Reserved pages in PowerPC

Ankita Garg ankita at
Thu Sep 16 22:08:06 EST 2010

Hi Ben,

On Thu, Sep 16, 2010 at 08:04:24PM +1000, Benjamin Herrenschmidt wrote:
> On Thu, 2010-09-16 at 10:53 +0530, Ankita Garg wrote:
> > 
> > With some debugging I found that that section has reserved pages. On
> > instrumenting the memblock_reserve() and reserve_bootmem() routines, I can see
> > that many of the memory areas are reserved for kernel and initrd by the
> > memblock reserve() itself. reserve_bootmem then looks at the pages already
> > reserved and marks them reserved. However, for the very last section, I see
> > that bootmem reserves it but I am unable to find a corresponding reservation
> > by the memblock code.
> It's probably RTAS (firmware runtime services). I'ts instanciated at
> boot from prom_init and we do favor high addresses for it below 1G iirc.

Thanks Ben for taking a look at this. So I checked the rtas messages on
the serial console and see the following:

instantiating rtas at 0x000000000f632000... done

Which does not correspond to the higher addresses that I see as reserved
(observation on a 16G machine).

Ankita Garg (ankita at
Linux Technology Center
IBM India Systems & Technology Labs,
Bangalore, India

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