Some changes in Parallel altered the GC behavior, and the adaptive-size-policy balancing mutator-throughput and generation/heap is specially tuned to the old GC behavior, so the heuristics cause some regressions in out-of-the-box performance observed in JDK-8333227, JDK-8338689 and JDK-8332485. All those regressions can be worked around using manually set generation/heap sizes. However, some work should be done to address the out-of-the-box performance of those benchmarks.

Improve the heuristics (such as, taking gc-frequency into account, proactive full-gc to clear out floating garbage in old-gen, lazy-generation shrinking, etc) to restore the out-of-the-box performance.