This is an Active Directory Domain Controller, so also a database, but a relatively small one.

What I don't understand, is that even in your example, if the guest OS shows 5.7GB of free memory, that is memory that SQL is not using, it can't be using it if the guest hasn't allocated it. And if SQL is not using it, the guest is not using it, then why would the host be using it?

Is this because the database is constantly cycling the "Free" memory" So this 5.7GB that was free 10 minutes ago is at a completely different memory location than the 5.7GB that is free right now, causing the host reclaimation of guest memory to not be able to keep up?