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 2016-12-12 Linux "Linux Programmer's Manual"
29 get_mempolicy \- retrieve NUMA memory policy for a thread
31 .B "#include <numaif.h>"
34 .BI "long get_mempolicy(int *" mode ", unsigned long *" nodemask ,
35 .BI " unsigned long " maxnode ", void *" addr ,
36 .BI " unsigned long " flags );
38 Link with \fI\-lnuma\fP.
42 retrieves the NUMA policy of the calling thread 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 thread's default policy
56 .BR set_mempolicy (2))
57 is returned, in the buffers pointed to by
61 The value returned in these arguments
62 may be used to restore the thread's policy to its state at
63 the time of the call to
66 .BR set_mempolicy (2).
71 must be specified as NULL.
76 .BR MPOL_F_MEMS_ALLOWED
77 (available since Linux 2.6.24), the
79 argument is ignored and the set of nodes (memories) that the
80 thread is allowed to specify in subsequent calls to
84 (in the absence of any
88 It is not permitted to combine
89 .B MPOL_F_MEMS_ALLOWED
99 then information is returned about the policy governing the memory
102 This policy may be different from the thread's default policy if
104 or one of the helper functions described in
106 has been used to establish a policy for the memory range containing
111 argument is not NULL, then
113 will store the policy mode and any optional
115 of the requested NUMA policy in the location pointed to by this argument.
118 is not NULL, then the nodemask associated with the policy will be stored
119 in the location pointed to by this argument.
121 specifies the number of node IDs
122 that can be stored into
123 .IR nodemask \(emthat
124 is, the maximum node ID plus one.
125 The value specified by
127 is always rounded to a multiple of
128 .IR "sizeof(unsigned\ long)*8" .
137 will return the node ID of the node on which the address
139 is allocated into the location pointed to by
141 If no page has yet been allocated for the specified address,
143 will allocate a page as if the thread had performed a read
144 (load) access to that address, and return the ID of the node
145 where that page was allocated.
153 and the thread's current policy is
154 .BR MPOL_INTERLEAVE ,
157 will return in the location pointed to by a non-NULL
160 the node ID of the next node that will be used for
161 interleaving of internal kernel pages allocated on behalf of the thread.
162 .\" Note: code returns next interleave node via 'mode' argument -Lee Schermerhorn
163 These allocations include pages for memory-mapped files in
164 process memory ranges mapped using the
168 flag for read accesses, and in memory ranges mapped with the
170 flag for all accesses.
172 Other flag values are reserved.
174 For an overview of the possible policies see
175 .BR set_mempolicy (2).
180 on error, \-1 is returned and
182 is set to indicate the error.
186 Part of all of the memory range specified by
190 points outside your accessible address space.
193 The value specified by
195 is less than the number of node IDs supported by the system.
198 specified values other than
222 and the current thread policy is not
223 .BR MPOL_INTERLEAVE .
227 .B MPOL_F_MEMS_ALLOWED
238 system call was added to the Linux kernel in version 2.6.7.
240 This system call is Linux-specific.
242 For information on library support, see
248 .BR set_mempolicy (2),