[dm-devel] Re: [PATCH 15/20] io-controller: map async requests to appropriate cgroup

[Ryo Tsuruta <ryov valinux co jp>]

Hi Vivek,

> +#ifdef CONFIG_TRACK_ASYNC_CONTEXT
> +	if (elv_bio_sync(bio)) {
> +		/* sync io. Determine cgroup from submitting task context. */
> +		cgroup = task_cgroup(current, io_subsys_id);
> +		return cgroup;
> +	}
> +
> +	/* Async io. Determine cgroup from with cgroup id stored in page */
> +	bio_cgroup_id = get_blkio_cgroup_id(bio);
> +
> +	if (!bio_cgroup_id)
> +		return NULL;
> +
> +	cgroup = blkio_cgroup_lookup(bio_cgroup_id);
> +#else
> +	cgroup = task_cgroup(current, io_subsys_id);
> +#endif
> +	return cgroup;
> +}

There is a case where a kernel thread (such as device-mapper drivers)
submits a sync IO instead of a task which originates the IO. I think
you should always use get_blkio_cgroup_id() to determine cgroup.

Thanks,
Ryo Tsuruta