RFR: 8346005: Parallel: Incorrect page size calculation with UseLargePages [v2]

[Albert Mingkun Yang]

> 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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into pgc-largepage
 - pgc-largepage

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Changes:
  - all: https://git.openjdk.org/jdk/pull/26700/files
  - new: https://git.openjdk.org/jdk/pull/26700/files/0a67ca44..5df3735a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26700&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26700&range=00-01

  Stats: 10715 lines in 306 files changed: 4992 ins; 4431 del; 1292 mod
  Patch: https://git.openjdk.org/jdk/pull/26700.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26700/head:pull/26700

PR: https://git.openjdk.org/jdk/pull/26700