roles/vmhost: Enable KSM

This commit adds a systemd unit to enable the Kernel Same-page Merging
daemon on VM hosts. This allows much greater virtual machine density,
especially when many VMs are running the same guest OS.

roles/vmhost/files/ksm.service

@@ -0,0 +1,12 @@
+# vim: set ft=dosini :
+[Unit]
+Description=Kernel Same-Page Merging
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/bin/sh -c "echo 1 > /sys/kernel/mm/ksm/run"
+ExecStop=/bin/sh -c "echo 0 > /sys/kernel/mm/ksm/run"
+
+[Install]
+WantedBy=multi-user.target