[Fedora-xen] Xen only showing 16GB of ram out of 28GB

[Daniel P. Berrange]

On Tue, Jul 17, 2007 at 05:32:11AM -0400, thewird wrote:
> I installed FC6 and FC7 and the limit exists on both even though FC7
> was supposed to be using a 64bit hypervisor which supports 32bit guests
> (which isn't the case). After various linux installs (including CentOS)
> and different configs (even replacing the hypervisor with its 64bit
> counterpart) I wasn't able to get a system showing all 28GB of ram AND
> work with 32bit guests.
> 
> Out of desperation I bought "Virtualization with Xen" on Amazon for
> more insight. Although the book isn't too helpful since at least half
> of it if not more, is advertising the commercial XenSource (why would I
> buy an expensive Xen book if I wanted to use the newb commercial
> software?) I was able to figure out how to install the latest version
> of Xen 3.1 from source. I got it to boot perfectly and was expecting to
> see all of my 28GB of ram when I ran top but to my dismay it only
> showed 16GB once again...

What architecture did you compile with Xen 3.1 ?  Because of the tricks
Xen does on i386, even if you have PAE enabled you stil won't see more
than 16 GB of RAM. I believe you need 64-bit HV to see all. You may or
may not also need a 64-bit Dom0 - I don't know for sure since I'm not
lucky enough to have more than 16 GB of RAM :-(

> Can someone please help me and tell me what am I doing wrong. Or am I
> going about this the wrong way? Basically I want to see all of my 28GB
> of ram and run 32bit guests. I read everywhere this can be done but it
> never works. Thank you to anyone who can help me solve this. If money
> is the problem, please say so and that can be arranged.

We're working on a kernl update for Fedora that will hopefully make it
possible to really run 32-bit guests on 64-bit hypervisor.  If you did
a compile from upstream Xen 3.1 kenrel this should be working for you
already though.

Dan.
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