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

To: "Mick.Jordan@xxxxxxx" <Mick.Jordan@xxxxxxx>, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Subject: Re: [Xen-devel] Design question for PV superpage support
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 03 Mar 2009 18:10:15 +0000
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Dave McCracken <dcm@xxxxxxxx>, Xen Developers List <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On 03/03/2009 17:06, "Mick Jordan" <Mick.Jordan@xxxxxxx> wrote:

> I agree with the first statement. I'm not sure what you mean by "emulate 2MB
> pages with fragmented 4K pages" unless you assume nested page table support or
> you just mean falling back to 4K pages. As for whether a change should be
> silent, I'm less clear on that. I certainly wouldn't consider it a fatal
> condition requiring domain termination, That position is consistent with the
> "optimization not correctness" view of using large tables. However, a guest
> might want to indicate in some way that it has downgraded

Yeah, I somehow forgot about this actually. Of course it is hard to
downgrade to non-2MB pages across save/restore, because the guest-owned
pagetables have the superpage mappings baked into them. Oh well, that makes
such graceful downgrade much less attractive to implement, so I withdraw the

 -- Keir

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