Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754377AbaGHUyw (ORCPT ); Tue, 8 Jul 2014 16:54:52 -0400 Received: from mail-la0-f43.google.com ([209.85.215.43]:63379 "EHLO mail-la0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752912AbaGHUyv (ORCPT ); Tue, 8 Jul 2014 16:54:51 -0400 Date: Wed, 9 Jul 2014 00:54:48 +0400 From: Cyrill Gorcunov To: Andrew Morton Cc: LKML , Linux MM , Pavel Emelyanov 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> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/