On howto and documentation, I generaly find this format
but on one of my server APC 3.0.19 does not like the "M" and crash apache
[apc-error] apc_mmap: mmap failed: Cannot allocate memory
With the same Debian Lenny, same PHP 5.2.17-dotdeb but apc 3.1.6, it run fine with or without the "M". With apc 3.1.7, I get a warning for each PHP-cli execution or apache restart
PHP Warning: PHP Startup: apc.shm_size now uses M/G suffixes, please update your ini files in Unknown on line 0
Witch apc version need the unit, and wich one doesn't like it at all?