linux-kernel - Re: [PATCH v7 8/8] fs/xfs: Add dax dedupe support

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Date:   Thu, 19 Aug 2021 20:08:09 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     "Darrick J. Wong" <djwong@...nel.org>,
        Christoph Hellwig <hch@....de>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        david <david@...morbit.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux NVDIMM <nvdimm@...ts.linux.dev>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v7 8/8] fs/xfs: Add dax dedupe support

On Sun, Aug 15, 2021 at 11:05 PM Shiyang Ruan <ruansy.fnst@...itsu.com> wrote:
>
> Introduce xfs_mmaplock_two_inodes_and_break_dax_layout() for dax files
> who are going to be deduped.  After that, call compare range function
> only when files are both DAX or not.
>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@...itsu.com>
> Reviewed-by: Darrick J. Wong <djwong@...nel.org>
> ---
>  fs/xfs/xfs_file.c    |  2 +-
>  fs/xfs/xfs_inode.c   | 57 ++++++++++++++++++++++++++++++++++++++++++++
>  fs/xfs/xfs_inode.h   |  1 +
>  fs/xfs/xfs_reflink.c |  4 ++--
>  4 files changed, 61 insertions(+), 3 deletions(-)
[..]
> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> index 13e461cf2055..86c737c2baeb 100644
> --- a/fs/xfs/xfs_reflink.c
> +++ b/fs/xfs/xfs_reflink.c
> @@ -1327,8 +1327,8 @@ xfs_reflink_remap_prep(
>         if (XFS_IS_REALTIME_INODE(src) || XFS_IS_REALTIME_INODE(dest))
>                 goto out_unlock;
>
> -       /* Don't share DAX file data for now. */
> -       if (IS_DAX(inode_in) || IS_DAX(inode_out))
> +       /* Don't share DAX file data with non-DAX file. */
> +       if (IS_DAX(inode_in) != IS_DAX(inode_out))
>                 goto out_unlock;

What if you have 2 DAX inodes sharing data and one is flipped to
non-DAX? Does that operation need to first go undo all sharing?