Re: [PATCH] mm: memcontrol: drop unnecessary task_will_free_mem() check.

[Michal Hocko <mhocko@kernel.org>]

On Wed 09-03-16 00:15:10, Tetsuo Handa wrote:
> Since mem_cgroup_out_of_memory() is called by
> mem_cgroup_oom_synchronize(true) via pagefault_out_of_memory() via
> page fault, and possible allocations between setting PF_EXITING and
> calling exit_mm() are tty_audit_exit() and taskstats_exit() which will
> not trigger page fault, task_will_free_mem(current) in
> mem_cgroup_out_of_memory() is never true.

What about exit_robust_list called from mm_release?

Anyway I guess we can indeed remove the check because try_charge will
bypass the charge if we are exiting so we shouldn't even reach this path
with PF_EXITING. But I haven't double checked. The above changelog seems
to be incorrect, though.

> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> ---
>  mm/memcontrol.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index ae8b81c..701bef1 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1254,11 +1254,11 @@ static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
> 	mutex_lock(&oom_lock);
>  
>  	/*
> -	 * If current has a pending SIGKILL or is exiting, then automatically
> -	 * select it.  The goal is to allow it to allocate so that it may
> -	 * quickly exit and free its memory.
> +	 * If current has a pending SIGKILL, then automatically select it.
> +	 * The goal is to allow it to allocate so that it may quickly exit
> +	 * and free its memory.
>  	 */
> -	if (fatal_signal_pending(current) || task_will_free_mem(current)) {
> +	if (fatal_signal_pending(current)) {
>  		mark_oom_victim(current);
>  		goto unlock;
>  	}
> -- 
> 1.8.3.1

-- 
Michal Hocko
SUSE Labs

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