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Subject: Re: [PATCH v2] mm: fix oom_kill event handling
To:     Roman Gushchin <guro@fb.com>, kernel-team@fb.com
Cc:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        linux-mm@kvack.org
References: <20180508124637.29984-1-guro@fb.com>
From:   Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Message-ID: <c5ca700a-46f7-9ba9-2c2e-fd4fd1cb16ea@yandex-team.ru>
Date:   Tue, 8 May 2018 16:26:26 +0300
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On 08.05.2018 15:46, Roman Gushchin wrote:
> Commit e27be240df53 ("mm: memcg: make sure memory.events is
> uptodate when waking pollers") converted most of memcg event
> counters to per-memcg atomics, which made them less confusing
> for a user. The "oom_kill" counter remained untouched, so now
> it behaves differently than other counters (including "oom").
> This adds nothing but confusion.
> 
> Let's fix this by adding the MEMCG_OOM_KILL event, and follow
> the MEMCG_OOM approach. This also removes a hack from
> count_memcg_event_mm(), introduced earlier specially for the
> OOM_KILL counter.
> 
> Signed-off-by: Roman Gushchin <guro@fb.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Vladimir Davydov <vdavydov.dev@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> Cc: linux-kernel@vger.kernel.org
> Cc: cgroups@vger.kernel.org
> Cc: linux-mm@kvack.org

Acked-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

> ---
>   include/linux/memcontrol.h | 26 ++++++++++++++++++++++----
>   mm/memcontrol.c            |  6 ++++--
>   mm/oom_kill.c              |  2 +-
>   3 files changed, 27 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 6cbea2f25a87..794475db7368 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -54,6 +54,7 @@ enum memcg_memory_event {
>   	MEMCG_HIGH,
>   	MEMCG_MAX,
>   	MEMCG_OOM,
> +	MEMCG_OOM_KILL,
>   	MEMCG_SWAP_MAX,
>   	MEMCG_SWAP_FAIL,
>   	MEMCG_NR_MEMORY_EVENTS,
> @@ -721,11 +722,8 @@ static inline void count_memcg_event_mm(struct mm_struct *mm,
>   
>   	rcu_read_lock();
>   	memcg = rcu_dereference(mm->memcg);
> -	if (likely(memcg)) {
> +	if (likely(memcg))
>   		count_memcg_events(memcg, idx, 1);
> -		if (idx == OOM_KILL)
> -			cgroup_file_notify(&memcg->events_file);
> -	}
>   	rcu_read_unlock();
>   }
>   
> @@ -736,6 +734,21 @@ static inline void memcg_memory_event(struct mem_cgroup *memcg,
>   	cgroup_file_notify(&memcg->events_file);
>   }
>   
> +static inline void memcg_memory_event_mm(struct mm_struct *mm,
> +					 enum memcg_memory_event event)
> +{
> +	struct mem_cgroup *memcg;
> +
> +	if (mem_cgroup_disabled())
> +		return;
> +
> +	rcu_read_lock();
> +	memcg = rcu_dereference(mm->memcg);
> +	if (likely(memcg))
> +		memcg_memory_event(memcg, event);
> +	rcu_read_unlock();
> +}
> +
>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>   void mem_cgroup_split_huge_fixup(struct page *head);
>   #endif
> @@ -757,6 +770,11 @@ static inline void memcg_memory_event(struct mem_cgroup *memcg,
>   {
>   }
>   
> +static inline void memcg_memory_event_mm(struct mm_struct *mm,
> +					 enum memcg_memory_event event)
> +{
> +}
> +
>   static inline bool mem_cgroup_low(struct mem_cgroup *root,
>   				  struct mem_cgroup *memcg)
>   {
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 10973671e562..38717630305d 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3772,7 +3772,8 @@ 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, OOM_KILL));
> +	seq_printf(sf, "oom_kill %lu\n",
> +		   atomic_long_read(&memcg->memory_events[MEMCG_OOM_KILL]));
>   	return 0;
>   }
>   
> @@ -5529,7 +5530,8 @@ static int memory_events_show(struct seq_file *m, void *v)
>   		   atomic_long_read(&memcg->memory_events[MEMCG_MAX]));
>   	seq_printf(m, "oom %lu\n",
>   		   atomic_long_read(&memcg->memory_events[MEMCG_OOM]));
> -	seq_printf(m, "oom_kill %lu\n", memcg_sum_events(memcg, OOM_KILL));
> +	seq_printf(m, "oom_kill %lu\n",
> +		   atomic_long_read(&memcg->memory_events[MEMCG_OOM_KILL]));
>   
>   	return 0;
>   }
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 8f7d8dd99e5d..6b74142a1259 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -868,7 +868,7 @@ static void __oom_kill_process(struct task_struct *victim)
>   
>   	/* Raise event before sending signal: task reaper must see this */
>   	count_vm_event(OOM_KILL);
> -	count_memcg_event_mm(mm, OOM_KILL);
> +	memcg_memory_event_mm(mm, MEMCG_OOM_KILL);
>   
>   	/*
>   	 * We should send SIGKILL before granting access to memory reserves
>