* Wei Yang <richard.weiyang@xxxxxxxxx> [241017 09:46]:
> Currently, when storing NULL on mas_root_expand(), the behavior could be
> improved.
>
> For example possible cases are:
>
> * store NULL at any range result a new node
> * store NULL at range [m, n] where m > 0 to a single entry tree result
> a new node with range [m, n] set to NULL
> * store NULL at range [m, n] where m > 0 to an empty tree result
> consecutive NULL slot
>
> This patch tries to improve in:
>
> * memory efficient by setting to empty tree instead of using a node
> * remove the possibility of consecutive NULL slot which will prohibit
> extended null in later operation
>
> 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 | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index a90c29156fe2..15d2124acc36 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -3335,6 +3335,24 @@ static inline void mas_root_expand(struct ma_state *mas, void *entry)
> unsigned long *pivots;
> int slot = 0;
>
> + if (!entry) {
> + /*
> + * We come here in two cases:
> + * 1. This is an empty tree
> + * 2. This is a single entry tree with range [0, 0]
> + *
> + * If this is an empty tree, the result should still be an
> + * empty tree no matter what the range is.
> + *
> + * If this is a single entry tree, we should set it to an
> + * empty tree if the range cover [0, 0]. Otherwise, we don't
> + * need to change it.
> + */
> + if (!mas->index && contents)
> + rcu_assign_pointer(mas->tree->ma_root, NULL);
> + return;
> + }
> +
This fix should be done in mas_store_root(), which will probably reduce
or remove your lengthy comment.
mas_root_expand() should... expand the root, and this isn't what is
happening now.
> node = mas_pop_node(mas);
> pivots = ma_pivots(node, type);
> slots = ma_slots(node, type);
> --
> 2.34.1
>
