Region probe filter for distributed memory system

A processing node for use in a distributed data processing system comprising:

• a memory accessing device having an associated cache;
• and
• a probe filter coupled to said memory accessing device for determining whether to issue a probe to at least one other processing node in response to a memory access request, comprising:
• a region probe filter directory for identifying regions of memory for which at least one cache line may be cached in the data processing system and a state of each region, wherein a size of each region corresponds to a plurality of cache lines;
• a line probe filter directory for identifying cache lines cached in the data processing system and a state of each cache line;
• and
• a controller for accessing said region probe filter directory and said line probe filter directory in response to said memory access request to determine whether to issue said probe, wherein said controller does not issue said probe in response to a read-only access request.

A method for filtering probe activity in a distributed data processing system comprising:

• receiving at a processing node a read-only access request to a memory associated with said processing node;
• determining whether an address of said read-only access request hits a region probe filter directory and a line probe filter directory, wherein said line probe filter directory has a plurality of entries each corresponding to cache lines, and said region probe filter directory has a plurality of entries each corresponding to regions of memory wherein each region comprises a plurality of cache lines;
• if said address of said read-only request misses in both said region probe filter directory and said line probe filter directory, creating an entry for said region in said region probe filter directory;
• fetching data from said memory corresponding to said read-only access request without sending a probe to any other node in said distributed data processing system;
• and
• sending said data to a requesting processing node.