RFR: 8348595: GenShen: Fix generational free-memory no-progress check [v3]

[Kelvin Nilsen]

On Mon, 10 Feb 2025 18:41:27 GMT, Paul Hohensee <phh at openjdk.org> wrote:

>> ShenandoahCriticalFreeThreshold represents a percentage of the "total size".  To calculate N% of the young generation size, we divide the generation size by 100 and then multiply by ShenandoahCriticalFreeThreshold.  This code is a bit different in the most recent revision.  Do you think it needs a comment?
>
> Yes :)

I've added a comment here.  Thanks.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23306#discussion_r1950933308