RFR: 8370850: Shenandoah: Simplify collector allocation to save unnecessary region iteration [v3]

[William Kemper]

On Tue, 4 Nov 2025 16:43:58 GMT, Xiaolong Peng <xpeng at openjdk.org> wrote:

>> I have added the can_allocate_in_new_region check back, it should have same behavior now.
>
> I have removed can_allocate_in_new_region again after merging @kdnilsen's change unifying accountings, since we don't have consistency in  accountings anymore.

We still need to enforce that requests for a young evacuation don't take memory that was reserved for old evacuations. `can_allocate_in_new_region` isn't about consistency between freeset and generation accounting, it's used to maintain old/young collector reserves.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28036#discussion_r2492277440