set_mempolicy — set default NUMA memory policy for a thread and its children
|const unsigned long *nodemask,|
|unsigned long maxnode
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
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.
must specify one of
MPOL_PREFERRED. All modes except
MPOL_DEFAULT require the caller
to specify via the
nodemask argument one or more
may also include an optional mode
flag. The supported mode flags are:
MPOL_F_STATIC_NODES(since Linux 2.6.26)
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
MPOL_F_RELATIVE_NODES(since Linux 2.6.26)
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
is required, it must contain at least one node that is
on-line, allowed by the process's current cpuset context,
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
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 mode defines a
strict policy that restricts memory allocation to the nodes
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
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 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
more than one node ID, the first node in the mask will be
selected as the preferred node. If the
maxnode arguments specify the
empty set, then the policy specifies "local allocation" (like
the system default policy discussed above).
returns 0; on error, −1 is returned and
errno is set to indicate the error.
Part of all of the memory range specified by
outside your accessible address space.
nodemask is nonempty, or
nodemask is empty. Or,
specifies more than a page worth of bits. Or,
specifies one or more node IDs that are greater than
the maximum supported node ID. Or, none of the node IDs
nodemask are on-line and
allowed by the process's current cpuset context, or
none of the specified nodes contain memory. Or, the
Insufficient kernel memory was available.
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).
This page is part of release 4.07 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
Copyright 2003,2004 Andi Kleen, SuSE Labs.
and Copyright 2007 Lee Schermerhorn, Hewlett Packard
Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
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Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date. The author(s) assume no
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the use of the information contained herein.
Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.
2006-02-03, mtk, substantial wording changes and other improvements
2007-08-27, Lee Schermerhorn <Lee.Schermerhornhp.com>
more precise specification of behavior.