linux-kernel - Re: [PATCH v2 00/10] fsdax,xfs: Add reflink&dedupe support for fsdax

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Date:   Sat, 13 Mar 2021 11:24:00 -0500
From:   Neal Gompa <ngompa13@...il.com>
To:     Adam Borowski <kilobyte@...band.pl>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>,
        Shiyang Ruan <ruansy.fnst@...itsu.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Jan Kara <jack@...e.cz>, Al Viro <viro@...iv.linux.org.uk>,
        Btrfs BTRFS <linux-btrfs@...r.kernel.org>,
        ocfs2-devel@....oracle.com, david <david@...morbit.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 00/10] fsdax,xfs: Add reflink&dedupe support for fsdax

On Sat, Mar 13, 2021 at 8:09 AM Adam Borowski <kilobyte@...band.pl> wrote:
>
> On Wed, Mar 10, 2021 at 02:26:43PM +0000, Matthew Wilcox wrote:
> > On Wed, Mar 10, 2021 at 08:21:59AM -0600, Goldwyn Rodrigues wrote:
> > > DAX on btrfs has been attempted[1]. Of course, we could not
> >
> > But why?  A completeness fetish?  I don't understand why you decided
> > to do this work.
>
> * xfs can shapshot only single files, btrfs entire subvolumes
> * btrfs-send|receive
> * enumeration of changed parts of a file
>

XFS cannot do snapshots since it lacks metadata COW. XFS reflinking is
primarily for space efficiency.



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