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

[Gleb Natapov]

On Thu, Feb 23, 2012 at 04:42:54PM +0000, Stefan Hajnoczi wrote:
> On Thu, Feb 23, 2012 at 3:40 PM, Peter Lieven <address@hidden> 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 :).
> 
That was attempted. It is called "page hinting", but AFAIK due to
complex locking issue attempt was abandoned.

--
                        Gleb.