8338583: NMT: Malloc overhead is calculated incorrectly

Reviewed-by: azafari, yan, gziemski

Author: kirleo2

src/hotspot/share/nmt/mallocHeader.hpp

@@ -127,6 +127,7 @@ class MallocHeader {
 
   inline MallocHeader(size_t size, MemTag mem_tag, uint32_t mst_marker);
 
+  inline static size_t malloc_overhead() { return sizeof(MallocHeader) + sizeof(uint16_t); }
   inline size_t size()  const { return _size; }
   inline MemTag mem_tag() const { return _mem_tag; }
   inline uint32_t mst_marker() const { return _mst_marker; }

src/hotspot/share/nmt/mallocTracker.hpp

@@ -166,7 +166,7 @@ class MallocMemorySnapshot {
   }
 
   inline size_t malloc_overhead() const {
-    return _all_mallocs.count() * sizeof(MallocHeader);
+    return _all_mallocs.count() * MallocHeader::malloc_overhead();
   }
 
   // Total malloc invocation count
@@ -269,7 +269,7 @@ class MallocTracker : AllStatic {
 
   // The overhead that is incurred by switching on NMT (we need, per malloc allocation,
   // space for header and 16-bit footer)
-  static const size_t overhead_per_malloc = sizeof(MallocHeader) + sizeof(uint16_t);
+  static inline size_t overhead_per_malloc() { return MallocHeader::malloc_overhead(); }
 
   // Parameter name convention:
   // memblock :   the beginning address for user data

src/hotspot/share/nmt/memTracker.hpp

@@ -72,7 +72,7 @@ class MemTracker : AllStatic {
 
   // Per-malloc overhead incurred by NMT, depending on the current NMT level
   static size_t overhead_per_malloc() {
-    return enabled() ? MallocTracker::overhead_per_malloc : 0;
+    return enabled() ? MallocTracker::overhead_per_malloc() : 0;
   }
 
   static inline void* record_malloc(void* mem_base, size_t size, MemTag mem_tag,