NUMA(7)                   (2012-08-05)                    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 effec-
          tive 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 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".

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          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

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               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 avail-
          able 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 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/.

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