Re: [Fastboot] Stupid kexec/kdump question...

From: Horms
Date: Wed Sep 27 2006 - 01:28:50 EST

On Tue, Sep 26, 2006 at 10:10:29PM -0700, Andrew Morton wrote:
> On Tue, 26 Sep 2006 11:25:06 -0400
> Valdis.Kletnieks@xxxxxx wrote:
> > OK, I'm running a Fedora Core 6 (rawhide actually) box with -18-mm1 kernel.
> > I've installed kexec-tools and similar, and am trying to get the kernels
> > built following the hints in Documentation/kdump/kdump.txt, but a few
> > questions arise:
> >
> > 1) Other than the fact that the Fedora userspace looks for a
> > ${kernelvers}kdump kernel, is there any reason the kdump kernel has
> > to match the running one, or can an older kernel be used?

The post-crash kernel is not realy dependant on the pre-crash kernel.
What is important is that either the kernel is relocatable
(which is being worked on for x86 and i386), or it is compiled to
run at a non-default address and that address corresponds
to the region reserved by the crashkernel command line parameter
passed to the pre-crash kernel.

The post-crash kernel will also need CONFIG_CRASH_DUMP

> > 2) I'm presuming that a massively stripped down kernel (no sound support,
> > no netfilter, no etc) that just has what's needed to mount the dump location
> > is sufficient?


> > 3) The docs recommend 'crashkernel=64M@16M', but that's 8% of my memory.
> > What will happen if I try '16M@16M' instead? Just slower copying due to
> > a smaller buffer cache space, or something more evil?

There is a lower bound to how small you can make the space, which
is basically how little memory space your post-crash kernel needs.
16M is probably pushing it, but 32M should be more than possible.
Experimentation is really the order of the day here.


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