Re: [Qemu-devel] [RFC kernel 0/2]A PV solution for KVM live migration optimization

On (Thu) 10 Mar 2016 [12:31:32], Jitendra Kolhe wrote:

On 3/8/2016 4:44 PM, Amit Shah wrote:

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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:

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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
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