linux-kernel - [PATCH] rbtree: fix jffs2 build issue due to renamed __rb_parent

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Message-ID: <1342624609.25411.118.camel@shinybook.infradead.org>
Date:	Wed, 18 Jul 2012 16:16:49 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	aarcange@...hat.com, riel@...hat.com, peterz@...radead.org,
	daniel.santos@...ox.com, axboe@...nel.dk, ebiederm@...ssion.com,
	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org
Subject: [PATCH] rbtree: fix jffs2 build issue due to renamed
 __rb_parent_color field

... and clean up the comments to better explain why it's acceptable to
do it this way instead of using rb_erase() "properly".

Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>
---
On Wed, 2012-07-18 at 12:40 +0100, David Woodhouse wrote:
> If you're going to make that comment redundant, you might as well remove
> it. And you might as well say that the trees are being *destroyed*
> (consumed) at this point, rather than just that there will be no further
> insert or erase operations. 

The comment on ver_insert() confused me too while I was looking at this,
so I've improved that as well.

A quick and dirty benchmark shows about a 10% performance improvement
when mounting a RAM-backed JFFS2 file system on Westmere. Thanks.

Acked-By: David Woodhouse <David.Woodhouse@...el.com> for the rest of
the series.

diff --git a/fs/jffs2/readinode.c b/fs/jffs2/readinode.c
index 1ea349f..ae81b01 100644
--- a/fs/jffs2/readinode.c
+++ b/fs/jffs2/readinode.c
@@ -394,8 +394,11 @@ static int jffs2_add_tn_to_tree(struct jffs2_sb_info *c,
 }
 
 /* Trivial function to remove the last node in the tree. Which by definition
-   has no right-hand -- so can be removed just by making its only child (if
-   any) take its place under its parent. */
+   has no right-hand child — so can be removed just by making its left-hand
+   child (if any) take its place under its parent. Since this is only done
+   when we're consuming the whole tree, there's no need to use rb_erase()
+   and let it worry about adjusting colours and balancing the tree. That
+   would just be a waste of time. */
 static void eat_last(struct rb_root *root, struct rb_node *node)
 {
 	struct rb_node *parent = rb_parent(node);
@@ -412,12 +415,12 @@ static void eat_last(struct rb_root *root, struct rb_node *node)
 		link = &parent->rb_right;
 
 	*link = node->rb_left;
-	/* Colour doesn't matter now. Only the parent pointer. */
 	if (node->rb_left)
-		node->rb_left->rb_parent_color = node->rb_parent_color;
+		node->rb_left->__rb_parent_color = node->__rb_parent_color;
 }
 
-/* We put this in reverse order, so we can just use eat_last */
+/* We put the version tree in reverse order, so we can use the same eat_last()
+   function that we use to consume the tmpnode tree (tn_root). */
 static void ver_insert(struct rb_root *ver_root, struct jffs2_tmp_dnode_info *tn)
 {
 	struct rb_node **link = &ver_root->rb_node;

-- 
dwmw2

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