From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932297Ab2AIQUy (ORCPT ); Mon, 9 Jan 2012 11:20:54 -0500 Received: from nm25-vm4.bullet.mail.ne1.yahoo.com ([98.138.91.185]:22177 "HELO nm25-vm4.bullet.mail.ne1.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S932211Ab2AIQUw convert rfc822-to-8bit (ORCPT ); Mon, 9 Jan 2012 11:20:52 -0500 X-Yahoo-Newman-Property: ymail-3 X-Yahoo-Newman-Id: 129682.8545.bm@omp1036.mail.ne1.yahoo.com DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=X-YMail-OSG:Received:X-Mailer:References:Message-ID:Date:From:Reply-To:Subject:To:Cc:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding; b=wjE/Nj/ACs0UNzYuRYYlSMkKREnKeeBohJjvXSazwNc1B7em53iejvos0C2o60kBsMjuRM1/hQFQSR7BfTX1mPKUOTli+gea28qK3IlFrQASQ+g+5zMK7+V7LwydAKTnkssXv799zN79ZSFctoXQmRobw0rQw0QYcqc6/g9PnJE=; X-YMail-OSG: QWpjxgoVM1mHHaIQgJroLs0yiizD4Jl8Tl7ORrtg3l84xUL ql15QNr8_Giee2nvg_keZc9Rar8fUFirS.9CSFdar0LC0N0vWxLWGLd.JSUA QXMyps0KgL2dMqJrm18yUSZGAGRtgK5aflLVmiQfD1LZyeIf7H_vnNE8Jali UBzoQVcmUAzok9ikmBY_CarNQUUWQFFUgp3QzQL8SNfkip1N7OSolcW6KT1u x2nVqDT9wNUsLV0mZQWzsTlAyhCyP4aSk4FG0s8mSG67_7ntKUuRPbD8UZg0 8Iy2UVFsVKAvkWNulo9InKLtQDz1cTHbl19xICBC7qPuIkeq4ilcZ4i5QW8u kl0ZiJ_IjjJeQEyyV4TxEoPbhEf4Mc6PGytiuOT8AqU5ufNikAVfPTQU4Jcn s_wLlAMrRF0QdAMblBjO4iuJAEADS42kjcRHNnWy70Hrigyp23BTriOSPazl qkJ1xdCkClKA9US.JoVvbPw-- X-Mailer: YahooMailWebService/0.8.115.331698 References: <1325993012.29526.YahooMailNeo@web38004.mail.mud.yahoo.com> <20120109151707.GB22175@thunk.org> <1326123988.9602.YahooMailNeo@web38004.mail.mud.yahoo.com> <20120109155016.GD22175@thunk.org> Message-ID: <1326126051.97658.YahooMailNeo@web38008.mail.mud.yahoo.com> Date: Mon, 9 Jan 2012 08:20:51 -0800 (PST) From: Shantanu Goel Reply-To: Shantanu Goel Subject: Re: [PATCH] ext4: Fix up range_end offset in range cyclic writeback To: "Ted Ts'o" Cc: Kernel In-Reply-To: <20120109155016.GD22175@thunk.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > So this was a performance issue that led you to this investigation? > How much of a performance issue are we talking about? It's a performance issue in the sense that background flush of the file can take much longer (we observed > 5 mins in some instances) than the 30 second kupdate interval. > If it's a correctness issue that might lead to data loss because > fsync() wasn't doing its jobs, that's obviously higher priority than a > performance issue. fsync() is not affected and works correctly with or without the patch since it does not use the range_cyclic writeback mode, AFAICT.  The only "correctness" issue would be if an application relies on kupdate which uses range_cyclic writeback to periodically flush the file as governed by the /proc/sys/vm/dirty_writeback_centisecs tunable.  We have some applications which lost more data than they expected due to the writeback not happening at expected intervals.  One could argue the bug is in the application since it could have guaranteed the file was flushed by using fsync hence my quotes around correctness.  Unfortunately, modifying the application is not an easy option for us to pursue at this time.  We just wish to have the patch merged upstream and the exact timing is not that critical. > Again, I just wanted to characterize this correctly in the commit --- > BTW, this is good stuff to include in the commit description so in the > future, developers trying to go through the history can understand why > a particular patch is important (perhaps to backport into an > enterprise distro release, etc.) Sure, will do in future. Thanks, Shantanu