RFR: JDK-8313319: [linux] mmap should use MAP_FIXED_NOREPLACE if available [v2]

[Thomas Stuefe]

On Wed, 16 Aug 2023 14:24:44 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.
>
> Thomas Stuefe 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 'openjdk:master' into JDK-8313319-MAP_FIXED_NOREPLACE
>  - DK-8313319-MAP_FIXED_NOREPLACE

Anybody else? Need a second review. Thanks!

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PR Comment: https://git.openjdk.org/jdk/pull/15170#issuecomment-1687775142