linux-kernel - [PATCH v2] maple_tree: simplify mas_wr_node

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Message-ID: <20240823081729.GA23434@systemsresearch.io>
Date: Fri, 23 Aug 2024 08:17:29 +0000
From: Hao Li <haoli.tcs@...il.com>
To: Liam.Howlett@...cle.com
Cc: akpm@...ux-foundation.org, maple-tree@...ts.infradead.org,
	haoli.tcs@...il.com, linux-kernel@...r.kernel.org
Subject: [PATCH v2] maple_tree: simplify mas_wr_node_walk for improved
 readability

Refactor mas_wr_node_walk to make the code more clear and easier to
understand. The main changes are:

1. Replace the forward-iterating loop with a backward-iterating loop.
 This simplifies the logic for determining the correct range
 containing mas->index.

2. Eliminate the ternary operator.

The new implementation maintains the same functionality as before, but
with improved readability. The performance characteristics remain
essentially the same, as we cannot predict which interval mas->index
will fall into.

Signed-off-by: Hao Li <haoli.tcs@...il.com>
---
 lib/maple_tree.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index fe1b01b29..0b3eb55d8 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -2203,7 +2203,7 @@ static inline void mas_node_or_none(struct ma_state *mas,
 static inline void mas_wr_node_walk(struct ma_wr_state *wr_mas)
 {
 	struct ma_state *mas = wr_mas->mas;
-	unsigned char count, offset;
+	int idx;
 
 	if (unlikely(ma_is_dense(wr_mas->type))) {
 		wr_mas->r_max = wr_mas->r_min = mas->index;
@@ -2213,16 +2213,14 @@ static inline void mas_wr_node_walk(struct ma_wr_state *wr_mas)
 
 	wr_mas->node = mas_mn(wr_mas->mas);
 	wr_mas->pivots = ma_pivots(wr_mas->node, wr_mas->type);
-	count = mas->end = ma_data_end(wr_mas->node, wr_mas->type,
+	mas->end = ma_data_end(wr_mas->node, wr_mas->type,
 				       wr_mas->pivots, mas->max);
-	offset = mas->offset;
-
-	while (offset < count && mas->index > wr_mas->pivots[offset])
-		offset++;
-
-	wr_mas->r_max = offset < count ? wr_mas->pivots[offset] : mas->max;
-	wr_mas->r_min = mas_safe_min(mas, wr_mas->pivots, offset);
-	wr_mas->offset_end = mas->offset = offset;
+	wr_mas->r_max = mas->max;
+	idx = mas->end - 1;
+	while (idx >= mas->offset && wr_mas->pivots[idx] >= mas->index)
+		wr_mas->r_max = wr_mas->pivots[idx--];
+	wr_mas->offset_end = mas->offset = idx + 1;
+	wr_mas->r_min = mas_safe_min(mas, wr_mas->pivots, mas->offset);
 }
 
 /*
-- 
2.21.0