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 2021-03-22 Linux "Linux Programmer's Manual"
29 get_mempolicy \- retrieve NUMA memory policy for a thread
31 NUMA (Non-Uniform Memory Access) policy library
32 .RI ( libnuma ", " \-lnuma )
34 .B "#include <numaif.h>"
37 .BI "long get_mempolicy(int *" mode ", unsigned long *" nodemask ,
38 .BI " unsigned long " maxnode ", void *" addr ,
39 .BI " unsigned long " flags );
43 retrieves the NUMA policy of the calling thread or of a memory address,
44 depending on the setting of
47 A NUMA machine has different
48 memory controllers with different distances to specific CPUs.
49 The memory policy defines from which node memory is allocated for
55 then information about the calling thread's default policy
57 .BR set_mempolicy (2))
58 is returned, in the buffers pointed to by
62 The value returned in these arguments
63 may be used to restore the thread's policy to its state at
64 the time of the call to
67 .BR set_mempolicy (2).
72 must be specified as NULL.
77 .BR MPOL_F_MEMS_ALLOWED
78 (available since Linux 2.6.24), the
80 argument is ignored and the set of nodes (memories) that the
81 thread is allowed to specify in subsequent calls to
85 (in the absence of any
89 It is not permitted to combine
90 .B MPOL_F_MEMS_ALLOWED
100 then information is returned about the policy governing the memory
103 This policy may be different from the thread's default policy if
105 or one of the helper functions described in
107 has been used to establish a policy for the memory range containing
112 argument is not NULL, then
114 will store the policy mode and any optional
116 of the requested NUMA policy in the location pointed to by this argument.
119 is not NULL, then the nodemask associated with the policy will be stored
120 in the location pointed to by this argument.
122 specifies the number of node IDs
123 that can be stored into
124 .IR nodemask \(emthat
125 is, the maximum node ID plus one.
126 The value specified by
128 is always rounded to a multiple of
129 .IR "sizeof(unsigned\ long)*8" .
138 will return the node ID of the node on which the address
140 is allocated into the location pointed to by
142 If no page has yet been allocated for the specified address,
144 will allocate a page as if the thread had performed a read
145 (load) access to that address, and return the ID of the node
146 where that page was allocated.
154 and the thread's current policy is
155 .BR MPOL_INTERLEAVE ,
158 will return in the location pointed to by a non-NULL
161 the node ID of the next node that will be used for
162 interleaving of internal kernel pages allocated on behalf of the thread.
163 .\" Note: code returns next interleave node via 'mode' argument -Lee Schermerhorn
164 These allocations include pages for memory-mapped files in
165 process memory ranges mapped using the
169 flag for read accesses, and in memory ranges mapped with the
171 flag for all accesses.
173 Other flag values are reserved.
175 For an overview of the possible policies see
176 .BR set_mempolicy (2).
181 on error, \-1 is returned and
183 is set to indicate the error.
187 Part of all of the memory range specified by
191 points outside your accessible address space.
194 The value specified by
196 is less than the number of node IDs supported by the system.
199 specified values other than
223 and the current thread policy is not
224 .BR MPOL_INTERLEAVE .
228 .B MPOL_F_MEMS_ALLOWED
239 system call was added to the Linux kernel in version 2.6.7.
241 This system call is Linux-specific.
243 For information on library support, see
249 .BR set_mempolicy (2),