Enabling and disabling RAM overcommitment

RAM overcommitment for virtual machines is only available if all of the compute nodes have enough swap space.

Prerequisites

• A swap file is created, as described in Adding swap space.

To enable RAM overcommitment for virtual machines

Use the command vinfra service compute create or vinfra service compute set with the --custom-param or --nova-compute-ram-allocation-ratio option. For example, to set the RAM overcommitment ratio to 1.5, run:

# vinfra service compute set --nova-compute-ram-allocation-ratio 1.5

To check that the ratio is successfully modified, execute the vinfra service compute show command:

# vinfra service compute show
+--------------+-------------------------------------------+
| Field        | Value                                     |
+--------------+-------------------------------------------+
| <...>        | <...>                                     |
| options      | cpu_model: ''                             |
|              | custom_params:                            |
|              | - config_file: nova.conf                  |
|              |   property: ram_allocation_ratio          |
|              |   section: DEFAULT                        |
|              |   service_name: nova-compute              |
|              |   value: 1.5                              |
| <...>        | <...>                                     |
+--------------+-------------------------------------------+

To disable RAM overcommitment for virtual machines

Change the ratio to 1 by running:

# vinfra service compute set --nova-compute-ram-allocation-ratio 1

In this case, the swap space is not required anymore and the swap file can be removed:

# /usr/libexec/vstorage-ui-agent/bin/configure-swap.sh --remove-all

Run this script on each node in the compute cluster to remove the swap file from all of the compute nodes.