--- old/src/hotspot/share/gc/z/zPage.inline.hpp	2019-07-26 14:17:29.925359321 +0200
+++ new/src/hotspot/share/gc/z/zPage.inline.hpp	2019-07-26 14:17:29.629349606 +0200
@@ -294,6 +294,9 @@
     return false;
   }
 
+  // Clear memory
+  ZUtils::zero(addr, size);
+
   _top = new_top;
 
   // Success
@@ -314,6 +317,9 @@
       return false;
     }
 
+    // Clear memory
+    ZUtils::zero(addr, size);
+
     const uintptr_t prev_top = Atomic::cmpxchg(new_top, &_top, old_top);
     if (prev_top == old_top) {
       // Success