From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965014AbcBCQkT (ORCPT ); Wed, 3 Feb 2016 11:40:19 -0500 Received: from asavdk4.altibox.net ([109.247.116.15]:58498 "EHLO asavdk4.altibox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964815AbcBCQkO (ORCPT ); Wed, 3 Feb 2016 11:40:14 -0500 Date: Wed, 3 Feb 2016 17:39:46 +0100 From: Sam Ravnborg To: Arnd Bergmann Cc: Russell King , Andrew Morton , Matthew Wilcox , Jan Kara , "Kirill A. Shutemov" , Ross Zwisler , Dan Williams , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, "David S. Miller" Subject: Re: [PATCH] [RFC] ARM: modify pgd_t definition for TRANSPARENT_HUGEPAGE_PUD Message-ID: <20160203163946.GA20360@ravnborg.org> References: <1773775.QWf7OyDGPh@wuerfel> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1773775.QWf7OyDGPh@wuerfel> User-Agent: Mutt/1.5.24 (2015-08-30) X-CMAE-Score: 0 X-CMAE-Analysis: v=2.1 cv=OIGHpXuB c=1 sm=1 tr=0 a=Ij76tQDYWdb01v2+RnYW5w==:117 a=Ij76tQDYWdb01v2+RnYW5w==:17 a=L9H7d07YOLsA:10 a=9cW_t1CCXrUA:10 a=s5jvgZ67dGcA:10 a=kj9zAlcOel0A:10 a=IGV7rFElmuYY5uF_6qYA:9 a=CjuIK1q_8ugA:10 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 03, 2016 at 02:21:48PM +0100, Arnd Bergmann wrote: > I ran into build errors on ARM after Willy's newly added generic > TRANSPARENT_HUGEPAGE_PUD support. We don't support this feature > on ARM at all, but the patch causes a build error anyway: > > In file included from ../kernel/memremap.c:17:0: > ../include/linux/pfn_t.h:108:7: error: 'pud_mkdevmap' declared as function returning an array > pud_t pud_mkdevmap(pud_t pud); > > We don't use a PUD on ARM, so pud_t is defined as pmd_t, which > in turn is defined as > > typedef unsigned long pgd_t[2]; > > on NOMMU and on 2-level MMU configurations. There is an (unused) > other definition using a struct around the array, which happens to > work fine here. > > There is a comment in the file about the fact the other version > is "easier on the compiler", and I've traced that version back > to linux-2.1.80 when ARM support was first merged back in 1998. > > It's probably a safe assumption that this is no longer necessary: > The same logic existed in asm-i386 at the time but was removed > a year later in 2.3.23pre3. The STRICT_MM_TYPECHECKS logic > also ended up getting copied into these files: > > arch/alpha/include/asm/page.h > arch/arc/include/asm/page.h > arch/arm/include/asm/pgtable-3level-types.h > arch/arm64/include/asm/pgtable-types.h > arch/ia64/include/asm/page.h > arch/parisc/include/asm/page.h > arch/powerpc/include/asm/page.h > arch/sparc/include/asm/page_32.h > arch/sparc/include/asm/page_64.h For the sparc32 case we use the simpler variants. According to the comment this is due to limitation in the way we pass arguments in the sparc32 ABI. But I have not tried to compare a kernel for sparc32 with and without the use of structs. For sparc64 we use the stricter types (structs). I did not check other architectures - but just wanted to tell that the right choice may be architecture dependent. Sam