I have a file server that used to operate fairly reliably with 1GB of  
RAM.  A few weeks ago the memory tested bad and the system would not  
boot, however the only known spares available were two 128MB modules  
giving me 256MB of ram.  Since bringing the server up with this  
amount of ram, I am able to achieve multiple vnlock-deadlocks
scenarios on a daily basis.  These cannot be recovered from and the  
system must be hardware reset.  The kernel is 2.1 and the a single  
file system is being served via NFS with imapd, teapop and sendmail  
processes accessing it.  It appears that the nfsd processes are the  
first to vnlock deadlock, which then cascade and are unstoppable.  An
interesting thing to note is that the system seems stable when it is  
freshly booted and barely using swap, but
once it gets deeper into swap the dead lock becomes eminent.  Since  
this problem only occurred every 2 to 3 weeks
with 1GB of ram and now is happening 2 to 3 times a day with 256MB of  
ram, I thought it might be a good time to start having a kernel  
expert investigate.