RFR: Allow young collection to suspend marking in old generation [v23]

[Roman Kennke]

On Wed, 10 Mar 2021 12:30:32 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> earthling-amzn has updated the pull request incrementally with three additional commits since the last revision:
>> 
>>  - Correct typo in assert message
>>  - Update generation memory usage during promotion
>>  - Report how long it takes to clear a cancel GC request
>
> Looks good!

Can you please merge latest from shenandoah master? "This branch cannot be rebased due to conflicts" *sigh*

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