diff mbox

[v2,08/20] rbtree: break out of rb_insert_color loop after tree rotation

Message ID 20170617093253.3990-9-kpraveen.lkml@gmail.com (mailing list archive)
State New, archived
Headers show

Commit Message

Praveen Kumar June 17, 2017, 9:32 a.m. UTC 
It is a well known property of rbtrees that insertion never requires more
than two tree rotations.  In our implementation, after one loop iteration
identified one or two necessary tree rotations, we would iterate and look
for more.  However at that point the node's parent would always be black,
which would cause us to exit the loop.

We can make the code flow more obvious by just adding a break statement
after the tree rotations, where we know we are done.  Additionally, in the
cases where two tree rotations are necessary, we don't have to update the
'node' pointer as it wouldn't be used until the next loop iteration, which
we now avoid due to this break statement.

Signed-off-by: Michel Lespinasse <walken@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: David Woodhouse <David.Woodhouse@intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Daniel Santos <daniel.santos@pobox.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[Linux commit 1f0528653e41ec230c60f5738820e8a544731399]

Ported to Xen.

Signed-off-by: Praveen Kumar <kpraveen.lkml@gmail.com>
---
 xen/common/rbtree.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

Comments

Dario Faggioli June 19, 2017, 5:10 p.m. UTC | #1 
On Sat, 2017-06-17 at 15:02 +0530, Praveen Kumar wrote:
> It is a well known property of rbtrees that insertion never requires
> more
> than two tree rotations.  In our implementation, after one loop
> iteration
> identified one or two necessary tree rotations, we would iterate and
> look
> for more.  However at that point the node's parent would always be
> black,
> which would cause us to exit the loop.
> 
> We can make the code flow more obvious by just adding a break
> statement
> after the tree rotations, where we know we are done.  Additionally,
> in the
> cases where two tree rotations are necessary, we don't have to update
> the
> 'node' pointer as it wouldn't be used until the next loop iteration,
> which
> we now avoid due to this break statement.
> 
> Signed-off-by: Michel Lespinasse <walken@google.com>
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Acked-by: David Woodhouse <David.Woodhouse@intel.com>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Daniel Santos <daniel.santos@pobox.com>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: "Eric W. Biederman" <ebiederm@xmission.com>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
> [Linux commit 1f0528653e41ec230c60f5738820e8a544731399]
> 
> Ported to Xen.
> 
> Signed-off-by: Praveen Kumar <kpraveen.lkml@gmail.com>
>
Now the patch has all the hunks. There's again some difference in '{'
placement, though, between this patch and the Linux commit.

More specifically, in the Linux commit, this:
> --- a/xen/common/rbtree.c
> +++ b/xen/common/rbtree.c
> @@ -110,16 +110,14 @@ void rb_insert_color(struct rb_node *node,
> struct rb_root *root)
>  
>              if (parent->rb_right == node)
>              {
>
Becomes:

  if (parent->rb_right == node) {

I appreciate that you may not be applying this specific modification
because the Xen style is different. But I actually think you should, as
this file is going to end up being mixed style anyway, so I'd
prioritize staying identical to Linux's commit.

Regards,
Dario
diff mbox

Patch

diff --git a/xen/common/rbtree.c b/xen/common/rbtree.c
index 49f73e2461..25902c0659 100644
--- a/xen/common/rbtree.c
+++ b/xen/common/rbtree.c
@@ -110,16 +110,14 @@  void rb_insert_color(struct rb_node *node, struct rb_root *root)
 
             if (parent->rb_right == node)
             {
-                register struct rb_node *tmp;
                 __rb_rotate_left(parent, root);
-                tmp = parent;
                 parent = node;
-                node = tmp;
             }
 
             rb_set_black(parent);
             rb_set_red(gparent);
             __rb_rotate_right(gparent, root);
+            break;
         } else {
             {
                 register struct rb_node *uncle = gparent->rb_left;
@@ -135,16 +133,14 @@  void rb_insert_color(struct rb_node *node, struct rb_root *root)
 
             if (parent->rb_left == node)
             {
-                register struct rb_node *tmp;
                 __rb_rotate_right(parent, root);
-                tmp = parent;
                 parent = node;
-                node = tmp;
             }
 
             rb_set_black(parent);
             rb_set_red(gparent);
             __rb_rotate_left(gparent, root);
+            break;
         }
     }