Date: Thu, 10 Mar 2016 13:00:00 +0530
From: Amit Shah <amit.shah@redhat.com>
To: Jitendra Kolhe <jitendra.kolhe@hpe.com>
Cc: liang.z.li@intel.com, dgilbert@redhat.com, ehabkost@redhat.com,
        kvm@vger.kernel.org, mst@redhat.com, quintela@redhat.com,
        linux-kernel@vger.kernel.org, qemu-devel@nongnu.org,
        linux-mm@kvack.org, pbonzini@redhat.com, akpm@linux-foundation.org,
        virtualization@lists.linux-foundation.org, rth@twiddle.net,
        mohan_parthasarathy@hpe.com, simhan@hpe.com
Subject: Re: [Qemu-devel] [RFC kernel 0/2]A PV solution for KVM live
 migration optimization
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On (Thu) 10 Mar 2016 [12:31:32], Jitendra Kolhe wrote:
> On 3/8/2016 4:44 PM, Amit Shah wrote:
> >>>> Hi,
> >>>>   An interesting solution; I know a few different people have been looking at
> >>>> how to speed up ballooned VM migration.
> >>>>
> >>>
> >>> Ooh, different solutions for the same purpose, and both based on the balloon.
> >>
> >> We were also tying to address similar problem, without actually needing to modify
> >> the guest driver. Please find patch details under mail with subject.
> >> migration: skip sending ram pages released by virtio-balloon driver
> >
> > The scope of this patch series seems to be wider: don't send free
> > pages to a dest at all, vs. don't send pages that are ballooned out.
> 
> Hi,
> 
> Thanks for your response. The scope of this patch series doesn’t seem to take care 
> of ballooned out pages. To balloon out a guest ram page the guest balloon driver does 
> a alloc_page() and then return the guest pfn to Qemu, so ballooned out pages will not 
> be seen as free ram pages by the guest.
> Thus we will still end up scanning (for zero page) for ballooned out pages during 
> migration. It would be ideal if we could have both solutions.

Yes, of course it would be nice to have both solutions.  My response was to the line:

> >>> Ooh, different solutions for the same purpose, and both based on the balloon.

which sounded misleading to me for a couple of reasons: 1, as you
describe, pages being considered by this patchset and yours are
different; and 2, as I mentioned in the other mail, this patchset
doesn't really depend on the balloon, and I believe it should not.


		Amit