linux-kernel - Re: [PATCH] mm/oom_kill: count global and memory cgroup oom kills

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Date:   Fri, 19 May 2017 17:34:18 +0100
From:   Roman Guschin <guroan@...il.com>
To:     Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...nel.org>, hannes@...xchg.org
Subject: Re: [PATCH] mm/oom_kill: count global and memory cgroup oom kills

2017-05-19 15:22 GMT+01:00 Konstantin Khlebnikov <khlebnikov@...dex-team.ru>:
> Show count of global oom killer invocations in /proc/vmstat and
> count of oom kills inside memory cgroup in knob "memory.events"
> (in memory.oom_control for v1 cgroup).
>
> Also describe difference between "oom" and "oom_kill" in memory
> cgroup documentation. Currently oom in memory cgroup kills tasks
> iff shortage has happened inside page fault.
>
> These counters helps in monitoring oom kills - for now
> the only way is grepping for magic words in kernel log.
>
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
> ---
>  Documentation/cgroup-v2.txt   |   12 +++++++++++-
>  include/linux/memcontrol.h    |    1 +
>  include/linux/vm_event_item.h |    1 +
>  mm/memcontrol.c               |    2 ++
>  mm/oom_kill.c                 |    6 ++++++
>  mm/vmstat.c                   |    1 +
>  6 files changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
> index dc5e2dcdbef4..a742008d76aa 100644
> --- a/Documentation/cgroup-v2.txt
> +++ b/Documentation/cgroup-v2.txt
> @@ -830,9 +830,19 @@ PAGE_SIZE multiple when read back.
>
>           oom
>
> +               The number of time the cgroup's memory usage was
> +               reached the limit and allocation was about to fail.
> +               Result could be oom kill, -ENOMEM from any syscall or
> +               completely ignored in cases like disk readahead.
> +               For now oom in memory cgroup kills tasks iff shortage
> +               has happened inside page fault.

>From a user's point of view the difference between "oom" and "max"
becomes really vague here,
assuming that "max" is described almost in the same words:

"The number of times the cgroup's memory usage was
about to go over the max boundary.  If direct reclaim
fails to bring it down, the OOM killer is invoked."

I wonder, if it's better to fix the existing "oom" value  to show what
it has to show, according to docs,
rather than to introduce a new one?

> +
> +         oom_kill
> +
>                 The number of times the OOM killer has been invoked in
>                 the cgroup.  This may not exactly match the number of
> -               processes killed but should generally be close.
> +               processes killed but should generally be close: each
> +               invocation could kill several processes at once.
>
>    memory.stat
>