RFR: 8346005: Parallel: Incorrect page size calculation with UseLargePages [v9]

[Joel Sikström]

On Fri, 3 Oct 2025 14:44:15 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> Refactor the heap-space and OS memory interface code to clearly separate two related but distinct concepts: `alignment` and `os-page-size`. These are now represented as two fields in `PSVirtualSpace`.
>> 
>> The parallel heap consists of four spaces: old, eden, from, and to. The first belongs to the old generation, while the latter three belong to the young generation.
>> 
>> The size of any space is always aligned to `alignment`, which also determines the unit for resizing. To keep the implementation simple while allowing flexible per-space commit and uncommit operations, each space must contain at least one OS page. As a result, `alignment` is always greater than or equal to `os-page-size`.
>> 
>> When using explicit large pages -- which require pre-allocating large pages before the VM starts -- the actual OS page size is not known until the heap has been reserved. The additional logic in `ParallelScavengeHeap::initialize` detects the OS page size in use and adjusts `alignment` if necessary.
>> 
>> Test: tier1–8
>
> Albert Mingkun Yang has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review

src/hotspot/share/gc/parallel/mutableNUMASpace.hpp line 129:

> 127: 
> 128:   size_t _base_space_size;
> 129:   void set_base_space_size(size_t v)                 { _base_space_size = v;      }

These are unused.

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PR Review Comment: https://git.openjdk.org/jdk/pull/26700#discussion_r2410189143