linux-kernel - Re: [PATCH] Remove process freezer from suspend to RAM pathway

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Message-Id: <200707031608.06348.nigel@nigel.suspend2.net>
Date:	Tue, 3 Jul 2007 16:08:05 +1000
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Matthew Garrett <mjg59@...f.ucam.org>,
	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org
Subject: Re: [PATCH] Remove process freezer from suspend to RAM pathway

Hi.

On Tuesday 03 July 2007 15:48:26 Benjamin Herrenschmidt wrote:
> 
> > Note, though, that this won't help at all when people use 
the "suspend-to-ram 
> > instead of powering down after writing a hibernation image" feature in 
> > (uswsusp | tuxonice). Fuse is just a broken idea in the first place, but 
> > given that it exists, we still need to find the underlying cause.
> 
> No, Fuse is not a broken idea in the first place. It's the freezer that
> is a totally broken idea. It has proven many times to be racy by design
> and cannot be made right. Ther usermode helper mess is just part of
> that, fuse is another example, etc etc ...

To some extent, I agree. I think the ideal solution would be to simply not 
schedule processes that are supposed to be frozen. But who wants to play with 
scheduler code? Not me!

> So I think Matthew is totally right. In fact, the presence of the
> freezer is the main reason why Paulus so far NACKed Johannes attempts at
> merging the PPC PM code with the generic code in kernel/power.c
> 
> We've been doing fine without it so far and intend to continue to do so.

Fuse depends on !PPC?
 
> As for suspend-to-disk, I refer you to the discussions we had in the
> past with Linus, where he explains I think quite clearly how wrong the
> current implementation of STR is :-)

I assume you mean STD. The problem there is that Linus doesn't care about STD. 
If he did, I dare say he'd think through the issues more thoroughly than he 
apparently has.
 
> Thing is, if you're going to do snapshots, you should probably not sync
> after you have "frozen" anyway.

Fully agree. But how do you stop things syncing while you're writing the image 
if you don't have a freezer or equivalent? (scheduler based, kexec.. they're 
all workarounds for this issue).

Regards,

Nigel
-- 
Nigel, Michelle and Alisdair Cunningham
5 Mitchell Street
Cobden 3266
Victoria, Australia

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