We currently have this 1:1 mapping of region and remembered set, as well as a 1:1 mapping between remembered set and G1CardSet. For young gen regions that are always collected together, we can have a single remembered set assigned to all the young regions. The easiest way to achieve this is to have one G1CardSet assigned to all young regions.

The expected benefit is reduction in the memory overhead of the remembered set and the remembered set merge time during collection pause.