Section (2) set_mempolicy
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_zsingle_quotesz_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_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
may also include an optional mode
flag. The supported mode flags are:
MPOL_F_STATIC_NODES(since Linux 2.6.26)
nodemaskspecifies physical node IDs. Linux will not remap the
nodemaskwhen the process moves to a different cpuset context, nor when the set of nodes allowed by the process_zsingle_quotesz_s current cpuset context changes.
MPOL_F_RELATIVE_NODES(since Linux 2.6.26)
nodemaskspecifies node IDs that are relative to the set of node IDs allowed by the process_zsingle_quotesz_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_zsingle_quotesz_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_zsingle_quotesz_s current cpuset
context, the memory policy reverts to local allocation. This effectively
overrides the specified policy until the process_zsingle_quotesz_s cpuset
context includes one or more of the nodes specified by
must include one of the following values:
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.
nodemaskmust be specified as NULL. If the local node contains no free memory, the system will attempt to allocate memory from a near by node.
This mode defines a strict policy that restricts memory allocation to the nodes specified in
nodemaskspecifies 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
nodemaskand so forth, until none of the specified nodes contain free memory. Pages will not be allocated from any node not specified in the
This mode interleaves page allocations across the nodes specified in
nodemaskin 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.
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
nodemaskspecifies more than one node ID, the first node in the mask will be selected as the preferred node. If the
maxnodearguments 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
maxnodearguments 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_zsingle_quotesz_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_zsingle_quotesz_s current cpuset context.
returns 0; on error, −1 is returned and
errno is set to indicate the error.
Part of all of the memory range specified by
maxnodepoints outside your accessible address space.
modeis invalid. Or,
nodemaskis nonempty, or
nodemaskis empty. Or,
maxnodespecifies more than a page worth of bits. Or,
nodemaskspecifies one or more node IDs that are greater than the maximum supported node ID. Or, none of the node IDs specified by
nodemaskare on-line and allowed by the process_zsingle_quotesz_s current cpuset context, or none of the specified nodes contain memory. Or, the
modeargument specified both
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 4.16 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
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2006-02-03, mtk, substantial wording changes and other improvements
2007-08-27, Lee Schermerhorn <Lee.Schermerhornhp.com>
more precise specification of behavior.