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)

Linux man-pages 6.7                                2023-10-31                                            numa(7)