linux-kernel - Re: Hibernation considerations

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Date:	Sun, 15 Jul 2007 20:40:28 +0300
From:	Al Boldi <a1426z@...ab.com>
To:	jimmy bahuleyan <knight.camelot@...il.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	Alan Stern <stern@...land.harvard.edu>,
	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>, david@...g.hm
Subject: Re: Hibernation considerations

jimmy bahuleyan wrote:
> Al Boldi wrote:
> > This should be the responsibility of the kexec'd hibernating kernel. 
> > Note though in (6), the normal kernel takes care of preparing devices,
> > then the hibernating kernel dumps the image and either calls S4 or S3. 
> > On resume from S3 it can immediately switch over to the normal kernel,
> > and from S4 the known bootup would occur.
> >
> >> (8) Hibernation and restore should not be too slow
> >>
> >>     In my opinion, if more than one minute is needed to hibernate the
> >> system with the help of certain hibernation framework, then this
> >> framework is not very useful in practice.  It might be useful to
> >> perform some special tasks (eg. moving a server to another place
> >> without taking it down), but it is not very useful, for example, to
> >> notebook users.
> >
> > The latest hibernating kexec patches boot a kexec'd modular kernel with
> > initramfs into crashkernel=16M@16M in less than one second.  Switch-back
> > is almost instant.  Add to this the time required to either store or
> > restore the image, and it may be obvious that this approach isn't
> > slower, but maybe even faster than the current swsusp.
>
> What about (9)? Would it be that a user choosing to build a kernel with
> hibernate support gets a additional modular kernel built (which he
> should then use for resumption) or he should configure & build the
> modular kernel independent of main kernel?
>
> Or will the Linux boot procedure change so that it always goes thru a
> modular part followed by kexec (just to be uniform)?
>
> Although the kexec approach seems interesting, the final user-scenario
> seems a bit complex (or confusing).

Well, it may sound confusing because it is so unexpectedly simple.  I didn't 
answer to (9) because from a user pov nothing should change, and everything 
should be scriptable such that the user wouldn't even notice the kernel 
using a new hibernation approach.


Thanks!

--
Al

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