8365823: Revert storing abstract and interface Klasses to non-class metaspace #27295

coleenp · 2025-09-15T13:28:45Z

This change removes the optimization to not store abstract and interface Klass metadata to non-class metaspace. Now all Klass metadata is in the Klass metaspace. This is simpler and less bug prone, and didn't help with the limitation of classes that can be stored in class metaspace materially.
Tested with tier1-4.

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Issue

JDK-8365823: Revert storing abstract and interface Klasses to non-class metaspace (Enhancement - P3)

Reviewers

Aleksey Shipilev (@shipilev - Reviewer) Review applies to fe44431f
Vladimir Kozlov (@vnkozlov - Reviewer)
Thomas Stuefe (@tstuefe - Reviewer) Review applies to fe44431f

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…etaspace

coleenp · 2025-09-15T13:29:37Z

/label assign @shipilev
to review.

bridgekeeper · 2025-09-15T13:30:42Z

👋 Welcome back coleenp! 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 · 2025-09-15T13:32:20Z

@coleenp 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:

8365823: Revert storing abstract and interface Klasses to non-class metaspace

Reviewed-by: kvn, shade, stuefe

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 86 new commits pushed to the master branch:

6e4e966: 8365792: GenShen: assertion "Generations aren't reconciled"
e4cb86d: 8367473: Shenandoah: Make the detailed evacuation metrics a runtime diagnostic option
4be4826: 8367450: Shenandoah: Log the composition of the collection set
... and 83 more: https://git.openjdk.org/jdk/compare/850f904a84186b514a9b79fd4625b4651e73149b...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 · 2025-09-15T13:33:59Z

@coleenp
The label assign is not a valid label.
The label @shipilev is not a valid label.
These labels are valid:

graal
serviceability
hotspot
hotspot-compiler
ide-support
i18n
shenandoah
jdk
javadoc
security
hotspot-runtime
jmx
build
nio
client
core-libs
compiler
net
hotspot-gc
hotspot-jfr

openjdk · 2025-09-15T13:34:17Z

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

graal
hotspot

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 · 2025-09-15T13:38:27Z

Webrevs

shipilev

First pass comments below.

Also, I looked at original change, and I wonder if we want to revert other changes as well. It looks to me they are fairly innocuous, TBH, so I have no strong opinion about them.

~~Changing final -> abstract in InvokerBytecodeGenerator: ad10493?diff=unified#diff-3b05b61400e7766115409b3f508d839fb51e450423822252ab2e18543427c764L249-R249~~ Reverted already with JDK-8341649.
JFR: ad10493?diff=unified#diff-d58d6d9783cb29084a15c42ecd7f59860a48be8bcfd9be0ee15a9d50209b576fR1-R160
Test: ad10493?diff=unified#diff-00138acd973f46c5f91674e5388ee82d2e7ed1b788ed551f34120cc761d228b7L1-R166

src/hotspot/share/oops/klass.cpp

src/hotspot/share/memory/metaspace.cpp

liach · 2025-09-15T14:13:51Z

Re InvokerBytecodeGenerator: it was rolled back almost immediately after the original patch due to performance regressions.

Co-authored-by: Aleksey Shipilëv <shipilev@amazon.de>

coleenp · 2025-09-15T14:34:10Z

The JFR changes were a slight refactoring, so I don't think they need to be changed back. The ClassFileParser.is_abstract() function is now unused. Well spoltted.

shipilev

This looks good to me, I have a few more questions:

shipilev · 2025-09-15T14:56:45Z

src/hotspot/share/memory/allocation.cpp

                                 MetaspaceObj::Type type, TRAPS) throw() {
  // Klass has its own operator new
  assert(type != ClassType, "class has its own operator new");
-  return Metaspace::allocate(loader_data, word_size, type, /*use_class_space*/ false, THREAD);


Question: now that ArrayKlass and InstanceKlass do not have ::new, the assert above is still valid? I am guessing all these inherit Klass::new?

Yes, all Klass allocation should call Klass::operator new(). Klass is derived from Metadata that's derived from MetaspaceObj. The Klass operator new hides the one in MetaspaceObj.

src/hotspot/share/ci/ciKlass.hpp

vnkozlov

Good.

This is not 1-to-1 back-out of #19157 . I assume it is because there were several additional follow up fixes.

Will 25u backport be the same?

coleenp · 2025-09-17T17:33:46Z

Yes, this wasn't just a backout. I stayed away from the JFR code refactoring, and there were other fixes for hidden classes that are already in JDK 25. And we added then backported a diagnostic flag, that this change removes.

coleenp · 2025-09-17T17:34:31Z

Yes, this change should backport cleanly to JDK 25 pending approval.
Thanks for reviewing Aleksey and Vladimir.

tstuefe

This looks good. In hindsight kind of scary that there are no tests to change back. But all Metaspace tests sit either on a layer below Metaspace::allocate or test class loading, which sits above this layer.

Some tests that check expected memory levels in class space and non-class metaspace could now run into problems, since the ratio between these numbers should shift (total consumption should be about identical). Maybe not. We'll see it when we see it.

src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/HotSpotMetaspaceConstantImpl.java

mgronlun

Commit: "Revert JFR changes from JDK-8338526 also." looks good.

Thanks

…on jvmci. Reran jvmci tests.

vnkozlov

Still good.

coleenp · 2025-09-19T11:51:51Z

Thanks Vladimir for re-reviewing.
/integrate

openjdk · 2025-09-19T11:54:35Z

Going to push as commit fa00b24.
Since your change was applied there have been 99 commits pushed to the master branch:

2bff417: 8367759: G1: Move G1UpdateRegionLivenessAndSelectForRebuildTask into its own file
1b9a116: 8367782: VerifyJarEntryName.java: Fix modifyJarEntryName to operate on bytes and re-introduce verifySignatureEntryName
65aea48: 8367859: Remove nio exception gensrc
... and 96 more: https://git.openjdk.org/jdk/compare/850f904a84186b514a9b79fd4625b4651e73149b...master

Your commit was automatically rebased without conflicts.

openjdk · 2025-09-19T11:54:42Z

@coleenp Pushed as commit fa00b24.

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

coleenp added 2 commits September 12, 2025 17:01

8365823: Revert storing abstract and interface Klasses to non-class m…

ec610f4

…etaspace

8365823: Revert storing abstract and interface Klasses to non-class m…

864e938

…etaspace

openjdk bot added graal graal-dev@openjdk.org hotspot hotspot-dev@openjdk.org rfr Pull request is ready for review labels Sep 15, 2025

shipilev reviewed Sep 15, 2025

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src/hotspot/share/oops/klass.cpp Show resolved Hide resolved

src/hotspot/share/memory/metaspace.cpp Outdated Show resolved Hide resolved

src/hotspot/share/memory/metaspace.cpp Outdated Show resolved Hide resolved

coleenp and others added 3 commits September 15, 2025 14:30

Restore comment.

48d0c6f

Update src/hotspot/share/memory/metaspace.cpp

2471bf5

Co-authored-by: Aleksey Shipilëv <shipilev@amazon.de>

Update src/hotspot/share/memory/metaspace.cpp

097c6b3

Co-authored-by: Aleksey Shipilëv <shipilev@amazon.de>

Remove CFP.is_abstract().

fe44431

shipilev approved these changes Sep 15, 2025

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vnkozlov approved these changes Sep 17, 2025

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tstuefe approved these changes Sep 18, 2025

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src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/HotSpotMetaspaceConstantImpl.java Show resolved Hide resolved

Revert JFR changes from JDK-8338526 also.

c333b8a

openjdk bot removed the ready Pull request is ready to be integrated label Sep 18, 2025

mgronlun reviewed Sep 18, 2025

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Some limited additional cleanup to HotSpotMetaspaceConstantImpl.java …

f1d08d6

…on jvmci. Reran jvmci tests.

vnkozlov approved these changes Sep 18, 2025

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openjdk bot added the ready Pull request is ready to be integrated label Sep 18, 2025

openjdk bot added the integrated Pull request has been integrated label Sep 19, 2025

openjdk bot closed this Sep 19, 2025

openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Sep 19, 2025

coleenp deleted the undo-klass branch September 19, 2025 11:59

8365823: Revert storing abstract and interface Klasses to non-class metaspace #27295

8365823: Revert storing abstract and interface Klasses to non-class metaspace #27295

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