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 effec-
       tive 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 only show up again 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 only shown 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 swap-
              per soon.

       writeback=<pages>
              Number of pages that are currently being written out to disk.

NOTES
       The Linux NUMA system calls and /proc interface are only available if the kernel was configured and built with  the  CON-
       FIG_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  dis-
       tributions include the development library and header in the separate numactl-devel package.

CONFORMING TO
       No standards govern NUMA interfaces.

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 3.25 of the Linux man-pages project.  A description of the project, and information about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



Linux                                                      2008-08-15                                                    NUMA(7)