vSphere High Performance Cookbook

Keeping memory free for VMkernel

The amount of memory the VMkernel will try to keep free can be achieved through the Mem.MemMinFreePct parameter. MemMinFreePct determines the amount of memory that the VMkernel should keep free. vSphere 4.1 introduced a dynamic threshold of the Soft, Hard, and Low state to set appropriate thresholds and prevent virtual machine performance issues, while protecting VMkernel. The different states, based on %pRAM which is still free, determines what type of memory reclamation techniques are being used.

For MemMinFreePct, using a default value of 6 percent can be inefficient when 256 gigabyte or 512 gigabyte systems are becoming more and more mainstream. A 6 percent threshold on a 512 gigabyte results in 30 gigabyte ...