NUMA(7)			   Linux Programmer's 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 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 inter-
       face 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 pol-
       icy for that memory range and on which nodes the pages have been	 allo-
       cated.

       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	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 unmapped pages associated
	      with this memory range.  These pages  may	 show  up  again  only
	      after  the process has attempted to reference them.  If the mem-
	      ory range represents a shared memory area or file mapping, other
	      processes may currently have additional pages mapped in a corre-
	      sponding 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 anony-
	      mous 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	avail-
       able  at <ftp://oss.sgi.com/www/projects/libnuma/download/>.  The pack-
       age 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 4.10 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)