Re: [Qemu-devel] linux guests and ksm performance

[Avi Kivity <avi@redhat.com>]

On 02/23/2012 06:42 PM, Stefan Hajnoczi wrote:
> On Thu, Feb 23, 2012 at 3:40 PM, Peter Lieven <pl@dlh.net> wrote:
> > However, in a virtual machine I have not observed the above slow down to
> > that extend
> > while the benefit of zero after free in a virtualisation environment is
> > obvious:
> >
> > 1) zero pages can easily be merged by ksm or other technique.
> > 2) zero (dup) pages are a lot faster to transfer in case of migration.
>
> The other approach is a memory page "discard" mechanism - which
> obviously requires more code changes than zeroing freed pages.
>
> The advantage is that we don't take the brute-force and CPU intensive
> approach of zeroing pages.  It would be like a fine-grained ballooning
> feature.
>
> I hope someone will follow up saying this has already been done or
> prototyped :).

It already exists - that's the balloon code.  Right now it's host
driven, but maybe we can modify it to allow the guest to initiate
balloon inflations.

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