linux-kernel - [PATCH v2 03/36] maple_tree: Avoid unnecessary ascending

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Date:   Fri,  5 May 2023 13:41:31 -0400
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     maple-tree@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Peng Zhang <zhangpeng.00@...edance.com>
Subject: [PATCH v2 03/36] maple_tree: Avoid unnecessary ascending

The maple tree node limits are implied by the parent.  When walking up
the tree, the limit may not be known until a slot that does not have
implied limits are encountered.  However, if the node is the left-most
or right-most node, the walking up to find that limit can be skipped.

This commit also fixes the debug/testing code that was not setting the
limit on walking down the tree as that optimization is not compatible
with this change.

Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
Reviewed-by: Peng Zhang <zhangpeng.00@...edance.com>
---
 lib/maple_tree.c                 | 11 ++++++++---
 tools/testing/radix-tree/maple.c |  4 ++++
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 555de3a8343e1..5b29d5a916f2c 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -1103,7 +1103,6 @@ static int mas_ascend(struct ma_state *mas)
 	enum maple_type a_type;
 	unsigned long min, max;
 	unsigned long *pivots;
-	unsigned char offset;
 	bool set_max = false, set_min = false;
 
 	a_node = mas_mn(mas);
@@ -1115,8 +1114,9 @@ static int mas_ascend(struct ma_state *mas)
 	p_node = mte_parent(mas->node);
 	if (unlikely(a_node == p_node))
 		return 1;
+
 	a_type = mas_parent_type(mas, mas->node);
-	offset = mte_parent_slot(mas->node);
+	mas->offset = mte_parent_slot(mas->node);
 	a_enode = mt_mk_node(p_node, a_type);
 
 	/* Check to make sure all parent information is still accurate */
@@ -1124,7 +1124,6 @@ static int mas_ascend(struct ma_state *mas)
 		return 1;
 
 	mas->node = a_enode;
-	mas->offset = offset;
 
 	if (mte_is_root(a_enode)) {
 		mas->max = ULONG_MAX;
@@ -1132,6 +1131,12 @@ static int mas_ascend(struct ma_state *mas)
 		return 0;
 	}
 
+	if (!mas->min)
+		set_min = true;
+
+	if (mas->max == ULONG_MAX)
+		set_max = true;
+
 	min = 0;
 	max = ULONG_MAX;
 	do {
diff --git a/tools/testing/radix-tree/maple.c b/tools/testing/radix-tree/maple.c
index 9286d3baa12d6..75df543e019c9 100644
--- a/tools/testing/radix-tree/maple.c
+++ b/tools/testing/radix-tree/maple.c
@@ -35259,6 +35259,7 @@ static void mas_dfs_preorder(struct ma_state *mas)
 
 	struct maple_enode *prev;
 	unsigned char end, slot = 0;
+	unsigned long *pivots;
 
 	if (mas->node == MAS_START) {
 		mas_start(mas);
@@ -35291,6 +35292,9 @@ static void mas_dfs_preorder(struct ma_state *mas)
 		mas_ascend(mas);
 		goto walk_up;
 	}
+	pivots = ma_pivots(mte_to_node(prev), mte_node_type(prev));
+	mas->max = mas_safe_pivot(mas, pivots, slot, mte_node_type(prev));
+	mas->min = mas_safe_min(mas, pivots, slot);
 
 	return;
 done:
-- 
2.39.2