linux-kernel - Re: Back to the future.

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Message-ID: <20070505114253.GA5119@ucw.cz>
Date:	Sat, 5 May 2007 11:42:54 +0000
From:	Pavel Machek <pavel@....cz>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pekka J Enberg <penberg@...helsinki.fi>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Back to the future.

Hi!

> > The "let's stop all kernel threads" is superstition. It's the same kind of 
> > superstition that made people write "sync" three times before turning off 
> > the power in the olden times. It's the kind of superstition that comes 
> > from "we don't do things right, so let's be vewy vewy quiet and _pray_ 
> > that it works when we are beign quiet".
> 
> Side note: while I think things should probably *work* even with user 
> processes going full bore while a snapshot it taken, I'll freely admit 
> that I'll follow that superstition far enough that I think it's probably a 
> good idea to try to quiesce the system to _some_ degree, and that stopping 
> user programs is a good idea. Partly because the whole memory shrinking 
> thing, and partly just because we should do the snapshot with hw IO queues 
> empty.
> 
> But I don't think it would necessarily be wrong (and in many ways it would 
> probably be *right*) to do that IO queue stopping at the queue level 
> rather than at a process level. Why stop processes just becasue you want 
> to clean out IO queues? They are two totally different things!

Actually, I'd like to stop I/O queues; if there was easy way to do
that, I'll happily switch. Notice that we'll need to stop 'I/O queues'
of the char devices, too...
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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