Michal Hocko wrote:
> On Wed 17-02-16 19:33:07, Tetsuo Handa wrote:
> > >From 4924ca3031444bfb831b2d4f004e5a613ad48d68 Mon Sep 17 00:00:00 2001
> > From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> > Date: Wed, 17 Feb 2016 16:35:12 +0900
> > Subject: [PATCH 4/6] mm,oom: exclude oom_task_origin processes if they are OOM-unkillable.
> >
> > oom_scan_process_thread() returns OOM_SCAN_SELECT when there is a
> > thread which returns oom_task_origin() == true. But it is possible
> > that that thread is marked as OOM-unkillable.
> >
> > This patch changes oom_scan_process_thread() not to select it
> > if it is marked as OOM-unkillable.
>
> oom_task_origin is only swapoff and ksm_store right now. I seriously
> doubt anybody sane will run them as OOM disabled (directly or
> indirectly).
I think that the OOM reaper will update such task as OOM-unkillable
after reaping that task's memory. This patch is intended for not to
fall into infinite loop after the OOM reaper updated it.
>
> But you have a point that returing anything but OOM_SCAN_CONTINUE for
> OOM_SCORE_ADJ_MIN from oom_scan_process_thread sounds suboptimal.
> Sure such a check would be racy but do we actually care about a OOM vs.
> oom_score_adj_write. I am dubious to say the least.
>
> So wouldn't it make more sense to check for OOM_SCORE_ADJ_MIN at the
> very top of oom_scan_process_thread instead?
Are you suggesting something like below?
(OOM_SCORE_ADJ_MIN check needs to be done after TIF_MEMDIE check)
enum oom_scan_t oom_scan_process_thread(struct oom_control *oc,
struct task_struct *task, unsigned long totalpages)
{
if (oom_unkillable_task(task, NULL, oc->nodemask))
return OOM_SCAN_CONTINUE;
/*
* This task already has access to memory reserves and is being killed.
* Don't allow any other task to have access to the reserves.
*/
if (test_tsk_thread_flag(task, TIF_MEMDIE)) {
if (!is_sysrq_oom(oc))
return OOM_SCAN_ABORT;
}
if (!task->mm || task->signal->oom_score_adj == OOM_SCORE_ADJ_MIN)
return OOM_SCAN_CONTINUE;
(...snipped...)
}
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