From c5bc94eef6466d3396b943c247576b6ac7efee4f Mon Sep 17 00:00:00 2001
From: Peter Hofer <peter.hofer@oracle.com>
Date: Tue, 7 May 2024 10:19:22 +0200
Subject: [PATCH] Revert "Disable sweeping due to low fragmentation."

This reverts commit d5c351c1c450dac36eea6ea636c2173efe4a52ed.
---
 .../compacting/PlanningVisitor.java           | 25 +++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/PlanningVisitor.java b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/PlanningVisitor.java
index 4473f77c3ed9e..2a778347c3787 100644
--- a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/PlanningVisitor.java
+++ b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/PlanningVisitor.java
@@ -33,6 +33,7 @@
 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.HeapParameters;
 import com.oracle.svm.core.genscavenge.ObjectHeaderImpl;
 import com.oracle.svm.core.genscavenge.Space;
 import com.oracle.svm.core.genscavenge.remset.BrickTable;
@@ -47,6 +48,8 @@
  * or overwrite dead objects.
  */
 public final class PlanningVisitor implements AlignedHeapChunk.Visitor {
+    private static final ResetNewLocationsForSweepingVisitor RESET_NEW_LOCATIONS_FOR_SWEEPING_VISITOR = new ResetNewLocationsForSweepingVisitor();
+
     private AlignedHeapChunk.AlignedHeader allocChunk;
     private Pointer allocPointer;
 
@@ -62,7 +65,9 @@ public boolean visitChunk(AlignedHeapChunk.AlignedHeader chunk) {
         Pointer objSeq = AlignedHeapChunk.getObjectsStart(chunk);
         UnsignedWord gapSize = WordFactory.zero();
         UnsignedWord objSeqSize = WordFactory.zero();
+
         UnsignedWord brickIndex = WordFactory.zero();
+        UnsignedWord totalUnusedBytes = WordFactory.zero();
 
         /* Initialize the move info structure at the chunk's object start location. */
         ObjectMoveInfo.setNewAddress(objSeq, allocPointer);
@@ -107,6 +112,7 @@ public boolean visitChunk(AlignedHeapChunk.AlignedHeader chunk) {
                     objSeq = p;
                     ObjectMoveInfo.setNextObjectSeqOffset(objSeq, WordFactory.zero());
 
+                    totalUnusedBytes = totalUnusedBytes.add(gapSize);
                     gapSize = WordFactory.zero();
                 }
 
@@ -141,6 +147,12 @@ public boolean visitChunk(AlignedHeapChunk.AlignedHeader chunk) {
             ObjectMoveInfo.setObjectSeqSize(objSeq, objSeqSize);
         }
 
+        totalUnusedBytes = totalUnusedBytes.add(HeapChunk.getEndOffset(chunk).subtract(HeapChunk.getTopOffset(chunk)));
+        if (!sweeping && shouldSweepBasedOnFragmentation(totalUnusedBytes)) {
+            sweeping = true;
+            chunk.setShouldSweepInsteadOfCompact(true);
+            ObjectMoveInfo.visit(chunk, RESET_NEW_LOCATIONS_FOR_SWEEPING_VISITOR);
+        }
         if (sweeping) {
             /*
              * Continue allocating for compaction after the swept memory. Note that this forfeits
@@ -173,8 +185,21 @@ private Pointer allocate(UnsignedWord size) {
         return p;
     }
 
+    private static boolean shouldSweepBasedOnFragmentation(UnsignedWord unusedBytes) {
+        UnsignedWord limit = HeapParameters.getAlignedHeapChunkSize().unsignedDivide(16);
+        return unusedBytes.aboveOrEqual(0) && unusedBytes.belowThan(limit);
+    }
+
     public void init(Space space) {
         allocChunk = space.getFirstAlignedHeapChunk();
         allocPointer = AlignedHeapChunk.getObjectsStart(allocChunk);
     }
+
+    private static class ResetNewLocationsForSweepingVisitor implements ObjectMoveInfo.Visitor {
+        @Override
+        public boolean visit(Pointer objSeq, UnsignedWord size, Pointer newAddress, Pointer nextObjSeq) {
+            ObjectMoveInfo.setNewAddress(objSeq, objSeq);
+            return true;
+        }
+    }
 }