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

To: "Mick.Jordan@xxxxxxx" <Mick.Jordan@xxxxxxx>, Dave McCracken <dcm@xxxxxxxx>
Subject: Re: [Xen-devel] Design question for PV superpage support
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Mon, 02 Mar 2009 17:54:06 +0000
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On 02/03/2009 17:45, "Mick Jordan" <Mick.Jordan@xxxxxxx> 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.

No, it doesn't mean that, which will be clear from Dave's response just now.


>> 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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