linux-kernel - Re: Hibernation considerations

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Date:	Mon, 16 Jul 2007 21:37:15 -0700 (PDT)
From:	david@...g.hm
To:	Al Boldi <a1426z@...ab.com>
cc:	Alan Stern <stern@...land.harvard.edu>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Huang, Ying" <ying.huang@...el.com>,
	Jeremy Maitin-Shepard <jbms@....edu>,
	Kyle Moffett <mrmacman_g4@....com>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pavel Machek <pavel@....cz>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: Hibernation considerations

On Mon, 16 Jul 2007, Al Boldi wrote:

> Alan Stern wrote:
>> On Mon, 16 Jul 2007, Al Boldi wrote:
>>> From a kexec'd hibernation kernel pov, both S3 and S4 look conceptually
>>> exactly the same.  The only difference is, in S3 the memory is in memory
>>> and in S4 the memory is on storage.  All device handling is exactly the
>>> same, so if there is a problem with device handling between the kexec'd
>>> hibernation kernel and the normal kernel, then that would have made
>>> itself visible.
>>
>> You have contradicted yourself.  "In S3 the memory is in memory and in
>> S4 the memory is on storage".  How does the memory get onto storage?
>> The kexec'd hibernation kernel writes it there.  To do so it accesses a
>> storage device.
>>
>> Consequently the device handling _cannot_ be exactly the same in S3 and
>> S4.
>
> Ok, you should have read this in the context of suspending/resuming from/to
> the normal kernel, and in that case they are exactly the same, i.e. kexec -e
> for suspend and kexec -j for resume.
>
> BTW, it would be really helpful if people would actually try the kexec
> hibernation patches, as this may yield a much more constructive discussion.

I would love to, but so far I don't see the nessasary pieces

once I kexec to the new kernel, how can it find out what pages of memory 
(and swap) need to be saved?

If i knew that then I could write a trivial perl program to save those 
pages with the appropriate headers to make a suspend file.

however, I'm now being told that that suspend file won't work if the 
machine is actually powered off, so there's a need to something more for 
the wake-up side of things as well.

David Lang
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