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=-9.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 B9C8FC433E1 for ; Wed, 19 Aug 2020 12:37:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9CC302072D for ; Wed, 19 Aug 2020 12:37:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728219AbgHSMhz (ORCPT ); Wed, 19 Aug 2020 08:37:55 -0400 Received: from mx2.suse.de ([195.135.220.15]:48386 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726752AbgHSMhp (ORCPT ); Wed, 19 Aug 2020 08:37:45 -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 E54ADAF92; Wed, 19 Aug 2020 12:38:10 +0000 (UTC) Date: Wed, 19 Aug 2020 14:37:43 +0200 From: Michal Hocko To: David Hildenbrand Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Wei Yang , Baoquan He , Pankaj Gupta , Oscar Salvador Subject: Re: [PATCH v1 02/11] mm/memory_hotplug: enforce section granularity when onlining/offlining Message-ID: <20200819123743.GF5422@dhcp22.suse.cz> References: <20200819101157.12723-1-david@redhat.com> <20200819101157.12723-3-david@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200819101157.12723-3-david@redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 19-08-20 12:11:48, David Hildenbrand wrote: > Already two people (including me) tried to offline subsections, because > the function looks like it can deal with it. But we really can only > online/offline full sections (e.g., we can only mark full sections > online/offline via SECTION_IS_ONLINE). > > Add a simple safety net that to document the restriction now. Current users > (core and powernv/memtrace) respect these restrictions. I do agree with the warning because it clarifies our expectations indeed. Se below for more questions. > Cc: Andrew Morton > Cc: Michal Hocko > Cc: Wei Yang > Cc: Baoquan He > Cc: Pankaj Gupta > Cc: Oscar Salvador > Signed-off-by: David Hildenbrand > --- > mm/memory_hotplug.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index c781d386d87f9..6856702af68d9 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -801,6 +801,11 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, > int ret; > struct memory_notify arg; > > + /* We can only online full sections (e.g., SECTION_IS_ONLINE) */ > + if (WARN_ON_ONCE(!nr_pages || > + !IS_ALIGNED(pfn | nr_pages, PAGES_PER_SECTION))) > + return -EINVAL; This looks looks unnecessarily cryptic to me. Do you want to catch full section operation that doesn't start at the usual section boundary? If yes the above doesn't work work unless I am missing something. Why don't you simply WARN_ON_ONCE(nr_pages % PAGES_PER_SECTION). !nr_pages doesn't sound like something interesting to care about or why do we care? -- Michal Hocko SUSE Labs