RFR: Allow young collection to suspend marking in old generation [v14]

[earthling-amzn]

On Mon, 1 Mar 2021 14:00:36 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> earthling-amzn has updated the pull request incrementally with three additional commits since the last revision:
>> 
>>  - Encode active generation and old generation marking status
>>  - Do not unset preemption request flag prematurely
>>  - Disable reference processing generational mode
>
> src/hotspot/share/gc/shenandoah/shenandoahHeapRegion.cpp line 524:
> 
>> 522:   printf("SHR::recycle(), setting region (%llx, %llx, %llx) to FREE\n",
>> 523:          (unsigned long long) bottom(), (unsigned long long) top(), (unsigned long long) end());
>> 524:   fflush(stdout);
> 
> In Hotspot, it's simpler to use tty->print_cr("...") for this, or even better use logging e.g. log_trace(gc)("...") or so.

I agree, I've taken out all the debug scaffolding.

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