8237198: ZGC: Share multi-mapping code in ZBackingFile

Reviewed-by: stefank, eosterlund, smonteith

src/hotspot/os/bsd/gc/z/zBackingFile_bsd.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -89,6 +89,10 @@ bool ZBackingFile::is_initialized() const {
   return _initialized;
 }
 
+void ZBackingFile::warn_commit_limits(size_t max) const {
+  // Does nothing
+}
+
 size_t ZBackingFile::size() const {
   return _size;
 }

src/hotspot/os/bsd/gc/z/zBackingFile_bsd.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2019, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -47,6 +47,8 @@ class ZBackingFile {
 
   bool is_initialized() const;
 
+  void warn_commit_limits(size_t max) const;
+
   size_t size() const;
 
   size_t commit(size_t offset, size_t length);