RFR: 8324649: Shenandoah: refactor implementation of free set [v40]

[Kelvin Nilsen]

> Several objectives:
> 1. Reduce humongous allocation failures by segregating regular regions from humongous regions
> 2. Do not retire regions just because an allocation failed within the region if the memory remaining within the region is large enough to represent a LAB
> 3. Track range of empty regions in addition to range of available regions in order to expedite humongous allocations
> 4. Treat collector reserves as available for Mutator allocations after evacuation completes
> 5. Improve encapsulation so as to enable an OldCollector reserve for future integration of generational Shenandoah
> 
> We have compared performance of existing FreeSet implementation with the proposed PR over a broad set of performance workloads and see that the impact is mostly neutral.
> 
> Comparing 105235.0 metrics from control, 220638.0 from experiment.
> Compare: 0.589s
>                           Most impacted benchmarks |                              Most impacted metrics
> -------------------------------------------------------------------------------------------------------
>                                  Shenandoah/jython |                                          cwr_total
> 
> 
>                                 Only in experiment |                                    Only in control
> -------------------------------------------------------------------------------------------------------
>                  crypto.signverify/trigger_failure |                        crypto.rsa/cmr_thread_roots
>                 extremem-large-31g/adjust_pointers |       scimark.sparse.small/concurrent_thread_roots
>             extremem-large-31g/calculate_addresses |              xml.transform/concurrent_thread_roots
>       crypto.signverify/class_unloading_rendezvous |                    mpegaudio/concurrent_weak_roots
>                                   serial/cmr_total |                        crypto.rsa/ctr_thread_roots
> 
> Shenandoah
> -------------------------------------------------------------------------------------------------------
> +5.64% jython/cwr_total p=0.00037
>   Control:      1.928ms (+/-272.40us)        170
>   Test:         2.037ms (+/-322.73us)        344

Kelvin Nilsen has updated the pull request incrementally with two additional commits since the last revision:

 - Make ShenadoahFreeSetPartitionId an enum class
 - Separate ShenandoahSimpleBitMap into distinct source files

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17561/files
  - new: https://git.openjdk.org/jdk/pull/17561/files/84c5875d..b64739ad

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17561&range=39
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17561&range=38-39

  Stats: 985 lines in 6 files changed: 389 ins; 330 del; 266 mod
  Patch: https://git.openjdk.org/jdk/pull/17561.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17561/head:pull/17561

PR: https://git.openjdk.org/jdk/pull/17561