Re: [Patch 0/8] V5 Implement crashkernel=auto

[Amerigo Wang]

Michael Ellerman wrote:
> On Wed, 2009-08-26 at 23:15 -0400, Amerigo Wang wrote:
>   
> > V4 -> V5:
> >  - Rename the global functions, as suggested by Andrew.
> >  - Save some macros, as suggested by Andrew.
> >  - Change the high threshold, from 32G to 4G.
> >  - Change the low threshold on ppc, suggested by ppc developers.
> >  - Make the mm part as a seperate function, suggest by Eric.
> >  - Make the IA64 code more readable.
> >  - Reorder the patchset again, since review from mm people is done.
> >
> > V3 -> V4:
> >  - Reorder the patches.
> >  - Really free the reserved memory, instead of remapping it.
> >    (Thanks to KAMEZAWA Hiroyuki!)
> >  - Release the reserved memory resource when the size is 0.
> >  - Use strict_strtoul() instead of simple_strtoul().
> >
> > V2 -> V3:
> >  - Use more clever way to calculate reserved memory size, especially for IA64.
> >  - Add that patch that implements shrinking reserved memory
> >
> > V1 -> V2:
> >  - Use include/asm-generic/kexec.h, suggested by Neil.
> >  - Rename a local variable, suggested by Fenghua.
> >  - Fix some style problems found by checkpatch.pl.
> >  - Unify the Kconfig docs.
> >
> > This series of patch implements automatically reserved memory for crashkernel,
> > by introducing a new boot option "crashkernel=auto". This idea is from Neil.
> >
> > In case of breaking user-space applications, it modifies this boot option after
> > it decides how much memory should be reserved.
> >
> > On different arch, the threshold and reserved memory size is different. Please
> > refer patch 7/8 which contains an update for the documentation.
> >
> > Patch 8/8 implements shrinking reserved memory at run-time, which is useful
> > when more than enough memory is reserved automatically.
> >
> > This patchset _is_ already tested on x86_64, IA64 and ppc64.
> >     
>
> I don't want to sound like a micro-kernel zealot, I'm not, but I'm still
> unconvinced as to why the auto logic needs to go in the kernel. What is
> the compelling reason that the kernel needs to do this calculation vs
> some userspace tool? We already have the syntax that allows defining a
> different crash size depending on the size of RAM.
>   

Take a look at the x86 part, it can not be done _directly_ in kernel 
command line with the syntax.

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