Since avastsvc.exe is scanning what you have in traffic, the more you use other processes, the more memory avast will use.
Some users tend to think that avast is using their bandwidth, when in fact avast is simply scanning the same bandwidth being used by other software.
So I would say that whatever memory avastsvc.exe *seems* to be using, in most cases the important thing is how much memory is free to be used by other processes.