6819077: G1: first GC thread coming late into the GC.
Summary: The first worker thread is delayed when entering the GC because it clears the card count table that is used in identifying hot cards. Replace the card count table with a dynamically sized evicting hash table that includes an epoch based counter.
Reviewed-by: iveresov, tonyp
6865703: G1: Parallelize hot card cache cleanup
Summary: Have the GC worker threads clear the hot card cache in parallel by having each worker thread claim a chunk of the card cache and process the cards in that chunk. The size of the chunks that each thread will claim is determined at VM initialization from the size of the card cache and the number of worker threads.
Reviewed-by: jmasa, tonyp