From 5dbc5ee51dbb7431c1dbd9533e888939677e1a6f Mon Sep 17 00:00:00 2001
From: Wei Yang <richard.weiyang@gmail.com>
Date: Wed, 13 Nov 2024 03:16:14 +0000
Subject: [PATCH] maple_tree: simplify split calculation
commit 4f6a6bed0bfef4b966f076f33eb4f5547226056a upstream.
Patch series "simplify split calculation", v3.
This patch (of 3):
The current calculation for splitting nodes tries to enforce a minimum
span on the leaf nodes. This code is complex and never worked correctly
to begin with, due to the min value being passed as 0 for all leaves.
The calculation should just split the data as equally as possible
between the new nodes. Note that b_end will be one more than the data,
so the left side is still favoured in the calculation.
The current code may also lead to a deficient node by not leaving enough
data for the right side of the split. This issue is also addressed with
the split calculation change.
[Liam.Howlett@Oracle.com: rephrase the change log]
Link: https://lkml.kernel.org/r/20241113031616.10530-1-richard.weiyang@gmail.com
Link: https://lkml.kernel.org/r/20241113031616.10530-2-richard.weiyang@gmail.com
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
lib/maple_tree.c | 23 ++++++-----------------
1 file changed, 6 insertions(+), 17 deletions(-)
diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index bf40f4327a598..b5d216bdd3a58 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -1890,11 +1890,11 @@ static inline int mab_no_null_split(struct maple_big_node *b_node,
* Return: The first split location. The middle split is set in @mid_split.
*/
static inline int mab_calc_split(struct ma_state *mas,
- struct maple_big_node *bn, unsigned char *mid_split, unsigned long min)
+ struct maple_big_node *bn, unsigned char *mid_split)
{
unsigned char b_end = bn->b_end;
int split = b_end / 2; /* Assume equal split. */
- unsigned char slot_min, slot_count = mt_slots[bn->type];
+ unsigned char slot_count = mt_slots[bn->type];
/*
* To support gap tracking, all NULL entries are kept together and a node cannot
@@ -1927,18 +1927,7 @@ static inline int mab_calc_split(struct ma_state *mas,
split = b_end / 3;
*mid_split = split * 2;
} else {
- slot_min = mt_min_slots[bn->type];
-
*mid_split = 0;
- /*
- * Avoid having a range less than the slot count unless it
- * causes one node to be deficient.
- * NOTE: mt_min_slots is 1 based, b_end and split are zero.
- */
- while ((split < slot_count - 1) &&
- ((bn->pivot[split] - min) < slot_count - 1) &&
- (b_end - split > slot_min))
- split++;
}
/* Avoid ending a node on a NULL entry */
@@ -2664,7 +2653,7 @@ static inline struct maple_enode
static inline unsigned char mas_mab_to_node(struct ma_state *mas,
struct maple_big_node *b_node, struct maple_enode **left,
struct maple_enode **right, struct maple_enode **middle,
- unsigned char *mid_split, unsigned long min)
+ unsigned char *mid_split)
{
unsigned char split = 0;
unsigned char slot_count = mt_slots[b_node->type];
@@ -2677,7 +2666,7 @@ static inline unsigned char mas_mab_to_node(struct ma_state *mas,
if (b_node->b_end < slot_count) {
split = b_node->b_end;
} else {
- split = mab_calc_split(mas, b_node, mid_split, min);
+ split = mab_calc_split(mas, b_node, mid_split);
*right = mas_new_ma_node(mas, b_node);
}
@@ -3076,7 +3065,7 @@ static int mas_spanning_rebalance(struct ma_state *mas,
mast->bn->b_end--;
mast->bn->type = mte_node_type(mast->orig_l->node);
split = mas_mab_to_node(mas, mast->bn, &left, &right, &middle,
- &mid_split, mast->orig_l->min);
+ &mid_split);
mast_set_split_parents(mast, left, middle, right, split,
mid_split);
mast_cp_to_nodes(mast, left, middle, right, split, mid_split);
@@ -3591,7 +3580,7 @@ static int mas_split(struct ma_state *mas, struct maple_big_node *b_node)
if (mas_push_data(mas, height, &mast, false))
break;
- split = mab_calc_split(mas, b_node, &mid_split, prev_l_mas.min);
+ split = mab_calc_split(mas, b_node, &mid_split);
mast_split_data(&mast, mas, split);
/*
* Usually correct, mab_mas_cp in the above call overwrites
--
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