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ext4: more efficient SEEK_DATA implementation

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Using SEEK_DATA in a huge sparse file can easily lead to sotflockups as
ext4_seek_data() iterates hole block-by-block. Fix the problem by using
returned hole size from ext4_map_blocks() and thus skip the hole in one
go.

Update also SEEK_HOLE implementation to follow the same pattern as
SEEK_DATA to make future maintenance easier.

Furthermore we add cond_resched() to both ext4_seek_data() and
ext4_seek_hole() to avoid softlockups in case evil user creates huge
fragmented file and we have to go through lots of extents.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Jan Kara
2016-03-09 23:11:13 -05:00
committed by Theodore Ts'o
parent e3fb8eb14e
commit 2d90c160e5
3 changed files with 106 additions and 61 deletions
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67
fs/ext4/inode.c
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@@ -5596,3 +5596,70 @@ int ext4_filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
return err;
}
/*
* Find the first extent at or after @lblk in an inode that is not a hole.
* Search for @map_len blocks at most. The extent is returned in @result.
*
* The function returns 1 if we found an extent. The function returns 0 in
* case there is no extent at or after @lblk and in that case also sets
* @result->es_len to 0. In case of error, the error code is returned.
*/
int ext4_get_next_extent(struct inode *inode, ext4_lblk_t lblk,
unsigned int map_len, struct extent_status *result)
{
struct ext4_map_blocks map;
struct extent_status es = {};
int ret;
map.m_lblk = lblk;
map.m_len = map_len;
/*
* For non-extent based files this loop may iterate several times since
* we do not determine full hole size.
*/
while (map.m_len > 0) {
ret = ext4_map_blocks(NULL, inode, &map, 0);
if (ret < 0)
return ret;
/* There's extent covering m_lblk? Just return it. */
if (ret > 0) {
int status;
ext4_es_store_pblock(result, map.m_pblk);
result->es_lblk = map.m_lblk;
result->es_len = map.m_len;
if (map.m_flags & EXT4_MAP_UNWRITTEN)
status = EXTENT_STATUS_UNWRITTEN;
else
status = EXTENT_STATUS_WRITTEN;
ext4_es_store_status(result, status);
return 1;
}
ext4_es_find_delayed_extent_range(inode, map.m_lblk,
map.m_lblk + map.m_len - 1,
&es);
/* Is delalloc data before next block in extent tree? */
if (es.es_len && es.es_lblk < map.m_lblk + map.m_len) {
ext4_lblk_t offset = 0;
if (es.es_lblk < lblk)
offset = lblk - es.es_lblk;
result->es_lblk = es.es_lblk + offset;
ext4_es_store_pblock(result,
ext4_es_pblock(&es) + offset);
result->es_len = es.es_len - offset;
ext4_es_store_status(result, ext4_es_status(&es));
return 1;
}
/* There's a hole at m_lblk, advance us after it */
map.m_lblk += map.m_len;
map_len -= map.m_len;
map.m_len = map_len;
cond_resched();
}
result->es_len = 0;
return 0;
}