[jdk21u-dev] RFR: 8313319: [linux] mmap should use MAP_FIXED_NOREPLACE if available

[Sergey Chernyshev]

On Fri, 14 Nov 2025 17:47:07 GMT, Sergey Chernyshev <schernyshev at openjdk.org> wrote:

> Hi all,
> 
> Please review the backport of JDK-8313319 that prevents unnecessary mmap-munmap cycle in systems that do not honor the address hint when mmapping memory without MAP_FIXED. Please see more details in #2475. This is (almost) a clean backport, with only a minor context conflict due to JDK-8315923 hasn't been backported to JDK 21.
> 
> Testing:
> 
> - jtreg standard test groups passed
> - gtests passed

Hi Thomas, thanks four your note! Yes, this backport is performance only. I haven't seen other problems of randmmap-patched kernel except for one with ZGC.

UPD. I missed the double definition of MAP_FIXED_NOREPLACE that came from JDK-8330520.

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PR Comment: https://git.openjdk.org/jdk21u-dev/pull/2476#issuecomment-3541657509