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

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Date:   Fri, 27 Aug 2021 11:36:11 +0800
From:   Shiyang Ruan <ruansy.fnst@...itsu.com>
To:     Dan Williams <dan.j.williams@...el.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 2021/8/20 11:08, Dan Williams wrote:
> 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?
> 

Yes, I think it is needed to unshare the extents when the DAX flags of 
the file is changed.  I'll look into it.


--
Thanks,
Ruan.