From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751956AbaKKVFB (ORCPT ); Tue, 11 Nov 2014 16:05:01 -0500 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.229]:13171 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751877AbaKKVE6 (ORCPT ); Tue, 11 Nov 2014 16:04:58 -0500 Date: Tue, 11 Nov 2014 16:04:48 -0500 From: Steven Rostedt To: Jan Kara Cc: Rik van Riel , LKML , Michal Hocko , linux-mm@kvack.org, Mel Gorman , Andrew Morton Subject: Re: [BUG] mm/page-writeback.c: divide by zero in pos_ratio_polynom not fixed Message-ID: <20141111160448.61354836@gandalf.local.home> In-Reply-To: <20141111201539.GA12333@quack.suse.cz> References: <20141101082325.7be0463f@gandalf.local.home> <20141111201539.GA12333@quack.suse.cz> X-Mailer: Claws Mail 3.10.1 (GTK+ 2.24.25; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.142:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 11 Nov 2014 21:15:39 +0100 Jan Kara wrote: > So I was looking into this but I have to say I don't understand where is > the problem. The registers clearly show that x_intercept - bdi_setpoint + 1 > == 0 (in 32-bit arithmetics). Given: > x_intercept = bdi_setpoint + span > > We have that span + 1 == 0 and that means that: > ((thresh - bdi_thresh + 8 * write_bw) * (u64)x >> 16) == -1 (again in > 32-bit arithmetics). But I don't see how that can realistically happen... > > Is this reproducible at all? > Unfortunately not. It only happened once, and I haven't been able to reproduce it again. -- Steve