On Tue 09-10-18 08:23:30, Michal Hocko wrote: > [Cc Oleg] JFYI there was new submission http://lkml.kernel.org/r/20181008011931epcms1p82dd01b7e5c067ea99946418bc97de46a@epcms1p8 > > 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 -- Michal Hocko SUSE Labs
