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(libc.info)Why Lock Pages

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Why Lock Pages
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   Because page faults cause paged out pages to be paged in
transparently, a process rarely needs to be concerned about locking
pages.  However, there are two reasons people sometimes are:

   * Speed.  A page fault is transparent only insofar as the process is
     not sensitive to how long it takes to do a simple memory access.
     Time-critical processes, especially realtime processes, may not be
     able to wait or may not be able to tolerate variance in execution
     speed.

     A process that needs to lock pages for this reason probably also
     needs priority among other processes for use of the CPU.  Note:
     Priority.

     In some cases, the programmer knows better than the system's demand
     paging allocator which pages should remain in real memory to
     optimize system performance.  In this case, locking pages can help.

   * Privacy.  If you keep secrets in virtual memory and that virtual
     memory gets paged out, that increases the chance that the secrets
     will get out.  If a password gets written out to disk swap space,
     for example, it might still be there long after virtual and real
     memory have been wiped clean.


   Be aware that when you lock a page, that's one fewer page frame that
can be used to back other virtual memory (by the same or other
processes), which can mean more page faults, which means the system
runs more slowly.  In fact, if you lock enough memory, some programs
may not be able to run at all for lack of real memory.