From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: with ECARTIS (v1.0.0; list xfs); Thu, 26 Oct 2006 01:58:10 -0700 (PDT) Received: from larry.melbourne.sgi.com (larry.melbourne.sgi.com [134.14.52.130]) by oss.sgi.com (8.12.10/8.12.10/SuSE Linux 0.7) with SMTP id k9Q8vuaG013770 for ; Thu, 26 Oct 2006 01:57:58 -0700 Date: Thu, 26 Oct 2006 18:57:00 +1000 From: David Chinner Subject: Re: [PATCH] Freeze bdevs when freezing processes. Message-ID: <20061026085700.GI8394166@melbourne.sgi.com> References: <1161576735.3466.7.camel@nigel.suspend2.net> <200610251432.41958.rjw@sisk.pl> <1161782620.3638.0.camel@nigel.suspend2.net> <200610252105.56862.rjw@sisk.pl> <20061026073022.GG8394166@melbourne.sgi.com> <1161850709.17293.23.camel@nigel.suspend2.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1161850709.17293.23.camel@nigel.suspend2.net> Sender: xfs-bounce@oss.sgi.com Errors-to: xfs-bounce@oss.sgi.com List-Id: xfs To: Nigel Cunningham Cc: David Chinner , "Rafael J. Wysocki" , Pavel Machek , Andrew Morton , LKML , xfs@oss.sgi.com 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). Cheers, Dave. -- Dave Chinner Principal Engineer SGI Australian Software Group