linux-kernel - Re: [PATCH v6 1/2] mm/oom_kill: Do not delay oom reaper when the victim is frozen

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Message-ID: <brzxqxiwpxwjr22mknh54mn3efrgd77w7mfnf3ojm7qm633gh5@gngras6lj57q>
Date: Fri, 29 Aug 2025 13:30:41 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: zhongjinji <zhongjinji@...or.com>
Cc: mhocko@...e.com, rientjes@...gle.com, shakeel.butt@...ux.dev,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        lorenzo.stoakes@...cle.com, surenb@...gle.com, liulu.liu@...or.com,
        feng.han@...or.com, tianxiaobin@...or.com, fengbaopeng@...or.com
Subject: Re: [PATCH v6 1/2] mm/oom_kill: Do not delay oom reaper when the
 victim is frozen

* zhongjinji <zhongjinji@...or.com> [250829 02:56]:
> The oom reaper is a mechanism to guarantee a forward process during OOM
> situation when the oom victim cannot terminate on its own (e.g. being
> blocked in uninterruptible state or frozen by cgroup freezer). In order
> to give the victim some time to terminate properly the oom reaper is
> delayed in its invocation. This is particularly beneficial when the oom
> victim is holding robust futex resources as the anonymous memory tear
> down can break those. [1]
> 
> On the other hand deliberately frozen tasks by the freezer cgroup will
> not wake up until they are thawed in the userspace and delay is
> effectively pointless. Therefore opt out from the delay for cgroup
> frozen oom victims.
> 
> Reference:
> [1] https://lore.kernel.org/all/20220414144042.677008-1-npache@redhat.com/T/#u
> 
> Signed-off-by: zhongjinji <zhongjinji@...or.com>

Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>

> ---
>  mm/oom_kill.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> index 25923cfec9c6..a5e9074896a1 100644
> --- a/mm/oom_kill.c
> +++ b/mm/oom_kill.c
> @@ -700,7 +700,14 @@ static void queue_oom_reaper(struct task_struct *tsk)
>  
>  	get_task_struct(tsk);
>  	timer_setup(&tsk->oom_reaper_timer, wake_oom_reaper, 0);
> -	tsk->oom_reaper_timer.expires = jiffies + OOM_REAPER_DELAY;
> +	tsk->oom_reaper_timer.expires = jiffies;
> +
> +	/*
> +	 * If the task is frozen by the cgroup freezer, the delay is unnecessary
> +	 * because it cannot exit until thawed. Skip the delay for frozen victims.
> +	 */
> +	if (!frozen(tsk))
> +		tsk->oom_reaper_timer.expires += OOM_REAPER_DELAY;
>  	add_timer(&tsk->oom_reaper_timer);
>  }
>  
> -- 
> 2.17.1
> 
>