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NUMA(4)		       FreeBSD Kernel Interfaces Manual		       NUMA(4)

     NUMA -- Non-Uniform Memory	Access

     options SMP
     options MAXMEMDOM=16

     #include <sys/numa.h>
     #include <sys/cpuset.h>
     #include <sys/bus.h>

     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.

     NUMA is enabled when the MAXMEMDOM	option is used in a kernel configura-
     tion file and is set to a value greater than 1.

     Thread and	process	NUMA policies are controlled with the
     numa_setaffinity(2) and numa_getaffinity(2) syscalls.

     The numactl(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:

	     The number	of VM domains which have been detected.

	     The default VM domain allocation policy.  Defaults	to "first-
	     touch-rr".	 The valid values are "first-touch", "first-touch-rr",
	     "rr", where "rr" is a short-hand for "round-robin."  See
	     numa_setaffinity(2) for more information about the	available

	     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

	     The map of	physical memory, grouped by VM domain.

     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 informa-

     The NUMA allocation policies are implemented as a policy and iterator in
     sys/vm/vm_domain.c	and sys/vm/vm_domain.h.	 Policy	information is avail-
     able in both struct thread	and struct proc.  Processes inherit NUMA pol-
     icy from parent processes and threads inherit NUMA	policy from parent
     threads.  Note that threads do not	explicitly inherit their NUMA policy
     from processes.  Instead, if no thread policy is set, the system will
     fall back to the process policy.

     For now, NUMA domain policies only	influence physical page	allocation in
     sys/vm/vm_phys.c.	This is	useful for userland memory allocation, but not
     for kernel	and driver memory allocation.  These features will be imple-
     mented in future work.

     numactl(1), numa_getaffinity(2), numa_setaffinity(2), bus_get_domain(9)

     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 first appeared
     in	FreeBSD	11.0.

     The numactl(1) tool first appeared	in FreeBSD 11.0.

     This manual page written by Adrian	Chadd <>.

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

FreeBSD	11.1			 May 10, 2015			  FreeBSD 11.1


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