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

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On Thu, 8 Mar 2012 17:38:18 -0800
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:

> On Fri, 9 Mar 2012 10:22:55 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
> 
> > On Thu, 8 Mar 2012 12:29:51 -0800
> > Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > 
> > > On Wed, 7 Mar 2012 19:14:49 -0800 (PST)
> > > David Rientjes <rientjes@xxxxxxxxxx> 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....

Thanks,
-Kame 

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