From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f171.google.com (mail-ig0-f171.google.com [209.85.213.171]) by kanga.kvack.org (Postfix) with ESMTP id C044C6B0031 for ; Tue, 8 Jul 2014 16:45:14 -0400 (EDT) Received: by mail-ig0-f171.google.com with SMTP id l13so738948iga.10 for ; Tue, 08 Jul 2014 13:45:14 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id ro7si2991891igb.54.2014.07.08.13.45.13 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 08 Jul 2014 13:45:13 -0700 (PDT) Date: Tue, 8 Jul 2014 13:45:11 -0700 From: Andrew Morton Subject: Re: [PATCH] mm: Don't forget to set softdirty on file mapped fault Message-Id: <20140708134511.4a32b7400a952541a31e9078@linux-foundation.org> In-Reply-To: <20140708204017.GG17860@moon.sw.swsoft.com> References: <20140708192151.GD17860@moon.sw.swsoft.com> <20140708131920.2a857d573e8cc89780c9fa1c@linux-foundation.org> <20140708204017.GG17860@moon.sw.swsoft.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Cyrill Gorcunov Cc: LKML , Linux MM , Pavel Emelyanov On Wed, 9 Jul 2014 00:40:17 +0400 Cyrill Gorcunov wrote: > On Tue, Jul 08, 2014 at 01:19:20PM -0700, Andrew Morton wrote: > > On Tue, 8 Jul 2014 23:21:51 +0400 Cyrill Gorcunov wrote: > > > > > Otherwise we may not notice that pte was softdirty because pte_mksoft_dirty > > > helper _returns_ new pte but not modifies argument. > > > > When fixing a bug, please describe the end-user visible effects of that > > bug. > > > > [for the 12,000th time :(] > > "we may not notice that pte was softdirty" I thought it's enough, because > that's the effect user sees -- pte is not dirtified where it should. > > Really sorry Andrew if I were not clear enough. What about: In case if page > fault happend on dirty filemapping the newly created pte may not > notice if old one were already softdirtified because pte_mksoft_dirty > doesn't modify its argument but rather returns new pte value. The user doesn't know or care about pte bits. What actually *happens*? Does criu migration hang? Does it lose data? Does it take longer? IOW, what would an end-user's bug report look like? It's important to think this way because a year from now some person we've never heard of may be looking at a user's bug report and wondering whether backporting this patch will fix it. Amongst other reasons. -- 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