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



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 set-
       ting 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_mempol-
       icy(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 absense 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 speci-
       fies  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 3.22 of the Linux man-pages project.  A description of the project, and informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                             2008-08-15                  GET_MEMPOLICY(2)