8333129: Move ShrinkHeapInSteps flag to Serial GC

[zhengyu123]

A trivial change that moves Serial GC specific flag ShrinkHeapInSteps to serial_globals.hpp

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Issue

• JDK-8333129: Move ShrinkHeapInSteps flag to Serial GC (Enhancement - P4)

Reviewers

• David Holmes (@dholmes-ora - Reviewer)
• Kim Barrett (@kimbarrett - Reviewer)

Reviewing

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[bridgekeeper]

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[openjdk]

@zhengyu123 This change now passes all automated pre-integration checks.

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

8333129: Move ShrinkHeapInSteps flag to Serial GC

Reviewed-by: dholmes, kbarrett

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At the time when this comment was updated there had been 80 new commits pushed to the master branch:

• 1b7d59f: 8333303: Issues with DottedVersion class
• e304a8a: 8333307: Don't suppress jpackage logging in tests when it is detecting packaging tools in the system
• 3634a91: 8332751: Broken link in VirtualMachine.html
• ffb0867: 8331485: Odd Results when Parsing Scientific Notation with Large Exponent
• 79f4998: 8321314: Reinstate disabling the compiler's default active annotation processing
• ec88c6a: 8332917: failure_handler should execute gdb "info threads" command on linux
• b3e29db: 8333108: Update vmTestbase/nsk/share/DebugeeProcess.java to don't use finalization
• 11e926c: 8332777: Update JCStress test suite
• 44c1845: 8330852: All callers of JvmtiEnvBase::get_threadOop_and_JavaThread should pass current thread explicitly
• 922e312: 8328611: Thread safety issue in com.sun.tools.jdi.ReferenceTypeImpl::classObject
• ... and 70 more: https://git.openjdk.org/jdk/compare/985b9ce79a2d620a8b8675d1ae6c9730d72a757f...master

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[openjdk]

@zhengyu123 The following label will be automatically applied to this pull request:

• hotspot

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[mlbridge]

Webrevs

• 00: Full (cbf1387d)

[zhengyu123]

/add label hotspot-gc

[zhengyu123]

/label add hotspot-gc

[openjdk]

@zhengyu123 Unknown command add - for a list of valid commands use /help.

[openjdk]

@zhengyu123
The hotspot-gc label was successfully added.

[dholmes-ora]

@zhengyu123 I don't think we can do this in quite such a direct way. This flag was added in JDK 9 under JDK-8146436 and applied to all GC's AFAICS. Over time it seems to have been relegated to only working with SerialGC, but I can still find articles that reference it for GC tuning e.g.

https://docs.oracle.com/en/java/javase/22/gctuning/factors-affecting-garbage-collection-performance.html

So if this is indeed only for SerialGC now then we need to check when it stopped applying elsewhere and whether all the relevant docs have been updated. Then I think we would need to deprecate it for non-Serial (which is tricky because the flag deprecation process isn't intended to be runtime selective like that). I need to flag this directly with our GC team

[kimbarrett]

@zhengyu123 I don't think we can do this in quite such a direct way. This flag was added in JDK 9 under JDK-8146436 and applied to all GC's AFAICS. Over time it seems to have been relegated to only working with SerialGC, but I can still find articles that reference it for GC tuning e.g.

The flag implementation was added in CardGeneration. I'm not certain, but I think that class was only ever used
by Serial and CMS.

[kimbarrett]

Looks good. Disavowing triviality to give @dholmes-ora a chance to comment further.

[zhengyu123]

I can confirm that ShrinkHeapInSteps flag is only used in CardGeneration and CardGeneration is only used in Serial and CMS in JDK9u source.

[dholmes-ora]

Apologies, I was mistakenly thinking that moving the flag would cause a runtime error for code not using Serial GC, but it will only cause an error if a VM were built without Serial GC support, which I don't think is possible.

I will file a RFE to get the GC Tuning guide updates (if @kimbarrett doesn't beat me to it :) ).

I also note that component-specific global flags don't advertise the fact they are global-specific.

[dholmes-ora]

Okay. Thanks

[zhengyu123]

/integrate

Thanks, @dholmes-ora and @kimbarrett

[openjdk]

Going to push as commit 79a78f0.
Since your change was applied there have been 90 commits pushed to the master branch:

• 2f2dc22: 8330981: ZGC: Should not dedup strings in the finalizer graph
• d481215: 8333005: Deadlock when setting or updating the inline cache
• 7ab74c5: 8333200: Test containers/docker/TestPids.java fails Limit value -1 is not accepted as unlimited
• a7864af: 8182774: Verify code in javap
• 778ad00: 8308642: Unhelpful pattern switch error: illegal fall-through to a pattern
• bb4aed9: 8332961: Parallel: Limit PSParallelCompact::verify_complete range
• 95c8a69: 8332032: C2: Remove ExpandSubTypeCheckAtParseTime flag
• ba323b5: 8333047: Remove arena-size-workaround in jvmtiUtils.cpp
• 22ef827: 8320396: Class-File API ClassModel::verify should include checks from hotspot/share/classfile/classFileParser.cpp
• 2ab8ab5: 8332858: References with escapes have broken positions after they are transformed
• ... and 80 more: https://git.openjdk.org/jdk/compare/985b9ce79a2d620a8b8675d1ae6c9730d72a757f...master

Your commit was automatically rebased without conflicts.

[openjdk]

@zhengyu123 Pushed as commit 79a78f0.

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