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

[Yudi Zheng]

On Thu, 31 Jul 2025 18:13:30 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> 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.

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");

-------------

PR Comment: https://git.openjdk.org/jdk/pull/26579#issuecomment-3148692596