RFR: 8338977: Parallel: Improve heap resizing heuristics [v6]

[Albert Mingkun Yang]

On Tue, 27 May 2025 01:02:22 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> 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.

`expand_heap_and_allocate` is invoked in both situations; also, heap is expanded inside `summary_phase` in order to hold all live-objs inside old-gen.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25000#discussion_r2108377133