* Wei Yang <richard.weiyang@xxxxxxxxx> [241017 22:40]:
> 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
>
> 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
I don't understand this. Do we actually store consecutive NULLs now?
This is a very odd change log for fixing an optimisation. Maybe start
by explaining how we end up with a node with a single value now, then
state how this code changes that?
>
> 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>
>
> ---
> v3: move change into mas_store_root()
> ---
> lib/maple_tree.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index db8b89487c98..03fbee9880eb 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -3439,7 +3439,11 @@ static inline void mas_root_expand(struct ma_state *mas, void *entry)
>
> static inline void mas_store_root(struct ma_state *mas, void *entry)
> {
> - if (likely((mas->last != 0) || (mas->index != 0)))
> + if (!entry) {
> + void *contents = mas_root_locked(mas);
> +
> + if (!mas->index && contents)
> + rcu_assign_pointer(mas->tree->ma_root, NULL);
You are changing what used to handle any range that wasn't 0 to handle
storing NULL.
This seems really broken.
> + } else if (likely((mas->last != 0) || (mas->index != 0)))
Isn't this exactly what you have above in the if statement?
> mas_root_expand(mas, entry);
> else if (((unsigned long) (entry) & 3) == 2)
> mas_root_expand(mas, entry);
> --
> 2.34.1
>
