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MBIND(2) Linux Programmer's Manual MBIND(2)
mbind - Set memory policy for a memory range
#include <numaif.h>
int mbind(void *addr, unsigned long len, int mode,
unsigned long *nodemask, unsigned long maxnode,
unsigned flags);
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 only be
allocated 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 according 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) system 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() only has an effect 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
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 bitmask 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 only use bits 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 memory.
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 memory. Allocations will then come
from the node with the next highest node ID specified in nodemask and so
forth, until none of the specified 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 specified, 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 allocation" 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 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 only available 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 3.32 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)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface