Internals : Active memory of a process

We have an Exchange 2010 Mailbox (virtual) server with 32GiB of RAM. Since a mailbox server grabs the entire available RAM by design, I would like to know if there is a way to get a rough estimate of the RAM actively used on the server. 

I first looked at the working set - private, because I read somewhere that it was the memory recently touched by the process, but it seems that Windows don't trim the working set unless there is pressure on the memory.

I did not find any other counter (or combination of counters) that seemed to relate to the memory actively used. 

I then looked at the hypervisor active memory counter for the VM and thats gives me about 15% of active memory, but I know this value is computed indirectly and not totally reliable and I saw example where overcommiting aggressively memory in the hypervisor level worked fine while aggressively downsizing the configured VM memory was not effective (because that may push the OS into a panic behavior).

I also looked at RAMMap and VMMap.