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

[earthling-amzn]

On Fri, 13 Nov 2020 17:40:07 GMT, Aleksey Shipilev <shade 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 270:
> 
>> 268: 
>> 269:   allocation_headroom -= MIN2(allocation_headroom, spike_headroom);
>> 270:   allocation_headroom -= MIN2(allocation_headroom, penalties);
> 
> ...in fact, maybe even penalties are not needed since we are widening the SD "windows" on degenerated/full GC? We can clean this up later if we are not sure.

I'll try testing without these adjustments as well.

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