| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON | The Linux Programming Interface |
GET_MEMPOLICY(2) Linux Programmer's Manual GET_MEMPOLICY(2)
get_mempolicy - Retrieve NUMA memory policy for a process
#include <numaif.h>
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 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_mempolicy() 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 subsequent calls to mbind(2) or set_mempolicy(2) [in the
absense 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 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).
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 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 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.)
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 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2008-08-15 GET_MEMPOLICY(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface