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

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Message-ID: <alpine.LSU.2.00.1112211555430.25868@eggly.anvils>
Date:	Wed, 21 Dec 2011 15:57:16 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [PATCH] radix_tree: expand comment on optimization

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;
 
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