Backing Guest vRAM with 1GB Pages

vSphere ESXi provides a limited support for backing guest vRAM with 1GB pages.

In order to use 1GB pages for backing guest memory you must apply the option sched.mem.lpage.enable1GPage = "TRUE" for the VM. You can set this under Advanced options when you select Edit Settings. You can only enable 1GB pages on a VM that is powered off.

A VM with 1GB pages enabled must have full memory reservation. Otherwise, the VM will not be able to power on. All of the vRAM for VMs with 1GB pages enabled is preallocated on power-on. Since these VMs have full memory reservation they are not affected by memory reclamation and their memory consumption stays at the maximum level for the entire lifetime of the VM.

1GB page vRAM backing is opportunistic and 1GB pages are allocated on a best effort basis. This includes cases where host CPUs do not have 1GB capabilities. To maximize the chances of having guest vRAM backed with 1GB pages, we recommended to start VMs requiring 1GB pages on a freshly booted host because over time the host RAM is fragmented.

A VM with 1GB pages enabled can be migrated to a different host. However, the 1GB page size might not be allocated on the destination host in the same amount as it was on the source host. You might also see part of vRAM backed with a 1GB page on the source host is no longer backed with a 1GB page on the destination host.

The opportunistic nature of 1GB pages extends to vSphere services such as HA and DRS that might not preserve 1GB page vRAM backing. These services are not aware of 1GB capabilities of destination host and do not take 1GB memory backing into account while making placement decisions.