RFR: Add generational full gc support

[Kelvin Nilsen]

On Fri, 27 Aug 2021 15:31:36 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> src/hotspot/share/gc/shenandoah/shenandoahFreeSet.cpp line 221:
>> 
>>> 219:       // that the PLAB be disabled for all future purposes.  We may want to introduce a new service to make the
>>> 220:       // PLABs parsable while still allowing the PLAB to serve future allocation requests that arise during the
>>> 221:       // next evacuation pass.
>> 
>> If I understand correctly, we already have this in ShenandoahHeap::ensure_parsability(bool retire_tlabs)
>
> Oh wait, probably not available for PLABs.

We'll probably come back later and do some "improvement" to this code.  Thanks.

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PR: https://git.openjdk.java.net/shenandoah/pull/61