mbind - set memory policy for a memory range
long mbind(void *addr, unsigned long len, int mode,
const unsigned long *nodemask, unsigned long maxnode,
Link with -lnuma.
() sets the NUMA memory policy, which consists of a policy mode and
zero or more nodes, for the memory range starting with addr
continuing for len
bytes. The memory policy defines from which node
memory is allocated.
If the memory range specified by the addr
includes an "anonymous" region of memory—that is a region of
memory created using the mmap
(2) system call with the
—or a memory-mapped file, mapped using the
(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
, 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
(2) system call and attached using the shmat
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
flags described below.
argument must specify one of MPOL_DEFAULT
(which are described in detail below). All policy modes
require the caller to specify the node or nodes to
which the mode applies, via the nodemask
argument may also include an optional mode flag
supported mode flags
- 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
- 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.
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
, 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
argument must include one of the following values:
- 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.
- 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.)
- 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.
- 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".
is passed in flags
, then the call fails with the error EIO
existing pages in the memory range don't follow the policy.
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
is also specified, then the call fails with the error
if some pages could not be moved.
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
) to use this flag. If MPOL_MF_STRICT
specified, then the call fails 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.
- 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
- 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.
- 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.
- Insufficient kernel memory was available.
- The flags argument included the MPOL_MF_MOVE_ALL flag and
the caller does not have the CAP_SYS_NICE privilege.
() 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
NUMA policy is not supported on a memory-mapped file range that was mapped with
mode can have different effects for mbind
(2). When MPOL_DEFAULT
is specified for
(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
(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
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.
is ignored on huge page mappings.
are available only on Linux
2.6.16 and later.