maple_tree: add comments and some minor cleanups to mas_wr_append()

Add comment for mas_wr_append(), move mas_update_gap() into
mas_wr_append(), and other cleanups to make mas_wr_modify() cleaner.

Link: https://lkml.kernel.org/r/20230524031247.65949-8-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

@@ -4311,6 +4311,12 @@ static inline unsigned char mas_wr_new_end(struct ma_wr_state *wr_mas)
 	return new_end;
 }
 
+/*
+ * mas_wr_append: Attempt to append
+ * @wr_mas: the maple write state
+ *
+ * Return: True if appended, false otherwise
+ */
 static inline bool mas_wr_append(struct ma_wr_state *wr_mas)
 {
 	unsigned char end = wr_mas->node_end;
@@ -4318,34 +4324,30 @@ static inline bool mas_wr_append(struct ma_wr_state *wr_mas)
 	struct ma_state *mas = wr_mas->mas;
 	unsigned char node_pivots = mt_pivots[wr_mas->type];
 
-	if ((mas->index != wr_mas->r_min) && (mas->last == wr_mas->r_max)) {
-		if (new_end < node_pivots)
-			wr_mas->pivots[new_end] = wr_mas->pivots[end];
+	if (mas->offset != wr_mas->node_end)
+		return false;
 
-		if (new_end < node_pivots)
-			ma_set_meta(wr_mas->node, maple_leaf_64, 0, new_end);
+	if (new_end < node_pivots) {
+		wr_mas->pivots[new_end] = wr_mas->pivots[end];
+		ma_set_meta(wr_mas->node, maple_leaf_64, 0, new_end);
+	}
 
+	if (mas->last == wr_mas->r_max) {
+		/* Append to end of range */
 		rcu_assign_pointer(wr_mas->slots[new_end], wr_mas->entry);
-		mas->offset = new_end;
 		wr_mas->pivots[end] = mas->index - 1;
-
-		return true;
-	}
-
-	if ((mas->index == wr_mas->r_min) && (mas->last < wr_mas->r_max)) {
-		if (new_end < node_pivots)
-			wr_mas->pivots[new_end] = wr_mas->pivots[end];
-
+		mas->offset = new_end;
+	} else {
+		/* Append to start of range */
 		rcu_assign_pointer(wr_mas->slots[new_end], wr_mas->content);
-		if (new_end < node_pivots)
-			ma_set_meta(wr_mas->node, maple_leaf_64, 0, new_end);
-
 		wr_mas->pivots[end] = mas->last;
 		rcu_assign_pointer(wr_mas->slots[end], wr_mas->entry);
-		return true;
 	}
 
-	return false;
+	if (!wr_mas->content || !wr_mas->entry)
+		mas_update_gap(mas);
+
+	return  true;
 }
 
 /*
@@ -4385,12 +4387,9 @@ static inline void mas_wr_modify(struct ma_wr_state *wr_mas)
 	if (new_end >= mt_slots[wr_mas->type])
 		goto slow_path;
 
-	if (wr_mas->entry && (wr_mas->node_end < mt_slots[wr_mas->type] - 1) &&
-	    (mas->offset == wr_mas->node_end) && mas_wr_append(wr_mas)) {
-		if (!wr_mas->content || !wr_mas->entry)
-			mas_update_gap(mas);
+	/* Attempt to append */
+	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))
 		return;