set_mempolicy man page on Archlinux

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SET_MEMPOLICY(2)	   Linux Programmer's Manual	      SET_MEMPOLICY(2)

       set_mempolicy  -	 set  default NUMA memory policy for a process and its

       #include <numaif.h>

       int set_mempolicy(int mode, unsigned long *nodemask,
			 unsigned long maxnode);

       Link with -lnuma.

       set_mempolicy() sets the NUMA memory policy  of	the  calling  process,
       which  consists	of a policy mode and zero or more nodes, to the values
       specified by the mode, nodemask and maxnode arguments.

       A NUMA machine has different memory  controllers	 with  different  dis‐
       tances  to  specific  CPUs.   The memory policy defines from which node
       memory is allocated for the process.

       This system call defines the  default  policy  for  the	process.   The
       process	policy	governs	 allocation  of pages in the process's address
       space outside of memory ranges controlled by a more specific policy set
       by  mbind(2).   The  process default policy also controls allocation of
       any pages for memory-mapped files mapped using the  mmap(2)  call  with
       the  MAP_PRIVATE	 flag  and  that  are  only  read [loaded] from by the
       process and of memory-mapped files mapped using the mmap(2)  call  with
       the  MAP_SHARED	flag,  regardless  of  the access type.	 The policy is
       applied only when a new page is allocated for the process.  For	anony‐
       mous memory this is when the page is first touched by the application.

       The   mode  argument  must  specify  one	 of  MPOL_DEFAULT,  MPOL_BIND,
       MPOL_INTERLEAVE, or  MPOL_PREFERRED.   All  modes  except  MPOL_DEFAULT
       require	the  caller  to	 specify via the nodemask argument one or more

       The mode argument may also include an optional  mode  flag.   The  sup‐
       ported mode flags are:

       MPOL_F_STATIC_NODES (since Linux 2.6.26)
	      A	 nonempty  nodemask  specifies	physical node ids.  Linux does
	      will not remap the nodemask when the process moves to a  differ‐
	      ent  cpuset  context,  nor  when the set of nodes allowed by the
	      process's current cpuset context changes.

       MPOL_F_RELATIVE_NODES (since Linux 2.6.26)
	      A nonempty nodemask specifies node ids that are relative to  the
	      set of node ids allowed by the process's current cpuset.

       nodemask	 points	 to a bit mask of node IDs that contains up to maxnode
       bits.   The  bit	 mask  size  is	 rounded  to  the  next	 multiple   of
       sizeof(unsigned long), but the kernel will use bits only up to maxnode.
       A NULL value of nodemask or a maxnode value of zero specifies the empty
       set  of	nodes.	If the value of maxnode is zero, the nodemask argument
       is ignored.

       Where a nodemask is required, it must contain at least one node that is
       on-line,	 allowed  by the process's current cpuset context, [unless the
       MPOL_F_STATIC_NODES mode flag is specified], and contains  memory.   If
       the MPOL_F_STATIC_NODES is set in mode and a required nodemask contains
       no nodes that are allowed by the process's current cpuset context,  the
       memory  policy reverts to local allocation.  This effectively overrides
       the specified policy until the process's cpuset context includes one or
       more of the nodes specified by nodemask.

       The MPOL_DEFAULT mode specifies that any nondefault process memory pol‐
       icy be removed, so that the memory policy "falls back"  to  the	system
       default	policy.	  The system default policy is "local allocation"—that
       is, allocate memory on the node of the CPU that triggered  the  alloca‐
       tion.   nodemask	 must  be specified as NULL.  If the "local node" con‐
       tains no free memory, the system will attempt to allocate memory from a
       "near by" node.

       The  MPOL_BIND mode defines a strict policy that restricts memory allo‐
       cation to the nodes specified in nodemask.  If nodemask specifies  more
       than one node, page allocations will come from the node with the lowest
       numeric node ID first, until that node contains no free memory.	 Allo‐
       cations	will  then  come  from	the node with the next highest node ID
       specified in nodemask and so forth, until none of the  specified	 nodes
       contain	free  memory.	Pages  will not be allocated from any node not
       specified in the nodemask.

       MPOL_INTERLEAVE interleaves page allocations across the nodes specified
       in  nodemask  in	 numeric  node ID order.  This optimizes for bandwidth
       instead of latency by spreading out pages and memory accesses to	 those
       pages  across  multiple nodes.  However, accesses to a single page will
       still be limited to the memory bandwidth of a single node.

       MPOL_PREFERRED sets the preferred node for allocation.  The kernel will
       try  to	allocate pages from this node first and fall back to "near by"
       nodes if the preferred node is low on free memory.  If nodemask	speci‐
       fies more than one node ID, the first node in the mask will be selected
       as the preferred node.  If the nodemask and maxnode  arguments  specify
       the  empty  set, then the policy specifies "local allocation" (like the
       system default policy discussed above).

       The process memory policy is preserved  across  an  execve(2),  and  is
       inherited by child processes created using fork(2) or clone(2).

       On  success,  set_mempolicy()  returns  0; on error, -1 is returned and
       errno is set to indicate the error.

       EFAULT Part of all of the memory range specified by nodemask and	 maxn‐
	      ode points outside your accessible address space.

       EINVAL mode  is	invalid.   Or,	mode  is  MPOL_DEFAULT and nodemask is
	      nonempty, or mode is MPOL_BIND or MPOL_INTERLEAVE	 and  nodemask
	      is empty.	 Or, maxnode specifies more than a page worth of bits.
	      Or, nodemask specifies one or more node  IDs  that  are  greater
	      than  the	 maximum  supported node ID.  Or, none of the node IDs
	      specified by nodemask are on-line and allowed by	the  process's
	      current  cpuset  context, or none of the specified nodes contain
	      memory.	  Or,	 the	mode	argument    specified	  both

       ENOMEM Insufficient kernel memory was available.

       The  set_mempolicy(), system call was added to the Linux kernel in ver‐
       sion 2.6.7.

       This system call is Linux-specific.

       Process policy is not remembered if the page is swapped out.  When such
       a  page is paged back in, it will use the policy of the process or mem‐
       ory range that is in effect at the time the page is allocated.

       For information on library support, see numa(7).

       get_mempolicy(2), getcpu(2),  mbind(2),	mmap(2),  numa(3),  cpuset(7),
       numa(7), numactl(8)

       This  page  is  part of release 3.65 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at

Linux				  2008-08-15		      SET_MEMPOLICY(2)

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