RFR: 8345687: Improve the implementation of SegmentFactories::allocateSegment [v7]

[Maurizio Cimadamore]

On Thu, 13 Mar 2025 05:46:44 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

>> Hi,
>> 
>> This patch improves the performance of a typical `Arena::allocate` in several ways:
>> 
>> - Delay the creation of the NativeMemorySegmentImpl. This avoids the merge of the instance with the one obtained from the call in the uncommon path, increasing the chance the object being scalar replaced.
>> - Split the allocation of over-aligned memory to a slow-path method.
>> - Align the memory to 8 bytes, allowing faster zeroing.
>> - Use a dedicated method to zero the just-allocated native memory, reduce code size and make it more straightforward.
>> - Make `VM.pageAlignDirectMemory` a `Boolean` instead of a `boolean` so that `false` value can be constant folded.
>> 
>> Please take a look and leave your reviews, thanks a lot.
>
> Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:
> 
>   expand wildcard imports

Marked as reviewed by mcimadamore (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/22610#pullrequestreview-2682620023