cnv-configuring-guest-memory-overcommitment.adoc

Configuring guest memory overcommitment

If your virtual workload requires more memory than available, you can use memory overcommitment to allocate all or most of the host’s memory to your virtual machine instances. Enabling memory overcommitment means you can maximize resources that are normally reserved for the host.

For example, if the host has 32 GB RAM, you can use memory overcommitment to fit 8 virtual machines with 4 GB RAM each. This allocation works under the assumption that the virtual machines will not use all of their memory at the same time.

Procedure

1. To explicitly tell the virtual machine instance that it has more memory available than was requested from the cluster, edit the virtual machine configuration file and set spec.domain.memory.guest to a higher value than spec.domain.resources.requests.memory. This process is called memory overcommitment.

   In this example, 1024M is requested from the cluster, but the virtual machine instance is told that it has 2048M available. As long as there is enough free memory available on the node, the virtual machine instance will consume up to 2048M.

   kind: VirtualMachine
   spec:
     template:
       domain:
       resources:
           requests:
             memory: 1024M
       memory:
           guest: 2048M

   Note	The same eviction rules as those for Pods apply to the virtual machine instance if the node is under memory pressure.

2. Create the virtual machine:

   $ oc create -f <file name>.yaml