1 ext4: inplace xattr block update fails to deduplicate blocks
3 From: Tahsin Erdogan <tahsin@google.com>
5 When an xattr block has a single reference, block is updated inplace
6 and it is reinserted to the cache. Later, a cache lookup is performed
7 to see whether an existing block has the same contents. This cache
8 lookup will most of the time return the just inserted entry so
9 deduplication is not achieved.
11 Running the following test script will produce two xattr blocks which
12 can be observed in "File ACL: " line of debugfs output:
14 mke2fs -b 1024 -I 128 -F -O extent /dev/sdb 1G
15 mount /dev/sdb /mnt/sdb
19 setfattr -n user.1 -v aaa /mnt/sdb/x
20 setfattr -n user.2 -v bbb /mnt/sdb/x
22 setfattr -n user.1 -v aaa /mnt/sdb/y
23 setfattr -n user.2 -v bbb /mnt/sdb/y
25 debugfs -R 'stat x' /dev/sdb | cat
26 debugfs -R 'stat y' /dev/sdb | cat
28 This patch defers the reinsertion to the cache so that we can locate
29 other blocks with the same contents.
31 Signed-off-by: Tahsin Erdogan <tahsin@google.com>
32 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
33 Reviewed-by: Andreas Dilger <adilger@dilger.ca>
35 fs/ext4/xattr.c | 4 +---
36 1 file changed, 1 insertion(+), 3 deletions(-)
38 diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
39 index cff4f41ced61..ad4ea1cf685f 100644
42 @@ -1815,9 +1815,6 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
43 ea_bdebug(bs->bh, "modifying in-place");
44 error = ext4_xattr_set_entry(i, s, handle, inode,
47 - ext4_xattr_block_cache_insert(ea_block_cache,
49 ext4_xattr_block_csum_set(inode, bs->bh);
50 unlock_buffer(bs->bh);
51 if (error == -EFSCORRUPTED)
52 @@ -1973,6 +1970,7 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode,
53 } else if (bs->bh && s->base == bs->bh->b_data) {
54 /* We were modifying this block in-place. */
55 ea_bdebug(bs->bh, "keeping this block");
56 + ext4_xattr_block_cache_insert(ea_block_cache, bs->bh);
61 2.13.2.932.g7449e964c-goog