1 .\" Copyright 2003,2004 Andi Kleen, SuSE Labs.
2 .\" and Copyright 2007 Lee Schermerhorn, Hewlett Packard
4 .\" %%%LICENSE_START(VERBATIM_PROF)
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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 2014-05-28 Linux "Linux Programmer's Manual"
29 set_mempolicy \- set default NUMA memory policy for a process 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 process,
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 process.
56 The process 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 process 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 process
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 application.
78 argument must specify one of
86 require the caller to specify via the
88 argument one or more nodes.
92 argument may also include an optional
98 .BR MPOL_F_STATIC_NODES " (since Linux 2.6.26)"
101 specifies physical node ids.
102 Linux will not remap the
104 when the process moves to a different cpuset context,
105 nor when the set of nodes allowed by the process's
106 current cpuset context changes.
108 .BR MPOL_F_RELATIVE_NODES " (since Linux 2.6.26)"
111 specifies node ids that are relative to the set of
112 node ids allowed by the process's current cpuset.
115 points to a bit mask of node IDs that contains up to
118 The bit mask size is rounded to the next multiple of
119 .IR "sizeof(unsigned long)" ,
120 but the kernel will use bits only up to
126 value of zero specifies the empty set of nodes.
136 is required, it must contain at least one node that is on-line,
137 allowed by the process's current cpuset context,
139 .B MPOL_F_STATIC_NODES
140 mode flag is specified],
143 .B MPOL_F_STATIC_NODES
148 contains no nodes that are allowed by the process's current cpuset context,
149 the memory policy reverts to
150 .IR "local allocation" .
151 This effectively overrides the specified policy until the process's
152 cpuset context includes one or more of the nodes specified by
157 mode specifies that any nondefault process memory policy be removed,
158 so that the memory policy "falls back" to the system default policy.
159 The system default policy is "local allocation"\(emthat is,
160 allocate memory on the node of the CPU that triggered the allocation.
162 must be specified as NULL.
163 If the "local node" contains no free memory, the system will
164 attempt to allocate memory from a "near by" node.
168 mode defines a strict policy that restricts memory allocation to the
173 specifies more than one node, page allocations will come from
174 the node with the lowest numeric node ID first, until that node
175 contains no free memory.
176 Allocations will then come from the node with the next highest
179 and so forth, until none of the specified nodes contain free memory.
180 Pages will not be allocated from any node not specified in the
184 interleaves page allocations across the nodes specified in
186 in numeric node ID order.
187 This optimizes for bandwidth instead of latency
188 by spreading out pages and memory accesses to those pages across
190 However, accesses to a single page will still be limited to
191 the memory bandwidth of a single node.
192 .\" NOTE: the following sentence doesn't make sense in the context
193 .\" of set_mempolicy() -- no memory area specified.
194 .\" To be effective the memory area should be fairly large,
195 .\" at least 1MB or bigger.
198 sets the preferred node for allocation.
199 The kernel will try to allocate pages from this node first
200 and fall back to "near by" nodes if the preferred node is low on free
204 specifies more than one node ID, the first node in the
205 mask will be selected as the preferred node.
210 arguments specify the empty set, then the policy
211 specifies "local allocation"
212 (like the system default policy discussed above).
214 The process memory policy is preserved across an
216 and is inherited by child processes created using
224 on error, \-1 is returned and
226 is set to indicate the error.
230 Part of all of the memory range specified by
234 points outside your accessible address space.
257 specifies more than a page worth of bits.
260 specifies one or more node IDs that are
261 greater than the maximum supported node ID.
262 Or, none of the node IDs specified by
264 are on-line and allowed by the process's current cpuset context,
265 or none of the specified nodes contain memory.
268 argument specified both
269 .B MPOL_F_STATIC_NODES
271 .BR MPOL_F_RELATIVE_NODES .
274 Insufficient kernel memory was available.
277 .BR set_mempolicy (),
278 system call was added to the Linux kernel in version 2.6.7.
280 This system call is Linux-specific.
282 Process policy is not remembered if the page is swapped out.
283 When such a page is paged back in, it will use the policy of
284 the process or memory range that is in effect at the time the
287 For information on library support, see
290 .BR get_mempolicy (2),