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Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimiz
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization |
Date: |
Wed, 9 Mar 2016 17:30:04 +0200 |
On Wed, Mar 09, 2016 at 03:27:54PM +0000, Li, Liang Z wrote:
> > On Mon, Mar 07, 2016 at 01:40:06PM +0200, Michael S. Tsirkin wrote:
> > > On Mon, Mar 07, 2016 at 06:49:19AM +0000, Li, Liang Z wrote:
> > > > > > No. And it's exactly what I mean. The ballooned memory is still
> > > > > > processed during live migration without skipping. The live
> > > > > > migration code is
> > > > > in migration/ram.c.
> > > > >
> > > > > So if guest acknowledged VIRTIO_BALLOON_F_MUST_TELL_HOST, we
> > can
> > > > > teach qemu to skip these pages.
> > > > > Want to write a patch to do this?
> > > > >
> > > >
> > > > Yes, we really can teach qemu to skip these pages and it's not hard.
> > > > The problem is the poor performance, this PV solution
> > >
> > > Balloon is always PV. And do not call patches solutions please.
> > >
> > > > is aimed to make it more
> > > > efficient and reduce the performance impact on guest.
> > >
> > > We need to get a bit beyond this. You are making multiple changes, it
> > > seems to make sense to split it all up, and analyse each change
> > > separately.
> >
> > Couldn't agree more.
> >
> > There are three stages in this optimization:
> >
> > 1) choosing which pages to skip
> >
> > 2) communicating them from guest to host
> >
> > 3) skip transferring uninteresting pages to the remote side on migration
> >
> > For (3) there seems to be a low-hanging fruit to amend
> > migration/ram.c:iz_zero_range() to consult /proc/self/pagemap. This would
> > work for guest RAM that hasn't been touched yet or which has been
> > ballooned out.
> >
> > For (1) I've been trying to make a point that skipping clean pages is much
> > more likely to result in noticable benefit than free pages only.
> >
>
> I am considering to drop the pagecache before getting the free pages.
>
> > As for (2), we do seem to have a problem with the existing balloon:
> > according to your measurements it's very slow; besides, I guess it plays
> > badly
>
> I didn't say communicating is slow. Even this is very slow, my solution use
> bitmap instead of
> PFNs, there is fewer data traffic, so it's faster than the existing balloon
> which use PFNs.
By how much?
> > with transparent huge pages (as both the guest and the host work with one
> > 4k page at a time). This is a problem for other use cases of balloon (e.g.
> > as a
> > facility for resource management); tackling that appears a more natural
> > application for optimization efforts.
> >
> > Thanks,
> > Roman.
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, (continued)
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Roman Kagan, 2016/03/04
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Li, Liang Z, 2016/03/04
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Michael S. Tsirkin, 2016/03/04
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Li, Liang Z, 2016/03/04
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Michael S. Tsirkin, 2016/03/05
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Li, Liang Z, 2016/03/07
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Michael S. Tsirkin, 2016/03/07
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Li, Liang Z, 2016/03/07
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Roman Kagan, 2016/03/09
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Li, Liang Z, 2016/03/09
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization,
Michael S. Tsirkin <=
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Li, Liang Z, 2016/03/09
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Michael S. Tsirkin, 2016/03/10
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Michael S. Tsirkin, 2016/03/09
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Roman Kagan, 2016/03/09
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Michael S. Tsirkin, 2016/03/09
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Roman Kagan, 2016/03/10
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Rik van Riel, 2016/03/09
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Roman Kagan, 2016/03/10
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Paolo Bonzini, 2016/03/04
- Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration optimization, Dr. David Alan Gilbert, 2016/03/04