Re: [PATCH v2 0/4] kexec-tools, x86: E820 memmap pass for kdump

[Vivek Goyal <vgoyal@redhat.com>]

On Mon, Feb 24, 2014 at 10:58:41PM +0800, WANG Chao wrote:
[..]
> > Approaches to avoid saved_max_pfn in calgary case:
> >   1) If done correctly from the beginning, the TCE table size would have
> >      been exposed via /sys and kexec-tools could simply add:
> >      calgary="128k|512K...|8M" which is already caught by pci-calgary and
> >      saved_max_pfn is not needed/touched anymore.
> >      -> Disadvantage: needs a new sysfs entry
> >   2) When finding max_pfn for calgary table size usage, we could try in 
> >      kdump case to use the highest memory (RAM or RESERVED) showing up
> >      in e820 map.
> 
> How could this replace saved_max_pfn? The highest memory in kdump can't
> necessarily be the real ram size. In kdump, RAM range is just part of the real
> ram, not mentioning we don't pass RESERVED range to kdump E820.

I vaguely remember there was some discussion about passing first kerne's
RAM as special reserved ranges. Say E820_RESERVED_KDUMP. And use that
to figure out saved_max_pfn.

I personally feel that just create a new command line parameter
"saved_max_pfn" and pass it to second kernel and be done with it. Modify
calgary code to first look for saved_max_pfn and if not present, calculate
saved_max_pfn from e820.

saved_max_pfn command line option is pretty ugly, not sure what are the
better options here.

Thanks
Vivek

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