Some questions about mc-mapping.c

1. option b is uesd for ? When the value range of b is 6~23, the following code results are the same, it seems to have no effect.

g_mem_size += (1 << page_shift);
g_mem_size = CEIL(g_mem_size, ENTRY_DIST);

2. What does the 4 in the code below mean?

/* initialize data */
int off_idx = (1<<page_shift) / 4;

3. What does the 4 in the code below mean?

for (i = 0; i < NUM_ENTRIES; i++) {
	int idx = i * ENTRY_DIST / 4;
	if (i == (NUM_ENTRIES - 1))
		list[idx] = 0;
	else
		list[idx] = (i+1) * ENTRY_DIST/4;
}

4. Finally, there are many problems while running mc-mapping on my machine, is there any good suggestion?

- ARM64 architecture
- 2cpus, 2 dies per CPU, 16 cores per die, so totally 16 * 2 * 2 = 64 cores
- 4 channels of DDR4， total 512GB of memory