METHOD AND SYSTEM FOR IMPLEMENTING MEMORY EFFICIENT TRACK AGING

摘要

Each time a track is referenced, a value representing the last referenced age is entered for a track entry in a last referenced age table (LRAT). The last referenced age table is indexed by track. A second table, an age frequency table (AFT), counts all segments in use in each reference age. The AFT is indexed by the reference age of the tracks. When a track is referenced, the number of segments used for the track is added to a segment count associated with the last referenced age of the track. The segment count tallies the total number of segments in use for the reference age for all tracks referenced to that age. The number of segments used for the previous last referenced age of the track is subtracted from the segment count associated with the previous last referenced age in the AFT. When free space is needed, tracks are discarded from the LRAT by reference age, the oldest first. The range of ages to be discarded in the LRAT is calculated in the AFT by counting the total amount of segments used by each reference age until the total number of segments needed is realized. Counting is started at the AFT entry with the oldest reference age. The reference age of the last counted entry in the AFT is the discard age. The LRAT is scanned for reference ages between the old age and the discard age, and those reference ages are discarded.