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GET_MEMPOLICY(2) Linux Programmer's Manual GET_MEMPOLICY(2)
NAME
get_mempolicy - retrieve NUMA memory policy for a process
SYNOPSIS
#include <numaif.h>
int get_mempolicy(int *mode, unsigned long *nodemask,
unsigned long maxnode, unsigned long addr,
unsigned long flags);
Link with -lnuma.
DESCRIPTION
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 distances 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 process's default policy
(as set by set_mempolicy(2)) is returned. The policy returned [mode and nodemask] may be
used to restore the process's policy to its state at the time of the call to get_mempol‐
icy() using set_mempolicy(2).
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 sub‐
sequent 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 policy 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 argu‐
ment. 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 multiple 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 allocated 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.
If flags specifies MPOL_F_NODE, but not MPOL_F_ADDR, and the process's current policy is
MPOL_INTERLEAVE, then get_mempolicy() will return in the location pointed to by a non-NULL
mode argument, the node ID of the next node that will be used for interleaving of internal
kernel pages allocated on behalf of the process. These allocations include pages for mem‐
ory-mapped files in process memory ranges mapped using the mmap(2) call with the MAP_PRI‐
VATE flag for read accesses, and in memory ranges mapped with the MAP_SHARED flag for all
accesses.
Other flag values are reserved.
For an overview of the possible policies see set_mempolicy(2).
RETURN VALUE
On success, get_mempolicy() returns 0; on error, -1 is returned and errno is set to indi‐
cate the error.
ERRORS
EFAULT Part of all of the memory range specified by nodemask and maxnode 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 cur‐
rent process policy is not MPOL_INTERLEAVE. Or, flags specified
MPOL_F_MEMS_ALLOWED with either MPOL_F_ADDR or MPOL_F_NODE. (And there are other
EINVAL cases.)
VERSIONS
The get_mempolicy() system call was added to the Linux kernel in version 2.6.7.
CONFORMING TO
This system call is Linux-specific.
NOTES
For information on library support, see numa(7).
SEE ALSO
getcpu(2), mbind(2), mmap(2), set_mempolicy(2), numa(3), numa(7), numactl(8)
COLOPHON
This page is part of release 3.74 of the Linux man-pages project. A description of the
project, information about reporting bugs, and the latest version of this page, can be
found at http://www.kernel.org/doc/man-pages/.
Linux 2008-08-15 GET_MEMPOLICY(2)
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