Lastly there was a discussion about that in the OpenVZ IRC channel and here's what I've picked up from it:
- OpenVZ vSwap is not like normal swap
- therefor it doesn't depend on the HW node swap size
but it is:
- happing in normal RAM
- like RAM allocation, but highly slowed down (so it's like swap from speed etc.)
Therefor yes, RAM + vSWAP of all containers should not be higher than total amount of memory (= totally no overselling).
However, always all RAM is used by all containers if needed and only limited if resources are busy. Same seems to apply for vSWAP - since it's located in memory, it cannot be used if all other containers use the total amount of their allocated RAM (if it fills HW total).
Don't take this as carved in stone - but I'm 90% sure I didn't get it that wrong
Hope this helps