The thaw fast path uses a threshold of 500 words to decide if we should copy all frames from the top stackChunk to the stack or just the top frame. Very few of the tests in test/jdk/java/lang/Thread/virtual/ and test/jdk/jdk/internal/vm/Continuation/ exercise the single-frame path, since the stacks are not that big. For the specific case of preemption on monitorenter, none of these groups of test exercise the single-frame thaw fast path.