8201490: Improve concurrent mark keep alive closure performance Summary: Avoid doing marking work unless absolutely required. Reviewed-by: sjohanss, kbarrett

8201487: Do not rebalance reference processing queues if not doing parallel reference processing Reviewed-by: sangheki, kbarrett

8200730: Fix debug=gc+phases time tracking in Remark and Cleanup Summary: Timing in Remark and Cleanup pauses did not use instance variables for the scoped timing objects, so these durations were always zero. Reviewed-by: sangheki, sjohanss

8200426: Make G1 code use _g1h members Summary: Consistently use _g1h member names for cached G1CollectedHeap* variables. Reviewed-by: sangheki, sjohanss

8200723: Suppress rs_length and predicted_cards sampling during mixed gcs Summary: Due to the impact of these measurements on pause time, their high difference to other collections during mixed collections, and their non-use during mixed collections, do not use rs_length and predicted_cards measurements done during mixed gc for the predictor. This avoids the young gen sizing after the mixed phase to be negatively affected by mixed collections. Reviewed-by: kbarrett, sjohanss

8154528: Reclaim regions emptied by marking in Remark pause Reviewed-by: shade, sjohanss