mirror of https://github.com/mkerrisk/man-pages
133 lines
3.8 KiB
Groff
133 lines
3.8 KiB
Groff
.\" Copyright 2003,2004 Andi Kleen, SuSE Labs.
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" 2006-02-03, mtk, substantial wording changes and other improvements
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.\"
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.TH SET_MEMPOLICY 2 "2006-02-07" "SuSE Labs" "Linux Programmer's Manual"
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.SH NAME
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set_mempolicy \- set default NUMA memory policy for a process and its children.
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.SH SYNOPSIS
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.nf
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.B "#include <numaif.h>"
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.sp
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.BI "int set_mempolicy(int " policy ", unsigned long *" nodemask ,
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.BI " unsigned long " maxnode );
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.fi
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.SH DESCRIPTION
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.BR set_mempolicy ()
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sets the NUMA memory policy of the calling process to
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.IR policy .
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A NUMA machine has different
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memory controllers with different distances to specific CPUs.
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The memory policy defines in which node memory is allocated for
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the process.
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This system call defines the default policy for the process;
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in addition a policy can be set for specific memory ranges using
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.BR mbind (2).
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The policy is only applied when a new page is allocated
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for the process.
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For anonymous memory this is when the page is first
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touched by the application.
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Available policies are
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.BR MPOL_DEFAULT ,
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.BR MPOL_BIND ,
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.BR MPOL_INTERLEAVE ,
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.BR MPOL_PREFERRED .
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All policies except
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.B MPOL_DEFAULT
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require the caller to specify the nodes to which the policy applies in the
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.I nodemask
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parameter.
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.I nodemask
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is pointer to a bit field of nodes that contains up to
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.I maxnode
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bits.
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The bit field size is rounded to the next multiple of
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.IR "sizeof(unsigned long)" ,
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but the kernel will only use bits up to
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.IR maxnode .
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The
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.B MPOL_DEFAULT
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policy is the default and means to allocate memory locally,
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i.e., on the node of the CPU that triggered the allocation.
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.I nodemask
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should be specified as NULL.
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The
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.B MPOL_BIND
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policy is a strict policy that restricts memory allocation to the
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nodes specified in
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.IR nodemask .
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There won't be allocations on other nodes.
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.B MPOL_INTERLEAVE
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interleaves allocations to the nodes specified in
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.IR nodemask .
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This optimizes for bandwidth instead of latency.
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To be effective the memory area should be fairly large,
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at least 1MB or bigger.
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.B MPOL_PREFERRED
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sets the preferred node for allocation.
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The kernel will try to allocate in this
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node first and fall back to other nodes if the preferred node is low on free
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memory.
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Only the first node in the
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.I nodemask
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is used.
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If no node is set in the mask, then the memory is allocated on
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the node of the CPU that triggered the allocation allocation (like
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.BR MPOL_DEFAULT ).
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The memory policy is preserved across an
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.BR execve (2),
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and is inherited by child processes created using
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.BR fork (2)
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or
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.BR clone (2).
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.SH NOTES
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Process policy is not remembered if the page is swapped out.
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.SH RETURN VALUE
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On success,
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.BR set_mempolicy ()
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returns 0;
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on error, \-1 is returned and
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.I errno
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is set to indicate the error.
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.\" .SH ERRORS
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.\" FIXME writeme -- no errors are listed on this page
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.\" .
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.\" .TP
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.\" .B EINVAL
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.\" .I mode is invalid.
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.SH "VERSIONS AND LIBRARY SUPPORT"
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See
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.BR mbind (2).
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.SH CONFORMING TO
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This system call is Linux specific.
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.SH SEE ALSO
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.BR mbind (2),
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.BR get_mempolicy (2),
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.BR numactl (8),
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.BR numa (3)
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