According to http://ext4.wiki.kernel.org/index.php/Ext4%5FHowto says:
Right now the maximum possible number of sub directories contained in a single directory in Ext3 is 32000. Ext4 breaks that limit and allows unlimited number of sub directories.
But the Wikipedia says:
In ext3 the number of subdirectories that a directory can contain is limited to 32,000. This limit has been raised to 64,000 in ext4, and with the "dir_nlink" feature it can go beyond this (although it will stop increasing the link count on the parent).
So to go beyond 64k do I need dir_nlink? I am specifically interested in Ubuntu 9.10 if that makes a difference.