From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id 747F86B003D for ; Thu, 5 Feb 2009 14:32:08 -0500 (EST) Date: Thu, 5 Feb 2009 20:31:21 +0100 From: Ingo Molnar Subject: Re: pud_bad vs pud_bad Message-ID: <20090205193121.GA31839@elte.hu> References: <498B2EBC.60700@goop.org> <20090205184355.GF5661@elte.hu> <498B35F9.601@goop.org> <20090205191017.GF20470@elte.hu> <498B3D80.1010206@goop.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <498B3D80.1010206@goop.org> Sender: owner-linux-mm@kvack.org To: Jeremy Fitzhardinge Cc: William Lee Irwin III , Linux Kernel Mailing List , Linux Memory Management List List-ID: * Jeremy Fitzhardinge wrote: > Ingo Molnar wrote: >> But the 32-bit check does the exact same thing but via a single binary >> operation: it checks whether any bits outside of those bits are zero - >> just via a simpler test that compiles to more compact code. >> >> So i'd go with the 32-bit version. (unless there are some >> sign-extension complications i'm missing - but i think we got rid of >> those already.) > > OK, fair enough. I wouldn't be surprised if gcc does that transform > anyway, but we may as well be consistent about it. i checked and it doesnt - at least 4.3.2 inserts an extra AND instruction. So the 32-bit version is really better. (beyond being more readable) Ingo -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org