On our server we have a LOT of RAM for our traffic levels (16GB). The HTTP processes regularly eat up all CPU and need to be restarted without even getting close to using swap memory, so I'm looking for ways to spend RAM to ease the load on Apache (and/or help the seperate MySQL server which may be breaking Apache).

I have many WordPress installs on the HTTPD instance so APC sometimes uses as much as 900MB of ram (according to the apc.php charts). Just in case I have apc.shm_size set to 1600MB which is more than it needs but not more than I can spare. This means there is usually lots of extra RAM available to APC but also very little turnover and fragmentation is never more than 1%.

Is this dangerous? Should I be slimming down APC to less than 1GB just on principle? Should I be expecting some turnover within APC in the name of bringing it's overall footprint down?

Having so much memory devoted to APC means that in top/htop every single httpd process shows ~1.9GB in the VIRT memory column. Obviously this is shared memory and not used per-process, but could it be hurting our server?

NOTE: The problem with the server remains unclear but the effect is that about 60 times a day all 8 CPU's fill up to 100% and everything stops working until Monit sees that Apache is broken and restarts it (Monin also saves the MySQL server). I'm not sure if APC is even part of the problem but I'm trying to optimize everything just in case.