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man:numa

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 The package is also included in some Linux distributions.  Some
     distributions  include  the development library and header in the sepa-
     rate 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 4.16 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)

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