Re: [tip:core/memblock] x86, memblock: Fix crashkernel allocation

["H. Peter Anvin" <h.peter.anvin@intel.com>]

On 10/07/2010 11:18 AM, Vivek Goyal wrote:
> 
> Ok, I was browsing through kexec-tools, x86 bzImage code and trying to
> refresh my memory what segments were being loaded and what were memory
> address concerns.
> 
> - relocatable bzImage (max addr 0x37ffffff, 896MB). 
> 	Though I don't know/understand where that 896MB come from.
> 
> - initrd (max addr 0x37ffffff, 896MB)
> 	Don't know why 896MB as upper limit

896 MB is presumably the (default!!) LOWMEM limit on 32 bits.  This is
actually wrong if vmalloc= is also specified on command line, though, or
with nonstandard compile-time options.

> - Purgatory (max addr 2G)
> 
> - A segment to keep elf headers (no limit)
> 	These are accessed when second kernel as fully booted so can be
> 	addressed in higher addresses.
> 
> - A backup segment to copy first 640K of memory (not aware of any limit)
> - Setup/parameter segment (no limit)
> 	- We don't really execute anything here and just access it for
>   	  command line.

Probably has a 4 GB limit, since I believe it only has a 32-bit pointer.

> So atleast for bzImage it looks that if we specify crashkernel=128M<896M, it
> will work.
> 
> So I am fine with above additional syntax for crashkernel=. May be we shall
> have to the deprecate the crashkernel=X<@0 syntax.
> 
> CCing kexec list, in case others have any comments.

It would be easy enough to either deprecate or make it an alias for
crashkernel=...<896M, which is basically what Yinghai's patch does.

	-hpa