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: rephrase the change log]
Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
CC: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
CC: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
CC: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
v3:
* Liam helps rephrase the change log
* add fix tag and cc stable
---
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 d0ae808f3a14..4f2950a1c38d 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -1863,11 +1863,11 @@ 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
@@ -1900,18 +1900,7 @@ 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 */
@@ -2377,7 +2366,7 @@ 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];
@@ -2390,7 +2379,7 @@ 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);
}
@@ -2877,7 +2866,7 @@ static void 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);
@@ -3365,7 +3354,7 @@ static void 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
--
2.34.1
