Re: [PATCH kernel] powerpc: Bump minimum zone order for 4K system page size

[Balbir Singh]

On 23/09/16 14:51, Alexey Kardashevskiy wrote:
> The moderm kernel on powernv platform cannot possibly boot with values
> less than 12 as the default DMA window of 2GB requires
> (2<<30)/4096 TCEs which is 4MB of contiguous memory, log2(4M) == 22
> so anything less than 12 won't work.
> 
> Signed-off-by: Alexey Kardashevskiy 
> ---
> 
> I am hitting this when switching the system page size from 64K to 4K and
> back. When I switch to 64K, zone order is set to 9 by default and
> it does not change when I switch to 4K as 9 is still within the limits.
> And there are other folks complaining about this too.
> ---
>  arch/powerpc/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 927d2ab..3516f16 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -637,7 +637,7 @@ config FORCE_MAX_ZONEORDER
>   int "Maximum zone order"
>   range 8 9 if PPC64 && PPC_64K_PAGES
>   default "9" if PPC64 && PPC_64K_PAGES
> - range 9 13 if PPC64 && !PPC_64K_PAGES
> + range 12 13 if PPC64 && !PPC_64K_PAGES
>   default "13" if PPC64 && !PPC_64K_PAGES
>   range 9 64 if PPC32 && PPC_16K_PAGES
>   default "9" if PPC32 && PPC_16K_PAGES
> 

Aneesh already submitted a patch for this

Balbir Singh.

[PATCH kernel] powerpc: Bump minimum zone order for 4K system page size

[Alexey Kardashevskiy]

The moderm kernel on powernv platform cannot possibly boot with values
less than 12 as the default DMA window of 2GB requires
(2<<30)/4096 TCEs which is 4MB of contiguous memory, log2(4M) == 22
so anything less than 12 won't work.

Signed-off-by: Alexey Kardashevskiy 
---

I am hitting this when switching the system page size from 64K to 4K and
back. When I switch to 64K, zone order is set to 9 by default and
it does not change when I switch to 4K as 9 is still within the limits.
And there are other folks complaining about this too.
---
 arch/powerpc/Kconfig | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 927d2ab..3516f16 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -637,7 +637,7 @@ config FORCE_MAX_ZONEORDER
int "Maximum zone order"
range 8 9 if PPC64 && PPC_64K_PAGES
default "9" if PPC64 && PPC_64K_PAGES
-   range 9 13 if PPC64 && !PPC_64K_PAGES
+   range 12 13 if PPC64 && !PPC_64K_PAGES
default "13" if PPC64 && !PPC_64K_PAGES
range 9 64 if PPC32 && PPC_16K_PAGES
default "9" if PPC32 && PPC_16K_PAGES
-- 
2.5.0.rc3