Re: [PATCH 1/4] x86_64: Switch to SPARSE_VIRTUAL

Christoph Lameter
2007-04-02T17:34:40Z

On Mon, 2 Apr 2007, Andi Kleen wrote:

> > No no no. For the gazillions time: All of 1-1 mapped kernel memory on
> > x86_64 needs a 2 MB page table entry. The virtual memmap uses the same.
> > There are *no* additional TLBs used.
>
> But why do you reserve an own virtual area then if you claim to not use any
> additional mappings?

The 1-1 area using mappings for 2MB pages right? So it uses a virtual 1-1
area. It already has a virtual mapping.

What we do for virtual memmap here is also use 2MB pages but order the
pages a bit different so that they provide a linear memory map.

So the number of TLBs in use stays the same. There are a few additional
higher level page table pages that are needed to provide the alternate
view that generates the linear mapping but that is just a couple of pages.