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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
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get_mempolicy(2) System Calls Manual get_mempolicy(2)
get_mempolicy - retrieve NUMA memory policy for a thread
NUMA (Non-Uniform Memory Access) policy library (libnuma, -lnuma)
#include <numaif.h>
long get_mempolicy(unsigned long maxnode;
int *mode,
unsigned long nodemask[(maxnode + ULONG_WIDTH - 1)
/ ULONG_WIDTH],
unsigned long maxnode, void *addr,
unsigned long flags);
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 or
MPOL_WEIGHTED_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 neither MPOL_INTERLEAVE nor
MPOL_WEIGHTED_INTERLEAVE. Or, flags specified
MPOL_F_MEMS_ALLOWED with either MPOL_F_ADDR or MPOL_F_NODE.
(And there are other EINVAL cases.)
Linux.
Linux 2.6.7.
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 the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-06-28 get_mempolicy(2)
Pages that refer to this page: mbind(2), migrate_pages(2), move_pages(2), set_mempolicy(2), syscalls(2), numa(3), cpuset(7), numa(7), migratepages(8), numactl(8)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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