Re: [Qemu-devel] [RFC] Buffers/caches in VirtIO Balloon driver stats

[Wei Wang <wei.w.wang@intel.com>]

On 09/12/2017 10:29 PM, Tomáš Golembiovský wrote:
> On Tue, 29 Aug 2017 20:01:53 +0800
> Wei Wang <wei.w.wang@intel.com> wrote:
>
> > On 08/29/2017 05:57 PM, Stefan Hajnoczi wrote:
> > > On Sun, Aug 27, 2017 at 11:30:33PM +0200, Tomáš Golembiovský wrote:
> > > > Hi,
> > > I have CCed the relevant mailing lists and people most recently involved
> > > in virtio-balloon discussions.  Hopefully this will help get the right
> > > people to see your questions.
> > >   
> > > > We'd like to include information about reclaimable memory into the
> > > > statistics in VirtiO Balloon driver. Namely, we'd like to include
> > > > counters for bufferes and caches of Linux kernel. The patch itself is
> > > > pretty trivial -- no problem there. But before we do that I'd like to
> > > > get some input from the QEMU community.
> > > >
> > > > 1) Is there any reason not to have the stats there?
> > Could you please share the usages of reclaimable memory via the stats?
> I'll go ahead then and start sending patches. What would be the proper
> course of action here? Send patch for the driver first, or send patch
> for QEMU first or send both patches right away?

If you have both ready, I think it would be fine to send them all.


> > > > 2) Considering the balloon device is multiplatform (Linux, BSD,
> > > > Windows), is there a problem with including buffers/caches? These seem
> > > > to be specific to the Linux virtual memory subsystem. Of course, other
> > > > OSes could just report zeros. Are there some internal stats on those
> > > > OSes that could be filled in? I don't now if such or similar statistic
> > > > are available on BSD. On Windows only SystemCache stat looks like
> > > > something relevant. Anyone familiar with those OSes has any suggestions?
> > > >
> > > >        
> > One of the solutions that I'm thinking about is to make virtio
> > platform-ware.
> This is not necessary. IIUC the driver does not need to send all the
> stats. We can simply treat those stats as specific to Linux driver and
> other drivers will not send them. Then QEMU will treat them as if zero
> was reported.

Just had a quick check, I think that should function well too.
QEMU will report -1 for the stats.

Best,
Wei