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

[Kelvin Nilsen]

On Tue, 9 Dec 2025 03:12:37 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> When old-gen consumes a small percentage of heap size, trigger when old-gen expands by more than ShenandoahMinOldGenGrowthPercent, with default value 50%, from the live data in old at time of previous old-gen mark.
>> 
>> When old-gen consumes a larger percentage of heap size, we trigger when old-gen expands by more than  ShenandoahMinOldGenGrowthRemainingHeapPercent, with default value 25%, of the memory not live in old at the last marking of old.
>
> 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/107e9e49...c7c22974

The outlier in trial 4 results from a late trigger, after 4.529s of GC idle time.  This late trigger caused us to experience an allocation failure during marking, resulting in a stop-the-world degenerated pause of 188.556 ms.  Other development efforts will mitigate issues with late triggering.

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

PR Comment: https://git.openjdk.org/jdk/pull/28561#issuecomment-3633883006