Re: why choose 896MB to the start point of ZONE_HIGHMEM

[Venkatram Tummala <venkatram867@xxxxxxxxx>]

Can you please explain the last statement. My understanding was - the exact conversion formula of virtual address to physical address in identity mapped segment is platform specific and in most cases, this is as simple as the addition of an offset. So we can do away with page tables to access memory mapped in identity mapped segment.

Am i missing something?

Regards,
Venkatram Tummala

On Tue, Apr 6, 2010 at 11:04 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:

On 04/06/2010 10:57 PM, Venkatram Tummala wrote:
> Just a note Chetan.
>
> We can't exactly say that we require "page table settings" to map that
> 896 MB of physical ram. It is an identity mapped segment (1-1 mapping).
> So, we dont require the "page tables".  Virtual address will be equal to
> Physical Address + Page Offset. It is just an addition of offset
>

No, we still need page tables for the identity-mapped segment.

       -hpa

--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.