Hi,

As of now the kdump kernel base is fixed to be 32MB. The intention of 
this patch is to modify that behaviour (for relocatable kernels)

* Regular kernel size may exceed 32MB, in this case we can't have kdump 
kernelbase as 32MB.

* crashkernel=auto also assumes that kdump kernelbase as 32MB, and it 
may also fail in reserving memory for kdump kernel.

On 11/27/2009 12:56 AM, Bernhard Walle wrote:

M. Mohan Kumar schrieb:

quoted

On 11/26/2009 12:22 AM, Bernhard Walle wrote:

quoted

M. Mohan Kumar schrieb:

quoted

Reserve memory for kdump kernel within RMO region

When the kernel size exceeds 32MB(observed with some distros), memory
for kdump kernel can not be reserved as kdump kernel base is assumed to
be 32MB always. When the kernel has CONFIG_RELOCATABLE option enabled,
provide the feature to reserve the memory for kdump kernel anywhere in
the RMO region.

Hi Bernhard,

quoted

Correct me if I'm wrong, but: CONFIG_RELOCATABLE is for the kernel that
gets loaded as crashkernel, not for the kernel that loads the
crashkernel. So it would be perfectly fine that a kernel that has not
CONFIG_RELOCATABLE set would load another kernel that has
CONFIG_RELOCATABLE set on an address != 32 M.

No, with relocatable option, the same kernel is used as both production
and kdump kernel.

Can be, but it's not strictly necessary. It depends what userland does.
Especially it's possible that a non-relocatable, self-compiled kernel
loads a relocatable distribution kernel as capture kernel.

Also, it would make sense to make the behaviour symmetric across
platforms. Currently we have:

  - x86 and ia64: Without offset on command line, use any offset
                  With offset on command line, use that offset and fail
                  if no memory is available at that offset.
  - ppc64: Always use 32M and ignore the offset.

If your patch gets applied, we have:

  - ppc64: With CONFIG_RELOCATABLE, use any offset
           With offset on command

I don't see why the behaviour on ppc64 should be completely different.

Having maintained kdump for SUSE for x86, ia64 and partly ppc64 in the
past, I always felt that ppc64 is more different from x86 than ia64 is
from x86. That's one more step into that direction without a technical
reason.

Having that all said: If your patch gets in mainline kernel, than we
should change the behaviour also for x86 and ia64.



Regards,
Bernhard

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