From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Thu, 26 Oct 2006 02:44:42 -0700 (PDT) Received: from cuda.sgi.com (cuda1.sgi.com [192.48.168.28]) by oss.sgi.com (8.12.10/8.12.10/SuSE Linux 0.7) with ESMTP id k9Q9iWaG025531 for ; Thu, 26 Oct 2006 02:44:33 -0700 Received: from ogre.sisk.pl (ogre.sisk.pl [217.79.144.158]) by cuda.sgi.com (Spam Firewall) with ESMTP id DE8EA4DB07A for ; Thu, 26 Oct 2006 02:43:45 -0700 (PDT) From: "Rafael J. Wysocki" Subject: Re: [PATCH] Freeze bdevs when freezing processes. Date: Thu, 26 Oct 2006 11:11:29 +0200 References: <1161576735.3466.7.camel@nigel.suspend2.net> <1161850709.17293.23.camel@nigel.suspend2.net> <20061026085700.GI8394166@melbourne.sgi.com> In-Reply-To: <20061026085700.GI8394166@melbourne.sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200610261111.30486.rjw@sisk.pl> Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: David Chinner Cc: Nigel Cunningham , Pavel Machek , Andrew Morton , LKML , xfs@oss.sgi.com Hi, On Thursday, 26 October 2006 10:57, David Chinner wrote: > Hi Nigel, > > On Thu, Oct 26, 2006 at 06:18:29PM +1000, Nigel Cunningham wrote: > > On Thu, 2006-10-26 at 17:30 +1000, David Chinner wrote: > > > We have daemons running in the background that can definitely do stuff > > > after a sync. hmm - one does try_to_freeze() after a wakeup, the > > > other does: > > > > > > if (unlikely(freezing(current))) { > > > set_bit(XBT_FORCE_SLEEP, &target->bt_flags); > > > refrigerator(); > > > } else { > > > clear_bit(XBT_FORCE_SLEEP, &target->bt_flags); > > > } > > > > > > before it goes to sleep. So that one (xfsbufd - metadata buffer flushing) > > > can definitely wake up after the sync and do work, and the other could if > > > the kernel thread freeze occurs after the sync. > > > > > > Another good question at this point - exactly how should we be putting > > > these thread to to sleep? Are both these valid methods for freezing them? > > > And should we be freezing when we wake up instead of before we go to > > > sleep? i.e. what are teh rules we are supposed to be following? > > > > As you have them at the moment, the threads seem to be freezing fine. > > The issue I've seen in the past related not to threads but to timer > > based activity. Admittedly it was 2.6.14 when I last looked at it, but > > there used to be a possibility for XFS to submit I/O from a timer when > > the threads are frozen but the bdev isn't frozen. Has that changed? > > I didn't think we've ever done that - periodic or delayed operations > are passed off to the kernel threads to execute. A stack trace > (if you still have it) would be really help here. > > Hmmm - we have a couple of per-cpu work queues as well that are > used on I/O completion and that can, in some circumstances, > trigger new transactions. If we are only flush metadata, then > I don't think that any more I/o will be issued, but I could be > wrong (maze of twisty passages). Well, I think this exactly is the problem, because worker_threads run with PF_NOFREEZE set (as I've just said in another message). Greetings, Rafael -- You never change things by fighting the existing reality. R. Buckminster Fuller