Re: [PATCH -mmotm 7/8] memcg: avoid oom during recharge at task move

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

On Fri, 6 Nov 2009 14:15:32 +0900
Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote:

> This recharge-at-task-move feature has extra charges(pre-charges) on "to"
> mem_cgroup during recharging. This means unnecessary oom can happen.
> 
> This patch tries to avoid such oom.
> 
> Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
> ---
>  mm/memcontrol.c |   27 +++++++++++++++++++++++++++
>  1 files changed, 27 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index f4b7116..7e96f3b 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -248,6 +248,7 @@ struct recharge_struct {
>  	struct mem_cgroup *from;
>  	struct mem_cgroup *to;
>  	struct task_struct *target;	/* the target task being moved */
> +	struct task_struct *working;	/* a task moving the target task */
>  	unsigned long precharge;
>  };
>  static struct recharge_struct recharge;
> @@ -1493,6 +1494,30 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
>  		if (mem_cgroup_check_under_limit(mem_over_limit))
>  			continue;
>  
> +		/* try to avoid oom while someone is recharging */
> +		if (recharge.working && current != recharge.working) {
> +			struct mem_cgroup *dest;
> +			bool do_continue = false;
> +			/*
> +			 * There is a small race that "dest" can be freed by
> +			 * rmdir, so we use css_tryget().
> +			 */
> +			rcu_read_lock();
> +			dest = recharge.to;
> +			if (dest && css_tryget(&dest->css)) {
> +				if (dest->use_hierarchy)
> +					do_continue = css_is_ancestor(
> +							&dest->css,
> +							&mem_over_limit->css);
> +				else
> +					do_continue = (dest == mem_over_limit);
> +				css_put(&dest->css);
> +			}
> +			rcu_read_unlock();
> +			if (do_continue)
> +				continue;
> +		}

I think it's better to do this here, rather than continue.

==
	if (do_continue) {
		mutex_lock(&memcg_tasklist_lock);
		mutex_unlock(&memcg_tasklist_lock);
		contiue;
	}
==

Thanks,
-Kame

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