svchost.exe memory usage up to 4Gb every hour, how to fix?
Process Explorer will tell you which services are running in a given svchost.exe process. You can use that information to narrow down the range of services that you need to start/stop to see what is using all of your memory.
In addition to Process Explorer, in Task Manager in Windows 7 you can right click on any of the processes and click "Go To Service(s). This will highlight which services are being run by this process.
It could be a sign of malware, see my post here
Use the "Alternate Method"
Read the "EDIT" section also.