From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 2 Aug 2001 03:45:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 2 Aug 2001 03:44:51 -0400 Received: from penguin.e-mind.com ([195.223.140.120]:21818 "EHLO penguin.e-mind.com") by vger.kernel.org with ESMTP id ; Thu, 2 Aug 2001 03:44:35 -0400 Date: Thu, 2 Aug 2001 09:45:17 +0200 From: Andrea Arcangeli To: Jeremy Higdon Cc: linux-kernel@vger.kernel.org Subject: Re: changes to kiobuf support in 2.4.(?)4 Message-ID: <20010802094517.I29065@athlon.random> In-Reply-To: <10108012254.ZM192062@classic.engr.sgi.com> <20010802084259.H29065@athlon.random> <10108020031.ZM229058@classic.engr.sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <10108020031.ZM229058@classic.engr.sgi.com>; from jeremy@classic.engr.sgi.com on Thu, Aug 02, 2001 at 12:31:52AM -0700 X-GnuPG-Key-URL: http://e-mind.com/~andrea/aa.gnupg.asc X-PGP-Key-URL: http://e-mind.com/~andrea/aa.asc Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 02, 2001 at 12:31:52AM -0700, Jeremy Higdon wrote: > By "mmap callback", you're referring to the mmap entry in the file_operations > structure? yes. > I am doing direct I/O. I'm using the kiobuf to hold the page addresses > of the user's data buffer, but I'm calling directly into my driver > after doing the map_user_kiobuf() (I have a read/write request, a file > offset, a byte count, and a set of pages to DMA into/out of, and that > gets directly translated into a SCSI command). > > It turns out that the old kmem_cache_alloc was very lightweight, so I > could get away with doing it once per I/O request, so I would indeed > profit by going back to a light weight kiobuf, or at least an optional > allocation of the bh and blocks arrays (perhaps turn them into pointers > to arrays?). I see your problem and it's a valid point indeed. But could you actually allocate the kiobuf in the file->f_iobuf pointer? I mean: could you allocate it at open/close too? That would be the way I prefer since you would need to allocate the bh anyways later (but with a flood of alloc/free). So if you could move the kiobufs allocation out of the fast path you would get a benefit too I believe. Andrea