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> 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.

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 at redhat.com <mailto:dgilbert at redhat.com> / Manchester, UK
> 
> 
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