RFR: 8345323: Parallel GC does not handle UseLargePages and UseNUMA gracefully

[Stefan Johansson]

On Thu, 5 Dec 2024 12:04:20 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

> This patch reverts the default value of `OldSize` to its previous setting prior to being obsoleted in [JDK-8333962](https://bugs.openjdk.org/browse/JDK-8333962). The change addresses an issue where `OldSize` being set to zero results in a default `MinHeapSize` that is too small to handle LargePages correctly. This problem is exemplified by `ParallelArguments::initialize_heap_flags_and_sizes`, as identified in [JDK-8345323](https://bugs.openjdk.org/browse/JDK-8345323).
> 
> Changing the default value of `OldSize` may have broader implications due to the complexity of the logic that determines default values for various flags. Altering one default can lead to cascading effects and potential breakages elsewhere. For these reasons, this patch restores the previous default value of `OldSize` to mitigate such risks.

Looks good, thanks for doing the fix.

Just a small comment on the comment.

src/hotspot/share/gc/shared/genArguments.cpp line 41:

> 39: 
> 40: // If InitialHeapSize or MinHeapSize is not set on cmdline, this variable,
> 41: // together with NewSize, are used to derive them.

Suggestion:

// together with NewSize, is used to derive them.

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Marked as reviewed by sjohanss (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/22575#pullrequestreview-2488189045
PR Review Comment: https://git.openjdk.org/jdk/pull/22575#discussion_r1875622629