According to Oracle documentation the dom0 memory settings do not need to be changed and are automatically set to 504 MB + 0.0205 * amount of physical memory (in MB). This would be great if it actually worked. I have installed two Oracle VM 2.2.1 systems one with 2 GB of RAM and one with 256 GB of RAM. Both systems were automatically configured by the Oracle VM installer with dom0 memory set to 254 MB. This was OK on the 2 GB system but caused extensive problems on the 256 GB system, which according to the documentation should have been set to 504 MB + 256 * 1024 * 0.0205 = 504 + 5374 or 5877 MB of RAM.
So, until a future release fixes this bug, when installing an Oracle VM 2.2.1 system always set the memory of dom0 by editing the boot line in /etc/grub/grub.conf and changing the value of dom0_memory to the proper setting.
FYI. The 256 GB system was using over 800 MB of RAM when performing live migrations on the Master/Utility Server.
