VM_G1TryInitiateConcMark presently performs various tests before and after the actual collection, in order to conditionally skip the collection or report back various kinds of failure. These are either duplicating some of the tests in do_collection_pause_at_safepoint or attempting to reverse engineer them from it's behavior. It would be better to have do_collection_pause_at_safepoint provide more information than a simple boolean success/failure result to its caller.