RFR: 8376839: GenShen: Improve performance of evacuations into the old generation

[Kelvin Nilsen]

On Tue, 3 Feb 2026 18:04:32 GMT, Kelvin Nilsen <kdnilsen at openjdk.org> wrote:

>> Somewhat surprisingly, we clear the card table for old regions when they are initially allocated: https://github.com/openjdk/jdk/blob/master/src/hotspot/share/gc/shenandoah/shenandoahFreeSet.cpp#L1558.
>
> So that happens when region r is first put into action (having been initially empty).  When we promote regions in place, it looks to me like we (currently) dirty up to top_before_promote, but we don't clean from top to end.  Is this a bug?

(I guess the bug would be "harmless", in that it might result in some rescan of data that is not really dirty.)

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PR Review Comment: https://git.openjdk.org/jdk/pull/29511#discussion_r2760333702