linux-kernel - Re: [PATCH] mm,oom: Bring OOM notifier callbacks to outside of OOM killer.

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Date:   Fri, 6 Jul 2018 07:39:42 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm,oom: Bring OOM notifier callbacks to outside of OOM
 killer.

On Tue 03-07-18 09:01:01, Paul E. McKenney wrote:
> On Tue, Jul 03, 2018 at 09:24:13AM +0200, Michal Hocko wrote:
> > On Mon 02-07-18 14:37:14, Paul E. McKenney wrote:
> > [...]
> > > commit d2b8d16b97ac2859919713b2d98b8a3ad22943a2
> > > Author: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > > Date:   Mon Jul 2 14:30:37 2018 -0700
> > > 
> > >     rcu: Remove OOM code
> > >     
> > >     There is reason to believe that RCU's OOM code isn't really helping
> > >     that much, given that the best it can hope to do is accelerate invoking
> > >     callbacks by a few seconds, and even then only if some CPUs have no
> > >     non-lazy callbacks, a condition that has been observed to be rare.
> > >     This commit therefore removes RCU's OOM code.  If this causes problems,
> > >     it can easily be reinserted.
> > >     
> > >     Reported-by: Michal Hocko <mhocko@...nel.org>
> > >     Reported-by: Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
> > >     Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > 
> > I would also note that waiting in the notifier might be a problem on its
> > own because we are holding the oom_lock and the system cannot trigger
> > the OOM killer while we are holding it and waiting for oom_callback_wq
> > event. I am not familiar with the code to tell whether this can deadlock
> > but from a quick glance I _suspect_ that we might depend on __rcu_reclaim
> > and basically an arbitrary callback so no good.
> > 
> > Acked-by: Michal Hocko <mhocko@...e.com>
> > 
> > Thanks!
> 
> Like this?

Thanks!
-- 
Michal Hocko
SUSE Labs