linux-kernel - Re: [PATCH 1/2] f2fs: use separate list iterator variable to call list_move

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Date:   Tue, 12 Apr 2022 17:40:27 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jakob Koschel <jakobkoschel@...il.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Mike Rapoport <rppt@...nel.org>,
        Brian Johannesmeyer <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: Re: [PATCH 1/2] f2fs: use separate list iterator variable to call
 list_move_tail()

On 2022/4/1 6:16, Jakob Koschel wrote:
> In preparation to limit the scope of a list iterator to the list
> traversal loop, use a dedicated pointer to point to the found element
> [1].
> 
> If no break is hit or the list is empty, 'next' will be NULL and
> list_move_tail() should be called explicitly on the head directly.
> 
> Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/
> Signed-off-by: Jakob Koschel <jakobkoschel@...il.com>
> ---
>   fs/f2fs/segment.c | 12 ++++++++----
>   1 file changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 22dfeb991529..81ef2c3d08e5 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -4175,16 +4175,20 @@ static void release_sit_entry_set(struct sit_entry_set *ses)
>   static void adjust_sit_entry_set(struct sit_entry_set *ses,
>   						struct list_head *head)
>   {
> -	struct sit_entry_set *next = ses;
> +	struct sit_entry_set *next = NULL, *iter = ses;
>   
>   	if (list_is_last(&ses->set_list, head))
>   		return;
>   
> -	list_for_each_entry_continue(next, head, set_list)
> -		if (ses->entry_cnt <= next->entry_cnt)
> +	list_for_each_entry_continue(iter, head, set_list)
> +		if (ses->entry_cnt <= iter->entry_cnt) {
> +			next = iter;
> +			list_move_tail(&ses->set_list, &iter->set_list);
>   			break;

return;

> +		}
>   
> -	list_move_tail(&ses->set_list, &next->set_list);
> +	if (!next)
> +		list_move_tail(&ses->set_list, head);

list_move_tail(&ses->set_list, head);

Then we don't need @next variable, right?

Thanks,

>   }
>   
>   static void add_sit_entry(unsigned int segno, struct list_head *head)
> 
> base-commit: d888c83fcec75194a8a48ccd283953bdba7b2550