nginx cache exceeded, cache manager busy

[wzpzning]

Hi,
     We are using nginx/0.8.15 on our front web server, mainly for caching and reverse proxy. Our cache is located in /dev/shm disk in order to obtain a better performance. Recently, we've found that sometimes the total size of the cache path would exceed the "max_size" in the configuration, and the process of "cache manager process" is quite busy, using 100% for one CPU. 
     We presume that the cache manager process might not be able to delete those expired files in time, because the read/write frequency on the cache disk is very high in our production environment, so the total size of the cache path sometimes exceeds the configuration. Is it correct? The configuration about it is "proxy_cache_path /dev/shm/nginx/cache/ levels=2:2 keys_zone=proxy-cache:154m max_size=4g inactive=72h ;"

     Could someone tell us how to fix this problem?  Thanks a lot.

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,182995,182995#msg-182995