# Re: \[v2\] powerpc/mm: Ensure "special" zones are empty

- From: Michael Ellerman \<mpe@ellerman.id.au\>
- Date: 2016-06-21 00:40:58 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2016/06/6481053
- Thread: https://ratatoskr.run/linuxppc-dev/2016/05/6480705/t.md

```text
On Wed, 2016-11-05 at 09:22:18 UTC, Oliver O'Halloran wrote:
> The mm zone mechanism was traditionally used by arch specific code to
> partition memory into allocation zones. However there are several zones
> that are managed by the mm subsystem rather than the architecture. Most
> architectures set the max PFN of these special zones to zero, however on
> powerpc we set them to ~0ul. This, in conjunction with a bug in
> free_area_init_nodes() results in all of system memory being placed in
> ZONE_DEVICE when enabled. Device memory cannot be used for regular kernel
> memory allocations so this will cause a kernel panic at boot. Given the
> planned addition of more mm managed zones (ZONE_CMA) we should aim to be
> consistent with every other architecture and set the max PFN for these
> zones to zero.
> 
> Signed-off-by: Oliver O'Halloran <oohall@gmail.com>
> Reviewed-by: Balbir Singh <bsingharora@gmail.com>
> Cc: <redacted>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/3079abe555511031e2ba5d1e21

cheers
```