linux-kernel - Re: [PATCH v5 1/2] mm/oom_kill: Do not delay oom reaper when the victim is frozen

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Message-ID: <20250826130144.21522-1-zhongjinji@honor.com>
Date: Tue, 26 Aug 2025 21:01:44 +0800
From: zhongjinji <zhongjinji@...or.com>
To: <shakeel.butt@...ux.dev>
CC: <akpm@...ux-foundation.org>, <cgroups@...r.kernel.org>,
	<feng.han@...or.com>, <liam.howlett@...cle.com>,
	<linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>, <liulu.liu@...or.com>,
	<lorenzo.stoakes@...cle.com>, <mhocko@...e.com>, <rientjes@...gle.com>,
	<tglx@...utronix.de>, <zhongjinji@...or.com>
Subject: Re: [PATCH v5 1/2] mm/oom_kill: Do not delay oom reaper when the victim is frozen

> +cgroups
> 
> On Mon, Aug 25, 2025 at 09:38:54PM +0800, zhongjinji wrote:
> > The OOM reaper can quickly reap a process's memory when the system
> > encounters OOM, helping the system recover. If the victim process is
> > frozen and cannot be unfrozen in time, the reaper delayed by two seconds
> > will cause the system to fail to recover quickly from the OOM state.
> > 
> > When an OOM occurs, if the victim is not unfrozen, delaying the OOM reaper
> > will keep the system in a bad state for two seconds. Before scheduling the
> > oom_reaper task, check whether the victim is in a frozen state. If the
> > victim is frozen, do not delay the OOM reaper.
> > 
> > Signed-off-by: zhongjinji <zhongjinji@...or.com>
> > ---
> >  mm/oom_kill.c | 40 +++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 39 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 25923cfec9c6..4b4d73b1e00d 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -683,6 +683,41 @@ static void wake_oom_reaper(struct timer_list *timer)
> >  	wake_up(&oom_reaper_wait);
> >  }
> >  
> > +/*
> > + * When the victim is frozen, the OOM reaper should not be delayed, because
> > + * if the victim cannot be unfrozen promptly, it may block the system from
> > + * quickly recovering from the OOM state.
> > + */
> > +static bool should_delay_oom_reap(struct task_struct *tsk)
> > +{
> > +	struct mm_struct *mm = tsk->mm;
> > +	struct task_struct *p;
> > +	bool ret;
> > +
> 
> On v2, shouldn't READ_ONCE(tsk->frozen) be enough instead of mm check
> and checks insode for_each_process()?

Thank you.
It is mainly to check the processes created by vfork. I believe no one would
put them into different cgroups, so I also think that READ_ONCE(tsk->frozen)
is enough. I will update it.

> > +	if (!mm)
> > +		return true;
> > +
> > +	if (!frozen(tsk))
> > +		return true;
> > +
> > +	if (atomic_read(&mm->mm_users) <= 1)
> > +		return false;
> > +
> > +	rcu_read_lock();
> > +	for_each_process(p) {