Re: [BUGFIX][PATCH] memcg: fix oom kill behavior v3

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Thu, 4 Mar 2010 13:04:06 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> On Wed, 3 Mar 2010 16:23:04 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > On Wed, 3 Mar 2010 09:38:44 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> > 
> > > On Wed, 3 Mar 2010 09:26:06 +0900
> > > Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:
> > > 
> > > > > I'll test this patch all through this night, and check whether it doesn't trigger
> > > > > global oom after memcg's oom.
> > > > > 
> > > > O.K. It works well.
> > > > Feel free to add my signs.
> > > > 
> > > > 	Reviewed-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> > > > 	Tested-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> > > > 
> > > 
> > > Thank you !
> > > 
> > > I'll apply Balbir's comment and post v3.
> > > 
> > 
> > rebased onto mmotm-Mar2.
> > tested on x86-64.
> > 
> I found a small race problem. This is the fix for it.
> 
> ===
> From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> 
> We must avoid making oom_lock of a newly created child be negative.
> 
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> ---
>  mm/memcontrol.c |    7 ++++++-
>  1 files changed, 6 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 3ce8c5b..9e25400 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1272,7 +1272,12 @@ static bool mem_cgroup_oom_lock(struct mem_cgroup *mem)
>  
>  static int mem_cgroup_oom_unlock_cb(struct mem_cgroup *mem, void *data)
>  {
> -	atomic_dec(&mem->oom_lock);
> +	/*
> +	 * There is a small race window where a new child can be created after
> +	 * we called mem_cgroup_oom_lock(). Use atomic_add_unless() to avoid
> +	 * making oom_lock of such a child be negative.
> +	 */
> +	atomic_add_unless(&mem->oom_lock, -1, 0);
>  	return 0;
>  }
>  


Thank you!. I'll merge this to v4.

-Kame


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