JVM instrumentation as part of dropwizard metrics has been moved to a separate metrics-jvm artifact in metrics-v3.0. After
CASSANDRA-5657, no jvm related metrics will be exported to any reporter configured via metrics-reporter-config, as this isn't part of metrics-core anymore. As memory and GC stats are essential for monitoring Cassandra, this turns out to be a blocker for us for upgrading to 2.2.
I've included a patch that would add the now separate metrics-jvm package and enables some of the provided metrics on startup in case a metrics reporter is used (-Dcassandra.metricsReporterConfigFile).