* Wei Yang <richard.weiyang@xxxxxxxxx> [241018 22:37]:
> Currently, when storing NULL on mas_store_root(), 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
> * it allows for multiple NULL entries by expanding root to
> store NULLs to an empty tree
>
> 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>
Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
>
> ---
> v3: move change into mas_store_root()
> v4: add a comment and simplify the logic a little
> adjust the change log a little
> ---
> lib/maple_tree.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index 2226e77c00cb..1205a5208cfe 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -3439,9 +3439,20 @@ static inline void mas_root_expand(struct ma_state *mas, void *entry)
> return;
> }
>
> +/*
> + * mas_store_root() - Storing value into root.
> + * @mas: The maple state
> + * @entry: The entry to store.
> + *
> + * There is no root node now and we are storing a value into the root - this
> + * function either assigns the pointer or expands into a node.
> + */
> static inline void mas_store_root(struct ma_state *mas, void *entry)
> {
> - if (likely((mas->last != 0) || (mas->index != 0)))
> + if (!entry) {
> + if (!mas->index)
> + rcu_assign_pointer(mas->tree->ma_root, NULL);
> + } else if (likely((mas->last != 0) || (mas->index != 0)))
> mas_root_expand(mas, entry);
> else if (((unsigned long) (entry) & 3) == 2)
> mas_root_expand(mas, entry);
> --
> 2.34.1
>
