RFR [1/7]: 8197569: Refactor eager reclaim for concurrent remembered set rebuilding

[Thomas Schatzl]

Hi all,

  can I have some reviews for the following change that refactors the
eager reclaim condition so that it can be later used for the policy
that determines for which regions G1 should rebuild the remembered set?
(And it's a reasonable refactoring on its own btw).

CR:
https://bugs.openjdk.java.net/browse/JDK-8197569
Webrev:
http://cr.openjdk.java.net/~tschatzl/8197569/webrev/
Testing:
hs-tier 1-5, mostly as part of other related changes

Thanks,
  Thomas