1 .\" Copyright 2003,2004 Andi Kleen, SuSE Labs.
2 .\" and Copyright 2007 Lee Schermerhorn, Hewlett Packard
4 .\" %%%LICENSE_START(VERBATIM_PROF)
5 .\" Permission is granted to make and distribute verbatim copies of this
6 .\" manual provided the copyright notice and this permission notice are
7 .\" preserved on all copies.
9 .\" Permission is granted to copy and distribute modified versions of this
10 .\" manual under the conditions for verbatim copying, provided that the
11 .\" entire resulting derived work is distributed under the terms of a
12 .\" permission notice identical to this one.
14 .\" Since the Linux kernel and libraries are constantly changing, this
15 .\" manual page may be incorrect or out-of-date. The author(s) assume no
16 .\" responsibility for errors or omissions, or for damages resulting from
17 .\" the use of the information contained herein.
19 .\" Formatted or processed versions of this manual, if unaccompanied by
20 .\" the source, must acknowledge the copyright and authors of this work.
23 .\" 2006-02-03, mtk, substantial wording changes and other improvements
24 .\" 2007-08-27, Lee Schermerhorn <Lee.Schermerhorn@hp.com>
25 .\" more precise specification of behavior.
27 .TH SET_MEMPOLICY 2 2015-05-07 Linux "Linux Programmer's Manual"
29 set_mempolicy \- set default NUMA memory policy for a thread and its children
32 .B "#include <numaif.h>"
34 .BI "long set_mempolicy(int " mode ", const unsigned long *" nodemask ,
35 .BI " unsigned long " maxnode );
37 Link with \fI\-lnuma\fP.
41 sets the NUMA memory policy of the calling thread,
42 which consists of a policy mode and zero or more nodes,
43 to the values specified by the
50 A NUMA machine has different
51 memory controllers with different distances to specific CPUs.
52 The memory policy defines from which node memory is allocated for
55 This system call defines the default policy for the thread.
56 The thread policy governs allocation of pages in the process's
57 address space outside of memory ranges
58 controlled by a more specific policy set by
60 The thread default policy also controls allocation of any pages for
61 memory-mapped files mapped using the
65 flag and that are only read [loaded] from by the thread
66 and of memory-mapped files mapped using the
70 flag, regardless of the access type.
71 The policy is applied only when a new page is allocated
73 For anonymous memory this is when the page is first
74 touched by the thread.
78 argument must specify one of
87 require the caller to specify via the
89 argument one or more nodes.
93 argument may also include an optional
99 .BR MPOL_F_STATIC_NODES " (since Linux 2.6.26)"
102 specifies physical node ids.
103 Linux will not remap the
105 when the process moves to a different cpuset context,
106 nor when the set of nodes allowed by the process's
107 current cpuset context changes.
109 .BR MPOL_F_RELATIVE_NODES " (since Linux 2.6.26)"
112 specifies node ids that are relative to the set of
113 node ids allowed by the process's current cpuset.
116 points to a bit mask of node IDs that contains up to
119 The bit mask size is rounded to the next multiple of
120 .IR "sizeof(unsigned long)" ,
121 but the kernel will use bits only up to
127 value of zero specifies the empty set of nodes.
137 is required, it must contain at least one node that is on-line,
138 allowed by the process's current cpuset context,
140 .B MPOL_F_STATIC_NODES
141 mode flag is specified],
144 .B MPOL_F_STATIC_NODES
149 contains no nodes that are allowed by the process's current cpuset context,
150 the memory policy reverts to
151 .IR "local allocation" .
152 This effectively overrides the specified policy until the process's
153 cpuset context includes one or more of the nodes specified by
158 mode specifies that any nondefault thread memory policy be removed,
159 so that the memory policy "falls back" to the system default policy.
160 The system default policy is "local allocation"\(emthat is,
161 allocate memory on the node of the CPU that triggered the allocation.
163 must be specified as NULL.
164 If the "local node" contains no free memory, the system will
165 attempt to allocate memory from a "near by" node.
169 mode defines a strict policy that restricts memory allocation to the
174 specifies more than one node, page allocations will come from
175 the node with the lowest numeric node ID first, until that node
176 contains no free memory.
177 Allocations will then come from the node with the next highest
180 and so forth, until none of the specified nodes contain free memory.
181 Pages will not be allocated from any node not specified in the
185 interleaves page allocations across the nodes specified in
187 in numeric node ID order.
188 This optimizes for bandwidth instead of latency
189 by spreading out pages and memory accesses to those pages across
191 However, accesses to a single page will still be limited to
192 the memory bandwidth of a single node.
193 .\" NOTE: the following sentence doesn't make sense in the context
194 .\" of set_mempolicy() -- no memory area specified.
195 .\" To be effective the memory area should be fairly large,
196 .\" at least 1MB or bigger.
199 sets the preferred node for allocation.
200 The kernel will try to allocate pages from this node first
201 and fall back to "near by" nodes if the preferred node is low on free
205 specifies more than one node ID, the first node in the
206 mask will be selected as the preferred node.
211 arguments specify the empty set, then the policy
212 specifies "local allocation"
213 (like the system default policy discussed above).
216 specifies "local allocation"; the memory is allocated on
217 the node of the CPU that triggered the allocation (the "local node").
222 arguments must specify the empty set.
223 If the "local node" is low on free memory,
224 the kernel will try to allocate memory from other nodes.
225 The kernel will allocate memory from the "local node"
226 whenever memory for this node is available.
227 If the "local node" is not allowed by the process's current cpuset context,
228 the kernel will try to allocate memory from other nodes.
229 The kernel will allocate memory from the "local node" whenever
230 it becomes allowed by the process's current cpuset context.
232 The thread memory policy is preserved across an
234 and is inherited by child threads created using
242 on error, \-1 is returned and
244 is set to indicate the error.
248 Part of all of the memory range specified by
252 points outside your accessible address space.
275 specifies more than a page worth of bits.
278 specifies one or more node IDs that are
279 greater than the maximum supported node ID.
280 Or, none of the node IDs specified by
282 are on-line and allowed by the process's current cpuset context,
283 or none of the specified nodes contain memory.
286 argument specified both
287 .B MPOL_F_STATIC_NODES
289 .BR MPOL_F_RELATIVE_NODES .
292 Insufficient kernel memory was available.
295 .BR set_mempolicy (),
296 system call was added to the Linux kernel in version 2.6.7.
298 This system call is Linux-specific.
300 Memory policy is not remembered if the page is swapped out.
301 When such a page is paged back in, it will use the policy of
302 the thread or memory range that is in effect at the time the
305 For information on library support, see
308 .BR get_mempolicy (2),