linux-kernel - Re: Hibernation Redesign

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Message-Id: <200707110711.26767.a1426z@gawab.com>
Date:	Wed, 11 Jul 2007 07:11:26 +0300
From:	Al Boldi <a1426z@...ab.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Jeremy Maitin-Shepard <jbms@....edu>
Cc:	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

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.

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?


Thanks!

--
Al

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