linux-kernel - Re: [BUGFIX][PATCH] memcg: fix wrong decision of noswap with softlimit.

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Message-ID: <20110612112228.GC19493@tiehlicka.suse.cz>
Date:	Sun, 12 Jun 2011 13:22:28 +0200
From:	Michal Hocko <mhocko@...e.cz>
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>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"bsingharora@...il.com" <bsingharora@...il.com>
Subject: Re: [BUGFIX][PATCH] memcg: fix wrong decision of noswap with
 softlimit.

On Thu 09-06-11 09:54:45, KAMEZAWA Hiroyuki wrote:
> I wonder this should go stable...
> ==
> From e2565de1c764057b75b4d9a1674d163b6c873cdd Mon Sep 17 00:00:00 2001
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Date: Thu, 9 Jun 2011 09:54:32 +0900
> Subject: [PATCH 2/2] Fix softlimit wrong check of noswap
> 
> Now, hierarchical reclaim doesn't make swap if memory's limit is
> equal to mem+swap limit. Because if reclaim does swap-out,
> it still hits mem+swap limit and there will be no progress.
> WHEN HITTING HARD LIMIT.
> 
> When it comes to softlimit, it works for kswapd. noswap is nonsense.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

Maybe the changelog should be more clear. What about something like:
"
Hierarchical reclaim doesn't swap out if memsw and resource limits are
same (memsw_is_minimum == true) because we would hit mem+swap limit
anyway (during hard limit reclaim).
If it comes to the solft limit we shouldn't consider memsw_is_minimum at
all because it doesn't make much sense. Either the soft limit is bellow
the hard limit and then we cannot hit mem+swap limit or the direct
reclaim takes a precedence.
"
Reviewed-by: Michal Hocko <mhocko@...e.cz>

> ---
>  mm/memcontrol.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 3baddcb..06825be 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1663,7 +1663,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem,
>  	excess = res_counter_soft_limit_excess(&root_mem->res) >> PAGE_SHIFT;
>  
>  	/* If memsw_is_minimum==1, swap-out is of-no-use. */
> -	if (root_mem->memsw_is_minimum)
> +	if (!check_soft && root_mem->memsw_is_minimum)
>  		noswap = true;
>  
>  	while (1) {
> -- 
> 1.7.4.1
> 
> 
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-- 
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9    
Czech Republic
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