lib/rbtree: avoid generating code twice for the cached versions

As was already noted in rbtree.h, the logic to cache rb_first (or
rb_last) can easily be implemented externally to the core rbtree api.

Change the implementation to do just that.  Previously the update of
rb_leftmost was wired deeper into the implmentation, but there were some
disadvantages to that - mostly, lib/rbtree.c had separate instantiations
for rb_insert_color() vs rb_insert_color_cached(), as well as rb_erase()
vs rb_erase_cached(), which were doing exactly the same thing save for
the rb_leftmost update at the start of either function.

   text	   data	    bss	    dec	    hex	filename
   5405	    120	      0	   5525	   1595	lib/rbtree.o-vanilla
   3827	     96	      0	   3923	    f53	lib/rbtree.o-patch

[dave@stgolabs.net: changelog addition]
  Link: http://lkml.kernel.org/r/20190628171416.by5gdizl3rcxk5h5@linux-r8p5
[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20190628045008.39926-1-walken@google.com
Signed-off-by: Michel Lespinasse <walken@google.com>
Acked-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>

1 files changed, 10 insertions, 17 deletions

diff --git a/include/linux/rbtree_augmented.h b/include/linux/rbtree_augmented.h
index 0f902ccb48b0..179faab29f52 100644
--- a/include/linux/rbtree_augmented.h
+++ b/include/linux/rbtree_augmented.h
@@ -30,10 +30,9 @@ struct rb_augment_callbacks {
 	void (*rotate)(struct rb_node *old, struct rb_node *new);
 };
 
-extern void __rb_insert_augmented(struct rb_node *node,
-				  struct rb_root *root,
-				  bool newleft, struct rb_node **leftmost,
+extern void __rb_insert_augmented(struct rb_node *node, struct rb_root *root,
 	void (*augment_rotate)(struct rb_node *old, struct rb_node *new));
+
 /*
  * Fixup the rbtree and update the augmented information when rebalancing.
  *
@@ -48,7 +47,7 @@ static inline void
 rb_insert_augmented(struct rb_node *node, struct rb_root *root,
 		    const struct rb_augment_callbacks *augment)
 {
-	__rb_insert_augmented(node, root, false, NULL, augment->rotate);
+	__rb_insert_augmented(node, root, augment->rotate);
 }
 
 static inline void
@@ -56,8 +55,9 @@ rb_insert_augmented_cached(struct rb_node *node,
 			   struct rb_root_cached *root, bool newleft,
 			   const struct rb_augment_callbacks *augment)
 {
-	__rb_insert_augmented(node, &root->rb_root,
-			      newleft, &root->rb_leftmost, augment->rotate);
+	if (newleft)
+		root->rb_leftmost = node;
+	rb_insert_augmented(node, &root->rb_root, augment);
 }
 
 #define RB_DECLARE_CALLBACKS(rbstatic, rbname, rbstruct, rbfield,	\
@@ -150,7 +150,6 @@ extern void __rb_erase_color(struct rb_node *parent, struct rb_root *root,
 
 static __always_inline struct rb_node *
 __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
-		     struct rb_node **leftmost,
 		     const struct rb_augment_callbacks *augment)
 {
 	struct rb_node *child = node->rb_right;
@@ -158,9 +157,6 @@ __rb_erase_augmented(struct rb_node *node, struct rb_root *root,
 	struct rb_node *parent, *rebalance;
 	unsigned long pc;
 
-	if (leftmost && node == *leftmost)
-		*leftmost = rb_next(node);
-
 	if (!tmp) {
 		/*
 		 * Case 1: node to erase has no more than 1 child (easy!)
@@ -260,8 +256,7 @@ static __always_inline void
 rb_erase_augmented(struct rb_node *node, struct rb_root *root,
 		   const struct rb_augment_callbacks *augment)
 {
-	struct rb_node *rebalance = __rb_erase_augmented(node, root,
-							 NULL, augment);
+	struct rb_node *rebalance = __rb_erase_augmented(node, root, augment);
 	if (rebalance)
 		__rb_erase_color(rebalance, root, augment->rotate);
 }
@@ -270,11 +265,9 @@ static __always_inline void
 rb_erase_augmented_cached(struct rb_node *node, struct rb_root_cached *root,
 			  const struct rb_augment_callbacks *augment)
 {
-	struct rb_node *rebalance = __rb_erase_augmented(node, &root->rb_root,
-							 &root->rb_leftmost,
-							 augment);
-	if (rebalance)
-		__rb_erase_color(rebalance, &root->rb_root, augment->rotate);
+	if (root->rb_leftmost == node)
+		root->rb_leftmost = rb_next(node);
+	rb_erase_augmented(node, &root->rb_root, augment);
 }
 
 #endif	/* _LINUX_RBTREE_AUGMENTED_H */