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

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Date:   Tue, 23 May 2017 09:27:04 +0200
From:   Michal Hocko <mhocko@...nel.org>
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>
Subject: Re: [PATCH] mm/oom_kill: count global and memory cgroup oom kills

On Fri 19-05-17 17:22:30, Konstantin Khlebnikov wrote:
> 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.

Have you considered adding memcg's oom alternative for the global case
as well. It would be useful to see how many times we hit the OOM
condition without killing anything. That could help debugging issues
when the OOM killer cannot be invoked (e.g. GFP_NO{FS,IO} contextx)
and the system cannot get out of the oom situation.
 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  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.
> +
> +	  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
>  
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 899949bbb2f9..2cdcebb78b58 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -55,6 +55,7 @@ enum memcg_event_item {
>  	MEMCG_HIGH,
>  	MEMCG_MAX,
>  	MEMCG_OOM,
> +	MEMCG_OOM_KILL,
>  	MEMCG_NR_EVENTS,
>  };
>  
> diff --git a/include/linux/vm_event_item.h b/include/linux/vm_event_item.h
> index d84ae90ccd5c..1707e0a7d943 100644
> --- a/include/linux/vm_event_item.h
> +++ b/include/linux/vm_event_item.h
> @@ -41,6 +41,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
>  		KSWAPD_LOW_WMARK_HIT_QUICKLY, KSWAPD_HIGH_WMARK_HIT_QUICKLY,
>  		PAGEOUTRUN, PGROTATED,
>  		DROP_PAGECACHE, DROP_SLAB,
> +		OOM_KILL,
>  #ifdef CONFIG_NUMA_BALANCING
>  		NUMA_PTE_UPDATES,
>  		NUMA_HUGE_PTE_UPDATES,
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 94172089f52f..416024837b81 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3574,6 +3574,7 @@ static int mem_cgroup_oom_control_read(struct seq_file *sf, void *v)
>  
>  	seq_printf(sf, "oom_kill_disable %d\n", memcg->oom_kill_disable);
>  	seq_printf(sf, "under_oom %d\n", (bool)memcg->under_oom);
> +	seq_printf(sf, "oom_kill %lu\n", memcg_sum_events(memcg, MEMCG_OOM_KILL));
>  	return 0;
>  }
>  
> @@ -5165,6 +5166,7 @@ static int memory_events_show(struct seq_file *m, void *v)
>  	seq_printf(m, "high %lu\n", memcg_sum_events(memcg, MEMCG_HIGH));
>  	seq_printf(m, "max %lu\n", memcg_sum_events(memcg, MEMCG_MAX));
>  	seq_printf(m, "oom %lu\n", memcg_sum_events(memcg, MEMCG_OOM));
> +	seq_printf(m, "oom_kill %lu\n", memcg_sum_events(memcg, MEMCG_OOM_KILL));
>  
>  	return 0;
>  }
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 04c9143a8625..c50bff3c3409 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -873,6 +873,12 @@ static void oom_kill_process(struct oom_control *oc, const char *message)
>  		victim = p;
>  	}
>  
> +	/* Raise event before sending signal: reaper must see this */
> +	if (!is_memcg_oom(oc))
> +		count_vm_event(OOM_KILL);
> +	else
> +		mem_cgroup_event(oc->memcg, MEMCG_OOM_KILL);
> +
>  	/* Get a reference to safely compare mm after task_unlock(victim) */
>  	mm = victim->mm;
>  	mmgrab(mm);
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 76f73670200a..fe80b81a86e0 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1018,6 +1018,7 @@ const char * const vmstat_text[] = {
>  
>  	"drop_pagecache",
>  	"drop_slab",
> +	"oom_kill",
>  
>  #ifdef CONFIG_NUMA_BALANCING
>  	"numa_pte_updates",
> 
> --
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-- 
Michal Hocko
SUSE Labs