[patch 3/4] io controller: Core IO controller implementation logic

[Vivek Goyal]

On Fri, Nov 07, 2008 at 12:21:45PM +0900, KAMEZAWA Hiroyuki wrote:
> On Thu, 06 Nov 2008 10:30:25 -0500
> vgoyal at redhat.com wrote:
> 
> > 
> > o Core IO controller implementation
> > 
> > Signed-off-by: Vivek Goyal <vgoyal at redhat.com>
> > 
> 
> 2 comments after a quick look.
> 
>  - I don't recommend generic work queue. More stacked dependency between "work"
>    is not good. (I think disk-driver uses "work" for their jobs.)

Sorry, I did not get this. Are you recommending that don't create a new
work queue, instead use existing work queue (say kblockd) to submit the bios
here?

I will look into it. I was little worried about a kblockd being overworked
in case of too many logical devices enabling IO controller.

> 
>  - It seems this bio-cgroup can queue the bio to infinite. Then, a process can submit
>    io unitl cause OOM.
>    (IIUC, Dirty bit of the page is cleared at submitting I/O. 
>     Then dirty_ratio can't help us.)
>    please add "wait for congestion by sleeping" code in bio-cgroup.

Yes, you are right. I need to put some kind of control on max number of
bios I can queue on a cgroup and after crossing the limit, I should put
the submitting task to sleep. (Something like request descriptor kind of
flow control implememented by elevators).

Thanks
Vivek