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/pid/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.

STANDARDS

       None.

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)