From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264178AbTGBQjL (ORCPT ); Wed, 2 Jul 2003 12:39:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264192AbTGBQjL (ORCPT ); Wed, 2 Jul 2003 12:39:11 -0400 Received: from dsl2.external.hp.com ([192.25.206.7]:37125 "EHLO dsl2.external.hp.com") by vger.kernel.org with ESMTP id S264178AbTGBQjJ (ORCPT ); Wed, 2 Jul 2003 12:39:09 -0400 Date: Wed, 2 Jul 2003 10:53:33 -0600 From: Grant Grundler To: Andi Kleen Cc: "David S. Miller" , James.Bottomley@steeleye.com, axboe@suse.de, suparna@in.ibm.com, linux-kernel@vger.kernel.org, alex_williamson@hp.com, bjorn_helgaas@hp.com Subject: Re: [RFC] block layer support for DMA IOMMU bypass mode II Message-ID: <20030702165333.GB11739@dsl2.external.hp.com> References: <1057077975.2135.54.camel@mulgrave> <20030702015701.6007ac26.ak@suse.de> <20030701.170323.59686965.davem@redhat.com> <20030702022244.030a8acc.ak@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20030702022244.030a8acc.ak@suse.de> User-Agent: Mutt/1.3.28i X-Home-Page: http://www.parisc-linux.org/ Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 02, 2003 at 02:22:44AM +0200, Andi Kleen wrote: > > What do you mean? You map only one 4K chunk, and this is used > > for all the sub-1K mappings. > > How should this work when the 1K mappings are spread all over memory? It couldn't merge in this case. > Maybe I'm missing something but from James description it sounds like the > block layer assumes that it can pass in a sglist with arbitary elements > and get it back remapped to continuous DMA addresses. In the x86-64 case, If the 1k elements are not physically contigous, I think most of them would get their own mapping. For x86-64, if an entry ends on a 4k alignment and the next one starts on a 4k alignment, could those be merged into one DMA segment that uses two adjacent mapping entries? Anyway, using a 4k FS block size (eg ext2) would be more efficient by allowing a 1:1 of SG elements and DMA mappings. grant