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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 only show up again
              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  only
              shown 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.

NOTES

       The  Linux  NUMA system calls and /proc interface are only available 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.

CONFORMING TO

       No standards govern NUMA interfaces.

SEE ALSO

       get_mempolicy(2),  mbind(2),  move_pages(2), set_mempolicy(2), numa(3),
       cpuset(7), numactl(8)

COLOPHON

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