get_mempolicy

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



NAME
       get_mempolicy - retrieve NUMA memory policy for a thread

SYNOPSIS
       #include <numaif.h>

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

       Link with -lnuma.

DESCRIPTION
       get_mempolicy() retrieves the NUMA policy of the calling thread 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 thread.

       If flags is specified as 0, then information about the calling thread's
       default policy (as set by set_mempolicy(2)) is returned, in the buffers
       pointed to by mode and nodemask.  The value returned in these arguments
       may be used to restore the thread's policy to its state at the time of
       the call to get_mempolicy() using set_mempolicy(2).  When flags is 0,
       addr must be specified as NULL.

       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
       thread 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 thread'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)*8.

       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 thread 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 thread'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 thread.  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 thread 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 5.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at
       https://www.kernel.org/doc/man-pages/.



Linux                             2017-09-15                  GET_MEMPOLICY(2)