--- old/src/hotspot/share/gc/z/zVirtualMemory.cpp	2020-08-28 12:23:56.121695286 +0200
+++ new/src/hotspot/share/gc/z/zVirtualMemory.cpp	2020-08-28 12:23:56.005694779 +0200
@@ -24,6 +24,7 @@
 #include "precompiled.hpp"
 #include "gc/shared/gcLogPrecious.hpp"
 #include "gc/z/zAddressSpaceLimit.hpp"
+#include "gc/z/zAddress.hpp"
 #include "gc/z/zGlobals.hpp"
 #include "gc/z/zVirtualMemory.inline.hpp"
 #include "services/memTracker.hpp"
@@ -43,8 +44,14 @@
 
   // Reserve address space
   if (!reserve(max_capacity)) {
-    log_error_pd(gc)("Failed to reserve enough address space for Java heap");
-    return;
+    // try to reserve with a reduced number of address bits
+    log_info_p(gc, init)("Re-configuring ZAddressBits to " SIZE_FORMAT ", allocation with " SIZE_FORMAT " failed", _address_bits_seen, ZAddressBits);
+    ZAddressBits = _address_bits_seen;
+    ZAddress::initialize();
+    if (!reserve(max_capacity)) {
+      log_error_pd(gc)("Failed to reserve enough address space for Java heap");
+      return;
+    }
   }
 
   // Initialize OS specific parts