File backed memory is "less" than heap memory, because it can be thrown away when needed instead of being swapped out to disk. And because reading the file pro

File backed memory is "less" than heap memory, because it can be thrown away when needed instead of being swapped out to disk. And because reading the file probably allocated file backed pages for it anyway unless you used O_DIRECT (and profiled it first.) There's also wired/mlock() memory which is "worse" than regular memory because it can't be swapped/evicted at all.