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

To: Dave McCracken <dcm@xxxxxxxx>
Subject: Re: [Xen-devel] Design question for PV superpage support
From: Mick Jordan <Mick.Jordan@xxxxxxx>
Date: Mon, 02 Mar 2009 09:45:06 -0800
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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.
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.?
Save/restore is definitely important for me and we do support it at present. I'm wondering if I might be able to "reapply" my 2MB mappings after a restore on a 4K system, given that these are just layered on a 1-1 mapping between physical/virtual for all allocated memory.


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