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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 1AEE6C433E1 for ; Thu, 20 Aug 2020 11:13:58 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id D9535207FB for ; Thu, 20 Aug 2020 11:13:57 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D9535207FB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 5DF9F8D000E; Thu, 20 Aug 2020 07:13:57 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 58FD48D0001; Thu, 20 Aug 2020 07:13:57 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 47D4F8D000E; Thu, 20 Aug 2020 07:13:57 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 322788D0001 for ; Thu, 20 Aug 2020 07:13:57 -0400 (EDT) Received: from smtpin11.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id EDE0D8248047 for ; Thu, 20 Aug 2020 11:13:56 +0000 (UTC) X-FDA: 77170687272.11.frog13_250a49227030 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin11.hostedemail.com (Postfix) with ESMTP id C3FAB180F8B82 for ; Thu, 20 Aug 2020 11:13:56 +0000 (UTC) X-HE-Tag: frog13_250a49227030 X-Filterd-Recvd-Size: 3446 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Thu, 20 Aug 2020 11:13:56 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 16BF9B804; Thu, 20 Aug 2020 11:14:22 +0000 (UTC) Date: Thu, 20 Aug 2020 13:13:49 +0200 From: Michal Hocko To: Oleg Nesterov Cc: Suren Baghdasaryan , christian.brauner@ubuntu.com, mingo@kernel.org, peterz@infradead.org, tglx@linutronix.de, esyr@redhat.com, christian@kellner.me, areber@redhat.com, shakeelb@google.com, cyphar@cyphar.com, adobriyan@gmail.com, akpm@linux-foundation.org, ebiederm@xmission.com, gladkov.alexey@gmail.com, walken@google.com, daniel.m.jordan@oracle.com, avagin@gmail.com, bernd.edlinger@hotmail.de, john.johansen@canonical.com, laoar.shao@gmail.com, timmurray@google.com, minchan@kernel.org, kernel-team@android.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 1/1] mm, oom_adj: don't loop through tasks in __set_oom_adj when not necessary Message-ID: <20200820111349.GE5033@dhcp22.suse.cz> References: <20200820002053.1424000-1-surenb@google.com> <20200820105555.GA4546@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200820105555.GA4546@redhat.com> X-Rspamd-Queue-Id: C3FAB180F8B82 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu 20-08-20 12:55:56, Oleg Nesterov wrote: > On 08/19, Suren Baghdasaryan wrote: > > > > Since the combination of CLONE_VM and !CLONE_SIGHAND is rarely > > used the additional mutex lock in that path of the clone() syscall should > > not affect its overall performance. Clearing the MMF_PROC_SHARED flag > > (when the last process sharing the mm exits) is left out of this patch to > > keep it simple and because it is believed that this threading model is > > rare. > > vfork() ? Could you be more specific? > > --- a/kernel/fork.c > > +++ b/kernel/fork.c > > @@ -1403,6 +1403,15 @@ static int copy_mm(unsigned long clone_flags, struct task_struct *tsk) > > if (clone_flags & CLONE_VM) { > > mmget(oldmm); > > mm = oldmm; > > + if (!(clone_flags & CLONE_SIGHAND)) { > > I agree with Christian, you need CLONE_THREAD This was my suggestion to Suren, likely because I've misrememberd which clone flag is responsible for the signal delivery. But now, after double checking we do explicitly disallow CLONE_SIGHAND && !CLONE_VM. So CLONE_THREAD is the right thing to check. > > + /* We need to synchronize with __set_oom_adj */ > > + mutex_lock(&oom_adj_lock); > > + set_bit(MMF_PROC_SHARED, &mm->flags); > > + /* Update the values in case they were changed after copy_signal */ > > + tsk->signal->oom_score_adj = current->signal->oom_score_adj; > > + tsk->signal->oom_score_adj_min = current->signal->oom_score_adj_min; > > + mutex_unlock(&oom_adj_lock); > > I don't understand how this can close the race with __set_oom_adj... > > What if __set_oom_adj() is called right after mutex_unlock() ? It will see > MMF_PROC_SHARED, but for_each_process() won't find the new child until > copy_process() does list_add_tail_rcu(&p->tasks, &init_task.tasks) ? Good point. Then we will have to move this thing there. Thanks! -- Michal Hocko SUSE Labs