Re: [PATCH] Tight check of pfn_valid on sparsemem - v4

Russell King - ARM Linux
2010-07-29T21:14:10Z

On Thu, Jul 29, 2010 at 02:55:53PM -0500, Christoph Lameter wrote:
> On Thu, 29 Jul 2010, Russell King - ARM Linux wrote:
>
> > And no, setting the sparse section size to 512kB doesn't work - memory is
> > offset by 256MB already, so you need a sparsemem section array of 1024
> > entries just to cover that - with the full 256MB populated, that's 512
> > unused entries followed by 512 used entries. That too is going to waste
> > memory like nobodies business.
>
> SPARSEMEM EXTREME does not handle that?
>
> Some ARMs seem to have MMUs. If so then use SPARSEMEM_VMEMMAP. You can map
> 4k pages for the mmap through a page table. Redirect unused 4k blocks to
> the NULL page.

We're going over old ground which has already been covered in this very
thread. I've no compunction to repeat the arguments.