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
       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

       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

       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 memory range
              represents a shared memory area or file mapping, other processes
              may currently have additional pages mapped in a corresponding
              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
              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.

              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 available at
       ⟨⟩.  The package 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 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

Linux                              2021-03-22                            NUMA(7)