[PATCH] inotify speedup

Bypass an inotify-related fastpath spinlock and several function calls on
systems which have no inotify watches registered.
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

fs/inotify.c

@@ -37,6 +37,7 @@
 #include <asm/ioctls.h>
 
 static atomic_t inotify_cookie;
+static atomic_t inotify_watches;
 
 static kmem_cache_t *watch_cachep;
 static kmem_cache_t *event_cachep;
@@ -422,6 +423,7 @@ static struct inotify_watch *create_watch(struct inotify_device *dev,
 	get_inotify_watch(watch);
 
 	atomic_inc(&dev->user->inotify_watches);
+	atomic_inc(&inotify_watches);
 
 	return watch;
 }
@@ -454,6 +456,7 @@ static void remove_watch_no_event(struct inotify_watch *watch,
 	list_del(&watch->d_list);
 
 	atomic_dec(&dev->user->inotify_watches);
+	atomic_dec(&inotify_watches);
 	idr_remove(&dev->idr, watch->wd);
 	put_inotify_watch(watch);
 }
@@ -532,6 +535,9 @@ void inotify_dentry_parent_queue_event(struct dentry *dentry, u32 mask,
 	struct dentry *parent;
 	struct inode *inode;
 
+	if (!atomic_read (&inotify_watches))
+		return;
+
 	spin_lock(&dentry->d_lock);
 	parent = dentry->d_parent;
 	inode = parent->d_inode;
@@ -1043,6 +1049,7 @@ static int __init inotify_setup(void)
 	inotify_max_user_watches = 8192;
 
 	atomic_set(&inotify_cookie, 0);
+	atomic_set(&inotify_watches, 0);
 
 	watch_cachep = kmem_cache_create("inotify_watch_cache",
 					 sizeof(struct inotify_watch),