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 mem-
       ory 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 pol-
       icy  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 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 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  speci-
	      fied 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 3.27 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)