Two Pages Of Copying

A process maps 1 GiB of private anonymous memory and writes to all of it, so every page is resident. It then calls fork(). The child writes one byte at offset 0 and one byte at offset 700 MiB, then calls _exit.

Pages are 4 KiB and transparent huge pages are off. How many 4 KiB pages of that region does the kernel copy?

0, because the region is anonymous and has no file to copy back to

262144, all of them, at the moment fork() returns

262144, but lazily, spread over the child's lifetime as it touches them