[libvirt] SetMaxMemory vs. SetMemory

Hello, I just took a look at the driver functions for SetMaxMemory and SetMemory, as they are not implemented yet for the ESX driver and Daniel Veillard was a bit surprised that they are missing, as he expects them to be simple to implement. The problem is that I'm not sure how the memory model of ESX maps to SetMaxMemory vs. SetMemory. An ESX virtual machine has a defined memory size. That's the size reported to the guest OS as the available "physical" memory size. Beside this ESX allows the user to control how the hypervisor satisfies this "physical" memory size. You can define a reservation and an upper limit. The hypervisor will at least use the reserved amount of real physical memory to satisfy the "physical" memory size, but will not use more than the upper limit. How does this map to SetMaxMemory and SetMemory? My first assumption was, SetMaxMemory defines the "physical" memory size and SetMemory defines the upper limit of real physical memory to satisfy the "physical" memory size. This assumption seems to be in sync with the QEMU driver from just looking at the code. But with Xen it seems to be different. If I call SetMaxMemory and SetMemory with 2GB than free inside the domain reports 2GB total memory. After I call SetMemory with 1GB, free reports 1GB of total memory. I'm confused. So, what is the intended semantic for SetMaxMemory and SetMemory? Regards, Matthias