Please note that in order to change tcp_max_syn_backlog
to a larger value, you might also have to change TCP_SYNQ_HSIZE defined in tcp.h (which would require a kernel recompile). For more info on tcp_max_syn_backlog
and other TCP variables, check this link out
Note that although the document covers the 2.4.x Linux Kernels, I've double checked the article for accuracy.
On my CentOS5.x system, I found TCP_SYNQ_HSIZE here;
#define TCP_SYNQ_HSIZE 512 /* Size of SYNACK hash table */
We also have a thread here in LQ
that covers RHEL-based kernel compiling (CentOS is based on RHEL).