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

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Message-ID: <20170806025042.anluiwr3bsr2z4ng@thunk.org>
Date:   Sat, 5 Aug 2017 22:50:42 -0400
From:   Theodore Ts'o <tytso@....edu>
To:     Andreas Dilger <adilger@...ger.ca>
Cc:     Tahsin Erdogan <tahsin@...gle.com>, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ext4: inplace xattr block update fails to deduplicate
 blocks

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

Thanks, applied.

					- Ted