Re: [PATCH 3/6] cgroup: introduce cgroup_taskset and use it insubsys->can_attach(), cancel_attach() and attach()

[KAMEZAWA Hiroyuki]

On Thu, 25 Aug 2011 10:20:49 +0200
Tejun Heo <tj@xxxxxxxxxx> wrote:

> Hello, KAMEZAWA.
> 

> > > @@ -5460,8 +5460,9 @@ static void mem_cgroup_clear_mc(void)
> > >  
> > >  static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
> > >  				struct cgroup *cgroup,
> > > -				struct task_struct *p)
> > > +				struct cgroup_taskset *tset)
> > >  {
> > > +	struct task_struct *p = cgroup_taskset_first(tset);
> > >  	int ret = 0;
> > >  	struct mem_cgroup *mem = mem_cgroup_from_cont(cgroup);
> > >  
> > 
> > Ah..hmm. I think this doesn't work as expected for memcg.
> > Maybe code like this will be required.
> 
> Hmmm... the above is basically identity transformation of the existing
> code.  If the above is broken, the current code is broken too.  Is it?
> 
Current code is not broken.

mem_cgroup_can_attach(....., task) need to do real job only when task->mm->owner
== task. In this modification, you pass a set of task at once.
So, mem_cgroup_can_attach() need to check _all_ tasks in tset rather than a
first task in tset. please scan and find mm->owner.

Anyway, if you merge this onto mm-tree first, I think I can have time to
write a fix up if complicated.

Thanks,
-Kame

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