linux-kernel - RE: [RFC qemu 0/4] A PV solution for live migration optimization

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Date:	Fri, 4 Mar 2016 09:36:22 +0000
From:	"Li, Liang Z" <liang.z.li@...el.com>
To:	Jitendra Kolhe <jitendra.kolhe@....com>,
	"dgilbert@...hat.com" <dgilbert@...hat.com>
CC:	"ehabkost@...hat.com" <ehabkost@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"mst@...hat.com" <mst@...hat.com>,
	"quintela@...hat.com" <quintela@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"amit.shah@...hat.com" <amit.shah@...hat.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"rth@...ddle.net" <rth@...ddle.net>,
	"mohan_parthasarathy@....com" <mohan_parthasarathy@....com>,
	"simhan@....com" <simhan@....com>
Subject: RE: [RFC qemu 0/4] A PV solution for live migration optimization

> > > * Liang Li (liang.z.li@...el.com) wrote:
> > > > The current QEMU live migration implementation mark the all the
> > > > guest's RAM pages as dirtied in the ram bulk stage, all these
> > > > pages will be processed and that takes quit a lot of CPU cycles.
> > > >
> > > > From guest's point of view, it doesn't care about the content in
> > > > free pages. We can make use of this fact and skip processing the
> > > > free pages in the ram bulk stage, it can save a lot CPU cycles and
> > > > reduce the network traffic significantly while speed up the live
> > > > migration process obviously.
> > > >
> > > > This patch set is the QEMU side implementation.
> > > >
> > > > The virtio-balloon is extended so that QEMU can get the free pages
> > > > information from the guest through virtio.
> > > >
> > > > After getting the free pages information (a bitmap), QEMU can use
> > > > it to filter out the guest's free pages in the ram bulk stage.
> > > > This make the live migration process much more efficient.
> > >
> > > 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
> 
> Thanks,
> - Jitendra
> 

Great! Thanks for your information.

Liang
> >
> > >   I wonder if it would be possible to avoid the kernel changes by
> > > parsing /proc/self/pagemap - if that can be used to detect
> > > unmapped/zero mapped pages in the guest ram, would it achieve the
> same result?
> > >