On Mon 30-05-16 13:40:17, Vladimir Davydov wrote:

On Mon, May 30, 2016 at 11:52:12AM +0200, Michal Hocko wrote:

quoted

On Mon 30-05-16 09:13:57, Michal Hocko wrote:

quoted

On Fri 27-05-16 19:48:30, Vladimir Davydov wrote:

quoted

On Thu, May 26, 2016 at 02:40:13PM +0200, Michal Hocko wrote:

[...]

quoted

quoted

@@ -839,6 +841,13 @@ void oom_kill_process(struct oom_control *oc, struct task_struct *p,
 	for_each_process(p) {
 		if (!process_shares_mm(p, mm))
 			continue;
+		/*
+		 * vforked tasks are ignored because they will drop the mm soon
+		 * hopefully and even if not they will not mind being oom
+		 * reaped because they cannot touch any memory.

They shouldn't modify memory, but they still can touch it AFAIK.

You are right. This means that the vforked child might see zero pages.
Let me think whether this is acceptable or not.

OK, I was thinking about it some more and I think you have a good point
here. I can see two options here:
- keep vforked task alive and skip the oom reaper. If the victim exits
  normally and the oom wouldn't get resolved the vforked task will be
  selected in the next round because the victim would clean up
  vfork_done state in  wait_for_vfork_done. We are still risking that
  the victim gets stuck though
- kill vforked task and so it would be reapable.

IMHO it all depends on what we're trying to achieve. If we want per task
oom, which could make some sense since a task can consume a lot of mem
via e.g. pipe buffers, we would go with option #1. However, it's rather
difficult to find out how much of kmem a task consumes w/o using kmemcg,
so IMHO per-mm approach makes more sense in general. In this case I
think we should kill both vforked task and its parent if their mm was
selected provided their oom_score_adj allows that.

Yes agreed. Going with per-mm is a safier behavior because the vast
majority of the consumed memory should be per mm not per task_struct.

-- 
Michal Hocko
SUSE Labs

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