Unable to understand "init_mempool", "malloc", etc functions

Hello,
I am using Keil uVision3 V3.55 for Si-labs C8051F02X series. I am using "init_mempool" function, so that I can use the functions like "malloc", "free", etc.
Here is my source code --

#include<c8051f020.h>
#include<stdlib.h>
void main(void)
{
unsigned char xdata  *ptr, *ptr1;
init_mempool(0x05,15);
ptr = malloc(10);
ptr1 = malloc(5);
         *ptr++ = 11;
        *ptr++ = 22;
        *ptr++ = 33;
        *ptr++ = 44;

         *ptr1++ = 1;
        *ptr1++ = 2;
        *ptr1++ = 3;

}

I am expecting that, all the above data to be put from the locations 0x05(in xdata) onwards. But, I found that "ptr1" points to 0x00(in xdata), and "ptr" points to 0x09(in xdata).
So, what is the role of "init_mempool" function here?
Why does "malloc" allocate memory from 0x00??

Thanks in advance,

Regards,
Heramb Phadke