NAME

     NUMA — Non-Uniform Memory Access

SYNOPSIS

     options MAXMEMDOM
     options NUMA

DESCRIPTION

     Non-Uniform Memory Access is a computer architecture design which involves unequal costs
     between processors, memory and IO devices in a given system.

     In a NUMA architecture, the latency to access specific memory or IO devices depends upon
     which processor the memory or device is attached to.  Accessing memory local to a processor
     is faster than accessing memory that is connected to one of the other processors.  FreeBSD
     implements NUMA-aware memory allocation policies.  By default it attempts to ensure that
     allocations are balanced across each domain.  Users may override the default domain
     selection policy using cpuset(1).

     NUMA support is enabled when the NUMA option is specified in the kernel configuration file.
     Each platform defines the MAXMEMDOM constant, which specifies the maximum number of
     supported NUMA domains.  This constant may be specified in the kernel configuration file.
     NUMA support can be disabled at boot time by setting the vm.numa.disabled tunable to 1.
     Other values for this tunable are currently ignored.

     Thread and process NUMA policies are controlled with the cpuset_getdomain(2) and
     cpuset_setdomain(2) syscalls.  The cpuset(1) tool is available for starting processes with a
     non-default policy, or to change the policy of an existing thread or process.

     Systems with non-uniform access to I/O devices may mark those devices with the local VM
     domain identifier.  Drivers can find out their local domain information by calling
     bus_get_domain(9).

   MIB Variables
     The operation of NUMA is controlled and exposes information with these sysctl(8) MIB
     variables:

     vm.ndomains
             The number of VM domains which have been detected.

     vm.phys_locality
             A table indicating the relative cost of each VM domain to each other.  A value of 10
             indicates equal cost.  A value of -1 means the locality map is not available or no
             locality information is available.

     vm.phys_segs
             The map of physical memory, grouped by VM domain.

IMPLEMENTATION NOTES

     The current NUMA implementation is VM-focused.  The hardware NUMA domains are mapped into a
     contiguous, non-sparse VM domain space, starting from 0.  Thus, VM domain information (for
     example, the domain identifier) is not necessarily the same as is found in the hardware
     specific information.  Policy information is available in both struct thread and struct
     proc.

SEE ALSO

     cpuset(1), cpuset_getaffinity(2), cpuset_setaffinity(2), bus_get_domain(9)

HISTORY

     NUMA first appeared in FreeBSD 9.0 as a first-touch allocation policy with a fail-over to
     round-robin allocation and was not configurable.  It was then modified in FreeBSD 10.0 to
     implement a round-robin allocation policy and was also not configurable.

     The numa_getaffinity(2) and numa_setaffinity(2) syscalls and the numactl(1) tool first
     appeared in FreeBSD 11.0 and were removed in FreeBSD 12.0.  The current implementation
     appeared in FreeBSD 12.0.

AUTHORS

     This manual page written by Adrian Chadd <adrian@FreeBSD.org>.

NOTES

     No statistics are kept to indicate how often NUMA allocation policies succeed or fail.