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

zhengyu123 · 2021-08-17T18:32:54Z

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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Issue

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

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Roman Kennke (@rkennke - Reviewer) ⚠️ Review applies to 98eedbd
Aleksey Shipilev (@shipilev - Reviewer) ⚠️ Review applies to 98eedbd

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bridgekeeper · 2021-08-17T18:33:02Z

👋 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 · 2021-08-17T18:34:53Z

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

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mlbridge · 2021-08-17T18:39:36Z

Webrevs

rkennke

Looks good to me!

openjdk · 2021-08-19T12:11:02Z

@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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shipilev

Looks fine, modulo a few suggestions.

shipilev · 2021-08-25T12:00:28Z

src/hotspot/share/gc/shenandoah/shenandoahMark.cpp

        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>


Suggested change

template <class T, bool CANCELLABLE,StringDedupMode STRING_DEDUP>

template <class T, bool CANCELLABLE, StringDedupMode STRING_DEDUP>

shipilev · 2021-08-25T12:04:11Z

src/hotspot/share/gc/shenandoah/shenandoahMark.inline.hpp

@@ -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);


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.

openjdk · 2021-08-25T12:09:05Z

@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

zhengyu123 · 2021-08-25T16:17:52Z

/integrate

openjdk · 2021-08-25T16:18:25Z

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

… into JDK-8267188-string-intern

openjdk · 2021-08-25T17:39:20Z

⚠️ @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).

zhengyu123 · 2021-08-25T20:14:44Z

/integrate

openjdk · 2021-08-25T20:16:31Z

Going to push as commit 7212561.

openjdk · 2021-08-25T20:16:41Z

@zhengyu123 Pushed as commit 7212561.

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

Zhengyu Gu added 4 commits August 17, 2021 08:32

v0

3ffc4e1

Merge branch 'master' into JDK-8267188-string-intern

fe2f8d2

v0

f689f0d

fix format

98eedbd

openjdk bot added the rfr Pull request is ready for review label Aug 17, 2021

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

rkennke approved these changes Aug 19, 2021

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openjdk bot added the ready Pull request is ready to be integrated label Aug 19, 2021

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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

Aleksey's comments

18e59bd

Zhengyu Gu added 2 commits August 25, 2021 13:35

Merge and fix conflicts

1faf31f

Merge branch 'JDK-8267188-string-intern' of github.com:zhengyu123/jdk…

a0a8b7d

… into JDK-8267188-string-intern

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

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

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	template <class T, bool CANCELLABLE,StringDedupMode STRING_DEDUP>
	template <class T, bool CANCELLABLE, StringDedupMode STRING_DEDUP>

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

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

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