[PATCH v3 4/6] maple_tree: break on convergence in mas_spanning_rebalance()

[Sidhartha Kumar]

This allows support for using the vacant height to calculate the worst
case number of nodes needed for wr_rebalance operation.
mas_spanning_rebalance() was seen to perform unnecessary node allocations.
We can reduce allocations by breaking early during the rebalancing loop
once we realize that we have ascended to a common ancestor.

Suggested-by: Liam Howlett <liam.howlett at oracle.com>
Reviewed-by: Wei Yang <richard.weiyang at gmail.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett at Oracle.com>
Signed-off-by: Sidhartha Kumar <sidhartha.kumar at oracle.com>
---
 lib/maple_tree.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 878a7740628c..c859c7253d69 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -2899,11 +2899,24 @@ static void mas_spanning_rebalance(struct ma_state *mas,
 		mast_combine_cp_right(mast);
 		mast->orig_l->last = mast->orig_l->max;
 
-		if (mast_sufficient(mast))
-			continue;
+		if (mast_sufficient(mast)) {
+			if (mast_overflow(mast))
+				continue;
+
+			if (mast->orig_l->node == mast->orig_r->node) {
+			       /*
+				* The data in b_node should be stored in one
+				* node and in the tree
+				*/
+				slot = mast->l->offset;
+				/* May be a new root stored in mast->bn */
+				if (mas_is_root_limits(mast->orig_l))
+					new_height++;
+				break;
+			}
 
-		if (mast_overflow(mast))
 			continue;
+		}
 
 		/* May be a new root stored in mast->bn */
 		if (mas_is_root_limits(mast->orig_l)) {
-- 
2.43.0