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rbtree: fix jffs2 build issue due to renamed __rb_parent_color field

PATCH In review Michel Lespinasse 2 participants 3 messages Jul 18, 2012

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Memory management Journalling flash file system V2 (JFFS2)
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Michel Lespinasse

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#0 lore raw

PATCH 1/1 rbtree: fix jffs2 build issue due to renamed __rb_parent_color field

When renaming rb_parent_color into __rb_parent_color to highlight the fact that people aren't expected to directly manipulate this, I broke the jffs2 build which was doing such direct manipulation in fs/jffs2/readinode.c . Fix this and add a comment explaining why this direct use is safe here.

Signed-off-by Michel Lespinasse <[email protected]>
---
 fs/jffs2/readinode.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
fs/jffs2/readinode.c +4 -2
index dc0437e..b00fc50 100644
@@ -395,7 +395,9 @@ 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. */
+   any) take its place under its parent. Note that we don't maintain the
+   usual rbtree invariants as there won't be further insert or erase
+   operations on the tree.*/
 static void eat_last(struct rb_root *root, struct rb_node *node)
 {
 	struct rb_node *parent = rb_parent(node);

@@ -414,7 +416,7 @@ static void eat_last(struct rb_root *root, struct rb_node *node)
 	*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 */
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#1 lore raw
Quoted 2 lines · Michel Lespinasse

Fix this and add a comment explaining why this direct use is safe here.

Note that there was already a comment which was *intended* to have that effect, right before the assignment:

        /* Colour doesn't matter now. Only the parent pointer. */

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.

Signature · 1 line
dwmw2
maintainer
#2 lore raw

PATCH 1/1 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 <[email protected]>

---

Quoted 4 lines · David Woodhouse

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 <[email protected]> for the rest of

the series.

fs/jffs2/readinode.c +8 -5
index 1ea349f..ae81b01 100644
@@ -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;
Signature · 1 line
dwmw2