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I love the idea, always have. Does a unikernel application need statically allocated amount of RAM or is there a way to have unikernel-programs allocate memory dynamically?

Maybe this is where garbage-collected language would be useful.

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Look at a live version of Erlang on Xen.

http://erlangonxen.org/

Press ESC on the front page and see the amount of GC ram reclaimed from Erlang's VM.

Memory Usage: 12MB -- is also kind of a baffling number.

Seems to me a unikernel app would have access to all the RAM in the system. It is, after all, the kernel itself.

Yea but the hypervisor has to know how much physical memory to give the unikernel.

The way it usually works is that the guest OS gets a certain allocation of RAM and if it doesn't want to use it all it can inform the hypervisor of which ranges don't need physical backing at the moment. From the guest's perspective this is often implemented using a "balloon" process/driver that reserves a large chunk of guest memory in order to return it to the hypervisor. It can also be handled by the guest having a more general memory hotplug capability.

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