Re: [PATCH] KVM simplified virtio balloon driver

[Marcelo Tosatti <marcelo-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>]

On Sat, Jan 19, 2008 at 04:37:43PM -0600, Anthony Liguori wrote:
> Avi Kivity wrote:
> >Rusty Russell wrote:
> >>After discussions with Anthony Liguori, it seems that the virtio
> >>balloon can be made even simpler.  Here's my attempt.
> >>
> >>Since the balloon requires Guest cooperation anyway, there seems
> >>little reason to force it to tell the Host when it wants to reuse a
> >>page.  It can simply fault it in.
> >>
> >>  
> >
> >Faulting is synchronous, while deflating is (or can be made) 
> >asynchronous. If the host needs to do some work to get the memory, the 
> >guest will be slowed down considerably.
> 
> Good point.  Basically, we have two page hinting operations which 
> roughly correspond to madvise(MADV_DONTNEED) and madvise(MADV_WILLNEED).

Also, the simplified driver does not handle errors at all.

I don't think that assuming madvise() can't fail is a good thing.



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