mbind

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



NAME
       mbind - set memory policy for a memory range

SYNOPSIS
       #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
       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 1 MB 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 fails 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 fails 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 fails with the error EIO if some pages could not be
       moved.

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

ERRORS
       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
       The mbind() 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).

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

COLOPHON
       This page is part of release 5.03 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                          MBIND(2)