VMAddressSpace::Put() is too hot to always write lock the address spaces

table. It is now inline and uses double-checked locking. This reduces the
contention on the lock to insignificant. Total -j8 Haiku image build speedup
is marginal, but the total kernel time drops 12%.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@34934 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/private/kernel/vm/VMAddressSpace.h

@@ -49,8 +49,8 @@ public:
 			int32				RefCount() const
 									{ return fRefCount; }
 
-			void				Get()	{ atomic_add(&fRefCount, 1); }
+	inline	void				Get()	{ atomic_add(&fRefCount, 1); }
-			void 				Put();
+	inline	void 				Put();
 			void				RemoveAndPut();
 
 			void				IncrementFaultCount()
@@ -107,6 +107,8 @@ public:
 	static	VMAddressSpace*		Get(team_id teamID);
 
 protected:
+	static	void				_DeleteIfUnreferenced(team_id id);
+
 	static	int					_DumpCommand(int argc, char** argv);
 	static	int					_DumpListCommand(int argc, char** argv);
 
@@ -129,6 +131,15 @@ protected:
 };
 
 
+void
+VMAddressSpace::Put()
+{
+	team_id id = fID;
+	if (atomic_add(&fRefCount, -1) == 1)
+		_DeleteIfUnreferenced(id);
+}
+
+
 class VMAddressSpace::AreaIterator {
 public:
 	AreaIterator()

src/system/kernel/vm/VMAddressSpace.cpp

@@ -148,23 +148,6 @@ VMAddressSpace::InitPostSem()
 }
 
 
-void
-VMAddressSpace::Put()
-{
-	bool remove = false;
-
-	rw_lock_write_lock(&sAddressSpaceTableLock);
-	if (atomic_add(&fRefCount, -1) == 1) {
-		sAddressSpaceTable.RemoveUnchecked(this);
-		remove = true;
-	}
-	rw_lock_write_unlock(&sAddressSpaceTableLock);
-
-	if (remove)
-		delete this;
-}
-
-
 /*! Deletes all areas in the specified address space, and the address
 	space by decreasing all reference counters. It also marks the
 	address space of being in deletion state, so that no more areas
@@ -293,6 +276,25 @@ VMAddressSpace::Get(team_id teamID)
 }
 
 
+/*static*/ void
+VMAddressSpace::_DeleteIfUnreferenced(team_id id)
+{
+	rw_lock_write_lock(&sAddressSpaceTableLock);
+
+	bool remove = false;
+	VMAddressSpace* addressSpace = sAddressSpaceTable.Lookup(id);
+	if (addressSpace != NULL && addressSpace->fRefCount == 0) {
+		sAddressSpaceTable.RemoveUnchecked(addressSpace);
+		remove = true;
+	}
+
+	rw_lock_write_unlock(&sAddressSpaceTableLock);
+
+	if (remove)
+		delete addressSpace;
+}
+
+
 /*static*/ int
 VMAddressSpace::_DumpCommand(int argc, char** argv)
 {