[GR-42666] Report correct generation capacities in SerialGCPerfData.

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

@@ -219,7 +219,7 @@ public UnsignedWord getMaximumYoungGenerationSize() {
     public UnsignedWord getCurrentHeapCapacity() {
         assert VMOperation.isGCInProgress() : "use only during GC";
         guaranteeSizeParametersInitialized();
-        return edenSize.add(survivorSize.multiply(2)).add(oldSize);
+        return edenSize.add(survivorSize).add(oldSize);
     }
 
     @Override
@@ -229,6 +229,19 @@ public UnsignedWord getSurvivorSpacesCapacity() {
         return survivorSize;
     }
 
+    @Override
+    @Uninterruptible(reason = "Ensure reading a consistent value.")
+    public UnsignedWord getYoungGenerationCapacity() {
+        guaranteeSizeParametersInitialized();
+        return edenSize.add(survivorSize);
+    }
+
+    @Override
+    public UnsignedWord getOldGenerationCapacity() {
+        guaranteeSizeParametersInitialized();
+        return oldSize;
+    }
+
     @Override
     public UnsignedWord getMaximumFreeAlignedChunksSize() {
         assert VMOperation.isGCInProgress() : "use only during GC";

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

@@ -151,6 +151,21 @@ public UnsignedWord getSurvivorSpacesCapacity() {
             return WordFactory.zero();
         }
 
+        @Override
+        public UnsignedWord getYoungGenerationCapacity() {
+            return getMaximumYoungGenerationSize();
+        }
+
+        @Override
+        public UnsignedWord getOldGenerationCapacity() {
+            UnsignedWord heapCapacity = getCurrentHeapCapacity();
+            UnsignedWord youngCapacity = getYoungGenerationCapacity();
+            if (youngCapacity.aboveThan(heapCapacity)) {
+                return WordFactory.zero(); // should never happen unless options change in between
+            }
+            return heapCapacity.subtract(youngCapacity);
+        }
+
         @Override
         public final UnsignedWord getMaximumFreeAlignedChunksSize() {
             return getMaximumYoungGenerationSize();

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

@@ -158,6 +158,12 @@ static boolean shouldCollectYoungGenSeparately(boolean defaultValue) {
      */
     UnsignedWord getSurvivorSpacesCapacity();
 
+    /** The capacity of the young generation, comprising the eden and survivor spaces. */
+    UnsignedWord getYoungGenerationCapacity();
+
+    /** The capacity of the old generation. */
+    UnsignedWord getOldGenerationCapacity();
+
     /**
      * The maximum number of bytes that should be kept readily available for allocation or copying
      * during collections.

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/jvmstat/SerialGCPerfData.java

@@ -28,6 +28,7 @@
 import org.graalvm.nativeimage.Platform;
 import org.graalvm.nativeimage.Platforms;
 
+import com.oracle.svm.core.genscavenge.CollectionPolicy;
 import com.oracle.svm.core.genscavenge.GCAccounting;
 import com.oracle.svm.core.genscavenge.GCImpl;
 import com.oracle.svm.core.genscavenge.HeapAccounting;
@@ -94,24 +95,26 @@ public void allocate() {
     public void update() {
         GCAccounting accounting = GCImpl.getGCImpl().getAccounting();
         HeapAccounting heapAccounting = HeapImpl.getHeapImpl().getAccounting();
+        CollectionPolicy policy = GCImpl.getPolicy();
+        policy.ensureSizeParametersInitialized();
 
-        long maxNewSize = GCImpl.getPolicy().getMaximumYoungGenerationSize().rawValue();
+        long maxNewSize = policy.getMaximumYoungGenerationSize().rawValue();
         youngCollector.invocations.setValue(accounting.getIncrementalCollectionCount());
         youngCollector.time.setValue(accounting.getIncrementalCollectionTotalNanos());
 
-        youngGen.capacity.setValue(heapAccounting.getYoungUsedBytes().rawValue());
+        youngGen.capacity.setValue(policy.getYoungGenerationCapacity().rawValue());
         youngGen.maxCapacity.setValue(maxNewSize);
 
         youngGen.spaces[0].used.setValue(heapAccounting.getEdenUsedBytes().rawValue());
         for (int i = 1; i < youngGen.spaces.length; i++) {
             youngGen.spaces[i].used.setValue(heapAccounting.getSurvivorSpaceAfterChunkBytes(i - 1).rawValue());
         }
 
-        long maxOldSize = GCImpl.getPolicy().getMaximumHeapSize().rawValue() - maxNewSize;
+        long maxOldSize = policy.getMaximumHeapSize().rawValue() - maxNewSize;
         oldCollector.invocations.setValue(accounting.getCompleteCollectionCount());
         oldCollector.time.setValue(accounting.getCompleteCollectionTotalNanos());
 
-        oldGen.capacity.setValue(accounting.getOldGenerationAfterChunkBytes().rawValue());
+        oldGen.capacity.setValue(policy.getOldGenerationCapacity().rawValue());
         oldGen.maxCapacity.setValue(maxOldSize);
 
         oldGen.spaces[0].used.setValue(accounting.getOldGenerationAfterChunkBytes().rawValue());