* Wei Yang <richard.weiyang@xxxxxxxxx> [241019 22:46]:
> The check in mab_calc_split() is to make sure the gap between
> [0, split] won't be too small. But we don't pass the correct min.
>
> First we may encounter a pivot[split] smaller than min. For example:
>
> mt_init_flags(mt, 0);
> for (count = 0; count <= 240; count++) {
> mas_set(&mas, count);
> mas_store(&mas, xa_mk_value(count));
> }
>
> On splitting root for storing 240, the pivot[split] is smaller than min.
> This result a huge (pivot[split] - min).
This is fine.
There is an open work item to make it more accurate at higher levels,
but it's not a problem as it is.
Each level upwards needs a better 'minimum span', meaning that the node
should have at least mas.min - mas.min + level * something.
It works today for leaves, somewhat.
>
> Second prev_l_mas.min is not initialized for the first iteration. This
> means on splitting leaf node, this value is mostly taking no effect.
No, it is set to 0. Not initialized would cause random data loss.
See MA_STATE() in the header.
>
> Since we are now calculating the split of mas->node, we should use the
> mas->min instead of prev_l_mas.min.
This sounds reasonable, but considering what this number is used for, I
don't see how it is working as well as it is today. I will need to look
deeper into this.
>
> 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>
> ---
> lib/maple_tree.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index 894dc5e9436e..c2d4b188646c 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -3357,7 +3357,7 @@ 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, mas->min);
> mast_split_data(&mast, mas, split);
> /*
> * Usually correct, mab_mas_cp in the above call overwrites
> --
> 2.34.1
>
