Question about reduced memory by balloon driver (QEMU specific?)

Hi guys, When a guest's memory is dynamically reduced with setMemory API (and "balloon" QMP API), I'm wondering whether the virtio-balloon driver in the guest is consuming such reduced memory. If so, how can I see that the memory virtio-balloon is consuming? and is it possible the virtio-balloon has such a huge memory even though it's a kernel module?? Thanks,