linux-kernel - Re: [patch 1/5] Extended crashkernel command line

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Date:	Tue, 11 Sep 2007 12:01:10 +0200
From:	Bernhard Walle <bwalle@...e.de>
To:	Vivek Goyal <vgoyal@...ibm.com>
Cc:	linux-arch@...r.kernel.org, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/5] Extended crashkernel command line

* Vivek Goyal <vgoyal@...ibm.com> [2007-09-11 08:15]:
> 
> "offset" seems to be optional in the new syntax. What happens if user does
> not specify offset. I think crash_base will be set to zero and system will
> try to reserve x amount of memory start at zero? That would fail?

That's handled in the architecture specific code -- because it's
different on each architecture and the architecture specific code does
memory reservation. IA64 already can handle this case (on IA64,
specifying 0 is the same than leaving out the base address, and that's
why I wanted to keep that semantics). I think it doesn't also make
sense on i386/x86_64 to choose 0 as real base address, because the
value below 1 MB is special for booting ...

> I think we should add some intelligence for automatic selection of "offset"
> if user has not specified one. Automatically choose a chunk of free memory.
> This takes away the headache from user for selecting a right place. In fact
> one "offset" might not be valid for all the systems. I remember, somebody
> had reported that ACPI tables were mapped lower in the address space and
> reserving memory for kdump had failed.

I think you're right -- with the relocatable kernel it makes sense to
have the kernel to decide where to reservate that memory. But that's
beyond of the scope of that patch series -- however, I can come up
with a solution, after that patch has been finished.

Thanks,
   Bernhard

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