linux-ext4 - Re: [PATCH 17/17] xfs: support for synchronous DAX faults

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Date:   Tue, 24 Oct 2017 15:29:08 -0600
From:   Ross Zwisler <ross.zwisler@...ux.intel.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Christoph Hellwig <hch@...radead.org>,
        linux-ext4@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-api@...r.kernel.org, linux-mm@...ck.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 17/17] xfs: support for synchronous DAX faults

On Tue, Oct 24, 2017 at 05:24:14PM +0200, Jan Kara wrote:
> From: Christoph Hellwig <hch@....de>
> 
> Return IOMAP_F_DIRTY from xfs_file_iomap_begin() when asked to prepare
> blocks for writing and the inode is pinned, and has dirty fields other
> than the timestamps.  In __xfs_filemap_fault() we then detect this case
> and call dax_finish_sync_fault() to make sure all metadata is committed,
> and to insert the page table entry.
> 
> Note that this will also dirty corresponding radix tree entry which is
> what we want - fsync(2) will still provide data integrity guarantees for
> applications not using userspace flushing. And applications using
> userspace flushing can avoid calling fsync(2) and thus avoid the
> performance overhead.
> 
> [JK: Added VM_SYNC flag handling]
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Jan Kara <jack@...e.cz>

I don't know enough about XFS dirty inode handling to be able to comment on
the changes in xfs_file_iomap_begin(), but the rest looks good.

Reviewed-by: Ross Zwisler <ross.zwisler@...ux.intel.com>