APC Configuration related issues

APC Configuration Issues
My php.ini has the following section for APC configuration:
[APC]
Apc.cache_by_default =on
APC.ENABLE_CLI =off
Apc.enabled =on
Apc.file_update_protection =2
Apc.filters = ""
Apc.gc_ttl =3600
Apc.max_file_size =1m
Apc.num_files_hint =1000
Apc.optimization =on
Apc.shm_segments =1
Apc.shm_size =800
Apc.slam_defense =off
Apc.stat =on
Apc.ttl =0
Apc.user_entries_hint =100
Apc.user_ttl =0

The explanation for Apc.shm_size is:
The size of each shared memory block (in megabytes, recommended value is 128~256). Some systems, including most BSD variants, have very few default shared memory block sizes.

When this value is set to 800, loading the data causes a memory overflow, but smaller (such as 300) is normal. Where can I find out the maximum allowable apc.shm_size of my system?

------Solution--------------------
Apc.shm_size (in megabytes, recommended value is 128~256).

How big is your memory? 800 that big. Real cow.

