RFR: 8368740: Serial: Swap eden and survivor spaces position in young generation [v2]

[Albert Mingkun Yang]

On Tue, 14 Oct 2025 07:40:07 GMT, Guoxiong Li <gli at openjdk.org> wrote:

>> Indeed; this happens when young-gen is still not empty after full-gc -- this is kind of an extreme scenario. Given there can be live objs inside survivor/eden, the only safe way to expand is to expand eden, as it's the final space in the new layout.
>> 
>> Consequently, `DefNewGeneration::max_capacity` is updated to ensure `capacity <= max_capacity`.
>
>> It seems not obey the eden/survivor ratio rule.
> 
> What about adding a comment (may be tagged as `TODO` or `FIXME`) in the code or filing an issue to state the potential problem?

End users can notice a change-of-behavior, so maybe we can have a release-note stating `SurvivorRatio` might not hold in the heap-almost-full situation. WDYT?

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PR Review Comment: https://git.openjdk.org/jdk/pull/27513#discussion_r2428357357