Don't forget the free page counter when switching to free page list

community/io/src/main/java/org/neo4j/io/pagecache/impl/muninn/FreePage.java

@@ -19,6 +19,8 @@
  */
 package org.neo4j.io.pagecache.impl.muninn;
 
+import java.util.concurrent.atomic.AtomicInteger;
+
 /**
  * A free page in the MuninnPageCache.freelist.
  *
@@ -28,16 +30,27 @@ final class FreePage
 {
     final long pageRef;
     int count;
-    FreePage next;
+    Object next;
 
     FreePage( long pageRef )
     {
         this.pageRef = pageRef;
     }
 
-    void setNext( FreePage next )
+    void setNext( Object next )
     {
         this.next = next;
-        this.count = next == null ? 1 : 1 + next.count;
+        if ( next == null )
+        {
+            count = 1;
+        }
+        else if ( next.getClass() == AtomicInteger.class )
+        {
+            count = 1 + ((AtomicInteger) next).get();
+        }
+        else
+        {
+            this.count = 1 + ((FreePage) next).count;
+        }
     }
 }

community/io/src/main/java/org/neo4j/io/pagecache/impl/muninn/MuninnPageCache.java

@@ -225,7 +225,7 @@ public MuninnPageCache(
 
         this.pages = new PageList( maxPages, cachePageSize, memoryManager, new SwapperSet(), victimPage );
 
-        UnsafeUtil.putObjectVolatile( this, freelistOffset, new AtomicInteger() );
+        setFreelistHead( new AtomicInteger() );
     }
 
     private static void verifyHacks()
@@ -760,10 +760,9 @@ private boolean compareAndSetFreelistHead( Object expected, Object update )
                 this, freelistOffset, expected, update );
     }
 
-    private Object getAndSetFreelistHead( Object newFreelistHead )
+    private void setFreelistHead( Object newFreelistHead )
     {
-        return UnsafeUtil.getAndSetObject(
-                this, freelistOffset, newFreelistHead );
+        UnsafeUtil.putObjectVolatile( this, freelistOffset, newFreelistHead );
     }
 
     /**
@@ -789,7 +788,7 @@ void continuouslySweepPages()
 
         // The last thing we do, is signalling the shutdown of the cache via
         // the freelist. This signal is looked out for in grabFreePage.
-        getAndSetFreelistHead( shutdownSignal );
+        setFreelistHead( shutdownSignal );
     }
 
     private int parkUntilEvictionRequired( int keepFree )
@@ -886,7 +885,11 @@ private void addFreePageToFreelist( long pageRef )
         do
         {
             current = getFreelistHead();
-            freePage.setNext( current instanceof FreePage ? (FreePage) current : null );
+            if ( current instanceof AtomicInteger && ((AtomicInteger) current).get() >= pages.getPageCount() )
+            {
+                current = null;
+            }
+            freePage.setNext( current );
         }
         while ( !compareAndSetFreelistHead( current, freePage ) );
     }