lkml.org 
[lkml]   [2020]   [Mar]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] mm: memcg: make memory.oom.group tolerable to task migration
On Tue 17-03-20 13:36:45, Roman Gushchin wrote:
[...]
> > > And the we can put something like
> > > if (WARN_ON_ONCE(!mem_cgroup_is_descendant(memcg, oom_domain)))
> > > goto out;
> > > to mem_cgroup_get_oom_group?
> >
> > This would be a user triggerable warning and that sounds like a bad idea
> > to me. We should just live with races. The only question I still do not
> > have a proper answer for is how much we do care. If we do not care all
> > that much about the original memcg then go with your patch. But if we
> > want to be slightly more careful then we should note the memcg in
> > oom_evaluate_task and use it when killing.
>
> But it won't close the race, right?
>
> oom_evaluate_task() can race with a task migration too, so we can record
> the old or the new cgroup.

Are you sure? I thought that cgroups iterator code would take care of
those races. The documentation doesn't tell much in that respect. Maybe
it would be good to add a clarification there.

> Then I'd stick with my original patch which solves the main problem here:
> unnecessary killing of too many tasks.

OK, I am fine with that. I couldn't convince myself that the other part
of the problem is serious enough. Maybe we will find workloads which do
care and we can add that later on.
--
Michal Hocko
SUSE Labs

\
 
 \ /
  Last update: 2020-03-18 13:32    [W:0.073 / U:0.304 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site