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Date: Wed, 11 Jan 2017 01:10:11 -0800
From: Christoph Hellwig <hch@infradead.org>
Subject: Re: Reading about CoW architecture / Performance Limits
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To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Christian Theune <ct@flyingcircus.io>, linux-xfs@vger.kernel.org

On Wed, Jan 11, 2017 at 12:05:44AM -0800, Darrick J. Wong wrote:
> > 3. There appears to be code that allows retroactively creating CoW for
> > two files that existed separately before. Is that (planned to be)
> > exposed to userland?
> 
> No plans for that at the moment.  There used to be a debugging knob, but
> it was ripped out before upstreaming the code.

I think he's asking for the dedup ioctl, which is supported.