RFR: Enforce max regions [v3]

[Kelvin Nilsen]

On Wed, 7 Dec 2022 18:22:40 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

>> Kelvin Nilsen has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix white space and add an assertion
>
> src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp line 1491:
> 
>> 1489:         // doing this work during a safepoint.  We cannot put humongous regions into the collection set because that
>> 1490:         // triggers the load-reference barrier (LRB) to copy on reference fetch.
>> 1491:         if (r->promote_humongous() == 0) {
> 
> See my comment in ::promote_humongous().
> 
> I think that method could directly call the requisite expansion code under those circumstances, so this code can move there, with (as I noted there) promotion always succeeding for humongous object arrays at least, but in general for all humongous objects that are deemed eligible for promotion by other criteria (see my note in ::promote_humongous() on potentially treating humongous primitive type arrays differently from humongous object arrays).

I like your ideas, but I'll suggest we tackle this in a future distinct pr.

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PR: https://git.openjdk.org/shenandoah/pull/179