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8261500: Shenandoah: reconsider region live data memory ordering #2503


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@shipilev shipilev commented Feb 10, 2021

Current Shenandoah region live data tracking uses default CAS updates to achieve atomicity of updates. Hotspot's default for atomic operations is memory_order_conservative, which emits two-way memory fences around the CASes at least on AArch64 and PPC64.

This seems to be excessive for live data tracking, and "relaxed" could be used instead. The only serious user of that data is collection set chooser, which runs at safepoint and so everything should be quiescent when that happens.

Additional testing:

  • Linux x86_64 hotspot_gc_shenandoah
  • Linux AArch64 hotspot_gc_shenandoah
  • Linux AArch64 tier1 with Shenandoah


  • Change must not contain extraneous whitespace
  • Commit message must refer to an issue
  • Change must be properly reviewed


  • JDK-8261500: Shenandoah: reconsider region live data memory ordering



$ git fetch pull/2503/head:pull/2503
$ git checkout pull/2503

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bridgekeeper bot commented Feb 10, 2021

👋 Welcome back shade! 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.

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openjdk bot commented Feb 10, 2021

@shipilev The following labels will be automatically applied to this pull request:

  • hotspot-gc
  • shenandoah

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

@openjdk openjdk bot added hotspot-gc shenandoah labels Feb 10, 2021
@shipilev shipilev marked this pull request as ready for review Feb 10, 2021
@openjdk openjdk bot added the rfr Pull request is ready for review label Feb 10, 2021
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@zhengyu123 zhengyu123 left a comment

Looks good

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openjdk bot commented Feb 10, 2021

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

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

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

8261500: Shenandoah: reconsider region live data memory ordering

Reviewed-by: zgu

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 25 new commits pushed to the master branch:

  • 40754f1: 4841153: java.awt.geom.Rectangle2D.add(double,double) documented incorrectly
  • 4caeb39: 8260380: Upgrade to LittleCMS 2.12
  • a772639: 8261298: LinuxPackage.c, getJvmLauncherLibPath RPM->DEB typo
  • 52fc01b: 8261268: LOAD_INSTANCE placeholders unneeded for parallelCapable class loaders
  • a3d6e37: 8261302: NMT: Improve malloc site table hashing
  • ad54d8d: 8260934: java/lang/StringBuilder/ fails without Compact Strings
  • 752f92b: 6211242: AreaAveragingScaleFilter(int, int): IAE is not specified
  • 3af334a: 6211257: BasicStroke.createStrokedShape(Shape): NPE is not specified
  • 4619f37: 8261472: BasicConstraintsExtension::toString shows "PathLen:2147483647" if there is no pathLenConstraint
  • 699a3cd: 8223188: Removed unnecessary #ifdef __cplusplus from .cpp sources
  • ... and 15 more:

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 Feb 10, 2021
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shipilev commented Feb 15, 2021


@openjdk openjdk bot closed this Feb 15, 2021
@openjdk openjdk bot added integrated Pull request has been integrated and removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Feb 15, 2021
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openjdk bot commented Feb 15, 2021

@shipilev Since your change was applied there have been 80 commits pushed to the master branch:

  • df0897e: 8261504: Shenandoah: reconsider ShenandoahJavaThreadsIterator::claim memory ordering
  • 745c0b9: 8261493: Shenandoah: reconsider bitmap access memory ordering
  • 4642730: 8261496: Shenandoah: reconsider pacing updates memory ordering
  • 7c93159: 8261503: Shenandoah: reconsider verifier memory ordering
  • d9744f6: 8261608: Move common CDS archive building code to archiveBuilder.cpp
  • 235da6a: 8261672: Reduce inclusion of classLoaderData.hpp
  • 95d7312: 8261585: Restore HandleArea used in Deoptimization::uncommon_trap
  • 849390a: 8260401: StackOverflowError on open WindowsPreferences
  • 735757f: 8261661: gc/stress/ fails because Reserved memory size is too big
  • e29c560: 8247514: Improve clhsdb 'findpc' ability to determine what an address points to by improving PointerFinder and PointerLocation classes
  • ... and 70 more:

Your commit was automatically rebased without conflicts.

Pushed as commit c6eedda.

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

@shipilev shipilev deleted the JDK-8261500-shenandoah-livedata-memord branch Feb 15, 2021
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