linux-kernel - Re: Back to the future.

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Message-ID: <alpine.LFD.0.98.0704271706100.9964@woody.linux-foundation.org>
Date:	Fri, 27 Apr 2007 17:18:57 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pekka J Enberg <penberg@...helsinki.fi>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Back to the future.

On Fri, 27 Apr 2007, Linus Torvalds wrote:
> 
> 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!

		Linus
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