[dm-devel] Re: [PATCH 09/25] io-controller: Common hierarchical fair queuing code in elevaotor layer

[Gui Jianfeng <guijianfeng cn fujitsu com>]

Vivek Goyal wrote:
...
> +static struct io_group *
> +io_group_chain_alloc(struct request_queue *q, void *key, struct cgroup *cgroup)
> +{
> +	struct io_cgroup *iocg;
> +	struct io_group *iog, *leaf = NULL, *prev = NULL;
> +	gfp_t flags = GFP_ATOMIC |  __GFP_ZERO;
> +
> +	for (; cgroup != NULL; cgroup = cgroup->parent) {
> +		iocg = cgroup_to_io_cgroup(cgroup);
> +
> +		iog = io_cgroup_lookup_group(iocg, key);
> +		if (iog != NULL) {
> +			/*
> +			 * All the cgroups in the path from there to the
> +			 * root must have a io_group for efqd, so we don't
> +			 * need any more allocations.
> +			 */
> +			break;
> +		}
> +
> +		iog = kzalloc_node(sizeof(*iog), flags, q->node);
> +		if (!iog)
> +			goto cleanup;
> +
> +		iog->iocg_id = css_id(&iocg->css);

  Hi Vivek,

  IMHO, The io_cgroup id is nothing more than keeping track the corresponding iocg.
  So why not just store iocg pointer in io_group and just get rid of this complexity.
  I'd like to post a patch to do this change, what's your opinion?

-- 
Regards
Gui Jianfeng