Installation guide

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