set_mempolicy — set default NUMA memory policy for a process and its children.
#include <numaif.h>
int
set_mempolicy( |
int | policy, |
unsigned long * | nodemask, | |
unsigned long | maxnode) ; |
set_mempolicy
() sets the
NUMA memory policy of the calling process to policy
.
A NUMA machine has different memory controllers with different distances to specific CPUs. The memory policy defines in which node memory is allocated for the process.
This system call defines the default policy for the process; in addition a policy can be set for specific memory ranges using mbind(2). 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.
Available policies are MPOL_DEFAULT
, MPOL_BIND
, MPOL_INTERLEAVE
, MPOL_PREFERRED
. All policies except
MPOL_DEFAULT
require the caller
to specify the nodes to which the policy applies in the
nodemask
parameter.
nodemask
is pointer
to a bit field of nodes that contains up to maxnode
bits. The bit field
size is rounded to the next multiple of sizeof(unsigned long), but the
kernel will only use bits up to maxnode
.
The MPOL_DEFAULT
policy is
the default and means to allocate memory locally, i.e., on
the node of the CPU that triggered the allocation. nodemask
should be specified as
NULL.
The MPOL_BIND
policy is a
strict policy that restricts memory allocation to the nodes
specified in nodemask
. There won't be
allocations on other nodes.
MPOL_INTERLEAVE
interleaves
allocations to the nodes specified in nodemask
. This optimizes for
bandwidth instead of latency. To be effective the memory area
should be fairly large, at least 1MB or bigger.
MPOL_PREFERRED
sets the
preferred node for allocation. The kernel will try to
allocate in this node first and fall back to other nodes if
the preferred node is low on free memory. Only the first node
in the nodemask
is
used. If no node is set in the mask, then the memory is
allocated on the node of the CPU that triggered the
allocation allocation (like MPOL_DEFAULT
).
The 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.
mbind(2), get_mempolicy(2), numactl(8), numa(3)
Copyright 2003,2004 Andi Kleen, SuSE Labs. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. 2006-02-03, mtk, substantial wording changes and other improvements |