> paging out has zero cost Paging out, as in removing a mapping, can be surprisingly costly, because you need to invalidate any cached TLB entries, possibly ev

> paging out has zero cost Paging out, as in removing a mapping, can be surprisingly costly, because you need to invalidate any cached TLB entries, possibly even in other CPUs. > each mmap file will need 1 page of physical memory Technically, a lower limit would be about 2 or so usable pages, because you can't use more than that simultaneously. However unmaps are expensive, so the system won't be too eager to page out. Also, for pages to be accessible, they need to be specified in the page table (actually tree, of virtual -> physical mappings). A random address may require about 1-3 pages for page table aside from the 1 page of actual data (but won't need more page tables for the next MB). > application X using GB of memory I think there is a difference between reserved, allocated and file-backed mmapped memory. Address space, file-backed mmapped memory is easily paged-out, not sure what different types of reserved addresses/memory are, but chrome probably doesn't have lots of mmapped memory that can be paged out. If it's modified, then it must be swapped, otherwise it's just reserved and possibly mapped, but never used memory.