Date: Mon, 14 Jul 2008 09:09:55 -0400
From: Vivek Goyal <vgoyal@redhat.com>
To: Nigel Cunningham <nigel@nigel.suspend2.net>
Cc: Andrew Morton <akpm@linux-foundation.org>,
       Huang Ying <ying.huang@intel.com>,
       "Eric W. Biederman" <ebiederm@xmission.com>,
       Pavel Machek <pavel@ucw.cz>, "Rafael J. Wysocki" <rjw@sisk.pl>,
       linux-kernel@vger.kernel.org, linux-pm@lists.linux-foundation.org,
       Kexec Mailing List <kexec@lists.infradead.org>,
       Horms <horms@verge.net.au>
Subject: Re: [PATCH -mm 1/2] kexec jump -v12: kexec jump
Message-ID: <20080714130955.GA16673@redhat.com>
References: <1215401122.4660.4.camel@caritas-dev.intel.com> <20080708145051.GA14745@redhat.com> <20080711122131.b6461ab1.akpm@linux-foundation.org> <20080711201149.GB3298@redhat.com> <1215824537.7319.7.camel@nigel-laptop>
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On Sat, Jul 12, 2008 at 11:02:17AM +1000, Nigel Cunningham wrote:
> Hi.
> 
> On Fri, 2008-07-11 at 16:11 -0400, Vivek Goyal wrote:
> > Hi Andrew,
> > 
> > We can use this patchset for hibernation, but can it be a better way of doing
> > things than what we already have, I don't know. Last time I had raised
> > this question and power people had various views. In the end, Pavel wanted
> > this patchset to be in.  Pavel, can tell more here...
> > 
> > To me this patchset looks interesting for couple of reasons.
> > 
> > - Looks like an interesting feature where one can have a separate kernel
> >   in memory and one can switch between the kernels on the fly. It can
> >   be modified to have more than one kernel in memory at a time.
> 
> I'm not sure how useful that would be, though. I already have
> functionality in TuxOnIce which allows you to resume a different image
> instead of powering off (roughly the same thing when combined with not
> removing the image after resuming). It was neat when testing to be able
> to switch back and forth, and I developed the code because I imagined
> that it could form part of the foundation for switching between a login
> screen and users' stored sessions. Is this what you're imagining?
> 

I did not think of that. I thought of two things.

- This can possibly be used for non-disruptive kernel crash dumping, where
  if a user wants to capture the snapshot of kernel and then continue
  to work. Thought, it might be little heavy weight solution and kernel
  state also has changed a bit by the time dump is captured (because of
  all the suspend code).

- One can have two distributions installed on a single system and switch
  between two booted kernels in few seconds.

> > - So far kexec was one directional. One can only kexec to new kernel and
> >   old kernel was gone. Now this patchset makes kexec functionality kind
> >   of bidirectional and this looks like logical extension and can lead
> >   to intersting use cases in future.
> 
> Ah. You mean keeping both kernels in memory at the same time? In the
> above, I was replacing one image with another.

Yes, here both the kernels will remain in the RAM. In fact it should be
easily possible to keep more than 2 kernels in memory and switch between
these.

Thanks
Vivek
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