RFR: 8371284: GenShen: Avoid unnecessary card marking [v3]

[Y. Srinivas Ramakrishna]

On Tue, 18 Nov 2025 23:06:47 GMT, Nityanand Rai <duke at openjdk.org> wrote:

>> Nityanand Rai has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Apply suggestions from code review
>>   
>>   Co-authored-by: Aleksey Shipilëv <shipilev at amazon.de>
>
> Here are GenShen results over 100+ sample collections
> 
> +1.90% philosophers/philosophers_duration p=0.00142 (Wilcoxon)
>   Control:      2.620s  (+/-173.82ms)        120
>   Test:         2.670s  (+/-205.24ms)        120
> 
> +1.68% finagle-chirper/finagle-chirper_duration p=0.00343 (Wilcoxon)
>   Control:      2.802s  (+/-130.38ms)        360
>   Test:         2.850s  (+/-131.25ms)        360
> 
> +1.04% rx-scrabble/rx-scrabble_duration p=0.00000 (Wilcoxon)
>   Control:    148.308ms (+/-  0.88ms)        320
>   Test:       149.855ms (+/-  0.60ms)        320
> 
> -2.48% scrabble/scrabble_duration p=0.00000 (Wilcoxon)
>   Control:    169.599ms (+/-  2.90ms)        200
>   Test:       165.399ms (+/-  3.40ms)        200
> 
> -2.24% scala-kmeans/scala-kmeans_duration p=0.00000 (Wilcoxon)
>   Control:    479.973ms (+/-  1.92ms)        200
>   Test:       469.219ms (+/-  1.98ms)        200

@nityarai08 : 

> Description states:
> 
> > Exclude young-young, old-old and honor UseCondCardMark in dirty card marking.
> 
> I don't see any change for the latter. I believe `UseCondCardMark` is already enabled with GenShen, and the barrier ode respects it.
> 
> Also `Exclude young-young, old-old` skips the part of the change that also skips `young->old`. I'd reword the synopsis to:
> 
> > Skips card marks for stores in young generation objects, old -> old, and null stores.
> 
> which I think is what the code does.
> 

Once description/synopsis is corrected, this PR looks good to go. Approved in anticipation.

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PR Comment: https://git.openjdk.org/jdk/pull/28204#issuecomment-3638042985