RFR: 8369013: Shenandoah: passive mode should support enabling ShenandoahCardBarrier [v2]

[William Kemper]

On Wed, 29 Oct 2025 01:13:53 GMT, Rui Li <duke at openjdk.org> wrote:

>> Add card barriers to passive mode to test out the price of card barriers. 
>> 
>> How this change is implemented is to instantiate the old region in passive mode - old region owns the card table so this would minimize the code change with a bit price of native memory. It does sound weird to have old gen in passive mode, but since passive mode is a just diagnostic mode, we'll go with it for the cleanliness of the change.
>
> Rui Li has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Move write table clean to degen

Looks good. Thank you!

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Marked as reviewed by wkemper (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/27966#pullrequestreview-3394917347