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    Command:

    set_mempolicy

    
    
    
    

    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  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  pro-
           cess  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 anonymous  mem-
           ory 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
           nodes.
    
           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, 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).
    
    
    

    RETURN VALUE

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

    ERRORS

           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
                  MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES.
    
           ENOMEM Insufficient kernel memory was available.
    
    
    

    VERSIONS

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

    Linux 2008-08-15 SET_MEMPOLICY(2)

    
    
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