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

[Miklos Szeredi]

On Tue, 17 Aug 2021 at 11:32, Dr. David Alan Gilbert
<dgilbert at redhat.com> 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.

If this is a performance issue, it should be fixed in a way that
doesn't require hand tuning like you suggest, I think.

I'm not sure what the  ext4/xfs case for per-file DAX is.  Maybe that
can help understand the virtiofs case as well.

Thanks,
Miklos