From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Chinner Subject: Re: endless sync on bdi_sched_wait()? 2.6.33.1 Date: Thu, 1 Apr 2010 09:12:54 +1100 Message-ID: <20100331221254.GI7671@dastard> References: <201003311907.31342.nuclearcat@nuclearcat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org To: Denys Fedorysychenko Return-path: Content-Disposition: inline In-Reply-To: <201003311907.31342.nuclearcat@nuclearcat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Wed, Mar 31, 2010 at 07:07:31PM +0300, Denys Fedorysychenko wrote: > I have a proxy server with "loaded" squid. On some moment i did sync, and > expecting it to finish in reasonable time. Waited more than 30 minutes, still > "sync". Can be reproduced easily. > > Here is some stats and info: > > Linux SUPERPROXY 2.6.33.1-build-0051 #16 SMP Wed Mar 31 17:23:28 EEST 2010 > i686 GNU/Linux > > SUPERPROXY ~ # iostat -k -x -d 30 > Linux 2.6.33.1-build-0051 (SUPERPROXY) 03/31/10 _i686_ (4 CPU) > > Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz > avgqu-sz await svctm %util > sda 0.16 0.01 0.08 0.03 3.62 1.33 88.94 > 0.15 1389.89 59.15 0.66 > sdb 4.14 61.25 6.22 25.55 44.52 347.21 24.66 > 2.24 70.60 2.36 7.49 > sdc 4.37 421.28 9.95 98.31 318.27 2081.95 44.34 > 20.93 193.21 2.31 24.96 > sdd 2.34 339.90 3.97 117.47 95.48 1829.52 31.70 > 1.73 14.23 8.09 98.20 ^^^^ ^^^^^ /dev/sdd is IO bound doing small random writeback IO. A service time of 8ms implies that it is doing lots of large seeks. If you've got GBs of data to sync and that's the writeback pattern, then sync will most definitely take a long, long time. it may be that ext4 is allocating blocks far apart rather than close together (as appears to be the case for /dev/sdc), so maybe this is is related to how the filesytems are aging or how full they are... Cheers, Dave. -- Dave Chinner david@fromorbit.com