MBIND(2) Linux Programmer's Manual MBIND(2)
mbind - set memory policy for a memory range
int mbind(void *addr, unsigned long len, int mode,
unsigned long *nodemask, unsigned long maxnode,
Link with -lnuma.
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 process policy of the process that causes the page to be allocated. This may not be the
process 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 accord-
ing to the process policy of the process that caused the page to be allocated. Again, this may not be the process 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) sys-
tem call, pages allocated for the anonymous or shared memory region will be allocated according to the policy specified, regardless 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 pol-
icy, then the policy has no effect. This default behavior may be overridden by the MPOL_MF_MOVE and MPOL_MF_MOVE_ALL flags described
The mode argument must specify one of MPOL_DEFAULT, MPOL_BIND, MPOL_INTERLEAVE or MPOL_PREFERRED. All policy modes except MPOL_DEFAULT
require the caller to specify via the nodemask argument, the node or nodes to which the mode applies.
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 process moves to a different cpuset
context, nor when the set of nodes allowed by the process'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 process'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 process's current cpuset context [unless the MPOL_F_STATIC_NODES mode flag is specified], and contains mem-
The MPOL_DEFAULT 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 process policy, which may have been set with set_mempolicy(2). If the mode of the process 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.
The MPOL_BIND 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 the lowest numeric node ID first, until that node contains no free mem-
ory. Allocations will then come from the node with the next highest node ID specified in nodemask and so forth, until none of the speci-
fied nodes contain free memory. Pages will not be allocated from any node not specified in the nodemask.
The MPOL_INTERLEAVE 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 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. This is the only way to specify "local allocation" for a range of memory via mbind().
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 process must be privileged (CAP_SYS_NICE) to use this flag. If MPOL_MF_STRICT is also speci-
fied, then the call will fail with the error EIO if some pages could not be moved.
On success, mbind() returns 0; on error, -1 is returned and errno is set to indicate the error.
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.
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 process'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.
The mbind() system call was added to the Linux kernel in version 2.6.7.
This system call is Linux-specific.
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 process's policy reverts to 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 process's 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 alloca-
tion" for a memory range, specify a mode of MPOL_PREFERRED with an empty set of nodes. This method will work for set_mempolicy(2), as
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.
get_mempolicy(2), getcpu(2), mmap(2), set_mempolicy(2), shmat(2), shmget(2), numa(3), cpuset(7), numa(7), numactl(8)
This page is part of release 3.53 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 MBIND(2)