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

[Bernd Mathiske]

On Fri, 16 Apr 2021 15:17:52 GMT, earthling-amzn <github.com+71722661+earthling-amzn at openjdk.org> wrote:

>> src/hotspot/share/gc/shenandoah/shenandoahFreeSet.cpp line 430:
>> 
>>> 428: 
>>> 429:   assert(r->is_empty(), "Region must be empty after flipping from mutator to GC.");
>>> 430:   r->set_affiliation(FREE);
>> 
>> Why is this block needed now?
>
> I think this could be an assert. The region should already be `FREE` at this point.

When debugging, I came across regions that were "trash" but not "FREE".

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