Integrated: JDK-8313319: [linux] mmap should use MAP_FIXED_NOREPLACE if available

[Thomas Stuefe]

On Sun, 6 Aug 2023 17:09:41 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> os::attempt_reserve_memory_at() is used to map memory at a specific address that we fancy. It is not used to replace an existing mapping (hence we omit MAP_FIXED). 
> 
> But it may result in the kernel creating a mapping at a different address if our wish address is blocked; we then have to unmap again. That mmap-munmap cycle is unnecessary.
> 
> MAP_FIXED_NOREPLACE exists since Linux 4.17 and prevents that unnecessary cycle . We should use that if available. We need to tiptoe around a bit to deal with building on old machines/running on old kernels, though.

This pull request has now been integrated.

Changeset: 3699666c
Author:    Thomas Stuefe <stuefe at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/3699666c9325b38d287e1d4d2576f8e3a662ae81
Stats:     49 lines in 2 files changed: 47 ins; 0 del; 2 mod

8313319: [linux] mmap should use MAP_FIXED_NOREPLACE if available

Reviewed-by: jsjolen, dholmes

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PR: https://git.openjdk.org/jdk/pull/15170