numa(7) - f39

1numa(7)                Miscellaneous Information Manual                numa(7)
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NAME

6       numa - overview of Non-Uniform Memory Architecture
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DESCRIPTION

9       Non-Uniform Memory Access (NUMA) refers to multiprocessor systems whose
10       memory is divided into multiple memory nodes.  The  access  time  of  a
11       memory  node depends on the relative locations of the accessing CPU and
12       the accessed node.  (This contrasts  with  a  symmetric  multiprocessor
13       system, where the access time for all of the memory is the same for all
14       CPUs.)  Normally, each CPU on a NUMA system has  a  local  memory  node
15       whose contents can be accessed faster than the memory in the node local
16       to another CPU or the memory on a bus shared by all CPUs.
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18   NUMA system calls
19       The Linux kernel implements the following  NUMA-related  system  calls:
20       get_mempolicy(2),   mbind(2),   migrate_pages(2),   move_pages(2),  and
21       set_mempolicy(2).  However, applications should normally use the inter‐
22       face provided by libnuma; see "Library Support" below.
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24   /proc/pid/numa_maps (since Linux 2.6.14)
25       This file displays information about a process's NUMA memory policy and
26       allocation.
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28       Each line contains  information  about  a  memory  range  used  by  the
29       process, displaying—among other information—the effective memory policy
30       for that memory range and on which nodes the pages have been allocated.
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32       numa_maps is a read-only file.  When /proc/pid/numa_maps is  read,  the
33       kernel  will  scan  the virtual address space of the process and report
34       how memory is used.  One line is displayed for each unique memory range
35       of the process.
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37       The  first  field of each line shows the starting address of the memory
38       range.  This field allows  a  correlation  with  the  contents  of  the
39       /proc/pid/maps  file,  which  contains the end address of the range and
40       other information, such as the access permissions and sharing.
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42       The second field shows the memory policy currently in  effect  for  the
43       memory  range.   Note  that the effective policy is not necessarily the
44       policy installed by the process for that memory  range.   Specifically,
45       if  the process installed a "default" policy for that range, the effec‐
46       tive policy for that range will be the process policy, which may or may
47       not be "default".
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49       The  rest of the line contains information about the pages allocated in
50       the memory range, as follows:
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52       N<node>=<nr_pages>
53              The number of pages allocated on  <node>.   <nr_pages>  includes
54              only  pages currently mapped by the process.  Page migration and
55              memory reclaim may have temporarily  unmapped  pages  associated
56              with  this memory range.  These pages may show up again only af‐
57              ter the process has attempted to reference them.  If the  memory
58              range  represents  a  shared  memory area or file mapping, other
59              processes may currently have additional pages mapped in a corre‐
60              sponding memory range.
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62       file=<filename>
63              The  file  backing  the  memory range.  If the file is mapped as
64              private, write accesses may have generated  COW  (Copy-On-Write)
65              pages in this memory range.  These pages are displayed as anony‐
66              mous pages.
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68       heap   Memory range is used for the heap.
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70       stack  Memory range is used for the stack.
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72       huge   Huge memory range.  The page counts shown are huge pages and not
73              regular sized pages.
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75       anon=<pages>
76              The number of anonymous page in the range.
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78       dirty=<pages>
79              Number of dirty pages.
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81       mapped=<pages>
82              Total  number  of mapped pages, if different from dirty and anon
83              pages.
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85       mapmax=<count>
86              Maximum mapcount (number of processes mapping a single page) en‐
87              countered  during the scan.  This may be used as an indicator of
88              the degree of sharing occurring in a given memory range.
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90       swapcache=<count>
91              Number of pages that have an associated entry on a swap device.
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93       active=<pages>
94              The number of pages on the active list.   This  field  is  shown
95              only  if different from the number of pages in this range.  This
96              means that some inactive pages exist in the  memory  range  that
97              may be removed from memory by the swapper soon.
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99       writeback=<pages>
100              Number of pages that are currently being written out to disk.
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STANDARDS

103       None.
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NOTES

106       The  Linux  NUMA system calls and /proc interface are available only if
107       the kernel was configured and built with the CONFIG_NUMA option.
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109   Library support
110       Link with -lnuma to get the system call definitions.  libnuma  and  the
111       required <numaif.h> header are available in the numactl package.
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113       However,  applications should not use these system calls directly.  In‐
114       stead, the higher level interface provided by the numa(3) functions  in
115       the  numactl  package is recommended.  The numactl package is available
116       at ⟨ftp://oss.sgi.com/www/projects/libnuma/download/⟩.  The package  is
117       also  included in some Linux distributions.  Some distributions include
118       the development library and header in the separate numactl-devel  pack‐
119       age.
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NAME

DESCRIPTION

STANDARDS

NOTES

SEE ALSO