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 59622C433E1 for ; Thu, 20 Aug 2020 11:29:36 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 235ED208DB for ; Thu, 20 Aug 2020 11:29:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 235ED208DB 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 625428D0007; Thu, 20 Aug 2020 07:29:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 5D7398D0001; Thu, 20 Aug 2020 07:29:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4EE328D0007; Thu, 20 Aug 2020 07:29:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0088.hostedemail.com [216.40.44.88]) by kanga.kvack.org (Postfix) with ESMTP id 3A2628D0001 for ; Thu, 20 Aug 2020 07:29:35 -0400 (EDT) Received: from smtpin03.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id E39C3249E for ; Thu, 20 Aug 2020 11:29:34 +0000 (UTC) X-FDA: 77170726668.03.kitty00_5f0b39027030 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin03.hostedemail.com (Postfix) with ESMTP id B5CDD28A4E8 for ; Thu, 20 Aug 2020 11:29:34 +0000 (UTC) X-HE-Tag: kitty00_5f0b39027030 X-Filterd-Recvd-Size: 3508 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf13.hostedemail.com (Postfix) with ESMTP for ; Thu, 20 Aug 2020 11:29:34 +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 341A4AC98; Thu, 20 Aug 2020 11:30:00 +0000 (UTC) Date: Thu, 20 Aug 2020 13:29:32 +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: <20200820112932.GG5033@dhcp22.suse.cz> References: <20200820002053.1424000-1-surenb@google.com> <20200820105555.GA4546@redhat.com> <20200820111349.GE5033@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200820111349.GE5033@dhcp22.suse.cz> X-Rspamd-Queue-Id: B5CDD28A4E8 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 13:13:55, Michal Hocko wrote: > 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. I have tried to remember but I have to say that after reading man page I am still confused. So what is the actual difference between CLONE_THREAD and CLONE_SIGHAND? Essentially all we care about from the OOM (and oom_score_adj) POV is that signals are delivered to all entities and that thay share signal struct. copy_signal is checking for CLONE_THREAD but CLONE_THREAD requires CLONE_SIGHAND AFAIU. So is there any cae where checking for CLONE_SIGHAND would wrong for our purpose? This is mostly an academic question because I do agree that checking for CLONE_THREAD is likely more readable. And in fact the MMF_PROC_SHARED is likely more suitable to be set in copy_signal. -- Michal Hocko SUSE Labs