ext4: fix extent_status fragmentation for plain files
[ Upstream commit 4068664e3c
]
Extents are cached in read_extent_tree_block(); as a result, extents
are not cached for inodes with depth == 0 when we try to find the
extent using ext4_find_extent(). The result of the lookup is cached
in ext4_map_blocks() but is only a subset of the extent on disk. As a
result, the contents of extents status cache can get very badly
fragmented for certain workloads, such as a random 4k read workload.
File size of /mnt/test is 33554432 (8192 blocks of 4096 bytes)
ext: logical_offset: physical_offset: length: expected: flags:
0: 0.. 8191: 40960.. 49151: 8192: last,eof
$ perf record -e 'ext4:ext4_es_*' /root/bin/fio --name=t --direct=0 --rw=randread --bs=4k --filesize=32M --size=32M --filename=/mnt/test
$ perf script | grep ext4_es_insert_extent | head -n 10
fio 131 [000] 13.975421: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [494/1) mapped 41454 status W
fio 131 [000] 13.975939: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [6064/1) mapped 47024 status W
fio 131 [000] 13.976467: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [6907/1) mapped 47867 status W
fio 131 [000] 13.976937: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [3850/1) mapped 44810 status W
fio 131 [000] 13.977440: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [3292/1) mapped 44252 status W
fio 131 [000] 13.977931: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [6882/1) mapped 47842 status W
fio 131 [000] 13.978376: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [3117/1) mapped 44077 status W
fio 131 [000] 13.978957: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [2896/1) mapped 43856 status W
fio 131 [000] 13.979474: ext4:ext4_es_insert_extent: dev 253,0 ino 12 es [7479/1) mapped 48439 status W
Fix this by caching the extents for inodes with depth == 0 in
ext4_find_extent().
[ Renamed ext4_es_cache_extents() to ext4_cache_extents() since this
newly added function is not in extents_cache.c, and to avoid
potential visual confusion with ext4_es_cache_extent(). -TYT ]
Signed-off-by: Dmitry Monakhov <dmonakhov@gmail.com>
Link: https://lore.kernel.org/r/20191106122502.19986-1-dmonakhov@gmail.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
parent
0c418786cb
commit
79ad149041
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@ -498,6 +498,30 @@ int ext4_ext_check_inode(struct inode *inode)
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return ext4_ext_check(inode, ext_inode_hdr(inode), ext_depth(inode), 0);
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}
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static void ext4_cache_extents(struct inode *inode,
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struct ext4_extent_header *eh)
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{
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struct ext4_extent *ex = EXT_FIRST_EXTENT(eh);
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ext4_lblk_t prev = 0;
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int i;
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for (i = le16_to_cpu(eh->eh_entries); i > 0; i--, ex++) {
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unsigned int status = EXTENT_STATUS_WRITTEN;
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ext4_lblk_t lblk = le32_to_cpu(ex->ee_block);
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int len = ext4_ext_get_actual_len(ex);
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if (prev && (prev != lblk))
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ext4_es_cache_extent(inode, prev, lblk - prev, ~0,
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EXTENT_STATUS_HOLE);
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if (ext4_ext_is_unwritten(ex))
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status = EXTENT_STATUS_UNWRITTEN;
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ext4_es_cache_extent(inode, lblk, len,
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ext4_ext_pblock(ex), status);
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prev = lblk + len;
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}
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}
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static struct buffer_head *
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__read_extent_tree_block(const char *function, unsigned int line,
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struct inode *inode, ext4_fsblk_t pblk, int depth,
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@ -532,26 +556,7 @@ __read_extent_tree_block(const char *function, unsigned int line,
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*/
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if (!(flags & EXT4_EX_NOCACHE) && depth == 0) {
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struct ext4_extent_header *eh = ext_block_hdr(bh);
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struct ext4_extent *ex = EXT_FIRST_EXTENT(eh);
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ext4_lblk_t prev = 0;
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int i;
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for (i = le16_to_cpu(eh->eh_entries); i > 0; i--, ex++) {
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unsigned int status = EXTENT_STATUS_WRITTEN;
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ext4_lblk_t lblk = le32_to_cpu(ex->ee_block);
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int len = ext4_ext_get_actual_len(ex);
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if (prev && (prev != lblk))
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ext4_es_cache_extent(inode, prev,
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lblk - prev, ~0,
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EXTENT_STATUS_HOLE);
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if (ext4_ext_is_unwritten(ex))
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status = EXTENT_STATUS_UNWRITTEN;
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ext4_es_cache_extent(inode, lblk, len,
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ext4_ext_pblock(ex), status);
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prev = lblk + len;
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}
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ext4_cache_extents(inode, eh);
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}
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return bh;
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errout:
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@ -899,6 +904,8 @@ ext4_find_extent(struct inode *inode, ext4_lblk_t block,
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path[0].p_bh = NULL;
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i = depth;
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if (!(flags & EXT4_EX_NOCACHE) && depth == 0)
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ext4_cache_extents(inode, eh);
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/* walk through the tree */
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while (i) {
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ext_debug("depth %d: num %d, max %d\n",
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