Open Stack

* Christophe de Dinechin (cdupontd at redhat.com) wrote:
> 
> 
> > On 2 Oct 2020, at 11:24, Dr. David Alan Gilbert <dgilbert at redhat.com> wrote:
> > 
> > * Fabiano Fidêncio (fidencio at redhat.com <mailto:fidencio at redhat.com>) wrote:
> >> Snir,
> >> 
> >> Firstly, let me reply to one specific bit of your email and also add a question.
> >> 
> >> [...]
> >> 
> >>> IIUC it's currently enabled by default (qemu), can it be disabled? if
> >>> not, is it planned to be configurable?
> >> 
> >> The current govmm codes only sets the "cache-size" when it's different
> >> from zero:
> >> https://github.com/intel/govmm/blob/master/qemu/qemu.go#L1256-L1258
> >> 
> >> So, setting virtio_fs_cache_size here
> >> https://github.com/kata-containers/kata-containers/blob/2.0-dev/src/runtime/cli/config/configuration-qemu-virtiofs.toml.in#L113-L114
> >> disables DAX.
> >> 
> >> A question I'd like to add to Snir's question is ...
> >> Wouldn't it be safer to have `virtio_fs_cache_size = 0` as a default
> >> value when using virtio-fs, at least till DAX gets solid?
> > 
> > I think that should work; the current qemu vhost-user-fs.c code has:
> > 
> >    DEFINE_PROP_SIZE("cache-size", VHostUserFS, conf.cache_size, 0),
> > 
> > so ommitting the property should give us 0 and cache disabled and
> > ommitting the property also means you work with upstream qemu's.
> > 
> > I do remember in older dev branches we had the default none-0
> > but finally found the error of our ways.
> 
> Do you have any idea of the timeline for the DAX issues to be resolved?
> 2.0 is a long-lived branch, presumably, so we want to have something
> in place that works when DAX is here.

I think full Dax might take a while; the kernel code is moving upstream,
but there are still a couple of nasty corner cases where we need to
figure out good solutions.

Dave

> You may want to look at https://bugzilla.redhat.com/show_bug.cgi?id=1876915#c30
> 
> > 
> > Dave
> > 
> > 
> >> [...]
> >> 
> >> Best Regards,
> >> -- 
> >> Fabiano Fidêncio
> >> 
> >> 
> >> _______________________________________________
> >> kata-dev mailing list
> >> kata-dev at lists.katacontainers.io <mailto:kata-dev at lists.katacontainers.io>
> >> http://lists.katacontainers.io/cgi-bin/mailman/listinfo/kata-dev <http://lists.katacontainers.io/cgi-bin/mailman/listinfo/kata-dev>
> > -- 
> > Dr. David Alan Gilbert / dgilbert at redhat.com <mailto:dgilbert at redhat.com> / Manchester, UK
> > 
> > 
> > _______________________________________________
> > kata-dev mailing list
> > kata-dev at lists.katacontainers.io <mailto:kata-dev at lists.katacontainers.io>
> > http://lists.katacontainers.io/cgi-bin/mailman/listinfo/kata-dev <http://lists.katacontainers.io/cgi-bin/mailman/listinfo/kata-dev>
-- 
Dr. David Alan Gilbert / dgilbert at redhat.com / Manchester, UK