From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752161AbaKKVQT (ORCPT ); Tue, 11 Nov 2014 16:16:19 -0500 Received: from cantor2.suse.de ([195.135.220.15]:51008 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751407AbaKKVQS (ORCPT ); Tue, 11 Nov 2014 16:16:18 -0500 Date: Tue, 11 Nov 2014 22:16:15 +0100 From: Jan Kara To: Steven Rostedt Cc: Jan Kara , 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: <20141111211615.GE32298@quack.suse.cz> References: <20141101082325.7be0463f@gandalf.local.home> <20141111201539.GA12333@quack.suse.cz> <20141111160448.61354836@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141111160448.61354836@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 11-11-14 16:04:48, Steven Rostedt wrote: > 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. BTW, how much memory does the machine have and what is /proc/sys/vm/dirty_ratio and /proc/sys/vm/dirty_background_ratio (or corresponding dirty_bytes, dirty_background_bytes if you are using them)? Honza -- Jan Kara SUSE Labs, CR