From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-la0-f47.google.com (mail-la0-f47.google.com [209.85.215.47]) by kanga.kvack.org (Postfix) with ESMTP id 653EC6B0037 for ; Tue, 8 Jul 2014 16:54:51 -0400 (EDT) Received: by mail-la0-f47.google.com with SMTP id s18so4339936lam.20 for ; Tue, 08 Jul 2014 13:54:50 -0700 (PDT) Received: from mail-lb0-x230.google.com (mail-lb0-x230.google.com [2a00:1450:4010:c04::230]) by mx.google.com with ESMTPS id kv5si13240827lbc.54.2014.07.08.13.54.49 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 08 Jul 2014 13:54:50 -0700 (PDT) Received: by mail-lb0-f176.google.com with SMTP id w7so4384592lbi.35 for ; Tue, 08 Jul 2014 13:54:49 -0700 (PDT) Date: Wed, 9 Jul 2014 00:54:48 +0400 From: Cyrill Gorcunov Subject: Re: [PATCH] mm: Don't forget to set softdirty on file mapped fault Message-ID: <20140708205448.GH17860@moon.sw.swsoft.com> References: <20140708192151.GD17860@moon.sw.swsoft.com> <20140708131920.2a857d573e8cc89780c9fa1c@linux-foundation.org> <20140708204017.GG17860@moon.sw.swsoft.com> <20140708134511.4a32b7400a952541a31e9078@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140708134511.4a32b7400a952541a31e9078@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: LKML , Linux MM , Pavel Emelyanov On Tue, Jul 08, 2014 at 01:45:11PM -0700, Andrew Morton wrote: > > 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? Ah, I see. Yes, the softdirty bit might be lost that usespace program won't see that a page was modified. So data lose is possible. > 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. Here is updated changelog, sounds better? --- In case if page fault happend on dirty filemapping the newly created pte may loose softdirty bit thus if a userspace program is tracking memory changes with help of a memory tracker (CONFIG_MEM_SOFT_DIRTY) it might miss modification of a memory page (which in worts case may lead to data inconsistency). -- 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