LAがすごい勢いで上がる(600を超える)
システムが重くなり、無反応になる
そのまま数分〜10分ぐらい、戻ってこない

という状況になりますね。

ちゃんと、

maxproc limit exceeded by uid 2001, please see tuning(7) and login.conf(5).
maxproc limit exceeded by uid 2001, please see tuning(7) and login.conf(5).
maxproc limit exceeded by uid 2001, please see tuning(7) and login.conf(5).
maxproc limit exceeded by uid 2001, please see tuning(7) and login.conf(5).
maxproc limit exceeded by uid 2001, please see tuning(7) and login.conf(5).
maxproc limit exceeded by uid 2001, please see tuning(7) and login.conf(5).
maxproc limit exceeded by uid 2001, please see tuning(7) and login.conf(5).
maxproc limit exceeded by uid 2001, please see tuning(7) and login.conf(5).
maxproc limit exceeded by uid 2001, please see tuning(7) and login.conf(5).
maxproc limit exceeded by uid 2001, please see tuning(7) and login.conf(5).

と出ているので、プロセス数のリミッター(150)は、効いているはずだと思うんだけど。