Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756639AbZF3WMW (ORCPT ); Tue, 30 Jun 2009 18:12:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754227AbZF3WMM (ORCPT ); Tue, 30 Jun 2009 18:12:12 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:54490 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753849AbZF3WML (ORCPT ); Tue, 30 Jun 2009 18:12:11 -0400 Date: Tue, 30 Jun 2009 15:10:49 -0700 (PDT) From: Linus Torvalds X-X-Sender: torvalds@localhost.localdomain To: Yinghai Lu cc: "H. Peter Anvin" , Ingo Molnar , Mikael Pettersson , Matthew Wilcox , Grant Grundler , Linux Kernel Mailing List , linux-pci@vger.kernel.org Subject: Re: [BUG 2.6.31-rc1] HIGHMEM64G causes hang in PCI init on 32-bit x86 In-Reply-To: <4A4A88A2.7010509@kernel.org> Message-ID: References: <200906261559.n5QFxJH8027336@pilspetsen.it.uu.se> <19013.29264.623540.275538@pilspetsen.it.uu.se> <4A45A5C1.5080701@zytor.com> <19013.59956.144640.331854@pilspetsen.it.uu.se> <20090629022911.GC20297@lackof.org> <4A484A8A.9020704@zytor.com> <19016.41349.636663.515540@pilspetsen.it.uu.se> <20090629112155.GJ5480@parisc-linux.org> <19016.44061.600652.676183@pilspetsen.it.uu.se> <4A490804.3040609@zytor.com> <4A494478.7020304@kernel.org> <4A494E3C.70304@kernel.org> <4A495C0D.2020807@zytor.com> <4A4966EF.6010809@kernel.org> <4A496D4B.3040608@kernel.org> <19017.53428.834539.389495@pilspetsen.it.uu.se> <4A4A25B1.5010102@zytor.com> <4A4A6888.30001@kernel.org> <4A4A6B1C.7030405@zytor.com> <4A4A701F.3050700@kernel.org> <4A4A81C9.9070008@zytor.com> <4A4A88A2.7010509@kernel.org> User-Agent: Alpine 2.01 (LFD 1184 2008-12-16) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1380 Lines: 40 On Tue, 30 Jun 2009, Yinghai Lu wrote: ? > +#define round_up(x, y) ({ __typeof__(x) __mask = (y)-1; \ > + ((x)+__mask) & ~__mask; }) > +#define round_down(x, y) ({ __typeof__(x) __mask = (y)-1; (x) & ~__mask; }) Yes, except we might as well simplify it. Do it without the statement expressions, using just a single 'y'. Like this: #define __round_mask(x,y) ((__typeof__(x))((y)-1)) #define round_up(x,y) (((x) | __round_mask(x,y))+1) #define round_down(x,y) ((x) & ~__round_mask(x,y)) (Yeah, it uses 'x' twice, but the second one is for 'typeof', which doesn't actually cause the value to be evaluated, so it's ok). Now those 'round_xyz()' operations will always return a value of a type that is the same as the type of 'x' except it's gone through the normal C integer promotion rules (ie if 'x' is a smaller type than 'int', then it will be promoted to 'int'). Not very well tested, but it _looks_ correct, and uses Peter's trick, and willlet the compiler notice that round_up(x,y)-1 is the same thing as x | (y-1) which it _could_ have perhaps figured out before, but now it's way more obvious. Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/