From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031372AbXDZRqh (ORCPT ); Thu, 26 Apr 2007 13:46:37 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1031380AbXDZRqh (ORCPT ); Thu, 26 Apr 2007 13:46:37 -0400 Received: from brick.kernel.dk ([80.160.20.94]:5412 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031378AbXDZRqg (ORCPT ); Thu, 26 Apr 2007 13:46:36 -0400 Date: Thu, 26 Apr 2007 19:42:54 +0200 From: Jens Axboe To: Nick Piggin Cc: David Chinner , Christoph Lameter , "Eric W. Biederman" , linux-kernel@vger.kernel.org, Mel Gorman , William Lee Irwin III , Badari Pulavarty , Maxim Levitsky Subject: Re: [00/17] Large Blocksize Support V3 Message-ID: <20070426174254.GD2017@kernel.dk> References: <463048FE.5000600@yahoo.com.au> <46304D50.1040706@yahoo.com.au> <46305327.2000206@yahoo.com.au> <4630593C.8070905@yahoo.com.au> <20070426092014.GT65285596@melbourne.sgi.com> <4630C326.2030906@yahoo.com.au> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4630C326.2030906@yahoo.com.au> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 27 2007, Nick Piggin wrote: > Why do we limit drivers to 128 sg entries? No particular reason, except than to avoid 2^bigger order allocations. 2MiB requests would require 3 contig pages to setup the sg list, which is (probably) a little troublesome especially since it's sometimes atomically allocated. Larger pages are by no means a prerequisite to getting larger requests, assuming your hardware can handle the bigger sglist. There are other ways of doing that, I've contemplated doing chained sglists and adding sg_for_each_segment() macros for iterating these things. Drivers that want larger sglists would then be required to update their sg mapping loop to use the provided macros. It wouldn't be too hard. -- Jens Axboe