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

To: Mick.Jordan@xxxxxxx, Xen Developers List <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] Design question for PV superpage support
From: Dave McCracken <dcm@xxxxxxxx>
Date: Mon, 2 Mar 2009 11:29:42 -0600
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On Monday 02 March 2009, Mick Jordan 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.
> This wouldn't work too well for me in the case of thread stacks because
> we need to map out parts of the stack and, although we want large
> virtual stacks, we don't want do dedicate that much physical memory. Is
> it really difficult to support mixed pages sizes in the general case,
> e.g., save/restore etc.?

What I am doing is populating the domain with 2M pages.  The hypervisor fills 
in all its internal arrays as if they were regular 4K pages.  The guest is 
then free to use mixed size pages.  The only significant difference is that 
when a guest does allocate a 2M page, it's guaranteed to be properly aligned 
at the machine page level so it can be mapped as a hugepage.   All 4K page 
allocations will continue to work.

Dave McCracken
Oracle Corp.

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