why the kernel need define ZONE_HIGHEM

[Mulyadi Santosa]

Hi...

On Wed, Oct 17, 2012 at 5:39 PM, Fan Yang <lljyangfan at gmail.com> wrote:
> HI ALL:
>     I don't knowe why the linux designer need to define the ZONE_HIGHEM, and
> why they defined it 896M.

my understanding about ZONE_HIGHMEM is that it is simply a pool of
pages, grouped so you can quickly know that if you want to use them,
you need to kmap() them first because they are normally beyond kernel
addressable space

896? simple, because that is the upper border of kernel addressable
space range. actually, it's 1 GiB, but since 128 MiB are reserved for
various need: vmalloc, kmap mapping etc, then you get 1 GiB - 128
MiB--> there you go 128 MiB

-- 
regards,

Mulyadi Santosa
Freelance Linux trainer and consultant

blog: the-hydra.blogspot.com
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