Re: pgd clarification

[Gigi Sullivan <sullivan@sikurezza.org>]

Aiee :)

   Hello!

   Even if I'm really far from understanding the memory management under
   Linux, I'll try to give my thoughts.

   Feel really free to correct my mistakes :)
   (What follows is intended for i386 arch)

On Mon, May 21, 2001 at 08:28:56PM +0530, Santosh Eraniose wrote:
> Hello,
> In the mm_struct structure I notice only an entry for pgd_t* pgd.
> Cannot a process memory space occupy more that 4MB of virtual addr space.
> In that case how is one pgd sufficient?
> 1pgd can address 1024*4*1024 =4MB. or a 4k page

   That is a pointer to a pgd_t data type which holds the 32-bit
   physical address of the process' Page Global Directory in memory
   (The one which is kept by the cr3 register - uhm I'm not sure
   about what I said above, so feel free to correct myself :))

   The PGD table has 1024 entries. 
   Eeach PGD's entry point to a Page Table which has 1024 entries too.
   Eeach PTE point to a 4K Page Frame.

   This can give us 1024 * 1024 * 4 * 1024 = 4GB of VMA
                     |------|-----|----|-----> from the Page Global Directory
                            |-----|----|-----> from the Page Tables
                                  |----|-----> from each PTE

   (I know nothing about 4MB Page Frames)

> I expected a list of pgd so that on a pagefault, the process would navigate

   The Page Global Directory is like an array (never looked at the code, tho)

> Thanks in advance.
> regards
> 
> --
> Santosh Eraniose

bye bye

                        -- gg sullivan

-- 
Lorenzo Cavallaro	`Gigi Sullivan' <sullivan@sikurezza.org>

Until I loved, life had no beauty;
I did not know I lived until I had loved. (Theodor Korner)

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