Re: [RFC] Tight check of pfn_valid on sparsemem

[Dave Hansen <dave@linux.vnet.ibm.com>]

On Tue, 2010-07-13 at 19:39 +0100, Russell King - ARM Linux wrote:
> On Tue, Jul 13, 2010 at 05:02:22PM +0900, KAMEZAWA Hiroyuki wrote:
> > How about stop using SPARSEMEM ? What's the benefit ? It just eats up
> > memory for mem_section[].
> 
> The problem with that approach is that sometimes the mem_map array
> doesn't fit into any memory banks.
> 
> We've gone around the loop of using flatmem with holes punched in it,
> to using discontigmem, and now to using sparsemem.  It seems none of
> these solutions does what we need for ARM.  I guess that's the price
> we pay for not having memory architected to be at any particular place
> in the physical memory map.

What's the ARM hardware's maximum addressable memory these days? 4GB?

A 4GB system would have 256 sections, which means 256*2*sizeof(unsigned
long) for the mem_section[].  That's a pretty small amount of RAM.

What sizes are the holes that are being punched these days?  Smaller
than 16MB?

-- Dave