I don't think memory mapping does anything to prevent false sharing. All threads still get the same data at the same address. You may get page alignment for the

I don't think memory mapping does anything to prevent false sharing. All threads still get the same data at the same address. You may get page alignment for the file, but the free-form data in the file still crosses page boundaries and cache lines. Also you don't get contention when you don't write to the memory. The speedup may be from just starting the work before the whole file is loaded, allowing the OS to prefetch the rest in parallel. You probably would get the same result if you loaded the file in smaller chunks.