strange behavior for cache manager

[cxfcxf]

Hi,
we are current running nginx version 1.7.6, we use nginx primarily as a
reverse proxy on linux.
we have encountered a strange behavior for nginx cache manager, 
everything is fine after restart nginx, the cache manage periodically spawn
new process to check the meta data and honor the max cache size we are
setting.
but after running for like 6 hours, it stopped honor the max cache size we
are setting and started to go over it and eventually reach full disk size.
no matter what we do (reduce the cache size to half of disk, reduce the
active time for the cache) as long as it go over it, it will just keep
growing.
i did some strace to the cache manager, and it just showing some normal
epoll_wait, but nothing will even get unlinked. the process spawn cache
manager perfectly fine.

PS. each time i restart nginx, after cache loader process completed, strace
to cache manage will show it starts to unlink file, and everything goes back
to normal. cache manage also starts to control cache and keep total cache
size under max cache size we set. after certain period of time. it will fail
again.

What could potentially cause this?

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,256168,256168#msg-256168