RFR: 8333457: GenShen: Move remembered set into new generational code [v2]

[William Kemper]

On Mon, 3 Jun 2024 23:23:43 GMT, Y. Srinivas Ramakrishna <ysr at openjdk.org> wrote:

>> William Kemper has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix typo in comment
>
> src/hotspot/share/gc/shenandoah/shenandoahMark.inline.hpp line 293:
> 
>> 291: 
>> 292:   assert((GENERATION == GLOBAL || GENERATION == NON_GEN), "Unexpected generation type");
>> 293:   return true;
> 
> For safety should this return `heap->is_in(obj)`, or if always returning `true` here, should it `assert(heap->is_in(obj), ...);`?
> 
> We should document the semantics of both `ShenandoahMark::in_generation()` and `ShenandoahGeneration::contains()` more precsiely than currently done, and audit uses to ensure the callers are cognizant of those sematics. For instance, it sometimes makes sense to have `_or_null` variants of these when a nullptr may be passed to these methods by callers, etc.

It makes sense to `assert(heap->is_in(obj))` here.

> src/hotspot/share/gc/shenandoah/shenandoahOldGeneration.cpp line 193:
> 
>> 191: 
>> 192:   if (ShenandoahCardBarrier) {
>> 193:     // TODO: Old and young generations should only be instantiated for generational mode
> 
> I assume that'll be in a follow-up as discussed at meeting this morning?

Yes, the old gen constructor should be able to assert that `ShenandoahCardBarrier` is on. The check is necessary because non-generational modes still instantiate the old generation.

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PR Review Comment: https://git.openjdk.org/shenandoah/pull/443#discussion_r1626342862
PR Review Comment: https://git.openjdk.org/shenandoah/pull/443#discussion_r1626341800