linux-kernel - Re: [PATCH v2 6/6] maple_tree: reorder mas->store

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Message-ID: <ou54b7osedufg2wvw5wz6mfhzepnkkckeuh34yyo2nwffvpfxb@jrjzdcmuxkdi>
Date: Tue, 25 Feb 2025 11:03:40 -0500
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Sidhartha Kumar <sidhartha.kumar@...cle.com>
Cc: linux-kernel@...r.kernel.org, maple-tree@...ts.infradead.org,
        linux-mm@...ck.org, akpm@...ux-foundation.org,
        richard.weiyang@...il.com
Subject: Re: [PATCH v2 6/6] maple_tree: reorder mas->store_type case
 statements

* Sidhartha Kumar <sidhartha.kumar@...cle.com> [250221 11:36]:
> Move the unlikely case that mas->store_type is invalid to be the last
> evaluated case and put liklier cases higher up.
> 
> Suggested-by: Liam Howlett <liam.howlett@...cle.com>
> Signed-off-by: Sidhartha <sidhartha.kumar@...cle.com>

Thanks for doing this.  There will probably be zero change in the
benchmarking besides instruction count, but it's low risk and low effort
to do.

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

> ---
>  lib/maple_tree.c | 51 ++++++++++++++++++++++++------------------------
>  1 file changed, 25 insertions(+), 26 deletions(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index 8fdd3f477198..36d7d7a27e32 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -4091,15 +4091,6 @@ static inline void mas_wr_store_entry(struct ma_wr_state *wr_mas)
>  	unsigned char new_end = mas_wr_new_end(wr_mas);
>  
>  	switch (mas->store_type) {
> -	case wr_invalid:
> -		MT_BUG_ON(mas->tree, 1);
> -		return;
> -	case wr_new_root:
> -		mas_new_root(mas, wr_mas->entry);
> -		break;
> -	case wr_store_root:
> -		mas_store_root(mas, wr_mas->entry);
> -		break;
>  	case wr_exact_fit:
>  		rcu_assign_pointer(wr_mas->slots[mas->offset], wr_mas->entry);
>  		if (!!wr_mas->entry ^ !!wr_mas->content)
> @@ -4121,6 +4112,14 @@ static inline void mas_wr_store_entry(struct ma_wr_state *wr_mas)
>  	case wr_rebalance:
>  		mas_wr_bnode(wr_mas);
>  		break;
> +	case wr_new_root:
> +		mas_new_root(mas, wr_mas->entry);
> +		break;
> +	case wr_store_root:
> +		mas_store_root(mas, wr_mas->entry);
> +		break;
> +	case wr_invalid:
> +		MT_BUG_ON(mas->tree, 1);
>  	}
>  
>  	return;
> @@ -4185,19 +4184,10 @@ static inline int mas_prealloc_calc(struct ma_wr_state *wr_mas, void *entry)
>  	unsigned char delta = height - wr_mas->vacant_height;
>  
>  	switch (mas->store_type) {
> -	case wr_invalid:
> -		WARN_ON_ONCE(1);
> -		break;
> -	case wr_new_root:
> -		ret = 1;
> -		break;
> -	case wr_store_root:
> -		if (likely((mas->last != 0) || (mas->index != 0)))
> -			ret = 1;
> -		else if (((unsigned long) (entry) & 3) == 2)
> -			ret = 1;
> -		else
> -			ret = 0;
> +	case wr_exact_fit:
> +	case wr_append:
> +	case wr_slot_store:
> +		ret = 0;
>  		break;
>  	case wr_spanning_store:
>  		if (wr_mas->sufficient_height < wr_mas->vacant_height)
> @@ -4217,10 +4207,19 @@ static inline int mas_prealloc_calc(struct ma_wr_state *wr_mas, void *entry)
>  	case wr_node_store:
>  		ret = mt_in_rcu(mas->tree) ? 1 : 0;
>  		break;
> -	case wr_append:
> -	case wr_exact_fit:
> -	case wr_slot_store:
> -		ret = 0;
> +	case wr_new_root:
> +		ret = 1;
> +		break;
> +	case wr_store_root:
> +		if (likely((mas->last != 0) || (mas->index != 0)))
> +			ret = 1;
> +		else if (((unsigned long) (entry) & 3) == 2)
> +			ret = 1;
> +		else
> +			ret = 0;
> +		break;
> +	case wr_invalid:
> +		WARN_ON_ONCE(1);
>  	}
>  
>  	return ret;
> -- 
> 2.43.0
>