Re: [Qemu-devel] [RFC 3/3] docs: document virtio-balloon stats

[Luiz Capitulino]

On Fri, 7 Dec 2012 15:01:36 +0000
Dietmar Maurer <address@hidden> wrote:

> > > Is it possible to extent those statistic to include buffer/cache values?
> > 
> > Yes, should be possible but the kernel virtio-balloon driver has to be
> > extended too (and I suspect this kind of change goes into the kernel first).
> 
> The current statistics are quite useless without that information, and

Maybe it's not possible to implement the feature you want to implement, but
I do get a ping once a while from people asking for these stats. Some of them
are people running virsh dommemstat which also makes use of that information.

> I guess it is impossible to such changes upstream within a reasonable time?

In the kernel, yes it would take a while.

> So what is the purpose of that 'stat-free-memory'? Can we change that to
> return the amount of free RAM including buffers?

That's kernel work, qemu is merely reporting what the kernel is making
available. But giving that you'll touch the kernel anyway, it's better
to add a new stat.

There are two other alternatives:

 1. add a query-memory-stats command to qemu-ga

     Pros: should be quicker and easier to modify/extend
     Cons: has the implications of running this from the guest user-space

 2. wait for the (kernel-based) auto-ballooning feature, which is on the
    works

     Pros: you do nothing and it's going to be completely automatic
     Cons: this is unlikely to be ready for the short term