[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Xen-devel] [PATCH v4 06/17] rbtree: adjust root color in rb_insert_color() only when necessary



From: Michel Lespinasse <walken@xxxxxxxxxx>

The root node of an rbtree must always be black.  However,
rb_insert_color() only needs to maintain this invariant when it has been
broken - that is, when it exits the loop due to the current (red) node
being the root.  In all other cases (exiting after tree rotations, or
exiting due to an existing black parent) the invariant is already
satisfied, so there is no need to adjust the root node color.

Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Acked-by: David Woodhouse <David.Woodhouse@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Daniel Santos <daniel.santos@xxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[Linux commit 6d58452dc066db61acdff7b84671db1b11a3de1c]

Ported to Xen.

Signed-off-by: Praveen Kumar <kpraveen.lkml@xxxxxxxxx>
---
 xen/common/rbtree.c | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/xen/common/rbtree.c b/xen/common/rbtree.c
index 5bf25c4ad8..b5d2a025d1 100644
--- a/xen/common/rbtree.c
+++ b/xen/common/rbtree.c
@@ -90,8 +90,21 @@ void rb_insert_color(struct rb_node *node, struct rb_root 
*root)
 {
        struct rb_node *parent, *gparent;
 
-       while ((parent = rb_parent(node)) && rb_is_red(parent))
-       {
+       while (true) {
+               /*
+                * Loop invariant: node is red
+                *
+                * If there is a black parent, we are done.
+                * Otherwise, take some corrective action as we don't
+                * want a red root or two consecutive red nodes.
+                */
+               parent = rb_parent(node);
+               if (!parent) {
+                       rb_set_black(node);
+                       break;
+               } else if (rb_is_black(parent))
+                       break;
+
                gparent = rb_parent(parent);
 
                if (parent == gparent->rb_left)
@@ -141,8 +154,6 @@ void rb_insert_color(struct rb_node *node, struct rb_root 
*root)
                        break;
                }
        }
-
-       rb_set_black(root->rb_node);
 }
 EXPORT_SYMBOL(rb_insert_color);
 
-- 
2.12.0


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel

 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.