How do you test a balloon memory driver?

I’ve wanted more support for virtualized DragonFly systems.  Sascha Wildner put together an experimental balloon memory driver to test out, and I ran it on two virtual machines separately, one with it loaded and one without, on the same host system.  The problem is, I can’t tell what it does.  The two machine reported almost the exact same RAM usage during a buildworld.

Any VMWare/virtualization experts out there able to tell me what needs to be tested to verify this?