RFR: Tune heuristic defaults and behavior for improved stability

[William Kemper]

On Tue, 31 Jan 2023 21:32:31 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

>> Also, some minor changes to logging.
>
> src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp line 150:
> 
>> 148:           range(0,100)                                                      \
>> 149:                                                                             \
>> 150:   product(uintx, ShenandoahLearningSteps, 10, EXPERIMENTAL,                 \
> 
> Relatedly, I'd suggest just removing the "(5)" in this comment in `shenandoahGeneration.cpp`:
> 
> 
>   // Changing the size of the generation will reset the times learned for the heuristic. The heuristic will need to
>   // relearn collection performance metrics. This also has the effect of preventing further capacity changes from the
>   // heuristics until at least ShenandoahLearningSteps(5) number of cycles has completed.
>   void increase_capacity(size_t increment);
>   void decrease_capacity(size_t decrement);

That whole comment is out of date, I'll remove it.

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PR: https://git.openjdk.org/shenandoah/pull/209