serving: The queue-proxy's memory slowly and constantly increases even if there is no request.

What version of Knative?

0.23.0

Expected Behavior

When there is no request sent to the pod, the memory usage of queue-proxy should be a constant or at least a stable value.

Actual Behavior

When there is no request sent to the pod, the memory usage slowly increases. Specifically, the queue-proxy’s memory is increasing. Don’t know if it is a memory leak.

Steps to Reproduce the Problem

1. In config-observability, set metrics.backend-destination: prometheus and metrics.request-metrics-backend-destination: prometheus
2. Set annotations of prometheus.io for ksvc you want at ksvc.spec.template.metadata.annotation where port is 9091 and path is /metrics
3. Create ksvc and watch the pod.