numa(7) - Linux manual page (original) (raw)

numa(7) Miscellaneous Information 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.

[1m/proc/[24mpid_/numamaps_ (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.

   _numamaps_ is a read-only file.  When _/proc/_pid_/numamaps_ 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>=<nrpages>_
          The number of pages allocated on _<node>_.  _<nrpages>_
          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.

STANDARDS top

   None.

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)](../man3/numa.3.html)
   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.

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Linux man-pages 6.10 2024-05-02 numa(7)