Re: [kvm-devel] [PATCH] KVM simplified virtio balloon driver

On Thursday 17 January 2008 15:01:46 Anthony Liguori wrote:

Rusty Russell wrote:

quoted

OTOH it's currently pretty obvious (and usually fatal) if the guest has
trouble meeting the balloon requirements.  A serious host needs a way of
detecting stress in the guest anyway, which this doesn't offer until it's
too late...

The question I'm interested in answering though is not if but when.  I
would like to know when the guest has reached it's target.

I'm saying that it will be v. quickly in all but "too much squeeze" case.

And while we do get the madvise call outs, it's possible that pages have
been faulted in since then.

But that's exactly what the balloon number *doesn't* tell you.  It can tell 
you that it's released pages back to be used by the OS, but not whether the 
OS has used them.

I think this number is good for debugging the balloon driver, but for anything 
else it's a false friend.

Rusty.
PS.  Please cut down mails when you reply.