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/.

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