RFR: 8341643: G1: Merged cards counter skewed by merge cards cache

[Thomas Schatzl]

Hi all,

   please review this change that subtracts the dummy cards from the merge cards counter at the end of the phase to keep its value correct.

E.g. previously log output with no actual cards being merged looks as follows:

 [0.991s][debug][gc,phases ] GC(11) Remembered Sets (ms): Min: 0.03, Avg: 0.03, Max: 0.03, Diff: 0.01, Sum: 0.11, Workers: 4
[0.991s][debug][gc,phases ] GC(11) Eager Reclaim (ms): skipped
[0.991s][debug][gc,phases ] GC(11) Merged Inline: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0, Workers: 4
[0.991s][debug][gc,phases ] GC(11) Merged ArrayOfCards: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0, Workers: 4
[0.991s][debug][gc,phases ] GC(11) Merged Howl: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0, Workers: 4
[0.991s][debug][gc,phases ] GC(11) Merged Full: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0, Workers: 4
[0.991s][debug][gc,phases ] GC(11) Merged Howl Inline: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0, Workers: 4
[0.991s][debug][gc,phases ] GC(11) Merged Howl ArrayOfCards: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0, Workers: 4
[0.991s][debug][gc,phases ] GC(11) Merged Howl BitMap: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0, Workers: 4
[0.991s][debug][gc,phases ] GC(11) Merged Howl Full: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0, Workers: 4
[0.991s][debug][gc,phases ] GC(11) Merged Cards: Min: 8, Avg: 8.0, Max: 8, Diff: 0, Sum: 32, Workers: 4

(Note that none of the other categories have non-zero values)
to

[0.991s][debug][gc,phases ] GC(11) Merged Cards: Min: 0, Avg: 0.0, Max: 0, Diff: 0, Sum: 0, Workers: 4


For the same test (gcbasher in this case).

Testing: gha, log messages

Thanks,
  Thomas

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

Commit messages:
 - 8341643

Changes: https://git.openjdk.org/jdk/pull/21390/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21390&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341643
  Stats: 10 lines in 1 file changed: 10 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/21390.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21390/head:pull/21390

PR: https://git.openjdk.org/jdk/pull/21390