Re: [PATCH V2] Btrfs: fix unnecessary while loop when search the free space, cache

[Liu Bo <bo.li.liu@oracle.com>]

On 10/18/2012 04:18 PM, Miao Xie wrote:
> When we find a bitmap free space entry, we may check the previous extent
> entry covers the offset or not. But if we find this entry is also a bitmap
> entry, we will continue to check the previous entry of the current one by
> a while loop. It is unnecessary because it is impossible that the extent
> entry which is in front of a bitmap entry can cover the offset of the entry
> after that bitmap entry.
> 

Looks good to me.

Reviewed-by: Liu Bo <bo.li.liu@oracle.com>

> Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
> ---
> Changelog v1 -> v2:
> - fix the same problem in the other place
> ---
>  fs/btrfs/free-space-cache.c |   30 ++++++++++--------------------
>  1 files changed, 10 insertions(+), 20 deletions(-)
> 
> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
> index 1027b85..557502c 100644
> --- a/fs/btrfs/free-space-cache.c
> +++ b/fs/btrfs/free-space-cache.c
> @@ -1250,18 +1250,13 @@ tree_search_offset(struct btrfs_free_space_ctl *ctl,
>  			 * if previous extent entry covers the offset,
>  			 * we should return it instead of the bitmap entry
>  			 */
> -			n = &entry->offset_index;
> -			while (1) {
> -				n = rb_prev(n);
> -				if (!n)
> -					break;
> +			n = rb_prev(&entry->offset_index);
> +			if (n) {
>  				prev = rb_entry(n, struct btrfs_free_space,
>  						offset_index);
> -				if (!prev->bitmap) {
> -					if (prev->offset + prev->bytes > offset)
> -						entry = prev;
> -					break;
> -				}
> +				if (!prev->bitmap &&
> +				    prev->offset + prev->bytes > offset)
> +					entry = prev;
>  			}
>  		}
>  		return entry;
> @@ -1287,18 +1282,13 @@ tree_search_offset(struct btrfs_free_space_ctl *ctl,
>  	}
>  
>  	if (entry->bitmap) {
> -		n = &entry->offset_index;
> -		while (1) {
> -			n = rb_prev(n);
> -			if (!n)
> -				break;
> +		n = rb_prev(&entry->offset_index);
> +		if (n) {
>  			prev = rb_entry(n, struct btrfs_free_space,
>  					offset_index);
> -			if (!prev->bitmap) {
> -				if (prev->offset + prev->bytes > offset)
> -					return prev;
> -				break;
> -			}
> +			if (!prev->bitmap &&
> +			    prev->offset + prev->bytes > offset)
> +				return prev;
>  		}
>  		if (entry->offset + BITS_PER_BITMAP * ctl->unit > offset)
>  			return entry;
>