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RE: [Xen-devel] what happens when a PoD page is touched?

To: James Harper <james.harper@xxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] what happens when a PoD page is touched?
From: Paul Durrant <Paul.Durrant@xxxxxxxxxx>
Date: Mon, 16 May 2011 10:16:49 +0100
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Cc: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, xen devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] what happens when a PoD page is touched?
> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-devel-
> bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Tim Deegan
> Sent: 16 May 2011 09:39
> To: James Harper
> Cc: George Dunlap; xen devel
> Subject: Re: [Xen-devel] what happens when a PoD page is touched?
> At 11:16 +0100 on 15 May (1305458171), James Harper wrote:
> > I'm finding that the time of boot and hibernation of Windows under
> > xen-4.0.2-rc3 when maxmem is set is a big problem - 40 seconds to
> > balloon down 512MB on my system. Hibernation is even worse with
> delays
> > of minutes or hours.
> >

Are you sure that your hibernation slowdown is not caused by your frontend 
retrying failed block writes? Since hibernation knows nothing of what is 
allocated to the balloon it may try to dump ballooned out pages (possibly 
because they border pages containing useful info) which the storage backend 
will fail to grant map and the blkif request will be errored. If you retry then 
clearly you'll just get another error so if you have some sort of retry/timeout 
mechanism in your hiber driver it may will explain the slowness you are seeing.


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