Is there a known reason why the LRU reference age for an LRU cache directory sometimes jumps up and down between two levels that differ by several days? For example my cache recently filled-up to the low-water mark it immediately jumped from 180 to 185 days, and since then it's been switching up and down between 178 and 184. In the past I've seen larger jumps, such as as 30 to 50 days. The LRU policy implementation seems to be a queue with accessed objects sent to the tail and old objects deleted at the head. The displayed LRU reference age is taken from the "lastref" value of first unlocked object from the queue head. If everything is working as expected, the reference age should be able to drop instantaneously, but it shouldn't be able to rise faster than 1 day per day. I'm using 2.6.18 with aufs on FreeBSD.
