workaround cgroup zero memory working set problem

[chuyee]

We observed zero container_memory_working_set_bytes metrics problem on nodes with cgroup (v1). The same problem is not observed on nodes with cgroup v2. For example:

$ kubectl get --raw /api/v1/nodes/<cgroup_node>/proxy/metrics/resource
container_memory_working_set_bytes{container="logrotate", namespace="...", pod="dev-5cd4cc79d6-s9cll"} \
0 1732247555792

$ kubectl get --raw /api/v1/nodes/<cgroup2_node>/proxy/metrics/resource
container_memory_working_set_bytes{container="logrotate", namespace="...",pod="dev-5cd4cc79d6-test"} \
1.37216e+06 1732247626298

The metrics-server logs:

metrics-server-77786dd5c5-w4skb metrics-server I1121 22:02:47.705690       \
1 decode.go:196] "Failed getting complete container metric" containerName="logrotate" \
containerMetric={"StartTime":"2024-10-23T13:12:07.815984128Z","Timestamp":"2024-11-21T22:02:41.755Z", \
"CumulativeCpuUsed":12016533431788,"MemoryUsage":0}
metrics-server-77786dd5c5-w4skb metrics-server I1121 22:02:47.706713       \
1 decode.go:104] "Failed getting complete Pod metric" pod=".../dev-5cd4cc79d6-s9cll"

On the cgroup v1 node:

$ kc exec -it dev-5cd4cc79d6-s9cll -c logrotate -- /bin/sh -c \
"cat /sys/fs/cgroup/memory/memory.usage_in_bytes; \
cat /sys/fs/cgroup/memory/memory.stat |grep -w total_inactive_file |cut -d' ' -f2"
212414464
214917120

On the cgroup v2 node:

$ kc exec -it dev-5cd4cc79d6-test -c logrotate -- /bin/sh -c \
"cat /sys/fs/cgroup/memory.current; \
cat /sys/fs/cgroup/memory.stat |grep -w inactive_file |cut -d' ' -f2"
212344832
210112512

As we can see, cgroup v1 node might return negative (truncated to zero) working set memory in some scenarios. The current metrics-server logic is, if one of the containers encounters this problem, the whole pod metrics will be discarded. This should be an overkill. Because the zero memory working set container usually takes a small % of whole pod resource usage. However if the whole PodMetrics is dropped, downstream component e.g. HPA is not able to autoscale the deployment/statefulset, etc., which can be considered to be a system degradation.

The patch workarounds the cgroup zero working set memory problem by keeping the PodMetrics unless all the containers in the pod encounter this problem at the same time.

What this PR does / why we need it:
workingSetBytes of 0 doesn't always indicate a terminated process

Which issue(s) this PR fixes :
Fixes #1330

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• ✅login: chuyee / (ab72bcb)

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