System and method for partitioned cache memory management

Claim 2

A storage system including main storage, a partitioned cache memory, a system controller and a user interface, wherein the data stored in the system is classified into k categories using a pre-specified scheme of classification and the cache partitioning defines a global sub-cache and k counterpart local sub-caches such that, when data is required via the user interface, it is supplied from the global sub-cache, data being staged from main storage, or form the appropriate local sub-cache, to the global sub-cache, as and if required, with data belonging to one of the categories being pushed from the global sub-cache to the corresponding one of the k sub-caches and other data being pushed from that sub-cache into main storage device, as and if required.

Claim 3

A system as claimed in claim 1, wherein the controller is arranged to maintain: a most recently referenced pointer that identifies the data item stored in the global sub-cache, irrespective of category, most recently referenced via the user interface, as determined by a pre-established formula; a global least recently referenced pointer that identifies the data item stored in the global sub-cache least recently referenced via the user interface, as determined by the pre-established formula; and K category pointers, each of which identifies the least recently referenced or lowest priority data item of its corresponding category in the corresponding sub-cache; whereby by staging required data via the subcache corresponding to its category and pushing data indicated by the global and corresponding category pointers the controller is able to store data items most recently referenced by the processor in the global sub-cache and, in each of K category sub-cache, only data items of the corresponding category.

Claim 5

A system as claimed in Claim 3, wherein when a data item requested via the user interface is already stored in one of the category sub-caches, the data item is staged to the global sub-cache, and a data item of the same category in main storage is staged into that category sub-cache.

Claim 8

A method as claimed in Claim 5, wherein the cache and data are partitioned by: dividing the cache into k category sub-caches and a global sub-cache; identifying each data item in main storage as belonging to one of k categories of data items, each category corresponding to one of the category sub-caches; storing in each of at least some of the k local sub-caches a plurality of data items belonging to the corresponding data category; storing in a global sub-cache data items belonging to any of the data categories: and when attempting to reference a first data item and, if the first data item is not located in the global sub-cache nor in any of the category sub-caches: removing a second data item from the global sub-cache, wherein the second data item is the least-recently-used or lowest priority data item in the global sub-cache; noting the data type of the second data item as type k; removing a third data item from a category sub-cache k, wherein the third data item is the least recently used or lowest priority data item in category sub-cache k; placing the second data item into category sub-cache k; designating the second data item as the most recently used or lowest priority data item in category sub-cache k.

Claim 9

A method as claimed in Claim 6, additionally comprising referencing a first data item and, if the first data item is stored in the global sub-cache, identifying the first data item as the most recently used or highest priority data item in the global sub-cache and wherein pointers are maintained to identify the highest priority data item in the global sub-cache and the lowest priority data items in each sub-cache.

Claim 10

A method as claimed in either Claim 6 or Claim 7, additionally comprising referencing a first data item and, if the first data item is stored in local sub-cache j: removing a second data item from the global sub-cache, wherein the second data item is the least recently used or lowest priority data item in the global sub-cache; noting the data type of the second data item as type k; if type k is different from type j, then: pre-fetching from the storage device into the category sub-cache j the most recently used or highest priority data item of type j that is in neither the global sub-cache nor in category sub-cache j; removing from the composite cache the least recently used or lowest priority data item in category sub-cache k; and designating the second data item as the most recently used or highest priority data item in category sub-cache k.

Claim 11

In a staged storage system in which data from a secondary storage is first staged to a cache before being accessed by a processor, a method comprising: classifying each stored data item into one of K categories using a pre-specified scheme of classification; partitioning the cache into a global sub-cache and K category sub-caches; receiving a request from the host processor for a first data item; 1) if the first data item is located in the global sub-cache, identifying the first data item as the most recently used or highest priority data item in the global sub-cache; 2) if the first data item is not located in the global sub-cache nor in any of the category sub-caches: removing a second data item from the global sub-cache, wherein the second data item is the least-recently-used or lowest priority data item in the global sub-cache; noting the data type of the second data item as type k; removing a third data item from a category sub-cache k, wherein the third data item is the least recently used or lowest priority data item in that category sub-cache k; placing the second data item into category sub-cache k; designating the second data item as the most recently used or highest priority data item in category sub-cache k; 3) if the first data item is located in category sub-cache j: removing a fourth data item from the global sub-cache, wherein the fourth data item is the least recently used or lowest priority data item in the global sub-cache; noting the data type of the fourth data item as type k; if type k is different from type j, then: pre-fetching from the secondary storage into the category sub-cache j the most recently used or highest priority data item of type j that is in neither the global sub-cache nor in category sub-cache j; removing from the cache the least recently used or lowest priority data item in category sub-cache k; designating the fourth data item as the most recently used data item in category sub-cache k.

Claim 12

In a staged storage system in which data from a secondary storage is first staged to a cache before being accessed by a processor, a method comprising: classifying each stored data item into one of K categories using a pre-specified scheme of classification; partitioning the cache into a global sub-cache and K category sub-caches; receiving a request from the host processor for a first data item; 1) if the first data item is located in the global sub-cache, identifying the first data item as the most recently used or highest priority data item in the global sub-cache; 2) if the first data item is not located in the global sub-cache nor in any of the category sub-caches: removing a second data item from the global sub-cache, wherein the second data item is the least-recently-used or lowest priority data item in the global sub-cache; noting the data type of the second data item as type k; removing a third data item from a category sub-cache k, wherein the third data item is the least recently used or lowest priority data item in that category sub-cache k; placing the second data item into category sub-cache k; designating the second data item as the most recently used or highest priority data item in category sub-cache k; 3) if the first data item is located in category sub-cache j: removing a fourth data item from the global sub-cache, wherein the fourth data item is the least recently used or lowest priority data item in the global sub-cache; noting the data type of the fourth data item as type k; if type k is different from type j, then: pre-fetching from the secondary storage into the category sub-cache j the most recently used or highest priority data item of type j that is in neither the global sub-cache nor in category sub-cache j; removing from the cache the least recently used or lowest priority data item in category sub-cache k; designating the fourth data item as the most recently used data item in category sub-cache k.