IIR I think it's a VM(?) that has certain limits, and because of those limits it's OK to run it in kernel-space. IIRC it's not Turning complete, and has a fixed

IIR I think it's a VM(?) that has certain limits, and because of those limits it's OK to run it in kernel-space. IIRC it's not Turning complete, and has a fixed run time. So Linux can just say "OK run this now" and not worry about scheduling. It's like putting a green thread in the kernel but to do this safely you need very strict restrictions (finite memory it can access, finite number of steps, etc). You can thus get speed-ups because there's no API, memory management, even scheduling.