Ganglia jvm metrics don't make sense because it's not clear which java process the metrics refer to. In fact, all hadoop java processes running on a node report their jvm metrics to the same namespace.
The metrics are exposed by the "jvm" context in JvmMetrics.java. This leads to confusing and nonsensical graphs in ganglia and maybe other monitoring tools.
One way to fix this is to make sure the process name is reported in the jvm context, making it clear which process is associated with the context, and separating out the jvm metrics per process.
This is marked as an "incompatible change" because the fix provided removes the JVM metrics and replaces it with process-specific metrics.