* Miklos Szeredi (miklos@xxxxxxxxxx) wrote: > On Tue, 17 Aug 2021 at 11:32, Dr. David Alan Gilbert > <dgilbert@xxxxxxxxxx> wrote: > > > > * Miklos Szeredi (miklos@xxxxxxxxxx) wrote: > > > On Tue, 17 Aug 2021 at 04:22, Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx> 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'd agree that would be nice; however: a) It looks like other filesystems already gave something admin selectable b) Trying to write clever heuristics is only going to work in some cases; being able to say 'DAX this directory' might work better in practice. > I'm not sure what the ext4/xfs case for per-file DAX is. Maybe that > can help understand the virtiofs case as well. Yep, I don't understand the case with real nvdimm hardware. Dave > Thanks, > Miklos > -- Dr. David Alan Gilbert / dgilbert@xxxxxxxxxx / Manchester, UK
