From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753189AbXC0IwA (ORCPT ); Tue, 27 Mar 2007 04:52:00 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753371AbXC0IwA (ORCPT ); Tue, 27 Mar 2007 04:52:00 -0400 Received: from smtp.osdl.org ([65.172.181.24]:45368 "EHLO smtp.osdl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753189AbXC0Iv7 (ORCPT ); Tue, 27 Mar 2007 04:51:59 -0400 Date: Tue, 27 Mar 2007 00:51:50 -0800 From: Andrew Morton To: Miklos Szeredi Cc: a.p.zijlstra@chello.nl, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [patch resend v4] update ctime and mtime for mmaped write Message-Id: <20070327005150.9177ae02.akpm@linux-foundation.org> In-Reply-To: References: <20070326140036.f3352f81.akpm@linux-foundation.org> <20070326153153.817b6a82.akpm@linux-foundation.org> <20070326232214.ee92d8c4.akpm@linux-foundation.org> <20070326234957.6b287dda.akpm@linux-foundation.org> <20070327001834.04dc375e.akpm@linux-foundation.org> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.17; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 27 Mar 2007 10:28:16 +0200 Miklos Szeredi wrote: > > > But Peter Staubach says a RH custumer has files written thorugh mmap, > > > which are not being backed up. > > > > Yes, I expect the backup problem is the major real-world hurt arising from > > this bug. > > > > But I expect we could adequately plug that problem at munmap()-time. Or, > > better, do_wp_page(). As I said - half-assed. > > > > It's a question if whether the backup problem is the only thing which is hurting > > in the real-world, or if people have other problems. > > > > (In fact, what's wrong with doing it in do_wp_page()? > > It's rather more expensive, than just toggling a bit. It shouldn't be, especially for filesystems which have one-second timestamp granularity. Filesystems which have s_time_gran=1 might hurt a bit, but no more than they will with write(). Actually, no - we'd only update the mctime once per page per writeback period (30 seconds by default) so the load will be small. It'll be more often if the user is doing a lot of pte-cleaning via msync() or fsync(), but then the m/ctime writes will be the least of their problems. I'd have thought there were more substantial problems with something that crude?