1 .\" Copyright 2003,2004 Andi Kleen, SuSE Labs.
2 .\" and Copyright 2007 Lee Schermerhorn, Hewlett Packard
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5 .\" manual provided the copyright notice and this permission notice are
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8 .\" Permission is granted to copy and distribute modified versions of this
9 .\" manual under the conditions for verbatim copying, provided that the
10 .\" entire resulting derived work is distributed under the terms of a
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13 .\" Since the Linux kernel and libraries are constantly changing, this
14 .\" manual page may be incorrect or out-of-date. The author(s) assume no
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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 2007-08-27 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 task
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
90 points to a bit mask of node IDs that contains up to
93 The bit mask size is rounded to the next multiple of
94 .IR "sizeof(unsigned long)" ,
95 but the kernel will only use bits up to
101 value of zero specifies the empty set of nodes.
111 mode is the default and means to allocate memory locally,
112 i.e., on the node of the CPU that triggered the allocation.
114 must be specified as NULL.
115 If the "local node" contains no free memory, the system will
116 attempt to allocate memory from a "near by" node.
120 mode defines a strict policy that restricts memory allocation to the
125 specifies more than one node, page allocations will come from
126 the node with the lowest numeric node ID first, until that node
127 contains no free memory.
128 Allocations will then come from the node with the next highest
131 and so forth, until none of the specified nodes contain free memory.
132 Pages will not be allocated from any node not specified in the
136 interleaves page allocations across the nodes specified in
138 in numeric node ID order.
139 This optimizes for bandwidth instead of latency
140 by spreading out pages and memory accesses to those pages across
142 However, accesses to a single page will still be limited to
143 the memory bandwidth of a single node.
144 .\" NOTE: the following sentence doesn't make sense in the context
145 .\" of set_mempolicy() -- no memory area specified.
146 .\" To be effective the memory area should be fairly large,
147 .\" at least 1MB or bigger.
150 sets the preferred node for allocation.
151 The kernel will try to allocate pages from this node first
152 and fall back to "near by" nodes if the preferred node is low on free
156 specifies more than one node ID, the first node in the
157 mask will be selected as the preferred node.
162 arguments specify the empty set, then the memory is allocated on
163 the node of the CPU that triggered the allocation (like
166 The process memory policy is preserved across an
168 and is inherited by child processes created using
176 on error, \-1 is returned and
178 is set to indicate the error.
182 Part of all of the memory range specified by
186 points outside your accessible address space.
209 specifies more than a page worth of bits.
212 specifies one or more node IDs that are
213 greater than the maximum supported node ID,
214 or are not allowed in the calling task's context.
215 .\" "calling task's context" refers to cpusets.
216 .\" No man page avail to ref. --Lee Schermerhorn
217 Or, none of the node IDs specified by
219 are on-line, or none of the specified nodes contain memory.
222 Insufficient kernel memory was available.
224 This system call is Linux-specific.
226 Process policy is not remembered if the page is swapped out.
227 When such a page is paged back in, it will use the policy of
228 the process or memory range that is in effect at the time the
230 .SS "Versions and Library Support"
236 .BR get_mempolicy (2),