NAME | DESCRIPTION | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

NUMA(7)                   Linux Programmer's Manual                  NUMA(7)

NAME         top

       numa - overview of Non-Uniform Memory Architecture

DESCRIPTION         top

       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         top

       No standards govern NUMA interfaces.

NOTES         top

       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.

SEE ALSO         top

       get_mempolicy(2), mbind(2), move_pages(2), set_mempolicy(2), numa(3),
       cpuset(7), numactl(8)

COLOPHON         top

       This page is part of release 4.08 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)