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8272725: G1: add documentation on needs_remset_update_t vs bool #5188

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@albertnetymk albertnetymk commented Aug 19, 2021

Simple type change in struct G1HeapRegionAttr.

Test: hotspot_gc


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  • JDK-8272725: G1: add documentation on needs_remset_update_t vs bool

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@bridgekeeper bridgekeeper bot commented Aug 19, 2021

👋 Welcome back ayang! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

@openjdk openjdk bot added the rfr label Aug 19, 2021
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@openjdk openjdk bot commented Aug 19, 2021

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

  • hotspot-gc

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

@openjdk openjdk bot added the hotspot-gc label Aug 19, 2021
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@mlbridge mlbridge bot commented Aug 19, 2021

Webrevs

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@tschatzl tschatzl commented Aug 20, 2021

The use of uint8_t in this case is intentional to have control of the size of the table, keeping it small and access time fairly small to minimize cache pollution. The size of bool is not defined in C++ after all. This could "waste" a lot of (cache) space.

When G1HeapRegionAttr has been introduced there has been a related performance issue with SPARC where this mattered which is gone now - I do not remember x64/x86 being particularly affected, but idk impact on the "new" ARM64 platform.

Anyway, it seems better to me to make sure that in this case we keep the size of the heap region attr controlled. It's being accessed for literally every reference multiple times.

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@kimbarrett kimbarrett commented Aug 20, 2021

A comment describing the rationale for the specific types might have been nice. I think there might have been something there in the past, but maybe removed with SPARC support. But I agree that this is a place where we really do care about low-level control.

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@albertnetymk albertnetymk commented Aug 20, 2021

I see; thank you for the explanation. How about I pivot this ticket/PR to adding some comment on the use of uint8_t?

@albertnetymk albertnetymk changed the title 8272725: G1: replace type needs_remset_update_t with bool 8272725: G1: add documentation on needs_remset_update_t vs bool Aug 20, 2021
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@tschatzl tschatzl left a comment

Lgtm.

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@openjdk openjdk bot commented Aug 23, 2021

@albertnetymk 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:

8272725: G1: add documentation on needs_remset_update_t vs bool

Reviewed-by: tschatzl, iwalulya

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 40 new commits pushed to the master branch:

  • 7454306: 8272526: Cleanup ThreadStateTransition class
  • 0597cde: 8221360: Eliminate Shared_DirtyCardQ_lock
  • 928b972: 8271930: Simplify end_card calculation in G1BlockOffsetTablePart::verify
  • 7f80683: 8272783: Epsilon: Refactor tests to improve performance
  • 22ef4f0: 5015261: NPE may be thrown if JDesktopIcon is set to null on a JInternalFrame
  • 9bc0232: 8269223: -Xcheck:jni WARNINGs working with fonts on Linux
  • 2ff4c01: 8271600: C2: CheckCastPP which should closely follow Allocate is sunk of a loop
  • ad92033: 8272736: [JVMCI] Add API for reading and writing JVMCI thread locals
  • 709b591: 8272553: several hotspot runtime/CommandLine tests don't check exit code
  • 1884072: 8265253: javac -Xdoclint:all gives "no comment" warning for code that can't be commented
  • ... and 30 more: https://git.openjdk.java.net/jdk/compare/73da66ffb707abf6dc38368a12e337d52597de25...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.

@openjdk openjdk bot added the ready label Aug 23, 2021
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@albertnetymk albertnetymk commented Aug 24, 2021

Thanks for the review.

/integrate

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@openjdk openjdk bot commented Aug 24, 2021

Going to push as commit 6e0328f.
Since your change was applied there have been 42 commits pushed to the master branch:

  • 2309b7d: 8253178: Replace LinkedList Impl in net.http.FilterFactory
  • 94f5e44: 8271258: @param with non-ascii variable names produces incorrect results
  • 7454306: 8272526: Cleanup ThreadStateTransition class
  • 0597cde: 8221360: Eliminate Shared_DirtyCardQ_lock
  • 928b972: 8271930: Simplify end_card calculation in G1BlockOffsetTablePart::verify
  • 7f80683: 8272783: Epsilon: Refactor tests to improve performance
  • 22ef4f0: 5015261: NPE may be thrown if JDesktopIcon is set to null on a JInternalFrame
  • 9bc0232: 8269223: -Xcheck:jni WARNINGs working with fonts on Linux
  • 2ff4c01: 8271600: C2: CheckCastPP which should closely follow Allocate is sunk of a loop
  • ad92033: 8272736: [JVMCI] Add API for reading and writing JVMCI thread locals
  • ... and 32 more: https://git.openjdk.java.net/jdk/compare/73da66ffb707abf6dc38368a12e337d52597de25...master

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot closed this Aug 24, 2021
@openjdk openjdk bot added integrated and removed ready rfr labels Aug 24, 2021
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@openjdk openjdk bot commented Aug 24, 2021

@albertnetymk Pushed as commit 6e0328f.

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

@albertnetymk albertnetymk deleted the boolean branch Aug 24, 2021
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