Re: [merged] mm-memcg-handle-non-error-oom-situations-more-gracefully.patch removed from -mm tree

[David Rientjes <rientjes@google.com>]

On Wed, 27 Nov 2013, Johannes Weiner wrote:

> > It appears as though this work is being developed in Linus's tree rather 
> > than -mm, so I'm asking if we should consider backing some of it out for 
> > 3.14 instead.
> 
> The changes fix a deadlock problem.  Are they creating problems that
> are worse than deadlocks, that would justify their revert?
> 

None that I am currently aware of, I'll continue to try them out.  I'd 
suggest just dropping the stable@kernel.org from the whole series though 
unless there is another report of such a problem that people are running 
into.

> Since we can't physically draw a perfect line, we should strive for a
> reasonable and intuitive line.  After that it's rapidly diminishing
> returns.  Killing something after that much reclaim effort without
> success is a completely reasonable and intuitive line to draw.  It's
> also the line that has been drawn a long time ago and we're not
> breaking this because of a micro optmimization.
> 

You don't think something like this is helpful after scanning a memcg will 
a large number of processes?

We've had this patch internally since we started using memcg, it has 
avoided some unnecessary oom killing.
---
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1836,6 +1836,13 @@ static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
 	if (!chosen)
 		return;
 	points = chosen_points * 1000 / totalpages;
+
+	/* One last chance to see if we really need to kill something */
+	if (mem_cgroup_margin(memcg) >= (1 << order)) {
+		put_task_struct(chosen);
+		return;
+	}
+
 	oom_kill_process(chosen, gfp_mask, order, points, totalpages, memcg,
 			 NULL, "Memory cgroup out of memory");
 }

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