From: Dmitry Monakhov <dmonakhov@xxxxxxxxx>
commit 4068664e3cd2312610ceac05b74c4cf1853b8325 upstream.
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@xxxxxxxxx>
Link: https://lore.kernel.org/r/20191106122502.19986-1-dmonakhov@xxxxxxxxx
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/ext4/extents.c | 47 +++++++++++++++++++++++++++--------------------
1 file changed, 27 insertions(+), 20 deletions(-)
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -510,6 +510,30 @@ int ext4_ext_check_inode(struct inode *i
return ext4_ext_check(inode, ext_inode_hdr(inode), ext_depth(inode), 0);
}
+static void ext4_cache_extents(struct inode *inode,
+ struct ext4_extent_header *eh)
+{
+ struct ext4_extent *ex = EXT_FIRST_EXTENT(eh);
+ ext4_lblk_t prev = 0;
+ int i;
+
+ for (i = le16_to_cpu(eh->eh_entries); i > 0; i--, ex++) {
+ unsigned int status = EXTENT_STATUS_WRITTEN;
+ ext4_lblk_t lblk = le32_to_cpu(ex->ee_block);
+ int len = ext4_ext_get_actual_len(ex);
+
+ if (prev && (prev != lblk))
+ ext4_es_cache_extent(inode, prev, lblk - prev, ~0,
+ EXTENT_STATUS_HOLE);
+
+ if (ext4_ext_is_unwritten(ex))
+ status = EXTENT_STATUS_UNWRITTEN;
+ ext4_es_cache_extent(inode, lblk, len,
+ ext4_ext_pblock(ex), status);
+ prev = lblk + len;
+ }
+}
+
static struct buffer_head *
__read_extent_tree_block(const char *function, unsigned int line,
struct inode *inode, ext4_fsblk_t pblk, int depth,
@@ -540,26 +564,7 @@ __read_extent_tree_block(const char *fun
*/
if (!(flags & EXT4_EX_NOCACHE) && depth == 0) {
struct ext4_extent_header *eh = ext_block_hdr(bh);
- struct ext4_extent *ex = EXT_FIRST_EXTENT(eh);
- ext4_lblk_t prev = 0;
- int i;
-
- for (i = le16_to_cpu(eh->eh_entries); i > 0; i--, ex++) {
- unsigned int status = EXTENT_STATUS_WRITTEN;
- ext4_lblk_t lblk = le32_to_cpu(ex->ee_block);
- int len = ext4_ext_get_actual_len(ex);
-
- if (prev && (prev != lblk))
- ext4_es_cache_extent(inode, prev,
- lblk - prev, ~0,
- EXTENT_STATUS_HOLE);
-
- if (ext4_ext_is_unwritten(ex))
- status = EXTENT_STATUS_UNWRITTEN;
- ext4_es_cache_extent(inode, lblk, len,
- ext4_ext_pblock(ex), status);
- prev = lblk + len;
- }
+ ext4_cache_extents(inode, eh);
}
return bh;
errout:
@@ -907,6 +912,8 @@ ext4_find_extent(struct inode *inode, ex
path[0].p_bh = NULL;
i = depth;
+ if (!(flags & EXT4_EX_NOCACHE) && depth == 0)
+ ext4_cache_extents(inode, eh);
/* walk through the tree */
while (i) {
ext_debug("depth %d: num %d, max %d\n",
