From 8ab820f076cad39859a9a674b44fd82f1abfb88b Mon Sep 17 00:00:00 2001
From: Ingo Weinhold <ingo_weinhold@gmx.de>
Date: Thu, 7 Jan 2010 14:09:56 +0000
Subject: [PATCH] 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 | 15 +++++++--
 src/system/kernel/vm/VMAddressSpace.cpp    | 36 ++++++++++++----------
 2 files changed, 32 insertions(+), 19 deletions(-)

diff --git a/headers/private/kernel/vm/VMAddressSpace.h b/headers/private/kernel/vm/VMAddressSpace.h
index 93b7b086ae..fd02bc6be6 100644
--- a/headers/private/kernel/vm/VMAddressSpace.h
+++ b/headers/private/kernel/vm/VMAddressSpace.h
@@ -49,8 +49,8 @@ public:
 			int32				RefCount() const
 									{ return fRefCount; }
 
-			void				Get()	{ atomic_add(&fRefCount, 1); }
-			void 				Put();
+	inline	void				Get()	{ atomic_add(&fRefCount, 1); }
+	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()
diff --git a/src/system/kernel/vm/VMAddressSpace.cpp b/src/system/kernel/vm/VMAddressSpace.cpp
index 492ccf24d4..fcaccfaa8f 100644
--- a/src/system/kernel/vm/VMAddressSpace.cpp
+++ b/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)
 {