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 memory policy of the thread that causes
   the  page  to  be  allocated.   This  may not be the thread 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 memory  policy  of  the  thread  that  caused  the  page  to  be
   allocated.  Again, this may not be the thread 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  of  which
   process  attached  to  the shared memory segment causes the allocation.
   If, however, 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
   below.

   The   mode  argument  must  specify  one  of  MPOL_DEFAULT,  MPOL_BIND,
   MPOL_INTERLEAVE, MPOL_PREFERRED, or MPOL_LOCAL (which are described  in
   detail below).  All policy modes except MPOL_DEFAULT require the caller
   to specify the node or  nodes  to  which  the  mode  applies,  via  the
   nodemask argument.

   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 not
          remap  the  nodemask when the thread moves to a different cpuset
          context, nor when the set  of  nodes  allowed  by  the  thread'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 thread'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
   ignored.   Where  a  nodemask is required, it must contain at least one
   node that is on-line, allowed by the thread's  current  cpuset  context
   (unless  the  MPOL_F_STATIC_NODES mode flag is specified), and contains
   memory.

   The mode argument must include one of the following values: 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 thread memory policy,  which  may
          have  been set with set_mempolicy(2).  If the mode of the thread
          memory 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 triggers the allocation.   For
          MPOL_DEFAULT, the nodemask and maxnode arguments must be specify
          the empty set of nodes.

   MPOL_BIND
          This mode  specifies  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
          This 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
          This  mode  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.

   MPOL_LOCAL (since Linux 3.8)
          This  mode specifies "local allocation"; the memory is allocated
          on the node of the CPU that triggered the allocation (the "local
          node").   The  nodemask  and  maxnode arguments must specify the
          empty set.  If the "local node"  is  low  on  free  memory,  the
          kernel will try to allocate memory from other nodes.  The kernel
          will allocate memory from the "local node" whenever  memory  for
          this  node  is available.  If the "local node" is not allowed by
          the thread's current cpuset context,  the  kernel  will  try  to
          allocate  memory  from  other  nodes.   The kernel will allocate
          memory from the "local node" whenever it becomes allowed by  the
          thread's  current  cpuset  context.   By  contrast, MPOL_DEFAULT
          reverts to the memory policy of the thread (which may be set via
          set_mempolicy(2));  that  policy  may  be  something  other than
          "local allocation".

   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
   memory 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  thread  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
          maxnode points outside your accessible address space.  Or, there
          was an unmapped hole in the specified memory range specified  by
          addr and len.

   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
          nodemask  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
          specified by nodemask are on-line and allowed  by  the  thread'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.

   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 thread's memory policy reverts to  the  system  default  policy  or
   local allocation.  When MPOL_DEFAULT is specified for a range of memory
   using mbind(), any pages subsequently allocated for that range will use
   the   thread's   memory  policy,  as  set  by  set_mempolicy(2).   This
   effectively removes the  explicit  policy  from  the  specified  range,
   "falling  back"  to  a  possibly nondefault policy.  To select explicit
   "local allocation" for a memory range, specify a mode of MPOL_LOCAL  or
   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 4.09 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
   https://www.kernel.org/doc/man-pages/.





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