Integrated: 8253650: Cleanup: remove alignment_hint parameter from os::reserve_memory

[Thomas Stuefe]

On Wed, 30 Sep 2020 10:08:09 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> Hi all,
> 
> since ancient times os::reserve_memory() carried around an "alignment_hint" parameter. It was undocumented but from the
> name it suggests it would cause os::reserve_memory() to try to align the start of the mapping to a given alignment.
> However, the only platform ever doing anything with this parameter was AIX, and there only in mmap() mode. All other
> platforms ignored the parameter.  So it can be removed, provided we fix the AIX case.
> Notes:
> - if one really needs alignment memory, there is os::reserve_memory_aligned() which guarantees the alignment. It will do
>   the usual over-reserving-and-chopping-away to do that.
> - On AIX there is a second reason why we align the mmap() result pointer to 64K, since we "fake" 64K pages in some
>   places. I disentangled that alignment handling from the caller provided alignment.
> - This affects os::reserve_memory() as well as the new os::reserve_memory_with_fd()
> - I also fixed comments in virtualSpace.cpp which do not apply anymore after JDK-8253638
> 
> Tests: tier1, manual builds and tests on AIX

This pull request has now been integrated.

Changeset: 44e6820c
Author:    Thomas Stuefe <stuefe at openjdk.org>
URL:       https://git.openjdk.java.net/jdk/commit/44e6820c
Stats:     92 lines in 12 files changed: 5 ins; 37 del; 50 mod

8253650: Cleanup: remove alignment_hint parameter from os::reserve_memory

Reviewed-by: stefank, tschatzl

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PR: https://git.openjdk.java.net/jdk/pull/430