Re: [PATCH][RFC] dirty balancing for cgroups

Peter Zijlstra
2008-07-14T13:37:07Z

On Wed, 2008-07-09 at 15:00 +0900, YAMAMOTO Takashi wrote:
> hi,
>
> the following patch is a simple implementation of
> dirty balancing for cgroups. any comments?
>
> it depends on the following fix:
> http://lkml.org/lkml/2008/7/8/428
>
> YAMAMOTO Takashi
>
>
> Signed-off-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
> ---

Yamamoto-san,

> @@ -408,7 +412,11 @@ get_dirty_limits(long *pbackground, long *pdirty, long *pbdi_dirty,
>
> *pbdi_dirty = bdi_dirty;
> clip_bdi_dirty_limit(bdi, dirty, pbdi_dirty);
> - task_dirty_limit(current, pbdi_dirty);
> + task_dirty = *pbdi_dirty;
> + task_dirty_limit(current, &task_dirty);
> + cgroup_dirty = *pbdi_dirty;
> + memdirtylimitcgroup_dirty_limit(current, &cgroup_dirty);
> + *pbdi_dirty = min(task_dirty, cgroup_dirty);
> }
> }

I think this is wrong - is basically breaks task dirty throttling within
groups. You'd need a multiplicative operation, something like:

bdi_dirty = dirty * p(bdi) * p(cgroup) * (1 - p(task))

However then we still have problems... see the next email further down
the thread.