Q. How can I tell how much memory the dynamic memory balloon driver is using?

A. The balloon driver used inside the VM to reclaim memory is implemented as a kernel level device driver (DMVSC), which means seeing the amount of memory used by the driver isn't explicitly possible within the guest OS—insight into kernel device driver memory is blocked. You can still get an idea of the amount of memory used by a balloon driver, because the DMVSC locks memory. So you can look at Driver Locked memory using RAMMap. Certain other drivers will lock some memory, but it's usually a very small amount, so most of the Driver Locked memory value will reflect the balloon driver size.

The two pictures below show the memory state before ballooning and after. Note the large difference in the Driver Locked value, which reflects the balloon size.

From the parent partition, you can use performance counters to get exact numbers by looking at the Hyper-V Dynamic Memory VM performance counters for the virtual machine (VM). The Removed Memory value reflects the memory claimed by the balloon driver, as shown here (the bottom value for the savdalclient VM).

Also in the picture, you can see Hyper-V Dynamic Memory Balancer, which reflects the dynamic memory operations for all VMs on the Hyper-V host.