[libvirt] libvirt memory usage statistics

Hello all, I am using libvirt version 1.1.1 on one of the nodes which has several VMs. When I used virsh dommemstat <domain UUID>, I am getting the following flags: actual, swap_in and rss. I am not able to get the unused memory that is associated with the virtual machine. Can I kindly know is there a documentation that describe the memory flags? Further, can I get help from the forum to obtain information about the unused memory associated with the virtual machine? Regards, Krishnaprasad