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NAME | DESCRIPTION | STANDARDS | NOTES | SEE ALSO | COLOPHON |
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numa(7) Miscellaneous Information Manual numa(7)
numa - overview of Non-Uniform Memory Architecture
Non-Uniform Memory Access (NUMA) refers to multiprocessor systems
whose memory is divided into multiple memory nodes. The access
time of a memory node depends on the relative locations of the
accessing CPU and the accessed node. (This contrasts with a
symmetric multiprocessor system, where the access time for all of
the memory is the same for all CPUs.) Normally, each CPU on a
NUMA system has a local memory node whose contents can be accessed
faster than the memory in the node local to another CPU or the
memory on a bus shared by all CPUs.
NUMA system calls
The Linux kernel implements the following NUMA-related system
calls: get_mempolicy(2), mbind(2), migrate_pages(2),
move_pages(2), and set_mempolicy(2). However, applications should
normally use the interface provided by libnuma; see "Library
Support" below.
[1m/proc/[24mpid/numa_maps (since Linux 2.6.14)
This file displays information about a process's NUMA memory
policy and allocation.
Each line contains information about a memory range used by the
process, displaying—among other information—the effective memory
policy for that memory range and on which nodes the pages have
been allocated.
numa_maps is a read-only file. When /proc/pid/numa_maps is read,
the kernel will scan the virtual address space of the process and
report how memory is used. One line is displayed for each unique
memory range of the process.
The first field of each line shows the starting address of the
memory range. This field allows a correlation with the contents
of the /proc/pid/maps file, which contains the end address of the
range and other information, such as the access permissions and
sharing.
The second field shows the memory policy currently in effect for
the memory range. Note that the effective policy is not
necessarily the policy installed by the process for that memory
range. Specifically, if the process installed a "default" policy
for that range, the effective policy for that range will be the
process policy, which may or may not be "default".
The rest of the line contains information about the pages
allocated in the memory range, as follows:
N<node>=<nr_pages>
The number of pages allocated on <node>. <nr_pages>
includes only pages currently mapped by the process. Page
migration and memory reclaim may have temporarily unmapped
pages associated with this memory range. These pages may
show up again only after the process has attempted to
reference them. If the memory range represents a shared
memory area or file mapping, other processes may currently
have additional pages mapped in a corresponding memory
range.
file=<filename>
The file backing the memory range. If the file is mapped
as private, write accesses may have generated COW (Copy-On-
Write) pages in this memory range. These pages are
displayed as anonymous pages.
heap Memory range is used for the heap.
stack Memory range is used for the stack.
huge Huge memory range. The page counts shown are huge pages
and not regular sized pages.
anon=<pages>
The number of anonymous page in the range.
dirty=<pages>
Number of dirty pages.
mapped=<pages>
Total number of mapped pages, if different from dirty and
anon pages.
mapmax=<count>
Maximum mapcount (number of processes mapping a single
page) encountered during the scan. This may be used as an
indicator of the degree of sharing occurring in a given
memory range.
swapcache=<count>
Number of pages that have an associated entry on a swap
device.
active=<pages>
The number of pages on the active list. This field is
shown only if different from the number of pages in this
range. This means that some inactive pages exist in the
memory range that may be removed from memory by the swapper
soon.
writeback=<pages>
Number of pages that are currently being written out to
disk.
None.
The Linux NUMA system calls and /proc interface are available only
if the kernel was configured and built with the CONFIG_NUMA
option.
Library support
Link with -lnuma to get the system call definitions. libnuma and
the required <numaif.h> header are available in the numactl
package.
However, applications should not use these system calls directly.
Instead, the higher level interface provided by the numa(3)
functions in the numactl package is recommended. The numactl
package is available at
⟨ftp://oss.sgi.com/www/projects/libnuma/download/⟩. The package is
also included in some Linux distributions. Some distributions
include the development library and header in the separate
numactl-devel package.
get_mempolicy(2), mbind(2), move_pages(2), set_mempolicy(2),
numa(3), cpuset(7), numactl(8)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 numa(7)
Pages that refer to this page: get_mempolicy(2), mbind(2), migrate_pages(2), move_pages(2), set_mempolicy(2), proc_pid_numa_maps(5), systemd.exec(5), cpuset(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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