From: Tahsin Erdogan Subject: [PATCH] ext4: inplace xattr block update fails to deduplicate blocks Date: Fri, 14 Jul 2017 17:25:29 -0700 Message-ID: <20170715002529.31045-1-tahsin@google.com> Cc: linux-kernel@vger.kernel.org, Tahsin Erdogan To: Theodore Ts'o , Andreas Dilger , linux-ext4@vger.kernel.org Return-path: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org When an xattr block has a single reference, block is updated inplace and it is reinserted to the cache. Later, a cache lookup is performed to see whether an existing block has the same contents. This cache lookup will most of the time return the just inserted entry so deduplication is not achieved. Running the following test script will produce two xattr blocks which can be observed in "File ACL: " line of debugfs output: mke2fs -b 1024 -I 128 -F -O extent /dev/sdb 1G mount /dev/sdb /mnt/sdb touch /mnt/sdb/{x,y} setfattr -n user.1 -v aaa /mnt/sdb/x setfattr -n user.2 -v bbb /mnt/sdb/x setfattr -n user.1 -v aaa /mnt/sdb/y setfattr -n user.2 -v bbb /mnt/sdb/y debugfs -R 'stat x' /dev/sdb | cat debugfs -R 'stat y' /dev/sdb | cat This patch defers the reinsertion to the cache so that we can locate other blocks with the same contents. Signed-off-by: Tahsin Erdogan --- fs/ext4/xattr.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index cff4f41ced61..ad4ea1cf685f 100644 --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -1815,9 +1815,6 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode, ea_bdebug(bs->bh, "modifying in-place"); error = ext4_xattr_set_entry(i, s, handle, inode, true /* is_block */); - if (!error) - ext4_xattr_block_cache_insert(ea_block_cache, - bs->bh); ext4_xattr_block_csum_set(inode, bs->bh); unlock_buffer(bs->bh); if (error == -EFSCORRUPTED) @@ -1973,6 +1970,7 @@ ext4_xattr_block_set(handle_t *handle, struct inode *inode, } else if (bs->bh && s->base == bs->bh->b_data) { /* We were modifying this block in-place. */ ea_bdebug(bs->bh, "keeping this block"); + ext4_xattr_block_cache_insert(ea_block_cache, bs->bh); new_bh = bs->bh; get_bh(new_bh); } else { -- 2.13.2.932.g7449e964c-goog