CentOS virt - Jan 2012 - centos 6 domU doesn't see all memory?

I'm running CentOS 6 x86_64 domU on CentOS 5 x86_64 dom0
The host is running 2.6.18-238.19.1.el5xen
The guest is 2.6.32-220.2.1.el6.x86_64

'xm list' on the host shows 512mb memory allocated.

'free -m' in the guest shows 224mb memory.

'xm mem-set 21 1024' (21 being the domU ID), 'xm list' now shows
1024mb, but in the guest I now see 736mb.

Anyone else seeing this? Any ideas on how to fix it?

Chris

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Chris Wik
Anu Internet Services Ltd
www.cwik.ch | www.anu.net