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Re: [Qemu-devel] [RFC Design Doc]Speed up live migration by skipping fre
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [RFC Design Doc]Speed up live migration by skipping free pages |
Date: |
Tue, 19 Apr 2016 20:12:02 +0100 |
User-agent: |
Mutt/1.5.24 (2015-08-30) |
* Michael S. Tsirkin (address@hidden) wrote:
> On Mon, Apr 18, 2016 at 11:08:31AM +0000, Li, Liang Z wrote:
> > Hi Dave,
> >
> > I am now working on how to benefit post-copy by skipping the free pages,
> > and I remember you have said we should let the destination know the info
> > of free pages so as to avoid request the free pages from the source.
> >
> > We have two solutions:
> >
> > a. send the migration dirty page bitmap to destination before post
> > copy start, so the destination can decide whether to request the pages or
> > place zero pages by checking the migration dirty page bitmap. The advantage
> > is that we can avoid sending the free pages. the disadvantage is that we
> > have
> > to send extra data to destination.
> >
> > b. Check the page request on the source side, if it's not a dirty page,
> > send a zero
> > page header to the destination.
> >
> > What's your opinion about them?
> >
> > Liang
> >
>
> Both are ad-hoc solutions imho.
>
> c. put the bitmap in a ramblock, check it on destination before
> requesting pages.
>
> This way it's migrated on-demand.
I can see where you're coming from, but I don't like this idea, because
sending data controlling the RAM migration process in RAM blocks controlled
by the same data just sounds too recursive to ever debug.
Dave
>
> --
> MST
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK