[GR-18214] Compacting garbage collection (non-default).

substratevm/CHANGELOG.md

@@ -23,6 +23,7 @@ This changelog summarizes major changes to GraalVM Native Image.
 * (GR-43837) `--report-unsupported-elements-at-runtime` is now enabled by default and the option is deprecated.
 * (GR-53359) Provide the `.debug_gdb_scripts` section that triggers auto-loading of `svmhelpers.py` in GDB. Remove single and double quotes from `ClassLoader.nameAndId` in the debuginfo.
 * (GR-47365) Include dynamic proxy metadata in the reflection metadata with the syntax `"type": { "proxy": [<interface list>] }`. This allows members of proxy classes to be accessed reflectively. `proxy-config.json` is now deprecated but will still be honored.
+* (GR-18214) In-place compacting garbage collection for the Serial GC old generation with `-H:+CompactingOldGen`.
 
 ## GraalVM for JDK 22 (Internal Version 24.0.0)
 * (GR-48304) Red Hat added support for the JFR event ThreadAllocationStatistics.

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/AdaptiveCollectionPolicy.java

@@ -155,11 +155,12 @@ public String getName() {
     public boolean shouldCollectCompletely(boolean followingIncrementalCollection) { // should_{attempt_scavenge,full_GC}
         guaranteeSizeParametersInitialized();
 
-        if (!followingIncrementalCollection && shouldCollectYoungGenSeparately(true)) {
+        if (!followingIncrementalCollection && shouldCollectYoungGenSeparately(!SerialGCOptions.useCompactingOldGen())) {
             /*
-             * Default to always doing an incremental collection first because we expect most of the
-             * objects in the young generation to be garbage, and we can reuse their leftover chunks
-             * for copying the live objects in the old generation with fewer allocations.
+             * With a copying collector, default to always doing an incremental collection first
+             * because we expect most of the objects in the young generation to be garbage, and we
+             * can reuse their leftover chunks for copying the live objects in the old generation
+             * with fewer allocations. With a compacting collector, there is no benefit.
              */
             return false;
         }

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/AlignedHeapChunk.java

@@ -24,6 +24,7 @@
  */
 package com.oracle.svm.core.genscavenge;
 
+import org.graalvm.nativeimage.c.struct.RawField;
 import org.graalvm.nativeimage.c.struct.RawStructure;
 import org.graalvm.word.Pointer;
 import org.graalvm.word.UnsignedWord;
@@ -33,6 +34,7 @@
 import com.oracle.svm.core.Uninterruptible;
 import com.oracle.svm.core.genscavenge.remset.RememberedSet;
 import com.oracle.svm.core.heap.ObjectVisitor;
+import com.oracle.svm.core.heap.RestrictHeapAccess;
 import com.oracle.svm.core.util.PointerUtils;
 
 import jdk.graal.compiler.api.directives.GraalDirectives;
@@ -50,17 +52,14 @@
  * Most allocation within a AlignedHeapChunk is via fast-path allocation snippets, but a slow-path
  * allocation method is available.
  * <p>
- * Objects in a AlignedHeapChunk have to be promoted by copying from their current HeapChunk to a
- * destination HeapChunk.
- * <p>
- * An AlignedHeapChunk is laid out:
+ * An AlignedHeapChunk is laid out as follows:
  *
  * <pre>
- * +===============+-------+--------+----------------------+
- * | AlignedHeader | Card  | First  | Object ...           |
- * | Fields        | Table | Object |                      |
- * |               |       | Table  |                      |
- * +===============+-------+--------+----------------------+
+ * +===============+-------+--------+-----------------+-----------------+
+ * | AlignedHeader | Card  | First  | Initial Object  | Object ...      |
+ * | Fields        | Table | Object | Move Info (only |                 |
+ * |               |       | Table  | Compacting GC)  |                 |
+ * +===============+-------+--------+-----------------+-----------------+
  * </pre>
  *
  * The size of both the CardTable and the FirstObjectTable depends on the used {@link RememberedSet}
@@ -78,15 +77,22 @@ private AlignedHeapChunk() { // all static
      */
     @RawStructure
     public interface AlignedHeader extends HeapChunk.Header<AlignedHeader> {
+        @RawField
+        boolean getShouldSweepInsteadOfCompact();
+
+        @RawField
+        void setShouldSweepInsteadOfCompact(boolean value);
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     public static void initialize(AlignedHeader chunk, UnsignedWord chunkSize) {
+        assert chunkSize.equal(HeapParameters.getAlignedHeapChunkSize()) : "expecting all aligned chunks to be the same size";
         HeapChunk.initialize(chunk, AlignedHeapChunk.getObjectsStart(chunk), chunkSize);
+        chunk.setShouldSweepInsteadOfCompact(false);
     }
 
     public static void reset(AlignedHeader chunk) {
-        HeapChunk.initialize(chunk, AlignedHeapChunk.getObjectsStart(chunk), HeapChunk.getEndOffset(chunk));
+        initialize(chunk, HeapChunk.getEndOffset(chunk));
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
@@ -98,6 +104,10 @@ public static Pointer getObjectsEnd(AlignedHeader that) {
         return HeapChunk.getEndPointer(that);
     }
 
+    public static boolean isEmpty(AlignedHeader that) {
+        return HeapChunk.getTopOffset(that).equal(getObjectsStartOffset());
+    }
+
     /** Allocate uninitialized memory within this AlignedHeapChunk. */
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     static Pointer allocateMemory(AlignedHeader that, UnsignedWord size) {
@@ -146,4 +156,20 @@ static boolean walkObjectsFromInline(AlignedHeader that, Pointer start, ObjectVi
     public static UnsignedWord getObjectsStartOffset() {
         return RememberedSet.get().getHeaderSizeOfAlignedChunk();
     }
+
+    @Fold
+    public static UnsignedWord getUsableSizeForObjects() {
+        return HeapParameters.getAlignedHeapChunkSize().subtract(getObjectsStartOffset());
+    }
+
+    public interface Visitor {
+        /**
+         * Visit an {@link AlignedHeapChunk}.
+         *
+         * @param chunk The {@link AlignedHeapChunk} to be visited.
+         * @return {@code true} if visiting should continue, {@code false} if visiting should stop.
+         */
+        @RestrictHeapAccess(access = RestrictHeapAccess.Access.NO_ALLOCATION, reason = "Must not allocate while visiting the heap.")
+        boolean visitChunk(AlignedHeapChunk.AlignedHeader chunk);
+    }
 }

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/CollectionPolicy.java

@@ -44,7 +44,7 @@ public interface CollectionPolicy {
     static String getInitialPolicyName() {
         if (SubstrateOptions.UseEpsilonGC.getValue()) {
             return "NeverCollect";
-        } else if (!SubstrateOptions.useRememberedSet()) {
+        } else if (!SerialGCOptions.useRememberedSet()) {
             return "OnlyCompletely";
         }
         String name = SerialGCOptions.InitialCollectionPolicy.getValue();