NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

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

NAME         top

       mbind - set memory policy for a memory range

SYNOPSIS         top

       #include <numaif.h>

       long mbind(void *addr, unsigned long len, int mode,
                  const unsigned long *nodemask, unsigned long maxnode,
                  unsigned flags);

       Link with -lnuma.

DESCRIPTION         top

       mbind() sets the NUMA memory policy, which consists of a policy mode
       and zero or more nodes, for the memory range starting with addr and
       continuing for len bytes.  The memory policy defines from which node
       memory is allocated.

       If the memory range specified by the addr and len arguments includes
       an "anonymous" region of memory—that is a region of memory created
       using the mmap(2) system call with the MAP_ANONYMOUS—or a memory-
       mapped file, mapped using the mmap(2) system call with the
       MAP_PRIVATE flag, pages will be allocated only according to the
       specified policy when the application writes (stores) to the page.
       For anonymous regions, an initial read access will use a shared page
       in the kernel containing all zeros.  For a file mapped with
       MAP_PRIVATE, an initial read access will allocate pages according to
       the memory policy of the thread that causes the page to be allocated.
       This may not be the thread that called mbind().

       The specified policy will be ignored for any MAP_SHARED mappings in
       the specified memory range.  Rather the pages will be allocated
       according to the memory policy of the thread that caused the page to
       be allocated.  Again, this may not be the thread that called mbind().

       If the specified memory range includes a shared memory region created
       using the shmget(2) system call and attached using the shmat(2)
       system call, pages allocated for the anonymous or shared memory
       region will be allocated according to the policy specified,
       regardless of which process attached to the shared memory segment
       causes the allocation.  If, however, the shared memory region was
       created with the SHM_HUGETLB flag, the huge pages will be allocated
       according to the policy specified only if the page allocation is
       caused by the process that calls mbind() for that region.

       By default, mbind() has an effect only for new allocations; if the
       pages inside the range have been already touched before setting the
       policy, then the policy has no effect.  This default behavior may be
       overridden by the MPOL_MF_MOVE and MPOL_MF_MOVE_ALL flags described
       below.

       The mode argument must specify one of MPOL_DEFAULT, MPOL_BIND,
       MPOL_INTERLEAVE, MPOL_PREFERRED, or MPOL_LOCAL (which are described
       in detail below).  All policy modes except MPOL_DEFAULT require the
       caller to specify the node or nodes to which the mode applies, via
       the nodemask argument.

       The mode argument may also include an optional mode flag.  The
       supported mode flags are:

       MPOL_F_STATIC_NODES (since Linux-2.6.26)
              A nonempty nodemask specifies physical node IDs.  Linux does
              not remap the nodemask when the thread moves to a different
              cpuset context, nor when the set of nodes allowed by the
              thread's current cpuset context changes.

       MPOL_F_RELATIVE_NODES (since Linux-2.6.26)
              A nonempty nodemask specifies node IDs that are relative to
              the set of node IDs allowed by the thread's current cpuset.

       nodemask points to a bit mask of nodes containing up to maxnode bits.
       The bit mask size is rounded to the next multiple of sizeof(unsigned
       long), but the kernel will use bits only up to maxnode.  A NULL value
       of nodemask or a maxnode value of zero specifies the empty set of
       nodes.  If the value of maxnode is zero, the nodemask argument is
       ignored.  Where a nodemask is required, it must contain at least one
       node that is on-line, allowed by the thread's current cpuset context
       (unless the MPOL_F_STATIC_NODES mode flag is specified), and contains
       memory.

       The mode argument must include one of the following values:

       MPOL_DEFAULT
              This mode requests that any nondefault policy be removed,
              restoring default behavior.  When applied to a range of memory
              via mbind(), this means to use the thread memory policy, which
              may have been set with set_mempolicy(2).  If the mode of the
              thread memory policy is also MPOL_DEFAULT, the system-wide
              default policy will be used.  The system-wide default policy
              allocates pages on the node of the CPU that triggers the
              allocation.  For MPOL_DEFAULT, the nodemask and maxnode
              arguments must be specify the empty set of nodes.

       MPOL_BIND
              This mode specifies a strict policy that restricts memory
              allocation to the nodes specified in nodemask.  If nodemask
              specifies more than one node, page allocations will come from
              the node with sufficient free memory that is closest to the
              node where the allocation takes place.  Pages will not be
              allocated from any node not specified in the IR nodemask .
              (Before Linux 2.6.26, page allocations came from the node with
              the lowest numeric node ID first, until that node contained no
              free memory.  Allocations then came from the node with the
              next highest node ID specified in nodemask and so forth, until
              none of the specified nodes contained free memory.)

       MPOL_INTERLEAVE
              This mode specifies that page allocations be interleaved
              across the set of nodes specified in nodemask.  This optimizes
              for bandwidth instead of latency by spreading out pages and
              memory accesses to those pages across multiple nodes.  To be
              effective the memory area should be fairly large, at least 1MB
              or bigger with a fairly uniform access pattern.  Accesses to a
              single page of the area will still be limited to the memory
              bandwidth of a single node.

       MPOL_PREFERRED
              This mode sets the preferred node for allocation.  The kernel
              will try to allocate pages from this node first and fall back
              to other nodes if the preferred nodes is low on free memory.
              If nodemask specifies more than one node ID, the first node in
              the mask will be selected as the preferred node.  If the
              nodemask and maxnode arguments specify the empty set, then the
              memory is allocated on the node of the CPU that triggered the
              allocation.

       MPOL_LOCAL (since Linux 3.8)
              This mode specifies "local allocation"; the memory is
              allocated on the node of the CPU that triggered the allocation
              (the "local node").  The nodemask and maxnode arguments must
              specify the empty set.  If the "local node" is low on free
              memory, the kernel will try to allocate memory from other
              nodes.  The kernel will allocate memory from the "local node"
              whenever memory for this node is available.  If the "local
              node" is not allowed by the thread's current cpuset context,
              the kernel will try to allocate memory from other nodes.  The
              kernel will allocate memory from the "local node" whenever it
              becomes allowed by the thread's current cpuset context.  By
              contrast, MPOL_DEFAULT reverts to the memory policy of the
              thread (which may be set via set_mempolicy(2)); that policy
              may be something other than "local allocation".

       If MPOL_MF_STRICT is passed in flags and mode is not MPOL_DEFAULT,
       then the call will fail with the error EIO if the existing pages in
       the memory range don't follow the policy.

       If MPOL_MF_MOVE is specified in flags, then the kernel will attempt
       to move all the existing pages in the memory range so that they
       follow the policy.  Pages that are shared with other processes will
       not be moved.  If MPOL_MF_STRICT is also specified, then the call
       will fail with the error EIO if some pages could not be moved.

       If MPOL_MF_MOVE_ALL is passed in flags, then the kernel will attempt
       to move all existing pages in the memory range regardless of whether
       other processes use the pages.  The calling thread must be privileged
       (CAP_SYS_NICE) to use this flag.  If MPOL_MF_STRICT is also
       specified, then the call will fail with the error EIO if some pages
       could not be moved.

RETURN VALUE         top

       On success, mbind() returns 0; on error, -1 is returned and errno is
       set to indicate the error.

ERRORS         top

       EFAULT Part or all of the memory range specified by nodemask and
              maxnode points outside your accessible address space.  Or,
              there was an unmapped hole in the specified memory range
              specified by addr and len.

       EINVAL An invalid value was specified for flags or mode; or addr +
              len was less than addr; or addr is not a multiple of the
              system page size.  Or, mode is MPOL_DEFAULT and nodemask
              specified a nonempty set; or mode is MPOL_BIND or
              MPOL_INTERLEAVE and nodemask is empty.  Or, maxnode exceeds a
              kernel-imposed limit.  Or, nodemask specifies one or more node
              IDs that are greater than the maximum supported node ID.  Or,
              none of the node IDs specified by nodemask are on-line and
              allowed by the thread's current cpuset context, or none of the
              specified nodes contain memory.  Or, the mode argument
              specified both MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES.

       EIO    MPOL_MF_STRICT was specified and an existing page was already
              on a node that does not follow the policy; or MPOL_MF_MOVE or
              MPOL_MF_MOVE_ALL was specified and the kernel was unable to
              move all existing pages in the range.

       ENOMEM Insufficient kernel memory was available.

       EPERM  The flags argument included the MPOL_MF_MOVE_ALL flag and the
              caller does not have the CAP_SYS_NICE privilege.

VERSIONS         top

       The mbind() system call was added to the Linux kernel in version
       2.6.7.

CONFORMING TO         top

       This system call is Linux-specific.

NOTES         top

       For information on library support, see numa(7).

       NUMA policy is not supported on a memory-mapped file range that was
       mapped with the MAP_SHARED flag.

       The MPOL_DEFAULT mode can have different effects for mbind() and
       set_mempolicy(2).  When MPOL_DEFAULT is specified for
       set_mempolicy(2), the thread's memory policy reverts to the system
       default policy or local allocation.  When MPOL_DEFAULT is specified
       for a range of memory using mbind(), any pages subsequently allocated
       for that range will use the thread's memory policy, as set by
       set_mempolicy(2).  This effectively removes the explicit policy from
       the specified range, "falling back" to a possibly nondefault policy.
       To select explicit "local allocation" for a memory range, specify a
       mode of MPOL_LOCAL or MPOL_PREFERRED with an empty set of nodes.
       This method will work for set_mempolicy(2), as well.

       Support for huge page policy was added with 2.6.16.  For interleave
       policy to be effective on huge page mappings the policied memory
       needs to be tens of megabytes or larger.

       MPOL_MF_STRICT is ignored on huge page mappings.

       MPOL_MF_MOVE and MPOL_MF_MOVE_ALL are available only on Linux 2.6.16
       and later.

SEE ALSO         top

       get_mempolicy(2), getcpu(2), mmap(2), set_mempolicy(2), shmat(2),
       shmget(2), numa(3), cpuset(7), numa(7), numactl(8)

COLOPHON         top

       This page is part of release 4.10 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                            2016-12-12                         MBIND(2)