There may be reasons to mmap a sparse file but I can't think of any. It sounds like you understand the forces at work here, but I am confused by your statement

There may be reasons to mmap a sparse file but I can't think of any. It sounds like you understand the forces at work here, but I am confused by your statements. Do you think that "pre-allocating" a sparse file is a valid alternative to writing 2GB of zeros to disk in this case?