Before you manage memory resources, you should understand how they are being virtualized and used by ESXi.
The VMkernel manages all physical RAM on the host. The VMkernel dedicates part of this managed physical RAM for its own use. The rest is available for use by virtual machines.
The virtual and physical memory space is divided into blocks called pages. When physical memory is full, the data for virtual pages that are not present in physical memory are stored on disk. Depending on processor architecture, pages are typically 4 KB or 2 MB. See Advanced Memory Attributes.