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

[Albert Mingkun Yang]

On Mon, 29 Sep 2025 06:54:39 GMT, Guoxiong Li <gli at openjdk.org> wrote:

>> Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   review
>
> src/hotspot/share/gc/serial/defNewGeneration.cpp line 478:
> 
>> 476: 
>> 477:   // Keep from/to and expand eden.
>> 478:   expand_eden_by(_virtual_space.uncommitted_size());
> 
> Just expanding eden space may go against the option `SurvivorRatio`.

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`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27513#discussion_r2386982306