thanks for your wonderful explanation, I delayed asking further questions till I read every ones posts, its much clearer now. :)
To make things clear, 896 MB is not a hardware limitation. The 3GB:1GB split can be configured during the kernel build but the split cannot be changed dynamically.
Actually someone further along in this thread mentioned that the value of LOWMEM / HIGHMEM can be a hardware constraint such as in the case of x86
Hope this clears the confusion.
Surely does, thank you. I have one more question, the memory between 896MB and 1GB (128 MB) is actually the kernel virtual memory that is dynamically mapped to highmem using kmap or used for vmalloc/IO right? and the 896 MB of physically memory which is directly accessible is what contains the actual page tables that make accessing high mem using the 128MB kernel virtual address space possible right?
You said page tables are stored in the 128 MB portion, I'm confused because the 128 MB is virtual and the page tables have to be stored in the 896 MB segment. no?
-Joel
