From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with ESMTP id 565636B004D for ; Thu, 30 Jul 2009 18:43:07 -0400 (EDT) Date: Fri, 31 Jul 2009 00:43:08 +0200 From: Jens Axboe Subject: Re: Bug in kernel 2.6.31, Slow wb_kupdate writeout Message-ID: <20090730224308.GJ12579@kernel.dk> References: <1786ab030907281211x6e432ba6ha6afe9de73f24e0c@mail.gmail.com> <20090730213956.GH12579@kernel.dk> <33307c790907301501v4c605ea8oe57762b21d414445@mail.gmail.com> <20090730221727.GI12579@kernel.dk> <33307c790907301534v64c08f59o66fbdfbd3174ff5f@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <33307c790907301534v64c08f59o66fbdfbd3174ff5f@mail.gmail.com> Sender: owner-linux-mm@kvack.org To: Martin Bligh Cc: Chad Talbott , linux-kernel@vger.kernel.org, linux-mm@kvack.org, wfg@mail.ustc.edu.cn, Michael Rubin , Andrew Morton , sandeen@redhat.com List-ID: On Thu, Jul 30 2009, Martin Bligh wrote: > > The test case above on a 4G machine is only generating 1G of dirty data. > > I ran the same test case on the 16G, resulting in only background > > writeout. The relevant bit here being that the background writeout > > finished quickly, writing at disk speed. > > > > I re-ran the same test, but using 300 100MB files instead. While the > > dd's are running, we are going at ~80MB/sec (this is disk speed, it's an > > x25-m). When the dd's are done, it continues doing 80MB/sec for 10 > > seconds or so. Then the remainder (about 2G) is written in bursts at > > disk speeds, but with some time in between. > > OK, I think the test case is sensitive to how many files you have - if > we punt them to the back of the list, and yet we still have 299 other > ones, it may well be able to keep the disk spinning despite the bug > I outlined.Try using 30 1GB files? If this disk starts spinning, then we have bigger bugs :-) > > Though it doesn't seem to happen with just one dd streamer, and > I don't see why the bug doesn't trigger in that case either. > > I believe the bugfix is correct independent of any bdi changes? Yeah I think so too, I'll run some more tests on this tomorrow and verify it there as well. -- Jens Axboe -- 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