RFR: Use PLABs for old gen allocations, including promotions. [v2]

[bmathiske]

On Fri, 16 Apr 2021 14:31:32 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> Bernd Mathiske has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Register filler objects for unsuccessful non-LAB evacuations.
>
> src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp line 882:
> 
>> 880:   return plab->allocate(size);
>> 881: }
>> 882: 
> 
> Is this a full (or almost full) copy of allocate_from_gclab_slow() ? Maybe this warrants some refactoring/sharing?

Yes, this is a full copy. Will refactor.

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PR: https://git.openjdk.java.net/shenandoah/pull/30