RFR: 8306920: G1: Calculate garbage bytes for evacuation failed regions from marked live bytes

[Thomas Schatzl]

Hi all,

  please review this refactoring that uses `G1ConcurrentMark`'s live bytes/marking to collect the amount of live bytes for evacuation failed regions instead of calculating it piecemeal while removing self-forwards.

The reason is that the functionality to keep evacuation failed regions in the remembered sets to clear them out quickly ([JDK-8140326](https://bugs.openjdk.org/browse/JDK-8140326)) needs the region's live bytes to determine whether the region is retained (i.e. put into the collection set candidates).

The live bytes for a region will be required in G1's post evacuation phase 1, but currently is calculated in post evacuation phase 2. I.e. this change avoids splitting up post evacuation phase 2 and shuffling around phases (it also makes assignment of live bytes to evacuation failed regions non-incremental, which makes it imo easier to understand).

The change does add, if there is an evacuation failure, a very short serial phase that calculates the final liveness bytes for a region (that is O(#worker threads)).
The reason for reusing `ConcurrentMark`'s liveness gathering infrastructure is because it's already there and there is no (problematic) overlap with its use during marking; i.e. marking only uses live byte array entries for regions that are marked through, and evacuation failure can only happen for regions in the (candidate) collection set, which g1 never marks through.

Testing: tier1-5

Thanks,
  Thomas

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Commit messages:
 - Add gc log messages testing
 - Remove test parameter changes
 - Minimize changes
 - Calculate garbage bytes for evacuation failed regions from marked live bytes

Changes: https://git.openjdk.org/jdk/pull/14118/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14118&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306920
  Stats: 57 lines in 10 files changed: 27 ins; 13 del; 17 mod
  Patch: https://git.openjdk.org/jdk/pull/14118.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14118/head:pull/14118

PR: https://git.openjdk.org/jdk/pull/14118