In some instances, a system with a large amount of memory requires special configuration in order for Oracle VM to install and launch correctly. If not, you could receive the following error on launch after installation:
kernel panic -not syncing: Out of memory and no killable processes
If you install Oracle VM from an ISO image or by using Oracle System Assistant, the dom0_mem parameter should be set correctly. If you install the Oracle VM software from PXE boot or some other customized environment and you have a large-memory system, you might need to recalculate the dom0_mem setting.
Workaround
Recalculate the dom0_mem setting using this formula:
dom0_mem = 502 + int(physical_mem * 0.0205)
For example, if your system has 128 GB of memory, you need to increase dom0_mem to 3188 MB:
dom0_mem=3188M
You can update the dom0_mem setting in the grub.conf file, or during installation by interrupting the boot process at grub menu and editing it there.
For more information on the dom0_mem setting, refer to the Installing Oracle VM Server documentation:
http://docs.oracle.com/cd/E35328_01/E35330/html/vmiug-server-dom0-memory.html