Patent ID: 7356651
Filing Date: 2008-04-08
Classification: G06F

Abstract:
1. A method for controlling a cache, comprising: managing each line or block of data in the cache by assigning each line or block of data to one of 7 or more states, wherein managing each line or block of data in the cache is performed by a cache state machine comprising 7 or more states and a collection of state transitions, wherein each cache state is associated with a control structure, and wherein each line is associated with a line control block comprising a set of line or block attributes; utilizing a hash object to speed up cache line lookup; enforcing a total maximum dirty line threshold; collecting statistics for each line including read access count, write access count, and time since flush; collecting statistics for the cache including cache hits, cache misses, and average access count; and wherein the 7 states are defined as: (1) Free—the cache lines do not contain valid data yet; (2) Clean—the cache lines contain valid clean data (no flush needed); (3) Dirty—the cache lines contain valid dirty data (need flush sometime later); (4) Sticky—the cache lines contain valid clean data that has been accessed at least twice (e.g. two or more reads); (5) StickyDirty—the cache lines contain valid dirty data that has been accessed at least twice (e.g. 1 write, 1 or more reads; or 2 or more writes, etc.); (6) Flush—the cache lines contain valid dirty data and are about to be written to a physical disk storage; and (7) Hash—the cache lines are in the process of getting valid data from either physical disk storage (read) or host (write).