[Virtio-fs] [PATCH v4 0/8] fuse,virtiofs: support per-file DAX

[Vivek Goyal]

On Tue, Aug 17, 2021 at 10:32:14AM +0100, Dr. David Alan Gilbert wrote:
> * Miklos Szeredi (miklos at szeredi.hu) wrote:
> > On Tue, 17 Aug 2021 at 04:22, Jeffle Xu <jefflexu at linux.alibaba.com> wrote:
> > >
> > > This patchset adds support of per-file DAX for virtiofs, which is
> > > inspired by Ira Weiny's work on ext4[1] and xfs[2].
> > 
> > Can you please explain the background of this change in detail?
> > 
> > Why would an admin want to enable DAX for a particular virtiofs file
> > and not for others?
> 
> Where we're contending on virtiofs dax cache size it makes a lot of
> sense; it's quite expensive for us to map something into the cache
> (especially if we push something else out), so selectively DAXing files
> that are expected to be hot could help reduce cache churn.

In that case probaly we should just make DAX window larger. I assume
that selecting which files to turn DAX on, will itself will not be
a trivial. Not sure what heuristics are being deployed to determine
that. Will like to know more about it.

Vivek