RFR: 8370039: GenShen: array copy SATB barrier improvements [v3]

[William Kemper]

On Sat, 15 Nov 2025 01:53:05 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:
>> 
>>   Revert "We can also filter out old when striclty marking young"
>>   
>>   This reverts commit c53c4f23f4401785e1049494b6c4e4b92f9a5701.
>
> Thank you for the clean up and corrections.
> 
> I am curious how you found this issue -- nice catch!
> 
> Any performance data to share, may be even from a microbenchmark perhaps or any other benchmark that exercises array copying -- may be something in DaCapo/Renaissance?

@ysramakrishna - I found the issue while carefully reading the code for the related SATB filtering PR that was integrated a couple of weeks ago. We have also seen Genshen spend more time flushing the SATBs before final mark and I believe this code contributed to that. I didn't see any notable performance improvements in benchmark scores, but there is also a correctness issue here that needs to be addressed.

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PR Comment: https://git.openjdk.org/jdk/pull/28183#issuecomment-3548670206