Virtual space manager for computer having a physical address extension feature
View Patent ↗A physical address extension feature maps multiple virtual memory spaces to an extended physical memory. A virtual space manager dynamically allocates pages of the physical memory to respective virtual spaces. The virtual space manager responds to a request from an application for allocation of a page of physical memory by returning a cookie indicating the allocated page. The virtual space manager responds to a request including the cookie by switching virtual address translation to the virtual memory space including the indicated page. The cookie is used to access a cookie cache of state information on the last page of virtual memory having been mapped into physical memory. For example, segments of the page store block map entries for snapshot copies, and the cookie cache caches the last-accessed values of the block numbers and their location within the page.
1. A digital computer comprising at least one processor for producing virtual addresses over a range of virtual addresses, at least one translation buffer coupled to said at least one processor for producing physical addresses from the virtual addresses in accordance with a current virtual-to-physical address mapping, and a random access memory being addressable by the physical addresses and coupled to said at least one processor for supplying data to said at least one processor, wherein the random access memory includes physical memory having a range of physical addresses that is greater than the range of virtual addresses, and the digital computer is programmed with a plurality of different virtual-to-physical address mappings for identical virtual addresses to define a plurality of respective virtual memory spaces having the different virtual-to-physical address mappings for the identical virtual addresses, and
wherein the digital computer is programmed with a virtual space manager, the virtual space manager including an allocation routine for responding to an allocation request from an application for allocation of at least one page of the physical memory by returning an indication of said at least one page of the physical memory, and a mapping routine for responding to a mapping request from the application, the mapping request including the indication of said at least one page of the physical memory, the mapping routine being executable by the digital computer for switching the current virtual-to-physical address mapping to a virtual-to-physical address mapping including the indicated said at least one page of the physical memory, and
wherein the indication of said at least one page of the physical memory is a cookie, and the digital computer is programmed with a cookie cache of state information on a last page of virtual memory having been mapped into the physical memory.
2. The digital computer as claimed in claim 1 , wherein the digital computer is programmed for responding to an application request including the cookie by accessing the cookie cache to determine whether the cookie identifies the last page of virtual memory having been mapped into the physical memory, and upon determining that the cookie identifies the last page of virtual memory having been mapped into the physical memory, accessing the last page of virtual memory without switching the current virtual-to-physical address mapping.
3. The digital computer as claimed in claim 1 , which is programmed for responding to an application request including the cookie by accessing the cookie cache to determine whether the cookie identifies a last page of virtual memory having been mapped into the physical memory, and upon determining that the cookie identifies the last page of virtual memory having been mapped into the physical memory, accessing the state information in the cookie cache to respond to the application request.
4. The digital computer as claimed in claim 3 , wherein the application request is a request for information about a mapping between a pair of data blocks, and the state information in the cookie cache includes a data block mapping in the last page of virtual memory having been mapped into the physical memory.
5. The digital computer as claimed in claim 1 , wherein the virtual space manager includes a routine for receiving from the application a specification of a virtual address and a number of pages for a virtual space to be allocated to the application and mapped to the physical memory.
6. A method of operating a digital computer having at least one processor for producing virtual addresses over a range of virtual addresses, at least one translation buffer coupled to said at least one processor for producing physical addresses from the virtual addresses in accordance with a current virtual-to-physical address mapping, and a random access memory being addressable by the physical addresses and coupled to said at least one processor for supplying data to said at least one processor, the random access memory containing physical memory having a range of physical addresses that is greater than the range of virtual addresses, wherein the digital computer is programmed with a plurality of different virtual-to-physical address mappings for identical virtual addresses to define a plurality of respective virtual memory spaces having the different virtual-to-physical address mappings for the identical virtual addresses, said method comprising:
the digital computer responding to an allocation request from an application for allocation of at least one page of memory by returning an indication of said at least one page of allocated memory in a virtual memory space; and
the digital computer responding to a mapping request from the application, the mapping request including the indication of said at least one page of allocated memory, the digital computer responding to the mapping request by switching the current virtual-to-physical address mapping to the virtual memory space including the indicated said at least one page of allocated memory,
wherein the indication of the page of allocated memory is a cookie, and the method includes caching, in a cookie cache, state information on a last page of virtual memory having been mapped into physical memory.
7. The method as claimed in claim 6 , which includes the digital computer responding to an application request including the cookie by accessing the cookie cache to determine whether the cookie identifies the last page of virtual memory having been mapped into physical memory, and upon determining that the cookie identifies the last page of virtual memory having been mapped into physical memory, accessing the last page of virtual memory without switching the current virtual-to-physical address mapping.
8. The method as claimed in claim 6 , which includes the digital computer responding to an application request including the cookie by accessing the cookie cache to determine whether the cookie identifies the last page of virtual memory having been mapped into physical memory, and upon determining that the cookie identifies the last page of virtual memory having been mapped into physical memory, accessing the state information in the cookie cache to respond to the application request.
9. The method as claimed in claim 8 , wherein the application request is a request for information about a mapping between a pair of data blocks, the state information in the cookie cache includes a data block mapping in the last page of virtual memory having been mapped into physical memory, and the method includes the digital computer accessing the data block mapping in the cookie cache in response to the application request.
10. The method as claimed in claim 6 , which includes the digital computer initially receiving from the application a specification of a virtual address and a number of pages for a virtual space to be allocated to the application and mapped to the physical memory.