rmap.c revision 31f2b0ebc01fd332cb0997f7ce9f9cde29af9e20
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/ksm.h> 53#include <linux/rmap.h> 54#include <linux/rcupdate.h> 55#include <linux/module.h> 56#include <linux/memcontrol.h> 57#include <linux/mmu_notifier.h> 58#include <linux/migrate.h> 59 60#include <asm/tlbflush.h> 61 62#include "internal.h" 63 64static struct kmem_cache *anon_vma_cachep; 65static struct kmem_cache *anon_vma_chain_cachep; 66 67static inline struct anon_vma *anon_vma_alloc(void) 68{ 69 return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL); 70} 71 72void anon_vma_free(struct anon_vma *anon_vma) 73{ 74 kmem_cache_free(anon_vma_cachep, anon_vma); 75} 76 77static inline struct anon_vma_chain *anon_vma_chain_alloc(void) 78{ 79 return kmem_cache_alloc(anon_vma_chain_cachep, GFP_KERNEL); 80} 81 82void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain) 83{ 84 kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain); 85} 86 87/** 88 * anon_vma_prepare - attach an anon_vma to a memory region 89 * @vma: the memory region in question 90 * 91 * This makes sure the memory mapping described by 'vma' has 92 * an 'anon_vma' attached to it, so that we can associate the 93 * anonymous pages mapped into it with that anon_vma. 94 * 95 * The common case will be that we already have one, but if 96 * if not we either need to find an adjacent mapping that we 97 * can re-use the anon_vma from (very common when the only 98 * reason for splitting a vma has been mprotect()), or we 99 * allocate a new one. 100 * 101 * Anon-vma allocations are very subtle, because we may have 102 * optimistically looked up an anon_vma in page_lock_anon_vma() 103 * and that may actually touch the spinlock even in the newly 104 * allocated vma (it depends on RCU to make sure that the 105 * anon_vma isn't actually destroyed). 106 * 107 * As a result, we need to do proper anon_vma locking even 108 * for the new allocation. At the same time, we do not want 109 * to do any locking for the common case of already having 110 * an anon_vma. 111 * 112 * This must be called with the mmap_sem held for reading. 113 */ 114int anon_vma_prepare(struct vm_area_struct *vma) 115{ 116 struct anon_vma *anon_vma = vma->anon_vma; 117 struct anon_vma_chain *avc; 118 119 might_sleep(); 120 if (unlikely(!anon_vma)) { 121 struct mm_struct *mm = vma->vm_mm; 122 struct anon_vma *allocated; 123 124 avc = anon_vma_chain_alloc(); 125 if (!avc) 126 goto out_enomem; 127 128 anon_vma = find_mergeable_anon_vma(vma); 129 allocated = NULL; 130 if (!anon_vma) { 131 anon_vma = anon_vma_alloc(); 132 if (unlikely(!anon_vma)) 133 goto out_enomem_free_avc; 134 allocated = anon_vma; 135 } 136 137 spin_lock(&anon_vma->lock); 138 /* page_table_lock to protect against threads */ 139 spin_lock(&mm->page_table_lock); 140 if (likely(!vma->anon_vma)) { 141 vma->anon_vma = anon_vma; 142 avc->anon_vma = anon_vma; 143 avc->vma = vma; 144 list_add(&avc->same_vma, &vma->anon_vma_chain); 145 list_add(&avc->same_anon_vma, &anon_vma->head); 146 allocated = NULL; 147 avc = NULL; 148 } 149 spin_unlock(&mm->page_table_lock); 150 spin_unlock(&anon_vma->lock); 151 152 if (unlikely(allocated)) 153 anon_vma_free(allocated); 154 if (unlikely(avc)) 155 anon_vma_chain_free(avc); 156 } 157 return 0; 158 159 out_enomem_free_avc: 160 anon_vma_chain_free(avc); 161 out_enomem: 162 return -ENOMEM; 163} 164 165static void anon_vma_chain_link(struct vm_area_struct *vma, 166 struct anon_vma_chain *avc, 167 struct anon_vma *anon_vma) 168{ 169 avc->vma = vma; 170 avc->anon_vma = anon_vma; 171 list_add(&avc->same_vma, &vma->anon_vma_chain); 172 173 spin_lock(&anon_vma->lock); 174 list_add_tail(&avc->same_anon_vma, &anon_vma->head); 175 spin_unlock(&anon_vma->lock); 176} 177 178/* 179 * Attach the anon_vmas from src to dst. 180 * Returns 0 on success, -ENOMEM on failure. 181 */ 182int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src) 183{ 184 struct anon_vma_chain *avc, *pavc; 185 186 list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) { 187 avc = anon_vma_chain_alloc(); 188 if (!avc) 189 goto enomem_failure; 190 anon_vma_chain_link(dst, avc, pavc->anon_vma); 191 } 192 return 0; 193 194 enomem_failure: 195 unlink_anon_vmas(dst); 196 return -ENOMEM; 197} 198 199/* 200 * Attach vma to its own anon_vma, as well as to the anon_vmas that 201 * the corresponding VMA in the parent process is attached to. 202 * Returns 0 on success, non-zero on failure. 203 */ 204int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma) 205{ 206 struct anon_vma_chain *avc; 207 struct anon_vma *anon_vma; 208 209 /* Don't bother if the parent process has no anon_vma here. */ 210 if (!pvma->anon_vma) 211 return 0; 212 213 /* 214 * First, attach the new VMA to the parent VMA's anon_vmas, 215 * so rmap can find non-COWed pages in child processes. 216 */ 217 if (anon_vma_clone(vma, pvma)) 218 return -ENOMEM; 219 220 /* Then add our own anon_vma. */ 221 anon_vma = anon_vma_alloc(); 222 if (!anon_vma) 223 goto out_error; 224 avc = anon_vma_chain_alloc(); 225 if (!avc) 226 goto out_error_free_anon_vma; 227 anon_vma_chain_link(vma, avc, anon_vma); 228 /* Mark this anon_vma as the one where our new (COWed) pages go. */ 229 vma->anon_vma = anon_vma; 230 231 return 0; 232 233 out_error_free_anon_vma: 234 anon_vma_free(anon_vma); 235 out_error: 236 unlink_anon_vmas(vma); 237 return -ENOMEM; 238} 239 240static void anon_vma_unlink(struct anon_vma_chain *anon_vma_chain) 241{ 242 struct anon_vma *anon_vma = anon_vma_chain->anon_vma; 243 int empty; 244 245 /* If anon_vma_fork fails, we can get an empty anon_vma_chain. */ 246 if (!anon_vma) 247 return; 248 249 spin_lock(&anon_vma->lock); 250 list_del(&anon_vma_chain->same_anon_vma); 251 252 /* We must garbage collect the anon_vma if it's empty */ 253 empty = list_empty(&anon_vma->head) && !ksm_refcount(anon_vma); 254 spin_unlock(&anon_vma->lock); 255 256 if (empty) 257 anon_vma_free(anon_vma); 258} 259 260void unlink_anon_vmas(struct vm_area_struct *vma) 261{ 262 struct anon_vma_chain *avc, *next; 263 264 /* Unlink each anon_vma chained to the VMA. */ 265 list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) { 266 anon_vma_unlink(avc); 267 list_del(&avc->same_vma); 268 anon_vma_chain_free(avc); 269 } 270} 271 272static void anon_vma_ctor(void *data) 273{ 274 struct anon_vma *anon_vma = data; 275 276 spin_lock_init(&anon_vma->lock); 277 ksm_refcount_init(anon_vma); 278 INIT_LIST_HEAD(&anon_vma->head); 279} 280 281void __init anon_vma_init(void) 282{ 283 anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma), 284 0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor); 285 anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, SLAB_PANIC); 286} 287 288/* 289 * Getting a lock on a stable anon_vma from a page off the LRU is 290 * tricky: page_lock_anon_vma rely on RCU to guard against the races. 291 */ 292struct anon_vma *page_lock_anon_vma(struct page *page) 293{ 294 struct anon_vma *anon_vma; 295 unsigned long anon_mapping; 296 297 rcu_read_lock(); 298 anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping); 299 if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON) 300 goto out; 301 if (!page_mapped(page)) 302 goto out; 303 304 anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON); 305 spin_lock(&anon_vma->lock); 306 return anon_vma; 307out: 308 rcu_read_unlock(); 309 return NULL; 310} 311 312void page_unlock_anon_vma(struct anon_vma *anon_vma) 313{ 314 spin_unlock(&anon_vma->lock); 315 rcu_read_unlock(); 316} 317 318/* 319 * At what user virtual address is page expected in @vma? 320 * Returns virtual address or -EFAULT if page's index/offset is not 321 * within the range mapped the @vma. 322 */ 323static inline unsigned long 324vma_address(struct page *page, struct vm_area_struct *vma) 325{ 326 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 327 unsigned long address; 328 329 address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT); 330 if (unlikely(address < vma->vm_start || address >= vma->vm_end)) { 331 /* page should be within @vma mapping range */ 332 return -EFAULT; 333 } 334 return address; 335} 336 337/* 338 * At what user virtual address is page expected in vma? 339 * checking that the page matches the vma. 340 */ 341unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma) 342{ 343 if (PageAnon(page)) { 344 if (vma->anon_vma != page_anon_vma(page)) 345 return -EFAULT; 346 } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) { 347 if (!vma->vm_file || 348 vma->vm_file->f_mapping != page->mapping) 349 return -EFAULT; 350 } else 351 return -EFAULT; 352 return vma_address(page, vma); 353} 354 355/* 356 * Check that @page is mapped at @address into @mm. 357 * 358 * If @sync is false, page_check_address may perform a racy check to avoid 359 * the page table lock when the pte is not present (helpful when reclaiming 360 * highly shared pages). 361 * 362 * On success returns with pte mapped and locked. 363 */ 364pte_t *page_check_address(struct page *page, struct mm_struct *mm, 365 unsigned long address, spinlock_t **ptlp, int sync) 366{ 367 pgd_t *pgd; 368 pud_t *pud; 369 pmd_t *pmd; 370 pte_t *pte; 371 spinlock_t *ptl; 372 373 pgd = pgd_offset(mm, address); 374 if (!pgd_present(*pgd)) 375 return NULL; 376 377 pud = pud_offset(pgd, address); 378 if (!pud_present(*pud)) 379 return NULL; 380 381 pmd = pmd_offset(pud, address); 382 if (!pmd_present(*pmd)) 383 return NULL; 384 385 pte = pte_offset_map(pmd, address); 386 /* Make a quick check before getting the lock */ 387 if (!sync && !pte_present(*pte)) { 388 pte_unmap(pte); 389 return NULL; 390 } 391 392 ptl = pte_lockptr(mm, pmd); 393 spin_lock(ptl); 394 if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) { 395 *ptlp = ptl; 396 return pte; 397 } 398 pte_unmap_unlock(pte, ptl); 399 return NULL; 400} 401 402/** 403 * page_mapped_in_vma - check whether a page is really mapped in a VMA 404 * @page: the page to test 405 * @vma: the VMA to test 406 * 407 * Returns 1 if the page is mapped into the page tables of the VMA, 0 408 * if the page is not mapped into the page tables of this VMA. Only 409 * valid for normal file or anonymous VMAs. 410 */ 411int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma) 412{ 413 unsigned long address; 414 pte_t *pte; 415 spinlock_t *ptl; 416 417 address = vma_address(page, vma); 418 if (address == -EFAULT) /* out of vma range */ 419 return 0; 420 pte = page_check_address(page, vma->vm_mm, address, &ptl, 1); 421 if (!pte) /* the page is not in this mm */ 422 return 0; 423 pte_unmap_unlock(pte, ptl); 424 425 return 1; 426} 427 428/* 429 * Subfunctions of page_referenced: page_referenced_one called 430 * repeatedly from either page_referenced_anon or page_referenced_file. 431 */ 432int page_referenced_one(struct page *page, struct vm_area_struct *vma, 433 unsigned long address, unsigned int *mapcount, 434 unsigned long *vm_flags) 435{ 436 struct mm_struct *mm = vma->vm_mm; 437 pte_t *pte; 438 spinlock_t *ptl; 439 int referenced = 0; 440 441 pte = page_check_address(page, mm, address, &ptl, 0); 442 if (!pte) 443 goto out; 444 445 /* 446 * Don't want to elevate referenced for mlocked page that gets this far, 447 * in order that it progresses to try_to_unmap and is moved to the 448 * unevictable list. 449 */ 450 if (vma->vm_flags & VM_LOCKED) { 451 *mapcount = 1; /* break early from loop */ 452 *vm_flags |= VM_LOCKED; 453 goto out_unmap; 454 } 455 456 if (ptep_clear_flush_young_notify(vma, address, pte)) { 457 /* 458 * Don't treat a reference through a sequentially read 459 * mapping as such. If the page has been used in 460 * another mapping, we will catch it; if this other 461 * mapping is already gone, the unmap path will have 462 * set PG_referenced or activated the page. 463 */ 464 if (likely(!VM_SequentialReadHint(vma))) 465 referenced++; 466 } 467 468 /* Pretend the page is referenced if the task has the 469 swap token and is in the middle of a page fault. */ 470 if (mm != current->mm && has_swap_token(mm) && 471 rwsem_is_locked(&mm->mmap_sem)) 472 referenced++; 473 474out_unmap: 475 (*mapcount)--; 476 pte_unmap_unlock(pte, ptl); 477 478 if (referenced) 479 *vm_flags |= vma->vm_flags; 480out: 481 return referenced; 482} 483 484static int page_referenced_anon(struct page *page, 485 struct mem_cgroup *mem_cont, 486 unsigned long *vm_flags) 487{ 488 unsigned int mapcount; 489 struct anon_vma *anon_vma; 490 struct anon_vma_chain *avc; 491 int referenced = 0; 492 493 anon_vma = page_lock_anon_vma(page); 494 if (!anon_vma) 495 return referenced; 496 497 mapcount = page_mapcount(page); 498 list_for_each_entry(avc, &anon_vma->head, same_anon_vma) { 499 struct vm_area_struct *vma = avc->vma; 500 unsigned long address = vma_address(page, vma); 501 if (address == -EFAULT) 502 continue; 503 /* 504 * If we are reclaiming on behalf of a cgroup, skip 505 * counting on behalf of references from different 506 * cgroups 507 */ 508 if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont)) 509 continue; 510 referenced += page_referenced_one(page, vma, address, 511 &mapcount, vm_flags); 512 if (!mapcount) 513 break; 514 } 515 516 page_unlock_anon_vma(anon_vma); 517 return referenced; 518} 519 520/** 521 * page_referenced_file - referenced check for object-based rmap 522 * @page: the page we're checking references on. 523 * @mem_cont: target memory controller 524 * @vm_flags: collect encountered vma->vm_flags who actually referenced the page 525 * 526 * For an object-based mapped page, find all the places it is mapped and 527 * check/clear the referenced flag. This is done by following the page->mapping 528 * pointer, then walking the chain of vmas it holds. It returns the number 529 * of references it found. 530 * 531 * This function is only called from page_referenced for object-based pages. 532 */ 533static int page_referenced_file(struct page *page, 534 struct mem_cgroup *mem_cont, 535 unsigned long *vm_flags) 536{ 537 unsigned int mapcount; 538 struct address_space *mapping = page->mapping; 539 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 540 struct vm_area_struct *vma; 541 struct prio_tree_iter iter; 542 int referenced = 0; 543 544 /* 545 * The caller's checks on page->mapping and !PageAnon have made 546 * sure that this is a file page: the check for page->mapping 547 * excludes the case just before it gets set on an anon page. 548 */ 549 BUG_ON(PageAnon(page)); 550 551 /* 552 * The page lock not only makes sure that page->mapping cannot 553 * suddenly be NULLified by truncation, it makes sure that the 554 * structure at mapping cannot be freed and reused yet, 555 * so we can safely take mapping->i_mmap_lock. 556 */ 557 BUG_ON(!PageLocked(page)); 558 559 spin_lock(&mapping->i_mmap_lock); 560 561 /* 562 * i_mmap_lock does not stabilize mapcount at all, but mapcount 563 * is more likely to be accurate if we note it after spinning. 564 */ 565 mapcount = page_mapcount(page); 566 567 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { 568 unsigned long address = vma_address(page, vma); 569 if (address == -EFAULT) 570 continue; 571 /* 572 * If we are reclaiming on behalf of a cgroup, skip 573 * counting on behalf of references from different 574 * cgroups 575 */ 576 if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont)) 577 continue; 578 referenced += page_referenced_one(page, vma, address, 579 &mapcount, vm_flags); 580 if (!mapcount) 581 break; 582 } 583 584 spin_unlock(&mapping->i_mmap_lock); 585 return referenced; 586} 587 588/** 589 * page_referenced - test if the page was referenced 590 * @page: the page to test 591 * @is_locked: caller holds lock on the page 592 * @mem_cont: target memory controller 593 * @vm_flags: collect encountered vma->vm_flags who actually referenced the page 594 * 595 * Quick test_and_clear_referenced for all mappings to a page, 596 * returns the number of ptes which referenced the page. 597 */ 598int page_referenced(struct page *page, 599 int is_locked, 600 struct mem_cgroup *mem_cont, 601 unsigned long *vm_flags) 602{ 603 int referenced = 0; 604 int we_locked = 0; 605 606 *vm_flags = 0; 607 if (page_mapped(page) && page_rmapping(page)) { 608 if (!is_locked && (!PageAnon(page) || PageKsm(page))) { 609 we_locked = trylock_page(page); 610 if (!we_locked) { 611 referenced++; 612 goto out; 613 } 614 } 615 if (unlikely(PageKsm(page))) 616 referenced += page_referenced_ksm(page, mem_cont, 617 vm_flags); 618 else if (PageAnon(page)) 619 referenced += page_referenced_anon(page, mem_cont, 620 vm_flags); 621 else if (page->mapping) 622 referenced += page_referenced_file(page, mem_cont, 623 vm_flags); 624 if (we_locked) 625 unlock_page(page); 626 } 627out: 628 if (page_test_and_clear_young(page)) 629 referenced++; 630 631 return referenced; 632} 633 634static int page_mkclean_one(struct page *page, struct vm_area_struct *vma, 635 unsigned long address) 636{ 637 struct mm_struct *mm = vma->vm_mm; 638 pte_t *pte; 639 spinlock_t *ptl; 640 int ret = 0; 641 642 pte = page_check_address(page, mm, address, &ptl, 1); 643 if (!pte) 644 goto out; 645 646 if (pte_dirty(*pte) || pte_write(*pte)) { 647 pte_t entry; 648 649 flush_cache_page(vma, address, pte_pfn(*pte)); 650 entry = ptep_clear_flush_notify(vma, address, pte); 651 entry = pte_wrprotect(entry); 652 entry = pte_mkclean(entry); 653 set_pte_at(mm, address, pte, entry); 654 ret = 1; 655 } 656 657 pte_unmap_unlock(pte, ptl); 658out: 659 return ret; 660} 661 662static int page_mkclean_file(struct address_space *mapping, struct page *page) 663{ 664 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 665 struct vm_area_struct *vma; 666 struct prio_tree_iter iter; 667 int ret = 0; 668 669 BUG_ON(PageAnon(page)); 670 671 spin_lock(&mapping->i_mmap_lock); 672 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { 673 if (vma->vm_flags & VM_SHARED) { 674 unsigned long address = vma_address(page, vma); 675 if (address == -EFAULT) 676 continue; 677 ret += page_mkclean_one(page, vma, address); 678 } 679 } 680 spin_unlock(&mapping->i_mmap_lock); 681 return ret; 682} 683 684int page_mkclean(struct page *page) 685{ 686 int ret = 0; 687 688 BUG_ON(!PageLocked(page)); 689 690 if (page_mapped(page)) { 691 struct address_space *mapping = page_mapping(page); 692 if (mapping) { 693 ret = page_mkclean_file(mapping, page); 694 if (page_test_dirty(page)) { 695 page_clear_dirty(page); 696 ret = 1; 697 } 698 } 699 } 700 701 return ret; 702} 703EXPORT_SYMBOL_GPL(page_mkclean); 704 705/** 706 * page_move_anon_rmap - move a page to our anon_vma 707 * @page: the page to move to our anon_vma 708 * @vma: the vma the page belongs to 709 * @address: the user virtual address mapped 710 * 711 * When a page belongs exclusively to one process after a COW event, 712 * that page can be moved into the anon_vma that belongs to just that 713 * process, so the rmap code will not search the parent or sibling 714 * processes. 715 */ 716void page_move_anon_rmap(struct page *page, 717 struct vm_area_struct *vma, unsigned long address) 718{ 719 struct anon_vma *anon_vma = vma->anon_vma; 720 721 VM_BUG_ON(!PageLocked(page)); 722 VM_BUG_ON(!anon_vma); 723 VM_BUG_ON(page->index != linear_page_index(vma, address)); 724 725 anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; 726 page->mapping = (struct address_space *) anon_vma; 727} 728 729/** 730 * __page_set_anon_rmap - setup new anonymous rmap 731 * @page: the page to add the mapping to 732 * @vma: the vm area in which the mapping is added 733 * @address: the user virtual address mapped 734 * @exclusive: the page is exclusively owned by the current process 735 */ 736static void __page_set_anon_rmap(struct page *page, 737 struct vm_area_struct *vma, unsigned long address, int exclusive) 738{ 739 struct anon_vma *anon_vma = vma->anon_vma; 740 741 BUG_ON(!anon_vma); 742 743 /* 744 * If the page isn't exclusively mapped into this vma, 745 * we must use the _oldest_ possible anon_vma for the 746 * page mapping! 747 * 748 * So take the last AVC chain entry in the vma, which is 749 * the deepest ancestor, and use the anon_vma from that. 750 */ 751 if (!exclusive) { 752 struct anon_vma_chain *avc; 753 avc = list_entry(vma->anon_vma_chain.prev, struct anon_vma_chain, same_vma); 754 anon_vma = avc->anon_vma; 755 } 756 757 anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON; 758 page->mapping = (struct address_space *) anon_vma; 759 page->index = linear_page_index(vma, address); 760} 761 762/** 763 * __page_check_anon_rmap - sanity check anonymous rmap addition 764 * @page: the page to add the mapping to 765 * @vma: the vm area in which the mapping is added 766 * @address: the user virtual address mapped 767 */ 768static void __page_check_anon_rmap(struct page *page, 769 struct vm_area_struct *vma, unsigned long address) 770{ 771#ifdef CONFIG_DEBUG_VM 772 /* 773 * The page's anon-rmap details (mapping and index) are guaranteed to 774 * be set up correctly at this point. 775 * 776 * We have exclusion against page_add_anon_rmap because the caller 777 * always holds the page locked, except if called from page_dup_rmap, 778 * in which case the page is already known to be setup. 779 * 780 * We have exclusion against page_add_new_anon_rmap because those pages 781 * are initially only visible via the pagetables, and the pte is locked 782 * over the call to page_add_new_anon_rmap. 783 */ 784 BUG_ON(page->index != linear_page_index(vma, address)); 785#endif 786} 787 788/** 789 * page_add_anon_rmap - add pte mapping to an anonymous page 790 * @page: the page to add the mapping to 791 * @vma: the vm area in which the mapping is added 792 * @address: the user virtual address mapped 793 * 794 * The caller needs to hold the pte lock, and the page must be locked in 795 * the anon_vma case: to serialize mapping,index checking after setting, 796 * and to ensure that PageAnon is not being upgraded racily to PageKsm 797 * (but PageKsm is never downgraded to PageAnon). 798 */ 799void page_add_anon_rmap(struct page *page, 800 struct vm_area_struct *vma, unsigned long address) 801{ 802 int first = atomic_inc_and_test(&page->_mapcount); 803 if (first) 804 __inc_zone_page_state(page, NR_ANON_PAGES); 805 if (unlikely(PageKsm(page))) 806 return; 807 808 VM_BUG_ON(!PageLocked(page)); 809 VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end); 810 if (first) 811 __page_set_anon_rmap(page, vma, address, 0); 812 else 813 __page_check_anon_rmap(page, vma, address); 814} 815 816/** 817 * page_add_new_anon_rmap - add pte mapping to a new anonymous page 818 * @page: the page to add the mapping to 819 * @vma: the vm area in which the mapping is added 820 * @address: the user virtual address mapped 821 * 822 * Same as page_add_anon_rmap but must only be called on *new* pages. 823 * This means the inc-and-test can be bypassed. 824 * Page does not have to be locked. 825 */ 826void page_add_new_anon_rmap(struct page *page, 827 struct vm_area_struct *vma, unsigned long address) 828{ 829 VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end); 830 SetPageSwapBacked(page); 831 atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */ 832 __inc_zone_page_state(page, NR_ANON_PAGES); 833 __page_set_anon_rmap(page, vma, address, 1); 834 if (page_evictable(page, vma)) 835 lru_cache_add_lru(page, LRU_ACTIVE_ANON); 836 else 837 add_page_to_unevictable_list(page); 838} 839 840/** 841 * page_add_file_rmap - add pte mapping to a file page 842 * @page: the page to add the mapping to 843 * 844 * The caller needs to hold the pte lock. 845 */ 846void page_add_file_rmap(struct page *page) 847{ 848 if (atomic_inc_and_test(&page->_mapcount)) { 849 __inc_zone_page_state(page, NR_FILE_MAPPED); 850 mem_cgroup_update_file_mapped(page, 1); 851 } 852} 853 854/** 855 * page_remove_rmap - take down pte mapping from a page 856 * @page: page to remove mapping from 857 * 858 * The caller needs to hold the pte lock. 859 */ 860void page_remove_rmap(struct page *page) 861{ 862 /* page still mapped by someone else? */ 863 if (!atomic_add_negative(-1, &page->_mapcount)) 864 return; 865 866 /* 867 * Now that the last pte has gone, s390 must transfer dirty 868 * flag from storage key to struct page. We can usually skip 869 * this if the page is anon, so about to be freed; but perhaps 870 * not if it's in swapcache - there might be another pte slot 871 * containing the swap entry, but page not yet written to swap. 872 */ 873 if ((!PageAnon(page) || PageSwapCache(page)) && page_test_dirty(page)) { 874 page_clear_dirty(page); 875 set_page_dirty(page); 876 } 877 if (PageAnon(page)) { 878 mem_cgroup_uncharge_page(page); 879 __dec_zone_page_state(page, NR_ANON_PAGES); 880 } else { 881 __dec_zone_page_state(page, NR_FILE_MAPPED); 882 mem_cgroup_update_file_mapped(page, -1); 883 } 884 /* 885 * It would be tidy to reset the PageAnon mapping here, 886 * but that might overwrite a racing page_add_anon_rmap 887 * which increments mapcount after us but sets mapping 888 * before us: so leave the reset to free_hot_cold_page, 889 * and remember that it's only reliable while mapped. 890 * Leaving it set also helps swapoff to reinstate ptes 891 * faster for those pages still in swapcache. 892 */ 893} 894 895/* 896 * Subfunctions of try_to_unmap: try_to_unmap_one called 897 * repeatedly from either try_to_unmap_anon or try_to_unmap_file. 898 */ 899int try_to_unmap_one(struct page *page, struct vm_area_struct *vma, 900 unsigned long address, enum ttu_flags flags) 901{ 902 struct mm_struct *mm = vma->vm_mm; 903 pte_t *pte; 904 pte_t pteval; 905 spinlock_t *ptl; 906 int ret = SWAP_AGAIN; 907 908 pte = page_check_address(page, mm, address, &ptl, 0); 909 if (!pte) 910 goto out; 911 912 /* 913 * If the page is mlock()d, we cannot swap it out. 914 * If it's recently referenced (perhaps page_referenced 915 * skipped over this mm) then we should reactivate it. 916 */ 917 if (!(flags & TTU_IGNORE_MLOCK)) { 918 if (vma->vm_flags & VM_LOCKED) 919 goto out_mlock; 920 921 if (TTU_ACTION(flags) == TTU_MUNLOCK) 922 goto out_unmap; 923 } 924 if (!(flags & TTU_IGNORE_ACCESS)) { 925 if (ptep_clear_flush_young_notify(vma, address, pte)) { 926 ret = SWAP_FAIL; 927 goto out_unmap; 928 } 929 } 930 931 /* Nuke the page table entry. */ 932 flush_cache_page(vma, address, page_to_pfn(page)); 933 pteval = ptep_clear_flush_notify(vma, address, pte); 934 935 /* Move the dirty bit to the physical page now the pte is gone. */ 936 if (pte_dirty(pteval)) 937 set_page_dirty(page); 938 939 /* Update high watermark before we lower rss */ 940 update_hiwater_rss(mm); 941 942 if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) { 943 if (PageAnon(page)) 944 dec_mm_counter(mm, MM_ANONPAGES); 945 else 946 dec_mm_counter(mm, MM_FILEPAGES); 947 set_pte_at(mm, address, pte, 948 swp_entry_to_pte(make_hwpoison_entry(page))); 949 } else if (PageAnon(page)) { 950 swp_entry_t entry = { .val = page_private(page) }; 951 952 if (PageSwapCache(page)) { 953 /* 954 * Store the swap location in the pte. 955 * See handle_pte_fault() ... 956 */ 957 if (swap_duplicate(entry) < 0) { 958 set_pte_at(mm, address, pte, pteval); 959 ret = SWAP_FAIL; 960 goto out_unmap; 961 } 962 if (list_empty(&mm->mmlist)) { 963 spin_lock(&mmlist_lock); 964 if (list_empty(&mm->mmlist)) 965 list_add(&mm->mmlist, &init_mm.mmlist); 966 spin_unlock(&mmlist_lock); 967 } 968 dec_mm_counter(mm, MM_ANONPAGES); 969 inc_mm_counter(mm, MM_SWAPENTS); 970 } else if (PAGE_MIGRATION) { 971 /* 972 * Store the pfn of the page in a special migration 973 * pte. do_swap_page() will wait until the migration 974 * pte is removed and then restart fault handling. 975 */ 976 BUG_ON(TTU_ACTION(flags) != TTU_MIGRATION); 977 entry = make_migration_entry(page, pte_write(pteval)); 978 } 979 set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); 980 BUG_ON(pte_file(*pte)); 981 } else if (PAGE_MIGRATION && (TTU_ACTION(flags) == TTU_MIGRATION)) { 982 /* Establish migration entry for a file page */ 983 swp_entry_t entry; 984 entry = make_migration_entry(page, pte_write(pteval)); 985 set_pte_at(mm, address, pte, swp_entry_to_pte(entry)); 986 } else 987 dec_mm_counter(mm, MM_FILEPAGES); 988 989 page_remove_rmap(page); 990 page_cache_release(page); 991 992out_unmap: 993 pte_unmap_unlock(pte, ptl); 994out: 995 return ret; 996 997out_mlock: 998 pte_unmap_unlock(pte, ptl); 999 1000 1001 /* 1002 * We need mmap_sem locking, Otherwise VM_LOCKED check makes 1003 * unstable result and race. Plus, We can't wait here because 1004 * we now hold anon_vma->lock or mapping->i_mmap_lock. 1005 * if trylock failed, the page remain in evictable lru and later 1006 * vmscan could retry to move the page to unevictable lru if the 1007 * page is actually mlocked. 1008 */ 1009 if (down_read_trylock(&vma->vm_mm->mmap_sem)) { 1010 if (vma->vm_flags & VM_LOCKED) { 1011 mlock_vma_page(page); 1012 ret = SWAP_MLOCK; 1013 } 1014 up_read(&vma->vm_mm->mmap_sem); 1015 } 1016 return ret; 1017} 1018 1019/* 1020 * objrmap doesn't work for nonlinear VMAs because the assumption that 1021 * offset-into-file correlates with offset-into-virtual-addresses does not hold. 1022 * Consequently, given a particular page and its ->index, we cannot locate the 1023 * ptes which are mapping that page without an exhaustive linear search. 1024 * 1025 * So what this code does is a mini "virtual scan" of each nonlinear VMA which 1026 * maps the file to which the target page belongs. The ->vm_private_data field 1027 * holds the current cursor into that scan. Successive searches will circulate 1028 * around the vma's virtual address space. 1029 * 1030 * So as more replacement pressure is applied to the pages in a nonlinear VMA, 1031 * more scanning pressure is placed against them as well. Eventually pages 1032 * will become fully unmapped and are eligible for eviction. 1033 * 1034 * For very sparsely populated VMAs this is a little inefficient - chances are 1035 * there there won't be many ptes located within the scan cluster. In this case 1036 * maybe we could scan further - to the end of the pte page, perhaps. 1037 * 1038 * Mlocked pages: check VM_LOCKED under mmap_sem held for read, if we can 1039 * acquire it without blocking. If vma locked, mlock the pages in the cluster, 1040 * rather than unmapping them. If we encounter the "check_page" that vmscan is 1041 * trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN. 1042 */ 1043#define CLUSTER_SIZE min(32*PAGE_SIZE, PMD_SIZE) 1044#define CLUSTER_MASK (~(CLUSTER_SIZE - 1)) 1045 1046static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount, 1047 struct vm_area_struct *vma, struct page *check_page) 1048{ 1049 struct mm_struct *mm = vma->vm_mm; 1050 pgd_t *pgd; 1051 pud_t *pud; 1052 pmd_t *pmd; 1053 pte_t *pte; 1054 pte_t pteval; 1055 spinlock_t *ptl; 1056 struct page *page; 1057 unsigned long address; 1058 unsigned long end; 1059 int ret = SWAP_AGAIN; 1060 int locked_vma = 0; 1061 1062 address = (vma->vm_start + cursor) & CLUSTER_MASK; 1063 end = address + CLUSTER_SIZE; 1064 if (address < vma->vm_start) 1065 address = vma->vm_start; 1066 if (end > vma->vm_end) 1067 end = vma->vm_end; 1068 1069 pgd = pgd_offset(mm, address); 1070 if (!pgd_present(*pgd)) 1071 return ret; 1072 1073 pud = pud_offset(pgd, address); 1074 if (!pud_present(*pud)) 1075 return ret; 1076 1077 pmd = pmd_offset(pud, address); 1078 if (!pmd_present(*pmd)) 1079 return ret; 1080 1081 /* 1082 * If we can acquire the mmap_sem for read, and vma is VM_LOCKED, 1083 * keep the sem while scanning the cluster for mlocking pages. 1084 */ 1085 if (down_read_trylock(&vma->vm_mm->mmap_sem)) { 1086 locked_vma = (vma->vm_flags & VM_LOCKED); 1087 if (!locked_vma) 1088 up_read(&vma->vm_mm->mmap_sem); /* don't need it */ 1089 } 1090 1091 pte = pte_offset_map_lock(mm, pmd, address, &ptl); 1092 1093 /* Update high watermark before we lower rss */ 1094 update_hiwater_rss(mm); 1095 1096 for (; address < end; pte++, address += PAGE_SIZE) { 1097 if (!pte_present(*pte)) 1098 continue; 1099 page = vm_normal_page(vma, address, *pte); 1100 BUG_ON(!page || PageAnon(page)); 1101 1102 if (locked_vma) { 1103 mlock_vma_page(page); /* no-op if already mlocked */ 1104 if (page == check_page) 1105 ret = SWAP_MLOCK; 1106 continue; /* don't unmap */ 1107 } 1108 1109 if (ptep_clear_flush_young_notify(vma, address, pte)) 1110 continue; 1111 1112 /* Nuke the page table entry. */ 1113 flush_cache_page(vma, address, pte_pfn(*pte)); 1114 pteval = ptep_clear_flush_notify(vma, address, pte); 1115 1116 /* If nonlinear, store the file page offset in the pte. */ 1117 if (page->index != linear_page_index(vma, address)) 1118 set_pte_at(mm, address, pte, pgoff_to_pte(page->index)); 1119 1120 /* Move the dirty bit to the physical page now the pte is gone. */ 1121 if (pte_dirty(pteval)) 1122 set_page_dirty(page); 1123 1124 page_remove_rmap(page); 1125 page_cache_release(page); 1126 dec_mm_counter(mm, MM_FILEPAGES); 1127 (*mapcount)--; 1128 } 1129 pte_unmap_unlock(pte - 1, ptl); 1130 if (locked_vma) 1131 up_read(&vma->vm_mm->mmap_sem); 1132 return ret; 1133} 1134 1135/** 1136 * try_to_unmap_anon - unmap or unlock anonymous page using the object-based 1137 * rmap method 1138 * @page: the page to unmap/unlock 1139 * @flags: action and flags 1140 * 1141 * Find all the mappings of a page using the mapping pointer and the vma chains 1142 * contained in the anon_vma struct it points to. 1143 * 1144 * This function is only called from try_to_unmap/try_to_munlock for 1145 * anonymous pages. 1146 * When called from try_to_munlock(), the mmap_sem of the mm containing the vma 1147 * where the page was found will be held for write. So, we won't recheck 1148 * vm_flags for that VMA. That should be OK, because that vma shouldn't be 1149 * 'LOCKED. 1150 */ 1151static int try_to_unmap_anon(struct page *page, enum ttu_flags flags) 1152{ 1153 struct anon_vma *anon_vma; 1154 struct anon_vma_chain *avc; 1155 int ret = SWAP_AGAIN; 1156 1157 anon_vma = page_lock_anon_vma(page); 1158 if (!anon_vma) 1159 return ret; 1160 1161 list_for_each_entry(avc, &anon_vma->head, same_anon_vma) { 1162 struct vm_area_struct *vma = avc->vma; 1163 unsigned long address = vma_address(page, vma); 1164 if (address == -EFAULT) 1165 continue; 1166 ret = try_to_unmap_one(page, vma, address, flags); 1167 if (ret != SWAP_AGAIN || !page_mapped(page)) 1168 break; 1169 } 1170 1171 page_unlock_anon_vma(anon_vma); 1172 return ret; 1173} 1174 1175/** 1176 * try_to_unmap_file - unmap/unlock file page using the object-based rmap method 1177 * @page: the page to unmap/unlock 1178 * @flags: action and flags 1179 * 1180 * Find all the mappings of a page using the mapping pointer and the vma chains 1181 * contained in the address_space struct it points to. 1182 * 1183 * This function is only called from try_to_unmap/try_to_munlock for 1184 * object-based pages. 1185 * When called from try_to_munlock(), the mmap_sem of the mm containing the vma 1186 * where the page was found will be held for write. So, we won't recheck 1187 * vm_flags for that VMA. That should be OK, because that vma shouldn't be 1188 * 'LOCKED. 1189 */ 1190static int try_to_unmap_file(struct page *page, enum ttu_flags flags) 1191{ 1192 struct address_space *mapping = page->mapping; 1193 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 1194 struct vm_area_struct *vma; 1195 struct prio_tree_iter iter; 1196 int ret = SWAP_AGAIN; 1197 unsigned long cursor; 1198 unsigned long max_nl_cursor = 0; 1199 unsigned long max_nl_size = 0; 1200 unsigned int mapcount; 1201 1202 spin_lock(&mapping->i_mmap_lock); 1203 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { 1204 unsigned long address = vma_address(page, vma); 1205 if (address == -EFAULT) 1206 continue; 1207 ret = try_to_unmap_one(page, vma, address, flags); 1208 if (ret != SWAP_AGAIN || !page_mapped(page)) 1209 goto out; 1210 } 1211 1212 if (list_empty(&mapping->i_mmap_nonlinear)) 1213 goto out; 1214 1215 /* 1216 * We don't bother to try to find the munlocked page in nonlinears. 1217 * It's costly. Instead, later, page reclaim logic may call 1218 * try_to_unmap(TTU_MUNLOCK) and recover PG_mlocked lazily. 1219 */ 1220 if (TTU_ACTION(flags) == TTU_MUNLOCK) 1221 goto out; 1222 1223 list_for_each_entry(vma, &mapping->i_mmap_nonlinear, 1224 shared.vm_set.list) { 1225 cursor = (unsigned long) vma->vm_private_data; 1226 if (cursor > max_nl_cursor) 1227 max_nl_cursor = cursor; 1228 cursor = vma->vm_end - vma->vm_start; 1229 if (cursor > max_nl_size) 1230 max_nl_size = cursor; 1231 } 1232 1233 if (max_nl_size == 0) { /* all nonlinears locked or reserved ? */ 1234 ret = SWAP_FAIL; 1235 goto out; 1236 } 1237 1238 /* 1239 * We don't try to search for this page in the nonlinear vmas, 1240 * and page_referenced wouldn't have found it anyway. Instead 1241 * just walk the nonlinear vmas trying to age and unmap some. 1242 * The mapcount of the page we came in with is irrelevant, 1243 * but even so use it as a guide to how hard we should try? 1244 */ 1245 mapcount = page_mapcount(page); 1246 if (!mapcount) 1247 goto out; 1248 cond_resched_lock(&mapping->i_mmap_lock); 1249 1250 max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK; 1251 if (max_nl_cursor == 0) 1252 max_nl_cursor = CLUSTER_SIZE; 1253 1254 do { 1255 list_for_each_entry(vma, &mapping->i_mmap_nonlinear, 1256 shared.vm_set.list) { 1257 cursor = (unsigned long) vma->vm_private_data; 1258 while ( cursor < max_nl_cursor && 1259 cursor < vma->vm_end - vma->vm_start) { 1260 if (try_to_unmap_cluster(cursor, &mapcount, 1261 vma, page) == SWAP_MLOCK) 1262 ret = SWAP_MLOCK; 1263 cursor += CLUSTER_SIZE; 1264 vma->vm_private_data = (void *) cursor; 1265 if ((int)mapcount <= 0) 1266 goto out; 1267 } 1268 vma->vm_private_data = (void *) max_nl_cursor; 1269 } 1270 cond_resched_lock(&mapping->i_mmap_lock); 1271 max_nl_cursor += CLUSTER_SIZE; 1272 } while (max_nl_cursor <= max_nl_size); 1273 1274 /* 1275 * Don't loop forever (perhaps all the remaining pages are 1276 * in locked vmas). Reset cursor on all unreserved nonlinear 1277 * vmas, now forgetting on which ones it had fallen behind. 1278 */ 1279 list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list) 1280 vma->vm_private_data = NULL; 1281out: 1282 spin_unlock(&mapping->i_mmap_lock); 1283 return ret; 1284} 1285 1286/** 1287 * try_to_unmap - try to remove all page table mappings to a page 1288 * @page: the page to get unmapped 1289 * @flags: action and flags 1290 * 1291 * Tries to remove all the page table entries which are mapping this 1292 * page, used in the pageout path. Caller must hold the page lock. 1293 * Return values are: 1294 * 1295 * SWAP_SUCCESS - we succeeded in removing all mappings 1296 * SWAP_AGAIN - we missed a mapping, try again later 1297 * SWAP_FAIL - the page is unswappable 1298 * SWAP_MLOCK - page is mlocked. 1299 */ 1300int try_to_unmap(struct page *page, enum ttu_flags flags) 1301{ 1302 int ret; 1303 1304 BUG_ON(!PageLocked(page)); 1305 1306 if (unlikely(PageKsm(page))) 1307 ret = try_to_unmap_ksm(page, flags); 1308 else if (PageAnon(page)) 1309 ret = try_to_unmap_anon(page, flags); 1310 else 1311 ret = try_to_unmap_file(page, flags); 1312 if (ret != SWAP_MLOCK && !page_mapped(page)) 1313 ret = SWAP_SUCCESS; 1314 return ret; 1315} 1316 1317/** 1318 * try_to_munlock - try to munlock a page 1319 * @page: the page to be munlocked 1320 * 1321 * Called from munlock code. Checks all of the VMAs mapping the page 1322 * to make sure nobody else has this page mlocked. The page will be 1323 * returned with PG_mlocked cleared if no other vmas have it mlocked. 1324 * 1325 * Return values are: 1326 * 1327 * SWAP_AGAIN - no vma is holding page mlocked, or, 1328 * SWAP_AGAIN - page mapped in mlocked vma -- couldn't acquire mmap sem 1329 * SWAP_FAIL - page cannot be located at present 1330 * SWAP_MLOCK - page is now mlocked. 1331 */ 1332int try_to_munlock(struct page *page) 1333{ 1334 VM_BUG_ON(!PageLocked(page) || PageLRU(page)); 1335 1336 if (unlikely(PageKsm(page))) 1337 return try_to_unmap_ksm(page, TTU_MUNLOCK); 1338 else if (PageAnon(page)) 1339 return try_to_unmap_anon(page, TTU_MUNLOCK); 1340 else 1341 return try_to_unmap_file(page, TTU_MUNLOCK); 1342} 1343 1344#ifdef CONFIG_MIGRATION 1345/* 1346 * rmap_walk() and its helpers rmap_walk_anon() and rmap_walk_file(): 1347 * Called by migrate.c to remove migration ptes, but might be used more later. 1348 */ 1349static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *, 1350 struct vm_area_struct *, unsigned long, void *), void *arg) 1351{ 1352 struct anon_vma *anon_vma; 1353 struct anon_vma_chain *avc; 1354 int ret = SWAP_AGAIN; 1355 1356 /* 1357 * Note: remove_migration_ptes() cannot use page_lock_anon_vma() 1358 * because that depends on page_mapped(); but not all its usages 1359 * are holding mmap_sem, which also gave the necessary guarantee 1360 * (that this anon_vma's slab has not already been destroyed). 1361 * This needs to be reviewed later: avoiding page_lock_anon_vma() 1362 * is risky, and currently limits the usefulness of rmap_walk(). 1363 */ 1364 anon_vma = page_anon_vma(page); 1365 if (!anon_vma) 1366 return ret; 1367 spin_lock(&anon_vma->lock); 1368 list_for_each_entry(avc, &anon_vma->head, same_anon_vma) { 1369 struct vm_area_struct *vma = avc->vma; 1370 unsigned long address = vma_address(page, vma); 1371 if (address == -EFAULT) 1372 continue; 1373 ret = rmap_one(page, vma, address, arg); 1374 if (ret != SWAP_AGAIN) 1375 break; 1376 } 1377 spin_unlock(&anon_vma->lock); 1378 return ret; 1379} 1380 1381static int rmap_walk_file(struct page *page, int (*rmap_one)(struct page *, 1382 struct vm_area_struct *, unsigned long, void *), void *arg) 1383{ 1384 struct address_space *mapping = page->mapping; 1385 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT); 1386 struct vm_area_struct *vma; 1387 struct prio_tree_iter iter; 1388 int ret = SWAP_AGAIN; 1389 1390 if (!mapping) 1391 return ret; 1392 spin_lock(&mapping->i_mmap_lock); 1393 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) { 1394 unsigned long address = vma_address(page, vma); 1395 if (address == -EFAULT) 1396 continue; 1397 ret = rmap_one(page, vma, address, arg); 1398 if (ret != SWAP_AGAIN) 1399 break; 1400 } 1401 /* 1402 * No nonlinear handling: being always shared, nonlinear vmas 1403 * never contain migration ptes. Decide what to do about this 1404 * limitation to linear when we need rmap_walk() on nonlinear. 1405 */ 1406 spin_unlock(&mapping->i_mmap_lock); 1407 return ret; 1408} 1409 1410int rmap_walk(struct page *page, int (*rmap_one)(struct page *, 1411 struct vm_area_struct *, unsigned long, void *), void *arg) 1412{ 1413 VM_BUG_ON(!PageLocked(page)); 1414 1415 if (unlikely(PageKsm(page))) 1416 return rmap_walk_ksm(page, rmap_one, arg); 1417 else if (PageAnon(page)) 1418 return rmap_walk_anon(page, rmap_one, arg); 1419 else 1420 return rmap_walk_file(page, rmap_one, arg); 1421} 1422#endif /* CONFIG_MIGRATION */ 1423