8370520: GenShen: Track and report on promotion failures #27962

earthling-amzn · 2025-10-23T22:46:00Z

Keep track of promotion failures. Report the number of failures and total number of bytes that could not be promoted. These changes were hoisted out of #27632.

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JDK-8370520: GenShen: Track and report on promotion failures (Enhancement - P4)

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Francesco Andreuzzi (@fandreuz - Author) Review applies to 1e80c2a9
Aleksey Shipilev (@shipilev - Reviewer)

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…romotion

…tion

bridgekeeper · 2025-10-23T22:48:01Z

👋 Welcome back wkemper! 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 · 2025-10-23T22:48:44Z

@earthling-amzn 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:

8370520: GenShen: Track and report on promotion failures

Reviewed-by: shade, fandreuzzi

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 30 new commits pushed to the master branch:

c25f352: 8341735: Rewrite the build/AbsPathsInImage.java test to not load the entire file at once
ebf9c5b: 8370250: Locale should mention the behavior for duplicate subtags
583ff20: 8370251: C2: Inlining checks for method handle intrinsics are too strict
... and 27 more: https://git.openjdk.org/jdk/compare/62f11cd4070f21ad82eebbb5319bdbbf4e13f9cf...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.

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openjdk · 2025-10-23T22:49:39Z

@earthling-amzn 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.

mlbridge · 2025-10-23T22:53:18Z

Webrevs

shipilev

Looks fine, with a nit.

shipilev · 2025-10-24T14:24:22Z

src/hotspot/share/gc/shenandoah/shenandoahOldGeneration.hpp

+  size_t get_promotion_failed_count() const { return _promotion_failure_count; }
+  size_t get_promotion_failed_words() const { return _promotion_failure_words; }


Shouldn't these be AtomicAccess::load(...)-s? I don't think you need memory ordering, but if you are doing the updates atomically somewhere, it stands to reason you want to match the loads with atomics as well.

kdnilsen · 2025-10-24T20:29:41Z

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

-
  const size_t gc_id = heap->control_thread()->get_gc_id();

+  AtomicAccess::inc(&_promotion_failure_count);


Just noticing that in the next code block, we acquire the heap->lock(). Could we just use that same heap lock to protect adjustments to _promotion_failure_count and _promotion_failure_words and then we would need to use Atomic access operations?

Should probably be ok to read these variables without lock. We're only logging these results when evacuation is no longer happening. Right?

Now that we have this new log message, can we get rid of the "promotion failure messages" for individual objects?

We only take the heap lock there conditionally when we haven't yet "squelched" the log message. We could change this to a log_debug(gc, plab) level message. The message is still useful when trying to understand the history and context for a how a thread became unable to promote. I'm not completely convinced there aren't still cases where a thread should be able to promote but can't for some (unknown) reason.

If we made this a log_debug(gc, plab) message, we could make the whole block of code conditional on the log level being enabled.

I'd be comfortable with that.

And only do the work for the message if the log level is enabled.

earthling-amzn · 2025-10-27T20:57:03Z

/integrate

openjdk · 2025-10-27T20:58:35Z

Going to push as commit 70aa367.
Since your change was applied there have been 32 commits pushed to the master branch:

e4e457f: 8366871: (javac) legacy.properties seems to be an obsolete file
8151251: 8370370: Add still more cases to WorstCaseTests
c25f352: 8341735: Rewrite the build/AbsPathsInImage.java test to not load the entire file at once
... and 29 more: https://git.openjdk.org/jdk/compare/62f11cd4070f21ad82eebbb5319bdbbf4e13f9cf...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-10-27T20:58:49Z

@earthling-amzn Pushed as commit 70aa367.

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

earthling-amzn added 2 commits October 23, 2025 14:49

Track and report number of objects and their total size that failed p…

0e1da60

…romotion

Actually log number of objects and their total size that failed promo…

1e80c2a

…tion

openjdk bot added hotspot-gc hotspot-gc-dev@openjdk.org shenandoah shenandoah-dev@openjdk.org labels Oct 23, 2025

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fandreuz approved these changes Oct 24, 2025

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shipilev approved these changes Oct 24, 2025

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Use atomic load when reading promotion failure counters

9213b8c

openjdk bot removed the ready Pull request is ready to be integrated label Oct 24, 2025

kdnilsen reviewed Oct 24, 2025

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shipilev approved these changes Oct 24, 2025

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openjdk bot added the ready Pull request is ready to be integrated label Oct 24, 2025

Change log level of detailed promotion failure message

a86e34c

And only do the work for the message if the log level is enabled.

openjdk bot removed the ready Pull request is ready to be integrated label Oct 24, 2025

earthling-amzn added 2 commits October 24, 2025 16:42

New method can be const

dac7a31

Fix build

96357b4

shipilev approved these changes Oct 27, 2025

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openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Oct 27, 2025

		size_t get_promotion_failed_count() const { return _promotion_failure_count; }
		size_t get_promotion_failed_words() const { return _promotion_failure_words; }


		const size_t gc_id = heap->control_thread()->get_gc_id();

		AtomicAccess::inc(&_promotion_failure_count);

8370520: GenShen: Track and report on promotion failures #27962

8370520: GenShen: Track and report on promotion failures #27962

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