[Cc Oleg]
On Fri 05-10-18 15:32:08, Yong-Taek Lee wrote:
> It is introduced by commit 44a70adec910 ("mm, oom_adj: make sure
> processes sharing mm have same view of oom_score_adj"). Most of
> user process's mm_users is bigger than 1 but only one thread group.
> In this case, for_each_process loop meaninglessly try to find processes
> which sharing same mm even though there is only one thread group.
>
> My idea is that target task's nr thread is smaller than mm_users if there
> are more thread groups sharing the same mm. So we can skip loop
I remember trying to optimize this but ended up with nothing that would
work reliable. E.g. what prevents a thread terminating right after we
read mm reference count and result in early break and other process
not being updated properly?
> if mm_user and nr_thread are same.
>
> test result
> while true; do count=0; time while [ $count -lt 10000 ]; do echo -1000 > /proc/
> 1457/oom_score_adj; count=$((count+1)); done; done;
Is this overhead noticeable in a real work usecases though? Or are you
updating oom_score_adj that often really?
> before patch
> 0m00.59s real 0m00.09s user 0m00.51s system
> 0m00.59s real 0m00.14s user 0m00.45s system
> 0m00.58s real 0m00.11s user 0m00.47s system
> 0m00.58s real 0m00.10s user 0m00.48s system
> 0m00.59s real 0m00.11s user 0m00.48s system
>
> after patch
> 0m00.15s real 0m00.07s user 0m00.08s system
> 0m00.14s real 0m00.10s user 0m00.04s system
> 0m00.14s real 0m00.10s user 0m00.05s system
> 0m00.14s real 0m00.08s user 0m00.07s system
> 0m00.14s real 0m00.08s user 0m00.07s system
>
> Signed-off-by: Lee YongTaek <ytk.lee@xxxxxxxxxxx>
> ---
> fs/proc/base.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index f9f72aee6d45..54b2fb5e9c51 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1056,6 +1056,7 @@ static int __set_oom_adj(struct file *file, int oom_adj,
> bool legacy)
> struct mm_struct *mm = NULL;
> struct task_struct *task;
> int err = 0;
> + int mm_users = 0;
>
> task = get_proc_task(file_inode(file));
> if (!task)
> @@ -1092,7 +1093,8 @@ static int __set_oom_adj(struct file *file, int oom_adj,
> bool legacy)
> struct task_struct *p = find_lock_task_mm(task);
>
> if (p) {
> - if (atomic_read(&p->mm->mm_users) > 1) {
> + mm_users = atomic_read(&p->mm->mm_users);
> + if ((mm_users > 1) && (mm_users != get_nr_threads(p)))
> {
> mm = p->mm;
> atomic_inc(&mm->mm_count);
> }
> --
>
> *
--
Michal Hocko
SUSE Labs
