[mm subsystem] A question about function page_table_range_init_count()

[mm subsystem] A question about function page_table_range_init_count()

[Hao Lee]

Hi, all

I encounter a problem when I read the source code of kernel 4.9.9.

In arch/x86/mm/init_32.c, at line 125 [1], there is a function named
page_table_range_init_count(...). I have analyzed some codes and find its
two parameters are PKMAP_BASE and FIXADDR_START.

Between Line 141 and Line 150, there is a for loop and I don't know what it
means, especially Line 144-Line147.

Could someone can give me some tips. Thanks a lot!

Here is the code:
[1]  http://lxr.free-electrons.com/source/arch/x86/mm/init_32.c?v=4.9#L125

Hao Lee
Thanks.
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[mm subsystem] A question about function page_table_range_init_count()

[Rik van Riel]

On Wed, 2017-03-15 at 22:12 +0800, Hao Lee wrote:
> Hi, all
> 
> I encounter a problem when I read the source code of kernel 4.9.9.
> 
> In arch/x86/mm/init_32.c, at line 125 [1], there is a function named
> page_table_range_init_count(...). I have analyzed some codes and find
> its two parameters are PKMAP_BASE and FIXADDR_START.
> 
> Between Line 141 and Line 150, there is a for loop and I don't know
> what it means, especially Line 144-Line147.
> 
> Could someone can give me some tips. Thanks a lot!
> 
The code iterates over the virtual memory addresses
specified, and counts the number of pmds (second level
page tables) that will be needed to map that address
space.