From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id ECD356B000A for ; Wed, 27 Jun 2018 10:26:22 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id l4-v6so2606164wmc.7 for ; Wed, 27 Jun 2018 07:26:22 -0700 (PDT) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id b4-v6si2050615wru.376.2018.06.27.07.26.21 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 27 Jun 2018 07:26:21 -0700 (PDT) Received: from pps.filterd (m0098419.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w5REJw2Y115920 for ; Wed, 27 Jun 2018 10:26:20 -0400 Received: from e12.ny.us.ibm.com (e12.ny.us.ibm.com [129.33.205.202]) by mx0b-001b2d01.pphosted.com with ESMTP id 2jv9h1g77a-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Wed, 27 Jun 2018 10:26:19 -0400 Received: from localhost by e12.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 27 Jun 2018 10:26:19 -0400 Date: Wed, 27 Jun 2018 07:28:22 -0700 From: "Paul E. McKenney" Subject: Re: [PATCH] mm,oom: Bring OOM notifier callbacks to outside of OOM killer. Reply-To: paulmck@linux.vnet.ibm.com References: <1529493638-6389-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20180621073142.GA10465@dhcp22.suse.cz> <2d8c3056-1bc2-9a32-d745-ab328fd587a1@i-love.sakura.ne.jp> <20180626170345.GA3593@linux.vnet.ibm.com> <20180626235014.GS3593@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Message-Id: <20180627142822.GV3593@linux.vnet.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Tetsuo Handa Cc: Michal Hocko , David Rientjes , linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org On Wed, Jun 27, 2018 at 07:52:23PM +0900, Tetsuo Handa wrote: > On 2018/06/27 8:50, Paul E. McKenney wrote: > > On Wed, Jun 27, 2018 at 05:10:48AM +0900, Tetsuo Handa wrote: > >> As far as I can see, > >> > >> - atomic_set(&oom_callback_count, 1); > >> + atomic_inc(&oom_callback_count); > >> > >> should be sufficient. > > > > I don't see how that helps. For example, suppose that two tasks > > invoked rcu_oom_notify() at about the same time. Then they could > > both see oom_callback_count equal to zero, both atomically increment > > oom_callback_count, then both do the IPI invoking rcu_oom_notify_cpu() > > on each online CPU. > > > > So far, so good. But rcu_oom_notify_cpu() enqueues a per-CPU RCU > > callback, and enqueuing the same callback twice in quick succession > > would fatally tangle RCU's callback lists. > > > > What am I missing here? > > You are pointing out that "number of rsp->call() is called" > "number of > rcu_oom_callback() is called" can happen if concurrently called, aren't you? Yes. Reusing an rcu_head before invocation of the earlier use is very bad indeed. ;-) > Then, you are not missing anything. You will need to use something equivalent > to oom_lock even if you can convert rcu_oom_notify() to use shrinkers. What should I look at to work out whether it makes sense to convert rcu_oom_notify() to shrinkers, and if so, how to go about it? Or are you simply asking me to serialize rcu_oom_notify()? (Which is of course not difficult, so please just let me know.) Thanx, Paul