[PATCH v3 14/15] maple_tree: Reduce resets during store setup

["Liam R. Howlett" <Liam.Howlett@oracle.com>]

mas_prealloc() may walk partially down the tree before finding that a
split or spanning store is needed.  When the write occurs, relax the
logic on resetting the walk so that partial walks will not restart, but
walks that have gone too far (a store that affects beyond the current
node) should be restarted.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---
 lib/maple_tree.c | 37 ++++++++++++++++++++++++++-----------
 1 file changed, 26 insertions(+), 11 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 4a111785360f..a3d602cfd030 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -5424,19 +5424,34 @@ static inline void mte_destroy_walk(struct maple_enode *enode,
 
 static void mas_wr_store_setup(struct ma_wr_state *wr_mas)
 {
+	if (mas_is_start(wr_mas->mas))
+		return;
+
 	if (unlikely(mas_is_paused(wr_mas->mas)))
-		mas_reset(wr_mas->mas);
+		goto reset;
 
-	if (!mas_is_start(wr_mas->mas)) {
-		if (mas_is_none(wr_mas->mas)) {
-			mas_reset(wr_mas->mas);
-		} else {
-			wr_mas->r_max = wr_mas->mas->max;
-			wr_mas->type = mte_node_type(wr_mas->mas->node);
-			if (mas_is_span_wr(wr_mas))
-				mas_reset(wr_mas->mas);
-		}
-	}
+	if (unlikely(mas_is_none(wr_mas->mas)))
+		goto reset;
+
+	/*
+	 * A less strict version of mas_is_span_wr() where we allow spanning
+	 * writes within this node.  This is to stop partial walks in
+	 * mas_prealloc() from being reset.
+	 */
+	if (wr_mas->mas->last > wr_mas->mas->max)
+		goto reset;
+
+	if (wr_mas->entry)
+		return;
+
+	if (mte_is_leaf(wr_mas->mas->node) &&
+	    wr_mas->mas->last == wr_mas->mas->max)
+		goto reset;
+
+	return;
+
+reset:
+	mas_reset(wr_mas->mas);
 }
 
 /* Interface */
-- 
2.39.2