python multiprocessing arguments: deep copy?
When you create a Process instance, under the hood Python issues a fork(). This creates a child process whose memory space is an exact copy of its parent -- so everything existing at the time of the fork is copied.
On Linux this is made efficient through "copy-on-write". From the fork man page:
fork() creates a child process that differs from the parent process only in its PID and PPID, and in the fact that resource utilizations are set to 0. File locks and pending signals are not inherited.
Under Linux, fork() is implemented using copy-on-write pages, so the only penalty that it incurs is the time and memory required to duplicate the parent's page tables, and to create a unique task structure for the child.