From: Eric Sandeen Subject: Re: What represent 646345728 bytes Date: Mon, 01 Feb 2010 11:34:42 -0600 Message-ID: <4B6710B2.9020701@redhat.com> References: <7618835.18201265033304935.JavaMail.www@wsfrf1112> <871vh427qr.fsf@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: paul.chavent@fnac.net, linux-ext4@vger.kernel.org To: "Aneesh Kumar K. V" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:36950 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752760Ab0BARe6 (ORCPT ); Mon, 1 Feb 2010 12:34:58 -0500 In-Reply-To: <871vh427qr.fsf@linux.vnet.ibm.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: Aneesh Kumar K. V wrote: > On Mon, 1 Feb 2010 15:08:24 +0100 (CET), wrote: >> Hi >> >> I'am writing an application that write a stream of pictures of fixed size on a disk. >> >> My app run on a self integrated gnu/linux (based on a 2.6.31.6-rt19 kernel). >> >> My media is formated with >> >> # mke2fs -t ext4 -L DATA -O large_file,^has_journal,extent -v /dev/sda3 >> [...] >> >> And it is mounted with >> >> # mount -t ext4 /dev/sda3 /var/data/ >> EXT4-fs (sda3): no journal >> EXT4-fs (sda3): delayed allocation enabled >> EXT4-fs: file extents enabled >> EXT4-fs: mballoc enabled >> EXT4-fs (sda3): mounted filesystem without journal >> >> My app opens the file with "O_WRONLY | O_CREAT | O_TRUNC | O_SYNC | O_DIRECT" flags. >> >> Each write takes ~4.2ms for 304K (it is very good since it is the write bandwidth of my hard drive). There is a write every 100ms. >> >> But every exactly 646345728 bytes, the write takes ~46ms. > > I guess that would be balance_dirty_pages starting to writeback the > delayed allocated pages. You can try if that changes by changing > /proc/sys/vm/dirty_ratio But he's doing direct IO... -Eric