linux-kernel - Re: [PATCH] memcg: deprecate memory.force

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Date:	Wed, 14 May 2014 11:45:50 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Johannes Weiner <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Tejun Heo <tj@...nel.org>, Hugh Dickins <hughd@...gle.com>,
	Greg Thelen <gthelen@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: [PATCH] memcg: deprecate memory.force_empty knob

On Tue 13-05-14 14:39:53, Andrew Morton wrote:
> On Tue, 13 May 2014 17:29:16 +0200 Michal Hocko <mhocko@...e.cz> wrote:
> 
> > force_empty has been introduced primarily to drop memory before it gets
> > reparented on the group removal. This alone doesn't sound fully
> > justified because reparented pages which are not in use can be reclaimed
> > also later when there is a memory pressure on the parent level.
> > 
> > Mark the knob CFTYPE_INSANE which tells the cgroup core that it
> > shouldn't create the knob with the experimental sane_behavior. Other
> > users will get informed about the deprecation and asked to tell us more
> > because I do not expect most users will use sane_behavior cgroups mode
> > very soon.
> > Anyway I expect that most users will be simply cgroup remove handlers
> > which do that since ever without having any good reason for it.
> > 
> > If somebody really cares because reparented pages, which would be
> > dropped otherwise, push out more important ones then we should fix the
> > reparenting code and put pages to the tail.
> > 
> > ...
> >
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -4793,6 +4793,10 @@ static int mem_cgroup_force_empty_write(struct cgroup_subsys_state *css,
> >  
> >  	if (mem_cgroup_is_root(memcg))
> >  		return -EINVAL;
> > +	pr_info("%s (%d): memory.force_empty is deprecated and will be removed.",
> > +			current->comm, task_pid_nr(current));
> > +	pr_cont(" Let us know if you know if it needed in your usecase at");
> > +	pr_cont(" linux-mm@...ck.org\n");
> >  	return mem_cgroup_force_empty(memcg);
> >  }
> >  
> 
> Do we really want to spam the poor user each and every time they use
> this?  Using pr_info_once() is kinder and gentler?

We do not catch all potential callers but it is true that some
configurations might have thousands of cgroups and the notify_on_release
handler will spam the log.

> From: Andrew Morton <akpm@...ux-foundation.org>
> Subject: memcg-deprecate-memoryforce_empty-knob-fix
> 
> - s/pr_info/pr_info_once/
> - fix garbled printk text
> 
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...e.cz>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>

Acked-by: Michal Hocko <mhocko@...e.cz>

> ---
> 
>  Documentation/cgroups/memory.txt |    2 +-
>  mm/memcontrol.c                  |    8 ++++----
>  2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff -puN Documentation/cgroups/memory.txt~memcg-deprecate-memoryforce_empty-knob-fix Documentation/cgroups/memory.txt
> --- a/Documentation/cgroups/memory.txt~memcg-deprecate-memoryforce_empty-knob-fix
> +++ a/Documentation/cgroups/memory.txt
> @@ -482,7 +482,7 @@ About use_hierarchy, see Section 6.
>    memory.kmem.usage_in_bytes == memory.usage_in_bytes.
>  
>    Please note that this knob is considered deprecated and will be removed
> -  in future.
> +  in the future.
>  
>    About use_hierarchy, see Section 6.
>  
> diff -puN mm/memcontrol.c~memcg-deprecate-memoryforce_empty-knob-fix mm/memcontrol.c
> --- a/mm/memcontrol.c~memcg-deprecate-memoryforce_empty-knob-fix
> +++ a/mm/memcontrol.c
> @@ -4799,10 +4799,10 @@ static int mem_cgroup_force_empty_write(
>  
>  	if (mem_cgroup_is_root(memcg))
>  		return -EINVAL;
> -	pr_info("%s (%d): memory.force_empty is deprecated and will be removed.",
> -			current->comm, task_pid_nr(current));
> -	pr_cont(" Let us know if you know if it needed in your usecase at");
> -	pr_cont(" linux-mm@...ck.org\n");
> +	pr_info_once("%s (%d): memory.force_empty is deprecated and will be "
> +		     "removed.  Let us know if it is needed in your usecase at "
> +		     "linux-mm@...ck.org\n",
> +		     current->comm, task_pid_nr(current));
>  	return mem_cgroup_force_empty(memcg);
>  }
>  
> _
> 

-- 
Michal Hocko
SUSE Labs
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