8199326: Remove G1 gc time stamp logic Summary: G1 gc time stamp logic is unused completely after JDK-8180415, so removing it. Reviewed-by: sangheki, sjohanss

8197932: Better split work in rebuild remembered sets phase Summary: Let threads rebuilding remembered sets yield after every G1RebuildRemSetChunkSize (default: 256kB) sized memory area to improve TTSP. Reviewed-by: sangheki, sjohanss

8197928: Only enqueue deferred cards with references into regions that have a tracked remembered set during GC Reviewed-by: sangheki, sjohanss