Bug 1046477 (part 2) - Don't measure the heap size of static atoms. r=froydnj.

xpcom/ds/nsAtomTable.cpp

@@ -106,7 +106,7 @@ public:
   // for |#ifdef NS_BUILD_REFCNT_LOGGING| access to reference count
   nsrefcnt GetRefCount() { return mRefCnt; }
 
-  size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const;
+  size_t SizeOfIncludingThis(MallocSizeOf aMallocSizeOf);
 };
 
 /**
@@ -470,11 +470,19 @@ AtomImpl::IsStaticAtom()
 }
 
 size_t
-AtomImpl::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
+AtomImpl::SizeOfIncludingThis(MallocSizeOf aMallocSizeOf)
 {
-  return aMallocSizeOf(this) +
-         nsStringBuffer::FromData(mString)->SizeOfIncludingThisIfUnshared(
+  size_t n = aMallocSizeOf(this);
+
+  // Don't measure static atoms. Nb: here "static" means "permanent", and while
+  // it's not guaranteed that permanent atoms are actually stored in static
+  // data, it is very likely. And we don't want to call |aMallocSizeOf| on
+  // static data, so we err on the side of caution.
+  if (!IsStaticAtom()) {
+    n += nsStringBuffer::FromData(mString)->SizeOfIncludingThisIfUnshared(
            aMallocSizeOf);
+  }
+  return n;
 }
 
 //----------------------------------------------------------------------
@@ -488,15 +496,6 @@ SizeOfAtomTableEntryExcludingThis(PLDHashEntryHdr* aHdr,
   return entry->mAtom->SizeOfIncludingThis(aMallocSizeOf);
 }
 
-static size_t
-SizeOfStaticAtomTableEntryExcludingThis(const nsAString& aKey,
-                                        nsIAtom* const& aData,
-                                        MallocSizeOf aMallocSizeOf,
-                                        void* aArg)
-{
-  return aKey.SizeOfExcludingThisIfUnshared(aMallocSizeOf);
-}
-
 void
 NS_SizeOfAtomTablesIncludingThis(MallocSizeOf aMallocSizeOf,
                                  size_t* aMain, size_t* aStatic)
@@ -507,9 +506,10 @@ NS_SizeOfAtomTablesIncludingThis(MallocSizeOf aMallocSizeOf,
                                             aMallocSizeOf)
          : 0;
 
+  // The atoms in the this table are almost certainly stored in static data, so
+  // we don't need a SizeOfEntry function.
   *aStatic = gStaticAtomTable
-           ? gStaticAtomTable->SizeOfIncludingThis(SizeOfStaticAtomTableEntryExcludingThis,
-                                                   aMallocSizeOf)
+           ? gStaticAtomTable->SizeOfIncludingThis(nullptr, aMallocSizeOf)
            : 0;
 }