RFR: 8327000: GenShen: Integrate updated Shenandoah implementation of FreeSet into GenShen [v8]

[Y. Srinivas Ramakrishna]

On Thu, 13 Jun 2024 22:22:01 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> The mainline implementation of ShenandoahFreeSet was recently updated.  This PR integrates the upstream changes
>> into Generational Shenandoah.
>
> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Minor refinements to test programs
>   
>   TestAllocIntArrays: comments to explain behavior.
>   TestOldGrowthTriggers: reduce the number of loop iterations so this test
>   will not time out on less powerful test platforms.

src/hotspot/share/gc/shenandoah/shenandoahFreeSet.hpp line 367:

> 365:   // evacuation reserves are unknown, is based in part on anticipated promotion as determined by analysis of live data
> 366:   // found during the previous GC pass which is one less than the current tenure age.
> 367:   void finish_rebuild(size_t young_cset_regions, size_t old_cset_regions, size_t num_old_regions,

For the documentation comments, for the individual public methods themselves, viz. `prepare_to_rebuild`, `finish_rebuild`, `find_regions_with_alloc_capacity` etc., it's easier to have a terser comment that describes the parameters to each call and their side-effect/result.

Then, in the callers of these methods (the implementation of the rebuild) you can place the commentary about how the rebuild is happening by stitching these methods together. Otherwise the header file can be confusing in the form of a narrative.

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/440#discussion_r1645267905