Re: [PATCH V5 00/12] Enable per-file/per-directory DAX operations V5

[Darrick J. Wong]

On Thu, Mar 12, 2020 at 11:49:32AM +1100, Dave Chinner wrote:
> On Wed, Mar 11, 2020 at 07:44:12AM +0100, Christoph Hellwig wrote:
> > On Wed, Mar 11, 2020 at 05:39:42PM +1100, Dave Chinner wrote:
> > > IOWs, the dax_associate_page() related functionality probably needs
> > > to be a filesystem callout - part of the aops vector, I think, so
> > > that device dax can still use it. That way XFS can go it's own way,
> > > while ext4 and device dax can continue to use the existing mechanism
> > > mechanisn that is currently implemented....
> > 
> > s/XFS/XFS with rmap/, as most XFS file systems currently don't have
> > that enabled we'll also need to keep the legacy path around.
> 
> Sure, that's trivially easy to handle in the XFS code once the
> callouts are in place.
> 
> But, quite frankly, we can enforce rmap to be enabled 
> enabled because nobody is using a reflink enabled FS w/ DAX right
> now. Everyone will have to mkfs their filesystems anyway to enable
> reflink+dax, so we simply don't allow reflink+dax to be enabled
> unless rmap is also enabled. Simple, easy, trivial.

Heh, this reminds me that I need to get that rmap performance analysis
report out to the list... it does have a fairly substantial performance
impact (in its current not-terribly-optimized state) but otoh enables
self-repair.

--D

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@xxxxxxxxxxxxx