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

[KAMEZAWA Hiroyuki <kamezawa hiroyu jp fujitsu com>]

On Tue, 1 Sep 2009 10:11:42 -0400
Vivek Goyal <vgoyal redhat com> wrote:
> > > > - Somebody also gave an example where there is a memory hogging process and
> > > >  possibly pushes out some processes to swap. It does not sound fair to
> > > >  charge those proccess for that swap writeout. These processes never
> > > >  requested swap IO.
> > 
> > I think that swap writeouts should be charged to the memory hogging
> > process, because the process consumes more resources and it should get
> > a penalty.
> > 
> 
> A process requesting memory gets IO penalty? IMHO, swapping is a kernel 
> mechanism and kernel's way of providing extended RAM. If we want to solve
> the issue of memory hogging by a process then right way to solve is to use
> memory controller and not by charging the process for IO activity.
> Instead, proabably a more suitable way is to charge swap activity to root
> group (where by default all the kernel related activity goes).   
> 

I agree. It't memcg's job.
(Support dirty_ratio in memcg is necessary, I think)

background-write-out-to-swap-for-memory-shortage should be handled
as kernel I/O. If swap-out-by-memcg bacause of its limit is a problem,
dirty_ratio for memcg should be implemetned.

Thanks,
-Kame