NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON
SET_MEMPOLICY(2) Linux Programmer's Manual SET_MEMPOLICY(2)
set_mempolicy - set default NUMA memory policy for a process and its children
#include <numaif.h>
int set_mempolicy(int mode, unsigned long *nodemask,
unsigned long maxnode);
Link with -lnuma.
set_mempolicy() sets the NUMA memory policy of the calling process, which
consists of a policy mode and zero or more nodes, to the values specified by
the mode, nodemask and maxnode arguments.
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.
This system call defines the default policy for the process. The process
policy governs allocation of pages in the process's address space outside of
memory ranges controlled by a more specific policy set by mbind(2). The
process default policy also controls allocation of any pages for memory mapped
files mapped using the mmap(2) call with the MAP_PRIVATE flag and that are
only read [loaded] from by the process and of memory mapped files mapped using
the mmap(2) call with the MAP_SHARED flag, regardless of the access type. The
policy is only applied when a new page is allocated for the process. For
anonymous memory this is when the page is first touched by the application.
The mode argument must specify one of MPOL_DEFAULT, MPOL_BIND, MPOL_INTERLEAVE
or MPOL_PREFERRED. All modes except MPOL_DEFAULT require the caller to
specify via the nodemask argument one or more nodes.
The mode argument may also include an optional mode flag. The supported mode
flags are:
MPOL_F_STATIC_NODES (since Linux 2.6.26)
A non-empty nodemask specifies physical node ids. Linux does will not
remap the nodemask when the process moves to a different cpuset
context, nor when the set of nodes allowed by the process's current
cpuset context changes.
MPOL_F_RELATIVE_NODES (since Linux 2.6.26)
A non-empty nodemask specifies node ids that are relative to the set of
node ids allowed by the process's current cpuset.
nodemask points to a bit mask of node IDs that contains up to maxnode bits.
The bit mask size is rounded to the next multiple of sizeof(unsigned long),
but the kernel will only use bits up to maxnode. A NULL value of nodemask or
a maxnode value of zero specifies the empty set of nodes. If the value of
maxnode is zero, the nodemask argument is ignored.
Where a nodemask is required, it must contain at least one node that is on-
line, allowed by the process's current cpuset context, [unless the
MPOL_F_STATIC_NODES mode flag is specified], and contains memory. If the
MPOL_F_STATIC_NODES is set in mode and a required nodemask contains no nodes
that are allowed by the process's current cpuset context, the memory policy
reverts to local allocation. This effectively overrides the specified policy
until the process's cpuset context includes one or more of the nodes specified
by nodemask.
The MPOL_DEFAULT mode specifies that any non-default process memory policy be
removed, so that the memory policy "falls back" to the system default policy.
The system default policy is "local allocation"-- i.e., allocate memory on the
node of the CPU that triggered the allocation. nodemask must be specified as
NULL. If the "local node" contains no free memory, the system will attempt to
allocate memory from a "near by" node.
The MPOL_BIND mode defines a strict policy that restricts memory allocation to
the nodes specified in nodemask. If nodemask specifies more than one node,
page allocations will come from the node with the lowest numeric node ID
first, until that node contains no free memory. Allocations will then come
from the node with the next highest node ID specified in nodemask and so
forth, until none of the specified nodes contain free memory. Pages will not
be allocated from any node not specified in the nodemask.
MPOL_INTERLEAVE interleaves page allocations across the nodes specified in
nodemask in numeric node ID order. This optimizes for bandwidth instead of
latency by spreading out pages and memory accesses to those pages across
multiple nodes. However, accesses to a single page will still be limited to
the memory bandwidth of a single node.
MPOL_PREFERRED sets the preferred node for allocation. The kernel will try to
allocate pages from this node first and fall back to "near by" nodes if the
preferred node is low on free memory. If nodemask specifies more than one
node ID, the first node in the mask will be selected as the preferred node.
If the nodemask and maxnode arguments specify the empty set, then the policy
specifies "local allocation" (like the system default policy discussed above).
The process memory policy is preserved across an execve(2), and is inherited
by child processes created using fork(2) or clone(2).
On success, set_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 mode is invalid. Or, mode is MPOL_DEFAULT and nodemask is non-empty,
or mode is MPOL_BIND or MPOL_INTERLEAVE and nodemask is empty. Or,
maxnode specifies more than a page worth of bits. Or, nodemask
specifies one or more node IDs that are greater than the maximum
supported node ID. Or, none of the node IDs specified by nodemask are
on-line and allowed by the process's current cpuset context, or none of
the specified nodes contain memory. Or, the mode argument specified
both MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES.
ENOMEM Insufficient kernel memory was available.
The set_mempolicy(), system call was added to the Linux kernel in version
2.6.7.
This system call is Linux-specific.
Process policy is not remembered if the page is swapped out. When such a page
is paged back in, it will use the policy of the process or memory range that
is in effect at the time the page is allocated.
For information on library support, see numa(7).
get_mempolicy(2), getcpu(2), mbind(2), mmap(2), numa(3), cpuset(7), numa(7),
numactl(8)
This page is part of release 3.21 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 SET_MEMPOLICY(2)