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

To: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, Dave McCracken <dcm@xxxxxxxx>, "Mick.Jordan@xxxxxxx" <Mick.Jordan@xxxxxxx>, Xen Developers List <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Design question for PV superpage support
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Mon, 02 Mar 2009 19:04:46 +0000
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On 02/03/2009 18:48, "Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx> wrote:

>> If you make this constraint then you risk creating domains
>> that you cannot
>> always conveniently restore. Obviously you would allocate 2MB extents
>> wherever possible, since that is the whole point of this
>> drawn out exercise.
> Understood.  This is a case where convenience and the primary objective
> conflict.  I can't think offhand of a way to do it, but restoring
> or migrating a 2MB-assumed domain into an environment where the
> vast majority of 2MB pages are emulated should probably raise a
> bright red flag somehow.  Or there needs to be some tool that
> can at least be queried as to how many 2MB pages are being emulated.
> But probably the right long-term answer is a 2MB Xen with a 2MB
> Linux when applications assume/prefer 2MB pages.

I'd certainly be okay with this new config option meaning 'must get 2MB
extents' for now. It can be improved if the apparent downsides bite in

 -- Keir

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