High Memory problem on 2.4.22 Linux, 2GB ppc card

[Ruksen INANIR <rukseninanir@gmail.com>]

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 ? Do i need  to 
change  TASK_SIZE or KERNEL_START?
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?

Thanks,
Rinanir.