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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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SET_MEMPOLICY(2) Linux Programmer's Manual SET_MEMPOLICY(2)
set_mempolicy - set default NUMA memory policy for a thread and its
children
#include <numaif.h>
long set_mempolicy(int mode, const unsigned long *nodemask,
unsigned long maxnode);
Link with -lnuma.
set_mempolicy() sets the NUMA memory policy of the calling thread,
which consists of a policy mode and zero or more nodes, to the values
specified by the mode, nodemask and maxnode arguments.
A NUMA machine has different memory controllers with different
distances to specific CPUs. The memory policy defines from which
node memory is allocated for the thread.
This system call defines the default policy for the thread. The
thread policy governs allocation of pages in the process's address
space outside of memory ranges controlled by a more specific policy
set by mbind(2). The thread default policy also controls allocation
of any pages for memory-mapped files mapped using the mmap(2) call
with the MAP_PRIVATE flag and that are only read (loaded) from by the
thread and of memory-mapped files mapped using the mmap(2) call with
the MAP_SHARED flag, regardless of the access type. The policy is
applied only when a new page is allocated for the thread. For
anonymous memory this is when the page is first touched by the
thread.
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 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 will
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 node IDs that contains 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 memory.
If the MPOL_F_STATIC_NODES is set in mode and a required nodemask
contains no nodes that are allowed by the process's current cpuset
context, the memory policy reverts to local allocation. This
effectively overrides the specified policy until the process's cpuset
context includes one or more of the nodes specified by nodemask.
The mode argument must include one of the following values:
MPOL_DEFAULT
This mode specifies that any nondefault thread memory policy
be removed, so that the memory policy "falls back" to the
system default policy. The system default policy is "local
allocation"—that is, allocate memory on the node of the CPU
that triggered the allocation. nodemask must be specified as
NULL. If the "local node" contains no free memory, the system
will attempt to allocate memory from a "near by" node.
MPOL_BIND
This mode defines 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.
MPOL_INTERLEAVE
This mode interleaves page allocations across the nodes
specified in nodemask in numeric node ID order. This
optimizes for bandwidth instead of latency by spreading out
pages and memory accesses to those pages across multiple
nodes. However, accesses to a single page 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 "near by" nodes if the preferred node 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 policy specifies "local allocation" (like the system
default policy discussed above).
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 process'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 process's current cpuset context.
The thread memory policy is preserved across an execve(2), and is
inherited by child threads created using fork(2) or clone(2).
On success, set_mempolicy() returns 0; on error, -1 is returned and
errno is set to indicate the error.
EFAULT Part of all of the memory range specified by nodemask and
maxnode points outside your accessible address space.
EINVAL mode is invalid. Or, mode is MPOL_DEFAULT and nodemask is
nonempty, or mode is MPOL_BIND or MPOL_INTERLEAVE and nodemask
is empty. Or, maxnode specifies more than a page worth of
bits. 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.
ENOMEM Insufficient kernel memory was available.
The set_mempolicy() system call was added to the Linux kernel in
version 2.6.7.
This system call is Linux-specific.
Memory policy is not remembered if the page is swapped out. When
such a page is paged back in, it will use the policy of the thread or
memory range that is in effect at the time the page is allocated.
For information on library support, see numa(7).
get_mempolicy(2), getcpu(2), mbind(2), mmap(2), numa(3), cpuset(7),
numa(7), numactl(8)
This page is part of release 4.15 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 SET_MEMPOLICY(2)
Pages that refer to this page: getcpu(2), get_mempolicy(2), mbind(2), migrate_pages(2), move_pages(2), syscalls(2), numa(3), numa_maps(5), cpuset(7), numa(7), migratepages(8), numactl(8)
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