During the planning of Hyper V, we allocated 2GB for parent partition and each Virtual Machine is statically assigned amount of RAM. However with Dynamic Memory feature available, the VM can dynamically expand or shrink according to Startup and Maximum value. This will evantually become a problem when VM take the RAM from parent partition which causing the Hyper V host to unresponsive state. To avoid this problem, you need to set Memory Reserve on the registry. Go to
Create a RED_DWORD value called Memory Reserve. Enter the value in MB. For example: 2048 for 2GB.
Finally reboot the physical Hyper V host to take effect.