linux-kernel - Re: [patch 3/8] mm: memcg: clean up fault accounting

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Message-ID: <20111124093349.GC26036@tiehlicka.suse.cz>
Date:	Thu, 24 Nov 2011 10:33:49 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <bsingharora@...il.com>, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 3/8] mm: memcg: clean up fault accounting

On Wed 23-11-11 16:42:26, Johannes Weiner wrote:
> From: Johannes Weiner <jweiner@...hat.com>
> 
> The fault accounting functions have a single, memcg-internal user, so
> they don't need to be global.  In fact, their one-line bodies can be
> directly folded into the caller.  

At first I thought that this doesn't help much because the generated
code should be exactly same but thinking about it some more it makes
sense.
We should have a single place where we account for events. Maybe we
should include also accounting done in mem_cgroup_charge_statistics
(this would however mean that mem_cgroup_count_vm_event would have to be
split). What do you think?

> And since faults happen one at a time, use this_cpu_inc() directly
> instead of this_cpu_add(foo, 1).

The generated code will be same but it is easier to read, so agreed.

> 
> Signed-off-by: Johannes Weiner <jweiner@...hat.com>

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

> ---
>  mm/memcontrol.c |   14 ++------------
>  1 files changed, 2 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 473b99f..d825af9 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -589,16 +589,6 @@ static void mem_cgroup_swap_statistics(struct mem_cgroup *memcg,
>  	this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_SWAPOUT], val);
>  }
>  
> -void mem_cgroup_pgfault(struct mem_cgroup *memcg, int val)
> -{
> -	this_cpu_add(memcg->stat->events[MEM_CGROUP_EVENTS_PGFAULT], val);
> -}
> -
> -void mem_cgroup_pgmajfault(struct mem_cgroup *memcg, int val)
> -{
> -	this_cpu_add(memcg->stat->events[MEM_CGROUP_EVENTS_PGMAJFAULT], val);
> -}
> -
>  static unsigned long mem_cgroup_read_events(struct mem_cgroup *memcg,
>  					    enum mem_cgroup_events_index idx)
>  {
> @@ -913,10 +903,10 @@ void mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx)
>  
>  	switch (idx) {
>  	case PGMAJFAULT:
> -		mem_cgroup_pgmajfault(memcg, 1);
> +		this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGFAULT]);
>  		break;
>  	case PGFAULT:
> -		mem_cgroup_pgfault(memcg, 1);
> +		this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGMAJFAULT]);
>  		break;
>  	default:
>  		BUG();
> -- 
> 1.7.6.4
> 

-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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