mmap cache can't open foo.php - Too many open files

[guarriman]

Hi.

I'm getting these error message on Apache version 2.2.3:

[Wed Mar 26 13:05:39 2008] [warn-phpd] mmap cache can't open /var/www/classes/Threads.php - Too many open files (pid 17650)
[Wed Mar 26 13:05:42 2008] [warn-phpd] mmap cache can't open /var/www/classes/User.php - Too many open files (pid 17650)
[Wed Mar 26 13:05:46 2008] [warn-phpd] mmap cache can't open /var/www/lib/Functions.php - Too many open files (pid 17650)

How can I fix it? What is 'mmap cache' (so that I can deep on it)?