numa(7)
NAME
numa - overview of Non-Uniform Memory Architecture
DESCRIPTION
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.
CONFORMING TO
No standards govern NUMA interfaces.
NOTES
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.
SEE ALSO
get_mempolicy(2), mbind(2), move_pages(2), set_mempolicy(2), numa(3), cpuset(7), numactl(8)
COLOPHON
This page is part of release 4.09 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/.
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
