Cache

LRU cache eviction strategy replaced with Segmented LRU strategy.
Now cache is represented as sequence of cache pages, ordered by "temperature" of data in them.
Data that is accessed more frequent will be in the hottest cache page, therefore it is less likely to be removed. Profit of this strategy relies on the pattern of user-data interaction. 
Anyway, when cache_pages_number is set to 1, SLRU degenerates into simple LRU. 

You can read more precise description here http://en.wikipedia.org/wiki/Cache_algorithms#Segmented_LRU