[kvmstats] fix memory searching

Also add some comments.

kvmstats/kvmstats

@@ -65,13 +65,22 @@ done
 for VM in $(virsh list --name --all)
 do
     echo "$VM"
+
+    # cpu
     virsh vcpucount --maximum --current "$VM"
+
+    # mem
     # libvirt store memory in KiB, POW must be lowered by 1
-    virsh domstats --balloon "$VM" | awk -F= '/balloon.maximum/ { print $2 / '$((POW / 1024))'}'
+    virsh dommemstat "$VM" 2>&- | awk 'BEGIN{ret=1}$1~/^actual$/{print $2 / '$((POW / 1024))';ret=0}END{exit ret}' ||
+        virsh dumpxml "$VM" | awk -F'[<>]' '$2~/^memory unit/{print $3/'$((POW / 1024))'}'
+
+    # disk
     for BLK in $(virsh domblklist "$VM" | sed '1,2d;/-$/d;/^$/d' | cut -d\  -f1)
     do
-        virsh domblkinfo "$VM" "$BLK"
+        virsh domblkinfo "$VM" "$BLK" 2>&-
     done | awk '/Physical:/ { size += $2 } END { print int(size / '${POW}') }'
+
+    # state
     virsh domstate "$VM" | grep -q '^running$' && echo yes || echo no
 done | xargs -n5 | {
     echo vm vcpu ram disk running