Reserving small amounts of memory with mem= (MPC85xx, 2.6.15 arch/ppc)

Scott Wood scottwood at
Sat Jun 14 01:31:14 EST 2008

Florian Boelstler wrote:
> Available system memory is only 384 MB (CAM0+CAM1+CAM2), which explains 
> why Linux "removed" the ramdisk, when it has been copied right below 
> 508M by U-Boot. Because at that time I was using initrd_high @ 1FC00000, 
> which is outside of mapped RAM.
> Is there an option to map less than 64M by a CAM entry?

CAM entries can be any power of 4 between 4K and 256M.  However, the 
code currently is hardcoded to use no more than 3 entries.  It shouldn't 
be too hard to change it to use a few more (see cam_mapin_ram(), 
mmu_mapin_ram(), and adjust_total_lowmem() in 

Alternately, do you have highmem enabled?  That will let you access the 
rest of the RAM that the CAM doesn't map, though I don't know if an 
initrd in highmem works.


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