Re: [PATCH] btrfs: delayed-ref: extract find_first_ref_head from find_ref_head

[Nikolay Borisov <nborisov@suse.com>]

On 15.10.2018 09:25, Lu Fengqi wrote:
> The find_ref_head shouldn't return the first entry even if no exact match
> is found. So move the hidden behavior to higher level.
> 
> Besides, remove the useless local variables in the btrfs_select_ref_head.
> 
> Signed-off-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>

Reviewed-by: Nikolay Borisov <nborisov@suse.com>

> ---
>  fs/btrfs/delayed-ref.c | 45 +++++++++++++++++++++++-------------------
>  1 file changed, 25 insertions(+), 20 deletions(-)
> 
> diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
> index 6e8be384398e..a92f104cf06f 100644
> --- a/fs/btrfs/delayed-ref.c
> +++ b/fs/btrfs/delayed-ref.c
> @@ -164,14 +164,28 @@ static struct btrfs_delayed_ref_node* tree_insert(struct rb_root_cached *root,
>  	return NULL;
>  }
>  
> +static struct btrfs_delayed_ref_head *find_first_ref_head(
> +		struct btrfs_delayed_ref_root *dr)
> +{
> +	struct rb_node *n;
> +	struct btrfs_delayed_ref_head *entry;
> +
> +	n = rb_first_cached(&dr->href_root);
> +	if (!n)
> +		return NULL;
> +
> +	entry = rb_entry(n, struct btrfs_delayed_ref_head, href_node);
> +
> +	return entry;
> +}
> +
>  /*
>   * find an head entry based on bytenr. This returns the delayed ref
>   * head if it was able to find one, or NULL if nothing was in that spot.
>   * If return_bigger is given, the next bigger entry is returned if no exact
> - * match is found. But if no bigger one is found then the first node of the
> - * ref head tree will be returned.
> + * match is found.
>   */
> -static struct btrfs_delayed_ref_head* find_ref_head(
> +static struct btrfs_delayed_ref_head *find_ref_head(
>  		struct btrfs_delayed_ref_root *dr, u64 bytenr,
>  		bool return_bigger)
>  {
> @@ -195,10 +209,9 @@ static struct btrfs_delayed_ref_head* find_ref_head(
>  		if (bytenr > entry->bytenr) {
>  			n = rb_next(&entry->href_node);
>  			if (!n)
> -				n = rb_first_cached(&dr->href_root);
> +				return NULL;
>  			entry = rb_entry(n, struct btrfs_delayed_ref_head,
>  					 href_node);
> -			return entry;
>  		}
>  		return entry;
>  	}
> @@ -358,33 +371,25 @@ struct btrfs_delayed_ref_head *btrfs_select_ref_head(
>  		struct btrfs_delayed_ref_root *delayed_refs)
>  {
>  	struct btrfs_delayed_ref_head *head;
> -	u64 start;
> -	bool loop = false;
>  
>  again:
> -	start = delayed_refs->run_delayed_start;
> -	head = find_ref_head(delayed_refs, start, true);
> -	if (!head && !loop) {
> +	head = find_ref_head(delayed_refs, delayed_refs->run_delayed_start,
> +			     true);
> +	if (!head && delayed_refs->run_delayed_start != 0) {
>  		delayed_refs->run_delayed_start = 0;
> -		start = 0;
> -		loop = true;
> -		head = find_ref_head(delayed_refs, start, true);
> -		if (!head)
> -			return NULL;
> -	} else if (!head && loop) {
> -		return NULL;
> +		head = find_first_ref_head(delayed_refs);
>  	}
> +	if (!head)
> +		return NULL;
>  
>  	while (head->processing) {
>  		struct rb_node *node;
>  
>  		node = rb_next(&head->href_node);
>  		if (!node) {
> -			if (loop)
> +			if (delayed_refs->run_delayed_start == 0)
>  				return NULL;
>  			delayed_refs->run_delayed_start = 0;
> -			start = 0;
> -			loop = true;
>  			goto again;
>  		}
>  		head = rb_entry(node, struct btrfs_delayed_ref_head,
>