Method for preserving memory affinity in a non-uniform memory access data processing system

Abstract

A method for preserving memory affinity in a computer system is disclosed. The method reduces and sometimes eliminates memory affinity loss due to process migration by restoring the proper memory affinity through dynamic page migration. The memory affinity access patterns of individual pages are tracked continuously. If a particular page is found almost always to be accessed from a particular remote access affinity domain for a certain number of times, and without any intervening requests from other access affinity domain, the page will migrate to that particular remote affinity domain so that the subsequent memory access becomes local memory access. As a result, the proper pages are migrated to increase memory affinity.

1 . A method for preserving memory affinity in a non-uniform memory access data processing system, said method comprising:
 in response to a request for memory access to a page within a first memory affinity domain, determining whether or not said request is initiated by a processor associated with said memory affinity domain;   in response to the determination that said request is not initiated by a processor associated with said memory affinity domain, determining whether or not there is a page ID match with an entry within a page migration tracking module associated with said memory affinity domain;   in response to the determination that there is no page ID match with any entry within said page migration tracking module, selecting an entry within said page migration tracking module and providing said entry with a new page ID and a new memory affinity ID;   in response to the determination that there is a page ID match with an entry within said page migration tracking module, determining whether or not there is a memory affinity ID match with said entry with the page ID field match;   in response to the determination that there is no memory affinity ID match, updating said entry with the page ID field match with a new memory affinity ID; and   in response to the determination that there is a memory affinity ID match, incrementing an access counter of said entry with the page ID field match.   
     
     
         2 . The method of  claim 1 , wherein said method further includes in a determination that said request is initiated by a processor associated with said memory affinity domain, serving said request. 
     
     
         3 . The method of  claim 1 , wherein said selecting further includes resetting an access counter of said entry. 
     
     
         4 . The method of  claim 1 , wherein said updating further includes resetting an access counter of said entry. 
     
     
         5 . The method of  claim 1 , wherein said memory affinity domain is defined as a group of memories that are in physical proximity, wherein any access to a memory within said memory affinity domain experiences identical memory access latency. 
     
     
         6 . The method of  claim 1 , wherein each memory affinity domain is associated within a page migration tracking module. 
     
     
         7 . The method of  claim 1 , wherein said selecting further includes selecting a least-recently-used entry. 
     
     
         8 . The method of  claim 7 , wherein said method further includes marking said entry as invalid. 
     
     
         9 . The method of  claim 1 , wherein said memory affinity tracking module includes a real page ID field, a memory affinity ID field, and an access counter field. 
     
     
         10 . The method of  claim 1 , wherein said method further includes alerting an operating system a page needs to be migrated to a remote processor and its memory affinity region.