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From:   Muchun Song <songmuchun@bytedance.com>
Date:   Mon, 27 Jun 2022 11:23:07 +0800
Message-ID: <CAMZfGtWQEFmyuDngPfg59D-+b9sf58m9qhGoVPSQ_jAGmgT+sg@mail.gmail.com>
Subject: Re: [PATCH mm v2] memcg: notify about global mem_cgroup_id space depletion
To:     Vasily Averin <vvs@openvz.org>
Cc:     Shakeel Butt <shakeelb@google.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>,
        Michal Hocko <mhocko@suse.com>, kernel@openvz.org,
        LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux Memory Management List <linux-mm@kvack.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Cgroups <cgroups@vger.kernel.org>
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On Mon, Jun 27, 2022 at 10:11 AM Vasily Averin <vvs@openvz.org> wrote:
>
> Currently, the host owner is not informed about the exhaustion of the
> global mem_cgroup_id space. When this happens, systemd cannot start a
> new service and receives a unique -ENOSPC error code.
> However, this can happen inside this container, persist in the log file
> of the local container, and may not be noticed by the host owner if he
> did not try to start any new services.
>
> Signed-off-by: Vasily Averin <vvs@openvz.org>
> ---
> v2: Roman Gushchin pointed that idr_alloc() should return unique -ENOSPC

If the caller can know -ENOSPC is returned by mkdir(), then I
think the user (perhaps systemd) is the best place to throw out the
error message instead of in the kernel log. Right?

Thanks.

>     if no free IDs could be found, but can also return -ENOMEM.
>     Therefore error code check was added before message output and
>     patch descriprion was adopted.
> ---
>  mm/memcontrol.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d4c606a06bcd..ffc6b5d6b95e 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5317,6 +5317,8 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
>                                  1, MEM_CGROUP_ID_MAX + 1, GFP_KERNEL);
>         if (memcg->id.id < 0) {
>                 error = memcg->id.id;
> +               if (error == -ENOSPC)
> +                       pr_notice_ratelimited("mem_cgroup_id space is exhausted\n");
>                 goto fail;
>         }
>
> --
> 2.36.1
>