linux-kernel - Re: [xfs-masters] Re: freeze vs freezer

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Date:	Wed, 2 Jul 2008 07:12:26 +1000
From:	Dave Chinner <david@...morbit.com>
To:	xfs-masters@....sgi.com
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Elias Oltmanns <eo@...ensachen.de>,
	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Kyle Moffett <mrmacman_g4@....com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	David Chinner <dgc@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>
Subject: Re: [xfs-masters] Re: freeze vs freezer

On Tue, Jul 01, 2008 at 04:35:43PM +0200, Rafael J. Wysocki wrote:
> On Tuesday, 1 of July 2008, Dave Chinner wrote:
> > On Tue, Jul 01, 2008 at 12:38:41AM +0200, Rafael J. Wysocki wrote:
> > > On Tuesday, 1 of July 2008, Dave Chinner wrote:
> > > > On Mon, Jun 30, 2008 at 11:00:43PM +0200, Rafael J. Wysocki wrote:
> > > > > On Monday, 30 of June 2008, Dave Chinner wrote:
> > > > > > On Sun, Jun 29, 2008 at 11:37:31PM -0700, Jeremy Fitzhardinge wrote:
> > > > > > > Dave Chinner wrote:
> > > > > > >> On Mon, Jun 30, 2008 at 01:22:47AM +0200, Rafael J. Wysocki wrote:
> > > > > > >>> Well, it seems we can handle this on the block layer level, by temporarily
> > > > > > >>> replacing the elevator with something that will selectively prevent fs I/O
> > > > > > >>> from reaching the layers below it.
> > > > > > >>
> > > > > > >> Why? What part of freeze_bdev() doesn't work for you?
> > > > > > >
> > > > > > > Well, my original problem - which is still an issue - is that a process  
> > > > > > > writing to a frozen XFS filesystem is stuck in D state, and therefore  
> > > > > > > cannot be frozen as part of suspend.
> > > > > 
> > > > > I thought we were talking about the post-freezer situation.
> > > > > 
> > > > > > Silly me - how could I forget the three headed monkey getting in
> > > > > > the way of our happy trip to beer island?
> > > > > > 
> > > > > > Seriously, though, how is stopping I/O in the elevator is going to
> > > > > > change that?
> > > > > 
> > > > > We can do that after creating the image and before we let devices run again.
> > > > > This way we won't need to worry about the freezer.
> > > > 
> > > > You're suggesting that you let processes trying to do I/O continue
> > > > until *after* the memory image is taken?
> > > 
> > > I'm not going to let the data get to the disk.
> > 
> > Yes, but you still haven't answered the original question - What are
> > you going to do with sync I/O that leaves a process in D state
> > because you've prevented the I/O from being completed?
> 
> I don't want to intercept those processes, just allow them to block on that I/O.

So you're going to allow them to go to D state somewhere. Ok, so
what's the problem with blocking them in vfs_check_frozen(), then?

> Do all of the filesystems implement the freezing?

Most of the major ones - those that implement ->write_super_lockfs()
should work just fine.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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