[warn-phpd] mmap cache can't open foo.php - Too many open files

My server Swap is empty

[guarriman]

Hi.

Using Apache version 2.2.3 on 'Linux CentOS', my webpages are very
slow and I get this error messages on my 'error_log' file:

[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)

Some data of my server:

[]# free -m
       total    used    free   shared  buffers   cached
Mem:     2693    267    2425     0     0     0
-/+ buffers/cache:    267    2425
Swap:      0     0     0
[]# ulimit -m
unlimited

As you see, my Host provider gave me a VPS server with Swap=0.

I've got PHP 5.2.5 and APC (a Cache System) 3.0.17. Does it something
to do with Apache?

Thank you very much.