8372684: G1: Missing load_acquire() in G1 allocation path

[tschatzl]

Hi all,

please review this change that changes some volatile atomics to the new Atomic construct, fixing some issue with missing load_acquire when allocating in G1HeapRegion::par_allocate().

That load_acquire seems necessary as when setting a new allocation region, there needs to be synchronization about the contents (top/end) of the heap region. Otherwise the allocating thread might get old/previous top values sent from the corresponding storestore (I changed to a release_store() in G1AllocRegion::update_alloc_region().

Similar issue exists in the handling of the retained regions.

I also made the G1AllocatorRegion::_dummy_region Atomic; synchronization is necessary for a single release_store at initialization. No further synchronization is necessary (just using relaxed loads) as its contents are never changed afterwards.

Performance testing, both manually on targeted benchmarks and a few general ones without differences.

Testing: gha, tier1-3

Thanks,
Thomas

---

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Issue

• JDK-8372684: G1: Missing load_acquire() in G1 allocation path (Bug - P2)

Reviewers

• Kim Barrett (@kimbarrett - Reviewer)
• Stefan Johansson (@kstefanj - Reviewer)

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8372684: G1: Missing load_acquire() in G1 allocation path

Reviewed-by: kbarrett, sjohanss

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At the time when this comment was updated there had been 38 new commits pushed to the master branch:

• 293fec7: 8372461: [IR Framework] Multiple test failures after JDK-8371789
• ca96366: 8372528: Unify atomic exchange and compare exchange
• 81b26ba: 8372685: C2 SuperWord: wrong requires in test after JDK-8371146
• ... and 35 more: https://git.openjdk.org/jdk/compare/c028369dcb0a677541b89117b0800125bc7c6c33...master

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[kimbarrett]

Looks good.

[tschatzl]

Thanks @kimbarrett @kstefanj for your reviews

/integrate

[openjdk]

Going to push as commit ef5e744.
Since your change was applied there have been 40 commits pushed to the master branch:

• 969eb1c: 8365861: test/jdk/sun/security/pkcs11/Provider/ tests skipped without SkippedException
• a6bc9b3: 8372588: [asan] serviceability/sa/TestJmapCore.java and TestJmapCoreMetaspace.java fail after recent improvements
• 293fec7: 8372461: [IR Framework] Multiple test failures after JDK-8371789
• ... and 37 more: https://git.openjdk.org/jdk/compare/c028369dcb0a677541b89117b0800125bc7c6c33...master

Your commit was automatically rebased without conflicts.

[openjdk]

@tschatzl Pushed as commit ef5e744.

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