Re: [PATCH] blkcg: stop iteration early if root_rl is the only request list

[Vivek Goyal <vgoyal@redhat.com>]

On Mon, Oct 22, 2012 at 10:15:37AM +0900, Jun'ichi Nomura wrote:
> __blk_queue_next_rl() finds next request list based on blkg_list
> while skipping root_blkg in the list.
> OTOH, root_rl is special as it may exist even without root_blkg.
> 
> Though the later part of the function handles such a case correctly,
> exiting early is good for readability of the code.
> 

Thanks for the patch Junichi. This one looks good to me.

Acked-by: Vivek Goyal <vgoyal@redhat.com>

Vivek

> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
> Cc: Vivek Goyal <vgoyal@redhat.com>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Jens Axboe <axboe@kernel.dk>
> ---
>  block/blk-cgroup.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index 54f35d1..a31e678 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -333,6 +333,9 @@ struct request_list *__blk_queue_next_rl(struct request_list *rl,
>  	 */
>  	if (rl == &q->root_rl) {
>  		ent = &q->blkg_list;
> +		/* There are no more block groups, hence no request lists */
> +		if (list_empty(ent))
> +			return NULL;
>  	} else {
>  		blkg = container_of(rl, struct blkcg_gq, rl);
>  		ent = &blkg->q_node;