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8261496: Shenandoah: reconsider pacing updates memory ordering #2501



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@shipilev shipilev commented Feb 10, 2021

Shenandoah pacer uses atomic operations to update budget, progress, allocations seen. 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 is excessive for pacing, as we do not piggyback memory effects on it. All pacing updates can use "relaxed".

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-8261496: Shenandoah: reconsider pacing updates memory ordering



$ git fetch pull/2501/head:pull/2501
$ git checkout pull/2501

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@bridgekeeper 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 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.


@shipilev shipilev marked this pull request as ready for review Feb 10, 2021
@openjdk openjdk bot added the rfr label Feb 10, 2021
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@mlbridge mlbridge bot commented Feb 10, 2021



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@zhengyu123 zhengyu123 left a comment

Looks good to me


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@openjdk 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:

8261496: Shenandoah: reconsider pacing updates 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 23 new commits pushed to the master branch:

  • 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
  • 05c6009: 8259656: changes broke _NT_SYMBOL_PATH in RunTests.gmk
  • ef7ee3f: 8225081: Remove Telia Company CA certificate expiring in April 2021
  • ... and 13 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 label Feb 10, 2021
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@shipilev shipilev commented Feb 15, 2021



@openjdk openjdk bot closed this Feb 15, 2021
@openjdk openjdk bot added integrated and removed ready rfr labels Feb 15, 2021
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@openjdk openjdk bot commented Feb 15, 2021

@shipilev Since your change was applied there have been 77 commits pushed to the master branch:

  • 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
  • dc46aa8: 8261534: Test sun/security/pkcs11/KeyAgreement/ fails on platforms where no nsslib artifacts are defined
  • f0d9829: 8261533: Java_sun_font_CFont_getCascadeList leaks memory according to Xcode
  • 06170b7: 8261662: Rename compute_loader_lock_object
  • ... and 67 more:

Your commit was automatically rebased without conflicts.

Pushed as commit 4642730.

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


@shipilev shipilev deleted the JDK-8261496-shenandoah-pacer-memord branch Feb 15, 2021
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