1 .\" Copyright 2003,2004 Andi Kleen, SuSE Labs.
2 .\" and Copyright 2007 Lee Schermerhorn, Hewlett Packard
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13 .\" Since the Linux kernel and libraries are constantly changing, this
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16 .\" the use of the information contained herein.
18 .\" Formatted or processed versions of this manual, if unaccompanied by
19 .\" the source, must acknowledge the copyright and authors of this work.
21 .\" 2006-02-03, mtk, substantial wording changes and other improvements
22 .\" 2007-08-27, Lee Schermerhorn <Lee.Schermerhorn@hp.com>
23 .\" more precise specification of behavior.
25 .TH SET_MEMPOLICY 2 2008-08-15 Linux "Linux Programmer's Manual"
27 set_mempolicy \- set default NUMA memory policy for a process and its children
30 .B "#include <numaif.h>"
32 .BI "int set_mempolicy(int " mode ", unsigned long *" nodemask ,
33 .BI " unsigned long " maxnode );
35 Link with \fI\-lnuma\fP.
39 sets the NUMA memory policy of the calling process,
40 which consists of a policy mode and zero or more nodes,
41 to the values specified by the
48 A NUMA machine has different
49 memory controllers with different distances to specific CPUs.
50 The memory policy defines from which node memory is allocated for
53 This system call defines the default policy for the process.
54 The process policy governs allocation of pages in the process's
55 address space outside of memory ranges
56 controlled by a more specific policy set by
58 The process default policy also controls allocation of any pages for
59 memory mapped files mapped using the
63 flag and that are only read [loaded] from by the process
64 and of memory mapped files mapped using the
68 flag, regardless of the access type.
69 The policy is only applied when a new page is allocated
71 For anonymous memory this is when the page is first
72 touched by the application.
76 argument must specify one of
84 require the caller to specify via the
86 argument one or more nodes.
90 argument may also include an optional
96 .BR MPOL_F_STATIC_NODES " (since Linux 2.6.26)"
99 specifies physical node ids.
100 Linux does will not remap the
102 when the process moves to a different cpuset context,
103 nor when the set of nodes allowed by the process's
104 current cpuset context changes.
106 .BR MPOL_F_RELATIVE_NODES " (since Linux 2.6.26)"
109 specifies node ids that are relative to the set of
110 node ids allowed by the process's current cpuset.
113 points to a bit mask of node IDs that contains up to
116 The bit mask size is rounded to the next multiple of
117 .IR "sizeof(unsigned long)" ,
118 but the kernel will only use bits up to
124 value of zero specifies the empty set of nodes.
134 is required, it must contain at least one node that is on-line,
135 allowed by the process's current cpuset context,
137 .B MPOL_F_STATIC_NODES
138 mode flag is specified],
141 .B MPOL_F_STATIC_NODES
146 contains no nodes that are allowed by the process's current cpuset context,
147 the memory policy reverts to
148 .IR "local allocation" .
149 This effectively overrides the specified policy until the process's
150 cpuset context includes one or more of the nodes specified by
155 mode specifies that any non-default process memory policy be removed,
156 so that the memory policy "falls back" to the system default policy.
157 The system default policy is "local allocation"--
158 i.e., allocate memory on the node of the CPU that triggered the allocation.
160 must be specified as NULL.
161 If the "local node" contains no free memory, the system will
162 attempt to allocate memory from a "near by" node.
166 mode defines a strict policy that restricts memory allocation to the
171 specifies more than one node, page allocations will come from
172 the node with the lowest numeric node ID first, until that node
173 contains no free memory.
174 Allocations will then come from the node with the next highest
177 and so forth, until none of the specified nodes contain free memory.
178 Pages will not be allocated from any node not specified in the
182 interleaves page allocations across the nodes specified in
184 in numeric node ID order.
185 This optimizes for bandwidth instead of latency
186 by spreading out pages and memory accesses to those pages across
188 However, accesses to a single page will still be limited to
189 the memory bandwidth of a single node.
190 .\" NOTE: the following sentence doesn't make sense in the context
191 .\" of set_mempolicy() -- no memory area specified.
192 .\" To be effective the memory area should be fairly large,
193 .\" at least 1MB or bigger.
196 sets the preferred node for allocation.
197 The kernel will try to allocate pages from this node first
198 and fall back to "near by" nodes if the preferred node is low on free
202 specifies more than one node ID, the first node in the
203 mask will be selected as the preferred node.
208 arguments specify the empty set, then the policy
209 specifies "local allocation"
210 (like the system default policy discussed above).
212 The process memory policy is preserved across an
214 and is inherited by child processes created using
222 on error, \-1 is returned and
224 is set to indicate the error.
228 Part of all of the memory range specified by
232 points outside your accessible address space.
255 specifies more than a page worth of bits.
258 specifies one or more node IDs that are
259 greater than the maximum supported node ID.
260 Or, none of the node IDs specified by
262 are on-line and allowed by the process's current cpuset context,
263 or none of the specified nodes contain memory.
266 argument specified both
267 .B MPOL_F_STATIC_NODES
269 .BR MPOL_F_RELATIVE_NODES .
272 Insufficient kernel memory was available.
275 .BR set_mempolicy (),
276 system call was added to the Linux kernel in version 2.6.7.
278 This system call is Linux-specific.
280 Process policy is not remembered if the page is swapped out.
281 When such a page is paged back in, it will use the policy of
282 the process or memory range that is in effect at the time the
285 For information on library support, see
288 .BR get_mempolicy (2),