linux-kernel - [PATCH 08/10] maple_tree: Add comments and some minor cleanups to mas_wr

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Date:   Mon, 15 May 2023 21:17:55 +0800
From:   Peng Zhang <zhangpeng.00@...edance.com>
To:     Liam.Howlett@...cle.com
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, maple-tree@...ts.infradead.org,
        Peng Zhang <zhangpeng.00@...edance.com>
Subject: [PATCH 08/10] 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.

Signed-off-by: Peng Zhang <zhangpeng.00@...edance.com>
---
 lib/maple_tree.c | 52 ++++++++++++++++++++++++++++++++++++------------
 1 file changed, 39 insertions(+), 13 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 20082ef8c396c..538e49feafbe4 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -4315,6 +4315,31 @@ 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
+ *
+ * Case 1:
+ *                       r_min   r_max/end_piv
+ *                 +-------+-------+
+ * original range: |       |offset |
+ *                 +-------+-------+
+ *                             +---+
+ *      overwrite:             |   |
+ *                             +---+
+ *                           index last
+ * Case 2:
+ *                       r_min   r_max/end_piv
+ *                 +-------+-------+
+ * original range: |       |offset |
+ *                 +-------+-------+
+ *                         +---+
+ *      overwrite:         |   |
+ *                         +---+
+ *                       index last
+ */
 static inline bool mas_wr_append(struct ma_wr_state *wr_mas)
 {
 	unsigned char end = wr_mas->node_end;
@@ -4322,7 +4347,11 @@ 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->offset == wr_mas->node_end))
+		return false;
+
 	if ((mas->index != wr_mas->r_min) && (mas->last == wr_mas->r_max)) {
+		/* Case 1 */
 		if (new_end < node_pivots)
 			wr_mas->pivots[new_end] = wr_mas->pivots[end];
 
@@ -4330,13 +4359,10 @@ static inline bool mas_wr_append(struct ma_wr_state *wr_mas)
 			ma_set_meta(wr_mas->node, maple_leaf_64, 0, new_end);
 
 		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)) {
+		mas->offset = new_end;
+	} else if ((mas->index == wr_mas->r_min) && (mas->last < wr_mas->r_max)) {
+		/* Case 2 */
 		if (new_end < node_pivots)
 			wr_mas->pivots[new_end] = wr_mas->pivots[end];
 
@@ -4346,10 +4372,13 @@ static inline bool mas_wr_append(struct ma_wr_state *wr_mas)
 
 		wr_mas->pivots[end] = mas->last;
 		rcu_assign_pointer(wr_mas->slots[end], wr_mas->entry);
-		return true;
+	} else {
+		return false;
 	}
 
-	return false;
+	if (!wr_mas->content || !wr_mas->entry)
+		mas_update_gap(mas);
+	return  true;
 }
 
 /*
@@ -4385,12 +4414,9 @@ 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;
-- 
2.20.1