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 3CDAFC6787D for ; Mon, 8 Oct 2018 02:53:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E7F412086D for ; Mon, 8 Oct 2018 02:53:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E7F412086D 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 S1726179AbeJHKCY (ORCPT ); Mon, 8 Oct 2018 06:02:24 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:12213 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725760AbeJHKCY (ORCPT ); Mon, 8 Oct 2018 06:02:24 -0400 Received: from fsav302.sakura.ne.jp (fsav302.sakura.ne.jp [153.120.85.133]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id w982qFn8099066; Mon, 8 Oct 2018 11:52:15 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav302.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav302.sakura.ne.jp); Mon, 08 Oct 2018 11:52:15 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav302.sakura.ne.jp) Received: from [192.168.1.8] (softbank060157066051.bbtec.net [60.157.66.51]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id w982qApH098949 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 8 Oct 2018 11:52:15 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Subject: Re: [PATCH] mm, oom_adj: avoid meaningless loop to find processes sharing mm To: ytk.lee@samsung.com, "mhocko@kernel.org" , "mhocko@suse.com" Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" References: <20181008011931epcms1p82dd01b7e5c067ea99946418bc97de46a@epcms1p8> From: Tetsuo Handa Message-ID: Date: Mon, 8 Oct 2018 11:52:09 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181008011931epcms1p82dd01b7e5c067ea99946418bc97de46a@epcms1p8> 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 2018/10/08 10:19, Yong-Taek Lee wrote: > @@ -1056,6 +1056,7 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy) > struct mm_struct *mm = NULL; > struct task_struct *task; > int err = 0; > + int mm_users = 0; > > task = get_proc_task(file_inode(file)); > if (!task) > @@ -1092,7 +1093,8 @@ static int __set_oom_adj(struct file *file, int oom_adj, bool legacy) > struct task_struct *p = find_lock_task_mm(task); > > if (p) { > - if (atomic_read(&p->mm->mm_users) > 1) { > + mm_users = atomic_read(&p->mm->mm_users); > + if ((mm_users > 1) && (mm_users != get_nr_threads(p))) { How can this work (even before this patch)? When clone(CLONE_VM without CLONE_THREAD/CLONE_SIGHAND) is requested, copy_process() calls copy_signal() in order to copy sig->oom_score_adj and sig->oom_score_adj_min before calling copy_mm() in order to increment mm->mm_users, doesn't it? Then, we will get two different "struct signal_struct" with different oom_score_adj/oom_score_adj_min but one "struct mm_struct" shared by two thread groups. > mm = p->mm; > atomic_inc(&mm->mm_count); > }