1GET_MEMPOLICY(2) Linux Programmer's Manual GET_MEMPOLICY(2)
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6 get_mempolicy - Retrieve NUMA memory policy for a process
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9 #include <numaif.h>
10 int get_mempolicy(int *mode, unsigned long *nodemask,
12 unsigned long maxnode, unsigned long addr,
13 unsigned long flags);
14 Link with -lnuma.
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18 get_mempolicy() retrieves the NUMA policy of the calling process or of
19 a memory address, depending on the setting of flags.
20 A NUMA machine has different memory controllers with different dis‐
22 tances to specific CPUs. The memory policy defines from which node
23 memory is allocated for the process.
24 If flags is specified as 0, then information about the calling
26 process's default policy (as set by set_mempolicy(2)) is returned. The
27 policy returned [mode and nodemask] may be used to restore the
28 process's policy to its state at the time of the call to get_mempol‐
29 icy() using set_mempolicy(2).
30 If flags specifies MPOL_F_MEMS_ALLOWED (available since Linux 2.6.24),
32 the mode argument is ignored and the set of nodes [memories] that the
33 process is allowed to specify in subsequent calls to mbind(2) or
34 set_mempolicy(2) [in the absense of any mode flags] is returned in
35 nodemask. It is not permitted to combine MPOL_F_MEMS_ALLOWED with
36 either MPOL_F_ADDR or MPOL_F_NODE.
37 If flags specifies MPOL_F_ADDR, then information is returned about the
39 policy governing the memory address given in addr. This policy may be
40 different from the process's default policy if mbind(2) or one of the
41 helper functions described in numa(3) has been used to establish a pol‐
42 icy for the memory range containing addr.
43 If the mode argument is not NULL, then get_mempolicy() will store the
45 policy mode and any optional mode flags of the requested NUMA policy in
46 the location pointed to by this argument. If nodemask is not NULL,
47 then the nodemask associated with the policy will be stored in the
48 location pointed to by this argument. maxnode specifies the number of
49 node IDs that can be stored into nodemask—that is, the maximum node ID
50 plus one. The value specified by maxnode is always rounded to a multi‐
51 ple of sizeof(unsigned long).
52 If flags specifies both MPOL_F_NODE and MPOL_F_ADDR, get_mempolicy()
54 will return the node ID of the node on which the address addr is allo‐
55 cated into the location pointed to by mode. If no page has yet been
56 allocated for the specified address, get_mempolicy() will allocate a
57 page as if the process had performed a read [load] access to that
58 address, and return the ID of the node where that page was allocated.
59 If flags specifies MPOL_F_NODE, but not MPOL_F_ADDR, and the process's
61 current policy is MPOL_INTERLEAVE, then get_mempolicy() will return in
62 the location pointed to by a non-NULL mode argument, the node ID of the
63 next node that will be used for interleaving of internal kernel pages
64 allocated on behalf of the process. These allocations include pages
65 for memory mapped files in process memory ranges mapped using the
66 mmap(2) call with the MAP_PRIVATE flag for read accesses, and in memory
67 ranges mapped with the MAP_SHARED flag for all accesses.
68 Other flag values are reserved.
70 For an overview of the possible policies see set_mempolicy(2).
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74 On success, get_mempolicy() returns 0; on error, -1 is returned and
75 errno is set to indicate the error.
76
78 EFAULT Part of all of the memory range specified by nodemask and maxn‐
79 ode points outside your accessible address space.
80 EINVAL The value specified by maxnode is less than the number of node
82 IDs supported by the system. Or flags specified values other
83 than MPOL_F_NODE or MPOL_F_ADDR; or flags specified MPOL_F_ADDR
84 and addr is NULL, or flags did not specify MPOL_F_ADDR and addr
85 is not NULL. Or, flags specified MPOL_F_NODE but not
86 MPOL_F_ADDR and the current process policy is not MPOL_INTER‐
87 LEAVE. Or, flags specified MPOL_F_MEMS_ALLOWED with either
88 MPOL_F_ADDR or MPOL_F_NODE. (And there are other EINVAL cases.)
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91 The get_mempolicy(), system call was added to the Linux kernel in ver‐
92 sion 2.6.7.
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95 This system call is Linux-specific.
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98 For information on library support, see numa(7).
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101 getcpu(2), mbind(2), mmap(2), set_mempolicy(2), numa(3), numa(7),
102 numactl(8)
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105 This page is part of release 3.22 of the Linux man-pages project. A
106 description of the project, and information about reporting bugs, can
107 be found at http://www.kernel.org/doc/man-pages/.
108Linux 2008-08-15 GET_MEMPOLICY(2)