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  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)