linux-kernel - [PATCH v3 04/10] maple_tree: Simplify mas_is_span

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Date:   Mon, 22 May 2023 13:06:50 +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 v3 04/10] maple_tree: Simplify mas_is_span_wr()

Make the code for detecting spanning writes more concise.

Signed-off-by: Peng Zhang <zhangpeng.00@...edance.com>
---
 lib/maple_tree.c | 35 ++++++++++++-----------------------
 1 file changed, 12 insertions(+), 23 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 3fe6a6685384..c47af84047a4 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -3728,43 +3728,32 @@ static inline void mas_store_root(struct ma_state *mas, void *entry)
  */
 static bool mas_is_span_wr(struct ma_wr_state *wr_mas)
 {
-	unsigned long max;
+	unsigned long max = wr_mas->r_max;
 	unsigned long last = wr_mas->mas->last;
-	unsigned long piv = wr_mas->r_max;
 	enum maple_type type = wr_mas->type;
 	void *entry = wr_mas->entry;
 
-	/* Contained in this pivot */
-	if (piv > last)
+	/* Contained in this pivot, fast path */
+	if (last < max)
 		return false;
 
-	max = wr_mas->mas->max;
-	if (unlikely(ma_is_leaf(type))) {
-		/* Fits in the node, but may span slots. */
+	if (ma_is_leaf(type)) {
+		max = wr_mas->mas->max;
 		if (last < max)
 			return false;
+	}
 
-		/* Writes to the end of the node but not null. */
-		if ((last == max) && entry)
-			return false;
-
+	if (last == max) {
 		/*
-		 * Writing ULONG_MAX is not a spanning write regardless of the
-		 * value being written as long as the range fits in the node.
+		 * The last entry of leaf node cannot be NULL unless it is the
+		 * rightmost node (writing ULONG_MAX), otherwise it spans slots.
+		 * If this is not leaf node, detect spanning store wr walk.
 		 */
-		if ((last == ULONG_MAX) && (last == max))
-			return false;
-	} else if (piv == last) {
-		if (entry)
-			return false;
-
-		/* Detect spanning store wr walk */
-		if (last == ULONG_MAX)
+		if (entry || last == ULONG_MAX)
 			return false;
 	}
 
-	trace_ma_write(__func__, wr_mas->mas, piv, entry);
-
+	trace_ma_write(__func__, wr_mas->mas, wr_mas->r_max, entry);
 	return true;
 }
 
-- 
2.20.1