Re: [PATCH v2 2/2] maple_tree: memset maple_big_node as a whole

["Liam R. Howlett" <Liam.Howlett@oracle.com>]

* Wei Yang <richard.weiyang@gmail.com> [240908 10:06]:
> In function mast_fill_bnode(), we first clear some fields of
> maple_big_node and set the 'type' unconditionally before return. This
> means we won't leverage any information in maple_big_node and it is safe
> to clear the whole structure.
> 
> In maple_big_node, we define slot and padding/gap in a union. And based
> on current definition of MAPLE_BIG_NODE_SLOTS/GAPS, padding is always
> less than slot and part of the gap is overlapped by slot.
> 
> For example on 64bit system:
> 
>   MAPLE_BIG_NODE_SLOT is 34
>   MAPLE_BIG_NODE_GAP  is 21
> 
> With this knowledge, current code may clear some space by twice. And
> this could be avoid by clearing the structure as a whole.
> 
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> CC: Liam R. Howlett <Liam.Howlett@Oracle.com>

Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>

> 
> ---
> v2: correct the change log on clearing all maple_big_node currently

Thanks!

> ---
>  lib/maple_tree.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index c3370c7449c2..b459fe1a3ebe 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -3134,10 +3134,7 @@ static inline void mast_fill_bnode(struct maple_subtree_state *mast,
>  	bool cp = true;
>  	unsigned char split;
>  
> -	memset(mast->bn->gap, 0, sizeof(unsigned long) * ARRAY_SIZE(mast->bn->gap));
> -	memset(mast->bn->slot, 0, sizeof(unsigned long) * ARRAY_SIZE(mast->bn->slot));
> -	memset(mast->bn->pivot, 0, sizeof(unsigned long) * ARRAY_SIZE(mast->bn->pivot));
> -	mast->bn->b_end = 0;
> +	memset(mast->bn, 0, sizeof(struct maple_big_node));
>  
>  	if (mte_is_root(mas->node)) {
>  		cp = false;
> -- 
> 2.34.1
>