Re: [patch] memcg: add oom killer delay

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

On Mon, 7 Feb 2011 18:13:22 -0800 (PST)
David Rientjes <rientjes@google.com> wrote:

> On Tue, 8 Feb 2011, KAMEZAWA Hiroyuki wrote:
> 
> > > +static int mem_cgroup_oom_delay_millisecs_write(struct cgroup *cgrp,
> > > +					struct cftype *cft, u64 val)
> > > +{
> > > +	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
> > > +	struct mem_cgroup *iter;
> > > +
> > > +	if (val > MAX_SCHEDULE_TIMEOUT)
> > > +		return -EINVAL;
> > > +
> > > +	for_each_mem_cgroup_tree(iter, memcg) {
> > > +		iter->oom_delay = msecs_to_jiffies(val);
> > > +		memcg_oom_recover(iter);
> > > +	}
> > > +	return 0;
> > 
> > Seems nicer and it seems you tries to update all children cgroups.
> > 
> > BTW, with above code, with following heirarchy,
> > 
> >     A
> >    /
> >   B  
> >  /
> > C
> > 
> > When a user set oom_delay in order as A->B->C, A,B,C can have 'different' numbers.
> > When a user set oom_delay in order as C->B->A, A,B,C will have the same numbers.
> > 
> > This intreface seems magical, or broken.
> > 
> 
> It's not really magical, it just means that if you change the delay for a 
> memcg that you do so for all of its children implicitly as well.
> 
But you didn't explain the bahavior in Documenation.

> An alternative would be to ensure that a child memcg may never have a 
> delay greater than the delay of its parent.  Would you prefer that 
> instead?
> 
I don't think such limitation makes sense.

My point is just that the behavior is very special in current memcg interfaces. 
They do
 - It's not allowed to set attribute to no-children, no-parent cgroup

So, please explain above behavior in Documenation.

Thanks,
-Kame


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