Root/mm/truncate.c

1/*
2 * mm/truncate.c - code for taking down pages from address_spaces
3 *
4 * Copyright (C) 2002, Linus Torvalds
5 *
6 * 10Sep2002 Andrew Morton
7 * Initial version.
8 */
9
10#include <linux/kernel.h>
11#include <linux/backing-dev.h>
12#include <linux/gfp.h>
13#include <linux/mm.h>
14#include <linux/swap.h>
15#include <linux/export.h>
16#include <linux/pagemap.h>
17#include <linux/highmem.h>
18#include <linux/pagevec.h>
19#include <linux/task_io_accounting_ops.h>
20#include <linux/buffer_head.h> /* grr. try_to_release_page,
21                   do_invalidatepage */
22#include <linux/cleancache.h>
23#include "internal.h"
24
25static void clear_exceptional_entry(struct address_space *mapping,
26                    pgoff_t index, void *entry)
27{
28    struct radix_tree_node *node;
29    void **slot;
30
31    /* Handled by shmem itself */
32    if (shmem_mapping(mapping))
33        return;
34
35    spin_lock_irq(&mapping->tree_lock);
36    /*
37     * Regular page slots are stabilized by the page lock even
38     * without the tree itself locked. These unlocked entries
39     * need verification under the tree lock.
40     */
41    if (!__radix_tree_lookup(&mapping->page_tree, index, &node, &slot))
42        goto unlock;
43    if (*slot != entry)
44        goto unlock;
45    radix_tree_replace_slot(slot, NULL);
46    mapping->nrshadows--;
47    if (!node)
48        goto unlock;
49    workingset_node_shadows_dec(node);
50    /*
51     * Don't track node without shadow entries.
52     *
53     * Avoid acquiring the list_lru lock if already untracked.
54     * The list_empty() test is safe as node->private_list is
55     * protected by mapping->tree_lock.
56     */
57    if (!workingset_node_shadows(node) &&
58        !list_empty(&node->private_list))
59        list_lru_del(&workingset_shadow_nodes, &node->private_list);
60    __radix_tree_delete_node(&mapping->page_tree, node);
61unlock:
62    spin_unlock_irq(&mapping->tree_lock);
63}
64
65/**
66 * do_invalidatepage - invalidate part or all of a page
67 * @page: the page which is affected
68 * @offset: start of the range to invalidate
69 * @length: length of the range to invalidate
70 *
71 * do_invalidatepage() is called when all or part of the page has become
72 * invalidated by a truncate operation.
73 *
74 * do_invalidatepage() does not have to release all buffers, but it must
75 * ensure that no dirty buffer is left outside @offset and that no I/O
76 * is underway against any of the blocks which are outside the truncation
77 * point. Because the caller is about to free (and possibly reuse) those
78 * blocks on-disk.
79 */
80void do_invalidatepage(struct page *page, unsigned int offset,
81               unsigned int length)
82{
83    void (*invalidatepage)(struct page *, unsigned int, unsigned int);
84
85    invalidatepage = page->mapping->a_ops->invalidatepage;
86#ifdef CONFIG_BLOCK
87    if (!invalidatepage)
88        invalidatepage = block_invalidatepage;
89#endif
90    if (invalidatepage)
91        (*invalidatepage)(page, offset, length);
92}
93
94/*
95 * This cancels just the dirty bit on the kernel page itself, it
96 * does NOT actually remove dirty bits on any mmap's that may be
97 * around. It also leaves the page tagged dirty, so any sync
98 * activity will still find it on the dirty lists, and in particular,
99 * clear_page_dirty_for_io() will still look at the dirty bits in
100 * the VM.
101 *
102 * Doing this should *normally* only ever be done when a page
103 * is truncated, and is not actually mapped anywhere at all. However,
104 * fs/buffer.c does this when it notices that somebody has cleaned
105 * out all the buffers on a page without actually doing it through
106 * the VM. Can you say "ext3 is horribly ugly"? Tought you could.
107 */
108void cancel_dirty_page(struct page *page, unsigned int account_size)
109{
110    if (TestClearPageDirty(page)) {
111        struct address_space *mapping = page->mapping;
112        if (mapping && mapping_cap_account_dirty(mapping)) {
113            dec_zone_page_state(page, NR_FILE_DIRTY);
114            dec_bdi_stat(mapping->backing_dev_info,
115                    BDI_RECLAIMABLE);
116            if (account_size)
117                task_io_account_cancelled_write(account_size);
118        }
119    }
120}
121EXPORT_SYMBOL(cancel_dirty_page);
122
123/*
124 * If truncate cannot remove the fs-private metadata from the page, the page
125 * becomes orphaned. It will be left on the LRU and may even be mapped into
126 * user pagetables if we're racing with filemap_fault().
127 *
128 * We need to bale out if page->mapping is no longer equal to the original
129 * mapping. This happens a) when the VM reclaimed the page while we waited on
130 * its lock, b) when a concurrent invalidate_mapping_pages got there first and
131 * c) when tmpfs swizzles a page between a tmpfs inode and swapper_space.
132 */
133static int
134truncate_complete_page(struct address_space *mapping, struct page *page)
135{
136    if (page->mapping != mapping)
137        return -EIO;
138
139    if (page_has_private(page))
140        do_invalidatepage(page, 0, PAGE_CACHE_SIZE);
141
142    cancel_dirty_page(page, PAGE_CACHE_SIZE);
143
144    ClearPageMappedToDisk(page);
145    delete_from_page_cache(page);
146    return 0;
147}
148
149/*
150 * This is for invalidate_mapping_pages(). That function can be called at
151 * any time, and is not supposed to throw away dirty pages. But pages can
152 * be marked dirty at any time too, so use remove_mapping which safely
153 * discards clean, unused pages.
154 *
155 * Returns non-zero if the page was successfully invalidated.
156 */
157static int
158invalidate_complete_page(struct address_space *mapping, struct page *page)
159{
160    int ret;
161
162    if (page->mapping != mapping)
163        return 0;
164
165    if (page_has_private(page) && !try_to_release_page(page, 0))
166        return 0;
167
168    ret = remove_mapping(mapping, page);
169
170    return ret;
171}
172
173int truncate_inode_page(struct address_space *mapping, struct page *page)
174{
175    if (page_mapped(page)) {
176        unmap_mapping_range(mapping,
177                   (loff_t)page->index << PAGE_CACHE_SHIFT,
178                   PAGE_CACHE_SIZE, 0);
179    }
180    return truncate_complete_page(mapping, page);
181}
182
183/*
184 * Used to get rid of pages on hardware memory corruption.
185 */
186int generic_error_remove_page(struct address_space *mapping, struct page *page)
187{
188    if (!mapping)
189        return -EINVAL;
190    /*
191     * Only punch for normal data pages for now.
192     * Handling other types like directories would need more auditing.
193     */
194    if (!S_ISREG(mapping->host->i_mode))
195        return -EIO;
196    return truncate_inode_page(mapping, page);
197}
198EXPORT_SYMBOL(generic_error_remove_page);
199
200/*
201 * Safely invalidate one page from its pagecache mapping.
202 * It only drops clean, unused pages. The page must be locked.
203 *
204 * Returns 1 if the page is successfully invalidated, otherwise 0.
205 */
206int invalidate_inode_page(struct page *page)
207{
208    struct address_space *mapping = page_mapping(page);
209    if (!mapping)
210        return 0;
211    if (PageDirty(page) || PageWriteback(page))
212        return 0;
213    if (page_mapped(page))
214        return 0;
215    return invalidate_complete_page(mapping, page);
216}
217
218/**
219 * truncate_inode_pages_range - truncate range of pages specified by start & end byte offsets
220 * @mapping: mapping to truncate
221 * @lstart: offset from which to truncate
222 * @lend: offset to which to truncate (inclusive)
223 *
224 * Truncate the page cache, removing the pages that are between
225 * specified offsets (and zeroing out partial pages
226 * if lstart or lend + 1 is not page aligned).
227 *
228 * Truncate takes two passes - the first pass is nonblocking. It will not
229 * block on page locks and it will not block on writeback. The second pass
230 * will wait. This is to prevent as much IO as possible in the affected region.
231 * The first pass will remove most pages, so the search cost of the second pass
232 * is low.
233 *
234 * We pass down the cache-hot hint to the page freeing code. Even if the
235 * mapping is large, it is probably the case that the final pages are the most
236 * recently touched, and freeing happens in ascending file offset order.
237 *
238 * Note that since ->invalidatepage() accepts range to invalidate
239 * truncate_inode_pages_range is able to handle cases where lend + 1 is not
240 * page aligned properly.
241 */
242void truncate_inode_pages_range(struct address_space *mapping,
243                loff_t lstart, loff_t lend)
244{
245    pgoff_t start; /* inclusive */
246    pgoff_t end; /* exclusive */
247    unsigned int partial_start; /* inclusive */
248    unsigned int partial_end; /* exclusive */
249    struct pagevec pvec;
250    pgoff_t indices[PAGEVEC_SIZE];
251    pgoff_t index;
252    int i;
253
254    cleancache_invalidate_inode(mapping);
255    if (mapping->nrpages == 0 && mapping->nrshadows == 0)
256        return;
257
258    /* Offsets within partial pages */
259    partial_start = lstart & (PAGE_CACHE_SIZE - 1);
260    partial_end = (lend + 1) & (PAGE_CACHE_SIZE - 1);
261
262    /*
263     * 'start' and 'end' always covers the range of pages to be fully
264     * truncated. Partial pages are covered with 'partial_start' at the
265     * start of the range and 'partial_end' at the end of the range.
266     * Note that 'end' is exclusive while 'lend' is inclusive.
267     */
268    start = (lstart + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
269    if (lend == -1)
270        /*
271         * lend == -1 indicates end-of-file so we have to set 'end'
272         * to the highest possible pgoff_t and since the type is
273         * unsigned we're using -1.
274         */
275        end = -1;
276    else
277        end = (lend + 1) >> PAGE_CACHE_SHIFT;
278
279    pagevec_init(&pvec, 0);
280    index = start;
281    while (index < end && pagevec_lookup_entries(&pvec, mapping, index,
282            min(end - index, (pgoff_t)PAGEVEC_SIZE),
283            indices)) {
284        mem_cgroup_uncharge_start();
285        for (i = 0; i < pagevec_count(&pvec); i++) {
286            struct page *page = pvec.pages[i];
287
288            /* We rely upon deletion not changing page->index */
289            index = indices[i];
290            if (index >= end)
291                break;
292
293            if (radix_tree_exceptional_entry(page)) {
294                clear_exceptional_entry(mapping, index, page);
295                continue;
296            }
297
298            if (!trylock_page(page))
299                continue;
300            WARN_ON(page->index != index);
301            if (PageWriteback(page)) {
302                unlock_page(page);
303                continue;
304            }
305            truncate_inode_page(mapping, page);
306            unlock_page(page);
307        }
308        pagevec_remove_exceptionals(&pvec);
309        pagevec_release(&pvec);
310        mem_cgroup_uncharge_end();
311        cond_resched();
312        index++;
313    }
314
315    if (partial_start) {
316        struct page *page = find_lock_page(mapping, start - 1);
317        if (page) {
318            unsigned int top = PAGE_CACHE_SIZE;
319            if (start > end) {
320                /* Truncation within a single page */
321                top = partial_end;
322                partial_end = 0;
323            }
324            wait_on_page_writeback(page);
325            zero_user_segment(page, partial_start, top);
326            cleancache_invalidate_page(mapping, page);
327            if (page_has_private(page))
328                do_invalidatepage(page, partial_start,
329                          top - partial_start);
330            unlock_page(page);
331            page_cache_release(page);
332        }
333    }
334    if (partial_end) {
335        struct page *page = find_lock_page(mapping, end);
336        if (page) {
337            wait_on_page_writeback(page);
338            zero_user_segment(page, 0, partial_end);
339            cleancache_invalidate_page(mapping, page);
340            if (page_has_private(page))
341                do_invalidatepage(page, 0,
342                          partial_end);
343            unlock_page(page);
344            page_cache_release(page);
345        }
346    }
347    /*
348     * If the truncation happened within a single page no pages
349     * will be released, just zeroed, so we can bail out now.
350     */
351    if (start >= end)
352        return;
353
354    index = start;
355    for ( ; ; ) {
356        cond_resched();
357        if (!pagevec_lookup_entries(&pvec, mapping, index,
358            min(end - index, (pgoff_t)PAGEVEC_SIZE), indices)) {
359            /* If all gone from start onwards, we're done */
360            if (index == start)
361                break;
362            /* Otherwise restart to make sure all gone */
363            index = start;
364            continue;
365        }
366        if (index == start && indices[0] >= end) {
367            /* All gone out of hole to be punched, we're done */
368            pagevec_remove_exceptionals(&pvec);
369            pagevec_release(&pvec);
370            break;
371        }
372        mem_cgroup_uncharge_start();
373        for (i = 0; i < pagevec_count(&pvec); i++) {
374            struct page *page = pvec.pages[i];
375
376            /* We rely upon deletion not changing page->index */
377            index = indices[i];
378            if (index >= end) {
379                /* Restart punch to make sure all gone */
380                index = start - 1;
381                break;
382            }
383
384            if (radix_tree_exceptional_entry(page)) {
385                clear_exceptional_entry(mapping, index, page);
386                continue;
387            }
388
389            lock_page(page);
390            WARN_ON(page->index != index);
391            wait_on_page_writeback(page);
392            truncate_inode_page(mapping, page);
393            unlock_page(page);
394        }
395        pagevec_remove_exceptionals(&pvec);
396        pagevec_release(&pvec);
397        mem_cgroup_uncharge_end();
398        index++;
399    }
400    cleancache_invalidate_inode(mapping);
401}
402EXPORT_SYMBOL(truncate_inode_pages_range);
403
404/**
405 * truncate_inode_pages - truncate *all* the pages from an offset
406 * @mapping: mapping to truncate
407 * @lstart: offset from which to truncate
408 *
409 * Called under (and serialised by) inode->i_mutex.
410 *
411 * Note: When this function returns, there can be a page in the process of
412 * deletion (inside __delete_from_page_cache()) in the specified range. Thus
413 * mapping->nrpages can be non-zero when this function returns even after
414 * truncation of the whole mapping.
415 */
416void truncate_inode_pages(struct address_space *mapping, loff_t lstart)
417{
418    truncate_inode_pages_range(mapping, lstart, (loff_t)-1);
419}
420EXPORT_SYMBOL(truncate_inode_pages);
421
422/**
423 * truncate_inode_pages_final - truncate *all* pages before inode dies
424 * @mapping: mapping to truncate
425 *
426 * Called under (and serialized by) inode->i_mutex.
427 *
428 * Filesystems have to use this in the .evict_inode path to inform the
429 * VM that this is the final truncate and the inode is going away.
430 */
431void truncate_inode_pages_final(struct address_space *mapping)
432{
433    unsigned long nrshadows;
434    unsigned long nrpages;
435
436    /*
437     * Page reclaim can not participate in regular inode lifetime
438     * management (can't call iput()) and thus can race with the
439     * inode teardown. Tell it when the address space is exiting,
440     * so that it does not install eviction information after the
441     * final truncate has begun.
442     */
443    mapping_set_exiting(mapping);
444
445    /*
446     * When reclaim installs eviction entries, it increases
447     * nrshadows first, then decreases nrpages. Make sure we see
448     * this in the right order or we might miss an entry.
449     */
450    nrpages = mapping->nrpages;
451    smp_rmb();
452    nrshadows = mapping->nrshadows;
453
454    if (nrpages || nrshadows) {
455        /*
456         * As truncation uses a lockless tree lookup, cycle
457         * the tree lock to make sure any ongoing tree
458         * modification that does not see AS_EXITING is
459         * completed before starting the final truncate.
460         */
461        spin_lock_irq(&mapping->tree_lock);
462        spin_unlock_irq(&mapping->tree_lock);
463
464        truncate_inode_pages(mapping, 0);
465    }
466}
467EXPORT_SYMBOL(truncate_inode_pages_final);
468
469/**
470 * invalidate_mapping_pages - Invalidate all the unlocked pages of one inode
471 * @mapping: the address_space which holds the pages to invalidate
472 * @start: the offset 'from' which to invalidate
473 * @end: the offset 'to' which to invalidate (inclusive)
474 *
475 * This function only removes the unlocked pages, if you want to
476 * remove all the pages of one inode, you must call truncate_inode_pages.
477 *
478 * invalidate_mapping_pages() will not block on IO activity. It will not
479 * invalidate pages which are dirty, locked, under writeback or mapped into
480 * pagetables.
481 */
482unsigned long invalidate_mapping_pages(struct address_space *mapping,
483        pgoff_t start, pgoff_t end)
484{
485    pgoff_t indices[PAGEVEC_SIZE];
486    struct pagevec pvec;
487    pgoff_t index = start;
488    unsigned long ret;
489    unsigned long count = 0;
490    int i;
491
492    pagevec_init(&pvec, 0);
493    while (index <= end && pagevec_lookup_entries(&pvec, mapping, index,
494            min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
495            indices)) {
496        mem_cgroup_uncharge_start();
497        for (i = 0; i < pagevec_count(&pvec); i++) {
498            struct page *page = pvec.pages[i];
499
500            /* We rely upon deletion not changing page->index */
501            index = indices[i];
502            if (index > end)
503                break;
504
505            if (radix_tree_exceptional_entry(page)) {
506                clear_exceptional_entry(mapping, index, page);
507                continue;
508            }
509
510            if (!trylock_page(page))
511                continue;
512            WARN_ON(page->index != index);
513            ret = invalidate_inode_page(page);
514            unlock_page(page);
515            /*
516             * Invalidation is a hint that the page is no longer
517             * of interest and try to speed up its reclaim.
518             */
519            if (!ret)
520                deactivate_page(page);
521            count += ret;
522        }
523        pagevec_remove_exceptionals(&pvec);
524        pagevec_release(&pvec);
525        mem_cgroup_uncharge_end();
526        cond_resched();
527        index++;
528    }
529    return count;
530}
531EXPORT_SYMBOL(invalidate_mapping_pages);
532
533/*
534 * This is like invalidate_complete_page(), except it ignores the page's
535 * refcount. We do this because invalidate_inode_pages2() needs stronger
536 * invalidation guarantees, and cannot afford to leave pages behind because
537 * shrink_page_list() has a temp ref on them, or because they're transiently
538 * sitting in the lru_cache_add() pagevecs.
539 */
540static int
541invalidate_complete_page2(struct address_space *mapping, struct page *page)
542{
543    if (page->mapping != mapping)
544        return 0;
545
546    if (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL))
547        return 0;
548
549    spin_lock_irq(&mapping->tree_lock);
550    if (PageDirty(page))
551        goto failed;
552
553    BUG_ON(page_has_private(page));
554    __delete_from_page_cache(page, NULL);
555    spin_unlock_irq(&mapping->tree_lock);
556    mem_cgroup_uncharge_cache_page(page);
557
558    if (mapping->a_ops->freepage)
559        mapping->a_ops->freepage(page);
560
561    page_cache_release(page); /* pagecache ref */
562    return 1;
563failed:
564    spin_unlock_irq(&mapping->tree_lock);
565    return 0;
566}
567
568static int do_launder_page(struct address_space *mapping, struct page *page)
569{
570    if (!PageDirty(page))
571        return 0;
572    if (page->mapping != mapping || mapping->a_ops->launder_page == NULL)
573        return 0;
574    return mapping->a_ops->launder_page(page);
575}
576
577/**
578 * invalidate_inode_pages2_range - remove range of pages from an address_space
579 * @mapping: the address_space
580 * @start: the page offset 'from' which to invalidate
581 * @end: the page offset 'to' which to invalidate (inclusive)
582 *
583 * Any pages which are found to be mapped into pagetables are unmapped prior to
584 * invalidation.
585 *
586 * Returns -EBUSY if any pages could not be invalidated.
587 */
588int invalidate_inode_pages2_range(struct address_space *mapping,
589                  pgoff_t start, pgoff_t end)
590{
591    pgoff_t indices[PAGEVEC_SIZE];
592    struct pagevec pvec;
593    pgoff_t index;
594    int i;
595    int ret = 0;
596    int ret2 = 0;
597    int did_range_unmap = 0;
598
599    cleancache_invalidate_inode(mapping);
600    pagevec_init(&pvec, 0);
601    index = start;
602    while (index <= end && pagevec_lookup_entries(&pvec, mapping, index,
603            min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
604            indices)) {
605        mem_cgroup_uncharge_start();
606        for (i = 0; i < pagevec_count(&pvec); i++) {
607            struct page *page = pvec.pages[i];
608
609            /* We rely upon deletion not changing page->index */
610            index = indices[i];
611            if (index > end)
612                break;
613
614            if (radix_tree_exceptional_entry(page)) {
615                clear_exceptional_entry(mapping, index, page);
616                continue;
617            }
618
619            lock_page(page);
620            WARN_ON(page->index != index);
621            if (page->mapping != mapping) {
622                unlock_page(page);
623                continue;
624            }
625            wait_on_page_writeback(page);
626            if (page_mapped(page)) {
627                if (!did_range_unmap) {
628                    /*
629                     * Zap the rest of the file in one hit.
630                     */
631                    unmap_mapping_range(mapping,
632                       (loff_t)index << PAGE_CACHE_SHIFT,
633                       (loff_t)(1 + end - index)
634                             << PAGE_CACHE_SHIFT,
635                        0);
636                    did_range_unmap = 1;
637                } else {
638                    /*
639                     * Just zap this page
640                     */
641                    unmap_mapping_range(mapping,
642                       (loff_t)index << PAGE_CACHE_SHIFT,
643                       PAGE_CACHE_SIZE, 0);
644                }
645            }
646            BUG_ON(page_mapped(page));
647            ret2 = do_launder_page(mapping, page);
648            if (ret2 == 0) {
649                if (!invalidate_complete_page2(mapping, page))
650                    ret2 = -EBUSY;
651            }
652            if (ret2 < 0)
653                ret = ret2;
654            unlock_page(page);
655        }
656        pagevec_remove_exceptionals(&pvec);
657        pagevec_release(&pvec);
658        mem_cgroup_uncharge_end();
659        cond_resched();
660        index++;
661    }
662    cleancache_invalidate_inode(mapping);
663    return ret;
664}
665EXPORT_SYMBOL_GPL(invalidate_inode_pages2_range);
666
667/**
668 * invalidate_inode_pages2 - remove all pages from an address_space
669 * @mapping: the address_space
670 *
671 * Any pages which are found to be mapped into pagetables are unmapped prior to
672 * invalidation.
673 *
674 * Returns -EBUSY if any pages could not be invalidated.
675 */
676int invalidate_inode_pages2(struct address_space *mapping)
677{
678    return invalidate_inode_pages2_range(mapping, 0, -1);
679}
680EXPORT_SYMBOL_GPL(invalidate_inode_pages2);
681
682/**
683 * truncate_pagecache - unmap and remove pagecache that has been truncated
684 * @inode: inode
685 * @newsize: new file size
686 *
687 * inode's new i_size must already be written before truncate_pagecache
688 * is called.
689 *
690 * This function should typically be called before the filesystem
691 * releases resources associated with the freed range (eg. deallocates
692 * blocks). This way, pagecache will always stay logically coherent
693 * with on-disk format, and the filesystem would not have to deal with
694 * situations such as writepage being called for a page that has already
695 * had its underlying blocks deallocated.
696 */
697void truncate_pagecache(struct inode *inode, loff_t newsize)
698{
699    struct address_space *mapping = inode->i_mapping;
700    loff_t holebegin = round_up(newsize, PAGE_SIZE);
701
702    /*
703     * unmap_mapping_range is called twice, first simply for
704     * efficiency so that truncate_inode_pages does fewer
705     * single-page unmaps. However after this first call, and
706     * before truncate_inode_pages finishes, it is possible for
707     * private pages to be COWed, which remain after
708     * truncate_inode_pages finishes, hence the second
709     * unmap_mapping_range call must be made for correctness.
710     */
711    unmap_mapping_range(mapping, holebegin, 0, 1);
712    truncate_inode_pages(mapping, newsize);
713    unmap_mapping_range(mapping, holebegin, 0, 1);
714}
715EXPORT_SYMBOL(truncate_pagecache);
716
717/**
718 * truncate_setsize - update inode and pagecache for a new file size
719 * @inode: inode
720 * @newsize: new file size
721 *
722 * truncate_setsize updates i_size and performs pagecache truncation (if
723 * necessary) to @newsize. It will be typically be called from the filesystem's
724 * setattr function when ATTR_SIZE is passed in.
725 *
726 * Must be called with inode_mutex held and before all filesystem specific
727 * block truncation has been performed.
728 */
729void truncate_setsize(struct inode *inode, loff_t newsize)
730{
731    i_size_write(inode, newsize);
732    truncate_pagecache(inode, newsize);
733}
734EXPORT_SYMBOL(truncate_setsize);
735
736/**
737 * truncate_pagecache_range - unmap and remove pagecache that is hole-punched
738 * @inode: inode
739 * @lstart: offset of beginning of hole
740 * @lend: offset of last byte of hole
741 *
742 * This function should typically be called before the filesystem
743 * releases resources associated with the freed range (eg. deallocates
744 * blocks). This way, pagecache will always stay logically coherent
745 * with on-disk format, and the filesystem would not have to deal with
746 * situations such as writepage being called for a page that has already
747 * had its underlying blocks deallocated.
748 */
749void truncate_pagecache_range(struct inode *inode, loff_t lstart, loff_t lend)
750{
751    struct address_space *mapping = inode->i_mapping;
752    loff_t unmap_start = round_up(lstart, PAGE_SIZE);
753    loff_t unmap_end = round_down(1 + lend, PAGE_SIZE) - 1;
754    /*
755     * This rounding is currently just for example: unmap_mapping_range
756     * expands its hole outwards, whereas we want it to contract the hole
757     * inwards. However, existing callers of truncate_pagecache_range are
758     * doing their own page rounding first. Note that unmap_mapping_range
759     * allows holelen 0 for all, and we allow lend -1 for end of file.
760     */
761
762    /*
763     * Unlike in truncate_pagecache, unmap_mapping_range is called only
764     * once (before truncating pagecache), and without "even_cows" flag:
765     * hole-punching should not remove private COWed pages from the hole.
766     */
767    if ((u64)unmap_end > (u64)unmap_start)
768        unmap_mapping_range(mapping, unmap_start,
769                    1 + unmap_end - unmap_start, 0);
770    truncate_inode_pages_range(mapping, lstart, lend);
771}
772EXPORT_SYMBOL(truncate_pagecache_range);
773

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