linux-kernel - [PATCH 09/10] maple_tree: Rework mas_wr_slot_store() to be cleaner and more efficient.

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Message-Id: <20230515131757.60035-10-zhangpeng.00@bytedance.com>
Date:   Mon, 15 May 2023 21:17:56 +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 09/10] maple_tree: Rework mas_wr_slot_store() to be cleaner and more efficient.

The code of mas_wr_slot_store() is messy, make it clearer and concise,
and add comments. In addition, get whether the two gaps are empty to
avoid calling mas_update_gap() all the time.

Signed-off-by: Peng Zhang <zhangpeng.00@...edance.com>
---
 lib/maple_tree.c | 79 +++++++++++++++++++++++++++---------------------
 1 file changed, 44 insertions(+), 35 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 538e49feafbe4..d558e7bcb6da8 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -4190,53 +4190,62 @@ static inline bool mas_wr_node_store(struct ma_wr_state *wr_mas)
  * @wr_mas: the maple write state
  *
  * Return: True if stored, false otherwise
+ *
+ * Case 1:
+ *                       r_min   r_max    lmax
+ *                 +-------+-------+-------+
+ * original range: |       |offset | end   |
+ *                 +-----------------------+
+ *                         +-----------+
+ * overwrite:              |           |
+ *                         +-----------+
+ *                        index       last
+ *
+ * Case 2:
+ *                       r_min   r_max    lmax
+ *                 +-------+-------+-------+
+ * original range: |       |offest | end   |
+ *                 +-------+---------------+
+ *                             +-----------+
+ * overwrite:                  |           |
+ *                             +-----------+
+ *                           index        last
  */
 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;
+	unsigned char offset_end = wr_mas->offset_end;
+	unsigned long lmax = wr_mas->end_piv; /* Logical max. */
+	bool gap = false;
 
-	if ((wr_mas->r_max > mas->last) && ((wr_mas->r_min != mas->index) ||
-				  (offset != wr_mas->node_end)))
-		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)
+	if (offset_end - offset != 1)
 		return false;
 
-	if (wr_mas->r_min == mas->index) {
-		/* overwriting two or more ranges with one. */
-		if (lmax == mas->last)
-			return false;
-
-		/* Overwriting all of offset and a portion of offset + 1. */
+	if (mas->index == wr_mas->r_min && mas->last < lmax) {
+		/* Case 1 */
+		gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset);
+		gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset + 1);
 		rcu_assign_pointer(wr_mas->slots[offset], wr_mas->entry);
 		wr_mas->pivots[offset] = mas->last;
-		goto done;
-	}
-
-	/* Doesn't end on the next range end. */
-	if (lmax != mas->last)
+	} else if (mas->index > wr_mas->r_min && mas->last == lmax) {
+		/* Case 2 */
+		gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset);
+		gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset + 1);
+		rcu_assign_pointer(wr_mas->slots[offset + 1], wr_mas->entry);
+		wr_mas->pivots[offset] = mas->index - 1;
+		mas->offset++; /* Keep mas accurate. */
+	} else {
 		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;
 }
 
@@ -4418,7 +4427,7 @@ 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;
-- 
2.20.1