4.2.3 Parameters that Control System Performance

The following parameters control aspects of system performance:

fs.file-max

Specifies the maximum number of open files for all processes. Increase the value of this parameter if you see messages about running out of file handles.

net.core.netdev_max_backlog

Specifies the size of the receiver backlog queue, which is used if an interface receives packets faster than the kernel can process them. If this queue is too small, packets are lost at the receiver, rather than on the network.

net.core.rmem_max

Specifies the maximum read socket buffer size. To minimize network packet loss, this buffer must be large enough to handle incoming network packets.

net.core.wmem_max

Specifies the maximum write socket buffer size. To minimize network packet loss, this buffer must be large enough to handle outgoing network packets.

net.ipv4.tcp_available_congestion_control

Displays the TCP congestion avoidance algorithms that are available for use. Use the modprobe command if you need to load additional modules such as tcp_htcp to implement the htcp algorithm.

net.ipv4.tcp_congestion_control

Specifies which TCP congestion avoidance algorithm is used.

net.ipv4.tcp_max_syn_backlog

Specifies the number of outstanding SYN requests that are allowed. Increase the value of this parameter if you see synflood warnings in your logs, and investigation shows that they are occurring because the server is overloaded by legitimate connection attempts.

net.ipv4.tcp_rmem

Specifies minimum, default, and maximum receive buffer sizes that are used for a TCP socket. The maximum value cannot be larger than net.core.rmem_max.

net.ipv4.tcp_wmem

Specifies minimum, default, and maximum send buffer sizes that are used for a TCP socket. The maximum value cannot be larger than net.core.wmem_max.

vm.swappiness

Specifies how likely the kernel is to write loaded pages to swap rather than drop pages from the system page cache. When set to 0, swapping only occurs to avoid an out of memory condition. When set to 100, the kernel swaps aggressively. For a desktop system, setting a lower value can improve system responsiveness by decreasing latency. The default value is 60.

Caution

This parameter is intended for use with laptops to reduce power consumption by the hard disk. Do not adjust this value on server systems.