From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759126Ab1LOQXA (ORCPT ); Thu, 15 Dec 2011 11:23:00 -0500 Received: from www.linutronix.de ([62.245.132.108]:37477 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759052Ab1LOQW7 (ORCPT ); Thu, 15 Dec 2011 11:22:59 -0500 Message-ID: <4EEA1EDD.9000609@linutronix.de> Date: Thu, 15 Dec 2011 17:22:53 +0100 From: Sebastian Andrzej Siewior User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.24) Gecko/20111114 Icedove/3.1.16 MIME-Version: 1.0 To: Alan Stern CC: Clemens Ladisch , Greg Kroah-Hartman , Sarah Sharp , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] usb: fix number of mapped SG DMA entries References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/15/2011 05:01 PM, Alan Stern wrote: >> Is there anything special you do to get into this kind of situation? >> Like 16GiB of memory on 32bit with highmem and a brutal disk/io test >> case so? > > As I understand it, the typical case is that two SG entries in a row > refer to adjacent pages of physical memory. The mapping routine then > collapses them into a single entry referring to all the pages. > > However, this is not the sort of thing you can deliberately cause, > unless you set up your SG list by hand. Thanks, both of you for the explanation. > > Alan Stern Sebastian