RFR: 8329223: Parallel: Parallel GC resizes heap even has -Xms = -Xmx [v5]

[Albert Mingkun Yang]

On Fri, 19 Apr 2024 14:43:05 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> src/hotspot/share/gc/shared/genArguments.cpp line 312:
>> 
>>> 310: 
>>> 311:     // Make sure MinOldSize <= OldSize
>>> 312:     MinOldSize = MIN2(MinOldSize, initial_old_size);
>> 
>> Do you have a test case that requires this? I'd expect `MIN3` above to be enough.
>
> Without this, gtest fails on MacOSX (https://github.com/zhengyu123/jdk/actions/runs/8743941793/job/23997262102)

I see; why is `MinOldSize` being adjusted here, instead of `initial_old_size`? In the `else` branch of `if (!FLAG_IS_CMDLINE(OldSize)) {`, we emit warning for user-set inconsistent `OldSize`, when it's above the max. For symmetry, I'd expect sth like this for the `else` part:


    if (initial_old_size > MaxOldSize) {
      log_warning(gc, ergo)(...);
      initial_old_size = MaxOldSize;
    } else if (initial_old_size < MinOldSize) {
      log_waring(gc, ergo)(...);
      initial_old_size = MinOldSize;
    }

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PR Review Comment: https://git.openjdk.org/jdk/pull/18539#discussion_r1572661928