On Mon, Jan 11, 2010 at 12:02 AM, Joel Fernandes <agnel.joel@xxxxxxxxx> wrote: > Hi, > The book Linux Kernel Development mentions a certain overhead which is > reduced in linux because the child is made to run first after it is > forked (instead of the parent) and if the child executes the exec > system call. > > Quoting Pg 32 (2nd edition): > "In do_fork() the child is woken up and run. Deliberately the kernel > runs the child process first. In the common case of the child simply > calling exec() immediately, this eliminates any copy-on-write overhead > that would occur if the parent ran first and began writing to the > address space" > > How does running exec() in child more efficient than having > copy-on-write trigger in the parent? Hi, In order to create a new process (fork), you will copy the whole of relevant info of address space from the parent. Now if the address space is shared and parent runs first for any change it makes, it will need to copy and then modify because it doesn't know if child needs it or not. Since mostly after fork, if you do an exec it is guaranteed that child will not need this address space and the whole of copy can be avoided by making child to run first. (In simple terms you can take decision early whether this address space is useful or not for child). Thanks - Manish > > Let me know if my question is clear, or if I should rephrase. > > Thanks! > -Joel > > -- > To unsubscribe from this list: send an email with > "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx > Please read the FAQ at http://kernelnewbies.org/FAQ > > -- Thanks - Manish ================================== [$\*.^ -- I miss being one of them ================================== -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
