RFR: 8345423: Shenandoah: Parallelize concurrent cleanup [v9]

[Xiaolong Peng]

> Concurrent cleanup after Shenandoah collection cycle is executed by single thread(Shenandoah control thread), since currently recycling trashed regions requires heap lock even it can be done w/o heap lock. This PR is a proposal to parallelize the execution of Shenandoah concurrent cleanup after making recycling trashed regions lock free. 
> 
> With the change the time execute Concurrent cleanup has been significantly improved by 10+ times, throughput/allocation rate is also improved significantly:
> 
> TIP:
> 
> [30.380s][info][gc] GC(1245) Concurrent cleanup (Young) 3491M->739M(4096M) 3.634ms
> [30.404s][info][gc] GC(1246) Concurrent cleanup (Young) 3258M->377M(4096M) 2.233ms
> [30.434s][info][gc] GC(1247) Concurrent cleanup (Young) 2887M->333M(4096M) 7.958ms
> [30.464s][info][gc] GC(1248) Concurrent cleanup (Young) 3134M->472M(4096M) 6.097ms
> [30.487s][info][gc] GC(1249) Concurrent cleanup (Young) 2922M->212M(4096M) 3.072ms
> [30.519s][info][gc] GC(1250) Concurrent cleanup (Young) 3404M->549M(4096M) 3.730ms
> [30.552s][info][gc] GC(1251) Concurrent cleanup (Young) 3542M->712M(4096M) 6.118ms
> [30.579s][info][gc] GC(1252) Concurrent cleanup (Young) 3257M->373M(4096M) 5.049ms
> [30.608s][info][gc] GC(1253) Concurrent cleanup (Young) 3390M->418M(4096M) 2.779ms
> 
> Parallelized:
> 
> [30.426s][info][gc] GC(1557) Concurrent cleanup (Young) 3208M->43M(4096M) 0.177ms
> [30.510s][info][gc] GC(1560) Concurrent cleanup (Young) 2938M->161M(4096M) 0.220ms
> [30.534s][info][gc] GC(1561) Concurrent cleanup (Young) 2960M->57M(4096M) 0.164ms
> [30.564s][info][gc] GC(1562) Concurrent cleanup (Young) 3189M->106M(4096M) 0.176ms
> [30.595s][info][gc] GC(1563) Concurrent cleanup (Young) 3389M->367M(4096M) 0.247ms
> [30.625s][info][gc] GC(1564) Concurrent cleanup (Young) 3662M->628M(4096M) 0.246ms
> [30.649s][info][gc] GC(1565) Concurrent cleanup (Young) 3190M->150M(4096M) 0.172ms
> [30.678s][info][gc] GC(1566) Concurrent cleanup (Young) 3225M->69M(4096M) 0.175ms
> [30.709s][info][gc] GC(1567) Concurrent cleanup (Young) 3250M->107M(4096M) 0.179ms
> [30.765s][info][gc] GC(1570) Concurrent cleanup (Young) 2932M->211M(4096M) 0.422ms
> 
> 
> JVM args for the tests: `-Xms4G -Xmx4G -XX:+AlwaysPreTouch -XX:+UseShenandoahGC -XX:+UnlockExperimentalVMOptions -XX:ShenandoahGCMode=generational -XX:-ShenandoahPacing -XX:+UseTLAB -Xlog:gc`
> 
> 
> For the same test test, but with large heap with 32G memory, the improvement on concurrent cleanup is much smaller, which might be related to less race and contention with mutator threads when the heap size i...

Xiaolong Peng has updated the pull request incrementally with one additional commit since the last revision:

  Address review comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/22538/files
  - new: https://git.openjdk.org/jdk/pull/22538/files/4507656e..1bce0d7e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=22538&range=08
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=22538&range=07-08

  Stats: 13 lines in 3 files changed: 3 ins; 3 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/22538.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22538/head:pull/22538

PR: https://git.openjdk.org/jdk/pull/22538