From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751234AbaBHBZa (ORCPT ); Fri, 7 Feb 2014 20:25:30 -0500 Received: from relay4-d.mail.gandi.net ([217.70.183.196]:53422 "EHLO relay4-d.mail.gandi.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751052AbaBHBZ2 (ORCPT ); Fri, 7 Feb 2014 20:25:28 -0500 X-Originating-IP: 50.43.14.201 Date: Fri, 7 Feb 2014 17:25:16 -0800 From: Josh Triplett To: David Rientjes Cc: Andrew Morton , Rashika Kheria , linux-kernel@vger.kernel.org, Rik van Riel , "Kirill A. Shutemov" , Jiang Liu , Michel Lespinasse , linux-mm@kvack.org Subject: Re: [PATCH 9/9] mm: Remove ifdef condition in include/linux/mm.h Message-ID: <20140208012515.GA18890@jtriplet-mobl1> References: <63adb3b97f2869d4c7e76d17ef4aa76b8cf599f3.1391167128.git.rashika.kheria@gmail.com> <20140207210705.GB13604@jtriplet-mobl1> <20140207143050.6bd35ed5c670a3ca143ba59a@linux-foundation.org> <20140207232711.GA16836@jtriplet-mobl1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 07, 2014 at 05:02:02PM -0800, David Rientjes wrote: > On Fri, 7 Feb 2014, Josh Triplett wrote: > > > > Why?? If CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID then, yes, we need it to be > > > global. Otherwise it's perfectly fine just being static in file scope. > > > This causes the compilation unit to break when you compile it, not wait > > > until vmlinux and find undefined references. > > > > > > I see no reason it can't be done like this in mm/page_alloc.c: > > > > > > #ifdef CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID > > > extern int __meminit __early_pfn_to_nid(unsigned long pfn); > > > > No, a .c file should not have an extern declaration in it. This should > > live in an appropriate header file, to be included in both page_alloc.c > > and any arch file that defines an overriding function. > > > > Ok, so you have religious beliefs about extern being used in files ending > in .c and don't mind the 2900 occurrences of it in the kernel tree and > desire 14 line obfuscation in header files with comments to what is being > defined in .c files such as "please see mm/page_alloc.c" as mm.h has. I (and many others) have very specific technical objections to not having the same prototype seen by both the definition and use of a function: that helps keep the prototype in sync with the definition(s), helps keep all definitions in sync if there are multiple such definitions, and eliminates -Wmissing-prototype warnings (which in addition to those benefits also help detect functions that should be made static or eliminated). And as mentioned before, those 14 lines can be significantly simplified; Rashika's patch already does one such simplification. Those 2900 occurrences should go away as well, and Rashika's previous patches have already fixed many of them. > > > Both of these options look much better than > > > > > > include/linux/mm.h: > > > > > > #if !defined(CONFIG_HAVE_MEMBLOCK_NODE_MAP) && \ > > > !defined(CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID) > > > static inline int __early_pfn_to_nid(unsigned long pfn) > > > { > > > return 0; > > > } > > > #else > > > /* please see mm/page_alloc.c */ > > > extern int __meminit early_pfn_to_nid(unsigned long pfn); > > > #ifdef CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID > > > /* there is a per-arch backend function. */ > > > extern int __meminit __early_pfn_to_nid(unsigned long pfn); > > > #endif /* CONFIG_HAVE_ARCH_EARLY_PFN_TO_NID */ > > > #endif > > > > > > where all this confusion is originating from. > > > > The proposal is to first simplify those ifdefs by eliminating the inner > > one in the #else; I agree with Andrew that we ought to go ahead and take > > that step given the patch at hand, and then figure out if there's an > > additional simplification possible. > > > > If additional simplification is possible? Yeah, it's __weak which is > designed for this purpose. No objections here if someone wants to write that patch. - Josh Triplett