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NUMA(7)			   Linux Programmer's Manual		       NUMA(7)

       numa - overview of Non-Uniform Memory Architecture

       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

       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 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:

	      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.

	      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.

	      The number of anonymous page in the range.

	      Number of dirty pages.

	      Total  number  of mapped pages, if different from dirty and anon

	      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.

	      Number of pages that have an associated entry on a swap device.

	      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.

	      Number of pages that are currently being written out to disk.

       No standards govern NUMA interfaces.

       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 ⟨⟩.  The	 pack‐
       age  is	also included in some Linux distributions.  Some distributions
       include the development library and header  in  the  separate  numactl-
       devel package.

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

       This page is part of release 3.65 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at

Linux				  2012-08-05			       NUMA(7)

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