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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 bu 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  informa-
       tion, 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 pro-
       cess  installed a "default" policy for that range, the effective policy for that range will be the process pol-
       icy, 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  pro-
              cess.  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 addi-
              tional 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 swapper 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 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.

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



Linux                             2008-08-15                           NUMA(7)