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NUMA(7) Linux Programmer's 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.
/proc/[number]/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.
No standards govern NUMA interfaces.
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 distribu‐
tions 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 release 5.07 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2012-08-05 NUMA(7)
Pages that refer to this page: migrate_pages(2), move_pages(2)
Copyright and license for this manual page
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