On a physical host running Ubuntu 12.04.4 LTS and serving as a hypervisor via qemu, hosting a single guest, I've issued:
To the host, which hung for several minutes before kicking me out of the console. I was unable to get back onto the host, and found that it had rebooted, which required manual intervention via the DRAC.
I'm trying to run through the logs now to see what might have caused this, but not finding anything obvious - which is to say I'm not sure what to show here to you folks. I'm not finding oom_killer tomfoolery in dmesg, kern.log, or syslog.
When the host came back up, swap was properly off and there was no swapping occurring on the host.