Re: [PATCH v2 00/11] DAX fsynx/msync support

Jan Kara
2015-11-16T14:41:42Z

On Fri 13-11-15 17:06:39, Ross Zwisler wrote:
> This patch series adds support for fsync/msync to DAX.
>
> Patches 1 through 7 add various utilities that the DAX code will eventually
> need, and the DAX code itself is added by patch 8. Patches 9-11 update the
> three filesystems that currently support DAX, ext2, ext4 and XFS, to use
> the new DAX fsync/msync code.
>
> These patches build on the recent DAX locking changes from Dave Chinner,
> Jan Kara and myself. Dave's changes for XFS and my changes for ext2 have
> been merged in the v4.4 window, but Jan's are still unmerged. You can grab
> them here:
>
> http://www.spinics.net/lists/linux-ext4/msg49951.html

I had a quick look and the patches look sane to me. I'll try to give them
more detailed look later this week. When thinking about the general design
I was wondering: When we have this infrastructure to track data potentially
lingering in CPU caches, would not it be a performance win to use standard
cached stores in dax_io() and mark corresponding pages as dirty in page
cache the same way as this patch set does it for mmaped writes? I have no
idea how costly are non-temporal stores compared to cached ones and how
would this compare to the cost of dirty tracking so this may be just
completely bogus...

Honza

--
Jan Kara <jack@suse.com>
SUSE Labs, CR