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

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Message-ID: <20160308111443.GN15443@grmbl.mre>
Date:	Tue, 8 Mar 2016 16:44:43 +0530
From:	Amit Shah <amit.shah@...hat.com>
To:	Jitendra Kolhe <jitendra.kolhe@....com>
Cc:	liang.z.li@...el.com, dgilbert@...hat.com, ehabkost@...hat.com,
	kvm@...r.kernel.org, mst@...hat.com, quintela@...hat.com,
	linux-kernel@...r.kernel.org, qemu-devel@...gnu.org,
	linux-mm@...ck.org, pbonzini@...hat.com, akpm@...ux-foundation.org,
	virtualization@...ts.linux-foundation.org, rth@...ddle.net,
	mohan_parthasarathy@....com, simhan@....com
Subject: Re: [RFC qemu 0/4] A PV solution for live migration optimization

On (Fri) 04 Mar 2016 [15:02:47], Jitendra Kolhe wrote:
> > >
> > > * 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

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.

		Amit