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Date:   Thu, 30 Apr 2020 19:04:43 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     Johannes Weiner <hannes@...xchg.org>, Roman Gushchin <guro@...com>,
        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 6:39 PM Yafang Shao <laoar.shao@...il.com> wrote:
>
> On Fri, May 1, 2020 at 2:27 AM Shakeel Butt <shakeelb@...gle.com> 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.
> >
>
> I have been confused by this behavior for several months and I think
> it will confuse more memcg users.
> We should keep the memcg oom behavior consistent with system oom - no
> oom kill if no process.
>
> What about bellow change ?
>

Seems fine to me. If others are ok with this, please do send a signed-off patch.

> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e28098e13f1c..25fbc37a747f 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -6086,6 +6086,9 @@ static ssize_t memory_max_write(struct
> kernfs_open_file *of,
>                         continue;
>                 }
>
> +               if (!cgroup_is_populated(memcg->css.cgroup))
> +                       break;
> +
>                 memcg_memory_event(memcg, MEMCG_OOM);
>                 if (!mem_cgroup_out_of_memory(memcg, GFP_KERNEL, 0))
>                         break;
>
> > 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;
> >  };
> >
> >  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))
> >                         break;
> >         }
> >
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 463b3d74a64a..5ace39f6fe1e 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -1098,7 +1098,7 @@ bool out_of_memory(struct oom_control *oc)
> >
> >         select_bad_process(oc);
> >         /* Found nothing?!?! */
> > -       if (!oc->chosen) {
> > +       if (!oc->chosen && !oc->no_warn) {
> >                 dump_header(oc, NULL);
> >                 pr_warn("Out of memory and no killable processes...\n");
> >                 /*
> > --
> > 2.26.2.526.g744177e7f7-goog
> >
> >
>
>
> --
> Thanks
> Yafang

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