Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

JDK-8312492: Remove THP sanity checks at VM startup #14967

Conversation

tstuefe
Copy link
Member

@tstuefe tstuefe commented Jul 21, 2023

When starting the JVM with -XX:+UseTransparentHugePages, we need to know if the OS supports THPs:

A) We could run on a super-old kernel (very unlikely, THPs are supported since 2.6.38 which is EOL since 2011)
B) We could run on a kernel built without THP support, e.g. an embedded device
C) We could run on a system with THPs disabled by the admin

The JVM does a little sanity test at startup: it maps an area the size of a huge page - but in small pages - then calls madvise(MADV_HUGEPAGE) on it. The JVM assumes if the madvise() worked, all is fine.

That sanity test may be expensive since we allocate (reserve AND commit) an area, then signal khugepaged to fold it into a huge page. That area could be large once the kernel supports 1 GB THP pages. We may end up committing 1 GB space at startup. In addition to that, depending on the THP defrag settings, the allocation may stall. Even if it does not stall it creates unnecessary work for both the JVM and khugepaged.

The sanity test is also not really useful since it will happily report success on systems with THPs disabled (case (C)). Arguably, that is the majority of cases on existing Linux installations.

The correct way is to check the proc fs whether THPs are enabled. But we already do that since JDK-8310233: "Fix THP detection on Linux". And that test detects all cases (A)(B)(C). Therefore we can completely remove the sanity checks for THPs.

I tested the patch manually in a number of settings with THPs enabled, disabled, and not compiled into the kernel at all. There is no behavioral difference because since JDK-8310233 we catch all relevant cases before ever entering this sanity test.

[1]

if ( ( UseTransparentHugePages && HugePages::supports_thp() == false) ||


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

Issue

  • JDK-8312492: Remove THP sanity checks at VM startup (Bug - P4)

Reviewers

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/14967/head:pull/14967
$ git checkout pull/14967

Update a local copy of the PR:
$ git checkout pull/14967
$ git pull https://git.openjdk.org/jdk.git pull/14967/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 14967

View PR using the GUI difftool:
$ git pr show -t 14967

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/14967.diff

Webrev

Link to Webrev Comment

@bridgekeeper
Copy link

bridgekeeper bot commented Jul 21, 2023

👋 Welcome back stuefe! 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
Copy link

openjdk bot commented Jul 21, 2023

@tstuefe The following label will be automatically applied to this pull request:

  • hotspot-runtime

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

@openjdk openjdk bot added the hotspot-runtime hotspot-runtime-dev@openjdk.org label Jul 21, 2023
@tstuefe tstuefe marked this pull request as ready for review July 21, 2023 08:11
@openjdk openjdk bot added the rfr Pull request is ready for review label Jul 21, 2023
@mlbridge
Copy link

mlbridge bot commented Jul 21, 2023

Webrevs

Copy link
Member

@dholmes-ora dholmes-ora left a comment

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Seems quite reasonable.

Thanks.

@openjdk
Copy link

openjdk bot commented Jul 24, 2023

@tstuefe This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8312492: Remove THP sanity checks at VM startup

Reviewed-by: dholmes, coleenp

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been 6 new commits pushed to the master branch:

  • 408987e: 8313307: java/util/Formatter/Padding.java fails on some Locales
  • 6fca289: 8313023: Return value corrupted when using CCS + isTrivial (mainline)
  • f8c2b7f: 8313231: Redundant if statement in ZoneInfoFile
  • 807ca2d: 8313316: Disable runtime/ErrorHandling/MachCodeFramesInErrorFile.java on ppc64le
  • ad34be1: 8312525: New test runtime/os/TestTrimNative.java#trimNative is failing: did not see the expected RSS reduction
  • d6245b6: 8310268: RISC-V: misaligned memory access in String.Compare intrinsic

Please see this link for an up-to-date comparison between the source branch of this pull request and the master branch.
As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

@openjdk openjdk bot added the ready Pull request is ready to be integrated label Jul 24, 2023
@tstuefe
Copy link
Member Author

tstuefe commented Jul 24, 2023

Seems quite reasonable.

Thanks.

Thank you David.

@tstuefe
Copy link
Member Author

tstuefe commented Jul 24, 2023

x86 error unrelated.

A second review would make me happy.

@tstuefe
Copy link
Member Author

tstuefe commented Jul 29, 2023

Friendly ping. Need a second review.

Copy link
Contributor

@coleenp coleenp left a comment

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Looks good. Thanks for the explanation.

@tstuefe
Copy link
Member Author

tstuefe commented Jul 31, 2023

Thank you @coleenp!

/integrate

@openjdk
Copy link

openjdk bot commented Jul 31, 2023

Going to push as commit 5362ec9.
Since your change was applied there have been 11 commits pushed to the master branch:

  • e47a84f: 8312489: Increase jdk.jar.maxSignatureFileSize default which is too low for JARs such as WhiteSource/Mend unified agent jar
  • 78f6799: 8293972: runtime/NMT/NMTInitializationTest.java#default_long-off failed with "Suspiciously long bucket chains in lookup table."
  • 97b6883: 8295059: test/langtools/tools/javap 12 test classes use com.sun.tools.classfile library
  • 3671d83: 8313252: Java_sun_awt_windows_ThemeReader_paintBackground release resources in early returns
  • b60e0ad: 8313207: Remove MetaspaceShared::_has_error_classes
  • 408987e: 8313307: java/util/Formatter/Padding.java fails on some Locales
  • 6fca289: 8313023: Return value corrupted when using CCS + isTrivial (mainline)
  • f8c2b7f: 8313231: Redundant if statement in ZoneInfoFile
  • 807ca2d: 8313316: Disable runtime/ErrorHandling/MachCodeFramesInErrorFile.java on ppc64le
  • ad34be1: 8312525: New test runtime/os/TestTrimNative.java#trimNative is failing: did not see the expected RSS reduction
  • ... and 1 more: https://git.openjdk.org/jdk/compare/402cb6a550f60c75f93c709b5e5902f3757a8acd...master

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Jul 31, 2023
@openjdk openjdk bot closed this Jul 31, 2023
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Jul 31, 2023
@openjdk
Copy link

openjdk bot commented Jul 31, 2023

@tstuefe Pushed as commit 5362ec9.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Labels
hotspot-runtime hotspot-runtime-dev@openjdk.org integrated Pull request has been integrated
3 participants