Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 18 Apr 2002 19:16:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 18 Apr 2002 19:16:21 -0400 Received: from gear.torque.net ([204.138.244.1]:59652 "EHLO gear.torque.net") by vger.kernel.org with ESMTP id ; Thu, 18 Apr 2002 19:16:20 -0400 Message-ID: <3CBF52AF.38B7DC49@torque.net> Date: Thu, 18 Apr 2002 19:11:43 -0400 From: Douglas Gilbert X-Mailer: Mozilla 4.78 [en] (X11; U; Linux 2.5.8-dj1 i686) X-Accept-Language: en MIME-Version: 1.0 To: Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: Bio pool & scsi scatter gather pool usage Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton wrote: > Right now, BIO_MAX_SECTORS is only 64k, and IDE can > take twice that. I'm not sure what the largest > request size is for SCSI - certainly 128k. Scatter gather lists in the scsi subsystem have a max length of 255. The actual maximum size is dictated by the HBA driver (sg_tablesize). The HBA driver can further throttle the size of a single transfer with max_sectors. Experiments with raw IO (both in 2.4 and 2.5) indicate that pages are not contiguous when the scatter gather list is built. On i386 this limits the maximum transfer size of a single scsi command to just less than 1 MB. Doug Gilbert - 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/