From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752525AbdGEXA6 (ORCPT ); Wed, 5 Jul 2017 19:00:58 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:34400 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752472AbdGEXA5 (ORCPT ); Wed, 5 Jul 2017 19:00:57 -0400 Date: Wed, 5 Jul 2017 16:00:55 -0700 From: Andrew Morton To: Michal Hocko Cc: Vlastimil Babka , Joonsoo Kim , Yang Shi , Mel Gorman , , LKML , Michal Hocko Subject: Re: [PATCH] mm: disallow early_pfn_to_nid on configurations which do not implement it Message-Id: <20170705160055.013fa5ff34bdf1f6efa4e6ce@linux-foundation.org> In-Reply-To: <20170704075803.15979-1-mhocko@kernel.org> References: <20170704075803.15979-1-mhocko@kernel.org> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 4 Jul 2017 09:58:03 +0200 Michal Hocko wrote: > From: Michal Hocko > > early_pfn_to_nid will return node 0 if both HAVE_ARCH_EARLY_PFN_TO_NID > and HAVE_MEMBLOCK_NODE_MAP are disabled. It seems we are safe now > because all architectures which support NUMA define one of them (with an > exception of alpha which however has CONFIG_NUMA marked as broken) so > this works as expected. It can get silently and subtly broken too > easily, though. Make sure we fail the compilation if NUMA is enabled and > there is no proper implementation for this function. If that ever > happens we know that either the specific configuration is invalid > and the fix should either disable NUMA or enable one of the above > configs. > > ... > > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -1055,6 +1055,7 @@ static inline struct zoneref *first_zones_zonelist(struct zonelist *zonelist, > !defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP) > static inline unsigned long early_pfn_to_nid(unsigned long pfn) > { > + BUILD_BUG_ON(IS_ENABLED(CONFIG_NUMA)); > return 0; > } > #endif Wouldn't this be more conventional? --- a/include/linux/mmzone.h~a +++ a/include/linux/mmzone.h @@ -1052,7 +1052,8 @@ static inline struct zoneref *first_zone #endif #if !defined(CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID) && \ - !defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP) + !defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP) && \ + !defined(CONFIG_NUMA) static inline unsigned long early_pfn_to_nid(unsigned long pfn) { return 0; _