On 11/23/2011 01:48 AM, Jérôme Gallard wrote: Welcome to the community. "Max Memory" is the cap amount of memory reserved for the domain at guest startup; qemu will not let the guest exceed this amount, but for typical guests, it starts the guest with this much memory reserved (the host's memory is used on-demand, though, so unless the guest actually touches this much memory, the host does not necessarily give up this much memory). "Used Memory" refers to the amount of memory that the guest informs the host that it is using. This requires guest cooperation, via the 'virtio memory balloon' device, so if the guest does not support this device, qemu must treat it the same as "Max Memory". On hosts that do support memory ballooning (most Linux guests support it by default, and you can install virtio drivers for Windows guests), then you can request that the guest use less memory by way of the 'virsh setmem' command (virDomainSetMemoryFlags API call), at which point libvirt issues a command for the guest to use its memory balloon device in order to reduce "Used Memory". -- Eric Blake eblake(a)redhat.com +1-919-301-3266 Libvirt virtualization library http://libvirt.org