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Date:	Mon, 28 Dec 2009 11:37:39 +0900
From:	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	containers@...ts.linux-foundation.org, linux-mm@...ck.org,
	Paul Menage <menage@...gle.com>,
	Li Zefan <lizf@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Pavel Emelyanov <xemul@...nvz.org>,
	Dan Malek <dan@...eddedalley.com>,
	Vladislav Buzov <vbuzov@...eddedalley.com>,
	Alexander Shishkin <virtuoso@...nd.org>,
	linux-kernel@...r.kernel.org,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH v4 3/4] memcg: rework usage of stats by soft limit

On Sun, 27 Dec 2009 04:09:01 +0200, "Kirill A. Shutemov" <kirill@...temov.name> wrote:
> Instead of incrementing counter on each page in/out and comparing it
> with constant, we set counter to constant, decrement counter on each
> page in/out and compare it with zero. We want to make comparing as fast
> as possible. On many RISC systems (probably not only RISC) comparing
> with zero is more effective than comparing with a constant, since not
> every constant can be immediate operand for compare instruction.
> 
> Also, I've renamed MEM_CGROUP_STAT_EVENTS to MEM_CGROUP_STAT_SOFTLIMIT,
> since really it's not a generic counter.
> 
> Signed-off-by: Kirill A. Shutemov <kirill@...temov.name>
> ---
>  mm/memcontrol.c |   19 ++++++++++++++-----
>  1 files changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 1d71cb4..36eb7af 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -69,8 +69,9 @@ enum mem_cgroup_stat_index {
>  	MEM_CGROUP_STAT_FILE_MAPPED,  /* # of pages charged as file rss */
>  	MEM_CGROUP_STAT_PGPGIN_COUNT,	/* # of pages paged in */
>  	MEM_CGROUP_STAT_PGPGOUT_COUNT,	/* # of pages paged out */
> -	MEM_CGROUP_STAT_EVENTS,	/* sum of pagein + pageout for internal use */
>  	MEM_CGROUP_STAT_SWAPOUT, /* # of pages, swapped out */
> +	MEM_CGROUP_STAT_SOFTLIMIT, /* decrements on each page in/out.
> +					used by soft limit implementation */
>  
>  	MEM_CGROUP_STAT_NSTATS,
>  };
> @@ -90,6 +91,13 @@ __mem_cgroup_stat_reset_safe(struct mem_cgroup_stat_cpu *stat,
>  	stat->count[idx] = 0;
>  }
>  
> +static inline void
> +__mem_cgroup_stat_set(struct mem_cgroup_stat_cpu *stat,
> +		enum mem_cgroup_stat_index idx, s64 val)
> +{
> +	stat->count[idx] = val;
> +}
> +
I think it would be better to name it __mem_cgroup_stat_set_safe.
And could you remove the definition of __mem_cgroup_stat_reset ?


Thanks,
Daisuke Nishimura.

>  static inline s64
>  __mem_cgroup_stat_read_local(struct mem_cgroup_stat_cpu *stat,
>  				enum mem_cgroup_stat_index idx)
> @@ -380,9 +388,10 @@ static bool mem_cgroup_soft_limit_check(struct mem_cgroup *mem)
>  
>  	cpu = get_cpu();
>  	cpustat = &mem->stat.cpustat[cpu];
> -	val = __mem_cgroup_stat_read_local(cpustat, MEM_CGROUP_STAT_EVENTS);
> -	if (unlikely(val > SOFTLIMIT_EVENTS_THRESH)) {
> -		__mem_cgroup_stat_reset_safe(cpustat, MEM_CGROUP_STAT_EVENTS);
> +	val = __mem_cgroup_stat_read_local(cpustat, MEM_CGROUP_STAT_SOFTLIMIT);
> +	if (unlikely(val < 0)) {
> +		__mem_cgroup_stat_set(cpustat, MEM_CGROUP_STAT_SOFTLIMIT,
> +				SOFTLIMIT_EVENTS_THRESH);
>  		ret = true;
>  	}
>  	put_cpu();
> @@ -515,7 +524,7 @@ static void mem_cgroup_charge_statistics(struct mem_cgroup *mem,
>  	else
>  		__mem_cgroup_stat_add_safe(cpustat,
>  				MEM_CGROUP_STAT_PGPGOUT_COUNT, 1);
> -	__mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_EVENTS, 1);
> +	__mem_cgroup_stat_add_safe(cpustat, MEM_CGROUP_STAT_SOFTLIMIT, -1);
>  	put_cpu();
>  }
>  
> -- 
> 1.6.5.7
> 
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