linux-kernel - Re: freeze vs freezer

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Date:	Thu, 26 Jun 2008 17:09:10 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	Elias Oltmanns <eo@...ensachen.de>
Cc:	Henrique de Moraes Holschuh <hmh@....eng.br>,
	Kyle Moffett <mrmacman_g4@....com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	David Chinner <dgc@....com>,
	Jeremy Fitzhardinge <jeremy@...p.org>, xfs-masters@....sgi.com,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: freeze vs freezer

Hi!

> >> Patch would be welcome, actually. It turns out blocking new
> >> IO-requests is not completely trivial.
> 
> Quite. But I'm not sure I see what this is all about yet. From the IDE
> and SCSI subsystems I remember that they block all I/O from higher levels
> once the suspend callbacks have been executed. I haven't made an effort
> to understand the freezer (or indeed anything related to hibernation)
> yet since I don't even use hibernation myself (only s2ram). Do you have

s2ram also uses freezer these days. Difference is s2ram does not
really need it.

> any suggestion where to start reading up on things so I can get an idea
> what the issues are and what you would like IDE / SCSI / ... to do?

I'd like block layer to block any process that tries to do I/O.

> > Is this the same thing the per-device IO-queue-freeze patches for
> >HDAPS also
> > need to do?  If so, you may want to talk to Elias Oltmanns
> > <eo@...ensachen.de> about it.  Added to CC.
> 
> Thanks for the heads up Henrique. Even though these issues seem to be
> related up to a certain degree, there probably are some important
> differences. When suspending a system, the emphasis is on leaving the
> system in a consistent state (think of journalled file systems), whereas
> disk shock protection is mainly concerned with stopping I/O as soon as
> possible. As yet, I cannot possibly say to what extend these two
> concepts can be reconciled in the sense of sharing some common code.

Actually, I believe requirements are same.

'don't do i/o in dangerous period'.

swsusp will just do sync() before entering dangerous period. That
provides consistent-enough state...
							Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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