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

COLOPHON
       This page is part of release 5.03 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)