[RFE] Gather container memory working set size

[mtodor]

Is your feature request related to a problem? Please describe.

kube-burner uses container_memory_rss (RSS) to collect metrics about memory usage.

I would suggest starting collecting container_memory_working_set_bytes (WSS). Many applications have stable and low RSS footprints, but the WSS is way bigger. Some examples are Postgres and Prometheus.

In most cases, when WSS reaches container resource limits, it will get OOMKilled. That's why I think that tracking the increase in WSS is more important than RSS.

Describe the solution you'd like

Add additional metrics to gather container_memory_working_set_bytes.

Describe alternatives you've considered

Replaces existing container_memory_rss with container_memory_working_set_bytes, but that will cause previously gathered results to be not comparable with the new ones.

Additional context

Article about cgroups and OOMKilled decisions. A lot of details, but it points out what Kubernetes compares and when OOMKilled will happen.

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