RFR: Mixed evacuation [v2]

[Kelvin Nilsen]

On Mon, 12 Apr 2021 19:49:29 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Chasing bug during prepare_for_old_collection
>>   
>>   One bug fix, a few cosmetic improvements, a change in loop structure to possibly avoid a gcc
>>   optimization error.
>
> src/hotspot/share/gc/shenandoah/heuristics/shenandoahHeuristics.cpp line 515:
> 
>> 513:   // evacuated.  In the future, this threshold percentage may be specified on
>> 514:   // the command line or preferrably determined by dynamic heuristics.
>> 515: #define CollectionThresholdGarbagePercent 50
> 
> We already have ShenandoahGarbageThreshold (defaults to 60 iirc) maybe we want to use this? Or use separate global/old/young thresholds?

I've made and tested this change now.  Appears to me that default of ShenandoahGarbageThreshold is 25.  On established stress workloads, this change has the effect of choosing larger collection sets for old-gen.

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

PR: https://git.openjdk.java.net/shenandoah/pull/29