man2/set_mempolicy.2

   1 .\" Copyright 2003,2004 Andi Kleen, SuSE Labs.
   2 .\" and Copyright 2007 Lee Schermerhorn, Hewlett Packard
   3 .\"
   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.
   8 .\"
   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.
  13 .\"
  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  15 .\" manual page may be incorrect or out-of-date.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.
  18 .\"
  19 .\" Formatted or processed versions of this manual, if unaccompanied by
  20 .\" the source, must acknowledge the copyright and authors of this work.
  21 .\" %%%LICENSE_END
  22 .\"
  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.
  26 .\"
  27 .TH SET_MEMPOLICY 2 2017-09-15 Linux "Linux Programmer's Manual"
  28 .SH NAME
  29 set_mempolicy \- set default NUMA memory policy for a thread and its children
  30 .SH SYNOPSIS
  31 .nf
  32 .B "#include <numaif.h>"
  33 .PP
  34 .BI "long set_mempolicy(int " mode ", const unsigned long *" nodemask ,
  35 .BI "                   unsigned long " maxnode );
  36 .PP
  37 Link with \fI\-lnuma\fP.
  38 .fi
  39 .SH DESCRIPTION
  40 .BR set_mempolicy ()
  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
  44 .IR mode ,
  45 .I nodemask
  46 and
  47 .I maxnode
  48 arguments.
  49 .PP
  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
  53 the thread.
  54 .PP
  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
  59 .BR mbind (2).
  60 The thread default policy also controls allocation of any pages for
  61 memory-mapped files mapped using the
  62 .BR mmap (2)
  63 call with the
  64 .B MAP_PRIVATE
  65 flag and that are only read (loaded) from by the thread
  66 and of memory-mapped files mapped using the
  67 .BR mmap (2)
  68 call with the
  69 .B MAP_SHARED
  70 flag, regardless of the access type.
  71 The policy is applied only when a new page is allocated
  72 for the thread.
  73 For anonymous memory this is when the page is first
  74 touched by the thread.
  75 .PP
  76 The
  77 .I mode
  78 argument must specify one of
  79 .BR MPOL_DEFAULT ,
  80 .BR MPOL_BIND ,
  81 .BR MPOL_INTERLEAVE ,
  82 .BR MPOL_PREFERRED ,
  83 or
  84 .BR MPOL_LOCAL
  85 (which are described in detail below).
  86 All modes except
  87 .B MPOL_DEFAULT
  88 require the caller to specify the node or nodes to which the mode applies,
  89 via the
  90 .I nodemask
  91 argument.
  92 .PP
  93 The
  94 .I mode
  95 argument may also include an optional
  96 .IR "mode flag" .
  97 The supported
  98 .I "mode flags"
  99 are:
 100 .TP
 101 .BR MPOL_F_STATIC_NODES " (since Linux 2.6.26)"
 102 A nonempty
 103 .I nodemask
 104 specifies physical node IDs.
 105 Linux will not remap the
 106 .I nodemask
 107 when the process moves to a different cpuset context,
 108 nor when the set of nodes allowed by the process's
 109 current cpuset context changes.
 110 .TP
 111 .BR MPOL_F_RELATIVE_NODES " (since Linux 2.6.26)"
 112 A nonempty
 113 .I nodemask
 114 specifies node IDs that are relative to the set of
 115 node IDs allowed by the process's current cpuset.
 116 .PP
 117 .I nodemask
 118 points to a bit mask of node IDs that contains up to
 119 .I maxnode
 120 bits.
 121 The bit mask size is rounded to the next multiple of
 122 .IR "sizeof(unsigned long)" ,
 123 but the kernel will use bits only up to
 124 .IR maxnode .
 125 A NULL value of
 126 .I nodemask
 127 or a
 128 .I maxnode
 129 value of zero specifies the empty set of nodes.
 130 If the value of
 131 .I maxnode
 132 is zero,
 133 the
 134 .I nodemask
 135 argument is ignored.
 136 .PP
 137 Where a
 138 .I nodemask
 139 is required, it must contain at least one node that is on-line,
 140 allowed by the process's current cpuset context,
 141 (unless the
 142 .B MPOL_F_STATIC_NODES
 143 mode flag is specified),
 144 and contains memory.
 145 If the
 146 .B MPOL_F_STATIC_NODES
 147 is set in
 148 .I mode
 149 and a required
 150 .I nodemask
 151 contains no nodes that are allowed by the process's current cpuset context,
 152 the memory policy reverts to
 153 .IR "local allocation" .
 154 This effectively overrides the specified policy until the process's
 155 cpuset context includes one or more of the nodes specified by
 156 .IR nodemask .
 157 .PP
 158 The
 159 .I mode
 160 argument must include one of the following values:
 161 .TP
 162 .B MPOL_DEFAULT
 163 This mode specifies that any nondefault thread memory policy be removed,
 164 so that the memory policy "falls back" to the system default policy.
 165 The system default policy is "local allocation"\(emthat is,
 166 allocate memory on the node of the CPU that triggered the allocation.
 167 .I nodemask
 168 must be specified as NULL.
 169 If the "local node" contains no free memory, the system will
 170 attempt to allocate memory from a "near by" node.
 171 .TP
 172 .B MPOL_BIND
 173 This mode defines a strict policy that restricts memory allocation to the
 174 nodes specified in
 175 .IR nodemask .
 176 If
 177 .I nodemask
 178 specifies more than one node, page allocations will come from
 179 the node with the lowest numeric node ID first, until that node
 180 contains no free memory.
 181 Allocations will then come from the node with the next highest
 182 node ID specified in
 183 .I nodemask
 184 and so forth, until none of the specified nodes contain free memory.
 185 Pages will not be allocated from any node not specified in the
 186 .IR nodemask .
 187 .IP
 188 .TP
 189 .B MPOL_INTERLEAVE
 190 This mode interleaves page allocations across the nodes specified in
 191 .I nodemask
 192 in numeric node ID order.
 193 This optimizes for bandwidth instead of latency
 194 by spreading out pages and memory accesses to those pages across
 195 multiple nodes.
 196 However, accesses to a single page will still be limited to
 197 the memory bandwidth of a single node.
 198 .\" NOTE:  the following sentence doesn't make sense in the context
 199 .\" of set_mempolicy() -- no memory area specified.
 200 .\" To be effective the memory area should be fairly large,
 201 .\" at least 1 MB or bigger.
 202 .TP
 203 .B MPOL_PREFERRED
 204 This mode sets the preferred node for allocation.
 205 The kernel will try to allocate pages from this node first
 206 and fall back to "near by" nodes if the preferred node is low on free
 207 memory.
 208 If
 209 .I nodemask
 210 specifies more than one node ID, the first node in the
 211 mask will be selected as the preferred node.
 212 If the
 213 .I nodemask
 214 and
 215 .I maxnode
 216 arguments specify the empty set, then the policy
 217 specifies "local allocation"
 218 (like the system default policy discussed above).
 219 .TP
 220 .BR MPOL_LOCAL " (since Linux 3.8)"
 221 .\" commit 479e2802d09f1e18a97262c4c6f8f17ae5884bd8
 222 .\" commit f2a07f40dbc603c15f8b06e6ec7f768af67b424f
 223 This mode specifies "local allocation"; the memory is allocated on
 224 the node of the CPU that triggered the allocation (the "local node").
 225 The
 226 .I nodemask
 227 and
 228 .I maxnode
 229 arguments must specify the empty set.
 230 If the "local node" is low on free memory,
 231 the kernel will try to allocate memory from other nodes.
 232 The kernel will allocate memory from the "local node"
 233 whenever memory for this node is available.
 234 If the "local node" is not allowed by the process's current cpuset context,
 235 the kernel will try to allocate memory from other nodes.
 236 The kernel will allocate memory from the "local node" whenever
 237 it becomes allowed by the process's current cpuset context.
 238 .PP
 239 The thread memory policy is preserved across an
 240 .BR execve (2),
 241 and is inherited by child threads created using
 242 .BR fork (2)
 243 or
 244 .BR clone (2).
 245 .SH RETURN VALUE
 246 On success,
 247 .BR set_mempolicy ()
 248 returns 0;
 249 on error, \-1 is returned and
 250 .I errno
 251 is set to indicate the error.
 252 .SH ERRORS
 253 .TP
 254 .B EFAULT
 255 Part of all of the memory range specified by
 256 .I nodemask
 257 and
 258 .I maxnode
 259 points outside your accessible address space.
 260 .TP
 261 .B EINVAL
 262 .I mode
 263 is invalid.
 264 Or,
 265 .I mode
 266 is
 267 .B MPOL_DEFAULT
 268 and
 269 .I nodemask
 270 is nonempty,
 271 or
 272 .I mode
 273 is
 274 .B MPOL_BIND
 275 or
 276 .B MPOL_INTERLEAVE
 277 and
 278 .I nodemask
 279 is empty.
 280 Or,
 281 .I maxnode
 282 specifies more than a page worth of bits.
 283 Or,
 284 .I nodemask
 285 specifies one or more node IDs that are
 286 greater than the maximum supported node ID.
 287 Or, none of the node IDs specified by
 288 .I nodemask
 289 are on-line and allowed by the process's current cpuset context,
 290 or none of the specified nodes contain memory.
 291 Or, the
 292 .I mode
 293 argument specified both
 294 .B MPOL_F_STATIC_NODES
 295 and
 296 .BR MPOL_F_RELATIVE_NODES .
 297 .TP
 298 .B ENOMEM
 299 Insufficient kernel memory was available.
 300 .SH VERSIONS
 301 The
 302 .BR set_mempolicy ()
 303 system call was added to the Linux kernel in version 2.6.7.
 304 .SH CONFORMING TO
 305 This system call is Linux-specific.
 306 .SH NOTES
 307 Memory policy is not remembered if the page is swapped out.
 308 When such a page is paged back in, it will use the policy of
 309 the thread or memory range that is in effect at the time the
 310 page is allocated.
 311 .PP
 312 For information on library support, see
 313 .BR numa (7).
 314 .SH SEE ALSO
 315 .BR get_mempolicy (2),
 316 .BR getcpu (2),
 317 .BR mbind (2),
 318 .BR mmap (2),
 319 .BR numa (3),
 320 .BR cpuset (7),
 321 .BR numa (7),
 322 .BR numactl (8)