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NUMA(7)                               Linux Programmer's Manual                              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  loca‐
       tions of the accessing CPU and the accessed node.  (This contrasts with a symmetric multipro‐
       cessor system, where the access time for all of the memory is the same for all  CPUs.)   Nor‐
       mally,  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 al‐
       lows a correlation with the contents of the /proc/<pid>/maps file, which contains the end ad‐
       dress 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 effec‐
       tive 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  un‐
              mapped  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  config‐
       ured 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 nu‐
       mactl package is available at ⟨ftp://oss.sgi.com/www/projects/libnuma/download/⟩.  The  pack‐
       age 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 5.10 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)