RFR: Allow young collection to suspend marking in old generation [v5]

[earthling-amzn]

On Wed, 24 Feb 2021 14:27:13 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> earthling-amzn has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Reserve correct number of task queues for rset scan
>
> src/hotspot/share/gc/shenandoah/shenandoahGeneration.cpp line 242:
> 
>> 240:   ShenandoahRegionIterator regions;
>> 241:   ShenandoahScanRememberedTask task(task_queues(), old_gen_task_queues(), rp, &regions);
>> 242:   heap->safepoint_workers()->run_task(&task);
> 
> Out of curiosity, any reason to use safepoint_workers instead of regular workers? Thanks.

I figured `ParallelGCThreads` would be greater than `ConcGCThreads`, looking closer I see that the regular workers get `_max_workers`. I could put a `ShenandoahWorkerScope` here and have it get the number of workers from `ShenandoahWorkerPolicy`?. We plan to move this code off the safepoint anyway.

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PR: https://git.openjdk.java.net/shenandoah/pull/19