RFR: 8284995: G1: Do not mark through Closed Archive regions during concurrent mark

[Thomas Schatzl]

Hi all,

  please review this change that skips CA regions during concurrent mark. This is achieved by keeping the ntams at bottom for these regions.
G1 Full GC already skips marking of CA regions.

Testing: tier1-5

Thanks,
  Thomas

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Commit messages:
 - initial change

Changes: https://git.openjdk.java.net/jdk/pull/8315/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8315&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284995
  Stats: 6 lines in 2 files changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8315.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8315/head:pull/8315

PR: https://git.openjdk.java.net/jdk/pull/8315