This is all with G1 verbose concurrent marking, e.g. requires building with _MARKING_VERBOSE_ non-zero.

CMTask::deal_with_reference with verbose marking will log a message indicating the worker thread and the address of the object being dealt with.

There are three callers of CMTask::deal_with_reference. Two of them are immediately preceded by similar logging to what deal_with_reference will do, with very slightly different wording. We don't really need those additional log messages.