RFR: 8373225: GenShen: More adaptive old-generation growth heuristics [v3]

[Kelvin Nilsen]

On Tue, 9 Dec 2025 22:53:03 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> Kelvin Nilsen has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 12 additional commits since the last revision:
>> 
>>  - Merge remote-tracking branch 'jdk/master' into more-adaptive-old-triggers-gh
>>  - Add comment to describe behavior of adjust_old_garbage_threshold()
>>  - Simplify representation of growth percentages
>>  - Change default value of ShenandoahMinOldGenGrowthRemainingHeapPercent
>>  - make old evac ratio adaptive
>>  - Merge remote-tracking branch 'jdk/master' into more-adaptive-old-triggers
>>  - change default value of ShenandoahMinOldGenGrowthRemainingHeapPercent
>>  - Merge remote-tracking branch 'jdk/master' into more-adaptive-old-triggers
>>  - Adjust test for new defaults
>>  - Merge remote-tracking branch 'jdk/master' into more-adaptive-old-triggers
>>  - ... and 2 more: https://git.openjdk.org/jdk/compare/b2386fa4...c7c22974
>
> src/hotspot/share/gc/shenandoah/shenandoahOldGeneration.cpp line 249:
> 
>> 247:     _live_bytes_after_last_mark + (_live_bytes_after_last_mark * _growth_percent_before_compaction) / 100;
>> 248:   size_t threshold_by_growth_into_percent_remaining = (size_t)
>> 249:     (_live_bytes_after_last_mark + ((ShenandoahHeap::heap()->soft_max_capacity() - _live_bytes_after_last_mark)
> 
> I need to protect against underflow here.  It might be that _live_bytes_after_last_mark is greater than soft_max_capacity().

Done and tested.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28561#discussion_r2608266583