[sorenjan]

Am I understanding the ballooning part right that this doesn't allocate all of the VM memory from the host until it's needed, and releases memory automatically when it's not needed anymore? So you can overprovision memory with multiple guests as long as the guests aren't using the memory at the same time?

[dizhn]

That's true but there are peculiarities. People usually don't do it on Windows VMs for instance. I myself do not use it at all but prox also does KSM (Kernel Samepage Merging) which activates when RAM usage is at a particular configurable level and helps a lot more than ballooning especially if your VMs and internals are similar.

[traverseda]

Yes, it requires a daemon running inside the VM and can be finicky though.