8280784: VM_Cleanup unnecessarily processes all thread oops

[shipilev]

Clean backport of performance enhancement for GCs that do concurrent thread roots (in JDK 17u those are Shenandoah and Z). On my machine, with Shenandoah running 20K threads, the safepoint cleanup time for "Cleanup" VM ops dropped from 2ms to nearly zero. A possible follow-up would be JDK-8280817, which would extend this to other "empty" ops.

Additional testing:

• Ad-hoc benchmarks
• Linux x86_64 fastdebug tier1, tier2
• Linux x86_64 fastdebug tier1, tier2 with -XX:+DeoptimizeALot
• Linux x86_64 fastdebug tier1, tier2 with -XX:+UseShenandoahGC

---

Progress

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

Issue

• JDK-8280784: VM_Cleanup unnecessarily processes all thread oops

Reviewers

• Stefan Karlsson (@stefank - Reviewer) ⚠️ Review applies to 02fce546

Reviewing

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk17u-dev pull/889/head:pull/889
$ git checkout pull/889

Update a local copy of the PR:
$ git checkout pull/889
$ git pull https://git.openjdk.org/jdk17u-dev pull/889/head

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Checkout this PR locally:
$ git pr checkout 889

View PR using the GUI difftool:
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Download this PR as a diff file:
https://git.openjdk.org/jdk17u-dev/pull/889.diff

[bridgekeeper]

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[openjdk]

This backport pull request has now been updated with issue from the original commit.

[openjdk]

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

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

8280784: VM_Cleanup unnecessarily processes all thread oops

Reviewed-by: stefank

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[mlbridge]

Webrevs

• 01: Full - Incremental (8fd5b689)
• 00: Full (02fce546)

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[shipilev]

@stefank, would you like to ack this?

[shipilev]

/integrate

[openjdk]

Going to push as commit fea3818.
Since your change was applied there has been 1 commit pushed to the master branch:

• f2c3f35: 8297088: Update LCMS to 2.14

Your commit was automatically rebased without conflicts.

[openjdk]

@shipilev Pushed as commit fea3818.

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