Okay, according to this page:
http://www.linux-kvm.org/page/Projects/auto-ballooning
the vm gives the memory to the host back, only when there is high memory pressure on the host.
so in your case: the host has enough memory, so it does not need it back from the vm
http://www.linux-kvm.org/page/Projects/auto-ballooning
the vm gives the memory to the host back, only when there is high memory pressure on the host.
so in your case: the host has enough memory, so it does not need it back from the vm