blob: 2e034a0b89abff5ccc2bc310255f18c6e5ac165c [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -07001/*
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 <hugh@veritas.com> 2003, 2004
18 */
19
20/*
21 * Lock ordering in mm:
22 *
23 * inode->i_sem (while writing or truncating, not reading or faulting)
24 * inode->i_alloc_sem
25 *
26 * When a page fault occurs in writing from user to file, down_read
27 * of mmap_sem nests within i_sem; in sys_msync, i_sem nests within
28 * down_read of mmap_sem; i_sem and down_write of mmap_sem are never
29 * taken together; in truncation, i_sem is taken outermost.
30 *
31 * mm->mmap_sem
32 * page->flags PG_locked (lock_page)
33 * mapping->i_mmap_lock
34 * anon_vma->lock
Hugh Dickinsb8072f02005-10-29 18:16:41 -070035 * mm->page_table_lock or pte_lock
Linus Torvalds1da177e2005-04-16 15:20:36 -070036 * zone->lru_lock (in mark_page_accessed)
Hugh Dickins5d337b92005-09-03 15:54:41 -070037 * swap_lock (in swap_duplicate, swap_info_get)
Linus Torvalds1da177e2005-04-16 15:20:36 -070038 * mmlist_lock (in mmput, drain_mmlist and others)
Linus Torvalds1da177e2005-04-16 15:20:36 -070039 * mapping->private_lock (in __set_page_dirty_buffers)
40 * inode_lock (in set_page_dirty's __mark_inode_dirty)
41 * sb_lock (within inode_lock in fs/fs-writeback.c)
42 * mapping->tree_lock (widely used, in set_page_dirty,
43 * in arch-dependent flush_dcache_mmap_lock,
44 * within inode_lock in __sync_single_inode)
45 */
46
47#include <linux/mm.h>
48#include <linux/pagemap.h>
49#include <linux/swap.h>
50#include <linux/swapops.h>
51#include <linux/slab.h>
52#include <linux/init.h>
53#include <linux/rmap.h>
54#include <linux/rcupdate.h>
55
56#include <asm/tlbflush.h>
57
58//#define RMAP_DEBUG /* can be enabled only for debugging */
59
60kmem_cache_t *anon_vma_cachep;
61
62static inline void validate_anon_vma(struct vm_area_struct *find_vma)
63{
64#ifdef RMAP_DEBUG
65 struct anon_vma *anon_vma = find_vma->anon_vma;
66 struct vm_area_struct *vma;
67 unsigned int mapcount = 0;
68 int found = 0;
69
70 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
71 mapcount++;
72 BUG_ON(mapcount > 100000);
73 if (vma == find_vma)
74 found = 1;
75 }
76 BUG_ON(!found);
77#endif
78}
79
80/* This must be called under the mmap_sem. */
81int anon_vma_prepare(struct vm_area_struct *vma)
82{
83 struct anon_vma *anon_vma = vma->anon_vma;
84
85 might_sleep();
86 if (unlikely(!anon_vma)) {
87 struct mm_struct *mm = vma->vm_mm;
88 struct anon_vma *allocated, *locked;
89
90 anon_vma = find_mergeable_anon_vma(vma);
91 if (anon_vma) {
92 allocated = NULL;
93 locked = anon_vma;
94 spin_lock(&locked->lock);
95 } else {
96 anon_vma = anon_vma_alloc();
97 if (unlikely(!anon_vma))
98 return -ENOMEM;
99 allocated = anon_vma;
100 locked = NULL;
101 }
102
103 /* page_table_lock to protect against threads */
104 spin_lock(&mm->page_table_lock);
105 if (likely(!vma->anon_vma)) {
106 vma->anon_vma = anon_vma;
107 list_add(&vma->anon_vma_node, &anon_vma->head);
108 allocated = NULL;
109 }
110 spin_unlock(&mm->page_table_lock);
111
112 if (locked)
113 spin_unlock(&locked->lock);
114 if (unlikely(allocated))
115 anon_vma_free(allocated);
116 }
117 return 0;
118}
119
120void __anon_vma_merge(struct vm_area_struct *vma, struct vm_area_struct *next)
121{
122 BUG_ON(vma->anon_vma != next->anon_vma);
123 list_del(&next->anon_vma_node);
124}
125
126void __anon_vma_link(struct vm_area_struct *vma)
127{
128 struct anon_vma *anon_vma = vma->anon_vma;
129
130 if (anon_vma) {
131 list_add(&vma->anon_vma_node, &anon_vma->head);
132 validate_anon_vma(vma);
133 }
134}
135
136void anon_vma_link(struct vm_area_struct *vma)
137{
138 struct anon_vma *anon_vma = vma->anon_vma;
139
140 if (anon_vma) {
141 spin_lock(&anon_vma->lock);
142 list_add(&vma->anon_vma_node, &anon_vma->head);
143 validate_anon_vma(vma);
144 spin_unlock(&anon_vma->lock);
145 }
146}
147
148void anon_vma_unlink(struct vm_area_struct *vma)
149{
150 struct anon_vma *anon_vma = vma->anon_vma;
151 int empty;
152
153 if (!anon_vma)
154 return;
155
156 spin_lock(&anon_vma->lock);
157 validate_anon_vma(vma);
158 list_del(&vma->anon_vma_node);
159
160 /* We must garbage collect the anon_vma if it's empty */
161 empty = list_empty(&anon_vma->head);
162 spin_unlock(&anon_vma->lock);
163
164 if (empty)
165 anon_vma_free(anon_vma);
166}
167
168static void anon_vma_ctor(void *data, kmem_cache_t *cachep, unsigned long flags)
169{
170 if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
171 SLAB_CTOR_CONSTRUCTOR) {
172 struct anon_vma *anon_vma = data;
173
174 spin_lock_init(&anon_vma->lock);
175 INIT_LIST_HEAD(&anon_vma->head);
176 }
177}
178
179void __init anon_vma_init(void)
180{
181 anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
182 0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor, NULL);
183}
184
185/*
186 * Getting a lock on a stable anon_vma from a page off the LRU is
187 * tricky: page_lock_anon_vma rely on RCU to guard against the races.
188 */
189static struct anon_vma *page_lock_anon_vma(struct page *page)
190{
191 struct anon_vma *anon_vma = NULL;
192 unsigned long anon_mapping;
193
194 rcu_read_lock();
195 anon_mapping = (unsigned long) page->mapping;
196 if (!(anon_mapping & PAGE_MAPPING_ANON))
197 goto out;
198 if (!page_mapped(page))
199 goto out;
200
201 anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
202 spin_lock(&anon_vma->lock);
203out:
204 rcu_read_unlock();
205 return anon_vma;
206}
207
208/*
209 * At what user virtual address is page expected in vma?
210 */
211static inline unsigned long
212vma_address(struct page *page, struct vm_area_struct *vma)
213{
214 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
215 unsigned long address;
216
217 address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
218 if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
219 /* page should be within any vma from prio_tree_next */
220 BUG_ON(!PageAnon(page));
221 return -EFAULT;
222 }
223 return address;
224}
225
226/*
227 * At what user virtual address is page expected in vma? checking that the
Hugh Dickinsee498ed2005-11-21 21:32:18 -0800228 * page matches the vma: currently only used on anon pages, by unuse_vma;
229 * and by extraordinary checks on anon pages in VM_UNPAGED vmas, taking
230 * care that an mmap of /dev/mem might window free and foreign pages.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700231 */
232unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
233{
234 if (PageAnon(page)) {
235 if ((void *)vma->anon_vma !=
236 (void *)page->mapping - PAGE_MAPPING_ANON)
237 return -EFAULT;
238 } else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
Hugh Dickinsee498ed2005-11-21 21:32:18 -0800239 if (!vma->vm_file ||
240 vma->vm_file->f_mapping != page->mapping)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700241 return -EFAULT;
242 } else
243 return -EFAULT;
244 return vma_address(page, vma);
245}
246
247/*
Nikita Danilov81b40822005-05-01 08:58:36 -0700248 * Check that @page is mapped at @address into @mm.
249 *
Hugh Dickinsb8072f02005-10-29 18:16:41 -0700250 * On success returns with pte mapped and locked.
Nikita Danilov81b40822005-05-01 08:58:36 -0700251 */
Carsten Otteceffc072005-06-23 22:05:25 -0700252pte_t *page_check_address(struct page *page, struct mm_struct *mm,
Hugh Dickinsc0718802005-10-29 18:16:31 -0700253 unsigned long address, spinlock_t **ptlp)
Nikita Danilov81b40822005-05-01 08:58:36 -0700254{
255 pgd_t *pgd;
256 pud_t *pud;
257 pmd_t *pmd;
258 pte_t *pte;
Hugh Dickinsc0718802005-10-29 18:16:31 -0700259 spinlock_t *ptl;
Nikita Danilov81b40822005-05-01 08:58:36 -0700260
Nikita Danilov81b40822005-05-01 08:58:36 -0700261 pgd = pgd_offset(mm, address);
Hugh Dickinsc0718802005-10-29 18:16:31 -0700262 if (!pgd_present(*pgd))
263 return NULL;
264
265 pud = pud_offset(pgd, address);
266 if (!pud_present(*pud))
267 return NULL;
268
269 pmd = pmd_offset(pud, address);
270 if (!pmd_present(*pmd))
271 return NULL;
272
273 pte = pte_offset_map(pmd, address);
274 /* Make a quick check before getting the lock */
275 if (!pte_present(*pte)) {
276 pte_unmap(pte);
277 return NULL;
Nikita Danilov81b40822005-05-01 08:58:36 -0700278 }
Hugh Dickinsc0718802005-10-29 18:16:31 -0700279
Hugh Dickins4c21e2f2005-10-29 18:16:40 -0700280 ptl = pte_lockptr(mm, pmd);
Hugh Dickinsc0718802005-10-29 18:16:31 -0700281 spin_lock(ptl);
282 if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) {
283 *ptlp = ptl;
284 return pte;
285 }
286 pte_unmap_unlock(pte, ptl);
287 return NULL;
Nikita Danilov81b40822005-05-01 08:58:36 -0700288}
289
290/*
Linus Torvalds1da177e2005-04-16 15:20:36 -0700291 * Subfunctions of page_referenced: page_referenced_one called
292 * repeatedly from either page_referenced_anon or page_referenced_file.
293 */
294static int page_referenced_one(struct page *page,
295 struct vm_area_struct *vma, unsigned int *mapcount, int ignore_token)
296{
297 struct mm_struct *mm = vma->vm_mm;
298 unsigned long address;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700299 pte_t *pte;
Hugh Dickinsc0718802005-10-29 18:16:31 -0700300 spinlock_t *ptl;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700301 int referenced = 0;
302
Linus Torvalds1da177e2005-04-16 15:20:36 -0700303 address = vma_address(page, vma);
304 if (address == -EFAULT)
305 goto out;
306
Hugh Dickinsc0718802005-10-29 18:16:31 -0700307 pte = page_check_address(page, mm, address, &ptl);
308 if (!pte)
309 goto out;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700310
Hugh Dickinsc0718802005-10-29 18:16:31 -0700311 if (ptep_clear_flush_young(vma, address, pte))
312 referenced++;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700313
Hugh Dickinsc0718802005-10-29 18:16:31 -0700314 /* Pretend the page is referenced if the task has the
315 swap token and is in the middle of a page fault. */
316 if (mm != current->mm && !ignore_token && has_swap_token(mm) &&
317 rwsem_is_locked(&mm->mmap_sem))
318 referenced++;
319
320 (*mapcount)--;
321 pte_unmap_unlock(pte, ptl);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700322out:
323 return referenced;
324}
325
326static int page_referenced_anon(struct page *page, int ignore_token)
327{
328 unsigned int mapcount;
329 struct anon_vma *anon_vma;
330 struct vm_area_struct *vma;
331 int referenced = 0;
332
333 anon_vma = page_lock_anon_vma(page);
334 if (!anon_vma)
335 return referenced;
336
337 mapcount = page_mapcount(page);
338 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
339 referenced += page_referenced_one(page, vma, &mapcount,
340 ignore_token);
341 if (!mapcount)
342 break;
343 }
344 spin_unlock(&anon_vma->lock);
345 return referenced;
346}
347
348/**
349 * page_referenced_file - referenced check for object-based rmap
350 * @page: the page we're checking references on.
351 *
352 * For an object-based mapped page, find all the places it is mapped and
353 * check/clear the referenced flag. This is done by following the page->mapping
354 * pointer, then walking the chain of vmas it holds. It returns the number
355 * of references it found.
356 *
357 * This function is only called from page_referenced for object-based pages.
358 */
359static int page_referenced_file(struct page *page, int ignore_token)
360{
361 unsigned int mapcount;
362 struct address_space *mapping = page->mapping;
363 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
364 struct vm_area_struct *vma;
365 struct prio_tree_iter iter;
366 int referenced = 0;
367
368 /*
369 * The caller's checks on page->mapping and !PageAnon have made
370 * sure that this is a file page: the check for page->mapping
371 * excludes the case just before it gets set on an anon page.
372 */
373 BUG_ON(PageAnon(page));
374
375 /*
376 * The page lock not only makes sure that page->mapping cannot
377 * suddenly be NULLified by truncation, it makes sure that the
378 * structure at mapping cannot be freed and reused yet,
379 * so we can safely take mapping->i_mmap_lock.
380 */
381 BUG_ON(!PageLocked(page));
382
383 spin_lock(&mapping->i_mmap_lock);
384
385 /*
386 * i_mmap_lock does not stabilize mapcount at all, but mapcount
387 * is more likely to be accurate if we note it after spinning.
388 */
389 mapcount = page_mapcount(page);
390
391 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
392 if ((vma->vm_flags & (VM_LOCKED|VM_MAYSHARE))
393 == (VM_LOCKED|VM_MAYSHARE)) {
394 referenced++;
395 break;
396 }
397 referenced += page_referenced_one(page, vma, &mapcount,
398 ignore_token);
399 if (!mapcount)
400 break;
401 }
402
403 spin_unlock(&mapping->i_mmap_lock);
404 return referenced;
405}
406
407/**
408 * page_referenced - test if the page was referenced
409 * @page: the page to test
410 * @is_locked: caller holds lock on the page
411 *
412 * Quick test_and_clear_referenced for all mappings to a page,
413 * returns the number of ptes which referenced the page.
414 */
415int page_referenced(struct page *page, int is_locked, int ignore_token)
416{
417 int referenced = 0;
418
419 if (!swap_token_default_timeout)
420 ignore_token = 1;
421
422 if (page_test_and_clear_young(page))
423 referenced++;
424
425 if (TestClearPageReferenced(page))
426 referenced++;
427
428 if (page_mapped(page) && page->mapping) {
429 if (PageAnon(page))
430 referenced += page_referenced_anon(page, ignore_token);
431 else if (is_locked)
432 referenced += page_referenced_file(page, ignore_token);
433 else if (TestSetPageLocked(page))
434 referenced++;
435 else {
436 if (page->mapping)
437 referenced += page_referenced_file(page,
438 ignore_token);
439 unlock_page(page);
440 }
441 }
442 return referenced;
443}
444
445/**
446 * page_add_anon_rmap - add pte mapping to an anonymous page
447 * @page: the page to add the mapping to
448 * @vma: the vm area in which the mapping is added
449 * @address: the user virtual address mapped
450 *
Hugh Dickinsb8072f02005-10-29 18:16:41 -0700451 * The caller needs to hold the pte lock.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700452 */
453void page_add_anon_rmap(struct page *page,
454 struct vm_area_struct *vma, unsigned long address)
455{
Linus Torvalds1da177e2005-04-16 15:20:36 -0700456 if (atomic_inc_and_test(&page->_mapcount)) {
Nick Piggin2822c1a2005-09-03 15:54:47 -0700457 struct anon_vma *anon_vma = vma->anon_vma;
Nick Piggin2822c1a2005-09-03 15:54:47 -0700458
459 BUG_ON(!anon_vma);
460 anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700461 page->mapping = (struct address_space *) anon_vma;
Nick Piggin2822c1a2005-09-03 15:54:47 -0700462
Nick Piggin4d7670e2005-09-03 15:54:48 -0700463 page->index = linear_page_index(vma, address);
Nick Piggin2822c1a2005-09-03 15:54:47 -0700464
Linus Torvalds1da177e2005-04-16 15:20:36 -0700465 inc_page_state(nr_mapped);
466 }
467 /* else checking page index and mapping is racy */
468}
469
470/**
471 * page_add_file_rmap - add pte mapping to a file page
472 * @page: the page to add the mapping to
473 *
Hugh Dickinsb8072f02005-10-29 18:16:41 -0700474 * The caller needs to hold the pte lock.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700475 */
476void page_add_file_rmap(struct page *page)
477{
478 BUG_ON(PageAnon(page));
Nick Pigginb5810032005-10-29 18:16:12 -0700479 BUG_ON(!pfn_valid(page_to_pfn(page)));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700480
481 if (atomic_inc_and_test(&page->_mapcount))
482 inc_page_state(nr_mapped);
483}
484
485/**
486 * page_remove_rmap - take down pte mapping from a page
487 * @page: page to remove mapping from
488 *
Hugh Dickinsb8072f02005-10-29 18:16:41 -0700489 * The caller needs to hold the pte lock.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700490 */
491void page_remove_rmap(struct page *page)
492{
Linus Torvalds1da177e2005-04-16 15:20:36 -0700493 if (atomic_add_negative(-1, &page->_mapcount)) {
494 BUG_ON(page_mapcount(page) < 0);
495 /*
496 * It would be tidy to reset the PageAnon mapping here,
497 * but that might overwrite a racing page_add_anon_rmap
498 * which increments mapcount after us but sets mapping
499 * before us: so leave the reset to free_hot_cold_page,
500 * and remember that it's only reliable while mapped.
501 * Leaving it set also helps swapoff to reinstate ptes
502 * faster for those pages still in swapcache.
503 */
504 if (page_test_and_clear_dirty(page))
505 set_page_dirty(page);
506 dec_page_state(nr_mapped);
507 }
508}
509
510/*
511 * Subfunctions of try_to_unmap: try_to_unmap_one called
512 * repeatedly from either try_to_unmap_anon or try_to_unmap_file.
513 */
514static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma)
515{
516 struct mm_struct *mm = vma->vm_mm;
517 unsigned long address;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700518 pte_t *pte;
519 pte_t pteval;
Hugh Dickinsc0718802005-10-29 18:16:31 -0700520 spinlock_t *ptl;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700521 int ret = SWAP_AGAIN;
522
Linus Torvalds1da177e2005-04-16 15:20:36 -0700523 address = vma_address(page, vma);
524 if (address == -EFAULT)
525 goto out;
526
Hugh Dickinsc0718802005-10-29 18:16:31 -0700527 pte = page_check_address(page, mm, address, &ptl);
528 if (!pte)
Nikita Danilov81b40822005-05-01 08:58:36 -0700529 goto out;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700530
531 /*
532 * If the page is mlock()d, we cannot swap it out.
533 * If it's recently referenced (perhaps page_referenced
534 * skipped over this mm) then we should reactivate it.
535 */
Hugh Dickins101d2be2005-11-21 21:32:16 -0800536 if ((vma->vm_flags & VM_LOCKED) ||
Linus Torvalds1da177e2005-04-16 15:20:36 -0700537 ptep_clear_flush_young(vma, address, pte)) {
538 ret = SWAP_FAIL;
539 goto out_unmap;
540 }
541
Linus Torvalds1da177e2005-04-16 15:20:36 -0700542 /* Nuke the page table entry. */
543 flush_cache_page(vma, address, page_to_pfn(page));
544 pteval = ptep_clear_flush(vma, address, pte);
545
546 /* Move the dirty bit to the physical page now the pte is gone. */
547 if (pte_dirty(pteval))
548 set_page_dirty(page);
549
Hugh Dickins365e9c872005-10-29 18:16:18 -0700550 /* Update high watermark before we lower rss */
551 update_hiwater_rss(mm);
552
Linus Torvalds1da177e2005-04-16 15:20:36 -0700553 if (PageAnon(page)) {
Hugh Dickins4c21e2f2005-10-29 18:16:40 -0700554 swp_entry_t entry = { .val = page_private(page) };
Linus Torvalds1da177e2005-04-16 15:20:36 -0700555 /*
556 * Store the swap location in the pte.
557 * See handle_pte_fault() ...
558 */
559 BUG_ON(!PageSwapCache(page));
560 swap_duplicate(entry);
561 if (list_empty(&mm->mmlist)) {
562 spin_lock(&mmlist_lock);
Hugh Dickinsf412ac02005-10-29 18:16:41 -0700563 if (list_empty(&mm->mmlist))
564 list_add(&mm->mmlist, &init_mm.mmlist);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700565 spin_unlock(&mmlist_lock);
566 }
567 set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
568 BUG_ON(pte_file(*pte));
569 dec_mm_counter(mm, anon_rss);
Hugh Dickins42946212005-10-29 18:16:05 -0700570 } else
571 dec_mm_counter(mm, file_rss);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700572
Linus Torvalds1da177e2005-04-16 15:20:36 -0700573 page_remove_rmap(page);
574 page_cache_release(page);
575
576out_unmap:
Hugh Dickinsc0718802005-10-29 18:16:31 -0700577 pte_unmap_unlock(pte, ptl);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700578out:
579 return ret;
580}
581
582/*
583 * objrmap doesn't work for nonlinear VMAs because the assumption that
584 * offset-into-file correlates with offset-into-virtual-addresses does not hold.
585 * Consequently, given a particular page and its ->index, we cannot locate the
586 * ptes which are mapping that page without an exhaustive linear search.
587 *
588 * So what this code does is a mini "virtual scan" of each nonlinear VMA which
589 * maps the file to which the target page belongs. The ->vm_private_data field
590 * holds the current cursor into that scan. Successive searches will circulate
591 * around the vma's virtual address space.
592 *
593 * So as more replacement pressure is applied to the pages in a nonlinear VMA,
594 * more scanning pressure is placed against them as well. Eventually pages
595 * will become fully unmapped and are eligible for eviction.
596 *
597 * For very sparsely populated VMAs this is a little inefficient - chances are
598 * there there won't be many ptes located within the scan cluster. In this case
599 * maybe we could scan further - to the end of the pte page, perhaps.
600 */
601#define CLUSTER_SIZE min(32*PAGE_SIZE, PMD_SIZE)
602#define CLUSTER_MASK (~(CLUSTER_SIZE - 1))
603
604static void try_to_unmap_cluster(unsigned long cursor,
605 unsigned int *mapcount, struct vm_area_struct *vma)
606{
607 struct mm_struct *mm = vma->vm_mm;
608 pgd_t *pgd;
609 pud_t *pud;
610 pmd_t *pmd;
Hugh Dickinsc0718802005-10-29 18:16:31 -0700611 pte_t *pte;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700612 pte_t pteval;
Hugh Dickinsc0718802005-10-29 18:16:31 -0700613 spinlock_t *ptl;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700614 struct page *page;
615 unsigned long address;
616 unsigned long end;
617 unsigned long pfn;
618
Linus Torvalds1da177e2005-04-16 15:20:36 -0700619 address = (vma->vm_start + cursor) & CLUSTER_MASK;
620 end = address + CLUSTER_SIZE;
621 if (address < vma->vm_start)
622 address = vma->vm_start;
623 if (end > vma->vm_end)
624 end = vma->vm_end;
625
626 pgd = pgd_offset(mm, address);
627 if (!pgd_present(*pgd))
Hugh Dickinsc0718802005-10-29 18:16:31 -0700628 return;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700629
630 pud = pud_offset(pgd, address);
631 if (!pud_present(*pud))
Hugh Dickinsc0718802005-10-29 18:16:31 -0700632 return;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700633
634 pmd = pmd_offset(pud, address);
635 if (!pmd_present(*pmd))
Hugh Dickinsc0718802005-10-29 18:16:31 -0700636 return;
637
638 pte = pte_offset_map_lock(mm, pmd, address, &ptl);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700639
Hugh Dickins365e9c872005-10-29 18:16:18 -0700640 /* Update high watermark before we lower rss */
641 update_hiwater_rss(mm);
642
Hugh Dickinsc0718802005-10-29 18:16:31 -0700643 for (; address < end; pte++, address += PAGE_SIZE) {
Linus Torvalds1da177e2005-04-16 15:20:36 -0700644 if (!pte_present(*pte))
645 continue;
646
647 pfn = pte_pfn(*pte);
Nick Pigginb5810032005-10-29 18:16:12 -0700648 if (unlikely(!pfn_valid(pfn))) {
649 print_bad_pte(vma, *pte, address);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700650 continue;
Nick Pigginb5810032005-10-29 18:16:12 -0700651 }
Linus Torvalds1da177e2005-04-16 15:20:36 -0700652
653 page = pfn_to_page(pfn);
654 BUG_ON(PageAnon(page));
Linus Torvalds1da177e2005-04-16 15:20:36 -0700655
656 if (ptep_clear_flush_young(vma, address, pte))
657 continue;
658
659 /* Nuke the page table entry. */
660 flush_cache_page(vma, address, pfn);
661 pteval = ptep_clear_flush(vma, address, pte);
662
663 /* If nonlinear, store the file page offset in the pte. */
664 if (page->index != linear_page_index(vma, address))
665 set_pte_at(mm, address, pte, pgoff_to_pte(page->index));
666
667 /* Move the dirty bit to the physical page now the pte is gone. */
668 if (pte_dirty(pteval))
669 set_page_dirty(page);
670
671 page_remove_rmap(page);
672 page_cache_release(page);
Hugh Dickins42946212005-10-29 18:16:05 -0700673 dec_mm_counter(mm, file_rss);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700674 (*mapcount)--;
675 }
Hugh Dickinsc0718802005-10-29 18:16:31 -0700676 pte_unmap_unlock(pte - 1, ptl);
Linus Torvalds1da177e2005-04-16 15:20:36 -0700677}
678
679static int try_to_unmap_anon(struct page *page)
680{
681 struct anon_vma *anon_vma;
682 struct vm_area_struct *vma;
683 int ret = SWAP_AGAIN;
684
685 anon_vma = page_lock_anon_vma(page);
686 if (!anon_vma)
687 return ret;
688
689 list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
690 ret = try_to_unmap_one(page, vma);
691 if (ret == SWAP_FAIL || !page_mapped(page))
692 break;
693 }
694 spin_unlock(&anon_vma->lock);
695 return ret;
696}
697
698/**
699 * try_to_unmap_file - unmap file page using the object-based rmap method
700 * @page: the page to unmap
701 *
702 * Find all the mappings of a page using the mapping pointer and the vma chains
703 * contained in the address_space struct it points to.
704 *
705 * This function is only called from try_to_unmap for object-based pages.
706 */
707static int try_to_unmap_file(struct page *page)
708{
709 struct address_space *mapping = page->mapping;
710 pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
711 struct vm_area_struct *vma;
712 struct prio_tree_iter iter;
713 int ret = SWAP_AGAIN;
714 unsigned long cursor;
715 unsigned long max_nl_cursor = 0;
716 unsigned long max_nl_size = 0;
717 unsigned int mapcount;
718
719 spin_lock(&mapping->i_mmap_lock);
720 vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
721 ret = try_to_unmap_one(page, vma);
722 if (ret == SWAP_FAIL || !page_mapped(page))
723 goto out;
724 }
725
726 if (list_empty(&mapping->i_mmap_nonlinear))
727 goto out;
728
729 list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
730 shared.vm_set.list) {
Hugh Dickins101d2be2005-11-21 21:32:16 -0800731 if (vma->vm_flags & VM_LOCKED)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700732 continue;
733 cursor = (unsigned long) vma->vm_private_data;
734 if (cursor > max_nl_cursor)
735 max_nl_cursor = cursor;
736 cursor = vma->vm_end - vma->vm_start;
737 if (cursor > max_nl_size)
738 max_nl_size = cursor;
739 }
740
741 if (max_nl_size == 0) { /* any nonlinears locked or reserved */
742 ret = SWAP_FAIL;
743 goto out;
744 }
745
746 /*
747 * We don't try to search for this page in the nonlinear vmas,
748 * and page_referenced wouldn't have found it anyway. Instead
749 * just walk the nonlinear vmas trying to age and unmap some.
750 * The mapcount of the page we came in with is irrelevant,
751 * but even so use it as a guide to how hard we should try?
752 */
753 mapcount = page_mapcount(page);
754 if (!mapcount)
755 goto out;
756 cond_resched_lock(&mapping->i_mmap_lock);
757
758 max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK;
759 if (max_nl_cursor == 0)
760 max_nl_cursor = CLUSTER_SIZE;
761
762 do {
763 list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
764 shared.vm_set.list) {
Hugh Dickins101d2be2005-11-21 21:32:16 -0800765 if (vma->vm_flags & VM_LOCKED)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700766 continue;
767 cursor = (unsigned long) vma->vm_private_data;
Hugh Dickins839b9682005-09-03 15:54:43 -0700768 while ( cursor < max_nl_cursor &&
Linus Torvalds1da177e2005-04-16 15:20:36 -0700769 cursor < vma->vm_end - vma->vm_start) {
770 try_to_unmap_cluster(cursor, &mapcount, vma);
771 cursor += CLUSTER_SIZE;
772 vma->vm_private_data = (void *) cursor;
773 if ((int)mapcount <= 0)
774 goto out;
775 }
776 vma->vm_private_data = (void *) max_nl_cursor;
777 }
778 cond_resched_lock(&mapping->i_mmap_lock);
779 max_nl_cursor += CLUSTER_SIZE;
780 } while (max_nl_cursor <= max_nl_size);
781
782 /*
783 * Don't loop forever (perhaps all the remaining pages are
784 * in locked vmas). Reset cursor on all unreserved nonlinear
785 * vmas, now forgetting on which ones it had fallen behind.
786 */
Hugh Dickins101d2be2005-11-21 21:32:16 -0800787 list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
788 vma->vm_private_data = NULL;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700789out:
790 spin_unlock(&mapping->i_mmap_lock);
791 return ret;
792}
793
794/**
795 * try_to_unmap - try to remove all page table mappings to a page
796 * @page: the page to get unmapped
797 *
798 * Tries to remove all the page table entries which are mapping this
799 * page, used in the pageout path. Caller must hold the page lock.
800 * Return values are:
801 *
802 * SWAP_SUCCESS - we succeeded in removing all mappings
803 * SWAP_AGAIN - we missed a mapping, try again later
804 * SWAP_FAIL - the page is unswappable
805 */
806int try_to_unmap(struct page *page)
807{
808 int ret;
809
Linus Torvalds1da177e2005-04-16 15:20:36 -0700810 BUG_ON(!PageLocked(page));
811
812 if (PageAnon(page))
813 ret = try_to_unmap_anon(page);
814 else
815 ret = try_to_unmap_file(page);
816
817 if (!page_mapped(page))
818 ret = SWAP_SUCCESS;
819 return ret;
820}
Nikita Danilov81b40822005-05-01 08:58:36 -0700821