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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 bu 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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       be found at http://www.kernel.org/doc/man-pages/.