High Memory problem on 2.4.22 Linux, 2GB ppc card

Ruksen INANIR rukseninanir at gmail.com
Mon Jun 30 19:22:08 EST 2008

Hi all,
   I am working on a PPC Motorola card, which runs Linux 2.4.22.  The 
card has 2 GB onboard memory. But with use 1456 MB of  the available 
memory.  To increase the memory capacity i  need  to  increase the used 
memory at least 64 MB. With CONFIG_HIGHMEM option all of the 2 GB memory 
can be used but, but the fc driver on the card has no high memory 
support, so this caused problems.
     Then i saw that the memory is limited to 1456 by
   #define MAX_LOW_MEM        0x5B000000  setting in pgtable.c.  I tried 
to increase it by 64 MB but i could only increase the value of 
MAX_LOW_MEM by 47 MB (1503 MB) without CONFIG_HIGHMEM option.

   1)Is there any other setting that i should set other than     
MAX_LOW_MEM to increase the usable memory to 1520 ?
   2)I knew that the addressable physical memory without high memory 
option was 1 G.  How was it possible to address 1503 MB without 
CONFIG_HIGHMEM ? What is the max usable memory for 2.4.22 kernel?


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