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

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Message-ID: <20160310093007.GA14065@rkaganb.sw.ru>
Date:	Thu, 10 Mar 2016 12:30:08 +0300
From:	Roman Kagan <rkagan@...tuozzo.com>
To:	Rik van Riel <riel@...hat.com>
CC:	"Michael S. Tsirkin" <mst@...hat.com>,
	"Li, Liang Z" <liang.z.li@...el.com>,
	"Dr. David Alan Gilbert" <dgilbert@...hat.com>,
	"ehabkost@...hat.com" <ehabkost@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"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>
Subject: Re: [Qemu-devel] [RFC qemu 0/4] A PV solution for live migration
 optimization

On Wed, Mar 09, 2016 at 02:38:52PM -0500, Rik van Riel wrote:
> On Wed, 2016-03-09 at 20:04 +0300, Roman Kagan wrote:
> > On Wed, Mar 09, 2016 at 05:41:39PM +0200, Michael S. Tsirkin wrote:
> > > On Wed, Mar 09, 2016 at 05:28:54PM +0300, Roman Kagan wrote:
> > > > 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 guess when you say clean you mean zero?
> > 
> > No I meant clean, i.e. those that could be evicted from RAM without
> > causing I/O.
> > 
> 
> Programs in the guest may have that memory mmapped.
> This could include things like libraries and executables.
> 
> How do you deal with the guest page cache containing
> references to now non-existent memory?
> 
> How do you re-populate the memory on the destination
> host?

I guess the confusion is due to the context I stripped from the previous
messages...  Actually I've been talking about doing full-fledged balloon
inflation before the migration, so, when it's deflated the guest will
fault in that data from the filesystem as usual.

Roman.