Region based split-directory scheme to adapt to large cache sizes

A method comprising:

• maintaining a plurality of node-based cache directories, wherein each node-based cache directory of the plurality of node-based cache directories corresponds to a given processing node of a plurality of processing nodes;
• tracking, by each node-based cache directory, which regions of memory have at least one cache line cached in a cache subsystem of a corresponding processing node, wherein a region comprises a plurality of cache lines;
• maintaining one or more memory-based cache directories;
• tracking, by each memory-based cache directory of the one or more memory-based cache directories, which regions of a corresponding memory address range have entries in any of the plurality of node-based cache directories;
• maintaining, by a first memory-based cache directory, an entry for each region of a first memory address range which has an entry in at least one node-based cache directory;
• and
• invalidating a given entry, corresponding to a given region, responsive to determining that all corresponding entries in the plurality of node-based cache directories have been invalidated.

An apparatus comprising:

• a plurality of processing nodes, wherein each processing node comprises one or more processors and a cache subsystem;
• and
• a plurality of node-based cache directories, wherein each node-based cache directory of the plurality of node-based cache directories corresponds to a given processing node of the plurality of processing nodes, and wherein each node-based cache directory is configured to:
• track which regions of memory have at least one cache line cached in a cache subsystem of the given processing node, wherein a region comprises a plurality of cache lines;
• and
• maintain a reference count for each entry of the cache directory, wherein the reference count tracks a number of cache lines of a corresponding region that are cached in any cache subsystem.

A method comprising:

• maintaining a plurality of node-based cache directories, wherein each node-based cache directory of the plurality of node-based cache directories corresponds to a given processing node of a plurality of processing nodes;
• tracking, by each node-based cache directory, which regions of memory have at least one cache line cached in a cache subsystem of a corresponding processing node, wherein a region comprises a plurality of cache lines;
• maintaining one or more memory-based cache directories;
• tracking, by each memory-based cache directory of the one or more memory-based cache directories, which regions of a corresponding memory address range have entries in any of the plurality of node-based cache directories;
• and
• maintaining a reference count for each entry of the cache directory, wherein the reference count tracks a number of cache lines of a corresponding region that are cached in any cache subsystem.