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

[William Kemper]

On Thu, 6 Nov 2025 17:24:21 GMT, Xiaolong Peng <xpeng at openjdk.org> wrote:

>> 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.
>
> I am confused again. My understanding is: we won't, that is is done by the partition, for young evacuation we will only look for regions in the Collector partition, if a region is FREE and reserved for old evacuations, the region will be in OldCollector partition.

My apologies, you're right. The `FREE` region we remember when looking for the region with the same affiliation as the request does come from the same partition as the second loop would have searched.

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PR Review Comment: https://git.openjdk.org/jdk/pull/28036#discussion_r2500097577