linux-kernel - Re: [PATCH v2] maple_tree: simplify mas_wr_node

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Message-ID: <8f98e3e8-b6c4-4888-bfc7-204bea32004b@bytedance.com>
Date: Fri, 23 Aug 2024 17:07:31 +0800
From: Peng Zhang <zhangpeng.00@...edance.com>
To: Hao Li <haoli.tcs@...il.com>
Cc: akpm@...ux-foundation.org, maple-tree@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Liam.Howlett@...cle.com
Subject: Re: [PATCH v2] maple_tree: simplify mas_wr_node_walk for improved
 readability



在 2024/8/23 16:17, Hao Li 写道:
> Refactor mas_wr_node_walk to make the code more clear and easier to
> understand. The main changes are:
> 
> 1. Replace the forward-iterating loop with a backward-iterating loop.
>   This simplifies the logic for determining the correct range
>   containing mas->index.
I don't think iterating in reverse is a good idea, it makes the code
different from everywhere else.
> 
> 2. Eliminate the ternary operator.
> 
> The new implementation maintains the same functionality as before, but
> with improved readability. The performance characteristics remain
> essentially the same, as we cannot predict which interval mas->index
> will fall into.
> 
> Signed-off-by: Hao Li <haoli.tcs@...il.com>
> ---
>   lib/maple_tree.c | 18 ++++++++----------
>   1 file changed, 8 insertions(+), 10 deletions(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index fe1b01b29..0b3eb55d8 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -2203,7 +2203,7 @@ static inline void mas_node_or_none(struct ma_state *mas,
>   static inline void mas_wr_node_walk(struct ma_wr_state *wr_mas)
>   {
>   	struct ma_state *mas = wr_mas->mas;
> -	unsigned char count, offset;
> +	int idx;
>   
>   	if (unlikely(ma_is_dense(wr_mas->type))) {
>   		wr_mas->r_max = wr_mas->r_min = mas->index;
> @@ -2213,16 +2213,14 @@ static inline void mas_wr_node_walk(struct ma_wr_state *wr_mas)
>   
>   	wr_mas->node = mas_mn(wr_mas->mas);
>   	wr_mas->pivots = ma_pivots(wr_mas->node, wr_mas->type);
> -	count = mas->end = ma_data_end(wr_mas->node, wr_mas->type,
> +	mas->end = ma_data_end(wr_mas->node, wr_mas->type,
>   				       wr_mas->pivots, mas->max);
> -	offset = mas->offset;
> -
> -	while (offset < count && mas->index > wr_mas->pivots[offset])
> -		offset++;
> -
> -	wr_mas->r_max = offset < count ? wr_mas->pivots[offset] : mas->max;
> -	wr_mas->r_min = mas_safe_min(mas, wr_mas->pivots, offset);
> -	wr_mas->offset_end = mas->offset = offset;
> +	wr_mas->r_max = mas->max;
> +	idx = mas->end - 1;
> +	while (idx >= mas->offset && wr_mas->pivots[idx] >= mas->index)
> +		wr_mas->r_max = wr_mas->pivots[idx--];
> +	wr_mas->offset_end = mas->offset = idx + 1;
> +	wr_mas->r_min = mas_safe_min(mas, wr_mas->pivots, mas->offset);
>   }
>   
>   /*