maple_tree: rework mas_wr_slot_store() to be cleaner and more efficient.

Get whether the two gaps to be overwritten are empty to avoid calling
mas_update_gap() all the time.  Also clean up the code and add comments.

Link: https://lkml.kernel.org/r/20230524031247.65949-9-zhangpeng.00@bytedance.comSigned-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

lib/maple_tree.c

@@ -4202,49 +4202,34 @@ static inline bool mas_wr_node_store(struct ma_wr_state *wr_mas)
 static inline bool mas_wr_slot_store(struct ma_wr_state *wr_mas)
 {
 	struct ma_state *mas = wr_mas->mas;
-	unsigned long lmax; /* Logical max. */
 	unsigned char offset = mas->offset;
+	bool gap = false;
 
-	if ((wr_mas->r_max > mas->last) && ((wr_mas->r_min != mas->index) ||
-				  (offset != wr_mas->node_end)))
+	if (wr_mas->offset_end - offset != 1)
 		return false;
 
-	if (offset == wr_mas->node_end - 1)
-		lmax = mas->max;
-	else
-		lmax = wr_mas->pivots[offset + 1];
-
-	/* going to overwrite too many slots. */
-	if (lmax < mas->last)
-		return false;
-
-	if (wr_mas->r_min == mas->index) {
-		/* overwriting two or more ranges with one. */
-		if (lmax == mas->last)
-			return false;
+	gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset);
+	gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset + 1);
 
-		/* Overwriting all of offset and a portion of offset + 1. */
+	if (mas->index == wr_mas->r_min) {
+		/* Overwriting the range and over a part of the next range. */
 		rcu_assign_pointer(wr_mas->slots[offset], wr_mas->entry);
 		wr_mas->pivots[offset] = mas->last;
-		goto done;
+	} else {
+		/* Overwriting a part of the range and over the next range */
+		rcu_assign_pointer(wr_mas->slots[offset + 1], wr_mas->entry);
+		wr_mas->pivots[offset] = mas->index - 1;
+		mas->offset++; /* Keep mas accurate. */
 	}
 
-	/* Doesn't end on the next range end. */
-	if (lmax != mas->last)
-		return false;
-
-	/* Overwriting a portion of offset and all of offset + 1 */
-	if ((offset + 1 < mt_pivots[wr_mas->type]) &&
-	    (wr_mas->entry || wr_mas->pivots[offset + 1]))
-		wr_mas->pivots[offset + 1] = mas->last;
-
-	rcu_assign_pointer(wr_mas->slots[offset + 1], wr_mas->entry);
-	wr_mas->pivots[offset] = mas->index - 1;
-	mas->offset++; /* Keep mas accurate. */
-
-done:
 	trace_ma_write(__func__, mas, 0, wr_mas->entry);
-	mas_update_gap(mas);
+	/*
+	 * Only update gap when the new entry is empty or there is an empty
+	 * entry in the original two ranges.
+	 */
+	if (!wr_mas->entry || gap)
+		mas_update_gap(mas);
+
 	return true;
 }
 
@@ -4391,7 +4376,7 @@ static inline void mas_wr_modify(struct ma_wr_state *wr_mas)
 	if (new_end == wr_mas->node_end + 1 && mas_wr_append(wr_mas))
 		return;
 
-	if ((wr_mas->offset_end - mas->offset <= 1) && mas_wr_slot_store(wr_mas))
+	if (new_end == wr_mas->node_end && mas_wr_slot_store(wr_mas))
 		return;
 	else if (mas_wr_node_store(wr_mas))
 		return;