8261500: Shenandoah: reconsider region live data memory ordering

[shipilev]

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

---

Progress

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Issue

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

Reviewers

• Zhengyu Gu (@zhengyu123 - Reviewer)

Download

$ git fetch https://git.openjdk.java.net/jdk pull/2503/head:pull/2503
$ git checkout pull/2503

[bridgekeeper]

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[openjdk]

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

• hotspot-gc
• shenandoah

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[mlbridge]

Webrevs

• 00: Full (354ba6b)

[zhengyu123]

Looks good

[openjdk]

@shipilev 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:

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/HugeCapacity.java 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: https://git.openjdk.java.net/jdk/compare/5183d8ae1eec86202eace2c4770f81edbc73cb68...master

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.

[shipilev]

/integrate

[openjdk]

@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/TestReclaimStringsLeaksMemory.java 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: https://git.openjdk.java.net/jdk/compare/5183d8ae1eec86202eace2c4770f81edbc73cb68...master

Your commit was automatically rebased without conflicts.

Pushed as commit c6eedda.

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