1 .\" Copyright 2003,2004 Andi Kleen, SuSE Labs.
2 .\" and Copyright 2007 Lee Schermerhorn, Hewlett Packard
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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 GET_MEMPOLICY 2 2008-08-15 Linux "Linux Programmer's Manual"
29 get_mempolicy \- retrieve NUMA memory policy for a process
31 .B "#include <numaif.h>"
34 .BI "int get_mempolicy(int *" mode ", unsigned long *" nodemask ,
35 .BI " unsigned long " maxnode ", unsigned long " addr ,
36 .BI " unsigned long " flags );
38 Link with \fI\-lnuma\fP.
42 retrieves the NUMA policy of the calling process or of a memory address,
43 depending on the setting of
46 A NUMA machine has different
47 memory controllers with different distances to specific CPUs.
48 The memory policy defines from which node memory is allocated for
54 then information about the calling process's default policy
56 .BR set_mempolicy (2))
62 may be used to restore the process's policy to its state at
63 the time of the call to
66 .BR set_mempolicy (2).
71 .BR MPOL_F_MEMS_ALLOWED
72 (available since Linux 2.6.24), the
74 argument is ignored and the set of nodes [memories] that the
75 process is allowed to specify in subsequent calls to
79 [in the absence of any
83 It is not permitted to combine
84 .B MPOL_F_MEMS_ALLOWED
94 then information is returned about the policy governing the memory
97 This policy may be different from the process's default policy if
99 or one of the helper functions described in
101 has been used to establish a policy for the memory range containing
106 argument is not NULL, then
108 will store the policy mode and any optional
110 of the requested NUMA policy in the location pointed to by this argument.
113 is not NULL, then the nodemask associated with the policy will be stored
114 in the location pointed to by this argument.
116 specifies the number of node IDs
117 that can be stored into
118 .IR nodemask \(emthat
119 is, the maximum node ID plus one.
120 The value specified by
122 is always rounded to a multiple of
123 .IR "sizeof(unsigned long)" .
132 will return the node ID of the node on which the address
134 is allocated into the location pointed to by
136 If no page has yet been allocated for the specified address,
138 will allocate a page as if the process had performed a read
139 [load] access to that address, and return the ID of the node
140 where that page was allocated.
148 and the process's current policy is
149 .BR MPOL_INTERLEAVE ,
152 will return in the location pointed to by a non-NULL
155 the node ID of the next node that will be used for
156 interleaving of internal kernel pages allocated on behalf of the process.
157 .\" Note: code returns next interleave node via 'mode' argument -Lee Schermerhorn
158 These allocations include pages for memory-mapped files in
159 process memory ranges mapped using the
163 flag for read accesses, and in memory ranges mapped with the
165 flag for all accesses.
167 Other flag values are reserved.
169 For an overview of the possible policies see
170 .BR set_mempolicy (2).
175 on error, \-1 is returned and
177 is set to indicate the error.
181 Part of all of the memory range specified by
185 points outside your accessible address space.
188 The value specified by
190 is less than the number of node IDs supported by the system.
193 specified values other than
217 and the current process policy is not
218 .BR MPOL_INTERLEAVE .
222 .B MPOL_F_MEMS_ALLOWED
233 system call was added to the Linux kernel in version 2.6.7.
235 This system call is Linux-specific.
237 For information on library support, see
243 .BR set_mempolicy (2),
248 This page is part of release 3.67 of the Linux
251 A description of the project,
252 information about reporting bugs,
253 and the latest version of this page,
255 \%http://www.kernel.org/doc/man\-pages/.