Minimizing Paging Activity

Many of the mechanisms discussed in the previous section, "Maximizing Shareability", will help reduce the amount of paging encountered when using shared objects. Here some additional generic software performance considerations are covered.

Any process that accesses a new page will cause a page fault. As this is an expensive operation, and because shared objects can be used by many processes, any reduction in the number of page faults generated by accessing a shared object will benefit the process and the system as a whole.

Organizing frequently used routines and their data to an adjacent set of pages will frequently improve performance because it improves the locality of reference. When a process calls one of these functions, it might already be in memory because of its proximity to the other frequently used functions. Similarly, grouping interrelated functions will improve locality of references. For example, if every call to the function foo() results in a call to the function bar(), place these functions on the same page. Tools like cflow(1), tcov(1), prof(1) and gprof(1) are useful in determining code coverage and profiling.

It is also advisable to isolate related functionality to its own shared object. The standard C library has historically been built containing many unrelated functions, and only rarely, for example, will any single executable use everything in this library. Because of its widespread use, it is also somewhat difficult to determine what set of functions are really the most frequently used. In contrast, when designing a shared object from scratch, it is better to maintain only related functions within the shared object. This will improve locality of reference and usually has the side effect of reducing the object's overall size.