[Cbe-oss-dev] Only 86MB of RAM available running Ubuntu 8.04 powerpc64-smp kernel on PS3

[Dan Munckton]

Hi Geoff

> Yes, all firmware versions to date give 128 MiB of boot memory.
> 
> The VMEMMAP authors didn't consider systems that don't have much
> memory when they did there design, so it doesn't really work well
> on PS3.  With your config it needs a 16MiB page of boot memory to
> add the extra hot plug memory.  The above message shows that this
> alloc failed, so the hot plug mem could not be added.  The system
> then continues to boot with just the 128 MiB of boot mem.
> 
> Looking at the .config here:
> 
>   http://launchpadlibrarian.net/13914707/config-2.6.24-16-powerpc64-smp
> 
> The trouble is that CONFIG_SPARSEMEM_VMEMMAP is set, and the kernel
> image is very big do to all the other options set.
> 
> You have two choices for your Hardy support.  The easier way, and
> better for PS3 users, is to make a ps3 specific kernel, the harder
> way is to tune the multi-platform kernel so that it boots on the PS3.
> 
> Either way, change to these:
> 
>   CONFIG_SPARSEMEM_VMEMMAP=n
>   CONFIG_FB_PS3_DEFAULT_SIZE_M=9
>   CONFIG_PS3_USE_LPAR_ADDR=n
> 
> -Geoff
> 

Interesting. Thanks for the explanation. I note that SPARSEMEM_VMEMMAP
and PS3_USE_LPAR_ADDR are both set to 'y' even in the
ps3_defconfig .config, so you're suggesting these options cannot be used
in such a big kernel until something like Ben's patch absorbed into the
vmemmap code. 

Are there likely to be any noticeable side-effects of losing these two
features?

I also noticed the FB is getting allocated an extra 9MB of space in the
hardy config. Obviously we can get by with only 9MB, so I presume the
motivation for 16MB would better support double-buffering/flipping is
that correct? What side effects would be incurred by setting this to
9MB?

I am probably going to propose to the Ubuntu Kernel Team that the PS3
kernel is supported as a "custom flavour" build again as it was in
gutsy/feisty. Do you think that an attempt to use the generic
powerpc64-smp flavour would be worth trying again with 2.6.2{5,6}?

Cheers

Dan