From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757937AbXD1ATb (ORCPT ); Fri, 27 Apr 2007 20:19:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757952AbXD1ATb (ORCPT ); Fri, 27 Apr 2007 20:19:31 -0400 Received: from smtp1.linux-foundation.org ([65.172.181.25]:52275 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757937AbXD1ATa (ORCPT ); Fri, 27 Apr 2007 20:19:30 -0400 Date: Fri, 27 Apr 2007 17:18:57 -0700 (PDT) From: Linus Torvalds To: "Rafael J. Wysocki" cc: Nigel Cunningham , Pekka J Enberg , LKML Subject: Re: Back to the future. In-Reply-To: Message-ID: References: <1177567481.5025.211.camel@nigel.suspend2.net> <200704280041.17617.rjw@sisk.pl> <200704280145.26253.rjw@sisk.pl> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 27 Apr 2007, Linus Torvalds wrote: > > The "let's stop all kernel threads" is superstition. It's the same kind of > superstition that made people write "sync" three times before turning off > the power in the olden times. It's the kind of superstition that comes > from "we don't do things right, so let's be vewy vewy quiet and _pray_ > that it works when we are beign quiet". Side note: while I think things should probably *work* even with user processes going full bore while a snapshot it taken, I'll freely admit that I'll follow that superstition far enough that I think it's probably a good idea to try to quiesce the system to _some_ degree, and that stopping user programs is a good idea. Partly because the whole memory shrinking thing, and partly just because we should do the snapshot with hw IO queues empty. But I don't think it would necessarily be wrong (and in many ways it would probably be *right*) to do that IO queue stopping at the queue level rather than at a process level. Why stop processes just becasue you want to clean out IO queues? They are two totally different things! Linus