Re: [PATCH] radix_tree: expand comment on optimization

From: Dave Chinner
Date: Wed Dec 21 2011 - 19:17:11 EST


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@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxx
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