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NAME

       get_mempolicy - Retrieve NUMA memory policy for a process

SYNOPSIS

       #include <numaif.h>

       int get_mempolicy(int *mode, unsigned long *nodemask,
                         unsigned long maxnode, unsigned long addr,
                         unsigned long flags);

       Link with -lnuma.

DESCRIPTION

       get_mempolicy()  retrieves the NUMA policy of the calling process or of
       a memory address, depending on the setting of flags.

       A  NUMA  machine  has  different  memory  controllers  with   different
       distances  to specific CPUs.  The memory policy defines from which node
       memory is allocated for the process.

       If flags  is  specified  as  0,  then  information  about  the  calling
       process's default policy (as set by set_mempolicy(2)) is returned.  The
       policy returned  [mode  and  nodemask]  may  be  used  to  restore  the
       process's   policy   to   its   state  at  the  time  of  the  call  to
       get_mempolicy() using set_mempolicy(2).

       If flags specifies MPOL_F_MEMS_ALLOWED (available since Linux  2.6.24),
       the  mode  argument is ignored and the set of nodes [memories] that the
       process is allowed to  specify  in  subsequent  calls  to  mbind(2)  or
       set_mempolicy(2)  [in  the  absence  of  any mode flags] is returned in
       nodemask.  It is not  permitted  to  combine  MPOL_F_MEMS_ALLOWED  with
       either MPOL_F_ADDR or MPOL_F_NODE.

       If  flags specifies MPOL_F_ADDR, then information is returned about the
       policy governing the memory address given in addr.  This policy may  be
       different  from  the process's default policy if mbind(2) or one of the
       helper functions described in numa(3) has  been  used  to  establish  a
       policy for the memory range containing addr.

       If  the  mode argument is not NULL, then get_mempolicy() will store the
       policy mode and any optional mode flags of the requested NUMA policy in
       the  location  pointed  to  by this argument.  If nodemask is not NULL,
       then the nodemask associated with the policy  will  be  stored  in  the
       location  pointed to by this argument.  maxnode specifies the number of
       node IDs that can be stored into nodemask--that is, the maximum node ID
       plus  one.   The  value  specified  by  maxnode  is always rounded to a
       multiple of sizeof(unsigned long).

       If flags specifies both MPOL_F_NODE  and  MPOL_F_ADDR,  get_mempolicy()
       will  return  the  node  ID  of  the  node on which the address addr is
       allocated into the location pointed to by mode.  If  no  page  has  yet
       been allocated for the specified address, get_mempolicy() will allocate
       a page as if the process had performed a read  [load]  access  to  that
       address, and return the ID of the node where that page was allocated.

       If  flags specifies MPOL_F_NODE, but not MPOL_F_ADDR, and the process's
       current policy is MPOL_INTERLEAVE, then get_mempolicy() will return  in
       the location pointed to by a non-NULL mode argument, the node ID of the
       next node that will be used for interleaving of internal  kernel  pages
       allocated  on  behalf  of the process.  These allocations include pages
       for memory mapped files in  process  memory  ranges  mapped  using  the
       mmap(2) call with the MAP_PRIVATE flag for read accesses, and in memory
       ranges mapped with the MAP_SHARED flag for all accesses.

       Other flag values are reserved.

       For an overview of the possible policies see set_mempolicy(2).

RETURN VALUE

       On success, get_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
              maxnode points outside your accessible address space.

       EINVAL The value specified by maxnode is less than the number  of  node
              IDs  supported  by  the system.  Or flags specified values other
              than MPOL_F_NODE or MPOL_F_ADDR; or flags specified  MPOL_F_ADDR
              and  addr is NULL, or flags did not specify MPOL_F_ADDR and addr
              is  not  NULL.   Or,  flags  specified   MPOL_F_NODE   but   not
              MPOL_F_ADDR    and   the   current   process   policy   is   not
              MPOL_INTERLEAVE.  Or, flags specified  MPOL_F_MEMS_ALLOWED  with
              either  MPOL_F_ADDR or MPOL_F_NODE.  (And there are other EINVAL
              cases.)

VERSIONS

       The get_mempolicy() 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).

SEE ALSO

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

COLOPHON

       This page is part of release 3.35 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
       be found at http://man7.org/linux/man-pages/.