From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ee0-f48.google.com (mail-ee0-f48.google.com [74.125.83.48]) by kanga.kvack.org (Postfix) with ESMTP id 1C74F6B0035 for ; Wed, 30 Apr 2014 17:24:04 -0400 (EDT) Received: by mail-ee0-f48.google.com with SMTP id e49so632729eek.35 for ; Wed, 30 Apr 2014 14:24:03 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTP id 43si32153223eei.145.2014.04.30.14.24.01 for ; Wed, 30 Apr 2014 14:24:02 -0700 (PDT) Message-ID: <53616957.1020309@redhat.com> Date: Wed, 30 Apr 2014 17:21:27 -0400 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH v5] mm,writeback: fix divide by zero in pos_ratio_polynom References: <20140429151910.53f740ef@annuminas.surriel.com> <5360C9E7.6010701@jp.fujitsu.com> <20140430093035.7e7226f2@annuminas.surriel.com> <20140430134826.GH4357@dhcp22.suse.cz> <20140430104114.4bdc588e@cuia.bos.redhat.com> <20140430120001.b4b95061ac7252a976b8a179@linux-foundation.org> <53614F3C.8020009@redhat.com> <20140430123526.bc6a229c1ea4addad1fb483d@linux-foundation.org> <20140430160218.442863e0@cuia.bos.redhat.com> <20140430131353.fa9f49604ea39425bc93c24a@linux-foundation.org> <20140430164255.7a753a8e@cuia.bos.redhat.com> <20140430140057.7d2a6e984b2ec987182d2a4e@linux-foundation.org> In-Reply-To: <20140430140057.7d2a6e984b2ec987182d2a4e@linux-foundation.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Michal Hocko , Masayoshi Mizuma , linux-kernel@vger.kernel.org, linux-mm@kvack.org, sandeen@redhat.com, jweiner@redhat.com, kosaki.motohiro@jp.fujitsu.com, fengguang.wu@intel.com, mpatlasov@parallels.com, Motohiro.Kosaki@us.fujitsu.com On 04/30/2014 05:00 PM, Andrew Morton wrote: > On Wed, 30 Apr 2014 16:42:55 -0400 Rik van Riel wrote: > >> On Wed, 30 Apr 2014 13:13:53 -0700 >> Andrew Morton wrote: >> >>> This was a consequence of 64->32 truncation and it can't happen any >>> more, can it? >> >> Andrew, this is cleaner indeed :) > > I'm starting to get worried about 32-bit wraparound in the patch > version number ;) > >> Masayoshi-san, does the bug still happen with this version, or does >> this fix the problem? >> > > We could put something like > > if (WARN_ON_ONCE(setpoint == limit)) > setpoint--; > > in there if we're not sure. But it's better to be sure! The more I look at the code, the more I am convinced that Michal is right, and we cannot actually hit the case that "limit - setpoint + 1 == 0". Setpoint always seems to be some in-between point. -- 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