Re: [PATCH 1/3] Further optimization of function rb_erase() in lib/rbtree.c

[Andrew Morton <akpm@linux-foundation.org>]

> Subject: [PATCH 1/3] Further optimization of function rb_erase() in lib/rbtree.c

Three distinct patches, all with the same title.

Please carefully choose a unique title for each patch in the series.

We push thousands and thousands of patches into Linux and it all gets
complex and confusing.  These little organisational things help us to
manage the volume and the complexity.

On Fri, 10 Apr 2009 12:23:46 +0200
"Wolfram Strepp" <wstrepp@gmx.de> wrote:

> This small patch-series reorganizes some lines in function rb_erase()
> in lib/rbtree.c, and as a result one if-condition can be omitted.
> Tested on x86.
> 
> 
> First, move some code around in order to make the next change more obvious.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Signed-off-by: Wolfram Strepp <wstrepp@gmx.de>
> 
> ---
>  lib/rbtree.c |   19 ++++++++++---------
>  1 file changed, 10 insertions(+), 9 deletions(-)
> Index: linux-2.6/lib/rbtree.c
> ===================================================================
> --- linux-2.6.orig/lib/rbtree.c
> +++ linux-2.6/lib/rbtree.c
> @@ -237,6 +237,16 @@ void rb_erase(struct rb_node *node, stru
>  		node = node->rb_right;
>  		while ((left = node->rb_left) != NULL)
>  			node = left;
> +
> +		if (rb_parent(old))
> +		{
> +			if (rb_parent(old)->rb_left == old)
> +				rb_parent(old)->rb_left = node;
> +			else
> +				rb_parent(old)->rb_right = node;
> +		} else
> +			root->rb_node = node;

You may as well fix the obvious coding-style error while moving the
code.  scripts/checkpatch.pl will detect this one.

>  		child = node->rb_right;
>  		parent = rb_parent(node);
>  		color = rb_color(node);
> @@ -253,15 +263,6 @@ void rb_erase(struct rb_node *node, stru
>  		node->rb_right = old->rb_right;
>  		node->rb_left = old->rb_left;
>  
> -		if (rb_parent(old))
> -		{
> -			if (rb_parent(old)->rb_left == old)
> -				rb_parent(old)->rb_left = node;
> -			else
> -				rb_parent(old)->rb_right = node;
> -		} else
> -			root->rb_node = node;
> -
>  		rb_set_parent(old->rb_left, node);
>  		if (old->rb_right)
>  			rb_set_parent(old->rb_right, node);