get_mempolicy


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  dis-
       tances  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_mempol-
       icy() 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 pol-
       icy 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 multi-
       ple 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 allo-
       cated 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

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 maxn-
              ode 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_INTER-
              LEAVE.  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 ver-
       sion 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/.



Linux                             2008-08-15                  GET_MEMPOLICY(2)
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