RFR: 8329223: Parallel: Parallel GC resizes heap even has -Xms = -Xmx [v2]

[Albert Mingkun Yang]

On Fri, 29 Mar 2024 00:47:02 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> Parallel GC resizes old gen even when setting -Xms == -Xmx. 
>> 
>> During GC argument setup, it always set `MinOldSize = GenAlignment` and does not make any adjustment when `-Xms == -Xmx`, while does the adjustment for young gen [here](https://github.com/openjdk/jdk/blob/master/src/hotspot/share/gc/shared/genArguments.cpp#L250)
>
> Zhengyu Gu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Cleanup

I see; seems that there can be conflicting constraints from min, init and max triplets. Maybe sth like:


  MinOldSize = MIN3(MaxOldSize,
                    InitialHeapSize - initial_young_size,
                    MinHeapSize - MinNewSize);

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PR Comment: https://git.openjdk.org/jdk/pull/18539#issuecomment-2057457007