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 BA4A6C43461 for ; Thu, 10 Sep 2020 12:05:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 83FDF207EA for ; Thu, 10 Sep 2020 12:05:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730388AbgIJMFQ (ORCPT ); Thu, 10 Sep 2020 08:05:16 -0400 Received: from mx2.suse.de ([195.135.220.15]:41100 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730244AbgIJMBk (ORCPT ); Thu, 10 Sep 2020 08:01:40 -0400 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 31B87AD36; Thu, 10 Sep 2020 12:01:40 +0000 (UTC) Date: Thu, 10 Sep 2020 14:01:23 +0200 From: Michal Hocko To: Laurent Dufour Cc: akpm@linux-foundation.org, David Hildenbrand , Oscar Salvador , rafael@kernel.org, nathanl@linux.ibm.com, cheloha@linux.ibm.com, stable@vger.kernel.org, Greg Kroah-Hartman , linux-mm@kvack.org, LKML Subject: Re: [PATCH] mm: don't rely on system state to detect hot-plug operations Message-ID: <20200910120123.GF28354@dhcp22.suse.cz> References: <20200909074011.GD7348@dhcp22.suse.cz> <9faac1ce-c02d-7dbc-f79a-4aaaa5a73d28@linux.ibm.com> <20200909090953.GE7348@dhcp22.suse.cz> <4cdb54be-1a92-4ba4-6fee-3b415f3468a9@linux.ibm.com> <20200909105914.GF7348@dhcp22.suse.cz> <74a62b00-235e-7deb-2814-f3b240fea25e@linux.ibm.com> <20200910072331.GB28354@dhcp22.suse.cz> <31cfdf35-618f-6f56-ef16-0d999682ad02@linux.ibm.com> <20200910111246.GE28354@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 10-09-20 13:35:32, Laurent Dufour wrote: > Le 10/09/2020 à 13:12, Michal Hocko a écrit : > > On Thu 10-09-20 09:51:39, Laurent Dufour wrote: > > > Le 10/09/2020 à 09:23, Michal Hocko a écrit : > > > > On Wed 09-09-20 18:07:15, Laurent Dufour wrote: > > > > > Le 09/09/2020 à 12:59, Michal Hocko a écrit : > > > > > > On Wed 09-09-20 11:21:58, Laurent Dufour wrote: > > > > [...] > > > > > > > For the point a, using the enum allows to know in > > > > > > > register_mem_sect_under_node() if the link operation is due to a hotplug > > > > > > > operation or done at boot time. > > > > > > > > > > > > Yes, but let me repeat. We have a mess here and different paths check > > > > > > for the very same condition by different ways. We need to unify those. > > > > > > > > > > What are you suggesting to unify these checks (using a MP_* enum as > > > > > suggested by David, something else)? > > > > > > > > We do have system_state check spread at different places. I would use > > > > this one and wrap it behind a helper. Or have I missed any reason why > > > > that wouldn't work for this case? > > > > > > That would not work in that case because memory can be hot-added at the > > > SYSTEM_SCHEDULING system state and the regular memory is also registered at > > > that system state too. So system state is not enough to discriminate between > > > the both. > > > > If that is really the case all other places need a fix as well. > > Btw. could you be more specific about memory hotplug during early boot? > > How that happens? I am only aware of https://lkml.kernel.org/r/20200818110046.6664-1-osalvador@suse.de > > and that doesn't happen as early as SYSTEM_SCHEDULING. > > That points has been raised by David, quoting him here: > > > IIRC, ACPI can hotadd memory while SCHEDULING, this patch would break that. > > > > Ccing Oscar, I think he mentioned recently that this is the case with ACPI. : Please, note that upstream has fixed that differently (and unintentionally) by : adding another boot state (SYSTEM_SCHEDULING), which is set before smp_init(). : That should happen before memory hotplug events even with memhp_default_state=online. : Backporting that would be too intrusive. Either I am confused or the above says that no hotplug should happen during SYSTEM_SCHEDULING even in the above case. I really have hard time to imagine how an early boot hotplug should even work. We start with a memory layout provided by a BIOS/FW and intiailize it statically. How would a hotplug even actually trigger that early? -- Michal Hocko SUSE Labs