Re: kernel-image-2.4.27-powerpc-smp-pmac unstable with CONFIG_HIGHMEM=y

[Sven Luther <sven.luther@wanadoo.fr>]

On Thu, Sep 30, 2004 at 03:09:17AM -0500, Branden Robinson wrote:
> Is anybody else running 2.4.x on a PowerMac Dual G4?  (I've got a "mirrored
> drive door" model[1].)
> 
> If I take the kernel-patch-powerpc-2.4.27 source package and rebuild it
> with config/powerpc-smp changed so that CONFIG_HIGHMEM=y (instead of being
> not set), the resulting kernel is horrendously unstable.
> 
> I can't even get through the boot process with processing segfaulting, or
> the dynamic linker failing to resolve symbols.
> 
> Returning to a "# CONFIG_HIGHMEM is not set" kernel that is otherwise
> identical is extremely stable and reliable.
> 
> Problem is, I've got a gig of RAM and, you know, I'd like to actually use
> it all.
> 
> Here's the beginning of dmesg with a non-highmem kernel:
> 
> Memory BAT mapping: BAT2=256Mb, BAT3=256Mb, residual: 512Mb
> Warning, memory limited to 512 Mb, use CONFIG_HIGHMEM to reach 1024 Mb
> Total memory = 512MB; using 1024kB for hash table (at c0600000)
> 
> Unfortunately I don't have the output of the highmem kernel anymore, but I
> can reboot the box into that horrible unstable kernel to collect it if need
> be.
> 
> If I had to speculate, I'd say these parameters have something to do with
> it:
> 
> CONFIG_HIGHMEM_START=0xfe000000
> CONFIG_LOWMEM_SIZE=0x30000000
> CONFIG_KERNEL_START=0xc0000000
> CONFIG_TASK_SIZE=0x80000000
> 
> [1] http://www.lowendmac.com/ppc/g4-125.html

Which is why you should be running 2.6 kernels on your powerpc box. The 2.4
kernels are largely abandoned by upstream powerpc developers, and are not the
default on powerpc in debian anymore. Especially for largely uncommon
situations like highmem and smp kernels, the latest 2.6 kernels are your
safest bet.

Friendly,

Sven Luther