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

[Venkatram Tummala <venkatram867@xxxxxxxxx>]

I completely agree with you. I was just trying to clarify Xianghua's statement "last 128 MB is used for HIGHMEM". I got the feeling that he thought that last 128MB can be used for vmalloc, IO and for HIGHMEM. So, i was clarifying that last 128MB is not "used for highmem" but it is used to support highmem.(among many other things). That was what i intended.

On Tue, Apr 6, 2010 at 7:09 PM, H. Peter Anvin <hpa@xxxxxxxxx> wrote:

On 04/06/2010 07:04 PM, Venkatram Tummala wrote:
> Hey Xiao,
>
> last 128MB is not used for highmem. last 128MB is used for data
> structures(page tables etc.) to support highmem .  Highmem is not
> something which is "INSIDE" Kernel's Virtual Address space. Highmem
> refers to a region of "Physical memory" which can be mapped into
> kernel's virtual address space through page tables.
>
> Regards,
> Venkatram Tummala
>

Not quite.

The vmalloc region is for *anything which is dynamically mapped*, which
includes I/O, vmalloc, and HIGHMEM (kmap).

       -hpa

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