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rbtree: break out of rb_insert_color loop after tree rotation

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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 <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Acked-by: David Woodhouse <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Daniel Santos <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: "Eric W. Biederman" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Michel Lespinasse 2012-10-08 16:30:42 -07:00 • committed by Linus Torvalds
commit 1f0528653e
1 changed files with 4 additions and 10 deletions
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14
lib/rbtree.c
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@ -109,18 +109,15 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
}
}
if (parent->rb_right == node)
{
register struct rb_node *tmp;
if (parent->rb_right == node) {
__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;
@ -134,18 +131,15 @@ void rb_insert_color(struct rb_node *node, struct rb_root *root)
}
}
if (parent->rb_left == node)
{
register struct rb_node *tmp;
if (parent->rb_left == node) {
__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;
}
}