maple_tree: introduce __mas_set_range()

mas_set_range() resets the node to MAS_START, which will cause a re-walk
of the tree to the range.  This is unnecessary when the maple state is
already at the correct location of the write.  Add a function that only
sets the range to avoid unnecessary re-walking of the tree.

Link: https://lkml.kernel.org/r/20230724183157.3939892-6-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/maple_tree.h

@@ -539,6 +539,22 @@ static inline void mas_reset(struct ma_state *mas)
  */
 #define mas_for_each(__mas, __entry, __max) \
 	while (((__entry) = mas_find((__mas), (__max))) != NULL)
+/**
+ * __mas_set_range() - Set up Maple Tree operation state to a sub-range of the
+ * current location.
+ * @mas: Maple Tree operation state.
+ * @start: New start of range in the Maple Tree.
+ * @last: New end of range in the Maple Tree.
+ *
+ * set the internal maple state values to a sub-range.
+ * Please use mas_set_range() if you do not know where you are in the tree.
+ */
+static inline void __mas_set_range(struct ma_state *mas, unsigned long start,
+		unsigned long last)
+{
+	mas->index = start;
+	mas->last = last;
+}
 
 /**
  * mas_set_range() - Set up Maple Tree operation state for a different index.
@@ -553,9 +569,8 @@ static inline void mas_reset(struct ma_state *mas)
 static inline
 void mas_set_range(struct ma_state *mas, unsigned long start, unsigned long last)
 {
-	       mas->index = start;
-	       mas->last = last;
-	       mas->node = MAS_START;
+	__mas_set_range(mas, start, last);
+	mas->node = MAS_START;
 }
 
 /**