linux-kernel - Re: [mmotm][BUGFIX][PATCH] memcg: fix softlimit css refcnt handling.

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Message-Id: <20090904190726.6442f3df.d-nishimura@mtf.biglobe.ne.jp>
Date:	Fri, 4 Sep 2009 19:07:26 +0900
From:	Daisuke Nishimura <d-nishimura@....biglobe.ne.jp>
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>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	d-nishimura@....biglobe.ne.jp,
	Daisuke Nishimura <nishimura@....nes.nec.co.jp>
Subject: Re: [mmotm][BUGFIX][PATCH] memcg: fix softlimit css refcnt
 handling.

On Fri, 4 Sep 2009 16:37:58 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:

> On Fri, 4 Sep 2009 15:40:50 +0900
> Daisuke Nishimura <nishimura@....nes.nec.co.jp> wrote:
> > > Ah, one more question. What memory.usage_in_bytes shows in that case ?
> > > If not zero, charge/uncharge coalescing is guilty.
> > > 
> > usage_in_bytes is 0.
> > I've confirmed by crash command that the mem_cgroup has extra ref counts.
> > 
> > I'll dig more..
> > 
> BTW, do you use softlimit ? I found this but...Hmm
> 
No.
I'm sorry I can't access my machine, so can't test this.

But I think this patch itself is needed and looks good.

	Reviewed-by: Daisuke Nishimura <nishimura@....nes.nec.co.jp>

Thanks,
Daisuke Nishimura.
> ==
> SoftLimit tree 'find next one' loop uses next_mz to remember
> next one to be visited if reclaimd==0.
> But css'refcnt handling for next_mz is not enough and it makes
> css->refcnt leak.
> 
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> 
> ---
>  mm/memcontrol.c |   11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> Index: mmotm-2.6.31-Aug27/mm/memcontrol.c
> ===================================================================
> --- mmotm-2.6.31-Aug27.orig/mm/memcontrol.c
> +++ mmotm-2.6.31-Aug27/mm/memcontrol.c
> @@ -2261,6 +2261,8 @@ unsigned long mem_cgroup_soft_limit_recl
>  		if (!reclaimed) {
>  			do {
>  				/*
> +				 * Loop until we find yet another one.
> +				 *
>  				 * By the time we get the soft_limit lock
>  				 * again, someone might have aded the
>  				 * group back on the RB tree. Iterate to
> @@ -2271,7 +2273,12 @@ unsigned long mem_cgroup_soft_limit_recl
>  				 */
>  				next_mz =
>  				__mem_cgroup_largest_soft_limit_node(mctz);
> -			} while (next_mz == mz);
> +				if (next_mz == mz) {
> +					css_put(&next_mz->mem->css);
> +					next_mz = NULL;
> +				} else /* next_mz == NULL or other memcg */
> +					break;
> +			} while (1);
>  		}
>  		mz->usage_in_excess =
>  			res_counter_soft_limit_excess(&mz->mem->res);
> @@ -2299,6 +2306,8 @@ unsigned long mem_cgroup_soft_limit_recl
>  			loop > MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS))
>  			break;
>  	} while (!nr_reclaimed);
> +	if (next_mz)
> +		css_put(&next_mz->mem->css);
>  	return nr_reclaimed;
>  }
>  
> 
> --
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> 



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