Why the page tables are needed for lowmem?

[Pranay Srivastava]

On Thu, Jun 19, 2014 at 8:51 AM, sandeep kumar
<coolsandyforyou at gmail.com> wrote:
> Hi All
>
> i was going through mm initialization code, and saw paging_init()
> implementation.
> it has a function map_lowmem().
>
> I was wondering why do we need page table entries for lowmem ??
>
I hope you understand how MMU and virtual memory works.

> because all the pages in lowmem can be addressed by kernel logical address
> and differ only an offset from the physical address. Why cant we simply add
> that offset to the virtual(logical) address and get the job done. Why waste
> some memory for creating PTEs for them?

Let's forget about lowmem or high mem. See the role of MMU and you'll
understand why it's needed.

>
> can any one clarify?
>
>
> --
> With regards,
> Sandeep Kumar Anantapalli,
>
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-- 
        ---P.K.S