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

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>, Dave McCracken <dcm@xxxxxxxx>, Mick.Jordan@xxxxxxx, Xen Developers List <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] Design question for PV superpage support
From: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Date: Mon, 2 Mar 2009 18:03:26 +0000 (GMT)
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> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
> It'd be nice to fall back to the case of not being able to 
> guarantee all 2MB
> extents are aligned and contiguous. So for example being able 
> to migrate to
> or restore on a system that currently doesn't have enough 
> contiguous memory.

Well, yes and no.  I believe the ONLY reason to use 2MB
pages is to achieve a significant performance advantage.
And I suspect emulating 2MB "virtual pages" on 4KB physical
pages will perform at least slightly worse than just
4KB-on-4KB, true?

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