Re: [patch v2] oom, memcg: fix exclusion of memcg threads after they have detached their mm

[KOSAKI Motohiro <kosaki.motohiro-+CUm20s59erQFUHtdCDX3A@public.gmane.org>]

On 12/14/2011 9:39 PM, David Rientjes wrote:
> oom, memcg: fix exclusion of memcg threads after they have detached their mm
> 
> The oom killer relies on logic that identifies threads that have already
> been oom killed when scanning the tasklist and, if found, deferring until
> such threads have exited.  This is done by checking for any candidate
> threads that have the TIF_MEMDIE bit set.
> 
> For memcg ooms, candidate threads are first found by calling
> task_in_mem_cgroup() since the oom killer should not defer if there's an
> oom killed thread in another memcg.
> 
> Unfortunately, task_in_mem_cgroup() excludes threads if they have
> detached their mm in the process of exiting so TIF_MEMDIE is never
> detected for such conditions.  This is different for global, mempolicy,
> and cpuset oom conditions where a detached mm is only excluded after
> checking for TIF_MEMDIE and deferring, if necessary, in
> select_bad_process().
> 
> The fix is to return true if a task has a detached mm but is still in the
> memcg or its hierarchy that is currently oom.  This will allow the oom
> killer to appropriately defer rather than kill unnecessarily or, in the
> worst case, panic the machine if nothing else is available to kill.
> 
> Signed-off-by: David Rientjes <rientjes-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
> ---
>  mm/memcontrol.c |   17 +++++++++++++----
>  1 files changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1109,10 +1109,19 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg)
>  	struct task_struct *p;
>  
>  	p = find_lock_task_mm(task);
> -	if (!p)
> -		return 0;
> -	curr = try_get_mem_cgroup_from_mm(p->mm);
> -	task_unlock(p);
> +	if (p) {
> +		curr = try_get_mem_cgroup_from_mm(p->mm);
> +		task_unlock(p);
> +	} else {
> +		/*
> +		 * All threads may have already detached their mm's, but the oom
> +		 * killer still needs to detect if they have already been oom
> +		 * killed to prevent needlessly killing additional tasks.
> +		 */
> +		curr = mem_cgroup_from_task(task);
> +		if (curr)
> +			css_get(&curr->css);
> +	}

Acked-by: KOSAKI Motohiro <kosaki.motohiro-+CUm20s59erQFUHtdCDX3A@public.gmane.org>


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