procfs: use faster rb_first_cached()

...  such that we can avoid the tree walks to get the node with the
smallest key.  Semantically the same, as the previously used rb_first(),
but O(1).  The main overhead is the extra footprint for the cached rb_node
pointer, which should not matter for procfs.

Link: http://lkml.kernel.org/r/20170719014603.19029-14-dave@stgolabs.net
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/generic.c

@@ -40,8 +40,8 @@ static int proc_match(unsigned int len, const char *name, struct proc_dir_entry
 
 static struct proc_dir_entry *pde_subdir_first(struct proc_dir_entry *dir)
 {
-	return rb_entry_safe(rb_first(&dir->subdir), struct proc_dir_entry,
-			     subdir_node);
+	return rb_entry_safe(rb_first_cached(&dir->subdir),
+			     struct proc_dir_entry, subdir_node);
 }
 
 static struct proc_dir_entry *pde_subdir_next(struct proc_dir_entry *dir)
@@ -54,7 +54,7 @@ static struct proc_dir_entry *pde_subdir_find(struct proc_dir_entry *dir,
 					      const char *name,
 					      unsigned int len)
 {
-	struct rb_node *node = dir->subdir.rb_node;
+	struct rb_node *node = dir->subdir.rb_root.rb_node;
 
 	while (node) {
 		struct proc_dir_entry *de = rb_entry(node,
@@ -75,8 +75,9 @@ static struct proc_dir_entry *pde_subdir_find(struct proc_dir_entry *dir,
 static bool pde_subdir_insert(struct proc_dir_entry *dir,
 			      struct proc_dir_entry *de)
 {
-	struct rb_root *root = &dir->subdir;
-	struct rb_node **new = &root->rb_node, *parent = NULL;
+	struct rb_root_cached *root = &dir->subdir;
+	struct rb_node **new = &root->rb_root.rb_node, *parent = NULL;
+	bool leftmost = true;
 
 	/* Figure out where to put new node */
 	while (*new) {
@@ -88,15 +89,16 @@ static bool pde_subdir_insert(struct proc_dir_entry *dir,
 		parent = *new;
 		if (result < 0)
 			new = &(*new)->rb_left;
-		else if (result > 0)
+		else if (result > 0) {
 			new = &(*new)->rb_right;
-		else
+			leftmost = false;
+		} else
 			return false;
 	}
 
 	/* Add new node and rebalance tree. */
 	rb_link_node(&de->subdir_node, parent, new);
-	rb_insert_color(&de->subdir_node, root);
+	rb_insert_color_cached(&de->subdir_node, root, leftmost);
 	return true;
 }
 
@@ -369,7 +371,7 @@ static struct proc_dir_entry *__proc_create(struct proc_dir_entry **parent,
 	ent->namelen = qstr.len;
 	ent->mode = mode;
 	ent->nlink = nlink;
-	ent->subdir = RB_ROOT;
+	ent->subdir = RB_ROOT_CACHED;
 	atomic_set(&ent->count, 1);
 	spin_lock_init(&ent->pde_unload_lock);
 	INIT_LIST_HEAD(&ent->pde_openers);
@@ -553,7 +555,7 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent)
 
 	de = pde_subdir_find(parent, fn, len);
 	if (de)
-		rb_erase(&de->subdir_node, &parent->subdir);
+		rb_erase_cached(&de->subdir_node, &parent->subdir);
 	write_unlock(&proc_subdir_lock);
 	if (!de) {
 		WARN(1, "name '%s'\n", name);
@@ -590,13 +592,13 @@ int remove_proc_subtree(const char *name, struct proc_dir_entry *parent)
 		write_unlock(&proc_subdir_lock);
 		return -ENOENT;
 	}
-	rb_erase(&root->subdir_node, &parent->subdir);
+	rb_erase_cached(&root->subdir_node, &parent->subdir);
 
 	de = root;
 	while (1) {
 		next = pde_subdir_first(de);
 		if (next) {
-			rb_erase(&next->subdir_node, &de->subdir);
+			rb_erase_cached(&next->subdir_node, &de->subdir);
 			de = next;
 			continue;
 		}

fs/proc/internal.h

@@ -40,7 +40,7 @@ struct proc_dir_entry {
 	const struct inode_operations *proc_iops;
 	const struct file_operations *proc_fops;
 	struct proc_dir_entry *parent;
-	struct rb_root subdir;
+	struct rb_root_cached subdir;
 	struct rb_node subdir_node;
 	void *data;
 	atomic_t count;		/* use count */

fs/proc/proc_net.c

@@ -196,7 +196,7 @@ static __net_init int proc_net_ns_init(struct net *net)
 	if (!netd)
 		goto out;
 
-	netd->subdir = RB_ROOT;
+	netd->subdir = RB_ROOT_CACHED;
 	netd->data = net;
 	netd->nlink = 2;
 	netd->namelen = 3;

fs/proc/root.c

@@ -210,7 +210,7 @@ struct proc_dir_entry proc_root = {
 	.proc_iops	= &proc_root_inode_operations, 
 	.proc_fops	= &proc_root_operations,
 	.parent		= &proc_root,
-	.subdir		= RB_ROOT,
+	.subdir		= RB_ROOT_CACHED,
 	.name		= "/proc",
 };