* Christophe de Dinechin (cdupontd@redhat.com) wrote:
On 2 Oct 2020, at 11:24, Dr. David Alan Gilbert <dgilbert@redhat.com> wrote:
* Fabiano Fidêncio (fidencio@redhat.com <mailto:fidencio@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/... 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
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-- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK