Re: [patch] mm, memcg: do not allow tasks to be attached with zero limit

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

On Wed, 7 Mar 2012 19:14:49 -0800 (PST)
David Rientjes <rientjes@google.com> wrote:

> This patch prevents tasks from being attached to a memcg if there is a
> hard limit of zero.  Additionally, the hard limit may not be changed to
> zero if there are tasks attached.
> 
> This is consistent with cpusets which do not allow tasks to be attached
> if there are no mems and prevents all mems from being removed if there
> are tasks attached.
> 
> Signed-off-by: David Rientjes <rientjes@google.com>

I hope Documenation/cgroup/memory.txt should be updated and make this behavior as 'spec'.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>


> ---
>  mm/memcontrol.c |   13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3868,9 +3868,14 @@ static int mem_cgroup_write(struct cgroup *cont, struct cftype *cft,
>  		ret = res_counter_memparse_write_strategy(buffer, &val);
>  		if (ret)
>  			break;
> -		if (type == _MEM)
> +		if (type == _MEM) {
> +			/* Don't allow zero limit with tasks attached */
> +			if (!val && cgroup_task_count(cont)) {
> +				ret = -ENOSPC;
> +				break;
> +			}
>  			ret = mem_cgroup_resize_limit(memcg, val);
> -		else
> +		} else
>  			ret = mem_cgroup_resize_memsw_limit(memcg, val);
>  		break;
>  	case RES_SOFT_LIMIT:
> @@ -5306,6 +5311,10 @@ static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
>  	int ret = 0;
>  	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgroup);
>  
> +	/* Don't allow tasks attached with a zero limit */
> +	if (!res_counter_read_u64(&memcg->res, RES_LIMIT))
> +		return -ENOSPC;
> +
>  	if (memcg->move_charge_at_immigrate) {
>  		struct mm_struct *mm;
>  		struct mem_cgroup *from = mem_cgroup_from_task(p);
> 

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