mirror of https://github.com/mkerrisk/man-pages
191 lines
6.3 KiB
Groff
191 lines
6.3 KiB
Groff
.\" Copyright (c) 2008, Linux Foundation, written by Michael Kerrisk
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.\" <mtk.manpages@gmail.com>
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.\" and Copyright 2003,2004 Andi Kleen, SuSE Labs.
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.\" numa_maps material Copyright (c) 2005 Silicon Graphics Incorporated.
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.\" Christoph Lameter, <cl@linux-foundation.org>.
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.\"
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.\" %%%LICENSE_START(VERBATIM)
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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.\" manual page may be incorrect or out-of-date.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. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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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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.\" %%%LICENSE_END
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.\"
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.TH NUMA 7 2021-03-22 "Linux" "Linux Programmer's Manual"
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.SH NAME
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numa \- overview of Non-Uniform Memory Architecture
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.SH DESCRIPTION
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Non-Uniform Memory Access (NUMA) refers to multiprocessor systems
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whose memory is divided into multiple memory nodes.
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The access time of a memory node depends on
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the relative locations of the accessing CPU and the accessed node.
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(This contrasts with a symmetric multiprocessor system,
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where the access time for all of the memory is the same for all CPUs.)
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Normally, each CPU on a NUMA system has a local memory node whose
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contents can be accessed faster than the memory in
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the node local to another CPU
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or the memory on a bus shared by all CPUs.
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.SS NUMA system calls
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The Linux kernel implements the following NUMA-related system calls:
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.BR get_mempolicy (2),
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.BR mbind (2),
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.BR migrate_pages (2),
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.BR move_pages (2),
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and
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.BR set_mempolicy (2).
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However, applications should normally use the interface provided by
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.IR libnuma ;
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see "Library Support" below.
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.SS /proc/[number]/numa_maps (since Linux 2.6.14)
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.\" See also Changelog-2.6.14
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This file displays information about a process's
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NUMA memory policy and allocation.
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.PP
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Each line contains information about a memory range used by the process,
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displaying\(emamong other information\(emthe effective memory policy for
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that memory range and on which nodes the pages have been allocated.
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.PP
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.I numa_maps
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is a read-only file.
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When
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.I /proc/<pid>/numa_maps
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is read, the kernel will scan the virtual address space of the
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process and report how memory is used.
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One line is displayed for each unique memory range of the process.
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.PP
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The first field of each line shows the starting address of the memory range.
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This field allows a correlation with the contents of the
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.I /proc/<pid>/maps
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file,
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which contains the end address of the range and other information,
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such as the access permissions and sharing.
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.PP
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The second field shows the memory policy currently in effect for the
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memory range.
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Note that the effective policy is not necessarily the policy
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installed by the process for that memory range.
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Specifically, if the process installed a "default" policy for that range,
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the effective policy for that range will be the process policy,
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which may or may not be "default".
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.PP
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The rest of the line contains information about the pages allocated in
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the memory range, as follows:
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.TP
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.I N<node>=<nr_pages>
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The number of pages allocated on
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.IR <node> .
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.I <nr_pages>
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includes only pages currently mapped by the process.
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Page migration and memory reclaim may have temporarily unmapped pages
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associated with this memory range.
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These pages may show up again only after the process has
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attempted to reference them.
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If the memory range represents a shared memory area or file mapping,
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other processes may currently have additional pages mapped in a
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corresponding memory range.
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.TP
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.I file=<filename>
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The file backing the memory range.
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If the file is mapped as private, write accesses may have generated
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COW (Copy-On-Write) pages in this memory range.
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These pages are displayed as anonymous pages.
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.TP
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.I heap
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Memory range is used for the heap.
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.TP
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.I stack
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Memory range is used for the stack.
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.TP
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.I huge
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Huge memory range.
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The page counts shown are huge pages and not regular sized pages.
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.TP
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.I anon=<pages>
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The number of anonymous page in the range.
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.TP
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.I dirty=<pages>
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Number of dirty pages.
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.TP
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.I mapped=<pages>
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Total number of mapped pages, if different from
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.IR dirty
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and
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.I anon
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pages.
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.TP
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.I mapmax=<count>
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Maximum mapcount (number of processes mapping a single page) encountered
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during the scan.
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This may be used as an indicator of the degree of sharing occurring in a
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given memory range.
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.TP
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.I swapcache=<count>
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Number of pages that have an associated entry on a swap device.
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.TP
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.I active=<pages>
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The number of pages on the active list.
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This field is shown only if different from the number of pages in this range.
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This means that some inactive pages exist in the memory range that may be
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removed from memory by the swapper soon.
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.TP
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.I writeback=<pages>
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Number of pages that are currently being written out to disk.
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.SH CONFORMING TO
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No standards govern NUMA interfaces.
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.SH NOTES
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The Linux NUMA system calls and
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.I /proc
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interface are available only
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if the kernel was configured and built with the
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.BR CONFIG_NUMA
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option.
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.SS Library support
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Link with \fI\-lnuma\fP
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to get the system call definitions.
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.I libnuma
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and the required
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.I <numaif.h>
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header are available in the
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.I numactl
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package.
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.PP
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However, applications should not use these system calls directly.
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Instead, the higher level interface provided by the
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.BR numa (3)
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functions in the
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.I numactl
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package is recommended.
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The
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.I numactl
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package is available at
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.UR ftp://oss.sgi.com\:/www\:/projects\:/libnuma\:/download/
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.UE .
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The package is also included in some Linux distributions.
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Some distributions include the development library and header
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in the separate
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.I numactl\-devel
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package.
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.SH SEE ALSO
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.BR get_mempolicy (2),
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.BR mbind (2),
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.BR move_pages (2),
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.BR set_mempolicy (2),
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.BR numa (3),
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.BR cpuset (7),
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.BR numactl (8)
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