[libvirt] libvirt memory flags

Hallo all, I am using libvirt version 1.1.1 on one of the nodes which has several VMs. When I executed the command, virsh dommemstat <domain UUID>, I am getting the following flags as output: actual, swap_in and rss. The API does not return "unused memory" flag that is associated to the virtual machine / domain. Can I kindly know is there a documentation that describes different memory flags? Further, can I get help from the forum to obtain information about the unused memory associated with the virtual machine / domain? Regards, Krishnaprasad