6.6-stable review patch. If anyone has any objections, please let me know.
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From: Wei Yang richard.weiyang@gmail.com
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(-)
--- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -1870,11 +1870,11 @@ static inline int mab_no_null_split(stru * 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 @@ -1907,18 +1907,7 @@ static inline int mab_calc_split(struct 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 */ @@ -2402,7 +2391,7 @@ 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]; @@ -2415,7 +2404,7 @@ static inline unsigned char mas_mab_to_n 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); }
@@ -2905,7 +2894,7 @@ static int mas_spanning_rebalance(struct 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); @@ -3413,7 +3402,7 @@ static int mas_split(struct ma_state *ma 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