[GR-54022] Build first-object table and reset card table in compacting GC without an extra pass.

PullRequest: graal/17771

Author: peter-hofer

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

@@ -297,7 +297,7 @@ public UnsignedWord getMaximumFreeAlignedChunksSize() {
         /*
          * Keep chunks ready for allocations in eden and for the survivor to-spaces during young
          * collections (although we might keep too many aligned chunks when large objects in
-         * unallocated chunks are also allocated). We could alternatively return
+         * unaligned chunks are also allocated). We could alternatively return
          * getCurrentHeapCapacity() to have chunks ready during full GCs as well.
          */
         UnsignedWord total = edenSize.add(survivorSize);

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

@@ -190,7 +190,8 @@ public boolean shouldCollectCompletely(boolean followingIncrementalCollection) {
             return false;
         }
 
-        if (minorCountSinceMajorCollection * avgMinorPause.getAverage() >= CONSECUTIVE_MINOR_TO_MAJOR_COLLECTION_PAUSE_TIME_RATIO * avgMajorPause.getPaddedAverage()) {
+        if (!SerialGCOptions.useCompactingOldGen() &&
+                        minorCountSinceMajorCollection * avgMinorPause.getAverage() >= CONSECUTIVE_MINOR_TO_MAJOR_COLLECTION_PAUSE_TIME_RATIO * avgMajorPause.getPaddedAverage()) {
             /*
              * When we do many incremental collections in a row because they reclaim sufficient
              * space, still trigger a complete collection when reaching a cumulative pause time

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

@@ -287,7 +287,7 @@ private void fixupReferencesBeforeCompaction(ChunkReleaser chunkReleaser, Timers
         try {
             AlignedHeapChunk.AlignedHeader aChunk = space.getFirstAlignedHeapChunk();
             while (aChunk.isNonNull()) {
-                ObjectMoveInfo.walkObjects(aChunk, fixupVisitor);
+                ObjectMoveInfo.walkObjectsForFixup(aChunk, fixupVisitor);
                 aChunk = HeapChunk.getNext(aChunk);
             }
         } finally {
@@ -399,18 +399,12 @@ private void compact(Timers timers) {
 
         Timer oldCompactionRememberedSetsTimer = timers.oldCompactionRememberedSets.start();
         try {
+            // Clear the card tables (which currently contain brick tables).
+            // The first-object tables have already been populated.
             chunk = space.getFirstAlignedHeapChunk();
             while (chunk.isNonNull()) {
-                /*
-                 * Clears the card table (which currently contains the brick table) and updates the
-                 * first object table.
-                 *
-                 * GR-54022: we should be able to avoid this pass and build the first object tables
-                 * during planning and reset card tables once we detect that we are finished with a
-                 * chunk during compaction. The remembered set bits are already set after planning.
-                 */
                 if (!AlignedHeapChunk.isEmpty(chunk)) {
-                    RememberedSet.get().enableRememberedSetForChunk(chunk);
+                    RememberedSet.get().clearRememberedSet(chunk);
                 } // empty chunks will be freed or reset before reuse, no need to reinitialize here
 
                 chunk = HeapChunk.getNext(chunk);

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

@@ -25,7 +25,7 @@
 package com.oracle.svm.core.genscavenge;
 
 /**
- * Least squares fitting on a data set to generate an equation y = b + a / x. Uses exponential decay
+ * Least squares fitting on a data set to generate an equation y = a + b / x. Uses exponential decay
  * to assign a higher weight to newly added data points and effectively drop old data points without
  * keeping a history.
  *

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

@@ -451,7 +451,7 @@ private Object copyAlignedObject(Object originalObj) {
             if (SerialGCOptions.useCompactingOldGen() && GCImpl.getGCImpl().isCompleteCollection()) {
                 /*
                  * In a compacting complete collection, the remembered set bit is set already during
-                 * marking and the first object table is built later during compaction.
+                 * marking and the first object table is built later during fix-up.
                  */
             } else {
                 /*

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/ObjectMoveInfo.java

@@ -26,8 +26,6 @@
 
 import static com.oracle.svm.core.Uninterruptible.CALLED_FROM_UNINTERRUPTIBLE_CODE;
 
-import com.oracle.svm.core.util.VMError;
-import jdk.graal.compiler.word.Word;
 import org.graalvm.word.Pointer;
 import org.graalvm.word.UnsignedWord;
 
@@ -37,10 +35,14 @@
 import com.oracle.svm.core.genscavenge.AlignedHeapChunk;
 import com.oracle.svm.core.genscavenge.HeapChunk;
 import com.oracle.svm.core.genscavenge.ObjectHeaderImpl;
+import com.oracle.svm.core.genscavenge.remset.AlignedChunkRememberedSet;
 import com.oracle.svm.core.genscavenge.remset.BrickTable;
+import com.oracle.svm.core.genscavenge.remset.FirstObjectTable;
 import com.oracle.svm.core.hub.LayoutEncoding;
+import com.oracle.svm.core.util.VMError;
 
 import jdk.graal.compiler.api.replacements.Fold;
+import jdk.graal.compiler.word.Word;
 
 /**
  * {@link PlanningVisitor} decides where objects will be moved and uses the methods of this class to
@@ -165,21 +167,46 @@ static boolean useCompressedLayout() {
      * @see AlignedHeapChunk#walkObjects
      */
     @Uninterruptible(reason = CALLED_FROM_UNINTERRUPTIBLE_CODE, mayBeInlined = true)
-    public static void walkObjects(AlignedHeapChunk.AlignedHeader chunkHeader, ObjectFixupVisitor visitor) {
-        Pointer p = AlignedHeapChunk.getObjectsStart(chunkHeader);
+    public static void walkObjectsForFixup(AlignedHeapChunk.AlignedHeader chunk, ObjectFixupVisitor visitor) {
+        FirstObjectTable.initializeTable(AlignedChunkRememberedSet.getFirstObjectTableStart(chunk), AlignedChunkRememberedSet.getFirstObjectTableSize());
+
+        Pointer p = AlignedHeapChunk.getObjectsStart(chunk);
         do {
-            Pointer nextObjSeq = getNextObjectSeqAddress(p);
-            Pointer objSeqEnd = p.add(getObjectSeqSize(p));
-            assert objSeqEnd.belowOrEqual(HeapChunk.getTopPointer(chunkHeader));
+            Pointer objSeq = p;
+            Pointer nextObjSeq = getNextObjectSeqAddress(objSeq);
+            Pointer objSeqNewAddress = getNewAddress(objSeq);
+            AlignedHeapChunk.AlignedHeader objSeqNewChunk = AlignedHeapChunk.getEnclosingChunkFromObjectPointer(objSeqNewAddress);
+            Pointer objSeqEnd = objSeq.add(getObjectSeqSize(objSeq));
+            assert objSeqEnd.belowOrEqual(HeapChunk.getTopPointer(chunk));
             while (p.notEqual(objSeqEnd)) {
                 assert p.belowThan(objSeqEnd);
                 Object obj = p.toObject();
                 UnsignedWord objSize = LayoutEncoding.getSizeFromObjectInlineInGC(obj);
+
+                /*
+                 * Add the object's new location to the first object table of the target chunk. Note
+                 * that we have already encountered that chunk and initialized its table earlier.
+                 *
+                 * Rebuilding the table is also required for swept chunks, where dead objects can
+                 * mean that another object is now the first object in a range.
+                 */
+                Pointer newAddress = objSeqNewAddress.add(p.subtract(objSeq));
+                UnsignedWord offset = newAddress.subtract(AlignedHeapChunk.getObjectsStart(objSeqNewChunk));
+                FirstObjectTable.setTableForObject(AlignedChunkRememberedSet.getFirstObjectTableStart(objSeqNewChunk), offset, offset.add(objSize));
+
                 if (!visitor.visitObjectInline(obj)) {
                     throw VMError.shouldNotReachHereAtRuntime();
                 }
+
                 p = p.add(objSize);
             }
+            if (nextObjSeq.isNonNull() && chunk.getShouldSweepInsteadOfCompact()) {
+                // We will write a filler object here, add the location to the first object table.
+                assert p.belowThan(nextObjSeq);
+                UnsignedWord offset = p.subtract(AlignedHeapChunk.getObjectsStart(chunk));
+                UnsignedWord size = nextObjSeq.subtract(p);
+                FirstObjectTable.setTableForObject(AlignedChunkRememberedSet.getFirstObjectTableStart(chunk), offset, offset.add(size));
+            }
             p = nextObjSeq;
         } while (p.isNonNull());
     }

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/PlanningVisitor.java

@@ -71,7 +71,7 @@ public boolean visitChunk(AlignedHeapChunk.AlignedHeader chunk) {
         UnsignedWord brickIndex = Word.zero();
 
         /* Initialize the move info structure at the chunk's object start location. */
-        ObjectMoveInfo.setNewAddress(objSeq, allocPointer);
+        ObjectMoveInfo.setNewAddress(objSeq, objSeq);
         ObjectMoveInfo.setObjectSeqSize(objSeq, Word.zero());
         ObjectMoveInfo.setNextObjectSeqOffset(objSeq, Word.zero());
 

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/SweepingVisitor.java

@@ -30,6 +30,8 @@
 import org.graalvm.word.UnsignedWord;
 
 import com.oracle.svm.core.config.ConfigurationValues;
+import com.oracle.svm.core.genscavenge.AlignedHeapChunk;
+import com.oracle.svm.core.genscavenge.HeapChunk;
 import com.oracle.svm.core.genscavenge.graal.nodes.FormatArrayNode;
 import com.oracle.svm.core.genscavenge.graal.nodes.FormatObjectNode;
 import com.oracle.svm.core.heap.FillerArray;
@@ -62,12 +64,15 @@ static int arrayBaseOffset() {
 
     @Override
     public boolean visit(Pointer objSeq, UnsignedWord size, Pointer newAddress, Pointer nextObjSeq) {
+        assert objSeq.equal(newAddress);
         if (nextObjSeq.isNonNull()) {
             Pointer gapStart = objSeq.add(size);
-            assert gapStart.belowOrEqual(nextObjSeq);
-            if (gapStart.notEqual(nextObjSeq)) {
-                writeFillerObjectAt(gapStart, nextObjSeq.subtract(gapStart));
-            }
+            assert gapStart.belowThan(nextObjSeq);
+            writeFillerObjectAt(gapStart, nextObjSeq.subtract(gapStart));
+            // Note that we have already added first object table entries for fillers during fixup.
+        } else {
+            AlignedHeapChunk.AlignedHeader chunk = AlignedHeapChunk.getEnclosingChunkFromObjectPointer(objSeq);
+            assert objSeq.add(size).equal(HeapChunk.getTopPointer(chunk));
         }
         return true;
     }

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/remset/AlignedChunkRememberedSet.java

@@ -53,7 +53,7 @@
 import jdk.graal.compiler.replacements.nodes.AssertionNode;
 import jdk.graal.compiler.word.Word;
 
-final class AlignedChunkRememberedSet {
+public final class AlignedChunkRememberedSet {
     private AlignedChunkRememberedSet() {
     }
 
@@ -63,7 +63,7 @@ public static int wordSize() {
     }
 
     @Fold
-    public static UnsignedWord getHeaderSize() {
+    static UnsignedWord getHeaderSize() {
         UnsignedWord headerSize = getFirstObjectTableLimitOffset();
         if (SerialGCOptions.useCompactingOldGen()) {
             // Compaction needs room for a ObjectMoveInfo structure before the first object.
@@ -74,7 +74,7 @@ public static UnsignedWord getHeaderSize() {
     }
 
     @Platforms(Platform.HOSTED_ONLY.class)
-    public static void enableRememberedSet(HostedByteBufferPointer chunk, int chunkPosition, List<ImageHeapObject> objects) {
+    static void enableRememberedSet(HostedByteBufferPointer chunk, int chunkPosition, List<ImageHeapObject> objects) {
         // Completely clean the card table and the first object table.
         CardTable.cleanTable(getCardTableStart(chunk), getCardTableSize());
         FirstObjectTable.initializeTable(getFirstObjectTableStart(chunk), getFirstObjectTableSize());
@@ -94,7 +94,7 @@ public static void enableRememberedSet(HostedByteBufferPointer chunk, int chunkP
 
     @AlwaysInline("GC performance")
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    public static void enableRememberedSetForObject(AlignedHeader chunk, Object obj, UnsignedWord objSize) {
+    static void enableRememberedSetForObject(AlignedHeader chunk, Object obj, UnsignedWord objSize) {
         Pointer fotStart = getFirstObjectTableStart(chunk);
         Pointer objectsStart = AlignedHeapChunk.getObjectsStart(chunk);
 
@@ -107,7 +107,7 @@ public static void enableRememberedSetForObject(AlignedHeader chunk, Object obj,
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    public static void enableRememberedSet(AlignedHeader chunk) {
+    static void enableRememberedSet(AlignedHeader chunk) {
         // Completely clean the card table and the first object table as further objects may be
         // added later on to this chunk.
         CardTable.cleanTable(getCardTableStart(chunk), getCardTableSize());
@@ -124,7 +124,7 @@ public static void enableRememberedSet(AlignedHeader chunk) {
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    public static void clearRememberedSet(AlignedHeader chunk) {
+    static void clearRememberedSet(AlignedHeader chunk) {
         CardTable.cleanTable(getCardTableStart(chunk), getCardTableSize());
     }
 
@@ -133,7 +133,7 @@ public static void clearRememberedSet(AlignedHeader chunk) {
      * the post-write barrier.
      */
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    public static void dirtyCardForObject(Object object, boolean verifyOnly) {
+    static void dirtyCardForObject(Object object, boolean verifyOnly) {
         Pointer objectPointer = Word.objectToUntrackedPointer(object);
         AlignedHeader chunk = AlignedHeapChunk.getEnclosingChunkFromObjectPointer(objectPointer);
         Pointer cardTableStart = getCardTableStart(chunk);
@@ -146,7 +146,7 @@ public static void dirtyCardForObject(Object object, boolean verifyOnly) {
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    public static void walkDirtyObjects(AlignedHeader chunk, UninterruptibleObjectVisitor visitor, boolean clean) {
+    static void walkDirtyObjects(AlignedHeader chunk, UninterruptibleObjectVisitor visitor, boolean clean) {
         Pointer objectsStart = AlignedHeapChunk.getObjectsStart(chunk);
         Pointer objectsLimit = HeapChunk.getTopPointer(chunk);
         UnsignedWord memorySize = objectsLimit.subtract(objectsStart);
@@ -212,7 +212,7 @@ private static void walkObjects(AlignedHeader chunk, Pointer start, Pointer end,
         }
     }
 
-    public static boolean verify(AlignedHeader chunk) {
+    static boolean verify(AlignedHeader chunk) {
         boolean success = true;
         success &= CardTable.verify(getCardTableStart(chunk), getCardTableEnd(chunk), AlignedHeapChunk.getObjectsStart(chunk), HeapChunk.getTopPointer(chunk));
         success &= FirstObjectTable.verify(getFirstObjectTableStart(chunk), AlignedHeapChunk.getObjectsStart(chunk), HeapChunk.getTopPointer(chunk));
@@ -242,7 +242,7 @@ static UnsignedWord getCardTableSize() {
     }
 
     @Fold
-    static UnsignedWord getFirstObjectTableSize() {
+    public static UnsignedWord getFirstObjectTableSize() {
         return getCardTableSize();
     }
 
@@ -294,7 +294,7 @@ private static Pointer getCardTableEnd(AlignedHeader chunk) {
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    private static Pointer getFirstObjectTableStart(AlignedHeader chunk) {
+    public static Pointer getFirstObjectTableStart(AlignedHeader chunk) {
         return getFirstObjectTableStart(HeapChunk.asPointer(chunk));
     }
 

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/remset/BrickTable.java

@@ -40,7 +40,7 @@
 /**
  * Inspired by the .NET CoreCLR GC, the {@link BrickTable} speeds up lookups of new object locations
  * after compaction by acting as a lookup table for {@link ObjectMoveInfo} structures. Each entry
- * stores a pointer to the start of the first such structure for the fraction of the chunk that it
+ * stores the offset of the start of the first such structure for the fraction of the chunk that it
  * covers. It borrows the memory of a chunk's {@link CardTable}.
  */
 public final class BrickTable {