linux-kernel - Re: [PATCH 3/7] memcg: add memory.scan

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Date:	Mon, 27 Jun 2011 10:49:41 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Ying Han <yinghan@...gle.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"bsingharora@...il.com" <bsingharora@...il.com>,
	Michal Hocko <mhocko@...e.cz>,
	"hannes@...xchg.org" <hannes@...xchg.org>
Subject: Re: [PATCH 3/7] memcg: add memory.scan_stat

On Fri, 24 Jun 2011 14:40:42 -0700
Ying Han <yinghan@...gle.com> wrote:

> On Tue, Jun 21, 2011 at 5:20 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@...fujitsu.com> wrote:
> > On Mon, 20 Jun 2011 23:49:54 -0700
> > Ying Han <yinghan@...gle.com> wrote:
> >
> >> On Wed, Jun 15, 2011 at 8:53 PM, KAMEZAWA Hiroyuki <
> >> kamezawa.hiroyu@...fujitsu.com> wrote:
> >>
> >> > From e08990dd9ada13cf236bec1ef44b207436434b8e Mon Sep 17 00:00:00 2001
> >> > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> >> > Date: Wed, 15 Jun 2011 14:11:01 +0900
> >> > Subject: [PATCH 3/7] memcg: add memory.scan_stat

> >> > +
> >> > +struct scanstat {
> >> > +       spinlock_t      lock;
> >> > +       unsigned long   stats[NR_SCANSTATS];    /* local statistics */
> >> > +       unsigned long   totalstats[NR_SCANSTATS];   /* hierarchical */
> >> > +};
> 
> I wonder why not extending the mem_cgroup_stat_cpu struct, and then we
> can use the per-cpu counters like others.
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index b7d2d79..5b8bbe9 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -138,6 +138,7 @@ struct mem_cgroup_stat_cpu {
>         long count[MEM_CGROUP_STAT_NSTATS];
>         unsigned long events[MEM_CGROUP_EVENTS_NSTATS];
>         unsigned long targets[MEM_CGROUP_NTARGETS];
> +       unsigned long reclaim_stats[MEMCG_RECLAIM_NSTATS];
>  };
> 

Hmm, do we have enough benefit to consume 72 bytes per cpu and make
read-side slow for this rarely updated counter ?

Thanks,
-Kame

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