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

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

SYNOPSIS
       #include <numaif.h>

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

       Link with -lnuma.

DESCRIPTION
       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 distances 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  alloca-
       tion  of any pages for memory mapped files mapped using the mmap(2) call with the MAP_PRI-
       VATE 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	anonymous
       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 node-
       mask argument one or more nodes.

       The mode argument may also include an optional mode flag.  The supported 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 different 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  pol-
       icy  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 policy be  removed,  so
       that the memory policy "falls back" to the system default policy.  The system default pol-
       icy is "local allocation"-- i.e., allocate memory on the node of the  CPU  that	triggered
       the allocation.	nodemask must be specified as NULL.  If the "local node" contains 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 allocation 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.	 Allocations 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 specifies 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 pro-
       cesses created using fork(2) or clone(2).

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

ERRORS
       EFAULT Part  of	all  of the memory range specified by nodemask and maxnode 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
	      MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES.

       ENOMEM Insufficient kernel memory was available.

VERSIONS
       The set_mempolicy(), system call was added to the Linux kernel in version 2.6.7.

CONFORMING TO
       This system call is Linux-specific.

NOTES
       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 memory range that is in effect at the
       time the page is allocated.

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

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

COLOPHON
       This page is part of release 3.55 of the Linux man-pages project.  A  description  of  the
       project,     and    information	  about    reporting	bugs,	 can	be    found    at
       http://www.kernel.org/doc/man-pages/.

Linux					    2008-08-15				 SET_MEMPOLICY(2)
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