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

Christoph Lameter
2010-07-29T19:55:59Z

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.