IPVS connection table size (the Nth power of 2)


Linux Kernel Configuration
└─>Networking support
└─>Networking options
└─>Network packet filtering framework (Netfilter)
└─>IP virtual server support
└─>IPVS connection table size (the Nth power of 2)
In linux kernel since version 2.6.12  
The IPVS connection hash table uses the chaining scheme to handle
hash collisions. Using a big IPVS connection hash table will greatly
reduce conflicts when there are hundreds of thousands of connections
in the hash table.

Note the table size must be power of 2. The table size will be the
value of 2 to the your input number power. The number to choose is
from 8 to 20, the default number is 12, which means the table size
is 4096. Don't input the number too small, otherwise you will lose
performance on it. You can adapt the table size yourself, according
to your virtual server application. It is good to set the table size
not far less than the number of connections per second multiplying
average lasting time of connection in the table. For example, your
virtual server gets 200 connections per second, the connection lasts
for 200 seconds in average in the connection table, the table size
should be not far less than 200x200, it is good to set the table
size 32768 (2**15).

Another note that each connection occupies 128 bytes effectively and
each hash entry uses 8 bytes, so you can estimate how much memory is
needed for your box.

You can overwrite this number setting conn_tab_bits module parameter
or by appending ip_vs.conn_tab_bits=? to the kernel command line
if IP VS was compiled built-in.