APC: opcode cache vs. user cache - set separate limits

I am trying to move from the typical combination of APC (for opcode) and Memcache (for my userdata) to a purely apc based cache. Given my usage structure it makes sense and performance is higher.

But unlike before, where the apc cache was limited to a reasonable size and did not affect my data cache, I am now worried that the opcode cache might grow relatively large so that the sum of opcode cache an datacache exceeds the limit. As far as I understand, this would result in a flush of the total cache.

Is there a way to mimic the behaviour, 开发者_JAVA百科as if apc was only an opcode cache and limit the opcode cache size to a reasonable limit, leaving the rest for user data?

Or should I try setting lower ttl values for the opcode cache, so it always gets flushed first?

It turned out, that my question is irrelevant. Due to the cache fragmentation problems, the cache is quickly marked as full. (see other posts on stackoverflow). As a consequence apc user cache should only be used selectively.