Ubuntu Manpage: numa - overview of Non-Uniform Memory Architecture

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.

NAME

DESCRIPTION

STANDARDS

NOTES

SEE ALSO