linux-kernel - Re: [PATCH] radix_tree: expand comment on optimization

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Message-ID: <20111222001707.GI23662@dastard>
Date:	Thu, 22 Dec 2011 11:17:07 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH] radix_tree: expand comment on optimization

On Wed, Dec 21, 2011 at 03:57:16PM -0800, Hugh Dickins wrote:
> Expand comment on optimization in radix_tree_range_tag_if_tagged(),
> along the lines proposed by Dave Chinner.
> 
> Signed-off-by: Hugh Dickins <hughd@...gle.com>
> ---
> And with -p2, this patch will also apply to the rtth tree.
> 
>  lib/radix-tree.c |    8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> --- mmotm/lib/radix-tree.c	2011-12-16 20:40:26.152758485 -0800
> +++ linux/lib/radix-tree.c	2011-12-21 14:57:20.073657540 -0800
> @@ -703,7 +703,13 @@ unsigned long radix_tree_range_tag_if_ta
>  			node = node->parent;
>  		}
>  
> -		/* optimization: no need to walk up from this node again */
> +		/*
> +		 * Small optimization: now clear that node pointer.
> +		 * Since all of this slot's ancestors now have the tag set
> +		 * from setting it above, we have no further need to walk
> +		 * back up the tree setting tags, until we update slot to
> +		 * point to another radix_tree_node.
> +		 */
>  		node = NULL;

Looks good. I might remember why it was done now ;)

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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