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 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 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 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_mem-
       policy() 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 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2008-08-15                                           GET_MEMPOLICY(2)