Provided by: freebsd-manpages_12.0-1_all 
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.