8370325: G1: Disallow GC for TLAB allocation

[tschatzl]

Hi all,

please review this change to the object allocation path to only allow direct allocation after failing TLAB allocation doing GCs.

Currently, when allocating an object, G1 (or actually any collector) first allocates from TLABs, then allocates from outside TLABs.

When G1 can't find space for a TLAB in the current region, it passes on control to G1CollectedHeap::attempt_allocation[_slow] that first tries to allocate that memory using a new region, or if that fails, do a GC. Potential allocation outside TLABs that would follow TLAB-allocation does the same.

G1's behavior to do a GC during failed TLAB allocation is problematic for the UseGCOverheadLimit functionality (https://bugs.openjdk.org/browse/JDK-8212084): if the GC overhead limit triggers in a TLAB allocation, it returns null for that TLAB allocation.
Control will be passed to outside-tlab allocation as described above. Since the garbage collections for TLAB allocations did free some memory (but because of exceeded gc overhead we returned null for the TLAB allocation), that allocation/collection for this outside-tlab allocation will succeed and return non-null to the mutator, effectively swallowing the information that GC overhead has been exceeded.

I split this out from the UseGCOverheadLimit change because I thought it is somewhat standalone, but I can merge it.

Testing: tier1-5, performance neutral after some tests

Hth,
Thomas

---

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Issue

• JDK-8370325: G1: Disallow GC for TLAB allocation (Enhancement - P4)

Reviewers

• Ivan Walulya (@walulyai - Reviewer)
• Albert Mingkun Yang (@albertnetymk - Reviewer)

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8370325: G1: Disallow GC for TLAB allocation

Reviewed-by: iwalulya, ayang

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At the time when this comment was updated there had been 56 new commits pushed to the master branch:

• ffcb158: 8320677: Printer tests use invalid '@run main/manual=yesno
• 3e20a93: 8370156: Fix jpackage IconTest
• be18e7e: 8064922: [macos] Test javax/swing/JTabbedPane/4624207/bug4624207.java fails
• ... and 53 more: https://git.openjdk.org/jdk/compare/c8679713402186b24608fa4c91397b6a4fd5ebf3...master

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• 02: Full - Incremental (23057abe)
• 01: Full - Incremental (83de6f25)
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[albertnetymk]

Maybe the title can be revised a bit -- sth like "G1: Disallow GC for TLAB allocation".

[tschatzl]

Maybe the title can be revised a bit -- sth like "G1: Disallow GC for TLAB allocation".

Much better, thanks!

[tschatzl]

Thanks @albertnetymk @walulyai for your reviews
/integrate

[openjdk]

Going to push as commit 027aea9.
Since your change was applied there have been 56 commits pushed to the master branch:

• ffcb158: 8320677: Printer tests use invalid '@run main/manual=yesno
• 3e20a93: 8370156: Fix jpackage IconTest
• be18e7e: 8064922: [macos] Test javax/swing/JTabbedPane/4624207/bug4624207.java fails
• ... and 53 more: https://git.openjdk.org/jdk/compare/c8679713402186b24608fa4c91397b6a4fd5ebf3...master

Your commit was automatically rebased without conflicts.

[openjdk]

@tschatzl Pushed as commit 027aea9.

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