Provided by: manpages-dev_3.01-1_all
get_mempolicy - Retrieve NUMA memory policy for a process
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.
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 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
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. (And there are other EINVAL cases.)
This system call is Linux-specific.
If the mode of the process policy or the policy governing allocations
at the specified address is MPOL_PREFERRED and this policy was
installed with an empty nodemask—specifying local allocation,
get_mempolicy() will return the mask of on-line node IDs in the
location pointed to by a non-NULL nodemask argument. This mask does
not take into consideration any administratively imposed restrictions
on the process’s context.
Versions and Library Support
mbind(2), mmap(2), set_mempolicy(2), numactl(8), numa(3)
This page is part of release 3.01 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/.