slow directory operation on huge dirs

[Wojciech Puchar]

>> this part works fine. The problem begins where it's already cached.
>> 
>> To get the problem you need BOTH of:
>> 
>> - large maxvnodes like half million
>> - large directory (in order of 100000 files)
>
> I remember very similar problem with slow access of directories with 80 000+ 
> files. It was always slow like frozen hell. There is some recommendation to

first - we have DIRHASH option and i have it enabled.
second - it is not just a problem of huge directory but both huge 
directory and large maxvnodes settings.

Large directories works fast when kern.maxvnodes is small and there is 
enough dirhash_maxmem.

it's clearly an error somewhere.