RFR: 8369013: Shenandoah: passive mode should support enabling ShenandoahCardBarrier

Tue Oct 28 17:33:38 UTC 2025

Add card barriers to passive mode to test out the price of card barriers. 

How this change is implemented is to instantiate the old region in passive mode - old region owns the card table so this would minimize the code change with a bit price of native memory. It does sound weird to have old gen in passive mode, but since passive mode is a just diagnostic mode, we'll go with it for the cleanliness of the change.

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Commit messages:
 - Missed UnlockDiagnosticVMOptions
 - Corrected copyright header
 - Addressed comments and added a test
 - 8369013: Shenandoah: passive mode should support enabling ShenandoahCardBarrier

Changes: https://git.openjdk.org/jdk/pull/27966/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27966&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369013
  Stats: 117 lines in 9 files changed: 104 ins; 7 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/27966.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27966/head:pull/27966

PR: https://git.openjdk.org/jdk/pull/27966