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Re: [Xen-devel] Xen 3.0 x86 + PAE with > 16 GB RAM?

To: "Petersson, Mats" <mats.petersson@xxxxxxx>
Subject: Re: [Xen-devel] Xen 3.0 x86 + PAE with > 16 GB RAM?
From: Derrik Pates <demon@xxxxxxxxxxxxx>
Date: Mon, 09 Jan 2006 08:24:26 -0500
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Petersson, Mats wrote:
> If I understand things right, the V40z is an AMD Opteron based system,
> which means that you could run x86-64.

This is correct, yes.

>                                        Is there any particular reason
> you don't want to do this? This would give you 63TB (or is that 63-7 =
> 56TB?) or addressable memory, with full 32-bit compatibility for
> user-mode code.  You'd obviously have to run the Guest Kernels in 64-bit
> mode as well... 

I'm considering this as well, but it's not quite so simple when running
a 32-bit guest OS - 64-bit guests are obviously a non-issue, but 32-bit
OSes need several userspace tools replaced with equivalents that
understand certain internal structures of the 64-bit kernel. I haven't
decided yet if the necessary hacking will be worthwhile to modify the
userspace tools for several OSes, or tweak the hypervisor (and
apparently the guest memory layouts as well, based on Keir's statements)
and use that instead.

> I'm not aware of any reason why this shouldn't be a "better" solution?

I'll agree it should be a higher-performance solution, at least, but I
have to make sure it all works right, as well... :) The fact is the
hardware in question hasn't even arrived yet, so it's something I still
have to look into.

Derrik Pates

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