RFR: 8329223: Parallel: Parallel GC resizes heap even if -Xms = -Xmx [v9]

[Albert Mingkun Yang]

On Wed, 24 Apr 2024 14:36:44 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:
> 
>   Reverse previous change

It's the failing assert in `CheckOldMin` that is causing the `pthread_mutex_destroy` error msg. (I can recreate the error msg on my linux after adding a `ASSERT_LT(2, 1)` there.)

Then, I think the current fix should be safe, and keeps existing tests happy.

The longer term fix should probably be removing `OldSize`...

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Marked as reviewed by ayang (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/18539#pullrequestreview-2023318216