Kernel as hypervisor: Andrea Arcangeli

You're now with Qumranet which is the company behind KVM. Can you briefly tell me about the design of KVM and how that differs from previous virtualization approaches such as Xen and VMware?

I really like this approach because when you start doing really advanced virtualizations features like swapping the guest memory and swapping different parts of the address space you start using the same algorithms that the normal Linux kernel is using for swapping normal processes and this avoids duplication of algorithms, and when the kernel is optimized to do better swapping the virtual machine gets the same benefits.

You have Linux itself taking on the role of the hypervisor, so you don't have a hypervisor and then a different OS running as the guest. So Linux is the lowest level OS on the machine.

Exactly. It's especially useful with features like shared memory between guests or ballooning, and when you want to have guarantees that a certain number of virtual machines won't run the hypervisor out of memory. You can just start a lot of swap and share the memory and balloon with the guest and everything works very nicely.