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Re: [Xen-devel] Yet another "Why can't I see all my RAM" question

To: Ian Pratt <m+Ian.Pratt@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] Yet another "Why can't I see all my RAM" question
From: "Christopher S. Aker" <caker@xxxxxxxxxxxx>
Date: Tue, 25 Apr 2006 18:54:24 -0500
Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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Ian Pratt wrote:
I know this has been asked a million times, and the typical answer is: that specific area of unallocable memory is used for ACPI data and framebuffers. However, I've got two identical machines, one running Xen-PAE, one running vanilla 2.6.16:

MemTotal:     16623588 kB

total_memory: 14336 (MB)

I was a little disappointed to discover that my investment in RAM is going to be underutilized in Xen. I would think if vanilla Linux can utilize all the available RAM that Xen would be able to, also.

PAE Xen currently won't see memory mapped above 16GB. Native Linux
doesn't have this restriction, it sees memory up to 64GB.

It would actually be fairly easy to make the Xen restriction "16GB plus
a bit" so that you'd get the full 16GB of RAM even with a large MMIO
whole in the address space. We might implement that, but using a 64b
hypervisor is definitely the preferred way forward.

OK. The problem there is supporting all of our existing 32b clients without forcing them to upgrade libs, etc (nightmare).

What's more likely to be implemented first? Support for 32b(w/pae?) domains on 64b Xen, or this extra bit support? Also, any feeling for when either of those would be implemented?


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