Another thing from the xen-users mailing list:
Apparently the way to specify the dom0 RAM at boot in Xen has changed. You should now specify the maximum memory –
dom0_mem=2G,max:2G instead of
Also, a new addition to the Xen Best Practices suggests preventing Xen from auto-ballooning the dom0 memory down by changing
/etc/xen/xl.conf to 0.