linux/mm/truncate.c
Hugh Dickins 792ceaefe6 mm/fs: fix pessimization in hole-punching pagecache
I wanted to revert my v3.1 commit d0823576bf ("mm: pincer in
truncate_inode_pages_range"), to keep truncate_inode_pages_range() in
synch with shmem_undo_range(); but have stepped back - a change to
hole-punching in truncate_inode_pages_range() is a change to
hole-punching in every filesystem (except tmpfs) that supports it.

If there's a logical proof why no filesystem can depend for its own
correctness on the pincer guarantee in truncate_inode_pages_range() - an
instant when the entire hole is removed from pagecache - then let's
revisit later.  But the evidence is that only tmpfs suffered from the
livelock, and we have no intention of extending hole-punch to ramfs.  So
for now just add a few comments (to match or differ from those in
shmem_undo_range()), and fix one silliness noticed in d0823576bf4b...

Its "index == start" addition to the hole-punch termination test was
incomplete: it opened a way for the end condition to be missed, and the
loop go on looking through the radix_tree, all the way to end of file.
Fix that pessimization by resetting index when detected in inner loop.

Note that it's actually hard to hit this case, without the obsessive
concurrent faulting that trinity does: normally all pages are removed in
the initial trylock_page() pass, and this loop finds nothing to do.  I
had to "#if 0" out the initial pass to reproduce bug and test fix.

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Lukas Czerner <lczerner@redhat.com>
Cc: Dave Jones <davej@redhat.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-07-23 15:10:55 -07:00

773 lines
23 KiB
C

/*
* mm/truncate.c - code for taking down pages from address_spaces
*
* Copyright (C) 2002, Linus Torvalds
*
* 10Sep2002 Andrew Morton
* Initial version.
*/
#include <linux/kernel.h>
#include <linux/backing-dev.h>
#include <linux/gfp.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/export.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/pagevec.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/buffer_head.h> /* grr. try_to_release_page,
do_invalidatepage */
#include <linux/cleancache.h>
#include "internal.h"
static void clear_exceptional_entry(struct address_space *mapping,
pgoff_t index, void *entry)
{
struct radix_tree_node *node;
void **slot;
/* Handled by shmem itself */
if (shmem_mapping(mapping))
return;
spin_lock_irq(&mapping->tree_lock);
/*
* Regular page slots are stabilized by the page lock even
* without the tree itself locked. These unlocked entries
* need verification under the tree lock.
*/
if (!__radix_tree_lookup(&mapping->page_tree, index, &node, &slot))
goto unlock;
if (*slot != entry)
goto unlock;
radix_tree_replace_slot(slot, NULL);
mapping->nrshadows--;
if (!node)
goto unlock;
workingset_node_shadows_dec(node);
/*
* Don't track node without shadow entries.
*
* Avoid acquiring the list_lru lock if already untracked.
* The list_empty() test is safe as node->private_list is
* protected by mapping->tree_lock.
*/
if (!workingset_node_shadows(node) &&
!list_empty(&node->private_list))
list_lru_del(&workingset_shadow_nodes, &node->private_list);
__radix_tree_delete_node(&mapping->page_tree, node);
unlock:
spin_unlock_irq(&mapping->tree_lock);
}
/**
* do_invalidatepage - invalidate part or all of a page
* @page: the page which is affected
* @offset: start of the range to invalidate
* @length: length of the range to invalidate
*
* do_invalidatepage() is called when all or part of the page has become
* invalidated by a truncate operation.
*
* do_invalidatepage() does not have to release all buffers, but it must
* ensure that no dirty buffer is left outside @offset and that no I/O
* is underway against any of the blocks which are outside the truncation
* point. Because the caller is about to free (and possibly reuse) those
* blocks on-disk.
*/
void do_invalidatepage(struct page *page, unsigned int offset,
unsigned int length)
{
void (*invalidatepage)(struct page *, unsigned int, unsigned int);
invalidatepage = page->mapping->a_ops->invalidatepage;
#ifdef CONFIG_BLOCK
if (!invalidatepage)
invalidatepage = block_invalidatepage;
#endif
if (invalidatepage)
(*invalidatepage)(page, offset, length);
}
/*
* This cancels just the dirty bit on the kernel page itself, it
* does NOT actually remove dirty bits on any mmap's that may be
* around. It also leaves the page tagged dirty, so any sync
* activity will still find it on the dirty lists, and in particular,
* clear_page_dirty_for_io() will still look at the dirty bits in
* the VM.
*
* Doing this should *normally* only ever be done when a page
* is truncated, and is not actually mapped anywhere at all. However,
* fs/buffer.c does this when it notices that somebody has cleaned
* out all the buffers on a page without actually doing it through
* the VM. Can you say "ext3 is horribly ugly"? Tought you could.
*/
void cancel_dirty_page(struct page *page, unsigned int account_size)
{
if (TestClearPageDirty(page)) {
struct address_space *mapping = page->mapping;
if (mapping && mapping_cap_account_dirty(mapping)) {
dec_zone_page_state(page, NR_FILE_DIRTY);
dec_bdi_stat(mapping->backing_dev_info,
BDI_RECLAIMABLE);
if (account_size)
task_io_account_cancelled_write(account_size);
}
}
}
EXPORT_SYMBOL(cancel_dirty_page);
/*
* If truncate cannot remove the fs-private metadata from the page, the page
* becomes orphaned. It will be left on the LRU and may even be mapped into
* user pagetables if we're racing with filemap_fault().
*
* We need to bale out if page->mapping is no longer equal to the original
* mapping. This happens a) when the VM reclaimed the page while we waited on
* its lock, b) when a concurrent invalidate_mapping_pages got there first and
* c) when tmpfs swizzles a page between a tmpfs inode and swapper_space.
*/
static int
truncate_complete_page(struct address_space *mapping, struct page *page)
{
if (page->mapping != mapping)
return -EIO;
if (page_has_private(page))
do_invalidatepage(page, 0, PAGE_CACHE_SIZE);
cancel_dirty_page(page, PAGE_CACHE_SIZE);
ClearPageMappedToDisk(page);
delete_from_page_cache(page);
return 0;
}
/*
* This is for invalidate_mapping_pages(). That function can be called at
* any time, and is not supposed to throw away dirty pages. But pages can
* be marked dirty at any time too, so use remove_mapping which safely
* discards clean, unused pages.
*
* Returns non-zero if the page was successfully invalidated.
*/
static int
invalidate_complete_page(struct address_space *mapping, struct page *page)
{
int ret;
if (page->mapping != mapping)
return 0;
if (page_has_private(page) && !try_to_release_page(page, 0))
return 0;
ret = remove_mapping(mapping, page);
return ret;
}
int truncate_inode_page(struct address_space *mapping, struct page *page)
{
if (page_mapped(page)) {
unmap_mapping_range(mapping,
(loff_t)page->index << PAGE_CACHE_SHIFT,
PAGE_CACHE_SIZE, 0);
}
return truncate_complete_page(mapping, page);
}
/*
* Used to get rid of pages on hardware memory corruption.
*/
int generic_error_remove_page(struct address_space *mapping, struct page *page)
{
if (!mapping)
return -EINVAL;
/*
* Only punch for normal data pages for now.
* Handling other types like directories would need more auditing.
*/
if (!S_ISREG(mapping->host->i_mode))
return -EIO;
return truncate_inode_page(mapping, page);
}
EXPORT_SYMBOL(generic_error_remove_page);
/*
* Safely invalidate one page from its pagecache mapping.
* It only drops clean, unused pages. The page must be locked.
*
* Returns 1 if the page is successfully invalidated, otherwise 0.
*/
int invalidate_inode_page(struct page *page)
{
struct address_space *mapping = page_mapping(page);
if (!mapping)
return 0;
if (PageDirty(page) || PageWriteback(page))
return 0;
if (page_mapped(page))
return 0;
return invalidate_complete_page(mapping, page);
}
/**
* truncate_inode_pages_range - truncate range of pages specified by start & end byte offsets
* @mapping: mapping to truncate
* @lstart: offset from which to truncate
* @lend: offset to which to truncate (inclusive)
*
* Truncate the page cache, removing the pages that are between
* specified offsets (and zeroing out partial pages
* if lstart or lend + 1 is not page aligned).
*
* Truncate takes two passes - the first pass is nonblocking. It will not
* block on page locks and it will not block on writeback. The second pass
* will wait. This is to prevent as much IO as possible in the affected region.
* The first pass will remove most pages, so the search cost of the second pass
* is low.
*
* We pass down the cache-hot hint to the page freeing code. Even if the
* mapping is large, it is probably the case that the final pages are the most
* recently touched, and freeing happens in ascending file offset order.
*
* Note that since ->invalidatepage() accepts range to invalidate
* truncate_inode_pages_range is able to handle cases where lend + 1 is not
* page aligned properly.
*/
void truncate_inode_pages_range(struct address_space *mapping,
loff_t lstart, loff_t lend)
{
pgoff_t start; /* inclusive */
pgoff_t end; /* exclusive */
unsigned int partial_start; /* inclusive */
unsigned int partial_end; /* exclusive */
struct pagevec pvec;
pgoff_t indices[PAGEVEC_SIZE];
pgoff_t index;
int i;
cleancache_invalidate_inode(mapping);
if (mapping->nrpages == 0 && mapping->nrshadows == 0)
return;
/* Offsets within partial pages */
partial_start = lstart & (PAGE_CACHE_SIZE - 1);
partial_end = (lend + 1) & (PAGE_CACHE_SIZE - 1);
/*
* 'start' and 'end' always covers the range of pages to be fully
* truncated. Partial pages are covered with 'partial_start' at the
* start of the range and 'partial_end' at the end of the range.
* Note that 'end' is exclusive while 'lend' is inclusive.
*/
start = (lstart + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
if (lend == -1)
/*
* lend == -1 indicates end-of-file so we have to set 'end'
* to the highest possible pgoff_t and since the type is
* unsigned we're using -1.
*/
end = -1;
else
end = (lend + 1) >> PAGE_CACHE_SHIFT;
pagevec_init(&pvec, 0);
index = start;
while (index < end && pagevec_lookup_entries(&pvec, mapping, index,
min(end - index, (pgoff_t)PAGEVEC_SIZE),
indices)) {
mem_cgroup_uncharge_start();
for (i = 0; i < pagevec_count(&pvec); i++) {
struct page *page = pvec.pages[i];
/* We rely upon deletion not changing page->index */
index = indices[i];
if (index >= end)
break;
if (radix_tree_exceptional_entry(page)) {
clear_exceptional_entry(mapping, index, page);
continue;
}
if (!trylock_page(page))
continue;
WARN_ON(page->index != index);
if (PageWriteback(page)) {
unlock_page(page);
continue;
}
truncate_inode_page(mapping, page);
unlock_page(page);
}
pagevec_remove_exceptionals(&pvec);
pagevec_release(&pvec);
mem_cgroup_uncharge_end();
cond_resched();
index++;
}
if (partial_start) {
struct page *page = find_lock_page(mapping, start - 1);
if (page) {
unsigned int top = PAGE_CACHE_SIZE;
if (start > end) {
/* Truncation within a single page */
top = partial_end;
partial_end = 0;
}
wait_on_page_writeback(page);
zero_user_segment(page, partial_start, top);
cleancache_invalidate_page(mapping, page);
if (page_has_private(page))
do_invalidatepage(page, partial_start,
top - partial_start);
unlock_page(page);
page_cache_release(page);
}
}
if (partial_end) {
struct page *page = find_lock_page(mapping, end);
if (page) {
wait_on_page_writeback(page);
zero_user_segment(page, 0, partial_end);
cleancache_invalidate_page(mapping, page);
if (page_has_private(page))
do_invalidatepage(page, 0,
partial_end);
unlock_page(page);
page_cache_release(page);
}
}
/*
* If the truncation happened within a single page no pages
* will be released, just zeroed, so we can bail out now.
*/
if (start >= end)
return;
index = start;
for ( ; ; ) {
cond_resched();
if (!pagevec_lookup_entries(&pvec, mapping, index,
min(end - index, (pgoff_t)PAGEVEC_SIZE), indices)) {
/* If all gone from start onwards, we're done */
if (index == start)
break;
/* Otherwise restart to make sure all gone */
index = start;
continue;
}
if (index == start && indices[0] >= end) {
/* All gone out of hole to be punched, we're done */
pagevec_remove_exceptionals(&pvec);
pagevec_release(&pvec);
break;
}
mem_cgroup_uncharge_start();
for (i = 0; i < pagevec_count(&pvec); i++) {
struct page *page = pvec.pages[i];
/* We rely upon deletion not changing page->index */
index = indices[i];
if (index >= end) {
/* Restart punch to make sure all gone */
index = start - 1;
break;
}
if (radix_tree_exceptional_entry(page)) {
clear_exceptional_entry(mapping, index, page);
continue;
}
lock_page(page);
WARN_ON(page->index != index);
wait_on_page_writeback(page);
truncate_inode_page(mapping, page);
unlock_page(page);
}
pagevec_remove_exceptionals(&pvec);
pagevec_release(&pvec);
mem_cgroup_uncharge_end();
index++;
}
cleancache_invalidate_inode(mapping);
}
EXPORT_SYMBOL(truncate_inode_pages_range);
/**
* truncate_inode_pages - truncate *all* the pages from an offset
* @mapping: mapping to truncate
* @lstart: offset from which to truncate
*
* Called under (and serialised by) inode->i_mutex.
*
* Note: When this function returns, there can be a page in the process of
* deletion (inside __delete_from_page_cache()) in the specified range. Thus
* mapping->nrpages can be non-zero when this function returns even after
* truncation of the whole mapping.
*/
void truncate_inode_pages(struct address_space *mapping, loff_t lstart)
{
truncate_inode_pages_range(mapping, lstart, (loff_t)-1);
}
EXPORT_SYMBOL(truncate_inode_pages);
/**
* truncate_inode_pages_final - truncate *all* pages before inode dies
* @mapping: mapping to truncate
*
* Called under (and serialized by) inode->i_mutex.
*
* Filesystems have to use this in the .evict_inode path to inform the
* VM that this is the final truncate and the inode is going away.
*/
void truncate_inode_pages_final(struct address_space *mapping)
{
unsigned long nrshadows;
unsigned long nrpages;
/*
* Page reclaim can not participate in regular inode lifetime
* management (can't call iput()) and thus can race with the
* inode teardown. Tell it when the address space is exiting,
* so that it does not install eviction information after the
* final truncate has begun.
*/
mapping_set_exiting(mapping);
/*
* When reclaim installs eviction entries, it increases
* nrshadows first, then decreases nrpages. Make sure we see
* this in the right order or we might miss an entry.
*/
nrpages = mapping->nrpages;
smp_rmb();
nrshadows = mapping->nrshadows;
if (nrpages || nrshadows) {
/*
* As truncation uses a lockless tree lookup, cycle
* the tree lock to make sure any ongoing tree
* modification that does not see AS_EXITING is
* completed before starting the final truncate.
*/
spin_lock_irq(&mapping->tree_lock);
spin_unlock_irq(&mapping->tree_lock);
truncate_inode_pages(mapping, 0);
}
}
EXPORT_SYMBOL(truncate_inode_pages_final);
/**
* invalidate_mapping_pages - Invalidate all the unlocked pages of one inode
* @mapping: the address_space which holds the pages to invalidate
* @start: the offset 'from' which to invalidate
* @end: the offset 'to' which to invalidate (inclusive)
*
* This function only removes the unlocked pages, if you want to
* remove all the pages of one inode, you must call truncate_inode_pages.
*
* invalidate_mapping_pages() will not block on IO activity. It will not
* invalidate pages which are dirty, locked, under writeback or mapped into
* pagetables.
*/
unsigned long invalidate_mapping_pages(struct address_space *mapping,
pgoff_t start, pgoff_t end)
{
pgoff_t indices[PAGEVEC_SIZE];
struct pagevec pvec;
pgoff_t index = start;
unsigned long ret;
unsigned long count = 0;
int i;
pagevec_init(&pvec, 0);
while (index <= end && pagevec_lookup_entries(&pvec, mapping, index,
min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
indices)) {
mem_cgroup_uncharge_start();
for (i = 0; i < pagevec_count(&pvec); i++) {
struct page *page = pvec.pages[i];
/* We rely upon deletion not changing page->index */
index = indices[i];
if (index > end)
break;
if (radix_tree_exceptional_entry(page)) {
clear_exceptional_entry(mapping, index, page);
continue;
}
if (!trylock_page(page))
continue;
WARN_ON(page->index != index);
ret = invalidate_inode_page(page);
unlock_page(page);
/*
* Invalidation is a hint that the page is no longer
* of interest and try to speed up its reclaim.
*/
if (!ret)
deactivate_page(page);
count += ret;
}
pagevec_remove_exceptionals(&pvec);
pagevec_release(&pvec);
mem_cgroup_uncharge_end();
cond_resched();
index++;
}
return count;
}
EXPORT_SYMBOL(invalidate_mapping_pages);
/*
* This is like invalidate_complete_page(), except it ignores the page's
* refcount. We do this because invalidate_inode_pages2() needs stronger
* invalidation guarantees, and cannot afford to leave pages behind because
* shrink_page_list() has a temp ref on them, or because they're transiently
* sitting in the lru_cache_add() pagevecs.
*/
static int
invalidate_complete_page2(struct address_space *mapping, struct page *page)
{
if (page->mapping != mapping)
return 0;
if (page_has_private(page) && !try_to_release_page(page, GFP_KERNEL))
return 0;
spin_lock_irq(&mapping->tree_lock);
if (PageDirty(page))
goto failed;
BUG_ON(page_has_private(page));
__delete_from_page_cache(page, NULL);
spin_unlock_irq(&mapping->tree_lock);
mem_cgroup_uncharge_cache_page(page);
if (mapping->a_ops->freepage)
mapping->a_ops->freepage(page);
page_cache_release(page); /* pagecache ref */
return 1;
failed:
spin_unlock_irq(&mapping->tree_lock);
return 0;
}
static int do_launder_page(struct address_space *mapping, struct page *page)
{
if (!PageDirty(page))
return 0;
if (page->mapping != mapping || mapping->a_ops->launder_page == NULL)
return 0;
return mapping->a_ops->launder_page(page);
}
/**
* invalidate_inode_pages2_range - remove range of pages from an address_space
* @mapping: the address_space
* @start: the page offset 'from' which to invalidate
* @end: the page offset 'to' which to invalidate (inclusive)
*
* Any pages which are found to be mapped into pagetables are unmapped prior to
* invalidation.
*
* Returns -EBUSY if any pages could not be invalidated.
*/
int invalidate_inode_pages2_range(struct address_space *mapping,
pgoff_t start, pgoff_t end)
{
pgoff_t indices[PAGEVEC_SIZE];
struct pagevec pvec;
pgoff_t index;
int i;
int ret = 0;
int ret2 = 0;
int did_range_unmap = 0;
cleancache_invalidate_inode(mapping);
pagevec_init(&pvec, 0);
index = start;
while (index <= end && pagevec_lookup_entries(&pvec, mapping, index,
min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1,
indices)) {
mem_cgroup_uncharge_start();
for (i = 0; i < pagevec_count(&pvec); i++) {
struct page *page = pvec.pages[i];
/* We rely upon deletion not changing page->index */
index = indices[i];
if (index > end)
break;
if (radix_tree_exceptional_entry(page)) {
clear_exceptional_entry(mapping, index, page);
continue;
}
lock_page(page);
WARN_ON(page->index != index);
if (page->mapping != mapping) {
unlock_page(page);
continue;
}
wait_on_page_writeback(page);
if (page_mapped(page)) {
if (!did_range_unmap) {
/*
* Zap the rest of the file in one hit.
*/
unmap_mapping_range(mapping,
(loff_t)index << PAGE_CACHE_SHIFT,
(loff_t)(1 + end - index)
<< PAGE_CACHE_SHIFT,
0);
did_range_unmap = 1;
} else {
/*
* Just zap this page
*/
unmap_mapping_range(mapping,
(loff_t)index << PAGE_CACHE_SHIFT,
PAGE_CACHE_SIZE, 0);
}
}
BUG_ON(page_mapped(page));
ret2 = do_launder_page(mapping, page);
if (ret2 == 0) {
if (!invalidate_complete_page2(mapping, page))
ret2 = -EBUSY;
}
if (ret2 < 0)
ret = ret2;
unlock_page(page);
}
pagevec_remove_exceptionals(&pvec);
pagevec_release(&pvec);
mem_cgroup_uncharge_end();
cond_resched();
index++;
}
cleancache_invalidate_inode(mapping);
return ret;
}
EXPORT_SYMBOL_GPL(invalidate_inode_pages2_range);
/**
* invalidate_inode_pages2 - remove all pages from an address_space
* @mapping: the address_space
*
* Any pages which are found to be mapped into pagetables are unmapped prior to
* invalidation.
*
* Returns -EBUSY if any pages could not be invalidated.
*/
int invalidate_inode_pages2(struct address_space *mapping)
{
return invalidate_inode_pages2_range(mapping, 0, -1);
}
EXPORT_SYMBOL_GPL(invalidate_inode_pages2);
/**
* truncate_pagecache - unmap and remove pagecache that has been truncated
* @inode: inode
* @newsize: new file size
*
* inode's new i_size must already be written before truncate_pagecache
* is called.
*
* This function should typically be called before the filesystem
* releases resources associated with the freed range (eg. deallocates
* blocks). This way, pagecache will always stay logically coherent
* with on-disk format, and the filesystem would not have to deal with
* situations such as writepage being called for a page that has already
* had its underlying blocks deallocated.
*/
void truncate_pagecache(struct inode *inode, loff_t newsize)
{
struct address_space *mapping = inode->i_mapping;
loff_t holebegin = round_up(newsize, PAGE_SIZE);
/*
* unmap_mapping_range is called twice, first simply for
* efficiency so that truncate_inode_pages does fewer
* single-page unmaps. However after this first call, and
* before truncate_inode_pages finishes, it is possible for
* private pages to be COWed, which remain after
* truncate_inode_pages finishes, hence the second
* unmap_mapping_range call must be made for correctness.
*/
unmap_mapping_range(mapping, holebegin, 0, 1);
truncate_inode_pages(mapping, newsize);
unmap_mapping_range(mapping, holebegin, 0, 1);
}
EXPORT_SYMBOL(truncate_pagecache);
/**
* truncate_setsize - update inode and pagecache for a new file size
* @inode: inode
* @newsize: new file size
*
* truncate_setsize updates i_size and performs pagecache truncation (if
* necessary) to @newsize. It will be typically be called from the filesystem's
* setattr function when ATTR_SIZE is passed in.
*
* Must be called with inode_mutex held and before all filesystem specific
* block truncation has been performed.
*/
void truncate_setsize(struct inode *inode, loff_t newsize)
{
i_size_write(inode, newsize);
truncate_pagecache(inode, newsize);
}
EXPORT_SYMBOL(truncate_setsize);
/**
* truncate_pagecache_range - unmap and remove pagecache that is hole-punched
* @inode: inode
* @lstart: offset of beginning of hole
* @lend: offset of last byte of hole
*
* This function should typically be called before the filesystem
* releases resources associated with the freed range (eg. deallocates
* blocks). This way, pagecache will always stay logically coherent
* with on-disk format, and the filesystem would not have to deal with
* situations such as writepage being called for a page that has already
* had its underlying blocks deallocated.
*/
void truncate_pagecache_range(struct inode *inode, loff_t lstart, loff_t lend)
{
struct address_space *mapping = inode->i_mapping;
loff_t unmap_start = round_up(lstart, PAGE_SIZE);
loff_t unmap_end = round_down(1 + lend, PAGE_SIZE) - 1;
/*
* This rounding is currently just for example: unmap_mapping_range
* expands its hole outwards, whereas we want it to contract the hole
* inwards. However, existing callers of truncate_pagecache_range are
* doing their own page rounding first. Note that unmap_mapping_range
* allows holelen 0 for all, and we allow lend -1 for end of file.
*/
/*
* Unlike in truncate_pagecache, unmap_mapping_range is called only
* once (before truncating pagecache), and without "even_cows" flag:
* hole-punching should not remove private COWed pages from the hole.
*/
if ((u64)unmap_end > (u64)unmap_start)
unmap_mapping_range(mapping, unmap_start,
1 + unmap_end - unmap_start, 0);
truncate_inode_pages_range(mapping, lstart, lend);
}
EXPORT_SYMBOL(truncate_pagecache_range);