> 
> i've just looked in i386 machdep code:
> avail memory=total memory-buffer cache size-kernel size-all kernel data
> size.

1) vmstat -s does not show pages used by uvm to manage memory!
2) uvm allocates real memory for vm_anon structs for each swap page.
sizeof(vm_anon)=16 on i386 so it need 4kB per megabyte of swap. 
with 520MB of swap it means 2MB physical unswappable memory beeing
allocated. with 8MB (without 384kB) it's too much!!

now i'm writing this mail while testing 8MB mem config with 30MB swap.

performance now is much better than linux, and memory consumption can be
reduced because i'm using bash as shell.

now i see that netbsd on 8MB slow 486 is very usable as router with nat,
dns, etc.. and sshd to be able to remotely log into. should go fast!

thank you for your all help!