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

Michal Hocko
2011-06-30T06:32:41Z

On Thu 30-06-11 12:32:29, KAMEZAWA Hiroyuki wrote:
> On Wed, 29 Jun 2011 13:00:43 -0700
> Andrew Morton <akpm@linux-foundation.org> wrote:
>
> > On Wed, 29 Jun 2011 19:03:25 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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@jp.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@jp.fujitsu.com>

Reviewed-by: Michal Hocko <mhocko@suse.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