Which feature of vSphere 5 can be used to reduce virtual machine memory overhead?

VMX Swap Files
Virtual machine executable (VMX) swap files allow the host to greatly reduce the amount of overhead memory
reserved for the VMX process.
NOTE VMX swap files are not related to the swap to host cache feature or to regular host-level swap files.
ESXi reserves memory per virtual machine for a variety of purposes. Memory for the needs of certain
components, such as the virtual machine monitor (VMM) and virtual devices, is fully reserved when a virtual
machine is powered on. However, some of the overhead memory that is reserved for the VMX process can be
swapped. The VMX swap feature reduces the VMX memory reservation significantly (for example, from about
50MB or more per virtual machine to about 10MB per virtual machine). This allows the remaining memory to
be swapped out when host memory is overcommitted, reducing overhead memory reservation for each virtual
machine.
The host creates VMX swap files automatically,