From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id 868596B004D for ; Thu, 30 Jul 2009 18:34:18 -0400 (EDT) Received: from spaceape12.eur.corp.google.com (spaceape12.eur.corp.google.com [172.28.16.146]) by smtp-out.google.com with ESMTP id n6UMYFxn022891 for ; Thu, 30 Jul 2009 23:34:16 +0100 Received: from wf-out-1314.google.com (wff28.prod.google.com [10.142.6.28]) by spaceape12.eur.corp.google.com with ESMTP id n6UMYDC8019467 for ; Thu, 30 Jul 2009 15:34:13 -0700 Received: by wf-out-1314.google.com with SMTP id 28so481414wff.12 for ; Thu, 30 Jul 2009 15:34:12 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20090730221727.GI12579@kernel.dk> References: <1786ab030907281211x6e432ba6ha6afe9de73f24e0c@mail.gmail.com> <20090730213956.GH12579@kernel.dk> <33307c790907301501v4c605ea8oe57762b21d414445@mail.gmail.com> <20090730221727.GI12579@kernel.dk> Date: Thu, 30 Jul 2009 15:34:12 -0700 Message-ID: <33307c790907301534v64c08f59o66fbdfbd3174ff5f@mail.gmail.com> Subject: Re: Bug in kernel 2.6.31, Slow wb_kupdate writeout From: Martin Bligh Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Jens Axboe 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: > 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? 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? M. -- 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