Re: [PATCH] ext4: inplace xattr block update fails to deduplicate blocks

Theodore Ts'o
2017-08-06T02:50:42Z

On Sat, Jul 15, 2017 at 02:49:05AM -0700, Andreas Dilger wrote:
> On Jul 14, 2017, at 5:25 PM, Tahsin Erdogan <tahsin@google.com> wrote:
> >
> > 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 <tahsin@google.com>
>
> Reviewed-by: Andreas Dilger <adilger@dilger.ca>

Thanks, applied.

- Ted