[PATCH 18/23] io-controller: blkio_cgroup patches from Ryo to track async bios.

[Rik van Riel]

Vivek Goyal wrote:
> o blkio_cgroup patches from Ryo to track async bios.
> 
> o This functionality is used to determine the group of async IO from page
>   instead of context of submitting task.
> 
> Signed-off-by: Hirokazu Takahashi <taka at valinux.co.jp>
> Signed-off-by: Ryo Tsuruta <ryov at valinux.co.jp>
> Signed-off-by: Vivek Goyal <vgoyal at redhat.com>

This seems to be the most complex part of the code so far,
but I see why this code is necessary.

Acked-by: Rik van Riel <riel at redhat.com>