System briefly freezes every time when a very large UFS directory is filled with files

[Yuri]

I have one directory that has ~1.2M files on UFS system.
Every time when the process that creates files there reaches a 
particular point (~0.9M files), system invariably freezes for ~10 
seconds, after which it continues and process succeeds.

I know that this is quite an extreme number of files but, other than 
this problem, it is usable in this setup.

Maybe someone can think of some fix or the immediate reason of such 
freezes? This isn't a good problem to have, even in the view of an 
extremity of this situation.

Yuri