linux-kernel - Re: [BUGFIX][PATCH 1/5] memcg use correct scan number at reclaim

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Message-ID: <20090312034918.GB23583@balbir.in.ibm.com>
Date:	Thu, 12 Mar 2009 09:19:18 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [BUGFIX][PATCH 1/5] memcg use correct scan number at reclaim

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-03-12 09:55:16]:

> Andrew, this [1/5] is a bug fix, others are not.
> 
> ==
> From: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> 
> Even when page reclaim is under mem_cgroup, # of scan page is determined by
> status of global LRU. Fix that.
> 
> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
>  mm/vmscan.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: mmotm-2.6.29-Mar10/mm/vmscan.c
> ===================================================================
> --- mmotm-2.6.29-Mar10.orig/mm/vmscan.c
> +++ mmotm-2.6.29-Mar10/mm/vmscan.c
> @@ -1470,7 +1470,7 @@ static void shrink_zone(int priority, st
>  		int file = is_file_lru(l);
>  		int scan;
> 
> -		scan = zone_page_state(zone, NR_LRU_BASE + l);
> +		scan = zone_nr_pages(zone, sc, l);

I have the exact same patch in my patch queue. BTW, mem_cgroup_zone_nr_pages is
buggy. We don't hold any sort of lock while extracting
MEM_CGROUP_ZSTAT (ideally we need zone->lru_lock). Without that how do
we guarantee that MEM_CGRUP_ZSTAT is not changing at the same time as
we are reading it?

>  		if (priority) {
>  			scan >>= priority;
>  			scan = (scan * percent[file]) / 100;
> 
> 

-- 
	Balbir
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