Many ESXi workloads present opportunities for sharing memory across virtual machines (as well as within a single virtual machine).
For example, several virtual machines might be running instances of the same guest operating system, have the same applications or components loaded, or contain common data. In such cases, a host uses a proprietary transparent page sharing technique to securely eliminate redundant copies of memory pages. With memory sharing, a workload running in virtual machines often consumes less memory than it would when running on physical machines. As a result, higher levels of overcommitment can be supported efficiently.
Use the Mem.ShareScanTime and Mem.ShareScanGHz advanced settings to control the rate at which the system scans memory to identify opportunities for sharing memory.
You can also disable sharing for individual virtual machines by setting the sched.mem.pshare.enable option to FALSE (this option defaults to TRUE). See Set Advanced Virtual Machine Attributes in the vSphere Web Client.
ESXi memory sharing runs as a background activity that scans for sharing opportunities over time. The amount of memory saved varies over time. For a fairly constant workload, the amount generally increases slowly until all sharing opportunities are exploited.
To determine the effectiveness of memory sharing for a given workload, try running the workload, and use
esxtop to observe the actual savings. Find the information in the
PSHARE field of the interactive mode in the Memory page.