Virtual machine backup

Abstract

A virtual machine backup method includes utilizing a log to indicate updates to memory of a virtual machine when the updates are evicted from a cache of the virtual machine. A guard band is determined that indicates a threshold amount of free space for the log. A determination is made that the guard band will be or has been encroached upon corresponding to indicating an update in the log. A backup image of the virtual machine is updated based, at least in part, on a set of one or more entries of the log, wherein the set of entries is sufficient to comply with the guard band. The set of entries is removed from the log.

What is claimed is: 
     
         1 . A method comprising:
 indicating, in a log, updates to memory of a virtual machine when the updates are evicted from a cache of the virtual machine;   determining a guard band for the log, wherein the guard band indicates a threshold amount of free space for the log;   determining that the guard band will be or has been encroached upon corresponding to indicating an update in the log;   updating a backup image of the virtual machine based, at least in part, on a set of one or more entries of the log, wherein the set of entries is sufficient to comply with the guard band; and   removing the set of entries from the log.   
     
     
         2 . The method of  claim 1 , wherein said determining a guard band comprises:
 determining a number of write-back cache lines in the cache;   determining a number of instructions in a pipeline for a processor unit that executes instructions issued by the virtual machine;   determining a number of additional instructions capable of being issued to the pipeline in the time taken to trigger an interrupt of the processor unit; and   defining the guard band based on a sum of the determined number of write-back cache lines, the determined number of instructions, and the determined number of additional instructions.   
     
     
         3 . The method of  claim 1 , wherein said determining a guard band comprises:
 determining a number of dirty cache lines in the cache;   determining a number of store instructions in a pipeline for a processor unit that executes instructions issued by the virtual machine;   determining a number of additional instructions capable of being issued to the pipeline in the time taken to trigger an interrupt of the processor unit; and   defining the guard band based on a sum of the determined number of dirty cache lines, the determined number of store instructions, and the determined number of additional instructions.   
     
     
         4 . The method of  claim 3  further comprising redefining the guard band in response to determining that another cache line has become dirty or that an additional store instruction has been issued to the pipeline. 
     
     
         5 . The method of  claim 1 , wherein the cache of the virtual machine comprises a write-through cache, wherein said indicating in the log updates to memory of a virtual machine is in response to updates by the virtual machine to a cache line in the cache. 
     
     
         6 . The method of  claim 1  further comprising marking a cache line in the cache of the virtual machine for logging in response to modification of the cache line. 
     
     
         7 . The method of  claim 1 , wherein each of the set of entries indicates a memory address of the virtual machine and data written to the memory address of the virtual machine, wherein updating the backup image based, at least in part, on the set of entries comprises indicating, for each memory address and data indicated in the set of entries, the data for updating a corresponding memory address of the backup image.