[PATCH] inotify speedup

Bypass an inotify-related fastpath spinlock and several function calls on
systems which have no inotify watches registered.

Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/inotify.c

···
 #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;
···
 	get_inotify_watch(watch);
 
 	atomic_inc(&dev->user->inotify_watches);
+	atomic_inc(&inotify_watches);
 
 	return 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);
 }
···
 {
 	struct dentry *parent;
 	struct inode *inode;
+
+	if (!atomic_read (&inotify_watches))
+		return;
 
 	spin_lock(&dentry->d_lock);
 	parent = dentry->d_parent;
···
 	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),