RFR: 8338977: Parallel: Improve heap resizing heuristics [v19]

[Albert Mingkun Yang]

On Sun, 6 Jul 2025 18:03:14 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   review
>
> src/hotspot/share/gc/parallel/psParallelCompact.cpp line 898:
> 
>> 896:       size_t target_capacity_bytes = total_live_words * HeapWordSize
>> 897:                                    + old_space->capacity_in_bytes() * (MarkSweepDeadRatio / 100.0)
>> 898:                                    + SpaceAlignment;
> 
> Why add `SpaceAlignment`, not `align_up` to `SpaceAlignment`?

The alignment is handled inside the callee. I just wanna leave a minimal delta in the old-gen so that old-gen is not completely full. Otherwise, the next young-gc can not promote anything and will be upgraded to full-gc directly. This is mostly for `UseAdaptiveSizePolicy == false`; if enabled, old-gen will also be resized after full-gc.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25000#discussion_r2188611386