RFR: 8375978: G1: Convert G1Policy to use Atomic<T>

[Kim Barrett]

On Wed, 21 Jan 2026 11:59:23 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> Hi all,
> 
>   please review this conversion of `G1Policy` to use `Atomic<T>`.
> 
> Also removed the unused `_young_list_max_length` instead of unnecessarily converting it.
> 
> Testing: gha
> 
> Thanks,
>   Thomas

Looks good, and trivial.

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Marked as reviewed by kbarrett (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/29344#pullrequestreview-3688328888