From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261960AbTFOGxP (ORCPT ); Sun, 15 Jun 2003 02:53:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261968AbTFOGxP (ORCPT ); Sun, 15 Jun 2003 02:53:15 -0400 Received: from dp.samba.org ([66.70.73.150]:63118 "EHLO lists.samba.org") by vger.kernel.org with ESMTP id S261960AbTFOGxN (ORCPT ); Sun, 15 Jun 2003 02:53:13 -0400 Date: Sun, 15 Jun 2003 17:06:11 +1000 From: Anton Blanchard To: "David S. Miller" Cc: davidm@hpl.hp.com, davidm@napali.hpl.hp.com, manfred@colorfullife.com, axboe@suse.de, linux-kernel@vger.kernel.org Subject: Re: problem with blk_queue_bounce_limit() Message-ID: <20030615070611.GE31148@krispykreme> References: <200306062013.h56KDcLe026713@napali.hpl.hp.com> <20030606.234401.104035537.davem@redhat.com> <16097.36514.763047.738847@napali.hpl.hp.com> <20030607.001140.08328499.davem@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20030607.001140.08328499.davem@redhat.com> User-Agent: Mutt/1.5.4i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org > But you're creating a new mapping for the old buffer. What if you had > a DMA API implementation which consolidates multiple mapping attempts > of the same buffer into a single mapping entry (along with a reference > count)? That would break the workaround. > > I hope nobody is doing this, it would probably break other things > we haven't considered yet. Dave, we talked about this ages ago as a possible alternative to skb recycling and persistent IOMMU mappings for those skbs. Unfortunately you need a hash to map from all of memory to a pci bus address for each host bridge (well IOMMU), and so far I cant think of anything that wouldnt chew gobs of RAM. Anton