8313319: [linux] mmap should use MAP_FIXED_NOREPLACE if available

[sercher]

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.

UPD: Apart from a minor context issue related to JDK-8315923, there was a second definition of MAP_FIXED_NOREPLACE, introduced by JDK-8330520 backport.

Testing:

• jtreg standard test groups passed
• gtests passed (aarch64 & amd64)

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• JDK-8313319 needs maintainer approval

Issue

• JDK-8313319: [linux] mmap should use MAP_FIXED_NOREPLACE if available (Enhancement - P4 - Requested)

Reviewers

• Thomas Stuefe (@tstuefe - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk21u-dev.git pull/2476/head:pull/2476
$ git checkout pull/2476

Update a local copy of the PR:
$ git checkout pull/2476
$ git pull https://git.openjdk.org/jdk21u-dev.git pull/2476/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 2476

View PR using the GUI difftool:
$ git pr show -t 2476

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk21u-dev/pull/2476.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back schernyshev! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[openjdk]

⚠️ @sercher This change is now ready for you to apply for maintainer approval. This can be done directly in each associated issue or by using the /approval command.

[mlbridge]

Webrevs

• 01: Full - Incremental (15e6daac)
• 00: Full (1c7c3805)

[sercher]

/approval request Clean backport, use MAP_FIXED_NOREPLACE flag when supported by kernel, this prevents unnecessary mmap-munmap cycle in systems that do not honor the address hint in mmap() system call.

[openjdk]

@sercher
8313319: The approval request has been created successfully.

[tstuefe]

Just to be clear, this downport's intent is performance, not outright failures, right?

I only know of two cases where we rely on fixed addressing, ZGC being one of them. The other would be class space reservation on Arm64. Do you see any other problems with the rand kernel patch outside of ZGC?

[sercher]

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.

[tstuefe]

Hmm

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.

Hmm. Something must have gone wrong with the backport of JDK-8330520. It took parts of 8313319 with it, it seems.

[tstuefe]

Patch is okay.

[sercher]

Hmm. Something must have gone wrong with the backport of JDK-8330520. It took parts of 8313319 with it, it seems.

Exactly. It was spotted in the review and passed nevertheless

[sercher]

Patch is okay.

Thank you!