Chapter 2. The

proc

File System

51

  kswapd

  Sets various values concerned with the kernel swap out daemon,

kswapd

. This file has

three values:

512 32 8

The first value sets the maximum number of pages that

kswapd

will attempt to free in a single

attempt. The larger this number, the more aggressively the kernel can move to free pages. The

second value sets the minimum number of times that

kswapd

attempts to free a page. The third

value sets the number of pages

kswapd

attempts to write in a single attempt. Proper tuning of this

final value can improve performance on a system using a lot of swap space by telling the kernel to

write pages in large chunks, minimizing the number of disk seeks.

  max_map_count

  Configures the maximum number of memory map areas a process may have.

In most cases, the default value of

65536

is appropriate.

  overcommit_memory

  When set to the default value of

0

the kernel estimates the amount of

memory available and fails requests that are blatantly invalid. Unfortunately, since memory is allo 

cated using a heuristic rather than a precise algorithm, it can sometimes overload the system.

If

overcommit_memory

is set to

1

, then the potential for system overload is increased, but so is

the performance for memory intensive tasks, such as those used by some scientific software.

For customers who need more less risk of over memory commitment, the following two option

have been added. Setting

overcommit_memory

to

2

fails a memory request adds up to more that

half of the physical RAM, plus swap. Setting it to

3

fails if a memory request adds up to more than

swap alone can hold.

  pagecache

  Controls the amount of memory used by the page cache. The values in

page 

cache

are percentages, and they work in a similar way as

buffermem

to enforce minimums and

maximums of available page cache memory.

  page cluster

  Sets the number of pages read in a single attempt. The default value of

4

, which

actually relates to 16 pages, is appropriate for most systems.

  pagetable_cache

  Controls the number of page tables that are cached on a per processor basis.

The first and second values relate to the minimum and maximum number of page tables to set aside,

respectively.

The

/usr/src/linux 2.4/Documentation/sysctl/vm.txt

file contains additional informa 

tion on these various files.

2.3.10.

/proc/sysvipc/

This directory contain information about System V IPC resources. The files in this directory relate to

System V IPC calls for messages (

msg

), semaphores (

sem

), and shared memory (

shm

).

2.3.11.

/proc/tty/

This directory contains information about the available and currently used tty devices on the system.

Originally called a teletype device, any character based data terminals are called tty devices.

In Linux, there are three different kinds of tty devices. Serial devices are used with serial connections,

such as over a modem or using a serial cable. Virtual terminals create the common console connection,

such as the virtual consoles available when pressing [Alt] [ F key ] at the system console. Pseudo

terminals create a two way communication that is used by some higher level applications, such as

X11. The

drivers

file is a list of the current tty devices in use:

serial

/dev/cua

5

64 127 serial:callout

serial

/dev/ttyS

4

64 127 serial

pty_slave

/dev/pts

136

0 255 pty:slave