RFR: 8255984: Shenandoah: "adaptive" heuristic is prone to missing load spikes [v2]

[Aleksey Shipilev]

On Fri, 13 Nov 2020 22:24:22 GMT, earthling-amzn <github.com+71722661+earthling-amzn at openjdk.org> wrote:

>> earthling-amzn has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Remove const qualifier from should_start_gc
>>    
>>    This lets the heuristics update state without const_casts.
>>  - Rename ShenandoahReactive flags to ShenandoahAdaptive flags.
>
> src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.cpp line 335:
> 
>> 333:   _last_sample_value(0),
>> 334:   _interval_ns(NANOUNITS / ShenandoahAdaptiveSampleFrequencyHz),
>> 335:   _rate(ShenandoahAdaptiveSampleSizeSeconds * ShenandoahAdaptiveSampleFrequencyHz, ShenandoahAdaptiveDecayFactor),
> 
> I get a warning here because `TruncatedSeq` constructor takes a signed `int` for length (SampleSize and Frequency are unsigned). Could we change that constructor?

We better not. I think it is fine to have explicit cast to `int` to avoid this warning.

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PR: https://git.openjdk.java.net/jdk/pull/1099