Messages in this thread | | | Date | Mon, 30 May 2016 11:47:53 +0300 | From | Vladimir Davydov <> | Subject | Re: [PATCH 3/6] mm, oom_adj: make sure processes sharing mm have same view of oom_score_adj |
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On Mon, May 30, 2016 at 09:07:05AM +0200, Michal Hocko wrote: > On Fri 27-05-16 19:18:21, Vladimir Davydov wrote: > > On Fri, May 27, 2016 at 01:18:03PM +0200, Michal Hocko wrote: > > ... > > > @@ -1087,7 +1105,25 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy) > > > unlock_task_sighand(task, &flags); > > > err_put_task: > > > put_task_struct(task); > > > + > > > + if (mm) { > > > + struct task_struct *p; > > > + > > > + rcu_read_lock(); > > > + for_each_process(p) { > > > + task_lock(p); > > > + if (!p->vfork_done && process_shares_mm(p, mm)) { > > > + p->signal->oom_score_adj = oom_adj; > > > + if (!legacy && has_capability_noaudit(current, CAP_SYS_RESOURCE)) > > > + p->signal->oom_score_adj_min = (short)oom_adj; > > > + } > > > + task_unlock(p); > > > > I.e. you write to /proc/pid1/oom_score_adj and get > > /proc/pid2/oom_score_adj updated if pid1 and pid2 share mm? > > IMO that looks unexpected from userspace pov. > > How much different it is from threads in the same thread group? > Processes sharing the mm without signals is a rather weird threading > model isn't it?
I think so too. I wouldn't be surprised if it turned out that nobody had ever used it. But may be there's someone out there who does.
> Currently we just lie to users about their oom_score_adj > in this weird corner case.
Hmm, looks like a bug, but nobody has ever complained about it.
> The only exception was OOM_SCORE_ADJ_MIN > where we really didn't kill the task but all other values are simply > ignored in practice. > > > May be, we'd better add mm->oom_score_adj and set it to the min > > signal->oom_score_adj over all processes sharing it? This would > > require iterating over all processes every time oom_score_adj gets > > updated, but that's a slow path. > > Not sure I understand. So you would prefer that mm->oom_score_adj might > disagree with p->signal->oom_score_adj?
No, I wouldn't. I'd rather agree that oom_score_adj should be per mm, because we choose the victim basing solely on mm stats.
What I mean is we don't touch p->signal->oom_score_adj of other tasks sharing mm, but instead store minimal oom_score_adj over all tasks sharing mm in the mm_struct whenever a task's oom_score_adj is modified. And use mm->oom_score_adj instead of signal->oom_score_adj in oom killer code. This would save us from any accusations of user API modifications and it would also make the oom code a bit easier to follow IMHO.
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