The heuristics that drive which old regions to collect during mixed GCs and which not, introduced by:
7132029: G1: mixed GC phase lasts for longer than it should
and maybe further fine-tuned by:
7146242: G1: alternative heuristic on deciding which old regions not to collect
introduced several develop -XX flags. It will be good to expose some of them to the users so that they can adjust the "space efficiency" vs. "pause times duration" trade-off to what they feel it's appropriate for them.
We should decide what the minimum number of flags is and make sure their names are reasonable.