Re: [RFC][PATCH] Clarify mem_cgroup lock handling and avoid races.

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Wed, 20 Feb 2008 12:10:53 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > On Wed, 20 Feb 2008 04:14:58 +0000 (GMT)
> > Hugh Dickins <hugh@veritas.com> wrote:
> > 
> >> On Wed, 20 Feb 2008, KAMEZAWA Hiroyuki wrote:
> >>> On Tue, 19 Feb 2008 15:40:45 +0000 (GMT)
> >>> Hugh Dickins <hugh@veritas.com> wrote:
> >>>
> >>>> A lot in common with yours, a lot not.  (And none of it addressing
> >>>> that issue of opt-out I raise in the last paragraph: haven't begun
> >>>> to go into that one, hoped you and Balbir would look into it.)
> >>>>
> >>> I have some trial patches for reducing atomic_ops by do_it_lazy method.
> >>> Now, I'm afraid that performence is too bad when there is *no* memory
> >>> pressure.
> >> But it isn't just the atomic ops, it's the whole business of
> >> mem_cgroup_charge_common plus mem_cgroup_uncharge_page per page.
> >>
> >> The existence of force_empty indicates that the system can get along
> >> without the charge on the page. 
> > Yes.
> > 
> >> What's needed, I think, is something in struct mm, a flag or a reserved value
> >> in mm->mem_cgroup, to say don't do any of this mem_cgroup stuff on me; and a cgroup
> >> fs interface to set that, in the same way as force_empty is done.
> > 
> > I agree here. I believe we need "no charge" flag at least to the root group.
> > For root group, it's better to have boot option if not complicated.
> 
> I don't think that would work very well. A boot option to turn off everything
> makes more sense. The reason why I say it would not work very well is
> 
Everything turn off is ok for me. 

At that case, we have to care following.
1. disable mounting memory controller
2. hide "memory" from /proc/cgroup

At lease, it seems we can agree on "everything turn off" option.

Thanks,
-Kame

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