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int get_mempolicy(int *mode, unsigned long *nodemask,
unsigned long maxnode, unsigned long addr,
unsigned long flags);
Link with -lnuma.
get_mempolicy() retrieves the NUMA policy of the calling process or of
a memory address, depending on the setting of flags.
A NUMA machine has different memory controllers with different dis-
tances to specific CPUs. The memory policy defines from which node
memory is allocated for the process.
If flags is specified as 0, then information about the calling pro-
cess's default policy (as set by set_mempolicy(2)) is returned. The
policy returned [mode and nodemask] may be used to restore the pro-
cess's policy to its state at the time of the call to get_mempolicy()
If flags specifies MPOL_F_MEMS_ALLOWED (available since Linux 2.6.24),
the mode argument is ignored and the set of nodes [memories] that the
process is allowed to specify in subsequent calls to mbind(2) or
set_mempolicy(2) [in the absence of any mode flags] is returned in
nodemask. It is not permitted to combine MPOL_F_MEMS_ALLOWED with
either MPOL_F_ADDR or MPOL_F_NODE.
If flags specifies MPOL_F_ADDR, then information is returned about the
policy governing the memory address given in addr. This policy may be
different from the process's default policy if mbind(2) or one of the
helper functions described in numa(3) has been used to establish a pol-
icy for the memory range containing addr.
If the mode argument is not NULL, then get_mempolicy() will store the
policy mode and any optional mode flags of the requested NUMA policy in
the location pointed to by this argument. If nodemask is not NULL,
then the nodemask associated with the policy will be stored in the
location pointed to by this argument. maxnode specifies the number of
node IDs that can be stored into nodemask--that is, the maximum node ID
plus one. The value specified by maxnode is always rounded to a multi-
ple of sizeof(unsigned long).
If flags specifies both MPOL_F_NODE and MPOL_F_ADDR, get_mempolicy()
will return the node ID of the node on which the address addr is allo-
cated into the location pointed to by mode. If no page has yet been
allocated for the specified address, get_mempolicy() will allocate a
page as if the process had performed a read [load] access to that
address, and return the ID of the node where that page was allocated.
On success, get_mempolicy() returns 0; on error, -1 is returned and
errno is set to indicate the error.
EFAULT Part of all of the memory range specified by nodemask and maxn-
ode points outside your accessible address space.
EINVAL The value specified by maxnode is less than the number of node
IDs supported by the system. Or flags specified values other
than MPOL_F_NODE or MPOL_F_ADDR; or flags specified MPOL_F_ADDR
and addr is NULL, or flags did not specify MPOL_F_ADDR and addr
is not NULL. Or, flags specified MPOL_F_NODE but not
MPOL_F_ADDR and the current process policy is not MPOL_INTER-
LEAVE. Or, flags specified MPOL_F_MEMS_ALLOWED with either
MPOL_F_ADDR or MPOL_F_NODE. (And there are other EINVAL cases.)
The get_mempolicy() system call was added to the Linux kernel in ver-
This system call is Linux-specific.
For information on library support, see numa(7).
getcpu(2), mbind(2), mmap(2), set_mempolicy(2), numa(3), numa(7),
Linux 2008-08-15 GET_MEMPOLICY(2)