While GCP provides CPU, network and disk usage metrics for instances, it doesn't provide memory usage metrics by default.
For Commander to retrieve memory metrics for a GCP instance, the Stackdriver agent must be installed on the instance. To learn how to install the Stackdriver agent, see Installing the Monitoring agent in the Google Cloud documentation.
You can install the agent from within GCP or through a Commander command workflow.
When the Stackdriver agent isn't installed, the value for all memory metrics is
In the following image, the Stackdriver agent isn't installed on the first four instances in the list but is installed on the last two.
Here's an example Performance Summary tab for a GCP Linux instance with the Stackdriver agent installed: