b) #define virt_to_page(kaddr) (mem_map + (__pa(kaddr) >> PAGE_SHIFT)) above macro is giving you struct page for a corresponding virtual address.
c) linear address to physical address translation is done by x86 processor (32 but without PAE) by doing traversal pgd->pte->page_phys_addr. OS sets up this entries and processor uses it.
Yes, above macro is not for ZONE_HIGHMEM. Because ZONE_HIGHMEM is not directly mapped by kernel.
Shailesh Jain
On Fri, Oct 23, 2009 at 2:01 PM, Shameem Ahamed <shameem.ahamed@xxxxxxxxx> wrote:
Hi Friends,
Please help me to figure out some basic concepts in MM.
>From the books, i learned that VMA to PA translation consists of traversing the full page directory, which consists of Global Directory, Middle Directory and Page Table.
I have also read that, VMA to PA translation is done using a macro virt_to_page defined as given below.
#define virt_to_page(kaddr) (mem_map + (__pa(kaddr) >> PAGE_SHIFT))
If
there is a macro, why we need code for traversing all the page
directories ?. This macro is a simple math, which points to an index
in global mem_map array, which contains all the pages in the system.
So my doubts are,
Is the macro only for ZONE_NORMAL (upto 896M, which is directly mapped by kernel) memory pages ?.
Is mem_map array contains pages upto ZONE_NORMAL ?
Is page traversing happens only for HIGH_MEM ?.
Regards,
Shameem
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