Re: Fw: Re: 2.6.12-rc2-mm2

[Indrek Kruusa <indrek.kruusa@xxxxxxxxxxx>]

Herbert Xu wrote:

> Andrew Morton <akpm@xxxxxxxx> wrote:
>  
>
> > dmesg is not clean though:
> >
> > TCP: time wait bucket table overflow
> > TCP: time wait bucket table overflow
> > TCP: time wait bucket table overflow
> > printk: 392 messages suppressed.
> >
> > What I did:
> > - "bombing" httpd with JMeter (from another computer)
> >    
>
> This is normal.  The number of TCP connections held by
> your server in the TIME_WAIT state is exceeding
> tcp_max_tw_buckets.
>
> Check out tcp(7) on what this means and how it may or
> may not be a problem for you.
>  


This poor Celeron machine has only 128MB RAM and tcp_max_tw_buckets were 
calculated (ipv4/tcp.c) to be 16384. I have found
that increasing this number by 2048 (that's 12.5%) = 18432 is enough to 
not get this overflow warning again (load average was over 90). Some 
other facts:

- my current machine has 512MB RAM and calculated tcp_max_tw_buckets is 
180000 (!)
- from Documentation/networking/ip-sysctl.txt: This limit exists only to 
prevent simple DoS attacks


I believe that those values are somewhat miscalculated. At least by 
changing calculation for machines with low memory a bit you will get 
some defence against poor shouting students who had to build 
load-balancing web-clusters ;)

thanks,
Indrek