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8267188: gc/stringdedup/TestStringDeduplicationInterned.java fails with Shenandoah #5151

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zhengyu123
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@zhengyu123 zhengyu123 commented Aug 17, 2021

Shenandoah currently enqueues deduplication candidates when marks object gray.

However, it can not do so when it scans roots, as it can potentially result lock rank inversion between stack watermark lock and dedup request buffer lock.

As the result, it can not enqueue as many as candidates as it should be able to, I believe JDK-8271834 is due to the same problem. I purpose we switch to enqueue candidates when we mark object black.

We are still not able to enqueue all candidates, only when they have displaced headers or have monitor inflating in progress. Upstream is working on removing displaced headers, we should revisit the logic afterward, or we can choose to deduplicate all string regardless their ages.

Test:

  • hotspot_gc_shenandoah
  • tier1 with -XX:+UseShenandoahGC and -XX:+UseStringDeduplication

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  • JDK-8267188: gc/stringdedup/TestStringDeduplicationInterned.java fails with Shenandoah

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bridgekeeper bot commented Aug 17, 2021

👋 Welcome back zgu! 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 Aug 17, 2021
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openjdk bot commented Aug 17, 2021

@zhengyu123 The following labels will be automatically applied to this pull request:

  • hotspot-gc
  • shenandoah

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

@openjdk openjdk bot added hotspot-gc hotspot-gc-dev@openjdk.org shenandoah shenandoah-dev@openjdk.org labels Aug 17, 2021
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mlbridge bot commented Aug 17, 2021

Webrevs

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Looks good to me!

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openjdk bot commented Aug 19, 2021

@zhengyu123 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:

8267188: gc/stringdedup/TestStringDeduplicationInterned.java fails with Shenandoah

Reviewed-by: rkennke, shade

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@openjdk openjdk bot added the ready Pull request is ready to be integrated label Aug 19, 2021
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Looks fine, modulo a few suggestions.

break;
}
}
}

template <class T, bool CANCELLABLE>
void ShenandoahMark::mark_loop_work(T* cl, ShenandoahLiveData* live_data, uint worker_id, TaskTerminator *terminator) {
template <class T, bool CANCELLABLE,StringDedupMode STRING_DEDUP>
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Suggested change
template <class T, bool CANCELLABLE,StringDedupMode STRING_DEDUP>
template <class T, bool CANCELLABLE, StringDedupMode STRING_DEDUP>

@@ -54,6 +68,7 @@ void ShenandoahMark::do_task(ShenandoahObjToScanQueue* q, T* cl, ShenandoahLiveD

if (task->is_not_chunked()) {
if (obj->is_instance()) {
dedup_string<STRING_DEDUP>(obj, req);
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I do wonder if it is faster to first let the closure process the outbound references, and then do dedup for the object? This way, parallel GC workers can do work while we are calling dedup_string here. This is one of the reasons why old code did dedup check after the queue push. In other words, move this call at the end of this block.

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openjdk bot commented Aug 25, 2021

@zhengyu123 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 JDK-8267188-string-intern
git fetch https://git.openjdk.java.net/jdk master
git merge FETCH_HEAD
# resolve conflicts and follow the instructions given by git merge
git commit -m "Merge master"
git push

@openjdk openjdk bot added merge-conflict Pull request has merge conflict with target branch and removed ready Pull request is ready to be integrated labels Aug 25, 2021
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/integrate

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openjdk bot commented Aug 25, 2021

@zhengyu123 This PR has not yet been marked as ready for integration.

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openjdk bot commented Aug 25, 2021

⚠️ @zhengyu123 This pull request contains merges that bring in commits not present in the target repository. Since this is not a "merge style" pull request, these changes will be squashed when this pull request in integrated. If this is your intention, then please ignore this message. If you want to preserve the commit structure, you must change the title of this pull request to Merge <project>:<branch> where <project> is the name of another project in the OpenJDK organization (for example Merge jdk:master).

@openjdk openjdk bot added ready Pull request is ready to be integrated and removed merge-conflict Pull request has merge conflict with target branch labels Aug 25, 2021
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/integrate

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openjdk bot commented Aug 25, 2021

Going to push as commit 7212561.

@openjdk openjdk bot closed this Aug 25, 2021
@openjdk openjdk bot added integrated Pull request has been integrated and removed ready Pull request is ready to be integrated labels Aug 25, 2021
@openjdk openjdk bot removed the rfr Pull request is ready for review label Aug 25, 2021
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@zhengyu123 Pushed as commit 7212561.

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

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