On Fri, Jan 21, 2011 at 3:01 AM, Russell King - ARM Linux
[off-list ref] wrote:

On Thu, Jan 20, 2011 at 09:20:47AM -0800, Dave Hansen wrote:

quoted

This problem actually exists without sparsemem, too. ?Discontigmem (at
least) does it as well.

We don't expect banks to cross sparsemem boundaries, or the older
discontigmem nodes (esp. as we used to store the node number.)
Discontigmem support has been removed now so that doesn't apply
anymore.

Our system can have 3 GiB of RAM in maximum.
In the near future, ARM APs can have up to 1 TiB with LPAE.

Since the size of section is 256 mib and NR_BANKS is defined as 8,
no ARM system can have more RAM than 2GiB in the current implementation.
If you want banks in meminfo not to cross sparsemem boundaries,
we need to find another way of physical memory specification in the kernel.

quoted

The x86 version of show_mem() actually manages to do this without any
#ifdefs, and works for a ton of configuration options. ?It uses
pfn_valid() to tell whether it can touch a given pfn.

x86 memory layout tends to be very simple as it expects memory to
start at the beginning of every region described by a pgdat and extend
in one contiguous block. ?I wish ARM was that simple.