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
       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  dis‐
       played 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 shar‐
       ing.

       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 repre‐
              sents  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 con‐
       figured 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 3.74 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 http://www.kernel.org/doc/man-pages/.



Linux                                       2012-08-05                                    NUMA(7)