a neat trick i found for reusing physical memory sebsite.pw

The author describes using a Linux memory-backed file (`memfd`) and a `MAP_PRIVATE` mapping to create copy-on-write duplicates without initially allocating extra physical memory. In a test, a 32 MiB mapping and its duplicate used 32.004 MiB of physical memory; writing to the duplicate allocated only the modified 4 KiB page.