man2/set_mempolicy.2

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  20 .\" 2006-02-03, mtk, substantial wording changes and other improvements
  21 .\"
  22 .TH SET_MEMPOLICY 2 2006-02-07 "Linux" "Linux Programmer's Manual"
  23 .SH NAME
  24 set_mempolicy \- set default NUMA memory policy for a process and its children.
  25 .SH SYNOPSIS
  26 .nf
  27 .B "#include <numaif.h>"
  28 .sp
  29 .BI "int set_mempolicy(int " policy ", unsigned long *" nodemask ,
  30 .BI "                  unsigned long " maxnode );
  31 .fi
  32 .SH DESCRIPTION
  33 .BR set_mempolicy ()
  34 sets the NUMA memory policy of the calling process to
  35 .IR policy .
  36
  37 A NUMA machine has different
  38 memory controllers with different distances to specific CPUs.
  39 The memory policy defines in which node memory is allocated for
  40 the process.
  41
  42 This system call defines the default policy for the process;
  43 in addition a policy can be set for specific memory ranges using
  44 .BR mbind (2).
  45 The policy is only applied when a new page is allocated
  46 for the process.
  47 For anonymous memory this is when the page is first
  48 touched by the application.
  49
  50 Available policies are
  51 .BR MPOL_DEFAULT ,
  52 .BR MPOL_BIND ,
  53 .BR MPOL_INTERLEAVE ,
  54 .BR MPOL_PREFERRED .
  55 All policies except
  56 .B MPOL_DEFAULT
  57 require the caller to specify the nodes to which the policy applies in the
  58 .I nodemask
  59 parameter.
  60 .I nodemask
  61 is pointer to a bit field of nodes that contains up to
  62 .I maxnode
  63 bits.
  64 The bit field size is rounded to the next multiple of
  65 .IR "sizeof(unsigned long)" ,
  66 but the kernel will only use bits up to
  67 .IR maxnode .
  68
  69 The
  70 .B MPOL_DEFAULT
  71 policy is the default and means to allocate memory locally,
  72 i.e., on the node of the CPU that triggered the allocation.
  73 .I nodemask
  74 should be specified as NULL.
  75
  76 The
  77 .B MPOL_BIND
  78 policy is a strict policy that restricts memory allocation to the
  79 nodes specified in
  80 .IR nodemask .
  81 There won't be allocations on other nodes.
  82
  83 .B MPOL_INTERLEAVE
  84 interleaves allocations to the nodes specified in
  85 .IR nodemask .
  86 This optimizes for bandwidth instead of latency.
  87 To be effective the memory area should be fairly large,
  88 at least 1MB or bigger.
  89
  90 .B MPOL_PREFERRED
  91 sets the preferred node for allocation.
  92 The kernel will try to allocate in this
  93 node first and fall back to other nodes if the preferred node is low on free
  94 memory.
  95 Only the first node in the
  96 .I nodemask
  97 is used.
  98 If no node is set in the mask, then the memory is allocated on
  99 the node of the CPU that triggered the allocation allocation (like
 100 .BR MPOL_DEFAULT ).
 101
 102 The memory policy is preserved across an
 103 .BR execve (2),
 104 and is inherited by child processes created using
 105 .BR fork (2)
 106 or
 107 .BR clone (2).
 108 .SH RETURN VALUE
 109 On success,
 110 .BR set_mempolicy ()
 111 returns 0;
 112 on error, \-1 is returned and
 113 .I errno
 114 is set to indicate the error.
 115 .\" .SH ERRORS
 116 .\" FIXME writeme -- no errors are listed on this page
 117 .\" .
 118 .\" .TP
 119 .\" .B EINVAL
 120 .\" .I mode is invalid.
 121 .SS "Versions and Library Support"
 122 See
 123 .BR mbind (2).
 124 .SH CONFORMING TO
 125 This system call is Linux specific.
 126 .SH NOTES
 127 Process policy is not remembered if the page is swapped out.
 128 .SH SEE ALSO
 129 .BR mbind (2),
 130 .BR get_mempolicy (2),
 131 .BR numactl (8),
 132 .BR numa (3)