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Date:   Thu, 30 Apr 2020 12:31:32 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Roman Gushchin <guro@...com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Greg Thelen <gthelen@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Cgroups <cgroups@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] memcg: oom: ignore oom warnings from memory.max

On Thu, Apr 30, 2020 at 12:06 PM Roman Gushchin <guro@...com> wrote:
>
> Hello, Shakeel!
>
> On Thu, Apr 30, 2020 at 11:27:12AM -0700, Shakeel Butt wrote:
> > Lowering memory.max can trigger an oom-kill if the reclaim does not
> > succeed. However if oom-killer does not find a process for killing, it
> > dumps a lot of warnings.
>
> Makes total sense to me.
>
> >
> > Deleting a memcg does not reclaim memory from it and the memory can
> > linger till there is a memory pressure. One normal way to proactively
> > reclaim such memory is to set memory.max to 0 just before deleting the
> > memcg. However if some of the memcg's memory is pinned by others, this
> > operation can trigger an oom-kill without any process and thus can log a
> > lot un-needed warnings. So, ignore all such warnings from memory.max.
> >
> > Signed-off-by: Shakeel Butt <shakeelb@...gle.com>
> > ---
> >  include/linux/oom.h | 3 +++
> >  mm/memcontrol.c     | 9 +++++----
> >  mm/oom_kill.c       | 2 +-
> >  3 files changed, 9 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/oom.h b/include/linux/oom.h
> > index c696c265f019..6345dc55df64 100644
> > --- a/include/linux/oom.h
> > +++ b/include/linux/oom.h
> > @@ -52,6 +52,9 @@ struct oom_control {
> >
> >       /* Used to print the constraint info. */
> >       enum oom_constraint constraint;
> > +
> > +     /* Do not warn even if there is no process to be killed. */
> > +     bool no_warn;
>
> I'd invert it to warn. Or maybe even warn_on_no_proc?
>

Sure.

> >  };
> >
> >  extern struct mutex oom_lock;
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 317dbbaac603..a1f00d9b9bb0 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -1571,7 +1571,7 @@ unsigned long mem_cgroup_size(struct mem_cgroup *memcg)
> >  }
> >
> >  static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
> > -                                  int order)
> > +                                  int order, bool no_warn)
> >  {
> >       struct oom_control oc = {
> >               .zonelist = NULL,
> > @@ -1579,6 +1579,7 @@ static bool mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
> >               .memcg = memcg,
> >               .gfp_mask = gfp_mask,
> >               .order = order,
> > +             .no_warn = no_warn,
> >       };
> >       bool ret;
> >
> > @@ -1821,7 +1822,7 @@ static enum oom_status mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int
> >               mem_cgroup_oom_notify(memcg);
> >
> >       mem_cgroup_unmark_under_oom(memcg);
> > -     if (mem_cgroup_out_of_memory(memcg, mask, order))
> > +     if (mem_cgroup_out_of_memory(memcg, mask, order, false))
> >               ret = OOM_SUCCESS;
> >       else
> >               ret = OOM_FAILED;
> > @@ -1880,7 +1881,7 @@ bool mem_cgroup_oom_synchronize(bool handle)
> >               mem_cgroup_unmark_under_oom(memcg);
> >               finish_wait(&memcg_oom_waitq, &owait.wait);
> >               mem_cgroup_out_of_memory(memcg, current->memcg_oom_gfp_mask,
> > -                                      current->memcg_oom_order);
> > +                                      current->memcg_oom_order, false);
> >       } else {
> >               schedule();
> >               mem_cgroup_unmark_under_oom(memcg);
> > @@ -6106,7 +6107,7 @@ static ssize_t memory_max_write(struct kernfs_open_file *of,
> >               }
> >
> >               memcg_memory_event(memcg, MEMCG_OOM);
> > -             if (!mem_cgroup_out_of_memory(memcg, GFP_KERNEL, 0))
> > +             if (!mem_cgroup_out_of_memory(memcg, GFP_KERNEL, 0, true))
>
> I wonder if we can handle it automatically from the oom_killer side?
> We can suppress warnings if oc->memcg is set and the cgroup scanning
> showed that there are no belonging processes?
>

What about the charging path? Do we not want such warnings from
charging paths? It might be due to some misconfiguration.

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