RFR: 8338977: Parallel: Improve heap resizing heuristics [v5]

[Zhengyu Gu]

On Sun, 18 May 2025 15:21:37 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> src/hotspot/share/gc/parallel/parallelScavengeHeap.cpp line 404:
>> 
>>> 402:     collect_at_safepoint(!should_run_young_gc);
>>> 403: 
>>> 404:     if (is_gc_overhead_limit_reached()) {
>> 
>> Maybe want to adopt current algorithm, start to clear soft references when approaching gc overhead limit?
>> Running a full gc and clearing all soft references without retrying allocation and throws OOM, seems a bit harsh.
>> 
>> People still use soft references for caches, reclaim soft references could potentially free large amount of memory.
>
> Revised a bit; the limitation of what we have on master is that it doesn't detect gc-overhead for young-gcs. If many young-gcs are run, gc-overhead checking should kick in as well.

I wonder if you should try `expand_heap_and_allocate()` under `_is_heap_almost_full` situation as well.  I am afraid that it might throw OOM before heap is fully expanded again, because compact GC does not expand heap.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25000#discussion_r2107963971