numa(7) — Linux manual page

NAME | DESCRIPTION | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

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

NAME         top

       numa - overview of Non-Uniform Memory Architecture

DESCRIPTION         top

       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 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
       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
              show up again only 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
              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         top

       No standards govern NUMA interfaces.

NOTES         top

       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 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.

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.13 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                          2021-03-22                        NUMA(7)

Pages that refer to this page: get_mempolicy(2)mbind(2)migrate_pages(2)move_pages(2)set_mempolicy(2)proc(5)systemd.exec(5)cpuset(7)