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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 30C78C43144 for ; Wed, 27 Jun 2018 10:52:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CF92426347 for ; Wed, 27 Jun 2018 10:52:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CF92426347 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=i-love.sakura.ne.jp 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 S1753663AbeF0Kwi (ORCPT ); Wed, 27 Jun 2018 06:52:38 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:19938 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750774AbeF0Kwh (ORCPT ); Wed, 27 Jun 2018 06:52:37 -0400 Received: from fsav304.sakura.ne.jp (fsav304.sakura.ne.jp [153.120.85.135]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id w5RAqO8w008963; Wed, 27 Jun 2018 19:52:24 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav304.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav304.sakura.ne.jp); Wed, 27 Jun 2018 19:52:24 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav304.sakura.ne.jp) Received: from [192.168.1.8] (softbank126074194044.bbtec.net [126.74.194.44]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id w5RAqNCD008959 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 27 Jun 2018 19:52:23 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH] mm,oom: Bring OOM notifier callbacks to outside of OOM killer. To: paulmck@linux.vnet.ibm.com Cc: Michal Hocko , David Rientjes , linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org 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> From: Tetsuo Handa Message-ID: Date: Wed, 27 Jun 2018 19:52:23 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180626235014.GS3593@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? > > Thanx, Paul 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? 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.