RFR: 8249676: [REDO] G1 incorrectly limiting young gen size when using the reserve can result in repeated full gcs

[Thomas Schatzl]

Hi,

  please review this re-application of JDK-8249676. The change passes two tier8 (plus tier1-7 which never were a problem)
  runs w/o problems; the crashes I reported in the original review are gone after recent (other) changes.

Note that this PR contains two commits: the vanilla original patch and an update to fix merge errors with the recent
IHOP changes.

Thanks,
  Thomas

-------------

Commit messages:
 - Merge issues resolved
 - Original patch

Changes: https://git.openjdk.java.net/jdk/pull/108/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=108&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8249676
  Stats: 380 lines in 3 files changed: 178 ins; 63 del; 139 mod
  Patch: https://git.openjdk.java.net/jdk/pull/108.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/108/head:pull/108

PR: https://git.openjdk.java.net/jdk/pull/108