export GPU_MAX_HEAP_SIZE="any value from 1 to 100"
Use the above command to set the environment variable GPU_MAX_HEAP_SIZE. The value is the percentage of device memory that you want donate to OpenCL.
export GPU_MAX_ALLOC_PERCENT="any value from 1 to 100"
The above command sets the environment variable to allocate memory beyond the restricted 25% by default. However, the above commands may work or may not work, depending upon the environment variables supported by your hardware.
If the above two doesn't work, then use
:~$ strings /usr/lib/libamdocl64.so | grep GPU
This command displays a list of variables supported by your GPU. You can tweak them around and find out which variable changes what. However, these changes may break the norms of optimization and this could result in poorer performance. Its provided for experimentation.