From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758228Ab2IEJDj (ORCPT ); Wed, 5 Sep 2012 05:03:39 -0400 Received: from mail.mev.co.uk ([62.49.15.74]:49878 "EHLO mail.mev.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750826Ab2IEJDh (ORCPT ); Wed, 5 Sep 2012 05:03:37 -0400 Message-ID: <50471558.4030505@mev.co.uk> Date: Wed, 5 Sep 2012 10:03:20 +0100 From: Ian Abbott User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120903 Thunderbird/15.0 MIME-Version: 1.0 To: Jan Kara CC: Ian Abbott , lkml , "linux-fsdevel@vger.kernel.org" Subject: Re: [PATCH v3] UDF: Add support for O_DIRECT References: <1343731212-4381-1-git-send-email-abbotti@mev.co.uk> <1346752179-28052-1-git-send-email-abbotti@mev.co.uk> <20120904143947.GC8656@quack.suse.cz> <50461A24.8070003@mev.co.uk> In-Reply-To: <50461A24.8070003@mev.co.uk> Content-Type: text/plain; charset="us-ascii"; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2012-09-04 16:11, Ian Abbott wrote: > On 2012-09-04 15:39, Jan Kara wrote: >> On Tue 04-09-12 10:49:39, Ian Abbott wrote: >>> Add support for the O_DIRECT flag. There are two cases to deal with: >> Out of curiosity, do you have a use for this feature or is it mostly >> academic interest? > > I'm planning to use it for an embedded project that needs to stream > large files off a CompactFlash card, but the data doesn't need to be in > the buffer cache as its only read once, and the system has very limited > memory bandwidth so I can't afford the the extra copy. The old version > of this project only supported FAT, but that limited the file size to > about 4GiB. The filesystem needs to be something reasonably > Windows-friendly, at least for adding the files to the CompactFlash card > in the first place. Actually, remembering back (the old project was about 3 years ago), the main reason for using O_DIRECT was it was causing too much memory fragmentation on my MMU-less embedded system. That and the extra overhead of managing the buffer cache for data that was only read once. -- -=( Ian Abbott @ MEV Ltd. E-mail: )=- -=( Tel: +44 (0)161 477 1898 FAX: +44 (0)161 718 3587 )=-