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SET_MEMPOLICY

Section: Linux Programmer's Manual (2)
Updated: 2006-02-07
Index Return to Main Contents
 

NAME

set_mempolicy - set default NUMA memory policy for a process and its children.  

SYNOPSIS

#include <numaif.h>

int set_mempolicy(int policy, unsigned long *nodemask,
                  unsigned long maxnode);
 

DESCRIPTION

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).  

RETURN VALUE

On success, set_mempolicy() returns 0; on error, -1 is returned and errno is set to indicate the error.  

CONFORMING TO

This system call is Linux specific.  

NOTES

Process policy is not remembered if the page is swapped out.  

Versions and Library Support

See mbind(2).  

SEE ALSO

mbind(2), get_mempolicy(2), numactl(8), numa(3)


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
CONFORMING TO
NOTES
Versions and Library Support
SEE ALSO




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