superpages and kmem on amd64

[Alan Cox]

On Sun, May 20, 2012 at 2:01 AM, Marko Zec <zec at fer.hr> wrote:

> Hi all,
>
> I'm playing with an algorithm which makes use of large contiguous blocks of
> kernel memory (ranging from 1M to 1G in size), so it would be nice if those
> could be somehow forcibly mapped to superpages.  I was hoping that the VM
> system would automagically map (merge) contiguous 4k pages to superpages,
> but
> apparently it doesn't:
>
> vm.pmap.pdpe.demotions: 2
> vm.pmap.pde.promotions: 543
> vm.pmap.pde.p_failures: 266253
> vm.pmap.pde.mappings: 0
> vm.pmap.pde.demotions: 31
>
>
No, your conclusion is incorrect.  These counts show that 543 superpage
mappings were created by promotion.

Alan