remove_rmap(struct page *page) 741 { 742 if (atomic_add_negative(-1, &page->_mapcount)) { 743 /* 744 * Now that the last pte has gone, s390 must transfer dirty 745 * flag from storage key to struct page. We can usually skip 746 * this if the page is anon, so about to be freed; but perhaps 747 * not if it's in swapcache - there might be another pte slot 748 * containing the swap entry, but page not yet written to swap. 749 */ 750 if ((!PageAnon(page) || PageSwapCache(page)) && 751 page_test_dirty(page)) { 752 page_clear_dirty(page); 753 set_page_dirty(page); 754 } 755 if (PageAnon(page)) 756 mem_cgroup_uncharge_page(page); 757 __dec_zone_page_state(page, 758 PageAnon(page) ? NR_ANON_PAGES : NR_FILE_MAPPED); 759 mem_cgroup_update_mapped_file_stat(page, -1); 760 /* 761 * It would be tidy to reset the PageAnon mapping here, 762 * but that might overwrite a racing page_add_anon_rmap 763 * which increments mapcount after us but sets mapping 764 * before us: so leave the reset to free_hot_cold_page, 765 * and remember that it's only reliable while mapped. 766 * Leaving it set also helps swapoff to reinstate ptes 767 * faster for those pages still in swapcache. 768 */ 769 } 770 } 771 772 /* 773 * Subfunctions of try_to_unmap: try_to_unmap_one called 774 * repeatedly from either try_to_unmap_anon or try_to_unmap_file. 775 */ 776 static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, 777 int migration) 778 { 779 struct mm_struct *mm = vma->vm_mm; 780 unsigned long address; 781 pte_t *pte; 782 pte_t pteval; 783 spinlock_t *ptl; 784 int ret = SWAP_AGAIN; 785 786 address = vma_address(page, vma); 787 if (address == -EFAULT) 788 goto out; 789 790 pte = page_check_address(page, mm, address, &ptl, 0); 791 if (!pte) 792 goto out; 793 794 /* 795 * If the page is mlock()d, we cannot swap it out. 796 * If it's recently referenced (perhaps page_referenced 797 * skipped over this mm) then we should reactivate it. 798 */ 799 if (!migration) { 800 if (vma->vm_flags & VM_LOCKED) { 801 ret = SWAP_MLOCK; 802 goto out_unmap; 803 } 804 if (ptep_clear_flush_young_notify(vma, address, pte)) { 805 ret = SWAP_FAIL; 806 goto out_unmap; 807 } 808 } 809 810 /* Nuke the page table entry. */ 811 flush_cache_page(vma, address, page_to_pfn(page)); 812 pteval = ptep_clear_flush_notify(vma, address, pte); 813 814 /* Move the dirty bit to the physical page now the pte is gone. */ 815 if (pte_dirty(pteval)) 816 set_page_dirty(page); 817 818 /* Update high watermark before we lower rss */ 819 update_hiwater_rss(mm); 820 821 if (PageAnon(page)) { 822 swp_entry_t entry = { .val = page_private(page) }; 823 824 if (PageSwapCache(page)) { 825 /* 826 * Store the swap location in the pte. 827 * See handle_pte_fault() ... 828 */ 829 swap_duplicate(entry); 830 if (list_empty(&mm->mmlist)) { 831 spin_lock(&mmlist_lock); 832 if (list_empty(&mm->mmlist)) 833 list_add(&mm->mmlist, &init_mm.mmlist); 834 spin_unlock(&mmlist_lock); 835 } 836 dec_mm_counter(mm, anon_rss); 837 } else if (PAGE_MIGRATION) { 838 /* 839 * Store the pfn of the page in a special migration 840 * pte. do_swap_page() will wait until the migration 841 * pte is removed and then restart fault handling. 842 */ 843 BUG_ON(!migration); 844 entry = make_migration_entry(page, pte_write(pteval)); 845 } 846 set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); 847 BUG_ON(pte_file(*pte)); 848 } else if (PAGE_MIGRATION && migration) { 849 /* Establish migration entry for a file page */ 850 swp_entry_t entry; 851 entry = make_migration_entry(page, pte_write(pteval)); 852 set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); 853 } else 854 dec_mm_counter(mm, file_rss); 855 856 857 page_remove_rmap(page); 858 page_cache_release(page); 859 860 out_unmap: 861 pte_unmap_unlock(pte, ptl); 862 out: 863 return ret; 864 } 865 866 /* 867 * objrmap doesn't work for nonlinear VMAs because the assumption that 868 * offset-into-file correlates with offset-into-virtual-addresses does not hold. 869 * Consequently, given a particular page and its ->index, we cannot locate the 870 * ptes which are mapping that page without an exhaustive linear search. 871 * 872 * So what this code does is a mini "virtual scan" of each nonlinear VMA which 873 * maps the file to which the target page belongs. The ->vm_private_data field 874 * holds the current cursor into that scan. Successive searches will circulate 875 * around the vma's virtual address space. 876 * 877 * So as more replacement pressure is applied to the pages in a nonlinear VMA, 878 * more scanning pressure is placed against them as well. Eventually pages 879 * will become fully unmapped and are eligible for eviction. 880 * 881 * For very sparsely populated VMAs this is a little inefficient - chances are 882 * there there won't be many ptes located within the scan cluster. In this case 883 * maybe we could scan further - to the end of the pte page, perhaps. 884 * 885 * Mlocked pages: check VM_LOCKED under mmap_sem held for read, if we can 886 * acquire it without blocking. If vma locked, mlock the pages in the cluster, 887 * rather than unmapping them. If we encounter the "check_page" that vmscan is 888 * trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN. 889 */ 890 #define CLUSTER_SIZE min(32*PAGE_SIZE, PMD_SIZE) 891 #define CLUSTER_MASK (~(CLUSTER_SIZE - 1)) 892 893 static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount, 894 struct vm_area_struct *vma, struct page *check_page) 895 { 896 struct mm_struct *mm = vma->vm_mm; 897 pgd_t *pgd; 898 pud_t *pud; 899 pmd_t *pmd; 900 pte_t *pte; 901 pte_t pteval; 902 spinlock_t *ptl; 903 struct page *page; 904 unsigned long address; 905 unsigned long end; 906 int ret = SWAP_AGAIN; 907 int locked_vma = 0; 908 909 address = (vma->vm_start + cursor) & CLUSTER_MASK; 910 end = address + CLUSTER_SIZE; 911 if (address < vma->vm_start) 912 address = vma->vm_start; 913 if (end > vma->vm_end) 914 end = vma->vm_end; 915 916 pgd = pgd_offset(mm, address); 917 if (!pgd_present(*pgd)) 918 return ret; 919 920 pud = pud_offset(pgd, address); 921 if (!pud_present(*pud)) 922 return ret; 923 924 pmd = pmd_offset(pud, address); 925 if (!pmd_present(*pmd)) 926 return ret; 927 928 /* 929 * MLOCK_PAGES => feature is configured. 930 * if we can acquire the mmap_sem for read, and vma is VM_LOCKED, 931 * keep the sem while scanning the cluster for mlocking pages. 932 */ 933 if (MLOCK_PAGES && down_read_trylock(&vma->vm_mm->mmap_sem)) { 934 locked_vma = (vma->vm_flags & VM_LOCKED); 935 if (!locked_vma) 936 up_read(&vma->vm_mm->mmap_sem); /* don't need it */ 937 } 938 939 pte = pte_offset_map_lock(mm, pmd, address, &ptl); 940 941 /* Update high watermark before we lower rss */ 942 update_hiwater_rss(mm); 943 944 for (; address < end; pte++, address += PAGE_SIZE) { 945 if (!pte_present(*pte)) 946 continue; 947 page = vm_normal_page(vma, address, *pte); 948 BUG_ON(!page || PageAnon(page)); 949 950 if (locked_vma) { 951 mlock_vma_page(page); /* no-op if already mlocked */ 952 if (page == check_page) 953 ret = SWAP_MLOCK; 954 continue; /* don't unmap */ 955 } 956 957 if (ptep_clear_flush_young_notify(vma, address, pte)) 958 continue; 959 960 /* Nuke the page table entry. */ 961 flush_cache_page(vma, address, pte_pfn(*pte)); 962 pteval = ptep_clear_flush_notify(vma, address, pte); 963 964 /* If nonlinear, store the file page offset in the pte. */ 965 if (page->index != linear_page_index(vma, address)) 966 set_pte_at(mm, address, pte, pgoff_to_pte(page->index)); 967 968 /* Move the dirty bit to the physical page now the pte is gone. */ 969 if (pte_dirty(pteval)) 970 set_page_dirty(page); 971 972 page_remove_rmap(page); 973 page_cache_release(page); 974 dec_mm_counter(mm, file_rss); 975 (*mapcount)--; 976 } 977 pte_unmap_unlock(pte - 1, ptl); 978 if (locked_vma) 979 up_read(&vma->vm_mm->mmap_sem); 980 return ret; 981 } 982 983 /* 984 * common handling for pages mapped in VM_LOCKED vmas 985 */ 986 static int try_to_mlock_page(struct page *page, struct vm_area_struct *vma) 987 { 988 int mlocked = 0; 989 990 if (down_read_trylock(&vma->vm_mm->mmap_sem)) { 991 if (vma->vm_flags & VM_LOCKED) { 992 mlock_vma_page(page); 993 mlocked++; /* really mlocked the page */ 994 } 995 up_read(&vma->vm_mm->mmap_sem); 996 } 997 return mlocked; 998 } 999 1000 /** 1001 * try_to_unmap_anon - unmap or unlock anonymous page using the object-based 1002 * rmap method 1003 * @page: the page to unmap/unlock 1004 * @unlock: request for unlock rather than unmap [unlikely] 1005 * @migration: unmapping for migration - ignored if @unlock 1006 * 1007 * Find all the mappings of a page using the mapping pointer and the vma chains 1008 * contained in the anon_vma struct it points to. 1009 * 1010 * This function is only called from try_to_unmap/try_to_munlock for 1011 * anonymous pages. 1012 * When called from try_to_munlock(), the mmap_sem of the mm containing the vma 1013 * where the page was found will be held for write. So, we won't recheck 1014 * vm_flags for that VMA. That should be OK, because that vma shouldn't be 1015 * 'LOCKED. 1016 */ 1017 static int try_to_unmap_anon(struct page *page, int unlock, int migration) 1018 { 1019 struct anon_vma *anon_vma; 1020 struct vm_area_struct *vma; 1021 unsigned int mlocked = 0; 1022 int ret = SWAP_AGAIN; 1023 1024 if (MLOCK_PAGES && unlikely(unlock)) 1025 ret = SWAP_SUCCESS; /* default for try_to_munlock() */ 1026 1027 anon_vma = page_lock_anon_vma(page); 1028 if (!anon_vma) 1029 return ret; 1030 1031 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) { 1032 if (MLOCK_PAGES && unlikely(unlock)) { 1033 if (!((vma->vm_flags & VM_LOCKED) && 1034 page_mapped_in_vma(page, vma))) 1035 continue; /* must visit all unlocked vmas */ 1036 ret = SWAP_MLOCK; /* saw at least one mlocked vma */ 1037 } else { 1038 ret = try_to_unmap_one(page, vma, migration); 1039 if (ret == SWAP_FAIL || !page_mapped(page)) 1040 break; 1041 } 1042 if (ret == SWAP_MLOCK) { 1043 mlocked = try_to_mlock_page(page, vma); 1044 if (mlocked) 1045 break; /* stop if actually mlocked page */ 1046 } 1047 } 1048 1049 page_unlock_anon_vma(anon_vma); 1050 1051 if (mlocked) 1052 ret = SWAP_MLOCK; /* actually mlocked the page */ 1053 else if (ret == SWAP_MLOCK) 1054 ret = SWAP_AGAIN; /* saw VM_LOCKED vma */ 1055 1056 return ret; 1057 } 1058 1059 /** 1060 * try_to_unmap_file - unmap/unlock file page using the object-based rmap method 1061 * @page: the page to unmap/unlock 1062 * @unlock: request for unlock rather than unmap [unlikely] 1063 * @migration: unmapping for migration - ignored if @unlock 1064 * 1065 * Find all the mappings of a page using the mapping pointer and the vma chains 1066 * contained in the address_space struct it points to. 1067 * 1068 * This function is only called from try_to_unmap/try_to_munlock for 1069 * object-based pages. 1070 * When called from try_to_munlock(), the mmap_sem of the mm containing the vma 1071 * where the page was found will be held for write. So, we won't recheck 1072 * vm_flags for that VMA. That should be OK, because that vma shouldn't be 1073 * 'LOCKED. 1074 */ 1075 static int try_to_unmap_file(struct page *page, int unlock, int migration) 1076 { 1077 struct address_space *mapping = page->mapping; 1078 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 1079 struct vm_area_struct *vma; 1080 struct prio_tree_iter iter; 1081 int ret = SWAP_AGAIN; 1082 unsigned long cursor; 1083 unsigned long max_nl_cursor = 0; 1084 unsigned long max_nl_size = 0; 1085 unsigned int mapcount; 1086 unsigned int mlocked = 0; 1087 1088 if (MLOCK_PAGES && unlikely(unlock)) 1089 ret = SWAP_SUCCESS; /* default for try_to_munlock() */ 1090 1091 spin_lock(&mapping->i_mmap_lock); 1092 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { 1093 if (MLOCK_PAGES && unlikely(unlock)) { 1094 if (!((vma->vm_flags & VM_LOCKED) && 1095 page_mapped_in_vma(page, vma))) 1096 continue; /* must visit all vmas */ 1097 ret = SWAP_MLOCK; 1098 } else { 1099 ret = try_to_unmap_one(page, vma, migration); 1100 if (ret == SWAP_FAIL || !page_mapped(page)) 1101 goto out; 1102 } 1103 if (ret == SWAP_MLOCK) { 1104 mlocked = try_to_mlock_page(page, vma); 1105 if (mlocked) 1106 break; /* stop if actually mlocked page */ 1107 } 1108 } 1109 1110 if (mlocked) 1111 goto out; 1112 1113 if (list_empty(&mapping->i_mmap_nonlinear)) 1114 goto out; 1115 1116 list_for_each_entry(vma, &mapping->i_mmap_nonlinear, 1117 shared.vm_set.list) { 1118 if (MLOCK_PAGES && unlikely(unlock)) { 1119 if (!(vma->vm_flags & VM_LOCKED)) 1120 continue; /* must visit all vmas */ 1121 ret = SWAP_MLOCK; /* leave mlocked == 0 */ 1122 goto out; /* no need to look further */ 1123 } 1124 if (!MLOCK_PAGES && !migration && (vma->vm_flags & VM_LOCKED)) 1125 continue; 1126 cursor = (unsigned long) vma->vm_private_data; 1127 if (cursor > max_nl_cursor) 1128 max_nl_cursor = cursor; 1129 cursor = vma->vm_end - vma->vm_start; 1130 if (cursor > max_nl_size) 1131 max_nl_size = cursor; 1132 } 1133 1134 if (max_nl_size == 0) { /* all nonlinears locked or reserved ? */ 1135 ret = SWAP_FAIL; 1136 goto out; 1137 } 1138 1139 /* 1140 * We don't try to search for this page in the nonlinear vmas, 1141 * and page_referenced wouldn't have found it anyway. Instead 1142 * just walk the nonlinear vmas trying to age and unmap some. 1143 * The mapcount of the page we came in with is irrelevant, 1144 * but even so use it as a guide to how hard we should try? 1145 */ 1146 mapcount = page_mapcount(page); 1147 if (!mapcount) 1148 goto out; 1149 cond_resched_lock(&mapping->i_mmap_lock); 1150 1151 max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK; 1152 if (max_nl_cursor == 0) 1153 max_nl_cursor = CLUSTER_SIZE; 1154 1155 do { 1156 list_for_each_entry(vma, &mapping->i_mmap_nonlinear, 1157 shared.vm_set.list) { 1158 if (!MLOCK_PAGES && !migration && 1159 (vma->vm_flags & VM_LOCKED)) 1160 continue; 1161 cursor = (unsigned long) vma->vm_private_data; 1162 while ( cursor < max_nl_cursor && 1163 cursor < vma->vm_end - vma->vm_start) { 1164 ret = try_to_unmap_cluster(cursor, &mapcount, 1165 vma, page); 1166 if (ret == SWAP_MLOCK) 1167 mlocked = 2; /* to return below */ 1168 cursor += CLUSTER_SIZE; 1169 vma->vm_private_data = (void *) cursor; 1170 if ((int)mapcount <= 0) 1171 goto out; 1172 } 1173 vma->vm_private_data = (void *) max_nl_cursor; 1174 } 1175 cond_resched_lock(&mapping->i_mmap_lock); 1176 max_nl_cursor += CLUSTER_SIZE; 1177 } while (max_nl_cursor <= max_nl_size); 1178 1179 /* 1180 * Don't loop forever (perhaps all the remaining pages are 1181 * in locked vmas). Reset cursor on all unreserved nonlinear 1182 * vmas, now forgetting on which ones it had fallen behind. 1183 */ 1184 list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list) 1185 vma->vm_private_data = NULL; 1186 out: 1187 spin_unlock(&mapping->i_mmap_lock); 1188 if (mlocked) 1189 ret = SWAP_MLOCK; /* actually mlocked the page */ 1190 else if (ret == SWAP_MLOCK) 1191 ret = SWAP_AGAIN; /* saw VM_LOCKED vma */ 1192 return ret; 1193 } 1194 1195 /** 1196 * try_to_unmap - try to remove all page table mappings to a page 1197 * @page: the page to get unmapped 1198 * @migration: migration flag 1199 * 1200 * Tries to remove all the page table entries which are mapping this 1201 * page, used in the pageout path. Caller must hold the page lock. 1202 * Return values are: 1203 * 1204 * SWAP_SUCCESS - we succeeded in removing all mappings 1205 * SWAP_AGAIN - we missed a mapping, try again later 1206 * SWAP_FAIL - the page is unswappable 1207 * SWAP_MLOCK - page is mlocked. 1208 */ 1209 int try_to_unmap(struct page *page, int migration) 1210 { 1211 int ret; 1212 1213 BUG_ON(!PageLocked(page)); 1214 1215 if (PageAnon(page)) 1216 ret = try_to_unmap_anon(page, 0, migration); 1217 else 1218 ret = try_to_unmap_file(page, 0, migration); 1219 if (ret != SWAP_MLOCK && !page_mapped(page)) 1220 ret = SWAP_SUCCESS; 1221 return ret; 1222 } 1223 1224 /** 1225 * try_to_munlock - try to munlock a page 1226 * @page: the page to be munlocked 1227 * 1228 * Called from munlock code. Checks all of the VMAs mapping the page 1229 * to make sure nobody else has this page mlocked. The page will be 1230 * returned with PG_mlocked cleared if no other vmas have it mlocked. 1231 * 1232 * Return values are: 1233 * 1234 * SWAP_SUCCESS - no vma's holding page mlocked. 1235 * SWAP_AGAIN - page mapped in mlocked vma -- couldn't acquire mmap sem 1236 * SWAP_MLOCK - page is now mlocked. 1237 */ 1238 int try_to_munlock(struct page *page) 1239 { 1240 VM_BUG_ON(!PageLocked(page) || PageLRU(page)); 1241 1242 if (PageAnon(page)) 1243 return try_to_unmap_anon(page, 1, 0); 1244 else 1245 return try_to_unmap_file(page, 1, 0); 1246 } 1247 1248