Memory fragmentation makes per-process page tables impractical, so a per-process identifier is used to disambiguate the pages of different processes from each other.
12.
An " incarnation number " is used to avoid ambiguity : a counter that will be incremented each time a process joins the group, and is treated as part of the process identifier.
13.
It is somewhat slow to remove the page table entries of a process; the OS may avoid reusing per-process identifier values to delay facing this or it may elect to suffer the huge waste of memory associated with pre-allocated ( necessary because of fragmentation ) per-process hash tables.
14.
The operating system kernel identifies each process by its process identifier . is a special process that is created when the system boots; after forking a child process becomes the swapper process ( sometimes also known as the " idle task " ) ., known as init, is the ancestor of every other process in the system.
