8289838: ZGC: OOM before clearing all SoftReferences

[fisk]

should_clear_soft_references() in mainline ZGC is based purely on the cause of the GC, but the GC cause being used to catch that we need to clear soft references is asynchronous. Another GC could start an instant before it is requested, such as a metadata threshold GC for example. Then the metadata threshold GC will be used instead.

Even if the other async GC that was requested is also of the kind that requires soft references to be cleared, such as a concurrently requested _z_allocation_stall GC, it is possible that the async GC request is performed after a soft reference was created, after a concurrent thread requests a _z_allocation_stall GC, but before that GC has reached mark_start, implying that the sequence number will look like it already got to run an entire GC before throwing, while in fact it did not.

---

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Issue

• JDK-8289838: ZGC: OOM before clearing all SoftReferences

Reviewers

• Albert Mingkun Yang (@albertnetymk - Reviewer) ⚠️ Review applies to 104bcd8d
• Thomas Schatzl (@tschatzl - Reviewer) ⚠️ Review applies to 104bcd8d

Reviewing

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[bridgekeeper]

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[openjdk]

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

• hotspot-gc

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[mlbridge]

Webrevs

• 01: Full (33406ed8)
• 00: Full (104bcd8d)

[openjdk]

@fisk 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:

8289838: ZGC: OOM before clearing all SoftReferences

Reviewed-by: ayang, 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 26 new commits pushed to the master branch:

• 16a041a: 8296142: CertAttrSet::(getName|getElements|delete) are mostly useless
• 6626a29: 8294845: Make globals accessed by G1 young gen revising atomic
• dac6ecc: 8295990: Improve make handling of strip flags
• 38c1f2a: 8296130: G1: Remove G1YoungCollector::_target_pause_time_ms
• 2bd24c4: 8295968: RISC-V: Rename some assembler intrinsic functions for RVV 1.0
• 1a58cb1: 8233697: CHT: Iteration parallelization
• 7619602: 8296136: Use correct register in aarch64_enc_fast_unlock()
• 47d513b: 8252075: Documentation error in LayoutManager2 interface
• 8de3eda: 8295476: Split G1 cost per byte predictor on gc phase
• 2634eff: 8295646: Ignore zero pairs in address descriptors read by dwarf parser
• ... and 16 more: https://git.openjdk.org/jdk/compare/274ea1db5b248968c1ff1c5c24d75f07fb8a0600...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.

[tschatzl]

Lgtm.

[openjdk]

@fisk this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout 8289838_soft_ref_trouble
git fetch https://git.openjdk.org/jdk master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

[fisk]

/integrate

[openjdk]

Going to push as commit 491d43c.
Since your change was applied there have been 29 commits pushed to the master branch:

• a1c349f: 8290063: IGV: Give the graphs a unique number in the outline
• b807470: 8296235: IGV: Change shortcut to delete graph from ctrl+del to del
• e15d241: 8295991: java/net/httpclient/CancelRequestTest.java fails intermittently
• 16a041a: 8296142: CertAttrSet::(getName|getElements|delete) are mostly useless
• 6626a29: 8294845: Make globals accessed by G1 young gen revising atomic
• dac6ecc: 8295990: Improve make handling of strip flags
• 38c1f2a: 8296130: G1: Remove G1YoungCollector::_target_pause_time_ms
• 2bd24c4: 8295968: RISC-V: Rename some assembler intrinsic functions for RVV 1.0
• 1a58cb1: 8233697: CHT: Iteration parallelization
• 7619602: 8296136: Use correct register in aarch64_enc_fast_unlock()
• ... and 19 more: https://git.openjdk.org/jdk/compare/274ea1db5b248968c1ff1c5c24d75f07fb8a0600...master

Your commit was automatically rebased without conflicts.

[openjdk]

@fisk Pushed as commit 491d43c.

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

[fisk]

Thanks for the reviews!