High performance mechanism for managing allocation of virtual memory

Abstract

The main storage of a system includes a virtual memory space containing a plurality of virtual frame buffers for storing information transferred from disk storage shared by a number of virtual processes being executed by the system. An associated buffer table and aging mechanism includes a buffer table storing a plurality of buffer table entries associated with the corresponding number of virtual buffers used for controlling access thereto and an age table containing entries associated with the buffer table entries containing forward and backward age pointers linked together defining the relative aging of the virtual frame buffers from the most recently used to least recently used. Each buffer table entry has a frequency reference counter which maintains a reference count defining the number of times that its associated virtual buffer has been uniquely accessed by the virtual processes. When a virtual frame buffer is required to made available as a replacement candidate, the system's input/output process scans the buffer table entries starting with the least recently used entry to locate an available buffer and examines reference counts contained in the buffer table entries and values derived from the age table indicating the depth or distance that such buffer table entries are from the least recently used position. When the frequency reference count and depth of a particular virtual buffer entry meets defined thresholds, the associated virtual buffer is used as the replacement candidate and its buffer entry is moved to a most recently used position by updating the age table forward and backward pointer entries.