On 21 Feb, 03:00, "sjdevn...@yahoo.com" <sjdevn...@yahoo.com> wrote: > On Feb 18, 2:58 pm, John Nagle <na...@animats.com> wrote: > > > Multiple processes are not the answer. That means loading multiple > > copies of the same code into different areas of memory. The cache > > miss rate goes up accordingly. > > A decent OS will use copy-on-write with forked processes, which should > carry through to the cache for the code.
True, but the principal issue with CPython and copy-on-write is the reference counting. Consider a large list shared with the child processes which is to be processed (either in part or in its entirety) by each of them. As soon as the child processes start referencing each of the elements, the reference count for each element object will need to be changed and pages will start to be copied for each child process. That's why John wants to avoid the reference counting of shared data and why the Unladen Swallow project has apparently considered storing reference counts in separate regions of memory. Such shared data is really "owned" by the parent process, so it makes little sense for the child processes to manage it with a view to collecting it later. After all, such data should have no cost to each of the child processes (except, perhaps, for the size of the address space referenced by each process, and any resource issues arising from managing that). Paul -- http://mail.python.org/mailman/listinfo/python-list
