From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 2 Apr 2003 04:19:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Wed, 2 Apr 2003 04:19:28 -0500 Received: from unthought.net ([212.97.129.24]:32483 "EHLO mail.unthought.net") by vger.kernel.org with ESMTP id ; Wed, 2 Apr 2003 04:19:27 -0500 Date: Wed, 2 Apr 2003 11:30:50 +0200 From: Jakob Oestergaard To: Kenny Simpson Cc: Benjamin LaHaise , linux-kernel@vger.kernel.org Subject: Re: mmap-related questions Message-ID: <20030402093049.GB17859@unthought.net> Mail-Followup-To: Jakob Oestergaard , Kenny Simpson , Benjamin LaHaise , linux-kernel@vger.kernel.org References: <20030401125020.E25225@redhat.com> <20030402031840.60077.qmail@web20005.mail.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20030402031840.60077.qmail@web20005.mail.yahoo.com> User-Agent: Mutt/1.3.28i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 01, 2003 at 07:18:40PM -0800, Kenny Simpson wrote: > --- Benjamin LaHaise wrote: > > the act of unmapping them transfers the > > dirty bit from the page > > tables into the page cache where fsync() acts on > > them. > > > Should this info be included with Mel Gorman's > excellent doc: > http://www.csn.ul.ie/~mel/projects/vm/guide/html/understand/node31.html#SECTION009411000000000000000 > Or is it there, but I missed it? > > > The > > one case this breaks down > > on is when the mmap()'d file is on NFS -- the > > reordering there can result in > > writebacks from mmap()s occuring in unexpected ways. > I sometimes wish mmap was not supported on NFS, or at > least require a special MAP_NFS flag be used. It has > caused lots of pain over the years. Could someone elaborate on this please? If my client does big_map = mmap(... some file ...) make_dirty(big_map) msync(first half of big_map) msync(second half of big_map) { crash during this } Then I am guaranteed that (unless the server crashes), the first half of big_map *will* have reached the server, but not that all of the second half has. Right? Like any local-disk backed file. Ignoring the case where the NFS *server* crashes, where could the write ordering differ, compared to local disk files ? In other words, what does Benjamin's "unexpected ways" refer to ? Thanks, -- ................................................................ : jakob@unthought.net : And I see the elder races, : :.........................: putrid forms of man : : Jakob Østergaard : See him rise and claim the earth, : : OZ9ABN : his downfall is at hand. : :.........................:............{Konkhra}...............: