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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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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.
Note: There is no glibc wrapper for this system call; see NOTES.
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.
Glibc does not provide a wrapper for this system call. 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 5.13 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 2021-03-22 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)
Copyright and license for this manual page
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