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_IN-
       TERLEAVE, MPOL_PREFERRED, or MPOL_LOCAL (which are described in  detail
       below).   All  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  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(un-
       signed  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-

       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 mode argument must include one of the following values:

              This  mode specifies that any nondefault thread memory policy be
              removed, so that the memory policy "falls back"  to  the  system
              default  policy.   The  system  default policy is "local alloca-
              tion"--that is, 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 at-
              tempt to allocate memory from a "near by" node.

              This  mode defines a strict policy that restricts memory alloca-
              tion 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, un-
              til none of the specified nodes contain free memory.  Pages will
              not be allocated from any node not specified in the nodemask.

              This mode interleaves page allocations across the  nodes  speci-
              fied  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, ac-
              cesses to a single page will still  be  limited  to  the  memory
              bandwidth of a single node.

              This  mode  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).

       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 ker-
              nel 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 process's current cpuset context, the kernel will try to al-
              locate memory from other nodes.  The kernel will allocate memory
              from  the  "local  node"  whenever  it  becomes  allowed  by the
              process's current cpuset context.

       The thread memory policy is preserved across an execve(2), and  is  in-
       herited by child threads created using fork(2) or clone(2).

       On success, set_mempolicy() returns 0; on error, -1 is returned and er-
       rno 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 5.05 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                             2017-09-15                  SET_MEMPOLICY(2)
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