RFR: 8338977: Parallel: Improve heap resizing heuristics [v22]

[SilenceZheng66]

On Tue, 16 Dec 2025 11:07:07 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> @albertnetymk Since my JVM's version is 25.191-b12, it does not support `-Xlog:gc*` configuration. I also know that your work aim to improve performance when `UseAdaptiveSizePolicy` enabled, but in my situation default configuration is disable that. Now I just curious about is it a bug when people use configurations as following and could raise full GC problems and heap can't expand. 
>> 
>> -Xmx2g
>> -Xms256M
>> -XX:-UseAdaptiveSizePolicy
>> 
>> I understand that's totally not your business, but if you know who can explain or confirm this "bug", just let me know, thx!
>
>> Since my JVM's version is 25.191-b12 ...
> 
> I thought it means JDK25... My apologies.
> 
>>  Now I just curious about is it a bug when people use configurations as following and could raise full GC problems and heap can't expand.
> 
> I think that behavior is definitely undesirable. Whether or not it's a bug can be subjective.
> 
> I believe this behavior has been fixed/improved in later releases of JDK. At least the following two tickets are relevant.
> 
> JDK-8328744: Parallel: Parallel GC throws OOM before heap is fully expanded
> Use max old-gen capacity to decide whether to start a "proactive" full-gc, instead of young-gc.
> 
> JDK-8338977: Parallel: Improve heap resizing heuristics 
> In `PSParallelCompact::summary_phase`, old-gen is expanded via `ParallelScavengeHeap::heap()->old_gen()->try_expand_till_size` even with `-XX:-UseAdaptiveSizePolicy`.
> 
> I wonder if you can try your benchmark(s) with newer JDKs and check if the problem persists.

Thanks! I thinks these two ticket solved the problem I met, which means newer version JDK will not have this issue any more😊. @albertnetymk

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PR Review Comment: https://git.openjdk.org/jdk/pull/25000#discussion_r2626467932