linux-kernel - Re: Hibernation Redesign

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Message-Id: <200707112246.54510.nigel@nigel.suspend2.net>
Date:	Wed, 11 Jul 2007 22:46:50 +1000
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	rjw@...k.pl, a1426z@...ab.com, jeremy@...p.org, jbms@....edu,
	pavel@....cz, nickpiggin@...oo.com.au,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: Hibernation Redesign

Hi.

On Wednesday 11 July 2007 22:24:04 Miklos Szeredi wrote:
> > No other _proper_ solutions have been proposed. Everyone who suggests 
removing 
> > the freezer also suggests implementing it all over again. It might be 
sending 
> > SIGSTOP to everything. It might be shifting the desk chairs around and 
> > creating a completely new kernel context, but they always have the same 
> > goal - stopping the existing activity, and they all come with their own 
> > issues (even if they're not obvious yet because the alternatives are 
> > currently vapourware to one extent or another).
> 
> Hey, I know precious little about drivers and power management, but I
> can clarly see, that
> 
>  a) stopping all tasks and requiring them to finish any syscall they
>  are in
> 
>  b) stopping tasks _in the driver_ that are trying to access the
>  harware during/after suspend
> 
> are completely different solutions, the later being much more fine
> grained and not having all of the mentioned problems that the former
> exhibits.

The point to freezing tasks isn't just to stop drivers doing work. It's also 
to stop userspace doing work and thereby increase reliability. The more work 
that is occuring while we're trying to write a hibernation image, the less 
reliable the hibernation will be (competing for memory and so on) and the 
slower it will be (competing for cycles etc).
 
> > IMHO, the real solution is to go back to the original issue and fix it 
> > properly. Make fuse filesystems play nicely with the existing freezer. 
I've 
> > just gone back and looked at the point where you started talking 
> > about "malicious filesystems". You talk about fuse imposing certain 
ordering 
> > in the userspace tasks being frozen. Please, say more. What ordering 
issues? 
> > Why? How can such ordering be determined programmatically?
> 
> It can't.  If you are interested, please read through that thread.  If
> something's still not clear, let's discuss it further.

You can say it "imposes certain ordering" but you can say what that ordering 
is?! How about mount order? That must be a good start.

Regards,

Nigel (off to bed now).
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