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

NAME
       mbind - set memory policy for a memory range

SYNOPSIS
       #include	<numaif.h>

       long mbind(void *addr, unsigned long len, int mode,
		  const	unsigned long *nodemask, unsigned long maxnode,
		  unsigned flags);

       Link with -lnuma.

DESCRIPTION
       mbind()	sets  the  NUMA	memory policy, which consists of a policy mode
       and zero	or more	nodes, for the memory range  starting  with  addr  and
       continuing  for	len  bytes.  The memory	policy defines from which node
       memory is allocated.

       If the memory range specified by	the addr and len arguments includes an
       "anonymous"  region of memory--that is a	region of memory created using
       the mmap(2) system call	with  the  MAP_ANONYMOUS--or  a	 memory-mapped
       file,  mapped  using the	mmap(2)	system call with the MAP_PRIVATE flag,
       pages will be allocated only according to the specified policy when the
       application  writes  [stores]  to  the page.  For anonymous regions, an
       initial read access will	use a shared page in the kernel	containing all
       zeros.  For a file mapped with MAP_PRIVATE, an initial read access will
       allocate	pages according	to the process	policy	of  the	 process  that
       causes  the  page  to  be  allocated.  This may not be the process that
       called mbind().

       The specified policy will be ignored for	any MAP_SHARED mappings	in the
       specified  memory  range.  Rather the pages will	be allocated according
       to the process policy of	the process that caused	the page to  be	 allo-
       cated.  Again, this may not be the process that called mbind().

       If  the	specified memory range includes	a shared memory	region created
       using the shmget(2) system call and attached using the shmat(2)	system
       call, pages allocated for the anonymous or shared memory	region will be
       allocated according to the policy specified, regardless	which  process
       attached	 to the	shared memory segment causes the allocation.  If, how-
       ever, the shared	memory region was created with the  SHM_HUGETLB	 flag,
       the huge	pages will be allocated	according to the policy	specified only
       if the page allocation is caused	by the process that calls mbind()  for
       that region.

       By  default,  mbind()  has  an  effect only for new allocations;	if the
       pages inside the	range have been	already	 touched  before  setting  the
       policy,	then  the  policy has no effect.  This default behavior	may be
       overridden by the MPOL_MF_MOVE and MPOL_MF_MOVE_ALL flags described be-
       low.

       The mode	argument must specify one of MPOL_DEFAULT, MPOL_BIND, MPOL_IN-
       TERLEAVE, or MPOL_PREFERRED.  All policy	modes except MPOL_DEFAULT  re-
       quire  the  caller  to  specify	via the	nodemask argument, the node or
       nodes to	which the mode applies.

       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 not
	      remap the	nodemask when the process moves	to a different	cpuset
	      context, nor when	the set	of nodes allowed by the	process's cur-
	      rent 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 nodes	containing 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 ig-
       nored.  Where a nodemask	is required, it	must contain at	least one node
       that  is	 on-line, allowed by the process's current cpuset context [un-
       less the	MPOL_F_STATIC_NODES mode flag is specified], and contains mem-
       ory.

       The  MPOL_DEFAULT  mode requests	that any nondefault policy be removed,
       restoring default behavior.  When applied to  a	range  of  memory  via
       mbind(),	 this means to use the process policy, which may have been set
       with set_mempolicy(2).  If the mode  of	the  process  policy  is  also
       MPOL_DEFAULT, the system-wide default policy will be used.  The system-
       wide default policy allocates pages on the node of the CPU  that	 trig-
       gers  the allocation.  For MPOL_DEFAULT,	the nodemask and maxnode argu-
       ments must be specify the empty set of nodes.

       The MPOL_BIND mode specifies a strict policy that restricts memory  al-
       location	 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.

       The MPOL_INTERLEAVE mode	specifies that page allocations	be interleaved
       across the set of nodes specified  in  nodemask.	  This	optimizes  for
       bandwidth instead of latency by spreading out pages and memory accesses
       to those	pages across multiple nodes.  To be effective the memory  area
       should  be  fairly  large, at least 1MB or bigger with a	fairly uniform
       access pattern.	Accesses to a single page of the area  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 other nodes
       if  the	preferred  nodes 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 memory is allocated on the node  of	the  CPU  that
       triggered the allocation.  This is the only way to specify "local allo-
       cation" for a range of memory via mbind().

       If MPOL_MF_STRICT is passed in flags and	mode is	not MPOL_DEFAULT, then
       the call	will fail with the error EIO if	the existing pages in the mem-
       ory range don't follow the policy.

       If MPOL_MF_MOVE is specified in flags, then the kernel will attempt  to
       move all	the existing pages in the memory range so that they follow the
       policy.	Pages that are shared with other processes will	not be	moved.
       If  MPOL_MF_STRICT  is also specified, then the call will fail with the
       error EIO if some pages could not be moved.

       If MPOL_MF_MOVE_ALL is passed in	flags, then the	kernel will attempt to
       move all	existing pages in the memory range regardless of whether other
       processes use the  pages.   The	calling	 process  must	be  privileged
       (CAP_SYS_NICE)  to use this flag.  If MPOL_MF_STRICT is also specified,
       then the	call will fail with the	error EIO if some pages	could  not  be
       moved.

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

ERRORS
       EFAULT Part or all of the memory	range specified	by nodemask and	 maxn-
	      ode points outside your accessible address space.	 Or, there was
	      an unmapped hole in the specified	memory range.

       EINVAL An invalid value was specified for flags or mode;	or addr	+  len
	      was less than addr; or addr is not a multiple of the system page
	      size.   Or,  mode	 is  MPOL_DEFAULT  and	nodemask  specified  a
	      nonempty	set; or	mode is	MPOL_BIND or MPOL_INTERLEAVE and node-
	      mask is empty.  Or, maxnode exceeds a kernel-imposed limit.  Or,
	      nodemask	specifies  one	or more	node IDs that are greater than
	      the maximum supported node ID.  Or, none of the node IDs	speci-
	      fied  by	nodemask are on-line and allowed by the	process's cur-
	      rent cpuset context, or none of the specified nodes contain mem-
	      ory.   Or,  the mode argument specified both MPOL_F_STATIC_NODES
	      and MPOL_F_RELATIVE_NODES.

       EIO    MPOL_MF_STRICT was specified and an existing page	was already on
	      a	 node  that  does  not	follow	the policy; or MPOL_MF_MOVE or
	      MPOL_MF_MOVE_ALL was specified and the kernel was	unable to move
	      all existing pages in the	range.

       ENOMEM Insufficient kernel memory was available.

       EPERM  The  flags  argument  included the MPOL_MF_MOVE_ALL flag and the
	      caller does not have the CAP_SYS_NICE privilege.

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

CONFORMING TO
       This system call	is Linux-specific.

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

       NUMA policy is not supported on a memory-mapped	file  range  that  was
       mapped with the MAP_SHARED flag.

       The  MPOL_DEFAULT  mode	can  have  different  effects  for mbind() and
       set_mempolicy(2).  When MPOL_DEFAULT is specified for set_mempolicy(2),
       the  process's policy reverts to	system default policy or local alloca-
       tion.  When MPOL_DEFAULT	is specified  for  a  range  of	 memory	 using
       mbind(),	 any  pages subsequently allocated for that range will use the
       process's policy, as set	by set_mempolicy(2).  This effectively removes
       the  explicit policy from the specified range, "falling back" to	a pos-
       sibly nondefault	policy.	 To select explicit "local allocation"	for  a
       memory  range,  specify	a  mode	of MPOL_PREFERRED with an empty	set of
       nodes.  This method will	work for set_mempolicy(2), as well.

       Support for huge	page policy was	added  with  2.6.16.   For  interleave
       policy  to be effective on huge page mappings the policied memory needs
       to be tens of megabytes or larger.

       MPOL_MF_STRICT is ignored on huge page mappings.

       MPOL_MF_MOVE and	MPOL_MF_MOVE_ALL are available only  on	 Linux	2.6.16
       and later.

SEE ALSO
       get_mempolicy(2),   getcpu(2),	mmap(2),  set_mempolicy(2),  shmat(2),
       shmget(2), numa(3), cpuset(7), numa(7), numactl(8)

COLOPHON
       This page is part of release 3.74 of the	Linux  man-pages  project.   A
       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       http://www.kernel.org/doc/man-pages/.

Linux				  2014-05-10			      MBIND(2)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

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