RFR: 8256265: G1: Improve parallelism in regions that failed evacuation [v19]

[Hamlin Li]

> Currently G1 assigns a thread per failed evacuated region. This can in effect serialize the whole process as often (particularly with region pinning) there is only one region to fix up.
> 
> This patch tries to improve parallelism when walking over the regions in chunks
> 
> Latest implementation scans regions in chunks to bring parallelism, it's based on JDK-8278917 which changes to uses prev bitmap to mark evacuation failure objs.
> 
> Here's the summary of performance data based on latest implementation, basically, it brings better and stable performance than baseline at "Post Evacuate Cleanup 1/remove self forwardee" phase. (Although some regression is spotted when calculate the results in geomean, becuase one pause time from baseline is far too small than others.)
> 
> The performance benefit trend is:
>  - pause time (Post Evacuate Cleanup 1) is decreased from 76.79% to 2.28% for average time, from 71.61% to 3.04% for geomean, when G1EvacuationFailureALotCSetPercent is changed from 2 to 90 (-XX:ParallelGCThreads=8)
>  - pause time (Post Evacuate Cleanup 1) is decreased from 63.84% to 15.16% for average time, from 55.41% to 12.45% for geomean, when G1EvacuationFailureALotCSetPercent is changed from 2 to 90 (-XX:ParallelGCThreads=<default=123>)
> ( Other common Evacuation Failure configurations are:
> -XX:+G1EvacuationFailureALot -XX:G1EvacuationFailureALotInterval=0 -XX:G1EvacuationFailureALotCount=0 )
> 
> For more detailed performance data, please check the related bug.

Hamlin Li has updated the pull request incrementally with one additional commit since the last revision:

  Albert review

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/7047/files
  - new: https://git.openjdk.java.net/jdk/pull/7047/files/4b672e66..a26c92d6

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=7047&range=18
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=7047&range=17-18

  Stats: 34 lines in 6 files changed: 2 ins; 17 del; 15 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7047.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7047/head:pull/7047

PR: https://git.openjdk.java.net/jdk/pull/7047