This is a very small function, inlining it save cpu cycles
by reducing register pressure and removing call/ret overhead.

It also reduces vmlinux text size by 744 bytes on a typical x86_64 build.

Before:

size vmlinux
   text	   data	    bss	    dec	    hex	filename
34812525	22177365	5685248	62675138	3bc58c2	vmlinux

After:

size vmlinux
   text	   data	    bss	    dec	    hex	filename
34811781	22177365	5685248	62674394	3bc55da	vmlinux

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/linux/rbtree.h | 16 +++++++++++++++-
 lib/rbtree.c           | 16 ----------------
 2 files changed, 15 insertions(+), 17 deletions(-)

diff --git a/include/linux/rbtree.h b/include/linux/rbtree.h
index 8d2ba3749866f500a492d267e5e13556f6aa3f55..484554900f7d3201d41fb29e04fb65fe331eee79 100644
--- a/include/linux/rbtree.h
+++ b/include/linux/rbtree.h
@@ -43,7 +43,21 @@ extern void rb_erase(struct rb_node *, struct rb_root *);
 /* Find logical next and previous nodes in a tree */
 extern struct rb_node *rb_next(const struct rb_node *);
 extern struct rb_node *rb_prev(const struct rb_node *);
-extern struct rb_node *rb_first(const struct rb_root *);
+
+/*
+ * This function returns the first node (in sort order) of the tree.
+ */
+static inline struct rb_node *rb_first(const struct rb_root *root)
+{
+	struct rb_node	*n;
+
+	n = root->rb_node;
+	if (!n)
+		return NULL;
+	while (n->rb_left)
+		n = n->rb_left;
+	return n;
+}
 extern struct rb_node *rb_last(const struct rb_root *);
 
 /* Postorder iteration - always visit the parent after its children */
diff --git a/lib/rbtree.c b/lib/rbtree.c
index 5114eda6309c9d867a3e1ed9358bf9b3b275eb71..b946eb4b759d3b65f5bc5d54d0377348962bdc56 100644
--- a/lib/rbtree.c
+++ b/lib/rbtree.c
@@ -460,22 +460,6 @@ void __rb_insert_augmented(struct rb_node *node, struct rb_root *root,
 }
 EXPORT_SYMBOL(__rb_insert_augmented);
 
-/*
- * This function returns the first node (in sort order) of the tree.
- */
-struct rb_node *rb_first(const struct rb_root *root)
-{
-	struct rb_node	*n;
-
-	n = root->rb_node;
-	if (!n)
-		return NULL;
-	while (n->rb_left)
-		n = n->rb_left;
-	return n;
-}
-EXPORT_SYMBOL(rb_first);
-
 struct rb_node *rb_last(const struct rb_root *root)
 {
 	struct rb_node	*n;
-- 
2.52.0.rc1.455.g30608eb744-goog