> Considering the computer has to read 40 GB of data from disk, map it to physical memory and then let the CPU has a rip of it
No it doesn't? Maybe it needs to set up page tables for 40GB, but it doesn't need to read the parts you're not using into memory, that's part of the point of memory-mapping like this - it sets up a page fault handler to load the page into memory when accessed, rather than needing to do it all up-front.
No it doesn't? Maybe it needs to set up page tables for 40GB, but it doesn't need to read the parts you're not using into memory, that's part of the point of memory-mapping like this - it sets up a page fault handler to load the page into memory when accessed, rather than needing to do it all up-front.