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

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

       #include <numaif.h>

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

       Link with -lnuma.

       set_mempolicy() sets the NUMA memory  policy  of  the  calling  thread,
       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 thread.

       This system call defines the default policy for the thread.  The thread
       policy  governs allocation of pages in the process's address space out-
       side of memory ranges controlled by  a  more  specific  policy  set  by
       mbind(2).   The  thread  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 thread 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 thread.  For anonymous memory
       this is when the page is first touched by the thread.

       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 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 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 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 thread 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 thread memory policy is  preserved  across  an  execve(2),  and  is
       inherited by child threads 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.

       Memory 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 thread or memory
       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 4.04 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

Linux                             2015-05-07                  SET_MEMPOLICY(2)
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