linux-kernel - Re: [PATCH] [Cleanup] memcg: export memory cgroup's swappiness v2

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Date:	Thu, 30 Jun 2011 08:32:32 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"bsingharora@...il.com" <bsingharora@...il.com>,
	Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH] [Cleanup] memcg: export memory cgroup's swappiness v2

On Thu 30-06-11 12:32:29, KAMEZAWA Hiroyuki wrote:
> On Wed, 29 Jun 2011 13:00:43 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Wed, 29 Jun 2011 19:03:25 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> > 
> > > Each memory cgroup has 'swappiness' value and it can be accessed by
> > > get_swappiness(memcg). The major user is try_to_free_mem_cgroup_pages()
> > > and swappiness is passed by argument. It's propagated by scan_control.
> > > 
> > > get_swappiness is static function but some planned updates will need to
> > > get swappiness from files other than memcontrol.c
> > > This patch exports get_swappiness() as mem_cgroup_swappiness().
> > > By this, we can remove the argument of swapiness from try_to_free...
> > > and drop swappiness from scan_control. only memcg uses it.
> > > 
> > 
> > > +extern unsigned int mem_cgroup_swappiness(struct mem_cgroup *mem);
> > > +unsigned int mem_cgroup_swappiness(struct mem_cgroup *memcg)
> > > +static int vmscan_swappiness(struct scan_control *sc)
> > 
> > The patch seems a bit confused about the signedness of swappiness.
> > 
> 
> ok, v3 here. Now, memcg's one use "int" because vm_swapiness is "int".
> ==
> 
> From af1bae8f2c6a8dbff048222bb45c7162b505f38b Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Date: Wed, 29 Jun 2011 18:24:49 +0900
> Subject: [PATCH] export memory cgroup's swappines by mem_cgroup_swappiness()
> 
> Each memory cgroup has 'swappiness' value and it can be accessed by
> get_swappiness(memcg). The major user is try_to_free_mem_cgroup_pages()
> and swappiness is passed by argument. It's propagated by scan_control.
> 
> get_swappiness is static function but some planned updates will need to
> get swappiness from files other than memcontrol.c
> This patch exports get_swappiness() as mem_cgroup_swappiness().
> By this, we can remove the argument of swapiness from try_to_free...
> and drop swappiness from scan_control. only memcg uses it.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

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

> 
> Changelog:
>   - adjusted signedness to vm_swappiness.
>   - drop swappiness from scan_control
> ---
>  include/linux/swap.h |   10 +++++++---
>  mm/memcontrol.c      |   15 +++++++--------
>  mm/vmscan.c          |   23 ++++++++++-------------
>  3 files changed, 24 insertions(+), 24 deletions(-)
> 
[...]
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 3e7d5e6..db70176 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
[...]
> @@ -4288,7 +4287,7 @@ static u64 mem_cgroup_swappiness_read(struct cgroup *cgrp, struct cftype *cft)
>  {
>  	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
>  
> -	return get_swappiness(memcg);
> +	return mem_cgroup_swappiness(memcg);
>  }

If you want to be type clean you should change this one as well. I
think it is worth it, though. The function is called only to return the
current value to userspace and mem_cgroup_swappiness_write guaranties
that it falls down into <0,100> interval. Additionally, cftype doesn't
have any read specialization for int values so you would need to use a
generic one. Finally if you changed read part you should change also
write part and add > 0 check which is a lot of code for not that good
reason.
-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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