Re: [PATCH v25 0/2] Virtio-balloon: support free page reporting

[Wei Wang <wei.w.wang@intel.com>]

On 02/02/2018 03:15 AM, Michael S. Tsirkin wrote:
> On Thu, Jan 25, 2018 at 05:14:04PM +0800, Wei Wang wrote:
> > This patch series is separated from the previous "Virtio-balloon
> > Enhancement" series. The new feature, VIRTIO_BALLOON_F_FREE_PAGE_HINT,
> > implemented by this series enables the virtio-balloon driver to report
> > hints of guest free pages to the host. It can be used to accelerate live
> > migration of VMs. Here is an introduction of this usage:
> >
> > Live migration needs to transfer the VM's memory from the source machine
> > to the destination round by round. For the 1st round, all the VM's memory
> > is transferred. From the 2nd round, only the pieces of memory that were
> > written by the guest (after the 1st round) are transferred. One method
> > that is popularly used by the hypervisor to track which part of memory is
> > written is to write-protect all the guest memory.
> >
> > The second feature enables the optimization of the 1st round memory
> > transfer - the hypervisor can skip the transfer of guest free pages in the
> > 1st round. It is not concerned that the memory pages are used after they
> > are given to the hypervisor as a hint of the free pages, because they will
> > be tracked by the hypervisor and transferred in the next round if they are
> > used and written.
> Could you post performance numbers please?

Yes, it was posted here https://lkml.org/lkml/2018/1/25/698

I just changed the host side to poll the vq so that we don't need kick 
in the driver, it works pretty well. I'll test a little bit more and 
post out a new version with new performance numbers attached in the 
cover letter.

Best,
Wei