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8316297: GenShen: Degenerated GCs fail to make progress #324

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kdnilsen
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@kdnilsen kdnilsen commented Sep 14, 2023

A recent change to the implementation of ShenandoahYoungGeneration::available() resulted in a budgeting shortfall during degenerated GC. The problem is that we degenerate after mutator allocations fail, at which time young available memory is in very short supply. The change to available() caused us to only see the mutator budget, which has been depleted. This resulted in a very high probability that degenerated GC would fail to make progress, forcing degenerated GC to upgrade to full GC.

This PR makes the Collector reserve memory visible to the function that computes evacuation budgets, thereby increasing the likelihood of a successful degenerated cycle and obviating the need for a Full GC.


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  • Change must not contain extraneous whitespace
  • Commit message must refer to an issue
  • Change must be properly reviewed (1 review required, with at least 1 Committer)

Issue

  • JDK-8316297: GenShen: Degenerated GCs fail to make progress (Bug - P3)

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Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/shenandoah.git pull/324/head:pull/324
$ git checkout pull/324

Update a local copy of the PR:
$ git checkout pull/324
$ git pull https://git.openjdk.org/shenandoah.git pull/324/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 324

View PR using the GUI difftool:
$ git pr show -t 324

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/shenandoah/pull/324.diff

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bridgekeeper bot commented Sep 14, 2023

👋 Welcome back kdnilsen! 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 Pull request is ready for review label Sep 14, 2023
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mlbridge bot commented Sep 14, 2023

Webrevs

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openjdk bot commented Sep 14, 2023

@kdnilsen 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:

8316297: GenShen: Degenerated GCs fail to make progress

Reviewed-by: wkemper

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 no new commits pushed to the master branch. If another commit should be pushed before you perform the /integrate command, your PR will be automatically rebased. If you prefer to avoid any potential 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 Pull request is ready to be integrated label Sep 14, 2023
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/integrate

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openjdk bot commented Sep 15, 2023

Going to push as commit 88365d1.

@openjdk openjdk bot added the integrated Pull request has been integrated label Sep 15, 2023
@openjdk openjdk bot closed this Sep 15, 2023
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Sep 15, 2023
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openjdk bot commented Sep 15, 2023

@kdnilsen Pushed as commit 88365d1.

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

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