8267894: Skip work for empty regions in G1 Full GC

[walulyai]

Hi all,

Please review this change to skip doing work on regions that were empty at the beginning of the Full GC in phases that execute on a per-region basis.

Testing: Tier 1-3.

---

Progress

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Issue

• JDK-8267894: Skip work for empty regions in G1 Full GC

Reviewers

• Stefan Johansson (@kstefanj - Reviewer)
• Thomas Schatzl (@tschatzl - Reviewer)

Reviewing

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[openjdk]

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

• hotspot-gc

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[mlbridge]

Webrevs

• 01: Full - Incremental (f196ea48)
• 00: Full (ea9582fb)

[kstefanj]

I think the change looks good in general, but maybe we should go with a "named" state for free regions. Either we change the name for the default value in G1FullGCHeapRegionAttr or we add a new state that we set for free regions. What do you think?

[walulyai]

I think the change looks good in general, but maybe we should go with a "named" state for free regions. Either we change the name for the default value in G1FullGCHeapRegionAttr or we add a new state that we set for free regions. What do you think?

AFAIK, changing the default value to "Free" instead of "Invalid" would suffice, however, need to clarify on how that is handled by assert(!is_invalid(obj), "not initialized yet"); which indicate some sort of transition from "Invalid" to "initialized".

[kstefanj]

I think the text "not initialized yet" is a bit wrong. We should never call is_skip_marking() for objects in "Invalid" regions, because there can't be any objects there. Same goes for "Free" regions. So I would change the assert to something like:

assert(!is_free(obj), "Should be no objects in free regions."); 

I agree that changing the default value should work. One benefit of using a new state could be to have a difference between free and not committed regions. But not sure it is worth the effort right now.

[kstefanj]

Looks good to me.

[openjdk]

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

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After integration, the commit message for the final commit will be:

8267894: Skip work for empty regions in G1 Full GC

Reviewed-by: sjohanss, 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 72 new commits pushed to the master branch:

• b7f75c0: 8271142: package help is not displayed for missing X11/extensions/Xrandr.h
• e8a289e: 8272609: Add string deduplication support to SerialGC
• b690f29: 8269687: pauth_aarch64.hpp include name is incorrect
• f77a1a1: 8272472: StackGuardPages test doesn't build with glibc 2.34
• 04a806e: 8270344: Session resumption errors
• d85560e: 8267161: Write automated test case for JDK-4479161
• 1ea437a: 8272720: Fix the implementation of loop unrolling heuristic with LoopPercentProfileLimit
• 86add21: 8223923: C2: Missing interference with mismatched unsafe accesses
• c701f6e: 8272739: Misformatted error message in EventHandlerCreator
• fb1dfc6: 8267185: Add string deduplication support to ParallelGC
• ... and 62 more: https://git.openjdk.java.net/jdk/compare/d06d0b9e9d9d27aa549455f19b9803752431bcbb...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.

[walulyai]

Thanks @kstefanj and @tschatzl for the reviews

/integrate

[openjdk]

Going to push as commit d542745.
Since your change was applied there have been 73 commits pushed to the master branch:

• 741f58c: 8272417: ZGC: fastdebug build crashes when printing ClassLoaderData
• b7f75c0: 8271142: package help is not displayed for missing X11/extensions/Xrandr.h
• e8a289e: 8272609: Add string deduplication support to SerialGC
• b690f29: 8269687: pauth_aarch64.hpp include name is incorrect
• f77a1a1: 8272472: StackGuardPages test doesn't build with glibc 2.34
• 04a806e: 8270344: Session resumption errors
• d85560e: 8267161: Write automated test case for JDK-4479161
• 1ea437a: 8272720: Fix the implementation of loop unrolling heuristic with LoopPercentProfileLimit
• 86add21: 8223923: C2: Missing interference with mismatched unsafe accesses
• c701f6e: 8272739: Misformatted error message in EventHandlerCreator
• ... and 63 more: https://git.openjdk.java.net/jdk/compare/d06d0b9e9d9d27aa549455f19b9803752431bcbb...master

Your commit was automatically rebased without conflicts.

[openjdk]

@walulyai Pushed as commit d542745.

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