8380526: G1: Remove "last young" use for the Prepare Mixed GC by tschatzl · Pull Request #30336 · openjdk/jdk

tschatzl · 2026-03-20T12:08:37Z

Hi all,

please review this change that removes the "Last Young" nomenclature for the "Prepare Mixed" gc. The additional name just confuses.

Testing: gha

Thanks,
Thomas

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Issue

JDK-8380526: G1: Remove "last young" use for the Prepare Mixed GC (Enhancement - P4)

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

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$ git fetch https://git.openjdk.org/jdk.git pull/30336/head:pull/30336
$ git checkout pull/30336

Update a local copy of the PR:
$ git checkout pull/30336
$ git pull https://git.openjdk.org/jdk.git pull/30336/head

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$ git pr checkout 30336

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Hi all, please review this change that makes `G1CollectorState` get the concurrent cycle state directly from `G1ConcurrentMark[Thread]` instead of, in multiple places set the current state separately. This is kind of error-prone, as https://bugs.openjdk.org/browse/JDK-8378952, which this change also implicitly fixes, shows. Other notes: * I expanded the `ServiceState` in `G1ConcurrentMarkThread` instead of adding a separate variable holding whether this is a full or undo concurrent cycle. This avoids potential races between those two too. * be more consistent with `Concurrent Cycle` (the whole thing) vs. `Concurrent Marking` throughout * renamed the "clear bitmap" state to "reset for next cycle` since clearing the bitmap is only one part of that subphase of the concurrent cycle. * made concurrent cycle state queries always go through `G1CollectorState` * fixed `in_something` to `is_in_something` for `G1CollectorState` as per style guideline * extended evacuation failure injection to include reset for next cycle for the `G1GCAllocationFailureALotDuringConcMark` value; I thought it does not hurt and it already covered both mark and rebuild or scrub Testing: tier1-5 Thanks, Thomas

Hi all, please review this change that changes `G1CollectorState` to use a single state variable for GC pause phasing instead of multiple bools. This reduces clutter checking validity of these flags, and imo makes the state very explicit with the usual advantages in readability. This is based on PR#30144, so please review that one first. Testing: tier1-5, gha Thanks, Thomas

…ause_type()` because it covers all types of pauses now

Hi all, please review this change that removes the "Last Young" nomenclature for the "Prepare Mixed" gc. The additional name just confuses. Testing: gha Thanks, Thomas

bridgekeeper · 2026-03-20T12:09:40Z

👋 Welcome back tschatzl! A progress list of the required criteria for merging this PR into pr/30330 will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2026-03-20T12:10:30Z

@tschatzl 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:

8380526: G1: Remove "last young" use for the Prepare Mixed GC

Reviewed-by: ayang, 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 12 new commits pushed to the master branch:

90eebaa: 8380516: HotSpot has two different ways of making Windows strtok_s available as strtok_r
fd2ef1b: 8380665: (dc) java/nio/channels/DatagramChannel/SendReceiveMaxSize.java could also test the loopback interface
cc29010: 8380664: Remove stub entries used in x86-32
... and 9 more: https://git.openjdk.org/jdk/compare/60a141c3b5c0dcbf1cccfc55dc5b6a457b6a9a12...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 · 2026-03-20T12:12:06Z

@tschatzl 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.

mlbridge · 2026-03-20T12:15:17Z

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openjdk-notifier · 2026-03-23T15:53:40Z

The parent pull request that this pull request depends on has now been integrated and the target branch of this pull request has been updated. This means that changes from the dependent pull request can start to show up as belonging to this pull request, which may be confusing for reviewers. To remedy this situation, simply merge the latest changes from the new target branch into this pull request by running commands similar to these in the local repository for your personal fork:

git checkout submit/8380526-remove-last-young
git fetch https://git.openjdk.org/jdk.git master
git merge FETCH_HEAD
# if there are conflicts, follow the instructions given by git merge
git commit -m "Merge master"
git push

openjdk · 2026-03-23T15:55:39Z

@tschatzl this pull request can not be integrated into master due to one or more merge conflicts. To resolve these merge conflicts and update this pull request you can run the following commands in the local repository for your personal fork:

git checkout submit/8380526-remove-last-young
git fetch https://git.openjdk.org/jdk.git master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

* reorder elements in Pause type to correspond to typical execution (i.e. Prepare Mixed last)

albertnetymk · 2026-03-24T10:49:10Z

src/hotspot/share/gc/g1/g1CollectorState.hpp


  // Phase getters
-  bool is_in_young_only_phase() const { return _phase == Phase::YoungNormal || _phase == Phase::YoungConcurrentStart || _phase == Phase::YoungLastYoung; }
+  bool is_in_young_only_phase() const { return _phase == Phase::YoungNormal || _phase == Phase::YoungConcurrentStart || _phase == Phase::YoungPrepareMixed; }


Maybe the impl can be broken into multiple lines.

_phase <= Phase::YoungPrepareMixed; or do we deliberately choose not to rely on the enum ordering?

Maybe the impl can be broken into multiple lines

I was going to do this in PR#30399

_phase <= Phase::YoungPrepareMixed; or do we deliberately choose not to rely on the enum ordering?

Deliberate, after changing it to explicit values in some earlier change.

tschatzl · 2026-03-24T15:34:48Z

Thanks @albertnetymk @walulyai for your reviews
/integrate

openjdk · 2026-03-24T15:36:18Z

Going to push as commit d0d85cd.
Since your change was applied there have been 12 commits pushed to the master branch:

90eebaa: 8380516: HotSpot has two different ways of making Windows strtok_s available as strtok_r
fd2ef1b: 8380665: (dc) java/nio/channels/DatagramChannel/SendReceiveMaxSize.java could also test the loopback interface
cc29010: 8380664: Remove stub entries used in x86-32
... and 9 more: https://git.openjdk.org/jdk/compare/60a141c3b5c0dcbf1cccfc55dc5b6a457b6a9a12...master

Your commit was automatically rebased without conflicts.

openjdk · 2026-03-24T15:36:36Z

@tschatzl Pushed as commit d0d85cd.

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

Thomas Schatzl and others added 10 commits March 10, 2026 09:32

Merge branch 'master' into 8080226-replace-bools-with-state-variables

8eb7575

* walulyai review

1d6fcd0

* rename of G1CollectorState::young_gc_pause_type() to just `::gc_p…

db36b98

…ause_type()` because it covers all types of pauses now

* enum to enum class

478f31b

* fix documentation

f76cf08

* initial version

91c1642

* fix include order

f98703a

8380526

bd301bf

Hi all, please review this change that removes the "Last Young" nomenclature for the "Prepare Mixed" gc. The additional name just confuses. Testing: gha Thanks, Thomas

openjdk bot changed the title ~~8380526~~ 8380526: G1: Remove "last young" use for the Prepare Mixed GC Mar 20, 2026

openjdk bot added the hotspot-gc hotspot-gc-dev@openjdk.org label Mar 20, 2026

openjdk bot added the rfr Pull request is ready for review label Mar 20, 2026

albertnetymk approved these changes Mar 20, 2026

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openjdk-notifier bot changed the base branch from pr/30330 to master March 23, 2026 15:53

openjdk bot added the merge-conflict Pull request has merge conflict with target branch label Mar 23, 2026

Merge branch 'master' into 8380526-remove-last-young

af31d0b

openjdk bot removed the merge-conflict Pull request has merge conflict with target branch label Mar 23, 2026

tschatzl added 2 commits March 24, 2026 10:00

* one more "last-young"

a6838e6

* reorder elements in Pause type to correspond to typical execution (i.e. Prepare Mixed last)

* naming

7e579e6

albertnetymk approved these changes Mar 24, 2026

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openjdk bot added the ready Pull request is ready to be integrated label Mar 24, 2026

walulyai approved these changes Mar 24, 2026

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openjdk bot mentioned this pull request Mar 24, 2026

8380541: G1: Add g1CollectorState.inline.hpp file #30399

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tschatzl deleted the submit/8380526-remove-last-young branch March 24, 2026 15:45

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8380526: G1: Remove "last young" use for the Prepare Mixed GC#30336

8380526: G1: Remove "last young" use for the Prepare Mixed GC#30336
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