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

From: H. Peter Anvin
Date: Tue Apr 06 2010 - 22:19:44 EST

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).


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

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