From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752249Ab1HHMW7 (ORCPT <rfc822;w@1wt.eu>);
	Mon, 8 Aug 2011 08:22:59 -0400
Received: from cantor2.suse.de ([195.135.220.15]:41808 "EHLO mx2.suse.de"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1750877Ab1HHMW6 (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 8 Aug 2011 08:22:58 -0400
Date: Mon, 8 Aug 2011 14:22:55 +0200
From: Michal Hocko <mhocko@suse.cz>
To: Konstantin Khlebnikov <khlebnikov@openvz.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Subject: Re: [PATCH v2] vmscan: reverse lru scanning order
Message-ID: <20110808122255.GC14803@tiehlicka.suse.cz>
References: <20110727111002.9985.94938.stgit@localhost6>
 <20110808110207.30777.30800.stgit@localhost6>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20110808110207.30777.30800.stgit@localhost6>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Mon 08-08-11 15:02:07, Konstantin Khlebnikov wrote:
> LRU scanning order was accidentially changed in commit v2.6.27-5584-gb69408e:
> "vmscan: Use an indexed array for LRU variables".
> Before that commit reclaimer always scan active lists first.
> 
> This patch just reverse it back.

I am still not sure I see why the ordering matters that much.
One thing that might matter is that shrink_list moves some pages from
active to inactive list if inactive is low so it makes sense to try to
shrink active before inactive. It would be a problem if inactive was
almost empty. Then we would just waste time by shrinking inactive first.
I am not sure how real problem is that, though. 

Whatever is the reason, I think it should be documented in the
changelog.
The change makes sense to me.

> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
> ---
>  include/linux/mmzone.h |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index be1ac8d..0094389 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -141,7 +141,8 @@ enum lru_list {
>  
>  #define for_each_lru(l) for (l = 0; l < NR_LRU_LISTS; l++)
>  
> -#define for_each_evictable_lru(l) for (l = 0; l <= LRU_ACTIVE_FILE; l++)
> +#define for_each_evictable_lru(l) \
> +	for (l = LRU_ACTIVE_FILE; (int)l >= LRU_INACTIVE_ANON; l--)
>  
>  static inline int is_file_lru(enum lru_list l)
>  {
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

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