Re: [PATCH 2/2] mm: oom: terminate the oom_evaluate_task() loop early

[Michal Hocko <mhocko@suse.com>]

On Mon 14-08-23 14:34:28, Peng Zhang wrote:
> From: ZhangPeng <zhangpeng362@huawei.com>
> 
> If task is allocating a lot of memory and has been marked to be killed
> first, then it gets the highest score (LONG_MAX). Therefore, there is no
> need to continue to calculate the points of other tasks. Just terminate
> the oom_evaluate_task() loop early, when the task with the highest score
> is found. By doing this, we can get some performance gains in
> select_bad_process().

The point of evaluating all tasks is that there might be pre-existing
oom victim still being torn down. If you cut this short you might kill
more tasks than necessary.

So I do not think we want this patch.

> To implement it, the return value of oom_evaluate_task() is modified.
> When the task with the highest score is found (points == LONG_MAX),
> oom_evaluate_task() will return 1 and the loop will terminate early.
> 
> Signed-off-by: ZhangPeng <zhangpeng362@huawei.com>
> ---
>  mm/oom_kill.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 10f7826c4035..02d11ae043aa 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -346,6 +346,8 @@ static int oom_evaluate_task(struct task_struct *task, void *arg)
>  	get_task_struct(task);
>  	oc->chosen = task;
>  	oc->chosen_points = points;
> +	if (points == LONG_MAX)
> +		return 1;
>  next:
>  	return 0;
>  abort:
> -- 
> 2.25.1

-- 
Michal Hocko
SUSE Labs