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Re: [Xen-devel] GPLPV memory ballooning and x32

To: James Harper <james.harper@xxxxxxxxxxxxxxxx>, Aravindh Puthiyaparambil <aravindh@xxxxxxxxxx>, Pasi Kärkkäinen <pasik@xxxxxx>
Subject: Re: [Xen-devel] GPLPV memory ballooning and x32
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 25 May 2010 09:04:23 +0100
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On 25/05/2010 08:18, "James Harper" <james.harper@xxxxxxxxxxxxxxxx> wrote:

>> This is not a regression from 3.1 presumably (3.1 does not implement
>> populate-on-demand at all)?
> On a similar subject, is it now possible to start a hvm domain in a 'ballooned
> down' state (via PoD perhaps) and then have PV drivers detect the
> 'unpopulated' pages and turn them into ballooned pages?

Yeah this is all implemented in the Citrix drivers. Someone involved in that
may be able to help.

 -- Keir

> For that to work, I would need to be able to do the following:
> . detect the unpopulated PoD pages via some hypercall(s)
> . allocate specific pages in Windows (MmAllocatePagesForMdl has Low and High
> address parameters which suggest this sort of ability...)
> . make sure Windows doesn't touch those pages when I allocate them (I guess it
> doesn't anyway but I can't look at the source to check...)
> . change the pages from PoD to 'empty' via some hypercall(s) - or maybe this
> isn't necessary... I can just allocate them to balloon down, and then 'touch'
> each page (to make xen populate it) then free them, as long as I remember
> which pages are PoD and which are 'empty'

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