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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.
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.
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 only show up again 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 only shown 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.
The Linux NUMA system calls and /proc interface are only available if the
kernel was configured and built with the CONFIG_NUMA option.
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.
No standards govern NUMA interfaces.
get_mempolicy(2), mbind(2), move_pages(2), set_mempolicy(2), numa(3),
cpuset(7), numactl(8)
This page is part of release 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2008-08-15 NUMA(7)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface