8277981: String Deduplication table is never cleaned up due to bad dead_factor_for_cleanup

[shipilev]

See the reproducer and analysis in the bug.

The root cause for this problem is that percent_of returns 0..100 (percent) value of nominator / denominator. Which means if we feed percent and 100 there, this is an identity operation, returning the same value. And we wanted the conversion from percent to factor instead.

The default value for StringDeduplicationCleanupDeadPercent is 5, which means (assuming dead_count <= entry_count) this erroneous conversion makes this condition always false:

bool StringDedup::Config::should_cleanup_table(size_t entry_count, size_t dead_count) {
  return (dead_count > _minimum_dead_for_cleanup) &&
         (dead_count > (entry_count * _dead_factor_for_cleanup));
}

Additional testing:

• Reproducer stress test does not leak anymore
• Linux x86_64 fastdebug tier1, -XX:+UseStringDeduplication
• Linux x86_64 fastdebug tier2, -XX:+UseStringDeduplication
• Linux x86_64 fastdebug tier3, -XX:+UseStringDeduplication

---

Progress

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Issue

• JDK-8277981: String Deduplication table is never cleaned up due to bad dead_factor_for_cleanup

Reviewers

• Zhengyu Gu (@zhengyu123 - Reviewer)
• Kim Barrett (@kimbarrett - Reviewer)
• Thomas Schatzl (@tschatzl - Reviewer)

Reviewing

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[openjdk]

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• hotspot-gc

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[mlbridge]

Webrevs

• 00: Full (88df2077)

[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:

8277981: String Deduplication table is never cleaned up due to bad dead_factor_for_cleanup

Reviewed-by: zgu, kbarrett, tschatzl

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 28 new commits pushed to the master branch:

• 98a9f03: 8277602: Deopt code does not extend the stack enough if the caller is an optimize entry blob
• 9150840: 8277899: Parallel: Simplify PSVirtualSpace::initialize logic
• 01cefc9: 8277977: Incorrect references to --enable-reproducible-builds in docs
• 69f56a0: 8264485: build.tools.depend.Depend.toString(byte[]) creates malformed hex strings
• fecf906: 8267928: Loop predicate gets inexact loop limit before PhaseIdealLoop::rc_predicate
• a5f2a58: 8277846: Implement fast-path for ASCII-compatible CharsetEncoders on ppc64
• ceae380: 8277843: [Vector API] scalar2vector generates incorrect type info for mask operations if Op_MaskAll is unavailable
• 3ee26c6: 8267767: Redundant condition check in SafepointSynchronize::thread_not_running
• d230fee: 8277931: Parallel: Remove unused PSVirtualSpace::expand_into
• fde6fe7: 8277824: Remove empty RefProcSubPhasesWorkerTimeTracker destructor
• ... and 18 more: https://git.openjdk.java.net/jdk/compare/c3a7f2f4bce9170c1630e01eebd4fcd174b44964...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.

[kimbarrett]

Looks good.

[shipilev]

Thanks for reviews. I'll wait out the 24 hours for Hotspot patches, and then push. Then I'll go plead to Rob about picking it up to 17.0.2.

[shipilev]

/integrate

[openjdk]

Going to push as commit 8d7958e.
Since your change was applied there have been 48 commits pushed to the master branch:

• bc6dce1: 8277736: G1: Allow forced evacuation failure of first N regions in collection set
• 0c29ee5: 8274319: Replace usages of Collections.sort with List.sort call in jdk.jfr
• f505396: 8277459: Add jwebserver tool
• 84aa0a1: 8278047: Few javax/imageio test regressed after JDK-8262297 fix
• fde0b95: 8277861: Terminally deprecate Thread.stop
• 70d5dff: 8275326: C2: assert(no_dead_loop) failed: dead loop detected
• 349328c: 8277777: [Vector API] assert(r->is_XMMRegister()) failed: must be in x86_32.ad
• c733193: 8262297: ImageIO.write() method will throw IndexOutOfBoundsException
• da2be99: 8277026: Remove blank lines remaining from snippet markup
• 0a01baa: 8277986: Typo in javadoc of java.util.zip.ZipEntry#setTime
• ... and 38 more: https://git.openjdk.java.net/jdk/compare/c3a7f2f4bce9170c1630e01eebd4fcd174b44964...master

Your commit was automatically rebased without conflicts.

[openjdk]

@shipilev Pushed as commit 8d7958e.

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