Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030426AbWLaSk5 (ORCPT ); Sun, 31 Dec 2006 13:40:57 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030432AbWLaSk5 (ORCPT ); Sun, 31 Dec 2006 13:40:57 -0500 Received: from smtp.ocgnet.org ([64.20.243.3]:54799 "EHLO smtp.ocgnet.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030426AbWLaSk4 (ORCPT ); Sun, 31 Dec 2006 13:40:56 -0500 Date: Mon, 1 Jan 2007 03:39:49 +0900 From: Paul Mundt To: "Robert P. J. Day" Cc: Arjan van de Ven , Denis Vlasenko , Linux kernel mailing list Subject: Re: replace "memset(...,0,PAGE_SIZE)" calls with "clear_page()"? Message-ID: <20061231183949.GA8323@linux-sh.org> Mail-Followup-To: Paul Mundt , "Robert P. J. Day" , Arjan van de Ven , Denis Vlasenko , Linux kernel mailing list References: <200612302149.35752.vda.linux@googlemail.com> <1167518748.20929.578.camel@laptopd505.fenrus.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1687 Lines: 35 On Sat, Dec 30, 2006 at 06:04:14PM -0500, Robert P. J. Day wrote: > fair enough. *technically*, not every call of the form > "memset(ptr,0,PAGE_SIZE)" necessarily represents an address that's on > a page boundary. but, *realistically*, i'm guessing most of them do. > just grabbing a random example from some grep output: > > arch/sh/mm/init.c: > ... > /* clear the zero-page */ > memset(empty_zero_page, 0, PAGE_SIZE); > ... > The problem with random grepping is that it doesn't give you any context. clear_page() isn't available in this case since we have a couple of different ways of implementing it, and the optimal approach is selected later on. There are also additional assumptions regarding alignment that don't allow clear_page() to be used directly as replacement for the memset() callsites (as has already been pointed out for some of the other architectures). While the empty_zero_page in this case sits on a full page boundary, others do not. You might find some places in drivers that do this where you might be able to optimize things slightly with a clear_page() (or copy_page() in the memcpy() case), but it's going to need a lot of manual auditing rather than a find and replace. Any sort of wins you get out of this would be marginal at best, anyways. The more interesting case would be page clustering/bulk page clearing with offload engines, and there's certainly room to build on the SGI patches for this. - 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/