8329134: Reconsider TLAB zapping

[shipilev]

We zap the entire TLAB on initial allocation (MemAllocator::mem_allocate_inside_tlab_slow), and then also rezap the object contents when object is allocated from the TLAB (ThreadLocalAllocBuffer::allocate). The second part seems excessive, given the TLAB is already fully zapped.

There is also no way to disable this zapping, like you would in other places with the relevant Zap* flags.

Fixing both these issues allows to improve fastdebug tests performance, e.g. in jcstress.

It also allows to remove the related Zero kludge.

Additional testing:

• Linux AArch64 server fastdebug, all tests
• MacOS AArch64 Zero fastdebug, bootcycle-images pass

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Progress

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Issue

• JDK-8329134: Reconsider TLAB zapping (Enhancement - P4)

Reviewers

• Stefan Karlsson (@stefank - Reviewer)
• Roman Kennke (@rkennke - Reviewer)

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[openjdk]

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

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8329134: Reconsider TLAB zapping

Reviewed-by: stefank, rkennke

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[mlbridge]

Webrevs

• 02: Full - Incremental (5bf36d05)
• 01: Full - Incremental (72bf1e8a)
• 00: Full (8fe98c4c)

[stefank]

This looks like a worth-while change. I listed a couple of nits that I think would be nice to clean up.

[stefank]

Thanks! Looks good.

[shipilev]

Thanks! I would wait for more reviews now.

[rkennke]

Looks good to me. Thank you!

[shipilev]

Thanks!

/integrate

[openjdk]

Going to push as commit 5698f7a.
Since your change was applied there have been 3 commits pushed to the master branch:

• 4a14cba: 8329213: Better validation for com.sun.security.ocsp.useget option
• 9f5464e: 8329353: ResolvedReferencesNotNullTest.java failed with Incorrect resolved references array, quxString should not be archived
• 3f5b75a: 8328541: Remove or update obsolete comment in JRootPane

Your commit was automatically rebased without conflicts.

[openjdk]

@shipilev Pushed as commit 5698f7a.

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

[pengxiaolong]

/backport jdk22u

[openjdk]

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