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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
GET_MEMPOLICY(2) Linux Programmer's Manual GET_MEMPOLICY(2)
get_mempolicy - retrieve NUMA memory policy for a thread
#include <numaif.h>
long get_mempolicy(int *mode, unsigned long *nodemask,
unsigned long maxnode, void *addr,
unsigned long flags);
Link with -lnuma.
get_mempolicy() retrieves the NUMA policy of the calling thread 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 thread.
If flags is specified as 0, then information about the calling
thread's default policy (as set by set_mempolicy(2)) is returned, in
the buffers pointed to by mode and nodemask. The value returned in
these arguments may be used to restore the thread's policy to its
state at the time of the call to get_mempolicy() using
set_mempolicy(2). When flags is 0, addr must be specified as NULL.
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 thread 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 thread'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 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 multiple of sizeof(unsigned long)*8.
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 thread 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 thread'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 thread. These allocations
include pages for memory-mapped files in process memory ranges mapped
using the mmap(2) call with the MAP_PRIVATE 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).
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
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 current thread 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.)
The get_mempolicy() system call was added to the Linux kernel in
version 2.6.7.
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),
numactl(8)
This page is part of release 4.12 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
https://www.kernel.org/doc/man-pages/.
Linux 2017-07-13 GET_MEMPOLICY(2)
Pages that refer to this page: mbind(2), migrate_pages(2), move_pages(2), set_mempolicy(2), syscalls(2), numa(3), numa_maps(5), cpuset(7), numa(7), migratepages(8), numactl(8)