RFR: 8337511: Implement JEP 404: Generational Shenandoah (Experimental) [v7]

[William Kemper]

On Mon, 18 Nov 2024 16:42:50 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> William Kemper has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 510 commits:
>> 
>>  - Merge branch 'merge-latest' into great-genshen-pr-redux
>>  - Use new CompactHeader forwarding APIs in generational mode
>>  - Merge remote-tracking branch 'jdk/master' into merge-latest
>>  - Merge
>>  - 8343649: Shenandoah: ShenandoahEvacInfo event does not follow JFR guidelines
>>    
>>    Reviewed-by: wkemper
>>  - Merge
>>  - 8343227: GenShen: Fold resource mark into management of preselected regions
>>    
>>    Reviewed-by: kdnilsen
>>  - Merge openjdk/jdk tip into great-genshen-pr-redux
>>  - Merge remote-tracking branch 'jdk/master' into merge-latest
>>  - Merge remote-tracking branch 'jdk/master' into merge-latest
>>  - ... and 500 more: https://git.openjdk.org/jdk/compare/889f9062...5e02b5d8
>
> src/hotspot/share/gc/shenandoah/shenandoahReferenceProcessor.cpp line 455:
> 
>> 453:     // Note: would be sufficient to mark only the card that holds the start of this Reference object.
>> 454:     heap->old_generation()->card_scan()->mark_range_as_dirty(cast_from_oop<HeapWord*>(reference), reference->size());
>> 455:   }
> 
> Two things:
>  a) This sounds like `card_table_barrier(reference, raw_referent)`? Since this code is getting called for every dropped reference, just checking a `ShenandoahCardBarrier` flag sounds more efficient. 
>  b) Is there a point in dirtying up to `reference->size()`?

Will test this.

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PR Review Comment: https://git.openjdk.org/jdk/pull/21273#discussion_r1849315332