SYSCTL TUNING
     sysctl(8) variables permit    system behavior    to be monitored    and controlled
     at    run-time.  Some    sysctls    simply report on the behavior of the system;
     others allow the system behavior to be modified; some may be set at boot
     time using    rc.conf(5), but    most will be set via sysctl.conf(5).  There
     are several hundred sysctls in the    system,    including many that appear to
     be    candidates for tuning but actually are not.  In    this document we will
     only cover    the ones that have the greatest    effect on the system.

     The vm.overcommit sysctl defines the overcommit behaviour of the vm sub-
     system.  The virtual memory system    always does accounting of the swap
     space reservation,    both total for system and per-user.  Corresponding
     values are    available through sysctl vm.swap_total,    that gives the total
     bytes available for swapping, and vm.swap_reserved, that gives number of
     bytes that    may be needed to back all currently allocated anonymous    mem-
     ory.

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