RFR: 8364760: G1: Remove obsolete code in G1MergeCardSetClosure

[Sangheon Kim]

On Tue, 5 Aug 2025 16:12:32 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> Hi all,
> 
>   please review this removal of some obsolete code.
> 
> Before JDK-8343782 G1 iterated remsets for humongous eager reclaim candidates by region, as there has been a 1:1 mapping between regions and (card-based) remembered sets.
> 
> With that change, all remembered set iteration should go via the group remsets (`G1CSetCandidateGroup`), and the code does, except for humongous eager reclaim candidates which handle their group remsets on the side (which is a separate issue).
> 
> This obsoleted some code in `G1MergeCardSetClosure` - it does not need to be a `G1HeapRegionClosure` any more, and for humongous regions we can directly do the iteration via the group rem set attached to the humongous starts region. I.e. inline that `merge_card_set_for_region()` method.
> 
> Testing: gha
> 
> Thanks,
>   Thomas

Marked as reviewed by sangheki (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/26645#pullrequestreview-3098588402