Re: [patch] mm, memcg: do not allow tasks to be attached with zero limit

[Michal Hocko <mhocko@suse.cz>]

On Tue 13-03-12 17:51:18, Johannes Weiner wrote:
> On Fri, Mar 09, 2012 at 10:57:06AM +0900, KAMEZAWA Hiroyuki wrote:
> > On Thu, 8 Mar 2012 17:38:18 -0800
> > Andrew Morton <akpm@linux-foundation.org> wrote:
> > 
> > > On Fri, 9 Mar 2012 10:22:55 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > > 
> > > > On Thu, 8 Mar 2012 12:29:51 -0800
> > > > Andrew Morton <akpm@linux-foundation.org> wrote:
> > > > 
> > > > > On Wed, 7 Mar 2012 19:14:49 -0800 (PST)
> > > > > David Rientjes <rientjes@google.com> wrote:
> > > > > 
> > > > > > This patch prevents tasks from being attached to a memcg if there is a
> > > > > > hard limit of zero.
> > > > > 
> > > > > We're talking about the memcg's limit_in_bytes here, yes?
> > > > > 
> > > > > > Additionally, the hard limit may not be changed to
> > > > > > zero if there are tasks attached.
> > > > > 
> > > > > hm, well...  why?  That would be user error, wouldn't it?  What is
> > > > > special about limit_in_bytes=0?  The memcg will also be unviable if
> > > > > limit_in_bytes=1, but we permit that.
> > > > > 
> > > > > IOW, confused.
> > > > > 
> > > > Ah, yes. limit_in_bytes < some small size can cause the same trouble.
> > > > Hmm... should we have configurable min_limit_in_bytes as sysctl or root memcg's
> > > > attaribute.. ?
> > > 
> > > Why do *anything*?  If the operator chose an irrational configuration
> > > then things won't work correctly and the operator will then fix the
> > > configuration?
> > > 
> > 
> > Because the result of 'error operaton' is SIGKILL to a task, which may be
> > owned by very importang customer of hosting service.
> > 
> > Isn't this severe punishment for error operation ?
> > 
> > Considering again, I have 2 thoughts.
> > 
> > - it should be guarded by MiddleWare, it's not kernel job !
> > - memcg should be more easy-to-use, friendly to users.
> > 
> > If the result is just an error as EINVAL or EBUSY, I may not be nervous....
> 
> You can still disable the OOM killer.  If you don't, you can always
> get killed, so I'm not convinced by this patch or a sysctl, either.

Agreed, kernel usually doesn't care about insane settings and it does
what it is told to do (why to safe somebody from shooting its own
foot?).

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic

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