I Should have RTFM: "The MADV_FREE operation can be applied only to private anonymous pages (see mmap(2)). In Linux before version 4.12, when freeing pages on

I Should have RTFM: "The MADV_FREE operation can be applied only to private anonymous pages (see mmap(2)). In Linux before version 4.12, when freeing pages on a swapless system, the pages in the given range are freed instantly, regardless of memory pressure."