8343218: Add option to disable allocating interface and abstract classes in non-class metaspace

[coleenp]

This change introduces a diagnostic flag to disable the change to allocate interface and abstract Klass metadata in the non-class metaspace. Testing for JDK 25 has completed with this feature in place, but there may be cases where we should disable this. A future change will be to remove this code.
Tested with tier1-4 with the flag off, and 1-4 with the flag on.

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8343218: Add option to disable allocating interface and abstract classes in non-class metaspace (Sub-task - P2)

Reviewers

• Thomas Stuefe (@tstuefe - Reviewer) Review applies to 79399d5d
• Aleksey Shipilev (@shipilev - Reviewer)
• David Holmes (@dholmes-ora - Reviewer) Review applies to 79399d5d
• Vladimir Kozlov (@vnkozlov - Reviewer)
• Yudi Zheng (@mur47x111 - Committer)

Reviewing

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[bridgekeeper]

👋 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]

@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:

8343218: Add option to disable allocating interface and abstract classes in non-class metaspace

Reviewed-by: shade, kvn, yzheng, stuefe, dholmes

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 55 new commits pushed to the master branch:

• 05f8a6f: 8360559: Optimize Math.sinh for x86 64 bit platforms
• b5f450a: 8364226: Better ECDSASignature Memory Management
• 6c52b73: 8209992: Align SSLSocket and SSLEngine Javadocs
• ... and 52 more: https://git.openjdk.org/jdk/compare/b9f7caed775e86e71f7d37789cb196fb1444ef12...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]

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

• hotspot

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]

Webrevs

• 01: Full - Incremental (b9e2e166)
• 00: Full (79399d5d)

[tstuefe]

Good

[shipilev]

Generally looks fine. Stylistic/process note, though: the RFE synopsis still reads that we are disabling the optimization. We are not doing it here, we are only guarding it with a flag. Either submit a new RFE or rename this bug?

[coleenp]

Okay, I fixed the titles and will discuss with @vnkozlov and @TobiHartmann next week about getting this into JDK 25 or not.

[dholmes-ora]

Looks fine for an added safety-guard. Thanks

[mur47x111]

Could you please apply the following patch?

diff --git a/src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/HotSpotMetaspaceConstantImpl.java b/src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/HotSpotMetaspaceConstantImpl.java
index 55d5492c2f8..fd08361f682 100644
--- a/src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/HotSpotMetaspaceConstantImpl.java
+++ b/src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/HotSpotMetaspaceConstantImpl.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -95,7 +95,7 @@ public boolean isCompressible() {
     }
 
     private boolean canBeStoredInCompressibleMetaSpace() {
-        if (metaspaceObject instanceof HotSpotResolvedJavaType t && !t.isArray()) {
+        if (!HotSpotVMConfig.config().useClassMetaspaceForAllClasses && metaspaceObject instanceof HotSpotResolvedJavaType t && !t.isArray()) {
             // As of JDK-8338526, interface and abstract types are not stored
             // in compressible metaspace.
             return !t.isInterface() && !t.isAbstract();
diff --git a/src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/HotSpotVMConfig.java b/src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/HotSpotVMConfig.java
index bc2e121fe90..449b315e467 100644
--- a/src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/HotSpotVMConfig.java
+++ b/src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/HotSpotVMConfig.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2011, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -67,6 +67,8 @@ static String getHostArchitectureName() {
 
     final boolean useCompressedOops = getFlag("UseCompressedOops", Boolean.class);
 
+    final boolean useClassMetaspaceForAllClasses = getFlag("UseClassMetaspaceForAllClasses", Boolean.class);
+
     final int objectAlignment = getFlag("ObjectAlignmentInBytes", Integer.class);
 
     final int klassOffsetInBytes = getFieldValue("CompilerToVM::Data::oopDesc_klass_offset_in_bytes", Integer.class, "int");

[vnkozlov]

Good.

[mur47x111]

LGTM

[vnkozlov]

Re-approved.

[shipilev]

Let's go!

[coleenp]

GHA looks clean
/integrate

[openjdk]

Going to push as commit da3a5da.
Since your change was applied there have been 57 commits pushed to the master branch:

• 0d0d93e: 8210765: Remove finalize method in CStrike.java
• d1e362e: 8363889: Update sun.print.PrintJob2D to use Disposer
• 05f8a6f: 8360559: Optimize Math.sinh for x86 64 bit platforms
• ... and 54 more: https://git.openjdk.org/jdk/compare/b9f7caed775e86e71f7d37789cb196fb1444ef12...master

Your commit was automatically rebased without conflicts.

[openjdk]

@coleenp Pushed as commit da3a5da.

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

[coleenp]

Thank you Aleksey,Thomas, David, Vladimir and Yudi.