linux-kernel - Re: Hibernation Redesign

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Message-Id: <200707111227.52609.rjw@sisk.pl>
Date:	Wed, 11 Jul 2007 12:27:51 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Al Boldi <a1426z@...ab.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Jeremy Maitin-Shepard <jbms@....edu>,
	Pavel Machek <pavel@....cz>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Hibernation Redesign

On Wednesday, 11 July 2007 06:11, Al Boldi wrote:
> Jeremy Fitzhardinge wrote:
> > Jeremy Maitin-Shepard wrote:
> > >   In
> > > addition, I recall that the Linux boot procedure on x86 and on some
> > > other platforms necessarily uses certain low-address memory, like the
> > > first 640K, which must be backed up regardless.
> >
> > Well, the traditional framebuffer/ISA space between 640k and 1M probably
> > needs to be identity mapped, but I don't think there's anything in there
> > which specifically needs to be save/restored (except framebuffer
> > contents, maybe?).
> >
> > > For these reasons, it seems that it would be easiest to simply backup
> > > the first e.g. 16 or 64 MB of memory, and not have to worry about
> > > loading the kernel at a non-standard address and specifying a
> > > complicated exact memmap.  Someone might prove me wrong, though.
> >
> > Yes, I suppose.  You're certain the old kernel's devices are completely
> > quiescent at that point?
> 
> That's exactly the problem; trying to save a state from within the kernel 
> would probably necessitate a freezer hack, which we are trying so dearly to 
> avoid.

Well, I don't think that avoiding the freezer whatever it takes would be a good
idea.  There needs to be some balance. ;-)

> The only way the kexec approach may be successful, is by completely relying 
> on the kexec'd hibernate-mode kernel to save state, otherwise we would be 
> back to square one.  And if that required a special boot procedure for the 
> kexec'd hibernate-mode kernel, then why not?

Because such things are very difficult for many users.  My experience with
the userland suspend shows that clearly.

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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