From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BB264C43142 for ; Wed, 27 Jun 2018 14:26:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7661626182 for ; Wed, 27 Jun 2018 14:26:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7661626182 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.vnet.ibm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965294AbeF0O0V (ORCPT ); Wed, 27 Jun 2018 10:26:21 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:50642 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S964916AbeF0O0U (ORCPT ); Wed, 27 Jun 2018 10:26:20 -0400 Received: from pps.filterd (m0098417.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w5REK6CG064544 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 mx0a-001b2d01.pphosted.com with ESMTP id 2jvb5wumnq-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! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 27 Jun 2018 10:26:16 -0400 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23032.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id w5REQFlP7864596 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 27 Jun 2018 14:26:15 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id DEAEBB206A; Wed, 27 Jun 2018 10:26:07 -0400 (EDT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BB88EB2064; Wed, 27 Jun 2018 10:26:07 -0400 (EDT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.159]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Wed, 27 Jun 2018 10:26:07 -0400 (EDT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 2791116CA20F; Wed, 27 Jun 2018 07:28:22 -0700 (PDT) Date: Wed, 27 Jun 2018 07:28:22 -0700 From: "Paul E. McKenney" To: Tetsuo Handa Cc: Michal Hocko , David Rientjes , linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org 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: User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18062714-0060-0000-0000-0000028345B1 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009263; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000266; SDB=6.01053094; UDB=6.00539924; IPR=6.00831018; MB=3.00021880; MTD=3.00000008; XFM=3.00000015; UTC=2018-06-27 14:26:18 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18062714-0061-0000-0000-00004598059B Message-Id: <20180627142822.GV3593@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-06-27_03:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=866 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1806210000 definitions=main-1806270158 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: 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