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 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 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 3.25 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)