man > numa(7)

numa(7)                           Miscellaneous Information 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 multi‐
       processor 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/pid/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.

STANDARDS
       None.

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 package
       is also included in some Linux distributions.  Some distributions include the development li‐
       brary 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)

Linux man-pages 6.7                          2023-10-31                                      numa(7)