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Re: [Xen-devel] Design question for PV superpage support

To: Mick.Jordan@xxxxxxx
Subject: Re: [Xen-devel] Design question for PV superpage support
From: Dave McCracken <dcm@xxxxxxxx>
Date: Mon, 2 Mar 2009 12:00:09 -0600
Cc: Xen Developers List <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Monday 02 March 2009, Mick Jordan wrote:
> On 03/02/09 08:43, Mick Jordan wrote:
> > On 03/02/09 05:54, Dave McCracken wrote:
> >> The solution I am working on for how to support Linux hugepages (Xen
> >> superpages) involves creating domains made up entirely of
> >> superpages.  I can create a working domain with superpages and am in
> >> the process of supporting it in save/restore.
> I'm assuming that this means that everything is upgraded from 4K to 2MB.
> E.g. pfn 0 = 0, pfn 1 = 2MB., etc., and the mfn<->pfn maps also.

No, actually, it doesn't do that.  The hypervisor allocates 2M pages, then 
expands them into 4K pages for the mfn<->pfn maps, etc.

The only effective difference is that any given 2M-aligned range of pfns is 
guaranteed to map to a contiguous 2M-aligned range of mfns.  Therefore the 
guest can safely allocate 2M pages.

Dave McCracken
Oracle Corp.

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