Host machine memory is the hardware backing for guest virtual memory and guest physical memory. Host machine memory must be at least slightly larger than the combined active memory of the virtual machines on the host. A virtual machine's memory size must be slightly larger than the average guest memory usage. Increasing the virtual machine memory size results in more overhead memory usage.
Problem
- Memory usage is constantly high (94% or greater) or constantly low (24% or less).
- Free memory consistently is 6% or less and swapping frequently occurs.
Cause
- The host probably is lacking the memory required to meet the demand. The active memory size is the same as the granted memory size, which results in memory resources that are not sufficient for the workload. Granted memory is too much if the active memory is constantly low.
- Host machine memory resources are not enough to meet the demand, which leads to memory reclamation and degraded performance.
- The active memory size is the same as the granted memory size, which results in memory resources that are not sufficient for the workload.
Solution
- Verify that VMware Tools is installed on each virtual machine. The balloon driver is installed with VMware Tools and is critical to performance.
- Verify that the balloon driver is enabled. The VMkernel regularly reclaims unused virtual machine memory by ballooning and swapping. Generally, this does not impact virtual machine performance.
- Reduce the memory space on the virtual machine, and correct the cache size if it is too large. This frees up memory for other virtual machines.
- If the memory reservation of the virtual machine is set to a value much higher than its active memory, decrease the reservation setting so that the VMkernel can reclaim the idle memory for other virtual machines on the host.
- Migrate one or more virtual machines to a host in a DRS cluster.
- Add physical memory to the host.
