Control logic for memory modification tracking with hierarchical dirty indicators

Abstract

A dirty memory that includes dirty indicators settable to indicate dirtied pages of memory is provided with control logic operable automatically to interrogate the dirty memory to identify dirty indicators that are set. Implementing the control of the dirty RAM in hardware or firmware enables interrogation of the dirty RAM to identify set dirty indicators in a rapid and reliable manner. The control logic can advantageously be operable to interrogate the dirty memory word-by-word to determine words including a set bit. A comparator can be provided for comparing bits of a word to a predetermined value to determine where a dirty indicator is set. The comparison could be performed serially for bits within a word, but it is advantageously done in parallel for the bits of the word. For example, by using associative memory, the interrogation of the dirty memory could be effected associatively in parallel to determine words including a word with a set bit. Address logic enables a determination of a memory page address corresponding to a set dirty indicator. This can be effected by computing the page address given a known dirty bit location and a known mapping between the dirty memory and main memory.