Re: [PATCH 0/4] [RFC] btrfs: offline dedupe

[Liu Bo <bo.li.liu@oracle.com>]

On Tue, Apr 16, 2013 at 04:17:15PM -0700, Mark Fasheh wrote:
> On Wed, Apr 17, 2013 at 12:50:04AM +0200, Marek Otahal wrote: could you
> > compare (appart from online/offline) your implementation to LiuBo's work?,
> > appeared on ML a while ago:
> > http://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg23656.html
> 
> Well that's the primary difference. Liu Bo's patch requires a format change
> also since it's done online. My patch requires no format change. So they're
> complimentary approaches in my opinion.
> 
> There's also the possibility that some other file systems could pick up the
> ioctl. Ocfs2 in particular should be able to.
> 
> 
> > It would be interesting if the two approaches could share some code, and
> > also confirmation that using one technique does not disregard using the
> > other in future.
> 
> Both features can exist together and probably should, I can see great uses
> for both cases.
> 
> I haven't looked at the patches but with respect to code sharing I'll take a
> look. My patches don't actually add any custom code for the actual "let's
> de-dupe this extent" as I re-use the code from btrfs_ioctl_clone().

In online dedup, I just make some changes in write path, as we regard dedup as a
special kind of compression, doing dedup as compression way is the goal.

The difference is where hash database is -- offline dedup puts it in userspace
while online dedup in kernel.

Although there might be no code that can be shared here, I agree that both
online and offline one are useful.

Good job.

thanks,
liubo