From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id B93A86B004F for ; Tue, 28 Jul 2009 15:11:35 -0400 (EDT) Received: from spaceape10.eur.corp.google.com (spaceape10.eur.corp.google.com [172.28.16.144]) by smtp-out.google.com with ESMTP id n6SJBZqM019319 for ; Tue, 28 Jul 2009 20:11:36 +0100 Received: from wf-out-1314.google.com (wfg24.prod.google.com [10.142.7.24]) by spaceape10.eur.corp.google.com with ESMTP id n6SJBIAF029889 for ; Tue, 28 Jul 2009 12:11:33 -0700 Received: by wf-out-1314.google.com with SMTP id 24so70539wfg.7 for ; Tue, 28 Jul 2009 12:11:32 -0700 (PDT) MIME-Version: 1.0 Date: Tue, 28 Jul 2009 12:11:31 -0700 Message-ID: <1786ab030907281211x6e432ba6ha6afe9de73f24e0c@mail.gmail.com> Subject: Bug in kernel 2.6.31, Slow wb_kupdate writeout From: Chad Talbott Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, wfg@mail.ustc.edu.cn, Martin Bligh , Michael Rubin , Andrew Morton , sandeen@redhat.com List-ID: I run a simple workload on a 4GB machine which dirties a few largish inodes like so: # seq 10 | xargs -P0 -n1 -i\{} dd if=/dev/zero of=/tmp/dump\{} bs=1024k count=100 While the dds are running data is written out at disk speed. However, once the dds have run to completion and exited there is ~500MB of dirty memory left. Background writeout then takes about 3 more minutes to clean memory at only ~3.3MB/s. When I explicitly sync, I can see that the disk is capable of 40MB/s, which finishes off the files in ~10s. [1] An interesting recent-ish change is "writeback: speed up writeback of big dirty files." When I revert the change to __sync_single_inode the problem appears to go away and background writeout proceeds at disk speed. Interestingly, that code is in the git commit [2], but not in the post to LKML. [3] This is may not be the fix, but it makes this test behave better. Thanks, Chad [1] I've plotted the dirty memory from /proc/meminfo and disk write speed from iostat at http://sites.google.com/site/cwtlinux/2-6-31-writeback-bug [2] git commit: http://mirror.celinuxforum.org/gitstat/commit-detail.php?commit=8bc3be2751b4f74ab90a446da1912fd8204d53f7 [3] LKML post: http://marc.info/?l=linux-kernel&m=119131601130372&w=2 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org